|
<<< Back to Sampling and Analytical Methods |
Printing Instructions |
For problems with accessibility in using figures, illustrations and PDFs in this method, please contact
the SLTC at (801) 233-4900. These procedures were designed and tested for internal use by OSHA personnel.
Mention of any company name or commercial product does not constitute endorsement by OSHA. |
Ozone In Workplace Atmospheres
(Impregnated Glass Fiber Filter)
[357 KB
PDF,
29 pages]
Related Information: Chemical Sampling -
Ozone
|
| Method no.: |
ID-214 |
| |
|
| Matrix: |
Air |
| |
|
OSHA Permissible Limits
Final Rule Limits: |
|
| |
|
Time Weighted
Average
(TWA): |
0.1 ppm * |
| |
|
Short-Term Exposure
Limit
(STEL): |
0.3 ppm * |
| |
|
| Transitional Limit (TWA): |
0.1 ppm |
| |
|
| Collection Device: |
An air sample is
collected using a calibrated sampling pump and a two-piece
polystyrene cassette containing two nitrite-impregnated glass
fiber filters (IGFFs). During collection, ozone reacts with the nitrite
impregnated on the filter collection device and converts it to nitrate via
oxidation. |
| |
|
Recommended Sampling Rate
(See Special Precautions below)
TWA:
TWA: |
0.25 to 0.5 liter per minute (L/min)
1.5 L/min |
| |
|
| Recommended Air Volume |
|
| TWA: |
90 L (180 min at 0.5 L/min).
Longer sampling times can be used (up to 480 min) when using 0.25 L/min flow
rate. |
| STEL: |
22.5 L (1.5 L/min for 15 min) |
| |
|
| Analytical Procedure: |
The reaction product is
extracted from the filters and blanks using deionized water and the extracts
are analyzed by ion chromatography as nitrate using UV-VIS
detector at 200 nm wavelength. A conductivity detector can also be used. |
|
|
Detection Limit
Qualitative:
Quantitative: |
0.008 ppm (90-L air sample)
0.032 ppm (22.5-L air sample)
0.03 ppm (90-L air sample)
0.11 ppm (22.5-L air sample) |
|
|
| Accuracy |
TWA |
STEL |
| Validated
Range: |
0.070 t 0.224 ppm |
0.330 ppm |
| CVT(pooled): |
0.045 |
0.054 (CV2 |
| Bias: |
+0.014 |
-0.015 |
| Overall
Error: |
±10.4% |
±12.3% |
|
|
| Method Classification: |
Validated Method |
|
|
| Special Precautions: |
Slight breakthrough (~7.5%) of
ozone was noted at approximately 0.4 ppm. If the expected ozone (O3)
concentration is more than 0.2 ppm, the recommended sampling rate can be
reduced to 0.25 L/min. |
| |
|
Date: March 1995
Date Revised: January 2008 |
Chemist: James C.
Ku |
|
|
* The U.S. Court of Appeals, Eleventh Circuit, has ruled that Final Rule
Limits of 29 CFR 1910.1000 be vacated. The Final Rule definition of "TWA" and
"STEL" have been retained. Although the Final Rule Limits have been vacated,
OSHA encourages industry and government to abide by these limits established
by scientific evidence (memorandum for Directorate Heads, Office Directors
and Regional Administrator from Roger Clark, Director of Compliance Programs
OSHA, 3/30/93). |
| |
|
Branch of Inorganic Methods Development
OSHA Salt Lake Technical Center
Sandy, Utah 84070 |
1. Introduction
This method describes the sample collection and analysis of airborne ozone (O3). Air samples are taken in
the breathing zone of workplace personnel, and analysis is performed by ion chromatography (IC) equipped with a UV-VIS
and conductivity detector. Nitrate analysis by conductivity is well established since the 1970s. Both UV-VIS
and conductivity detectors are suggested in this method to allow versatility and offer the possibility of excluding
interferences by switching detectors. This method is not applicable for collection and analysis of bulk or wipe
samples.
The January 2008 method revision consists of updated instructions for the preparation of IGFFs. The purpose of the updated instructions is to describe techniques to be used for the preparation of
media with low residual nitrate levels and also for the reduction of nitrate formation during media storage. These instructions are presented in Section 2.1.3.
1.1 History
Many previous attempts were made to measure ozone in occupational environments. All have various shortcomings and
demonstrate the past degree of difficulty in developing an adequate method. A chronological presentation of some of
the methods OSHA has used or evaluated is discussed below:
1.1.1 Detector tubes: The major drawback of detector tubes is the need to use a cumbersome statistical technique
to assess Time Weighted Average (TWA) exposures.
1.1.2 KI and AKI methods: An early method to determine occupational exposure to ozone in the workplace involved
collection in neutral potassium iodide (KI) solution and analysis by colorimetry (Ref. 5.1).
A modification involved collecting samples in an alkaline potassium iodide (AKI) solution and analyzing them by
colorimetry after acidifying with sulfamic acid (Ref. 5.2). It has been reported
(Ref. 5.3) that the reaction of ozone with AKI to produce iodine is not quantitative
and is concentration dependent. Therefore, a conversion equation must be used to convert the values equivalent to the neutral
KI method.
1.1.3 OSHA KIBRT (potassium iodide-potassium bromide-sodium thiosulfate) (Ref. 5.4): This
method resolved some of the stability and interference problems associated with prior methods which used KI.
1.1.4 Trans-stilbene (Ref. 5.5): Previous work has been reported using glass beads coated
with trans-stilbene for collecting ozone (Ref. 5.6). Preliminary tests showed
that this method was affected by humidity as low as 50 % relative humidity (RH) (Ref. 5.7).
To compensate for this humidity problem, an impinger sampling method using a collection solution (as stated in
chronological list below) was developed at the OSHA-SLTC (Ref. 5.5). Although
this method could be used under controlled conditions as a reference method in the laboratory, the 90%
acetonitrile in water is flammable and should not be used for field use. Alternative non-flammable
collection solutions were not found during this study.
1.1.5 Direct-Readers AID Model 560 (Ref. 5.8) or AED-030 (Ref. 5.9): A strip chart recorder to record data was used to document for both direct-readers compliance monitoring. The AID
Model 560 also required a battery recharge every 8 to 10 hours, making it inconvenient. The AED-030
can be used for only 4 to 5 hours with batteries; a line voltage power converter or replacement batteries is
necessary for longer periods.
1.1.6 Recently, it has been reported (Ref. 5.10) that the measurement of ozone can be done
using a commercially available passive sampling device containing a nitrite-impregnated filter.
According to the manufacturer, the shelf-life of the sampling portion of the passive device is
conservatively 4 weeks from the nitrite impregnation date to the analysis date. Based on the nitrite principle,
OSHA Method ID-214 was developed as an active sampling system. The commercially available passive
system was initially tested and some of the data is included in the backup report (Section 4.)
Because of sensitivity (Section 4.10) and potential interference considerations of the passive
sampler, this active sampling method is more suitable for OSHA compliance purposes.
A chronological summary of OSHA SLTC ozone monitoring techniques is shown below:
| Date |
Method |
Principle |
Collection Medium |
Major
Advantages |
Major Disadvantages |
| 1960s - present |
Detector tubes |
Oxidation of indigo by ozone resulting in white color |
Direct-read |
Simple, rapid |
Interferences, more a spot check for exposure measurement |
| Before 1977 |
1% Neutral buffered KI |
Reaction with KI |
1% KI, phosphate buffer, pH=6.8 |
Simple, rapid, and sensitive |
Bubbler, unstable, and interferences from all oxidants |
| 1977 - 80 |
Alkaline KI |
Reaction with KI |
1% KI, 1.0 N NaOH, pH>11 |
Simple, rapid, and sensitive |
Bubbler, unstable, sampling rate dependence, and interferences from all oxidants |
| 1983 - 92 |
Ozone meter (AID Model 560) |
Chemilumines-
ence |
Direct reading instrument |
Very sensitive, direct-reading, very specific |
No data logging and bulky instrument requiring ethylene (flammable gas) or Ethychem (ethylene
in CO2) |
| 1986 |
Neutral buffered (KIBRT) |
Reaction with KI and Na2S2O3. Measurement of excess I2 |
1% KI, a known amount of thiosulfate, 2% KBr |
Simple, rapid sensitive, stable and some independence from sampling rate |
Bubbler, interferences from all oxidants. Potential contam-
ination. |
| 1990 - 91 (Lab use only) |
Glass beads trans-stilbene |
Reaction with olefins |
Glass beads coated with trans-stilbene |
Simple, rapid, sensitive and O3 specific |
Recovery dependent on humidity |
| 1990 - 91 (Lab use only) |
trans-stilbene and mesitol |
Reaction with olefins |
0.05% trans-stilbene + 0.5% mesitol in a mixture of acetonitrile/
water (9:1) |
Simple, rapid, sensitive and O3 specific |
Flammable liquid, bubbler used for sample collection |
| 1992 - present |
Ozone meter (AED-030) |
Semi-conductor sensor |
Direct reading instrument |
Simple, rapid, sensitive and easy to use |
No data logging capacity, instrument treads to drift |
| This method |
IGFF |
Reaction with nitrite |
Nitrite-coated IGFFs |
Simple, rapid, sensitive |
Interference from SO2 |
1.2 Principle
Ozone is collected using two nitrite-impregnated glass fiber filters (IGFFs). The second IGFF serves as a backup
filter. The collected O3 converts nitrite (NO2¯) to nitrate (NO3¯) via oxidation
as shown by the following chemical reaction:
NO2¯ + O3
NO3¯ + O2 |
The resultant NO3¯ is analyzed by IC using a UV-VIS detector at a wavelength of
200 nm. A gravimetric conversion factor is used to calculate the amount of O3 collected from the
amount of NO3¯ found.
1.3 Advantages and Disadvantages
1.3.1 This method has adequate sensitivity for determining compliance with the OSHA Permissible Exposure Limit
(PEL) of 0.1 ppm for O3 exposure. The method is also capable of monitoring Food and Drug Administration
limit of 0.05 ppm O3 in enclosed spaces (21 CFR 801.415). The U.S. Environmental Protection Agency
(EPA) has established a National Ambient Air Quality Standard (NAAQS) for O3 at 0.12 ppm for a 1-hour
average. The method is capable of monitoring for the EPA limit provided a sampling rate of at least 0.5 L/min is
used. All three limits have been used to determine Indoor Air Quality (IAQ) in relation to O3 exposure.
1.3.2 The method is simple, rapid, and easily automated.
1.3.3 The method is "relatively" specific for O3 (as NO3¯) in the presence of
other nitrogen-containing substances, such as nitrogen dioxide (NO2).
1.3.4 The sampling device is small, portable, and contains no liquid.
1.3.5 Desorption and preparation of samples for analyses involve simple procedures and equipment.
1.3.6 Samples can be analyzed using either a UV-VIS or conductivity detector. The majority of the validation was
performed using a UV-VIS detector.
1.3.7 One disadvantage is that sulfur dioxide (SO2) gas and soluble particulate nitrate compounds
interfere when collected on the same IGFFs (Section 4.9). A pretube containing a chromate
compound can be used to remove any SO2 and allow O3 to react with the IGFFs. Significant
levels of soluble nitrate substances should not normally be encountered in an occupational setting unless these
substances are in use. Examples of soluble substances are potassium or sodium nitrate.
1.3.8 Another disadvantage of the method is the tedious preparation and storage of the IGFFs
(Section 2.1.3).
1.4 Methods Performance
A synopsis of the method performance is presented below. Further information can be found in
Section 4.
1.4.1 This method was validated over the concentration range of 0.070 to 0.224 ppm. An air volume of 90 L and a
flow rate of 0.5 L/min were used.
1.4.2 The qualitative detection limit was 0.37 µg/mL or 1.85 µg (as NO3¯) when using a 5-mL
solution volume. This corresponds to 0.008 ppm O3 for a 90-L air volume.
1.4.3 The quantitative detection limit was 1.25 µg/mL or 6.25 µg (as NO3¯) when using a 5-mL
solution volume. This corresponds to 0.03 ppm O3 for a 90-L air volume. A 50-µL sample loop and a
detector setting of 2 absorbance units (AU) for full-scale output were used.
1.4.4 The sensitivity of the analytical method, when using the instrument parameters listed in
Section 3.6.3, was calculated from the slope of a linear working range
curve (0.5 to 10.0 µg/mL NO3¯). The sensitivity was 3.7 × 105 area units per 1 µg/mL. A Dionex
Series 4500i ion chromatograph with a Linear UVIS-206 UV detector and AI450 computer software was used
(Dionex, Sunnyvale, CA).
| |
TWA |
STEL |
| CV |
0.045 |
0.054 |
| Bias |
+0.014 |
-0.015 |
| OE |
±10.4% |
±12.3% |
1.4.5 The total pooled coefficient of variation (CV), bias, and total overall error (OE) for
TWA and STEL-type determinations are shown below:
1.4.6 The collection efficiency at 2 times the PEL was 100%. Samples were collected from a generated test
atmosphere of 0.20 ppm O3 for 180 min at 0.5 L/min.
1.4.7 For TWA measurements, two breakthrough tests were performed at concentrations of 0.22 and 0.4 ppm O3.
Using a sampling time of 240 min and an average sample flow rate of 0.5 L/min, no breakthrough was found at a
concentration of 0.22 ppm O3, and the average breakthrough was 7.5% at a concentration of 0.4 ppm O3.
However, no breakthrough was found at a concentration of 0.6 ppm O3 after reducing the flow rate to
approximately 0.25 L/min and a sampling time of 240 min. For STEL, no breakthrough was found at a concentration of
0.33 ppm O3 using a sampling time of 15 min and an average sample flow rate of 1.5 L/min.
1.4.8 Samples can be stored at ambient (20 to 25°C) temperature for a period of 30 days. Results show the mean
sample recovery after 30 days storage was within ±10% of results at Day 0.
1.4.9 The mean blank recovery after 30 days storage was 5 µg compared to 1.5 µg on Day 0 (as total nitrate). A
final solution volume of 5 mL was used.
1.5 Interferences
1.5.1 Sampling: Because O3 is analyzed as nitrate, particulate nitrate compounds may interfere
(positive) in the analysis if collected on the same IGFFs. Sulfur dioxide in the presence of O3 will
also interfere (negative). If interference from SO2 is expected, an oxidizer pretube, such as the tube
commonly used for converting NO to NO2 (OSHA Method
ID-182
or
ID-190), can be used to effectively
remove SO2 and allow O3 to pass through the IGFFs. These oxidizer tubes must be passivated
in the ozone atmosphere prior to use.
1.5.2 Analytical: Any substance that absorbs UV at 20 nm and has the same retention time as NO3¯ is an
interference when using the UV-VIS detector. If the possibility of an interference exists, changing
the analytical conditions (detector settings, chromatographic column, eluent flow rate, strength, etc.) may
circumvent the problem. Substances that have the same retention time as NO3¯ and are conductive may
interfere when analyzed by conductivity. Most interferences may be resolved by changing detectors (i.e., changing
from conductivity to UV-VIS or vice-versa).
1.6 Industrial Uses and Products of Ozone
(Ref. 5.11)
1.6.1 Ozone is used mainly for: purification of drinking water; industrial waste treatment; deodorization of air
and sewage gases; bleaching of waxes, oils, wet paper, and textile; production of peroxides; and as a bactericide.
1.6.2 Ozone is also used as: an oxidizing agent in several chemical processes (acids, aldehydes, and ketones from
unsaturated fatty acids); steroid hormone formation; removal of chlorine from nitric acid; and oxidation of
phenols and cyanides.
1.7 Physical and Chemical Properties (Refs.
5.11-5.12)
Ozone has a pungent odor, is a strong irritant, and is highly toxic by inhalation. It is strong oxidizing agent and
a dangerous fire and explosion risk when in contact with organic materials. It is more soluble in water than
oxygen; however, the minimal solubility results in the liberation of significant amounts of ozone after water is
purified with ozone.
| CAS No. |
10028-15-6 |
| Chemical formula |
O3 |
| Formula weight |
47.997 |
| Specific gravity |
1.6 (liquid) @ -183°C |
| Melting point |
-192°C |
| Boiling point |
-112°C |
| Vapor density (air = 1) |
1.65 |
| Synonym |
Triatomic oxygen |
| Appearance and odor |
Colorless at concentrations noted in industry. Pungent characteristic odor usually associated
with electric sparks. |
1.8 Toxicology (Ref. 5.13)
Information listed within this section is a synopsis of current knowledge of the physiological effects of O3
and is not intended to be used as a basis for OSHA policy.
Ozone is highly injurious and potentially lethal to experimental animals at concentrations as low as a few parts
per million (ppm). A study in which young mice were exposed to 1 ppm ozone for 1 or 2 days reported damage to
alveolar tissue. Human populations chronically exposed to lower concentrations of ozone were observed to have
adverse changes in lung function. Human volunteers exposed to 0.5 ppm ozone for 3 hours per day, 6 days per week,
for 12 weeks showed significant adverse changes in lung function. Another report showed a 20 percent reduction in
timed vital lung capacity in persons exposed to average concentrations of ozone of 1.5 ppm for 2 hours. Welders
exposed to maximal ozone concentrations of 9 ppm were observed to have pulmonary congestion. Recent studies
indicate ozone may contribute to inflammation in human bronchial tubes. Further information regarding toxic effects
of ozone can be found in Ref. 5.12.
2. Sampling
Note: Particulate nitrate compounds or SO2, gas interfere in the analysis of NO3¯ if collected
on the same IGFFs. However, if interference from SO2 is expected, a pretube, such as the tube used for
converting NO to NO2, can be used to effectively remove SO2, and allow O3 to pass
through to the IGFFs. If the amount of SO2 in the area to be sampled is unknown, detector tubes (OSHA SLTC
Product Evaluation No. 12 for recommended tubes) can be used to screen the area or a long-term sampling
method (OSHA SLTC Method ID-200) can be used
to determine if SO2 is present prior to O3 sampling. If particulate nitrate compounds are
present in the air, contact OSHA-SLTC. If these compounds are soluble and present in sufficient
quantity, an alternate method employing direct-reading instruments may have to be used.
2.1 Equipment
2.1.1 Calibrated personal sampling pumps capable of sampling within ±5% of the recommended flow rate of 0.5 L/min
are used.
2.1.2 Tygon or other flexible tubing for connecting pumps to samples.
2.1.3 Sampling media:
Impregnated glass fiber filters (IGFFs) are used for sample collection and are prepared following the instructions below:
Apparatus
a. Glass fiber filters (GFFs), 37-mm (Gelman Sciences , Ann Arbor, MI ,Type A/E, product number 61652)
b. Glass beakers, 400-500-mL and 10-20mL
c. 100-mL volumetric flask
d. Eppendorf pipet capable of dispensing 0.4 mL or glass pipet capable of dispensing 0.4 mL
e. Oven capable of heating to 100 °C (to dry the impregnated filters there must be a nitrogen atmosphere in the oven, or use a desiccator with a nitrogen atmosphere)
f. Forceps
g. Cassette gel sealing bands
h. Two-section polystyrene cassettes, 37-mm diameter with end plugs (Millipore Corp. Bedford MA, part number MAWP037 AO)
i. Chemicals (Reagent grade or better)
Sodium nitrite (NaNO2), 99.99%
Potassium carbonate (KCO3), 99%
Glycerol, 99.5%
Note: Before coating, the glass fiber filter must be thoroughly cleaned with deionized water to remove any trace amounts of soluble nitrate compounds. Filter impregnation requires the use of very
pure chemicals, and careful handling of both chemicals and IGFFs to avoid contamination from ambient ozone in the air and soluble nitrate containing chemicals. The sodium nitrite, IGFFs, and loaded
cassettes should be protected from ambient ozone in aluminized bags.
Procedure
a. Clean each GFF one at a time using three 400 or 500-mL beakers filled with deionized water. Take the GFF out of the box with cleaned forceps. Swish it back and forth in the first beaker, then in
the second beaker, and finally in the third beaker. Place it on a clean; nitrate-free surface to support the outside edge of the GFF (we used the lips of 20-mL beakers). Place the filters into an
oven to dry for 30 min at 100 °C. Remove the filters from the oven when they are dry and allow them to cool to room temperature for 15-30 min.
b. Prepare the impregnating solution just prior to use. The impregnating solution, in the volumetric flask, will become contaminated from the air slowly, such that the nitrate levels become too high
after 4 hours. To make the solution place 0.3 g NaNO2, 0.28 g KCO3, and 1 mL of glycerol in a 100 mL volumetric flask and dilute to the mark with deionized water. Shake the flask well to mix the
contents.
c. Place each cleaned filter on a 10 or 20-mL beaker.
d. Slowly add 0.4 mL of the impregnating solution, making sure the entire filter is saturated with the solution.
e. Carefully place each beaker (with impregnated filter on top) into a drying oven with a nitrogen atmosphere, at 100 °C, for 30 min. If a drying oven with nitrogen atmosphere is not available, dry
the filters for 1-2 hours in a desiccator under nitrogen. Ambient air contains ozone, so the filters must be protected from contamination by used of a nitrogen atmosphere.
f. Cool the filters a few minutes. Using forceps remove the IGFFs from the beakers and load the cassettes with two filters, one on top of the other both with the rough side up (grid side down).
g. Firmly close the cassette, make sure the end plugs are in place, and seal it with a gel band. Once the gel band is dry, place the cassette into an aluminized bag for storage until used in the
workplace. Instruct the industrial hygienist to return the cassette to the analytical laboratory using the aluminized bag for transport. Any IGFFs not used to load cassettes should be immediately
placed into aluminized bags for storage.
h. IGFFs stored in this fashion are stable for at least 45 days.
2.1.4 A stopwatch and bubble tube or meter to calibrate pumps.
2.1.5 Various lengths of polyvinyl chloride (PVC) tubing to connect sampling tubes to pumps.
2.1.6 Oxidizer tube for removing SO2 in the sampled air.
If there is reason to suspect the sampled air could contain SO2, an oxidizer tube must be used to remove
the SO2. See Figure 1 below and also
Section 4.9 for further details.
Oxidizer tubes normally used to convert nitric oxide to nitrogen dioxide will suffice; however, the contents of
the tubes must be passivated with O3 prior to use. Oxidizer tubes can be obtained from SKC Inc., Eighty
Four, PA as a Special Order item. The manufacturer or the user can passivate the oxidizer tubes prior to use, and
a shelf-life after passivation of one to two years should be observed. Passivation requires special ozone-generating
equipment. Oxidizer tubes and any Tygon tubing used in sampling must be conditioned with ozone using the following
procedure (Note: The O3 generation system used to validate this method and condition the oxidizer tubes
and Tygon tubing is further discussed in
Section 4.2.1. Other comparable systems can be
used.):
- Connect one end of each open oxidizer tube to the ozone generation system with short pieces of Tygon tubing.
(Note that this tubing will also be passivated and should be used as the oxidizer-cassette
connector when taking a sample using an oxidizer tube.)
- Set the O3 concentration for the generation system at approximately 0.1 ppm.
- Set the sampling pumps at approximately 0.5 L/min flow rates. Connect the other end of the open oxidizer tube
to each sampling pump using Tygon tubing.
- Condition the oxidizer tubes for 4 h. Stop the sampling pumps and cap the tubes using plastic caps or flame
seal. The shelf-life of the oxidizer should be 1 to 2 years.
2.2 Sampling Procedure
2.2.1 Remove both plastic end plugs from the cassette and connect the cassette to the calibrated sampling pump,
making sure the sampled air enters the rough side of the IGFF. Use an oxidizer tube only if SO2 is
suspected of being present in the sampled air (Figure 1). Place the sampling device on the employee such that air
is sampled from the breathing zone.
Figure 1. Ozone sampler with oxidizer tube. |
2.2.2 Use a flow rate of 0.5 L/min and a sampling time of 180 min. Take additional samples as necessary. A 0.25
L/min flow rate and a sampling time up to 480 min can also be used.
2.2.3 After sampling, immediately replace both plastic end plugs tightly in the cassette and apply OSHA Form 21
seals in such a way as to secure the end plugs.
2.2.4 Record the sampling conditions such as sampling time, air volume, flow rate, etc. on the OSHA 91A. When
other compounds are known or suspected to be present in the air, record such information and transmit with the
samples.
2.2.5 Handle a blank filter and cassette in exactly the same manner as the sample cassettes except that no air is
drawn through it. Use the same lot and preparation date of IGFF/cassettes for blank and collected samples. Prepare
at least one blank filter and cassette for each batch of ten samples.
2.2.6 Send the samples and blanks to the laboratory as soon as possible with the OSHA 91A paperwork requesting
ozone analysis.
3. Analysis
3.1 Safety Precautions
3.1.1 Review appropriate IC instrument manuals, UV-VIS detector or spectral array detector maintenance manual, and
the Standard Operating Procedure (SOP) for proper instrument operation
(Ref. 5.14).
Note: The SOP is a written procedure for a specific instrument. It is suggested that SOPs be prepared for each type
of instrument used in a lab to enhance safe and effective operation.
3.1.2 Observe laboratory safety regulations and practices.
3.1.3. Review any MSDSs provided with reagents and samples. Observe all precautions. Many chemicals are hazardous.
Use appropriate personal protective equipment such as safety glasses, goggles, face shields, gloves, and lab coat
when handling these chemicals.
3.2 Equipment
3.2.1 Ion chromatograph (Model 4000i or 4500i Dionex, Sunnyvale, CA) equipped with a UV-VIS detector
(Linear UVIS-206, Multiple wavelength detector, Linear Instruments Corporation, Reno, NV) or a
conductivity detector.
3.2.2 Automatic sampler (Dionex Model AS-1) and 0.5-mL sample vials/caps (Dionex part no. 38011).
3.2.3 Laboratory automation system: Ion chromatograph interfaced with a data reduction system (AI450, Dionex).
3.2.4 Separator and guard columns, anion (Model HPIC-AS9 and AG9, Dionex).
3.2.5 Forceps.
3.2.6 Disposable beakers (10 and 50 mL).
3.2.7 Cassette opener (SKC E-Z Opener, Cat. No. 225-13-5, SKC) or similar tool such as a coin or a screwdriver.
3.2.8 Disposable syringes (1 mL).
3.2.9 Syringe prefilters, 0.5-µm pore size (part no. SLSR 025 NS, Millipore Corp.,Bedford, MA).
Note: Some syringe prefilters are not cation- or anion-free. Blank reagent solutions should be filtered and analyzed
first to determine potential contamination and suitability with the analyte.
3.2.10 Miscellaneous volumetric glassware: Pipettes, volumetric flasks, Erlenmeyer flasks, graduated cylinders,
and beakers.
3.2.11 Equipment for eIuent degassing (vacuum pump, ultrasonic bath).
3.2.12 Analytical balance (0.01 mg).
3.2.13 Scintillation vials, 20 mL, with polypropylene- or Teflon-lined caps.
3.2.14
Treated glass fiber filters (IGFFs from
Section 2.1.3) for spiking or matrix matching
(if necessary).
3.3 Reagents - All chemicals should be at least reagent grade.
3.3.1 Principal reagents:
Sodium carbonate (Na2CO3), 99%
Sodium bicarbonate (NaHCO3), 99%
Sodium nitrate (NaNO3), 99.9%
Deionized water (DI H2O)
3.3.2 Eluent (1.0 mM Na2CO3 + 1.0 mM NaHCO3):
Dissolve 0.424 g Na2CO3 and 0.336 g NaHCO3 in 4.0 L DI H2O. Sonicate
this solution and degas under vacuum for 15 min.
Nitrate (NO3¯) stock standard (1,000 µg/mL):
Dissolve and dilute 1.3710 g of NaN03 to 1.0 L with DI H20. Prepare every 6 months.
Note: The laboratory should have an effective, independent quality control (QC) program in place and QC samples of
the analyte should be routinely analyzed along with field samples. Depending on the capabilities of the program, QC
samples can either be generated using the collection media and substance (O3) under controlled conditions,
or media can be spiked with the analyte (NO3¯). lf QC samples are not routinely prepared and analyzed,
two different standard stock solutions should always be prepared and these solutions should routinely be compared to
each other. Always prepare the stocks from two different sources or, as last resort, from different lots.
3.3.4 Nitrate (N03¯) standard solutions, 100, 10, and 1 µg/mL: Pipette
appropriate volumes of the 1,000 µg/mL as NO3¯ stock standard into volumetric flasks and dilute to
the mark with eluent. Prepare monthly.
3.4 Working Standard Preparation - Prepare fresh prior to beginning the analysis.
3.4.1 Prepare NO3¯ working standards in eluent. A suggested scheme for preparing a series of working
standards using 10-mL final solution volumes is shown below:
working std
(µg/mL) |
std solution
(µg/mL) |
aliquot
(mL) |
eluent added
(mL) |
0.5
1.0 *
2.0
5.0
10.0 |
1.0
1.0
10.0
10.0
10.0 |
5.0
-
2.0
5.0
- |
5.0
-
8.0
5.0
- |
* Already prepared in Section 3.3.4 |
3.4.2 To prepare each working standard (Working Std) listed above, transfer an appropriate amount of the Std
Solution to a disposable beaker, pipette an appropriate aliquot (Aliquot) of the specified standard solution
(prepared in Section 3.3.4) from the disposable beaker to an appropriate container
(scintillation vial, Erlenmeyer flask, etc.). Add the specified amount of eluent (Eluent Added).
3.4.3 As an alternative, pipette each aliquot into a 10-mL volumetric flask and dilute to volume with eluent.
3.5 Sample Preparation
3.5.1 Carefully open each cassette with a cassette opener (or similar tool, such as a coin or a screwdriver),
remove each IGFF and transfer each filter using a clean forceps into separate 20-mL scintillation
vials.
3.5.2
Pipette 5.0 mL of DI H2O into each vial. Make sure the filter is wetted. Cap the vials using
polyethylene-lined plastic caps.
Note: Alternate desorption volumes can be used and are dependent on the analytical sensitivity desired. For most
industrial hygiene samples, 5-mL volumes will allow for analysis of ozone (as NO3¯) within the range of
the standards specified.
3.5.3 Allow the samples to sit for at least 15 min. Occasionally swirl each solution.
3.5.4 If the sample solutions contain particulate, remove the particles using a prefilter and syringe.
3.6 Analysis
It is imperative that the large nitrite peak (from the sampling media) is adequately separated from the nitrate
peak. This can be assured by desorbing an IGFF (Section 3.2.14) with eluent, spiking the
solution with a known amount of nitrate working standard, and analyzing this solution prior to analysis. The
chromatogram shown below (Comparison of a Standard and a Sample) demonstrates the peaks obtainable from a sample
and a standard without any matrix-matching. Peak characteristics of the nitrate in the standard and
sample are similar, retention times appear very close, and there is adequate separation of nitrite and nitrate. If
a comparison of a spiked sample and a nitrate standard indicates poor separation or significantly different NO3¯
retention times, matrix-matching or a change in analytical conditions should occur. A new column could
be used or the eluent strength may be changed to facilitate separation. If matrix-matching of
standards and samples is the only alternative, standards should be prepared with treated filters in the same
fashion as samples.
Comparison of a Standard and a Sample
 |
| Text Version: This figure shows a sample chromatogram
superimposed over a standard chromatogram. The sample chromatogram shows the
chromatographic separation of the nitrite peak from the nitrate peak in a
sample. The retention times for the nitrate peak in the sample and the nitrate
peak in the standard are almost identical and show that the separation of
nitrite and nitrate is adequate. |
3.6.1 Pipette or pour a 0.5- to 0.6-mL portion of each standard or sample into separate automatic sampler vials.
Place a filtercap into each vial. The large filter portion of the cap should face the solution.
3.6.2 Load the automatic sampler with labeled samples, standards, and blanks.
3.6.3
Set up the ion chromatograph in accordance with the SOP (Ref. 5.14). Typical
operating conditions for a Dionex 4000i or 4500i with a UV-VIS detector (Spectral Array detector) and
an automated sampler are listed below:
Ion chromatograph with UV detector * at 200 nm wavelength
| Eluent: |
1.0 mM NaCO3/1.0 mM NaHCO3 |
| Column temperature: |
ambient |
| Anion precolumn: |
AG9 |
| Anion separator column: |
AS9 |
| Output range: |
2 absorbance units full scale (AUFS) |
| Rise time: |
5 sec |
| Sample injection loop: |
50 uL |
| |
|
| Pump |
|
| |
|
| Pump pressure: |
~900 psi |
| Flow rate: |
2 mL/min |
| |
|
| Chromatogram |
|
| |
|
| Run time: |
5 min |
| Peak retention time: |
~3.00 min for NO3¯ |
* For detection using a conductivity detector, output range and rise time are not used. A sensitivity setting on
the conductivity detector of 0.1 µS is used. All other settings are similar.
Soluble nitrate compounds can interfere when using either UV or conductivity detector. Response to nitrate using
either detector is similar and appears to be dependent on column conditions, eluent strength, and sensitivity
settings.
3.6.4 Analyze samples, standards, and blanks according to SOP
(Ref. 5.14).
3.7 Calculations
3.7.1 After the analysis is completed, retrieve the peak areas or heights. Obtain hard copies of chromatograms
from a printer. A chromatogram of a sample collected at an ozone concentration of approximately 2 times the PEL
for 180 min is shown below:
| ret time |
component name |
concentration |
height |
area |
| 3.22 |
nitrate |
6.142 µg/mL |
218782 |
2202892 |
 |
| Text Version: This
figure shows a sample chromatogram superimposed over a blank sample
chromatogram. The sample chromatogram represents nitrate from an ozone
concentration of approximately two times the PEL for a 180 min sample. The
nitrate normally occurring in a blank sample is shown for illustrative
purposes. Detector response and column retention times were obtained using
equipment and analytical conditions specified in this method. |
* Relative absorbance units using a UV-VIS detector
Note: The nitrate normally contained in a blank is only shown for illustration purposes. Peak heights, peak area, and
retention times are instrument dependent and were obtained using equipment specified in
Section 3.2.
3.7.2 Prepare a concentration-response curve by plotting the peak areas or peak heights versus the concentration
of the NO3¯ standards in µg/mL.
3.7.3 Determine total µg for each sample and blank. Perform a blank correction for each IGFF. Subtract the total
µg blank value from each total µg sample value.
Ab = (µg/mL NO3¯)b × (Sol Vol)b × (CF)
As = (µg/mL NO3¯)s × (Sol Vol)s × (CF)
A = As - Ab |
Then calculate the air concentration of O3 (in ppm) for each air sample:
| ppm O3 = |
A × (Mol Vol)
AV × (Mol Wt) |
| where: |
|
|
| Ab |
= |
Total µg O3 in blank |
| As |
= |
Total µg O3 in sample |
| A |
= |
µg O3 after blank correction |
| (µg/mL NO3¯)b |
= |
Amount found
(from calibration curve) in blank |
| (µg/mL NO3¯)s |
= |
Amount found
(from calibration curve) in sample |
| (Sol Vol)b |
= |
Blank solution volume (mL) from
Section 3.5.2
(normally 5 mL) |
| (SoI Vol)s |
= |
Sample solution volume (mL) from
Section 3.5.2
(normally 5 mL) |
| CF |
= |
Conversion factor = O3/NO3¯ = 0.7742 |
| Mol Vol |
= |
Molar volume (L/mol) = 24.45 (25°C and 760 mmHg) |
| AV |
= |
Air volume (L) |
| Mol Wt |
= |
Molecular weight for O3 = 47.997 (g/mol) |
3.8 Add the results of the first and second filters to give one final O3 concentration. If a significant
amount of analyte (>25 % of first filter) is found on the back-up (second) filter, breakthrough may
have occurred. Report possible breakthrough as a note on the report form.
3.9 Report results to the industrial hygienist as ppm O3.
4. Backup Data
This method has been validated for 90-L, 180-min samples taken at a flow rate of 0.5 L/min. The method validation was
conducted at different concentration levels near the OSHA TWA PEL of 0.1 ppm O3. In addition, 15-min
samples were also validated near the OSHA Final Rule STEL of 0.3 ppm. The sampling medium used during the validation
consisted of a two-section polystyrene cassette containing two IGFFs. The second IGFF serves as a backup
filter. During collection efficiency and breakthrough tests, two separate cassettes containing one IGFF each per
sample were used. The IGFFs were prepared as described in
Section 2.1.3. The 37-mm
GFFs were obtained commercially from Gelman Sciences (Lot no. 130404, Product no. 61652, Type A/E, Ann Arbor, MI).
In addition, a separate experiment of a passive monitor for O3 was conducted early in the evaluation. The
passive monitor (Ogawa & Co., USA, Inc., Pompano Beach, FL) operates on a principle similar to the reaction used
for this active sampler. The monitor was tested to determine potential OSHA compliance use.
The validation consisted of the following experiments and discussion:
- An analysis of 20 spiked samples (7 samples each at 1 and 2 times, and 6 samples at 0.5 times the TWA PEL) to
evaluate analytical recovery as desorption efficiency (DE).
- A sampling and analysis of 22 samples (7 samples each at 1 and 2 times, and 8 samples at 0.5 times the TWA PEL)
collected from dynamically generated test atmospheres at 50% RH to determine bias and overall error. Samples at a
concentration near the STEL (0.3 ppm) were also taken.
- A determination of the sampling medium collection efficiency at approximately 2 times the TWA PEL.
- A determination of potential breakthrough.
- An evaluation of storage stability at room (20-25°C temperatures for 26 collected samples.
- A determination of any significant humidity effects during sampling.
- A determination of the qualitative and quantitative detection limits.
- Comparison of sampling methods - impinger vs. treated filter vs. passive monitor (AKI vs. IGFF vs. OPS).
- Interface study.
- Shelf-life of the IGFFs.
- Summary.
A generation system was assembled as shown in
Figure 2, and used for all experiments except the
analysis, shelf-life study, and detection limit determinations. All samples were analyzed by IC using a UV-VIS
detector. All known concentrations of generated test atmospheres were determined using the AKI method for ozone (Ref.
5.2). All sampling tests were conducted using side-by-side IC and AKI samples. These samples were
then analyzed using the conditions recommended in their methods.
All results were calculated from concentration vs. response curves and statistically examined for outliers. In
addition, the analytical recovery (Section 4.1) and sampling and analysis results (Section
4.2) were tested for homogeneity of variance. Possible outliers were deter-mined using the Treatment of Outliers
Test (Ref. 5.15). Homogeneity of variance was determined using Bartlett's test (Ref.
5.16). Statistical evaluation was conducted according to the Inorganic Methods Evaluation Protocol (Ref.
5.17). The overall error (OE) (Ref. 5.17) was calculated using the equation:
OEi% = ±(|biasi| +
2CVi) X 100% (at the 95% confidence level)
Where i is the respective sample pool being examined.
Block Diagram of the Laboratory Generation System
 |
|
Figure 2 |
|
Text Version: Lab air passes through an Air Purifier and then
enters the Flow-Temp-Humidity Control System. Lab Water passes through
an Ionic Exchange Column, where it is purified, and then enters the
Flow-Temp-Humidity Control System. The Flow-Temp-Humidity Control System
generates properly conditioned dilution air that enters the Mixing
Chamber. Ozone is produced by the Ozone Generator System and it enters
the Mixing Chamber to be completely mixed with dilution air to produce
the ozone test atmosphere. The ozone test atmosphere enters the Active
Sampling Manifold. The Active Sampling Manifold provides a means to
sample the ozone atmosphere such as described in OSHA Method ID 214. The
ozone test atmosphere next enters an Ozone Passive Exposure Chamber where
diffusive samplers can be exposed to the ozone test atmosphere. The
ozone test atmosphere next passes through a Dry Test Meter where the
total air/ozone volume is measured. Finally, the ozone test atmosphere
enters the laboratory Exhaust system and goes to waste. |
4.1 Analytical Recovery
Ozone oxidizes sodium nitrite to sodium nitrate on the filter. To test the relative analytical capability of this
method, sodium nitrate was used as the analytical spike. Twenty samples were prepared by adding known amounts of NO3
(as NaNO3) stock solution to the IGFFs to determine desorption efficiencies (DEs) for the analytical
portion of the method.
4.1.1 Procedure: Each IGFF was spiked using a 25- or 50-µL syringe (Hamilton Microliter/Gastight Syringe,
Hamilton Co., Reno, NV). The IGFF samples were inside cassettes when spiked with aqueous solutions. Spikes were
either 11.5, 23.0, and 46.0 µg NO3¯. These levels correspond to approximately 0.5, 1, and 2 times the
TWA PEL for a 90-L air sample at a 0.5-L/min flow rate. The cassettes were allowed to
sit overnight and then analyzed.
4.1.2 Results: Desorption efficiencies are presented in Table 1. As shown, the average DE is very close to
1.0. No DE corrections are necessary for O3 collection using IGFFs.
Table 1
Ozone (as NO3¯) Analysis - Desorption Efficiency (DE) |
|
| level (¯) |
N |
mean DE |
SD |
CV1 |
|
0.5 × PEL
1 × PEL
2 × PEL
all levels |
6
7
7
20 |
0.979
1.025
0.977
0.994 |
0.055
0.029
0.47
- |
0.056
0.028
0.048
0.045 * |
*CV1 (pooled) |
4.2 Sampling and Analysis
To determine the precision and accuracy of the method, known concentrations of O3 were generated,
samples were collected, and analyzed.
4.2.1 Procedure:
- Test atmospheres of O3 were generated using two ozone generators (Model 565, ThermoElectron
Instruments, Hopkinton, MA) simultaneously to achieve as high O3 concentrations as possible. The O3
gas was diluted with filtered, humidified air using the system shown in Figure 2 and discussed below. A glass
mixing chamber was used to facilitate blending of ozone with the diluent air.
- Dynamic generation system
A Miller-Nelson Research Inc. flow, temperature, and humidity control system (Model HCS-301,
Monterey, CA) was used to control and condition the dilution airstream. All generation system fittings and
connections were Teflon. The O3 concentrations were varied by adjusting the dilution airstream
Volume. The dilution airstream was adjusted using the mass flow controller of the Miller-Nelson
system. For this experiment, the system was set to generate test atmospheres at 50% RH and 25°C. Test
atmosphere concentrations were approximately 0.5, 1, and 2 times the OSHA TWA PEL and at the OSHA STEL.
- The total flow rate of the generation system was measured using a dry test meter.
- IGFF/cassette samples were attached to the Teflon sampling manifold using Gilian Gil-Air SC
pumps (Gilian Instrument Corp., W. Caldwell, NJ) to draw the O3 test atmosphere through the IGFF
samples. Pump flow rates were approximately 0.5 and 1.5 L/min and sampling times were 180 and 15 min for TWA and
STEL experiments, respectively.
4.2.2 Results: The results are shown in Tables 2a and
2b.
The spiked sample (Table
1) and test atmosphere sample (Table 2a) results each passed the Bartlett's test and were pooled to determine
a CVT for the TWA sampling and analytical method.
Table 2a
Ozone sampling and Analysis - TWA PEL Determinations |
|
| level (¯) |
N |
ave recovery |
SD |
CV2 |
OE2 (±%) |
|
0.5
1
2
all levels |
8
7
7
22 |
1.032
1.071
0.937
1.014 |
0.060
0.023
0.028
- |
0.059
0.022
0.030
0.041* |
14.9
11.5
12.3
9.7 ** |
* CV2 (pooled) - ** OE2 (pooled) |
The total pooled coefficients of variation (CVT), bias, and total overall error
(OET) are as follows:
| CVT (pooled) = 0.045 |
bias = + 0.014 |
OET = 10.4% |
(Note: The CVT and OET values include data from
Section 4.1 and are
calculated using equations specified in Refs.
5.16-5.17.)
Table 2b
Ozone Sampling and Analysis - STEL PEL Determination
(Known O3 Concentration = 0.33 ppm) |
|
| level(¯) |
N |
mean ppm found |
SD |
CV |
recovery |
OE |
|
| STEL |
5 |
0.325 |
0.018 |
0.054 |
98.5% |
±12.3% |
|
4.3 Collection Efficiency
Procedure: Seven IGFF/cassettes were used to collect a concentration of approximately 2 times the OSHA TWA
PEL for 180 min at 0.5 L/min (50% RH and 25°C. The amounts of O3 gas collected on the first and second
IGFFs were determined. The collection efficiency (CE) was calculated by dividing the amount of O3
collected in the first filter by the total amount of O3 collected in the first and second IGFFs.
Results: The results in Table 3 show a CE of 100%. No O3 was found in the second IGFF for the CE
experiment and indicates the IGFFs have adequate collection of O3 near the PEL.
Table 3
Collection Efficiency (CE)
2 × PEL - 25°C - 50% RH |
|
| |
ppm O3
|
| sample no. |
1st IGFF |
2nd IGFF |
CE, % |
|
1
2
3
4
5
6
7 |
0.209
0.220
0.203
0.216
0.211
0.204
0.206 |
ND
ND
ND
ND
ND
ND
ND |
100.0
100.0
100.0
100.0
100.0
100.0
100.0 |
|
| Notes: |
(a) |
Sampled at 0.5 L/min for 180 min. |
| |
(b) |
Samples desorbed using a sample solution volume of 5.0 mL |
| |
(c) |
ND = None detectable (< 0.008 ppm O3) |
4.4 Breakthrough
(Note: Breakthrough is defined as > 5 % loss of analyte from the first IGFF to a backup IGFF at 50% RH)
Procedure: The same procedure as the CE experiment (Section 4.3) was used with two
exceptions: In addition to the 2 × concentration, the generation concentration was increased to a level
approximately 4 times the TWA PEL, and samples were taken at approximately 0.5 L/min for 240 min. Another test was
conducted for 6 times the TWA PEL using a sampling rate of approximately 0.25 L/min for 240 min. Due to limitations
on the O3 generators and the generation system, larger O3 concentrations could not be
achieved.
The amount of breakthrough for each sampling cassette was calculated by dividing the amount collected in the second
IGFF by the total amount of O3 collected in the first and second IGFFs.
Results: For measurements near the TWA PEL, no breakthrough of O3 into the second section
was found at an approximate concentration of 0.2 ppm O3 (Table 4a), and indicates the first IGFF has
adequate retention of O3 at 2 times TWA PEL. However, the average breakthrough was 7.5% at an
approximate concentration of 0.4 ppm O3 (Table 4b) for 240 min at 0.5 L/min flow
rate. No break-through was found at the approximate concentration of 0.6 ppm O3 (Table
4c) when using a lower flow rate of 0.25 L/min. For the STEL, no breakthrough was found at approximate
concentration of 0.3 ppm O3 (Table 4d) for 15 min at 1.5 L/min sample collection
flow rate.
Table 4a
Breakthrough Study - 0.5 L/min
2 × PEL - 25°C - 50% RH |
|
| |
ppm O3
|
| sample no. |
1st IGFF |
2nd IGFF |
Breakthrough, % |
|
1
2
3
4
5
6 |
0.242
0.281
0.190
0.227
0.238
0.215 |
ND
ND
ND
ND
ND
ND |
0
0
0
0
0
0 |
|
| Notes: |
(a) |
Sampled at - 0.5 L/min for 240 min |
| |
(b) |
Due to the larger sampling period and thus larger mass collected, the first IGFF was desorbed using larger
sample solution volumes of 10.0 mL. |
| |
(c) |
ND = None detectable (< 0.008 ppm O3) |
Table 4b
Breakthrough Study - 0.5 L/min
4 × PEL - 25°C - 50% RH |
|
| |
ppm O3
|
| sample no. |
1st IGFF |
2nd IGFF |
CE, % |
|
1
2
3
4
5
6 |
0.425
0.385
0.395
0.363
0.383
0.342 |
ND
ND
ND
ND
ND
ND |
0
0
0
0
0
0 |
|
| Notes: |
(a) |
Sampled at - 0.5 L/min for 240 min |
| |
(b) |
Due to the larger sampling period and thus larger mass collected, the first IGFF was desorbed using larger
sample solution volumes of 15.0 mL. |
| |
(c) |
Statistical analysis - N = 8; mean = 7.5; SD = 1.5; CV = 0.20 |
Table 4c
Breakthrough Study - 0.25 L/min
4 × PEL - 25°C - 50% RH |
|
|
ppm O3
|
| sample no. |
1st IGFF |
2nd IGFF |
Breakthrough, % |
|
1
2
3
4
5
6 |
0.563
0.600
0.586
0.661
0.566
0.558 |
ND
ND
ND
ND
ND
ND |
0
0
0
0
0
0 |
|
| Notes: |
(a) |
Sampled at - 0.25 L/min for 240 min |
| |
(b) |
Due to the larger sampling period and thus larger mass collected, the first IGFF was desorbed using larger
sample solution volumes of 10.0 mL. |
| |
(c) |
ND = None detectable (<0.008 ppm O3) |
Table 4d
Breakthrough Study - 1.5 L/min
1 × PEL - 25°C - 50% RH |
|
|
ppm O3
|
| sample no. |
1st IGFF |
2nd IGFF |
Breakthrough, % |
|
1
2
3
4
5
6 |
0.440
0.308
0.333
0.346
0.306
0.334 |
ND
ND
ND
ND
ND
ND |
0
0
0
0
0
0 |
|
| Notes: |
(a) |
Sampled at - 1.5 L/min for 15 min |
| |
(b) |
Samples desorbed using a sample solution volume of 5.0 mL |
| |
(c) |
ND = None detectable (< 0.032 ppm O3) |
4.5 Storage Stability
Procedure: A study was conducted to assess the stability of the NO2¯ + O3
reaction product, NO3¯ on the IGFFs. A room temperature storage stability study using 26 samples taken
near the OSHA TWA PEL of 0.1 ppm was performed. All samples were stored under normal laboratory conditions
(20-25°C) in a plastic bag in a drawer. Seven samples were initially desorbed and analyzed; seven more samples
were desorbed and analyzed after 5 days, followed by six samples at 15, and 30 days, respectively.
Results: The mean of samples analyzed after 30 days was within 10% of the mean of samples analyzed the
first day, as shown in Table 5 and Figure 3 below.
Table 5
Storage Stability - Ozone
(25°C, and 50% RH)
(Known O3 Concentration = 0.123 ppm) |
|
| Day |
N |
Mean O3Found |
SD |
CV |
Recovery (%) |
|
1
5
15
30 |
7
7
6
6 |
0.122
0.120
0.135
0.116 |
0.005
0.004
0.002
0.006 |
0.038
0.036
0.015
0.052 |
99.2
97.6
109.8
94.3 |
|
Storage Stability
Figure 3 |
| Text Version: Figure 3 is a graph of the
storage stability data shown in Table 5. The graph shows percent ozone
recovery-plotted on the y-axis against days of storage time-plotted on the
x-axis. The storage stability is excellent, with approximately 94% of the ozone
recovered after 30 days of ambient storage. |
4.6 Humidity Study
Procedure: A study was conducted to determine any effect on recovery results when samples are
collected at different humidities. Samples were taken using the generation system and procedure described in
Section 4.2. Test atmospheres were generated at 25°C and at approximately 0.5, 1, and 2 times the OSHA TWA PEL.
Relative humidities of 30%, 50%, and 80% were used at each concentration level tested.
Results: Results of the humidity tests are listed in Table 6. An F test was used to determine if any
significant effect occurred when sampling at different RHs. As shown, at the 99% confidence level, the calculated F
values are much smaller than critical F values (Ref. 5.16) for all the concentrations
tested; therefore, no significant difference in results occurred across the RH ranges tested.
Table 6
Humidity Test - Ozone
25°C |
|
| Level |
RH, % |
N |
Mean O3
Found |
SD |
CV |
Taken |
Recovery, % |
Fcrit |
Fcalc |
|
| 0.5 × PEL |
30
50
80 |
7
8
7 |
0.073
0.072
0.060 |
0.008
0.004
0.001 |
0.107
0.059
0.024 |
0.070
0.070
0.058 |
104
103
103 |
5.93 |
0.02 |
|
| 1 × PEL |
30
50
80 |
6
7
7 |
0.119
0.118
0.101 |
0.007
0.003
0.002 |
0.059
0.022
0.022 |
0.115
0.110
0.098 |
103
107
103 |
6.11 |
2.62 |
|
| 2 × PEL |
30
50
80 |
7
7
7 |
0.174
0.222
0.231 |
0.005
0.006
0.006 |
0.030
0.028
0.027 |
0.172
0.224
0.237 |
101
99.1
97.5 |
6.01 |
2.71 |
|
4.7 Qualitative and Quantitative Detection Limit Study
A modification of the National Institute for Occupational Safety and Health (NIOSH) detection limit calculations
(Refs. 5.18-5.19) was used to calculate detection limits.
Procedure: Low concentration samples were prepared by spiking aqueous standards prepared from NaNO3
(Section 3.3.4) at five different concentrations on the IGFFs. Samples were analyzed using a
50-µL sample injection loop and a UV-VIS detector setting of 2 AUFS.
Results: The IGFF spiked sample results are shown in Table 7 for qualitative and quantitative
detection limits, respectively. The qualitative detection limit is 0.37 µg/mL as NO3¯ at the 99.8%
confidence level. The quantitative detection limit is 1.25 µg/mL as NO3¯. Using a 90-L
air volume and a 5-mL sample solution volume, the qualitative and quantitative detection limits are
0.008 ppm and 0.03 ppm, respectively, as O3.
Table 7
Qualitative and Quantitative Detection Limits (NIOSH Method) |
|
|
O3 (as NO3¯) Level
|
| Sample No. |
Blank
PA |
0.1 µg/mL
PA |
0.2 µg/mL
PA |
0.5 µg/mL
PA |
1.0 µg/mL
PA |
|
1
2
3
4
5
6 |
2.05
1.98
2.02
2.03
2.02
1.74* |
2.73
2.60
1.81*
2.60
2.68
2.69 |
2.25
3.15
3.15
3.23
4.55*
3.79 |
3.17
4.15
3.21
4.09
4.12
3.24 |
5.87
4.99
4.98
5.76
5.81
5.81 |
|
* Outlier
PA - Integrated Peak Area (NO3¯)/100,000 |
The average responses of the low-level calibration samples were plotted to obtain the linear regression equation (Y
= mX + b), and the predicted responses ( i)
at each X.
Using the equations:
 |
|
Q2 = (3.33)Q1 |
| Text Version: First subtract each
obtained response from its predicted response, and then square that difference.
Sum all these values. Divide the sum by the number of data points minus two.
Take the square root of that value. The result is the standard error of the
regression line. |
| Therefore, |
Q1 |
= |
(3Sy)/m = 0.37 µg/mL as NO3¯ |
| |
|
|
1.85 µg as NO3¯ (5-mL sample volume) |
| |
|
|
0.008 ppm O3 (90-L air volume) |
| |
Q2 |
= |
(3.33)Q1 |
| |
|
|
0.027 ppm O3 (90-L air volume) |
| where: |
|
| B |
= |
mean blank response |
| b |
= |
intercept of the regression |
| m |
= |
analytical sensitivity or slope as calculated by linear regression |
| SY |
= |
standard error of the regression = 0.21667 |
| N |
= |
number of data points |
| Q1 |
= |
qualitative detection limit |
| Q2 |
= |
quantitative detection limit |
The Correlation Coefficient (r) and Coefficient of Determination (r2)
for the above data were r = 0.986
and r2 = 0. 972.
4.8 Comparison of Sampling Methods
This method was compared with the classical AKI approach and a passive monitor method. The Ogawa passive sampler
(OPS), developed by the Harvard School of Public Health (HSPH), was originally designed to sample for nitrogen
oxides in the environment. Modifications allowed its use to monitor ambient environmental ozone. The reaction
principle and analysis are similar to this lGFF method; however, the impregnating solution is slightly different
(and proprietary for the passive system), and the samples are analyzed by IC for nitrate ion using conductivity
detection instead of UV-VIS Prior to using the OPS method for this comparison, the sampling rate was examined. Due
to face velocity dependence, sampling rates are critical to the performance of the passive monitor during this
comparison. The determination of sampling rate is detailed in the Appendix.
Procedure: In order to compare performance, the IGFF/cassettes (this study), AKI samples, and OPSs
were collected side by side from the generation system at approximately 0.5, 1 and 2 times the PEL. The
IGFF/cassettes and OPSs were analyzed by IC. The AKI samples were analyzed by a colorimetric procedure further
described in Ref. 5.2. The average sampling rate as determined by SLTC for the face
velocity
achieved, 21.93 cm3/min, was used for OPSs.
Results: Table 8 shows the results of the comparison study. As shown, the IGFF/cassettes, the AKI
samples, and OPSs are in good agreement except that OPSs are slightly higher for 1 times and lower for 2 times PEL.
Table 8
Comparison of Methods (Summary)
(25°C and 50% RH) |
|
| Set # |
Method |
O3 Found, ppm |
N |
SD |
CV |
|
| 1 |
AKI
IGFF
OPS |
0.070
0.072
0.073 |
3
8
4 |
0.006
0.004
0.003 |
0.086
0.056
0.041 |
| 2 |
AKI
IGFF
OPS |
0.110
0.118
0.129 |
3
7
7 |
0.002
0.003
0.017 |
0.018
0.025
0.132 |
| 3 |
AKI
IGFF
OPS |
0.224
0.210
0.187 |
3
7
7 |
0.008
0.006
0.012 |
0.036
0.029
0.064 |
|
| where: |
AKI Alkaline potassium iodide (Ref. 5.2) |
| |
IGFF Impregnated glass fiber filter (this study) |
| |
OPS Ogawa passive sample for ozone (Refs.
5.10 and
5.20) |
NOTE: Although the passive monitor performed reasonably well during the comparison, detection limit calculations
indicate potential problems may be incurred for OSHA compliance use. The monitor was originally designed for
environmental (24-h) use. Using the manufacturer's stated detection limit of 200 ppb-h as
analyzed using IC and a conductivity detector (the manufacturer's recommended analytical technique), an 8-h
detection limit of 0.025 ppm would be obtained (using a UV-VIS detector SLTC indicates a quantitative detection limit
of about 0.1 ppm-h; however, for STEL or intermittent sampling the monitor still appears not
sufficiently sensitive). This would necessitate 7 to 8-h sampling and would not be ' conducive to STEL
or intermittent sampling occasionally required in monitoring situations. The monitor appears beneficial in industrial
hygiene situations provided large concentrations ( > 0.1 to 0.2 ppm O3) are present or 7 to 8-h
sampling is performed. The study to determine applicability was halted after preliminary determinations indicated the
passive monitor also suffered from the same negative interference from SO2 as the active sampler (Section
4.9). In a recent paper (Ref. 5.10), the authors indicated that SO2
should not
interfere with the passive sampler collection of O3; however, experiments to verify this were not
presented in the paper.
4.9 Interference Study
As previously discussed in Section 1, oxidizing gases have interfered with the determination
of O3
in previous methods (Refs.
5.1-5.2,
5.4).
Several tests were conducted to evaluate any possible interference from NO2 or SO2.
Procedure: Possible interferences from NO2 and SO2 were tested using several
sets of IGFF/cassette samples. A test was conducted by taking four samples at approximately 6 ppm NO2
and compared to four samples without NO2 which served as "control" samples. Several tests were
conducted to evaluate any SO2 interference by comparing results of six samples with SO2 to
another four to six samples without SO2, present. These tests included two different SO2
concentrations and use of oxidizer tubes for removal of SO2 from the sampled air prior to O3
reaction with the treated filters.
Two different kinds of oxidizer tubes were evaluated. Both were manufactured by SKC Inc. (Eighty Four, PA) and are
used to convert nitric oxide (NO) to nitrogen dioxide (NO2) during sampling for NO. The two types of
oxidizer tubes are:
Tube Label
|
Substrate
|
Abbrev.
|
| Oxidizer Special |
Chromate impregnated sand |
OS |
| Misc-Spec |
Chromate impregnated material
(Composition of substrate unknown) |
MS |
Both tube labels are designations given by SKC. Chromate impregnated sorbent has been shown to effectively remove
SO2 during ozone sampling (Ref.
5.21). All samples were taken at a flow rate of
about 0.5 L/min for 180 min. The generation system concentration was approximately 1.5 times the TWA PEL for ozone.
Results: Table 9 shows the results of the IGFF/cassette sample sets:
Sample Set No.
|
Description
|
| 1) |
O3 with and without NO2 |
| 2) |
O3 with and without SO2 (3.41 ppm) |
| 3) |
O3 with and without SO2 (1.06 ppm) |
| 4) |
O3 with and without SO2 (0.35 ppm) |
| 5) |
O3 + SO2 with and without OS oxidizer |
| 6) |
O3 + SO2 with OS oxidizer before and after conditioning |
| 7) |
O3 + SO2 with and without MS oxidizer |
| 8) |
O3 + SO2 with MS oxidizer before and after conditioning |
| 9) |
Comparison study between 50% and 80% RH for O3 +SO2 with MS oxidizer after
conditioning. |
Note: Oxidizer tube conditioning is based on the procedure discussed in
Section 2.
Table 9
Interference Study - Ozone
(25°C - 50% RH and 1.5 ×PEL) |
|
| Sample Set # |
Interferant
Concn, ppm |
Oxidizer
(Yes or No) |
Conditioning
(Yes or No) |
N
# |
Mean O3,
ppm |
SD O3,
ppm |
CV% |
|
| 1 |
NO2, 6.38
NO2, 0 |
No
NA |
NA
NA |
4
4 |
0.129
0.134 |
0.007
0.003 |
5.5
20. |
| 2 |
SO2, 3.41
SO2, 0 |
No
NA |
NA
NA |
| |
