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Printing Instructions
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For problems with accessibility in using figures, illustrations and PDF 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. |
Formaldehyde
(Diffusive Samplers)
[282 KB PDF]
Related Information: Chemical Sampling -
Formaldehyde
|
| Method no.: |
1007 |
| |
|
| Control no.: |
T-1007-FV-01-0505-M |
| |
|
| Target concentration: |
0.75 ppm (0.92 mg/m3) |
| OSHA PEL: |
0.75 ppm (0.92 mg/m3) (TWA); 2 ppm (2.5
mg/m3) (STEL) |
| OSHA Action level: |
0.5 ppm (0.61 mg/m3) (TWA) |
| ACGIH TLV: |
0.3 ppm (0.37 mg/m3) (ceiling) |
| |
|
| Procedure: |
Diffusive samples are collected by
exposing either Assay Technology ChemDisk Aldehyde Monitor 571 (ChemDisk-AL),
SKC UMEx 100 Passive Sampler (UMEx 100), or Supelco DSD-DNPH Diffusive
Sampling Device (DSD-DNPH) to workplace air. Samples are extracted with
acetonitrile and analyzed by LC using a UV detector. |
| |
|
Recommended sampling time
For UMEx 100, ChemDisk-AL,
and DSD-DNPH: |
240 min (TWA); 15 min (STEL) |
| |
|
| Reliable quantitation limit: |
| sampler |
RQL |
SEE* |
| (ppb) |
(μg/m3) |
(%) |
|
ChemDisk-AL
UMEx 100
DSD-DNPH |
1.88
5.68
0.58 |
2.30
6.93
0.70 |
7.8
8.2
7.5 |
|
| |
*For samples where sampling
site atmospheric pressure and temperature are known. When either or both
of these values are unknown, see Section 4.4 for applicable standard
errors of estimate. |
| |
|
| Special requirements: |
Report sampling site atmospheric pressure and temperature when using diffusive samplers.
Store samplers in a refrigerator both before and after sampling.
For quantitative results, use an active sampling procedure such as OSHA Method 52 when monitoring exposures resulting from the use of formalin solutions. These diffusive samplers failed validation when formalin was the source of formaldehyde. (Section 4.9)
Do not use these diffusive samplers if the ozone level is greater than 0.5 ppm. (Section 4.9)
Do not use these diffusive samplers if the humidity is 10% or less. (Section 4.9)
Place samples into manufacturer-supplied aluminized bags immediately after sampling.
|
| |
|
| Status of method: |
Evaluated method. This method has been
subjected to established evaluation procedures of the Methods Development
Team. |
| |
|
| May 2005 |
Mary Eide |
| |
|
Methods Development Team
Industrial Hygiene Chemistry Division
OSHA Salt Lake Technical Center
Sandy UT 84070-6406 |
1. General Discussion
For problems with accessibility in using figures and illustrations in this method, please contact the author 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.
1.1 Background
1.1.1 History
The purpose of this work was to validate a diffusive sampler for
formaldehyde. The 3M formaldehyde monitor 3721, used in OSHA Method
ID-2051, adsorbed the formaldehyde onto a bisulfite-impregnated paper, and used chromotropic acid to detect formaldehyde. These samplers
could be used for only TWA sampling with a minimum of 4 hours sampled. The PEL for formaldehyde has a 2 ppm STEL, so a diffusive sampler
that could measure STEL level was desired. The three diffusive sampling devices used in this method are Assay Technology ChemDisk 571
Aldehyde Monitor (ChemDisk-AL), SKC UMEx 100 Passive Sampler (UMEx 100), and Supelco DSD-DNPH Diffusive Sampling Device (DSD-DNPH). All
three of these samplers use 2,4-dinitrophenyl hydrazine (DNPH), in the presence of a strong acid, to derivatize the formaldehyde into a
unique derivative. Other aldehydes and ketones will form their own unique derivative. The analysis is by liquid chromatography (LC) with a
UV detector at 365 nm. The sensitivity of these samplers was much greater than the bisulfite impregnated paper, so these samplers can be
used for STEL sampling. The reaction of the carbonyl containing chemical with DNPH to form the hydrazone derivative and water is shown
below:
 |
In the case of formaldehyde R1 and R2 are hydrogens.
The test atmospheres used in this work were dynamically generated by introducing the formaldehyde/water solution into a heated manifold, and
then diluting the resultant vapor with a measured stream of air at a known flow, temperature, and humidity. The formaldehyde/water solution
was freshly prepared by bubbling formaldehyde gas produced by heating paraformaldehyde into deionized water. A nitrogen gas stream carried
the formaldehyde gas into the water. The concentration of the formaldehyde in solution was determined by titration following the procedure
in OSHA Method 52.2 This solution was stable for at least 1 week. Theoretical test atmosphere concentration was calculated from the test
atmosphere generation parameters, and it was confirmed using OSHA Method 52.3 The average of active sampling method results was 99.4% of
theoretical for side-by-side samples that were collected simultaneously for every diffusive sampler test. Theoretical test atmosphere
concentrations (verified by active sample results) were used in subsequent calculations.
Sampling test atmospheres generated using formalin (formaldehyde/water solution stabilized with methyl alcohol) at ambient temperatures can
produce low results for diffusive samplers that have been calibrated with formaldehyde when compared to results from active samplers. This
discrepancy has been cited in the literature and it was confirmed by experimental work performed in this method (Section 4.9), and may be as
much as 35%.4,5 The root cause of the inconsistency is the reversible chemical reaction of formaldehyde and methyl alcohol to form primarily methoxymethanol and trace levels of dimethoxymethane.6 Both formaldehyde and methoxymethanol react to form the formaldehyde derivative on
reagent coated active and diffusive samplers. Methoxymethanol and dimethoxymethane have different diffusive sampling rates than
formaldehyde. Sampling rate for diffusive samplers is dependant on the chemical being sampled, while sampling rate for active samplers is
independent of the chemical being sampled, as the sampling rate is the flow rate of the sampling pump.
This uncorrectable bias for formaldehyde diffusive samplers will always exist in workplaces where formalin is used, and may be greater than
the accuracy requirement of ±25% for TWA samples and ±35% for STEL samples, required by the OSHA standard for formaldehyde.7 For
quantitative results, an active sampling procedure such as OSHA Method 528 should be used when monitoring exposures resulting from the use of
formalin solutions.
The laboratory test atmosphere issue can be resolved by increasing the temperature of the vapor generator such that it is sufficient to
reverse the formation of methoxymethanol and dimethoxymethane and accordingly reform formaldehyde. Diffusive and active sampling results
from such a test atmosphere are similar. This effect was also confirmed in this work (Section 4.11). Conditions in the workplace may not
be sufficient to reverse the formation of methoxymethanol and dimethoxymethane, and their unknown proportions in workplace atmospheres can
cause erroneous diffusive sampling results for formaldehyde.
Ozone is an interference for samplers using DNPH derivatization. Ozone can react with the DNPH, decreasing the amount available for
derivatizing the formaldehyde, or it can decrease the amount of formaldehyde-DNPH already produced.9 Most urban pollution levels are below
0.5 ppm ozone. Tests of an atmosphere of 0.577 ppm ozone showed a recovery of 92.5% for ChemDisk-AL, 92.6% for UMEx 100, and 92.5% for
DSD-DNPH. Higher ozone levels showed more of a loss (Section 4.9).
The diffusive samplers in this work performed best in relative humidities (RH) above 10% (Section 4.9). At relative humidities lower than
10% the tested results were significantly lower when compared to theoretical. This indicates that water is a necessary component of the
reaction between formaldehyde and DNPH.
Storing samplers at elevated temperatures causes the DNPH to decompose, forming 2,4-dinitroaniline, which may co-elute with the
DNPH-formaldehyde derivative. EPA recommends storing samplers both before and after sampling at 4 °C.10,11 This decomposition was also
observed by NIOSH, a significant increase of a peak at the retention time of the formaldehyde-DNPH derivative was observed when DNPH coated
silica gel air samplers were stored at 40 °C (104 °F) overnight.12
1.1.2 Toxic effects (This section is for information only and should not be taken as the basis of OSHA policy.)13
OSHA has stated "Formaldehyde has the potential to cause cancer in humans." Concentrations of 0.5 to 2 ppm may cause eye, respiratory, and
skin irritation. Rats exposed to 2 ppm formaldehyde developed benign nasal tumors. Structural changes in epithelial cells in human nasal
passages have been observed. The perception of formaldehyde by odor and/or eye irritation may diminish with time as the body adapts to the
formaldehyde concentration in the workplace air. It can cause skin sensitization. Formaldehyde is genotoxic showing properties of both an
initiator and a promoter.
1.1.3 Workplace exposure14
Formaldehyde is consistently listed in the top 25 chemicals produced in the U.S. Some of the formaldehyde produced in the U.S. is produced
and consumed in the same facility through a closed system. Most of the commercial production is as a formalin solution. The rest of the
commercial production is as formaldehyde gas and paraformaldehyde. Formaldehyde is used in the production of urea-formaldehyde,
phenol-formaldehyde, melamine, and polyacetal resins. It is used in the production of many organic chemicals, including dyes, fertilizers,
disinfectants and germicides. It is used as a preservative for shampoos, conditioners, and paints, as an embalming fluid, as a hardening
agent, as an oil well corrosion inhibitor, as a reducing agent in the recovery of gold and silver, as a fungicide for other plant products,
as a component in the manufacture of fiberboard, particle board and plywood, and as a permanent-press treatment for fabrics. Formaldehyde
exposure may come from the vapors from formaldehyde gas, formalin solution, or solid paraformaldehyde. Exposures also come from cutting,
heating, and other manipulations of the formaldehyde containing resins, fiber products and wood products. Formaldehyde is a component of
diesel exhaust.
1.1.4 Physical properties and other descriptive information15,16
| synonyms: |
formic aldehyde; methyl aldehyde; methylanal;
methylene oxide; oxomethane; oxymethylene |
| IMIS17 |
1290 |
| CAS number: |
50-00-0 |
| boiling point: |
-19.5 °C (-3.1 °F) |
| melting point: |
-92 °C (-133.6 °F) |
| molecular weight: |
30.03 |
| vapor pressure: |
1.33 kPa @ -88 °C |
| flash point: |
50 °C (122 °F) (closed cup aqueous solution
with 15% methyl alcohol) |
| appearance: |
colorless gas; aqueous solutions with methyl
alcohol are clear liquid |
| vapor density: |
1.08 (air = 1.0) |
| molecular formula: |
CH2O |
| odor: |
pungent, slightly musty |
| lower explosive limit: |
7 to 73% by volume |
| specific gravity: |
0.815 at -20/4 °C |
| solubility: |
very soluble in water, up to 55%; soluble in
alcohol, ether |
| structure: |
 |
This method was evaluated according to the OSHA SLTC "Evaluation Guidelines for
Air Sampling Methods Utilizing Chromatographic Analysis"
18.
The Guidelines define analytical parameters, specify required laboratory tests, statistical calculations and acceptance criteria. The
analyte air concentrations throughout this method are based on the recommended sampling and analytical parameters. Air concentrations in ppm
are referenced to 25°C and 101.3 kPa (760 mmHg).
1.2 Limit defining parameters
1.2.1 Detection limit of the analytical procedure
The detection limit of the analytical procedure (DLAP) is 4.26 pg. This is the amount of analyte that will give a detector response that is
significantly different from the response of a reagent blank. (Section 4.1)
1.2.2 Detection limit of the overall
procedure
The detection limits of the overall procedure (DLOP) are shown in Table 1.2.2. These are the amounts of formaldehyde spiked on the respective
sampler that will give detector responses that are significantly different from the responses of the respective sampler blanks. (Section 4.2)
|
Table 1.2.2
Detection Limits of the Overall Procedure
|
| sampler |
ng |
ppb |
μg/m3 |
|
| ChemDisk-AL |
2.25 |
0.56 |
0.69 |
| UMEx 100 |
14.9 |
1.70 |
2.08 |
| DSD-DNPH |
3.56 |
0.17 |
0.21 |
|
|
1.2.3 Reliable quantitation limit
The reliable quantitation limits (RQL) are shown in Table 1.2.3. These are
the amounts of formaldehyde spiked on the respective samplers that will give
detector responses that are considered the lower limits for precise
quantitative measurements. (Section 4.2) |
Table 1.2.3
Reliable Quantitation Limits
|
| sampler |
ng |
ppb |
mg/m3 |
EE |
|
| ChemDisk-AL |
7.49 |
1.88 |
2.30 |
99.5 |
| UMEx 100 |
49.5 |
5.68 |
6.93 |
99.3 |
| DSD-DNPH |
11.9 |
0.58 |
0.70 |
99.5 |
|
|
EE = extraction efficiency |
|
1.2.4 Instrument calibration
The standard error of estimate is 0.051 μg over the range of 3.92 to 31.34 μg/sample. This range corresponds to 0.25 to 2 times the TWA
target concentration for DSD-DNPH. (Section 4.3)
1.2.5 Precision
The precisions of the overall procedure at the 95% confidence level were calculated from the ambient temperature 17-day storage test for
samples collected from a dynamically generated atmosphere of 0.75 ppm (0.92 mg/m3) formaldehyde. The precision includes the sampling rate
variability of 7.71% for ChemDisk-AL, 8.06% for UMEx 100, and 7.54% for DSD-DNPH. There are different precision values given, depending on
whether both, either, or neither temperature (T) or atmospheric pressure (P) are known at the sampling site. If the sampling site
temperature is unknown, it is assumed to be 22.2 ± 15°C (72 ± 27°F) and a variability of ±7.7% is included. If the atmospheric pressure is
not known, it is estimated from the sampling site elevation and a variability of ±3% is included. (Section 4.4)
Table 1.2.5
Precision of the Overall Procedure
|
| known conditions |
ChemDisk-AL
precision (± %) |
UMEx 100
precision (± %) |
DSD-DNPH
precision (± %) |
|
| both T & P |
15.3 |
16.0 |
14.8 |
| only T |
16.3 |
17.0 |
15.9 |
| only P |
21.6 |
22.0 |
21.2 |
| neither T nor P |
22.3 |
22.7 |
22.0 |
|
1.2.6 Recovery
The recovery of formaldehyde from samples used in a 17-day storage test remained above 95.2, 94.6, and 95.8% when the samples were stored at
23°C for ChemDisk-ALs, UMEx 100s, and DSD-DNPHs, respectively. All samples were stored in manufacturer-supplied aluminized bags to protect
them from ambient formaldehyde. (Section 4.5)
1.2.7 Reproducibility
Six samples for each of the three types of samplers were collected from a controlled test atmosphere and submitted for analysis by the OSHA
Salt Lake Technical Center. The samples were analyzed according to a draft copy of this procedure after 27 days of storage at 4 °C. No
individual sample result deviated from its theoretical value by more than the precision reported in Section 1.2.5 for known temperature and
pressure. (Section 4.6)
2. Sampling Procedure
All safety practices that apply to the work area being sampled should be followed. The sampling equipment should be attached to the worker
in such a manner that it will not interfere with work performance or safety.
2.1 Apparatus
ChemDisk 571 Aldehyde Monitor, containing a glass fiber filter coated with DNPH and phosphoric acid (Assay Technology, Inc., catalog no.
571, lot 571AT1D03).
SKC UMEx 100 Passive Sampler, containing a silica tape coated with DNPH and phosphoric acid (SKC, Inc., catalog no. 500-100, lots 2527A,
2233C, and 2756).
DSD-DNPH Diffusive Samplers for Aldehydes, containing a beaded silica gel coated with DNPH and phosphoric acid (Supelco, Inc., lot SP0403H01). A reusable sampler holder was used to hold DSD-DNPH (Supelco, Inc., catalog no. 21019-U).
A thermometer and barometer to determine the sampling site air temperature and atmospheric pressure while sampling.
2.2 Reagents
None required
2.3 Technique
Refrigerate all samplers before and after use.
2.3.1 ChemDisk-AL (In general, follow the manufacture’s instructions supplied with the samplers.)
Immediately before sampling, tear open the aluminum foil pouch at the notches, and remove the sampler. Remove the plastic cover from
the face that has the holes, and save the cover. Place the sampler in the holder. Save the plastic disc-shaped sampler cover to put
on the sampler after sampling is completed. If the sampler is the ChemDisk II design, tear open the aluminum foil pouch, attach the
clip to the sampler, and open the cover. Caution - The sampler begins to sample immediately after the foil pouch
is opened and plastic cover is removed.
Record the start time on the OSHA 91A form or equivalent monitoring record.
Attach the sampler to the worker near his/her breathing zone with the side that has the holes facing forward. Assure that the area
directly in front of the sampler is unobstructed throughout the sampling period.
At the end of the sampling period, detach the sampler from the worker and replace the cover. Place the sampler immediately into the
plastic disc-shaped sampler holder and snap it shut. (In newer models, close the attached lid securely.) Then place it into the
unused manufacturer-supplied aluminized bag, pull off the protective strip from the adhesive, and close it securely. Fold the sealed
flap one more time. Any failure to seal the sample in the manufacturer-supplied aluminized bag could result in the sample continuing
to collect formaldehyde from the workplace and from ambient air while in transit. Label the aluminized bag with pertinent sampling
information. Place a form OSHA-21 seal across the folded top of the bag. Record the stop time on the OSHA 91A form.
Verify that the sampling times are properly recorded on OSHA 91A form for each sample. Also, identify blank samples on this form.
The following steps should be performed in a low background area for a set of samplers as soon as possible after sampling.
Submit at least one blank sample with each set of samples. Ready a blank by removing the sampler from its pouch and place it in an
unused aluminized bag, seal the bag, label properly, fold the closure side of the bag down, and place the form OSHA-21 seal across
the folded top of the bag.
Record the room temperature and atmospheric pressure or elevation above sea level of the sampling site on OSHA 91A form.
List any chemical compounds that could be considered potential interferences that are being used in the sampling area.
Submit the samples to the laboratory for analysis as soon as possible after sampling. If delay is unavoidable, store the samples in
a refrigerator. Ship any bulk samples separate from the air samples.
2.3.2 UMEx 100 (In general, follow the manufacture’s instructions supplied with the samplers.)
The samplers come individually sealed in manufacturer-supplied aluminized bags. When ready to begin sampling, tear the top off at
the notches, being careful to not tear the bag on the sampler side of the closure. Save the aluminized bag to place the sampler in
after sampling. Open the closure and pull out the sampler. Pull the green band down to the opposite end from the clip, exposing a
face covered with holes. Caution - The sampler begins to sample immediately after the green band is moved to expose the face covered
with holes.
Record the start time on the back of the sampler and on the OSHA 91A form or equivalent monitoring record.
Attach the sampler to the worker near his/her breathing zone with the side covered with holes facing forward. Assure that the area
directly in front of the sampler is unobstructed throughout the sampling period.
At the end of the sampling period, detach the sampler from the worker and slide the green band over the face with holes. Record the
stop time on the back of the sampler and on the OSHA 91A form. Place the sampler back into the manufacturer-supplied aluminized bag
and close it securely. Fold the top of the bag under the closure and then seal each sampler with a form OSHA-21 seal over the folded
top of the aluminum bag. Any failure to seal the sample in the manufacturer-supplied aluminized bag could result in the sample
continuing to collect formaldehyde from the workplace and from ambient air in transit.
Verify that the sampling times are properly recorded on the OSHA 91A form for each sample. Also, identify blank samples on this form.
The following steps should be performed in a low background area for a set of samplers as soon as possible after sampling.
Send at least one blank sampler with each set of samplers. Ready a blank by opening the manufacturer-supplied aluminized bag,
removing the sampler, open then immediately close the green band, replace it in the manufacturer-supplied aluminized bag, close the
bag, fold the bag at the closure, and place a form OSHA-21 seal over the folded edge of the bag.
Record the room temperature and atmospheric pressure or elevation above sea level of the sampling site on OSHA 91A form.
List any chemical compounds that could be considered potential interferences that are being used in the sampling area.
Submit the samples to the laboratory for analysis as soon as possible after sampling. If delay is unavoidable, store the samples in
a refrigerator. Ship any bulk samples separate from the air samples.
2.3.3 DSD-DNPH (In general, follow the manufacturer's instructions.)
The sampler comes in an aluminized bag. A re-useable sampler holder is also needed to perform sampling. The Supelco re-useable
sampler holder looks like an open tube with large holes all over it, and a pen-clip on one side. Open the manufacturer-supplied
aluminized bag by cutting with scissors along the dashed line. Remove the sampler from the aluminized bag and place into the holder.
Save the aluminized bag to put the sampler back in for shipment. Caution- The sampler begins to sample immediately after the
aluminized bag is opened.
Record the start time on the OSHA 91A form or equivalent monitoring record.
Attach the sampler to the worker near his/her breathing zone. Assure that the area directly in front of the sampler is unobstructed
throughout the sampling period.
At the end of the sampling period, immediately detach the sampler from the worker, remove from the holder, and place it in the
manufacturer-supplied aluminized bag, close it securely, fold the bag near the closure, and place the form OSHA-21 seal across the
folded top of the bag. Record the stop time on OSHA 91A form. Any failure to seal the sample in the manufacturer-supplied aluminized
bag could result in the sample continuing to collect formaldehyde from the workplace and from ambient air in transit.
Verify that the sampling times are properly recorded on the OSHA 91A form for each sample. Also, identify blank samples on this form.
Prepare a blank in a contaminate-free area by removing an unused sampler from its manufacturer-supplied aluminized bag, immediately
replacing it, close the bag, fold the top of the bag, and seal with the form OSHA-21 seal over the folded top of the bag.
Record the room temperature and atmospheric pressure or elevation above sea level of the sampling site on the OSHA 91A form.
List any chemical compounds that could be considered potential interferences which are being used in the sampling area.
Submit the samples to the laboratory for analysis as soon as possible after sampling. If delay is unavoidable, store the samples in
a refrigerator. Ship any bulk samples separate from the air samples.
2.4 Sampler capacity (Section 4.7)
The sampling rate and capacity of the ChemDisk-AL, UMEx 100, and DSD-DNPH were determined by sampling a dynamically generated test
atmosphere of formaldehyde (1.5 ppm) at an average of 78% relative humidity and 23°C for increasing time intervals. A sampling rate of
13.56 mL/min for ChemDisk-ALs, 29.77 mL/min for UMEx 100s, and 70.45 mL/min for DSD-DNPHs was determined. The sampler capacity was not
exceeded after more than 10 hours of sampling at 1.5 ppm formaldehyde.
2.5 Extraction efficiency (Section 4.8)
It is the responsibility of each analytical laboratory to determine the extraction efficiency because the laboratory techniques may
be different than those listed in this evaluation and may influence the results.
2.5.1 ChemDisk-AL
The mean extraction efficiency for formaldehyde from dry ChemDisk-AL over the range of RQL to 2 times the target concentration (0.007
to 5.74 micrograms per sample) was 100.1%. The extraction efficiency was not affected by the presence of water.
Extracted samples remain stable for at least 24 h.
2.5.2 UMEx 100
The mean extraction efficiency for formaldehyde from dry UMEx 100 over the range of RQL to 2 times the target concentration (0.05 to
12.36 micrograms per sample) was 99.8%. The extraction efficiency was not affected by the presence of water.
Extracted samples remain stable for at least 24 h.
2.5.3 DSD-DNPH
The mean extraction efficiency for formaldehyde from dry DSD-DNPH over the range of RQL to 2 times the target concentration (0.012 to
31.34 micrograms per sample) was 100.0%. The extraction efficiency was not affected by the presence of water.
Extracted samples remain stable for at least 24 h.
2.6 Recommended sampling time and sampling rate
2.6.1 ChemDisk-AL
Sample with ChemDisk-AL for up to 240 min to collect TWA (long-term) samples, and for 15 min to collect STEL (short-term) samples. The
sampling rate is 13.56 mL/min at NTP.
When short-term samples are collected, the air concentration equivalent to the reliable quantitation limit becomes larger. For
example, the reliable quantitation limit for ChemDisk-AL is 0.03 ppm (0.037 mg/m3) for formaldehyde when 0.2 L (15 min) is sampled.
2.6.2 UMEx 100
Sample with UMEx 100 for up to 240 min to collect TWA (long-term) samples, and for 15 min to collect STEL (short-term) samples. The sampling
rate is 29.77 mL/min at NTP.
When short-term samples are collected, the air concentration equivalent to the reliable quantitation limit becomes larger. For
example, the reliable quantitation limit for UMEx 100 is 0.09 ppm (0.11 mg/m3) for formaldehyde when 0.45 L (15 min) is sampled.
2.6.3 DSD-DNPH
Sample with DSD-DNPH for up to 240 min to collect TWA (long-term) samples, and for 15 min to collect STEL (short-term) samples. The
sampling rate is 70.45 mL/min at NTP.
When short-term samples are collected, the air concentration equivalent to the reliable quantitation limit becomes larger. For
example, the reliable quantitation limit for DSD-DNPH is 0.0092 ppm (0.011 mg/m3) for formaldehyde when 1.06 L (15 min) is
collected.
2.7 Interferences, sampling (Section 4.9)
Reverse diffusion
Reverse diffusion is a measure of the ability of the sorbent within a diffusive sampler to retain the analyte collected. Reverse
diffusion was measured by first exposing two sets of samplers to humid air containing the analyte for one hour and then additionally
exposing one of the sets for three hours to contaminate free humid air with an average humidity of 76% at 23°C. Comparison of the
two sets showed an average recovery of 100.7% for ChemDisk-AL, 101.3% for UMEx 100, and 100.6% for DSD-DNPH, indicating no loss to
reverse diffusion.
Low humidity
The recovery for ChemDisk-AL was 93.5% of theoretical, UMEx 100 was 95.5% of theoretical, and DSD-DNPH was 95.4% of theoretical of a
test atmosphere of two times the target concentration of formaldehyde and having an average relative humidity of 20% at 23°C for four
hours.
At humidities lower than 20% the samplers had lower recoveries when compared with theoretical, the lower the humidity the lower the
recovery. The recoveries ranged from 85.4% at 15% relative humidity to 66.1% at 5% relative humidity for ChemDisk-AL, from 89.7% at
15% relative humidity to 76.2% at 5% relative humidity for UMEx 100, and 89.4% at 15% relative humidity to 77.2% at 5% relative
humidity for DSD-DNPH.
Low concentration
The average recovery for ChemDisk-AL was 96.7% of theoretical, UMEx 100 was 98.5% of theoretical, and DSD-DNPH was 99.6% of
theoretical when sampling a test atmosphere containing 0.075 ppm formaldehyde and having an average relative humidity of 79% at 23°C.
Interference
The ability of diffusive samplers to collect formaldehyde in the presence of an interference was determined by sampling a test
atmosphere containing an average relative humidity of 78% at 23°C and containing 2 ppm formaldehyde along with 2 ppm acetaldehyde, 2
ppm butyraldehyde, 2 ppm benzaldehyde, and 0.2 ppm glutaraldehyde. The formaldehyde concentration from the samples remained above
99.7% of theoretical for ChemDisk-AL, 99.3% for UMEx 100, and 100.0% for DSD-DNPH.
Ozone is a known interference for active samplers using DNPH to derivatize formaldehyde.19 The ozone can react with the DNPH
decreasing the amount available to react, or it can decrease the amount of formaldehyde-DNPH derivative already formed. Tests were
conducted by exposing samplers to an atmosphere of 0.78 ppm formaldehyde at an average relative humidity of 79% at 23°C for 240 min
and then exposing them to ever increasing concentrations of ozone, for 240 minutes, to determine the extent of the ozone
interference. ChemDisk-AL recoveries ranged from 96.6% at an ozone concentration of 0.154 ppm to 87.3% at an ozone concentration of
0.719 ppm. UMEx 100 recoveries ranged from 96.9% at an ozone concentration of 0.154 ppm to 87.3% at an ozone concentration of 0.719
ppm. DSD-DNPH recoveries ranged from 97.1% at an ozone concentration of 0.154 ppm to 87.0% at an ozone concentration of 0.719 ppm.
Formaldehyde solutions stabilized with methyl alcohol (formalin) allow formaldehyde to react with methyl alcohol to form mainly
methoxymethanol and some dimethoxymethane, which have different sampling rates than formaldehyde. Four different formaldehyde
solutions, containing differing concentrations of methyl alcohol, were tested to determine the percentage from theory of the recovery
for each diffusive sampler. For the solution containing 7-8% methyl alcohol the recovery was 86.8% of theory for ChemDisk-AL, 86.6%
for UMEx 100, and 86.4% for DSD-DNPH. For the three solutions containing 10-15% methyl alcohol the recoveries ranged from 69.3% to
72.7% of theory on ChemDisk-AL, 68.7% to 70.9% for UMEx100, and 69.0% to 71.5% for DSD-DNPH. The active sampler recoveries from
these tests averaged 99.8%. These variations indicate an uncorrectable bias in sampling with these diffusive samplers.
3. Analytical Procedure
Adhere to the rules set down in your Chemical Hygiene Plan20. Avoid skin contact and inhalation of all chemicals and review all appropriate MSDSs before beginning this analytical procedure.
3.1 Apparatus
A liquid chromatograph equipped with a UV detector. A Waters 600 Controller and pump, with a Waters 2487 Dual wavelength absorbance
Detector, and a Waters 717 plus Autosampler was used for this evaluation. A Pinnacle TO-11 5 μm 250 × 4.6-mm column (Restek Corporation,
Bellefonte, PA) was used in this evaluation.
An electronic integrator or other suitable means of measuring LC detector response for analysis of the active samplers. A Waters
Millenium32 Data System was used in this evaluation.
Light-impervious (amber) glass vials with PTFE-lined caps. In this evaluation, 4-mL vials were used. The DSD-DNPH and UMEx100 samples
also required 1-mL inserts to place the supernatant into after extraction.
A dispenser capable of delivering 2.0 mL of extracting solvent to prepare standards and samples. If a dispenser is not available, a
2.0-mL volumetric pipet may be used.
Class A volumetric flasks - 10-mL and other convenient sizes for preparing standards.
Class A volumetric pipets for making analytical standards.
Calibrated 10-μL syringe for preparing standards.
Rotator. A Fisher Roto Rack was used to extract the samples.
3.2 Reagents
Formaldehyde-DNPH derivative, [CAS no. 1081-15-8], reagent grade or better. The formaldehyde-DNPH derivative used in this evaluation was
A.C.S. reagent grade (lot no. LB18595) purchased from Supelco (Bellefonte, PA). The derivative is light sensitive, so all solutions must
be protected from light.
Acetonitrile, [CAS no. 75-05-8], reagent grade or better. The acetonitrile used in this evaluation was 99.9+% HPLC grade
(lot no. 042316) purchased from Fisher (Pittsburg, PA).
Phosphoric acid, [CAS no. 7664-38-2], reagent grade or better. The phosphoric acid used in this evaluation was 85.9% Baker-Analyzed
(lot no. D25821) purchased from J.T. Baker (Phillipsburg, NJ).
Deionized water, 18 megaohm. A Barnstead NANOpure Diamond water deionizer was used in this evaluation.
The LC mobile phase consisted of 65% acetonitrile/35% deionized water/0.2% phosphoric acid by volume.
If the formaldehyde-DNPH derivative is not used as an analytical standard, the analytical standards can be prepared with the following
chemicals:
Formaldehyde [CAS no. 50-00-0], reagent grade or better. The formaldehyde used in this evaluation was 37% (lot no. 15902 CO) purchased
from Aldrich Chemical Company (Milwaukee, WI). The formaldehyde solution should be titrated every 6 months following the procedure found
in OSHA Method 52.21
2,4-Dinitrophenylhydrazine (DNPH), [CAS no. 119-26-6], moist solid containing >30% water, reagent grade or better. The DNPH used in this
evaluation was 99% (lot no. 7627JK) purchased from Aldrich Chemical Company (Milwaukee, WI). DNPH is light sensitive, so all solutions
and samples should be protected from the light in light-impervious containers. The DNPH was purified by recrystalization from hot
acetonitrile and dried with a nitrogen stream. There is formaldehyde in ambient air that can react with DNPH as it dries if air is used
to dry the crystals, so it is important to use a nitrogen atmosphere when recrystalizing the DNPH. The DNPH will need to be
recrystalized when a significant background of formaldehyde-DNPH is found in reagent blank. Store DNPH under a nitrogen blanket.
DNPH standard solution. The solution was composed of 1-g recrystalized DNPH and 5-mL phosphoric acid in 1 L acetonitrile. This solution was
used to prepare analytical standards by injecting the formaldehyde stock solution into this solution. All solutions and containers are
placed under a nitrogen blanket to prevent absorption of ambient formaldehyde.
3.3 Standard preparation
Prepare concentrated stock standards of formaldehyde-DNPH in acetonitrile. Concentrated stock standards keep at least two weeks in the
freezer if protected from light. Prepare working analytical standards by diluting these stock standards with the extracting solution
delivered from the same dispenser used to extract the samples. Prepare fresh dilutions with each analysis. The concentration of the
stocks are corrected for the difference in the molecular weights of the formaldehyde (MW = 30.03) and formaldehyde-DNPH (MW = 210.15).
Dilutions of the stock standards are prepared, the concentration range for standards used to analyze DSD-DNPH for this evaluation was
0.01 to 109.7 μg/mL formaldehyde-DNPH or the equivalent as formaldehyde was 0.002 to 15.67 μg/mL (0.004 to 31.34 μg/sample when
multiplied by the 2-mL extraction volume).
An alternate procedure for preparing analytical standards is to use the commercially available formaldehyde and a solution of recrystalized
DNPH in acetonitrile (DNPH standard solution contains 1-g DNPH, 5-mL phosphoric acid in 1-L acetonitrile). It is important that DNPH be
recrystalized and dried with nitrogen to prevent the formaldehyde in the ambient air from reacting with DNPH as it dries, causing
contamination. Stock solutions of formaldehyde are prepared in water, and microliter amounts are spiked into 2 mL of DNPH standard
solution. A stock solution of 10 μL/mL formalin in water is equivalent to 4.01 mg/mL or 4.01 μg/μL (for a density of 1.083 and 37% w/w
formaldehyde in the solution). A spike of 3 μL of this stock solution into 2 mL of DNPH standard solution is equivalent to 6.02 μg/mL
formaldehyde (12.04 ug/sample) in DNPH standard solution.
Bracket sample concentrations with standard concentrations. If, upon analysis, sample concentrations fall outside the range of prepared
standards, prepare and analyze additional standards to include in the calibration curve or dilute high samples with extraction solvent
and reanalyze the diluted samples.
The calibration curve is plotted by comparing area counts to μg/mL. To obtain the mass per sample the concentration in μg/mL is
multiplied by the 2 mL extraction volume.
3.4 Sample preparation
3.4.1 ChemDisk-AL (In general, follow the manufacturer’s instructions.)
Remove the sampler from the aluminized bag.
Pry the back end cap off with tweezers or a small screwdriver, remove the coated glass fiber filter, and place into a
light-impervious (amber) 4-mL vial.
The newer Chemdisk II model comes with an attached cap. Open the cap, place a probe or pointed forceps in one of the holes of the
diffusion screen and pry off the diffusion screen. Remove the coated filter and place into a light-impervious 4-mL vial.
Add 2.0 mL of acetonitrile to each vial and immediately cap the vials with PTFE-lined caps.
Rotate on a rotator for 15 min.
3.4.2 UMEx 100 (In general, follow the manufacturer's instructions.)
Remove the sampler from the aluminized bag.
Push the green closure band to the center of the sampler and pry it off from the side (pliers work well to grab the edge of the green
band to pry it off). At the bottom of the sampler there is a tab which you push in to make the top of the sampler come off.
Inside are two squares of coated silica tape. Remove each one and place each into its own light-impervious (amber) 4-mL vial.
While the manufacturer says the second, inner section, is a blank, tests in this method showed that the amount of formaldehyde found
on the inner section increased with higher concentrations in the test atmospheres, so it was assumed to be part of the sample, not a
back-up or blank.
Add 2.0 mL of acetonitrile to each vial and immediately seal the vials with PTFE-lined caps.
Place samples on a rotator for 15 min. Immediately pour the supernatant (liquid in the vial) into a 1-mL insert for the 4-mL vial,
place the insert back into the vial, and cap the vial. The formaldehyde-DNPH derivative will decrease in solution with time if left
in contact with the silica tape. If samples are not transferred within 5 minutes after completing rotation, re-rotate the samples
for 5 min, and immediately transfer the sample supernatant.
3.4.3 DSD-DNPH (In general, follow the manufacturer's instructions.)
Remove the sampler from the aluminized bag.
Remove the white translucent part. Dynamically extract the DNPH-coated silica gel inside the sampler using a syringe filter with
2 mL of acetonitrile into a light-impervious (amber) 4-mL vial.
Alternately, place the DNPH-coated silica gel into a light-impervious (amber) 4-mL vial, add 2.0 mL of acetonitrile to each vial and
immediately seal the vials with PTFE-lined caps. Rotate samples on a rotator for 15 min. Immediately pour the supernatant into a
1-mL insert for the 4-mL vial, separate from the silica gel, and place the insert back into the vial and cap. The formaldehyde-DNPH
derivative will decrease in solution with time if left in contact with the silica gel. If samples are not transferred within 5 min
after completing rotation, re-rotate the samples for 5 min, and immediately transfer the sample supernatant.
3.5 Analysis
Liquid chromatograph conditions:
| mobile phase: |
1 mL/min of 35% water/ 65% acetonitrile/0.2%
phosphoric acid (v/v/v) |
|
 |
| Figure 3.5.1 A chromatogram of 18.9 μg/mL formaldehyde
in acetonitrile with DNPH. [Key: 1) DNPH, 2) formaldehyde as the DNPH
derivative.] |
|
detector
wavelength: |
365 nm |
| injection volume: |
10 μL |
| output range: |
2 AUFS |
| column: |
Restek Pinnacle TO-11 5 μm 250 ×
4.6 mm |
| retention times: |
DNPH (3.9 min); formaldehyde (4.8
min) |
|
|
|
| |
|
|
|
|
|
|
|
|
| |
|
|
An external standard (ESTD) calibration method is used. A calibration curve can be constructed by plotting response of standard injections
versus micrograms/milliliter of analyte. (Note: the samples are extracted with 2 mL of acetonitrile so the mass per sample is the μg/mL x 2
mL.) Bracket the samples with freshly prepared analytical standards over the range of concentrations. (Section 3.3)
 |
Figure 3.5.2 Calibration curve for
formaldehyde.
(y = 1.89E5x = 752) |
3.6 Interferences (analytical)
Any compound that produces a LC response and has a similar retention time as the analyte is a potential interference. If any
potential interferences were reported, they should be considered before samples are extracted. Generally, chromatographic conditions
can be altered to separate an interference from the analyte.
When necessary, the identity or purity of an analyte peak may be confirmed by additional analytical data, such as GC-mass spectrometry,
or monitoring an alternant wavelength such as 254 or 280 nm (Section 4.10).
3.7 Calculations
The amount of analyte for the samples is obtained from the appropriate calibration curve in terms of micrograms per milliliter, uncorrected
for extraction efficiency. This amount is then corrected by subtracting the total amount (if any) found on the blank. Blank correct each
section of the UMEx 100 with its corresponding section in the blank, then add the results together. The air concentration is calculated
using the following formulas.
| M = [(Ca - Cbka) + (Cb - Cbkb)](2mL) |
where: |
M is micrograms per sample
Ca is μg/mL found on main section of sample from calibration curve
Cb is μg/mL found on second section of sample (UMEx 100 only) from
calibration curve
Cbka is μg/mL found on main section of blank sample from calibration curve
Cbkb is μg/mL found on second section of blank (UMEx 100 only) from
calibration curve
2mL is the extraction volume |
| |
|
|
| RSS = RNTP |
TSS |
3/2 |
PNTP |
| ( |
|
) |
( |
|
) |
| TNTP |
|
PSS |
|
where: |
RSS is the sampling rate at sampling site
RNTP is the sampling rate at NTP conditions (ChemDisk-AL=13.56 mL/min, UMEx100=29.77 mL/min, and DSD-DNPH=70.45 mL/min)
TSS is the sampling site temperature in K
TNTP is 298.2 K
PSS is the sampling site pressure in mmHg
PNTP is 760 mmHg |
|
|
where: |
CM is concentration by weight (μg/L
= mg/m3)
M is micrograms per sample
RSS is the sampling rate at the sampling site
t is the sampling time
EE is extraction efficiency, in decimal form
1000 is a conversion factor to convert the sampling rate mL/min to L/min |
| |
|
|
|
|
where: |
CV is concentration by volume (ppm)
VM = 24.46 at NTP
CM is concentration by weight
Mr is molecular weight of 30.0 |
|
|
|
|
| If the sampling site temperature was not given, assume that it is 22.2°C. If the sampling site atmospheric pressure was not given,
calculate an approximate value based on the sampling site elevation level from the following equation. |
|
|
|
|
|
PSS = AE2 - BE + 760 |
where: |
PSS is the approximate atmospheric pressure
in mmHg
E is the sampling site elevation, ft
A is 3.887 10-7 mmHg/ft2
B is 0.02748 mmHg/ft |
4. Backup data
General background information about the determination of detection limits and precision of the overall procedure is found in the "Evaluation
Guidelines for Air Sampling Methods Utilizing Chromatography Analysis"22 . The Guidelines define analytical parameters, specify
required laboratory tests, statistical calculations and acceptance criteria.
4.1 Detection limit of the analytical procedure (DLAP)
The DLAP is measured as the mass of analyte introduced onto the chromatographic column. Ten analytical standards were prepared with equally
decending increments with the highest standard containing 11.3 ng/mL. This is the concentration that would produce a peak at least 10 times
the response of a reagent blank near the elution time of the analyte. These standards, and the reagent blank were analyzed with the
recommended analytical parameters (10-μL injection), and the data obtained were used to determine the required parameters (standard error of
estimate and slope) for the calculation of the DLAP. Values of 22.75 and 32.31 were obtained for the slope and standard error of estimate
respectively. DLAP was calculated to be 4.26 pg.
Table
4.1
Detection Limit of the Analytical Procedure
|
|

Figure 4.1 Plot of data in Table 4.1 used to determine the DLAP. (y =22.75x
+ 4.14) |
|
concentration (ng/mL) |
mass
on column (pg) |
area
counts
(µV•s) |
|
| 0 |
0 |
0 |
| 1.13 |
11.3 |
256 |
| 2.26 |
22.6 |
494 |
| 3.39 |
33.9 |
796 |
| 4.52 |
45.2 |
1017 |
| 5.65 |
56.5 |
1338 |
| 6.78 |
67.8 |
1557 |
| 7.91 |
79.1 |
1780 |
| 9.04 |
90.4 |
2046 |
| 10.17 |
101.7 |
2372 |
| 11.30 |
113.0 |
2531 |
|
4.2 Detection limit of the overall procedure (DLOP) and reliable quantitation limit (RQL)
DLOP is measured as mass per sample and expressed as equivalent air concentrations, based on the recommended sampling parameters.
Ten samplers were spiked with equally descending increments of analyte, such that the highest sampler loading was 56.5 ng/sample for
ChemDisk-AL and DSD-DNPH, and 452 ng/sample for SKC UMEx 100. This is the amount spiked on a sampler that would produce a peak
approximately 10 times the response of a sample blank. These spiked samplers, and the sample blank were analyzed with the
recommended analytical parameters, and the data obtained used to calculate the required parameters (standard error of estimate and
the slope) for the calculation of the DLOP. Values of 111 and 83.2 were obtained for the slope and standard error of estimate for
ChemDisk-AL, respectively. The DLOP for ChemDisk-AL was calculated to be 2.25 ng/sample (0.56 ppb based on 240 min). Values of 120
and 594 were obtained for the slope and standard error of estimate for UMEx 100, respectively. The DLOP for UMEx 100 was calculated
to be 14.9 ng/sample (1.7 ppb). Values of 112 and 133 were obtained for the slope and standard error of estimate for DSD-DNPH,
respectively. The DLOP for DSD-DNPH was calculated to be 3.56 ng/sample (0.17 ppb).
Table
4.2.1
Detection Limit of the Overall Procedure for ChemDisk-AL
|
|

Figure 4.2.1 Plot of data in Table 4.2.1 used to determine the DLOP/RQL for
ChemDisk-AL. (y = 111x + 322) |
mass per sample
(ng) |
area
counts
(µV•s) |
|
| 0 |
313 |
| 5.65 |
967 |
| 11.3 |
1612 |
| 17.0 |
2101 |
| 22.6 |
2945 |
| 28.3 |
3504 |
| 33.9 |
3954 |
| 39.6 |
4804 |
| 45.2 |
5414 |
| 50.9 |
5913 |
| 56.5 |
6639 |
|
Table
4.2.2
Detection Limit of the Overall Procedure for UMEx 100
|
|

Figure 4.2.2 Plot of data in Table 4.2.2 used to determine the DLOP/RQL for
UMEx 100. (y = 120x + 5408) |
mass per sample
(ng) |
area
counts
(µV•s) |
|
| 0 |
5612 |
| 45.2 |
11224 |
| 90.4 |
16356 |
| 136 |
21235 |
| 181 |
26541 |
| 226 |
33052 |
| 271 |
36647 |
| 316 |
43851 |
| 362 |
48654 |
| 407 |
54673 |
| 452 |
59534 |
|
Table
4.2.2
Detection Limit of the Overall Procedure for UMEx 100
|
|

Figure 4.2.3 Plot of data in Table 4.2.3 used to determine the DLOP/RQL for
DSD-DNPH. (y = 112x + 333) |
mass per sample
(ng) |
area
counts
(µV•s) |
|
| 0 |
300 |
| 5.65 |
919 |
| 11.3 |
1596 |
| 17.0 |
2297 |
| 22.6 |
3014 |
| 28.3 |
3412 |
| 33.9 |
3912 |
| 39.6 |
4919 |
| 45.2 |
5582 |
| 50.9 |
6014 |
| 56.5 |
6533 |
|
The RQL is considered the lower limit for precise quantitative measurements. It is determined from
the regression line parameters obtained for the calculation of the DLOP, providing 75% to 125% of the analyte is recovered. The RQLs
for the various media are listed in Table 4.2.4.
|
|

Figure 4.2.4 Chromatogram of a peak near the RQL on ChemDisk-AL. (Key: 1
= formaldehyde)
|
Table 4.2.4
Reliable Quantitation Limits
|
| sampler |
ng |
ppb |
μg/m3 |
EE |
|
| ChemDisk-AL |
7.49 |
1.88 |
2.30 |
99.5 |
| UMEx 100 |
49.5 |
5.68 |
6.93 |
99.3 |
| DSD-DNPH |
11.9 |
0.58 |
0.70 |
99.5 |
|
| EE =
extraction efficiency |
|
4.3 Instrument calibration
The standard error of estimate was determined from the linear regression of data points from standards over a range that covers 0.25 to 2
times the TWA target concentration. A calibration curve for DSD-DNPH samples was constructed and shown in Figure 3.5.2 from the six
injections of five standards. The standard error of estimate is 0.069 μg/mL.
Table 4.3
Instrument Calibration for DSD-DNPH Samples
|
| standard concn (μg/mL) |
area counts
(μV•s) |
|
| 1.96 |
350361 |
361024 |
350982 |
354675 |
353392 |
358132 |
| 3.92 |
750107 |
750992 |
748941 |
749243 |
750123 |
755923 |
| 7.84 |
1501151 |
1498251 |
1509918 |
1502208 |
1498322 |
1503128 |
| 11.76 |
2229123 |
2226189 |
2218391 |
2228424 |
2230119 |
2219872 |
| 15.67 |
2959210 |
2954912 |
2960123 |
2958381 |
2961022 |
2955670 |
|
4.4 Precision (overall procedure)
The precisions of the overall procedure at the 95% confidence level for the ambient temperature 17-day storage test (at the target
concentration) for the diffusive samplers are given in Table 4.4. They each include the sampling rate variability of 7.71% for ChemDisk-AL,
8.06% for UMEx 100, and 7.49% for DSD-DNPH. There are different values given, depending on whether both, either, or neither temperature (T)
or atmospheric pressure (P) are known at the sampling site. If the sampling site temperature is unknown, it is assumed to be 22.2 ± 15°C
(72 ± 27°F) and a variability of ±7.7% is included. If the atmospheric pressure is not known, it is estimated from the sampling site
elevation and a variability of ±3% is included.
Table 4.4
Standard Error of Estimate and Precision of the Overall Procedure
|
| known
conditions |
ChemDisk-AL
error (%) |
ChemDisk-AL
precision
(± %) |
UMEx 100
error (%) |
UMEx 100
precision
(± %) |
DSD-DNPH
error (%) |
DSD-DNPH
precision
(± %) |
|
| both T & P |
7.78 |
15.3 |
8.15 |
16.0 |
7.54 |
14.8 |
| only T |
8.34 |
16.3 |
8.68 |
17.0 |
8.12 |
15.9 |
| only P |
11.0 |
21.6 |
11.2 |
22.0 |
10.8 |
21.2 |
| neither T nor P |
11.4 |
22.3 |
11.6 |
22.7 |
11.2 |
22.0 |
|
4.5 Storage test
4.5.1 ChemDisk-AL
Storage samples for formaldehyde were prepared by collecting samples from a controlled test atmosphere using the recommended sampling
conditions. The concentration of formaldehyde was at the target concentration with an average relative humidity of 78% and
temperature of 23 °C. Thirty-three storage samples were prepared and all were stored in aluminized bags. Three samples were
analyzed on the day of generation. Fifteen of the samples were stored at refrigerated temperature (4°C) and the other fifteen were
stored in a closed drawer at ambient temperature (about 22°C). At 3-4 day intervals, three samples were selected from each of the
two storage sets and analyzed. Sample results are not corrected for extraction efficiency.
Table 4.5.1
Storage Test for Formaldehyde on ChemDisk-AL
|
time
(days) |
ambient storage
recovery (%) |
refrigerated
storage
recovery (%) |
|
| 0 |
100.2 |
99.7 |
98.9 |
|
|
|
| 3 |
97.7 |
100.3 |
98.6 |
98.6 |
100.4 |
99.8 |
| 7 |
99.7 |
98.8 |
96.8 |
98.9 |
99.7 |
98.8 |
| 10 |
98.4 |
97.9 |
95.9 |
98.5 |
98.1 |
99.9 |
| 14 |
97.2 |
94.9 |
95.6 |
96.9 |
99.3 |
98.6 |
| 17 |
95.8 |
93.9 |
94.9 |
97.8 |
98.3 |
98.9 |
|

Figure 4.5.1.1 Ambient storage test for formaldehyde collected on
ChemDisk-AL. |
|

Figure 4.5.1.2 Refrigerated storage test for formaldehyde collected on
ChemDisk-AL. |
4.5.2 UMEx 100
Storage samples for formaldehyde were prepared by collecting samples from a controlled test atmosphere using the recommended sampling
conditions. The concentration of formaldehyde was at the target concentration with an average relative humidity of 78% and temperature of
23 °C. Thirty-three storage samples were prepared and all were place in aluminized bags. Three samples were analyzed on the day of
generation. Fifteen of the samples were stored at refrigerated temperature (4°C) and the other fifteen were stored in a closed drawer at
ambient temperature (about 22°C). At 3-4 day intervals, three samples were selected from each of the two storage sets and analyzed.
Sample results are not corrected for extraction efficiency.
Table 4.5.2
Storage Test for Formaldehyde on UMEx 100
|
time
(days) |
ambient storage
recovery (%) |
refrigerated
storage
recovery (%) |
|
| 0 |
100.9 |
98.3 |
99.4 |
|
|
|
| 3 |
99.9 |
98.4 |
97.0 |
98.1 |
97.9 |
99.6 |
| 7 |
98.2 |
99.6 |
97.2 |
99.9 |
98.3 |
97.4 |
| 10 |
98.4 |
96.7 |
97.4 |
98.4 |
99.2 |
97.2 |
| 14 |
96.5 |
94.4 |
93.9 |
98.0 |
97.5 |
96.9 |
| 17 |
95.3 |
94.1 |
93.8 |
96.1 |
95.2 |
94.3 |
|

Figure 4.5.2.1 Ambient storage test for formaldehyde collected on UMEx
100. |
|

Figure 4.5.2.2 Refrigerated storage test for formaldehyde collected on
UMEx 100. |
4.5.3 DSD-DNPH
Storage samples for formaldehyde were prepared by collecting samples from a controlled test atmosphere using the recommended sampling
conditions. The concentration of formaldehyde was at the target concentration with an average relative humidity of 78% and temperature of
23 °C. Thirty-three storage samples were prepared and all were stored in aluminized bags. Three samples were analyzed on the day of
generation. Fifteen of the tubes were stored at refrigerated temperature (4°C) and the other fifteen were stored in a closed drawer at
ambient temperature (about 22°C). At 3-4 day intervals, three samples were selected from each of the two storage sets and analyzed.
Sample results are not corrected for extraction efficiency.
Table 4.5.3
Storage Test for Formaldehyde on DSD-DNPH
|
time
(days) |
ambient storage
recovery (%) |
refrigerated
storage
recovery (%) |
|
| 0 |
100.4 |
99.5 |
98.7 |
|
|
|
| 3 |
97.0 |
98.5 |
99.6 |
97.1 |
99.9 |
98.9 |
| 7 |
97.4 |
97.0 |
98.3 |
99.5 |
99.8 |
98.3 |
| 10 |
97.1 |
98.4 |
96.9 |
99.0 |
98.6 |
97.8 |
| 14 |
97.9 |
95.7 |
96.1 |
98.3 |
97.3 |
99.1 |
| 17 |
94.4 |
96.5 |
95.9 |
98.9 |
99.3 |
97.9 |
|

Figure 4.5.3.1 Ambient storage test for formaldehyde collected on
DSD-DNPH. |
|

Figure 4.5.3.2 Refrigerated storage test for formaldehyde collected on
DSD-DNPH. |
4.6 Reproducibility
Six samples of each of the three types of samplers were prepared by collecting them from a controlled
test atmosphere that was similar to that which was used in the collection of the storage samples. The samples were submitted to the
OSHA Salt Lake Technical Center for analysis, along with a draft copy of this method. The samples were analyzed after being stored
for 27 days at 4 °C. Sample results were corrected for extraction efficiency. No sample result for formaldehyde had a deviation
greater than the precision of the overall procedure determined in Section 4.4. |
Table
4.6.1
Reproducibility Data for Formaldehyde using ChemDisk AL
|
theoretical
(μg/sample) |
recovered
(μg/sample) |
recovery
(%) |
deviation (%) |
|
| 2.99 |
2.87 |
96.0 |
-4.0 |
| 2.99 |
3.03 |
101.3 |
+1.3 |
| 2.99 |
2.95 |
98.6 |
-1.4 |
| 2.99 |
2.88 |
96.3 |
-3.7 |
| 2.99 |
3.09 |
103.3 |
+3.3 |
| 2.99 |
2.83 |
94.6 |
-5.4 |
|
|
Table
4.6.2
Reproducibility Data for Formaldehyde using
UMEx 100
|
|
theoretical
(μg/sample) |
recovered
(μg/sample) |
recovery
(%) |
deviation (%) |
|
|
|
| 6.24 |
6.34 |
101.6 |
+1.6 |
|
| 6.24 |
5.86 |
93.9 |
-6.1 |
|
| 6.24 |
5.98 |
95.8 |
-4.2 |
|
| 6.24 |
6.28 |
100.6 |
+0.6 |
|
| 6.24 |
5.87 |
94.1 |
-5.9 |
|
| 6.24 |
5.79 |
92.8 |
-7.2 |
|
|
|
|
Table
4.6.3
Reproducibility Data for Formaldehyde using
DSD-DNPH
|
theoretical
(μg/sample) |
recovered
(μg/sample) |
recovery
(%) |
deviation (%) |
|
| 16.3 |
16.7 |
102.5 |
+2.5 |
| 16.3 |
15.1 |
92.6 |
-7.4 |
| 16.3 |
15.6 |
95.7 |
-4.3 |
| 16.3 |
16.6 |
101.8 |
+1.8 |
| 16.3 |
15.5 |
95.1 |
| | | |