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| September 2004 |
Mary Eide |
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Methods Development Team
Industrial Hygiene Chemistry Division
OSHA Salt Lake Technical Center
Sandy UT 84070-6406
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Introduction
The purpose of this study was to determine the sampling rate variation
(SRV) for the Supelco, Inc. DSD-DNPH Diffusive Sampler for Aldehydes (DSD-DNPH). These samplers are intended by the manufacturer
to measure the amount of formaldehyde and other aldehydes present in workplace
air. The sampler uses
2,4-dinitrophenylhydrazine (DNPH) chemistry to produce a stable aldehyde
derivative.
SRV has been established by OSHA as a measure of sampling error for
diffusive samplers.1 SRV is the diffusive sampler equivalent of the often cited ±5% sampling pump
error used for active samplers. It is a unique number that is experimentally
determined for each individual design of diffusive sampler, because the SRV is
presumed to be a function of sampler design. SRV provides the sampling error
component of the Sampling and Analytical Error (SAE) calculations.2
SRV has been defined as the pooled relative standard deviation of
sampling rates obtained in a modified version of the 16-run factor test
described in the NIOSH testing protocol for diffusive samplers.3 This test is based on determination of
diffusive sampling rates for aldehydes in test atmospheres containing five
different aldehydes. The test requires
sample collection from 16 different combinations of high and low analyte
concentration, short and long sampling time, high and low face velocity, high
and low relative humidity, high and low interference level, and parallel and
perpendicular sampler orientation to air flow direction in a sampling
chamber.
The formaldehyde atmosphere was generated from a solution of
formaldehyde in water freshly prepared from paraformaldehyde. Formaldehyde is sold commercially as a
solution in water that is stabilized with methyl alcohol. The methyl alcohol can react with the
formaldehyde forming methoxymethanol and dimethoxymethane (non-formaldehyde
species).4 These non-formaldehyde species are unstable
and readily decompose back to formaldehyde and methyl alcohol.5 These non-formaldehyde species readily react
with the derivatizing agent, whether DNPH or 2-(hydroxymethyl)piperidine, to
form the formaldehyde derivative. The test atmospheres produced from
paraformaldehyde and from formaldehyde/water solution, contain mostly
formaldehyde, while the atmospheres produced from formaldehyde that has been
stabilized with methyl alcohol contain formaldehyde and non-formaldehyde
species. The non-formaldehyde species
are of higher molecular weight than formaldehyde and, therefore, they have
different diffusive sampling rates. This
difference in the sampling rates causes lower loadings of formaldehyde
derivative on the diffusive samplers when compared to the active samplers taken
from the same test atmosphere. This
difference could result in formaldehyde results for the diffusive sampler which
are as much as 35% lower than the active samplers.6 Diffusive samplers, with sampling rates
determined using test atmospheres prepared from paraformaldehyde, give
analytical results similar to active samplers when sampling the same test
atmosphere produced using paraformaldehyde. This study employed formaldehyde
test atmospheres generated with formaldehyde solution (prepared from
paraformaldehyde) to establish sampling rates for DSD-DNPH. Therefore, sampling rates shown here are for
formaldehyde alone. Formaldehyde
atmospheres in the workplace could result from formaldehyde stabilized with
methyl alcohol, and would contain the non-formaldehyde species. Formaldehyde results from diffusive samplers
would be lower than results from active samplers when both types of samplers
were used to sample these atmospheres.
Reagents
Acetaldehyde, Aldrich Chemical Company, 99.5+%, lot CO 02962AO
Benzaldehyde, Aldrich Chemical Company, 99.5+%, lot 00208TI
Butyraldehyde, Aldrich Chemical Company, 99.5+%, lot BO 03519DI
Glutaraldehyde, Aldrich Chemical Company, 50%, lot 01907 CI
Paraformaldehyde, Aldrich Chemical Company, 95+%, lot 08710 AA
Acetonitrile, Fisher Chemical Company, 99.9%, lot 031027
Phosphoric acid, JT Baker, Baker-analyzed, 85.9%, lot D25821
2,4-Dinitrophenylhydrazine (DNPH), Aldrich Chemical Company, lot 7627JK (DNPH is light sensitive, so all solutions and samples should be protected from the light in light-impervious containers.)
Toluene, Alfa-Aesar, 99.8%, lot K06M13
N,N-Dimethylformamide (DMF), Aldrich Chemical Company, 99.8%, lot 04643LA
A freshly prepared solution of formaldehyde in water was prepared by heating paraformaldehyde at 80 °C, and bubbling the vapor through
deionized water. These mixtures were quantitated by titration7
and diluted with deionized water to obtain the desired concentration before use
in the vapor generation system.
Two different neat aldehyde mixtures were prepared. The first mixture was 1:1 (by volume) ratio of butyraldehyde:benzaldehyde, and the second
mixture was 1:1:0.1 (by volume) of the formaldehyde solution:acetaldehyde:glutaraldehyde. These mixtures were used to generate
the test
atmospheres and to prepare standards.
DNPH extracting solution for extracting DSD-DNPH and DNPH coated glass fiber filters. The solution was composed of 1-g DNPH and
5-mL phosphoric acid in 1-L acetonitrile. The same solution was used to prepare
analytical standards. The DNPH was purified by recrystalization from hot
acetonitrile.
DNPH glass fiber filter coating solution. The solution was composed of 4-g DNPH
and 20-mL phosphoric acid in 1-L acetonitrile. The DNPH was purified by
recrystalization from hot acetonitrile
Adsorbent tube extracting solution. The solution was composed of 0.2 µL/mL DMF
(used as internal standard) in toluene.
Sampling Media
Supelco, Inc. DSD-DNPH Diffusive Samplers for Aldehydes (DSD-DNPH), lot SP0403H01
containing a beaded silica gel coated with DNPH and phosphoric acid.
SKC 226-117 and 226-54 sampling tubes, lot 2952, containing XAD-2 coated with 10% (w/w) 2-(hydroxymethyl)piperidine (HMP XAD-2). These
sampling tubes were packed with the same adsorbent, but contained differing amounts of the coated resin in the tubes, and thus have different
amounts of formaldehyde background. The 226-54 has two sections containing 45- and 23-mg coated resin, and is used for short-term sampling.
The 226-117 has two sections containing 150- and 75-mg coated resin, and is used for long-term samples. These sampling tubes were used to
establish the concentrations of acetaldehyde, butyraldehyde, and formaldehyde in test atmospheres.
Glass fiber filters coated with 2-mg DNPH and 10-µL phosphoric acid (DNPH GFF). The cassette was loaded with three coated filters, with a
spacer between each filter, and an extra spacer on the top to emulate open face sampling. These filters were used to establish the
benzaldehyde and glutaraldehyde concentrations in the test atmospheres. The DNPH GFF were prepared by placing glass fiber
filters on a clean glass plate and pipetting 0.5 mL of the DNPH glass fiber
filter coating solution following the procedure found in OSHA Method 64 Glutaraldehyde.8 The filters were allowed to dry 20 minutes in a hood, then they were placed in a light impervious
container (brown glass jar) loosely sealed with a lid, allowed to dry completely overnight in a drawer. The next day the lid was tightly
sealed and the jar was then placed into
a freezer for storage.
Apparatus
Shaker. An Eberbach shaker was used to extract the adsorbent tubes.
Rotator. A Fisher Roto Rack was used to extract the DSD-DNPH
and DNPH GFF samples.
Gas chromatograph (GC) with a nitrogen-phosphorus detector. An Agilent 6890 gas chromatograph with a 7683 injector, and 3396 Series II
integrator was used for analysis of HMP XAD-2 samples. Separations were performed using a Restek Stabilwax DB capillary column (60-meter x
0.32-mm x 1-µm df). (Restek Corporation, Bellefonte PA).
An electronic integrator or some other suitable means of measuring peak areas. A Waters Millennium32 Data System was used in this
evaluation.
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 analysis of DSD-DNPH and DNPH GFF samples. A 4.6-
× 250-mm column packed with 5µm Pinnacle TO-11 (Restek Corporation, Bellefonte
PA) was used in this evaluation.
Humid air generator. A Miller-Nelson Model HCS-401 Flow-Temperature-Humidity Control System was used to generate humid
air for use with controlled test atmospheres.
This instrument was equipped with a 500 L/min mass flow controller.
Relative humidity and temperature tester. An Omega Digital Thermo-hygrometer Model RH411 was used to
determine the relative humidity and
temperature of the test atmospheres within the exposure chamber. The probe was calibrated by the manufacturer.
Gas test meter. An Equimeter no. 750 gas meter was used to measure dilution flow rates. This meter had been checked at several flows
against a Singer DTM 115 gas meter (that had been tested by the local natural gas distributor and found to be accurate).
| |
Figure 1. This is a diagram of the test atmosphere generation and sampling apparatus. The air stream of a known flow and humidity is
introduced into the apparatus from the Miller Nelson Flow-Temperature-Humidity Control System. The aldehyde mixtures come from the ISCO
syringe pumps and are teed into the air stream. The stream is heated to vaporize the aldehydes. The air and aldehydes flow into a glass
mixing chamber to form a homogeneous test atmosphere. This test atmosphere then flows to the exposure chamber. The exposure chamber is large
enough for the diffusive samplers to fit inside, and has side ports from which active
samples can be taken. The test atmosphere then flows
out of the exposure chamber into the exhaust. |
Syringe pumps. The two aldehyde mixtures were metered into the system using two Isco 100DM syringe pumps equipped with a cooling/heating
jacket and an insulating cover. Both pumps were operated in the constant flow mode. The temperature of water in the cooling jacket was
maintained at 19 °C with a Forma Scientific Model RH411 Bath and Circulator.
The chemical vapors were generated by pumping the two aldehyde mixtures through a short length of 0.53-mm uncoated fused silica capillary
tubing into a vapor generator where they were heated and evaporated into the dilution air stream (Figure 1). The entire apparatus was placed in
a walk-in hood. The glass vapor generator consisted of a 15-cm length of 5-cm
diameter piece of glass tubing with a side port for introduction of the capillary tubing. The glass tube of the vapor generator was wrapped with heating
tape to evaporate the chemicals in the mixture. A Miller Nelson Flow-Temperature-Humidity
controller was used to regulate the humidity, temperature, and volume of the
dilution stream of air. The test atmosphere passed into a glass mixing chamber (76-cm x 30-cm) from the vapor
generator, and then into a glass exposure chamber (76-cm x 20-cm). The humidity and temperature were measured at the exit of the exposure
chamber by an Omega Digital Thermo-hygrometer. Face velocities of the test atmospheres were calculated by dividing the volumetric flow of
each atmosphere by the cross-sectional area available for the air flow in each
chamber. The cross-sectional area available for the air flow
was the cross-sectional area of the chamber reduced by the cross-sectional areas of the samplers.
Experimental
Sample Analysis
The HMP XAD-2 adsorbent tubes were opened, each section was placed into a separate 2-mL vial, and 1-mL of toluene with 0.25 µL/mL DMF as the
internal standard was pipetted into each vial. The vials were sealed and were placed on a shaker for 1 hour. Standards were prepared by
injecting microliter amounts of aldehyde spiking solutions, prepared by diluting
both aldehyde mixture solutions, into vials containing 150 mg of the HMP
XAD-2 resin for high standards, and
45-mg portions for low standards. Standards were prepared with the same amount of coated
resin as was contained in the samples. Standard blanks of each amount of resin
were analyzed, due to the background amount of formaldehyde present. The
standards were allowed to react overnight. The standards were blank corrected before plotting
in the calibration curve. The standards were extracted
in the same manner as the samples.
Adsorbent tubes were analyzed by gas chromatography (GC) with a nitrogen-phosphorus detector. Separations were performed using a Restek
Stabilwax DB capillary column (60-meter x 0.32-mm x 1-µm df). The injection volume was 1 µL with a 1:10 split. The GC temperature program was
60 °C for 4 min then 7 °C/min to 220 °C and hold for 2 min. The hydrogen carrier gas was 2.5 mL/min, hydrogen detector gas was 2 mL/min, the
nitrogen auxillary gas was 10 mL/min, and the detector air was 60 mL/min. The injector temperature was 220 °C and the detector temperature
was 260 °C.
DNPH standards were prepared by injecting microliter amounts of spiking
solutions, prepared by diluting both aldehyde mixture solutions, into 4-mL
light-impervious (amber)
vials containing 2 mL of DNPH extracting solution. Standards were allowed to
react for 1 hour.
DSD-DNPH and the DNPH GFF were placed into amber 4-mL vials, 2 mL of the
DNPH extracting solution was added, they were capped, and then they were extracted
for ½ hour on a Fisher Roto Rack. The
supernatant on the DSD-DNPH was immediately removed and placed into a separate
vial for analysis. It is important to
either dynamically extract the DSD-DNPH with the Supelco syringe filtering
system or to use the procedure described above, as the concentration of DNPH
derivatives decreases in solution with time when left in contact with the
silica gel. It is not necessary to
transfer the supernatant of the DNPH GFF samples.
DSD-DNPH and the coated glass fiber filters were analyzed using a liquid
chromatograph equipped with a UV detector. A 4.6 × 250-mm column packed with 5-µm Pinnacle TO-11 was used in this study.
The injection volume was 10 µL. The mobile phase was 65:35:0.02
acetonitrile:water:phosphoric acid pumped at 1 mL/min. The analytical wavelength was 365 nm.
Extraction efficiency
It was not necessary to perform an extraction efficiency study of the aldehydes from HMP XAD-2, as the same medium was spiked
with the aldehydes in the mixture to make the analytical standards.9
The extraction efficiency study of the DNPH GFF was performed by spiking the five aldehydes onto the DNPH GFF, in amber vials, and
allowing them to react overnight in a drawer. Six filters at each of six levels were spiked. The loadings studied were: acetaldehyde 1 to
86.4 µg/sample; benzaldehyde 1 to 208.4 µg/sample; butyraldehyde 1 to 141.6 µg/sample; formaldehyde 0.3 to 22 µg/sample; and glutaraldehyde
0.2 to 9.8 µg/sample.
The extraction efficiency study of the DSD-DNPH was performed by spiking
the five aldehydes onto the coated silica gel, in amber vials, and allowing
them to react overnight in a drawer. Six
samples at each of six levels were spiked. The loadings studied were: acetaldehyde, 1 to 120 µg/sample;
benzaldehyde, 1 to 187 µg/sample; butyraldehyde, 1 to 152 µg/sample;
formaldehyde, 0.5 to 29.4 µg/sample; and glutaraldehyde, 0.3 to 9.8 µg/sample.
Sampling rate and capacity
The sampling rate and capacity of DSD-DNPH for
each of the aldehydes was determined by exposing sets of three diffusive samplers
to the aldehyde mixture for increasing time periods. The test atmosphere contained acetaldehyde (2
ppm or 3.6 mg/m3), benzaldehyde (2 ppm or 8.82 mg/m3),
butyraldehyde (2 ppm or 5.9 mg/m3), formaldehyde (0.75 ppm or 0.92
mg/m3) and glutaralehyde (0.2 ppm or 0.8 mg/m3). This test atmosphere level will be referred
to as the 1x, and the 1/10 of this level as 0.1x in this study. Unless otherwise noted, the sampler
orientation was parallel to the flow direction of the test atmosphere. The average relative humidity, temperature,
and face velocity of the test atmospheres, except in the factor tests, was 77%,
30 °C, and 0.4 m/s respectively. Six
active samplers were collected with each set of three diffusive samplers. Active samplers consisted of three DNPH GFF
and three HMP XAD-2. The sampling rates
were 100 mL/min for DNPH GFF, and 50 mL/min for HMP XAD-2 samplers
Reverse diffusion tests were performed by sampling the 1x concentration for one-half the total sampling time, and then sampling clean humid
air for the remainder of the sampling time. Eight diffusive samplers were exposed for 2 hours, four were removed and analyzed, and then the
other four were exposed for 2 hours to clean, humid air and then analyzed. The relative humidity, temperature, and face velocity were 76%,
29 °C and 0.4 m/s respectively.
Factor tests
A 16-run factor test was performed using a modified version10 of the NIOSH Factor Test.11
NIOSH has identified six factors that can affect the
performance of diffusive samplers: analyte concentration, face velocity, relative humidity, exposure time, interferant, and sampler
orientation. Sixty-four experimental runs (26) would be required to fully evaluate combinations of each factor at two levels. NIOSH
recognized that this would be an excessive number of tests, and has devised a 16-run fraction of the full factorial that is capable of
revealing any of these factors having a significant effect, free of two-factor interactions, on sampler performance. Some
of the two and
three-factor interactions can also be screened by this design. The test is based on comparison of each factor effect to experimental error so
that the significance of that effect can be determined. Experimental conditions are shown in Table 1. Interferant was provided by the
components of the aldehyde mixture, for example if formaldehyde was examined, then acetaldehyde, benzaldehyde, butyraldehyde, and
glutaraldehyde were the interferants, and the levels were either high (1x) or low
(0.1x).
Table 1
Experimental Design of the Factor Test |
|
run
no. |
analyte
concn |
RH
(%, °C) |
inter
level |
time
(min) |
face vel
(m/s) |
sampler
orien |
|
| 1 |
0.1x |
21,30 |
low |
120 |
1.9 |
perp |
| 2 |
1x |
19,29 |
low |
30 |
0.2 |
perp |
| 3 |
0.1x |
80,30 |
low |
30 |
2.0 |
paral |
| 4 |
1x |
80,30 |
low |
120 |
0.2 |
paral |
| 5 |
0.1x |
21,30 |
high |
120 |
0.2 |
paral |
| 6 |
1x |
20,30 |
high |
30 |
1.8 |
paral |
| 7 |
0.1x |
79,30 |
high |
30 |
0.2 |
perp |
| 8 |
1x |
79,30 |
high |
120 |
1.8 |
perp |
| 9 |
1x |
80,29 |
high |
30 |
0.2 |
paral |
| 10 |
0.1x |
77,30 |
high |
120 |
1.8 |
paral |
| 11 |
1x |
20,30 |
high |
120 |
0.2 |
perp |
| 12 |
0.1x |
21,31 |
high |
30 |
1.9 |
perp |
| 13 |
1x |
77,30 |
low |
30 |
1.8 |
perp |
| 14 |
0.1x |
78,30 |
low |
120 |
0.2 |
perp |
| 15 |
1x |
21,29 |
low |
120 |
1.8 |
paral |
| 16 |
0.1x |
20,29 |
low |
30 |
0.2 |
paral |
concn = concentration; inter = interfence; face vel = face velocity; orien = orientation; perp = perpendicular; paral = parallel
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Results and Discussion
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Table 2
Extraction Efficiency (%) |
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|
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medium |
acet |
benz |
buty |
form |
glut |
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|
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DNPH GFF |
100.0 |
100.1 |
100.0 |
100.0 |
100.0 |
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DSD-DNPH |
99.7 |
100.4 |
100.3 |
100.0 |
100.2 |
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acet = acetaldehyde; benz = benzaldehyde; buty = butyraldehyde; form = formaldehyde; and glut = glutaraldehyde
|
Extraction efficiency
A summary of the average extraction efficiencies is in Table 2. The extraction efficiencies were high and constant over the ranges studied.
Sampling rate and capacity
Sampling rates were calculated by dividing mass collected (corrected for extraction efficiency) by sampling time multiplied by the actual
concentration of the test atmosphere (sampling rate = µg/(min x µg/L)).
Sampling rate, in L/min, was converted to mL/min,
the same units often used for adsorbent tubes. Theoretical concentrations were
calculated from the test atmosphere generation apparatus operation parameters. The actual test atmosphere was determined from
the HMP XAD-2 and DNPH GFF results. The
actual test atmosphere was about 98% of the theoretical concentrations (Table
3). The selection of active medium used
to establish actual test atmosphere concentrations was based on the existence
of validated methodology and on technical considerations. The results from HMP XAD-2 tubes were used
for acetaldehyde, butyraldehyde, and formaldehyde. The results for DNPH GFF were used for
benzaldehyde and glutaraldehyde. The
same sampling time was used for the active and passive samplers for each test
run. All samples were analyzed as soon
as possible after collection. Sampling
rates and capacity results are in Table 4 and Figure 2. The sampling rates were determined at ambient
temperature and pressure and converted to their equivalent at 25°C and 760 mmHg.
Table 3
Sampling Rate and Capacity Test Atmospheres (ppm) |
|
| source |
acet |
benz |
buty |
form |
glut |
|
| theoretical concn |
2.13 |
2.01 |
2.09 |
0.76 |
0.21 |
| DNPH GFF results |
1.83 |
1.98 |
2.01 |
0.72 |
0.20 |
| HMP XAD-2 results |
2.11 |
1.88 |
2.04 |
0.75 |
na |
na = not applicable |
Table 4
Sampling Rate and Capacity (mL/min) |
|
| time (min) |
acet |
benz |
buty |
form |
glut |
|
| 5 |
55.78 |
35.39 |
43.20 |
67.66 |
37.89 |
| 10 |
56.42 |
36.57 |
44.32 |
68.32 |
38.54 |
| 15 |
57.13 |
37.12 |
45.55 |
68.88 |
39.47 |
| 30 |
57.83 |
37.33 |
45.99 |
70.32 |
40.01 |
| 60 |
59.02 |
37.51 |
46.24 |
71.24 |
40.68 |
| 120 |
59.43 |
37.91 |
46.33 |
71.59 |
40.79 |
| 180 |
59.31 |
37.37 |
45.78 |
70.78 |
40.15 |
| 240 |
58.77 |
36.39 |
44.54 |
68.65 |
39.63 |
| 360 |
53.44 |
33.08 |
40.86 |
62.18 |
36.14 |
| 480 |
44.87 |
27.47 |
33.89 |
52.54 |
30.79 |
|
Figure 2. This is a plot of the sampling rate and capacity data presented in Table 4.
|
| |
Table 5
Average Sampling Rate (mL/min) and RSD (%) |
| |
|
| |
|
acet |
benz |
buty |
form |
glut |
| |
|
| |
30-240 min |
58.87 |
37.30 |
45.78 |
70.52 |
40.25 |
| |
RSD |
1.18 |
1.16 |
1.21 |
0.91 |
1.12 |
| |
DSD-DNPH
sampling rate |
59.4 |
38.2 |
46.4 |
71.9 |
na |
| |
na = not available |
The sampling rates were fairly constant from 30 to 240 minutes. The
capacity of the sampler for a component is presumed to be exceeded when the
apparent sampling rate for that component decreases rapidly. It should be noted that the atmosphere of
acetaldehyde was 2 ppm, while the PEL is 100 ppm, so the capacity results for a
sampler at the PEL will be significantly lower than what appears in Table 4. Since the sampling rates were noticeably
lower at 360 minutes, one could assume that the capacity at the PEL would be
exceeded before 15 minutes of sampling. The average sampling rates for 30 to 240
minutes are listed in Table 5, along with their RSD. The DSD-DNPH sampling rates
in Table 5 were obtained from Supelco, Inc. 12
| |
Table 6
Reverse Diffusion |
| |
|
| |
|
acet |
benz |
buty |
form |
glut |
| |
|
| |
recovery (%) |
100.2 |
100.3 |
100.0 |
100.2 |
99.3 |
| |
|
Reverse diffusion occurs when the compound is lost from the sampler
after collection. All diffusive samplers have
the potential for reverse diffusion. These DNPH derivatives are not volatile,
but loss could occur through other means so this experiment was performed. The
recovery was calculated by dividing the average recovery after 4 hours by the
average recovery after 2 hours. The recoveries were all near 100%.
The effects of increasing face velocity on the sampling rates are shown in Figure 3. The most dramatic effects occur at low to medium
velocities. The overall effect is similar to the ones observed for 3M 3520 OVMs13, SKC
575-002. 14
| |
Table 7
Effect of Increasing Face Velocity on Sampling
Rates of DSD-DNPH (ml/min) |
| |
|
| |
face vel (m/s) |
acet |
benz |
buty |
form |
glut |
|
|
|
0.2 |
56.53 |
35.49 |
42.15 |
68.45 |
37.33 |
|
0.3 |
58.38 |
36.30 |
43.24 |
69.25 |
39.28 |
|
0.5 |
59.66 |
38.07 |
45.62 |
70.99 |
40.86 |
|
1.0 |
61.66 |
40.12 |
47.48 |
73.98 |
42.39 |
|
1.8 |
66.94 |
42.76 |
49.85 |
79.84 |
45.28 |
|
|
Figure 3. This is a plot of the effects of increasing face velocity on sampling
rates from Table 7.
|
Factor Test
The results of the factor test are presented in Table 8. The sampling rates were determined at
ambient temperature and pressure, but are expressed at
25 °C and 760 mmHg.
Table 8
Factor Test Results (mL/min) |
|
| test |
acet |
benz |
buty |
form |
glut |
|
| 1 |
67.16 |
42.21 |
49.72 |
79.99 |
45.13 |
| 2 |
57.27 |
35.75 |
42.32 |
68.83 |
37.88 |
| 3 |
67.05 |
41.99 |
49.45 |
79.91 |
44.93 |
| 4 |
57.45 |
36.70 |
44.49 |
69.03 |
38.14 |
| 5 |
56.72 |
35.68 |
42.99 |
68.77 |
37.53 |
| 6 |
66.30 |
41.90 |
49.49 |
79.19 |
45.01 |
| 7 |
57.57 |
36.35 |
43.02 |
69.54 |
38.24 |
| 8 |
66.95 |
42.77 |
49.89 |
79.71 |
45.28 |
| 9 |
58.54 |
37.17 |
45.34 |
71.05 |
39.77 |
| 10 |
66.89 |
41.72 |
49.81 |
79.36 |
44.39 |
| 11 |
58.88 |
40.01 |
43.59 |
69.49 |
39.91 |
| 12 |
66.72 |
41.83 |
49.05 |
79.44 |
44.11 |
| 13 |
66.93 |
42.97 |
49.91 |
79.96 |
44.34 |
| 14 |
58.85 |
36.81 |
43.52 |
70.55 |
38.67 |
| 15 |
66.33 |
42.15 |
49.28 |
79.86 |
45.17 |
| 16 |
56.63 |
35.49 |
42.18 |
68.45 |
37.33 |
|
| |
Table 9
Percent RSDs of Average Sampling Rates |
| |
|
| |
|
acet |
benz |
buty |
form |
glut |
| |
|
| |
ave (mL/min) |
62.27 |
39.47 |
46.50 |
74.57 |
41.61 |
| |
RSD (%) |
7.58 |
7.60 |
7.02 |
7.13 |
8.08 |
| |
pooled RSD (%) |
|
|
7.49 |
|
|
| |
|
| |
Table 10
Analysis of Factor Data of Test Error |
| |
|
| |
|
acet |
benz |
buty |
form |
glut |
| |
|
| |
error |
0.32 |
0.48 |
0.31 |
0.35 |
0.37 |
| |
MSE (mL/min) |
0.73 |
1.09 |
0.70 |
0.80 |
0.85 |
| |
|
| |
Table 11
Analysis of Factor Data Effect Results |
| |
|
| |
|
acet |
benz |
buty |
form |
glut |
| |
|
| |
concn |
0.18 |
0.84 |
0.82 |
0.17 |
0.76 |
| |
RH |
0.73 |
0.17 |
1.22 |
0.79 |
0.25 |
| |
interfer |
0.16 |
0.38 |
0.42 |
0.01 |
0.39 |
| |
time |
0.38 |
0.53 |
0.46 |
0.06 |
0.39 |
| |
lin vel |
12.4 |
4.98 |
8.77 |
12.7 |
7.51 |
| |
orient |
0.76 |
0.68 |
0.36 |
0.30 |
0.19 |
| |
interaction |
none |
none |
none |
none |
none |
| |
|
| |
Table 12
Precision Data (% RSD) |
| |
|
| |
|
acet |
benz |
buty |
form |
glut |
| |
|
| |
HMP XAD-2 |
2.6 |
4.8 |
2.2 |
2.5 |
na |
| |
DNPH GFF |
5.2 |
2.1 |
3.3 |
4.1 |
2.4 |
| |
DSD-DNPH |
2.9 |
2.4 |
2.6 |
2.5 |
2.9 |
| |
|
| |
na = not applicable |
| |
|
| |
Table 13
Package Integrity Test |
| |
|
| |
|
acet |
benz |
buty |
form |
glut |
| |
|
| |
µg found |
0.41 |
<DL |
<DL |
<DL |
<DL |
| |
µg blank |
<DL |
<DL |
<DL |
<DL |
<DL |
| |
DL (µg) |
0.1 |
0.1 |
0.1 |
0.1 |
0.1 |
| |
|
| |
DL = detection limit |
| |
|
Average sampling rates and their percent RSDs are shown in Table 9. There percent RSDs were found to be homogenous by the Cochran Test
at 95% confidence limits.15 The
pooled percent RSD, 7.49%, is the sampling rate variation for the DSD-DNPH as
determined by this work.
The data in Table 8 was further analyzed to detect factor effects following the NIOSH protocol for diffusive samplers.16 The minimum significant effect (MSE) was calculated for each
component by multiplying
experimental error of the factor test by the appropriate t statistic for the nine degrees of freedom (2.26 is the t statistic at the 95%
confidence level for nine degrees of freedom). The MSE for each aldehyde is found in Table
10. The analysis gave a numerical factor effect
result for each aldehyde component for each of the seven factors. The absolute value of the normalized ratio of effect/MSE is shown in Table
11. Any ratio above 1 is significant at the 95% confidence level, and that effect should be studied further in additional experiments. The
results for interferant may be somewhat equivocal because the remainder of the mixture was considered the interference, such as acetaldehyde,
benzaldehyde, butyraldehyde, and glutaraldehyde were interferants for formaldehyde. Face velocity had the most significant effect on the
sampling rates, and humidity also had a significant effect for butyraldehyde.
Precision
The pooled relative standard deviations between sets of 3 sample results for each
medium were calculated for each aldehyde from the factor tests. The precision data of the
diffusive and active
samplers for each component were comparable. While data is presented in Table 12 for both types of active samplers, the active sampler for
acetaldehyde, butyraldehyde, and formaldehyde was HMP coated XAD-2 tubes, and the active sampler for benzaldehyde and glutaraldehyde was DNPH
GFF.
Package integrity
Formaldehyde and acetaldehyde are common components in the air, especially in urban areas, as they are natural by-products of
internal combustion
engines. The integrity of unopened DSD-DNPH, lot SP0404H01, was checked by placing them in the exposure chamber, for 100 hours,
while the 1x factor tests were performed. The diffusive samplers were exposed to 0.75 to 2 ppm for
each component.
Conclusions
The sampling rate variation for DSD-DNPH is ±7.49% as determined by this work. Sampling rate variation is a function of the design of diffusive samplers, and is not dependent on the sorbent inside, or the chemical tested. This sampling rate variation may be used for other
chemicals collected using this diffusive sampler under conditions that approximate conditions of these tests. This sampling rate variation would
also apply if a different sorbent was placed inside the diffusive sampler for
sampling other chemicals.
Sampling rate variation is used by OSHA as the sampling error component of the SAE (Sampling and Analytical Error).17 The analytical error
component is periodically updated from the analysis of quality control samples. Each analyte will have a unique SAE.
References
1 Hendricks, W., Development of a Protocol for Laboratory Testing of Diffusive Samplers, www.osha.gov, (accessed 11/24/03).
2 Hendricks, W., Development of a Protocol for Laboratory Testing of Diffusive Samplers, www.osha.gov, (accessed 11/24/03).
3 Hendricks, W., Development of a Protocol for Laboratory Testing of Diffusive Samplers, www.osha.gov, (accessed 11/24/03).
4 Walker, J., Formaldehyde, Reinhold Publishing
Corporation: New York, 1953, p 74.
5 Pengelly, I, Groves, J.A., Levin, J.O., and Lindahl, R., An Investigation into the Differences in Composition of Formaldehyde Atmospheres Generated from Different Source Materials and the Consequences for Diffusive Sampling, Ann. Occup. Hyg., 1996, Vol.40, No.5, pp 555-567.
6 Pengelly, I, Groves, J.A., Levin, J.O., and Lindahl, R., An Investigation into the Differences in Composition of Formaldehyde Atmospheres Generated from Different Source Materials and the Consequences for Diffusive Sampling, Ann. Occup. Hyg., 1996, Vol.40, No.5, pp 555-567.
7 OSHA Method 52 Formaldehyde, www.osha.gov, (accessed 11/24/03).
8 OSHA Method 64 Glutaraldehyde, www.osha.gov, (accessed 11/24/03).
9 OSHA Methods 52 and 64, www.osha.gov, (accessed 11/24/03).
10 Hendricks, W., Development of a Protocol for Laboratory Testing of Diffusive Samplers, www.osha.gov, accessed 11/24/03.
11 Cassinelli, M. E., Hull, R.D., Crable, J.V., and Teass, A.W, "Protocol for the Evaluation of Passive Monitors", Diffusive Sampling; An Alternative Approach to Workplace Air Monitoring, Berlin, A., Brown, R.H., Saunders, K.J., Eds., Royal Society of Chemistry, Burlinghouse, London, pp. 190-202, 1987.
12 DSD-DNPH Application Manual, www.sigma-aldrich.co.jp/supelco/pdf/DSD-DNPH_manual_V3.2.PDF,
(accessed 12/11/03).
13 Hendricks, W., Development of a Protocol for Laboratory Testing of Diffusive Samplers, www.osha.gov, (accessed
12/11/03).
14 Hendricks, W., Determination of the Sampling Rate Variation for
SKC 575 Series Passive Samplers, www.osha.gov, (accessed 12/11/03).
15 Anderson, R.L., Practical Statistics for Analytical Chemists, Van Nostrand Reinhold Co., New York, 1987, p 62.
16 Cassinelli, M.E., Hull, R.D., Crable, J.V., and Teass, A.W., "Protochol for the Evaluation of Passive Monitors", Diffusive Sampling: An Alternative Approach to Workplace Air Monitoring, Berlin, A., Brown, R.H., Saunders, K.J., Eds., Royal Society of Chemistry, Burlinghouse, London, pp 190-202, 1987.
17 Sampling and Analysis, www.osha.gov, (accessed
12/11/03).
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