[Advances in Chemistry] Formaldehyde Volume 210 (Analytical Chemistry and Toxicology) || Field...

11 Field Evaluations of Sampling and Analytical Methods for Formaldehyde

E U G E N E R. KENNEDY, DAVID L . SMITH, and CHARLES L . GERACI , JR. National Institute for Occupational Safety and Health, Cincinnati, O H 45226

A field evaluation to compare NIOSH method Ρ&CAM 354 [2-(benzylamino)ethanol-coated sorbent] with NIOSH Ρ&CAM 318 (oxidative sorbent), Ρ&CAM 125 (impinger and chromotropic acid), and a 2,4-dinitrophenylhydrazine-coated silica gel sorbent tube method was conducted in three different environments: a formaldehyde production facility, a hospital dialysis unit, and a fiberglass insulation production facility. Results from these studies indicated that one of the methods, Ρ&CAM 318, had sample stability problems and was not suitable for monitoring that required sample storage for any length of time. No apparent difference was found between the other methods in all of the studies, but the limitations of Ρ&CAM 354 at levels less than 0.25 mg/m3 (0.2 ppm) were documented. This limitation was due mainly to the presence of a background level of formaldehyde on the sampling tube.

I N T H E D E V E L O P M E N T O F S A M P L I N G A N D A N A L Y T I C A L M E T H O D S for workplace contaminants, one of the most difficult and often overlooked tasks is field evaluation of the method. Previous work in our laboratories has shown that field testing of sampling and analytical methods has defined certain problem areas in various sampling and analytical methods. In a study performed by Hill (I) the instability of certain pesticides under field conditions was noted. Other field studies on polynuclear aromatic hydrocarbons have been used to determine which stage of a two-stage sampler contains the various compounds of interest. This type of information is not readily available from laboratory-generated samples unless extensive study of the field environment has been done. Variations in concentration due to drafts, currents in the workplace, and other variables and conditions under which the contaminant is formed and exists cannot be duplicated easily in the laboratory and may cause variation between laboratory and field evaluation studies. Also, the cost of duplicating field conditions in the laboratory may be prohibitive.

A major problem in performing a field evaluation is that the "true"

This chapter not subject to U.S. copyright. Published 1985 American Chemical Society

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In Formaldehyde; Turoski, V.; Advances in Chemistry; American Chemical Society: Washington, DC, 1985.

152 F O R M A L D E H Y D E : A N A L Y T I C A L CHEMISTRY A N D T O X I C O L O G Y

concentration of the contaminant in the workplace cannot be determined. However, if a number of sampling and analytical methods are used for the measurement, an estimation of the actual concentration can be made. With the number of sampling and analytical methods for formaldehyde, this compound provided a good candidate for field evaluation.

Experimental Sampling Sites. Three different sites were used in these field evaluations.

These were a formaldehyde production facility, a hospital dialysis unit, and a fiberglass insulation production facility. Each of these locations had very different workplace environments. The source of formaldehyde in each location was quite different. In the production facility, formalin (ca. 50%) and paraformaldehyde were the sources; in the dialysis unit, 5 % and 37 % formalin solutions were the only source; in the fiberglass production facility, potential sources of formaldehyde included free formaldehyde, formaldehyde adsorbed on particulate or fibers, and particulate and form aldehyde-generating particulate from the resin system chemically degrading in the sampling system.

Method Description. Four methods were used in these studies. They were a published procedure by Beasley et al. (2) [2,4-dinitrophenylhydrazine (DNP) method], NIOSH P & C A M 354 (3, 4), NIOSH P & C A M 318 (5, 6), and NIOSH P & C A M 125 (7-9). The DNP method uses silica gel sorbent coated with a solution of hydrochloric acid, iV,iV-dimethylformamide, and 2,4-dinitrophenylhydrazine and packed into sampling tubes. The 2,4-dinitrophenylhydrazone of formaldehyde is formed on the coated sorbent, desorbed with acetonitrile, and determined by high-performance liquid chromatography.

NIOSH P & C A M 318 is based on the oxidation of formaldehyde to formate by a proprietary charcoal sorbent. The formate ion is desorbed with hydrogen peroxide solution and quantitated by ion chromatography. NIOSH P & C A M 354 uses a reagent-coated sorbent for collection of formaldehyde. This reagent [2-(benzyl-amino)ethanol] reacts with formaldehyde to form 3-benzyloxazolidine, a five-membered cyclic derivative. This compound is desorbed from the sorbent with iso-octane and determined by capillary gas chromatography. NIOSH P & C A M 125 was adapted by NIOSH from the Intersociety Committee. It uses an impinger filled with 1 % sodium bisulfite for collection of formaldehyde. This solution is reacted with chromotropic acid and sulfuric acid and turns purple in the presence of formaldehyde. The amount of formaldehyde in the resulting solution is determined spectrophotometrically at 580 nm.

Cellulose ester membrane prefilters were used on half of the samplers in the field evaluation in the fiberglass production facility. After sampling, the prefilters were placed in Nalgene cross-linked polyethylene (CPE) sample bottles with 10 mL of 1 % sodium bisulfite solution. These samples were analyzed for formaldehyde by method P & C A M 125 described earlier.

Al l samples and filters were blank corrected. Blank values are noted in Tables I-III.

Apparatus. Samples were collected with M D A model 808 Accuhaler sampling pumps with 50-cm3/min orifices installed for the field evaluations in the formaldehyde production, facility and hospital dialysis unit. In the fiberglass production facility a large vacuum pump (Gast M D L 0522) with critical orifices (0.05 L/min, made from sections of capillary tubing and Millipore critical orifices, 1.0 L/ min) was used for sample collection. A device shown in Figure 1 was used to hold the samples during all of the field evaluations. This device was constructed from

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11. K E N N E D Y E T A L , Field Evaluations 153

Figure 1. Device used to hold samples during all field evaluations.

0.5-in. (12.8-mm) plexiglas sheet stock, a 7-in. (17.8-cm) plastic laboratory funnel, and 0.25-in. (6.4-mm) polypropylene male connectors to hold the sampling tubes. Pumps or a vacuum source was connected to the tubes, and the air being sampled was drawn in through the funnel opening. This device provided a homogeneous atmosphere for the sampling. Laboratory tests with this device indicated relative standard deviations for sets of 12 samples of less than 10 % could be obtained.

Sampling Protocol. Samples were collected 12 at a time with the device shown in Figure 1. Each run consisted of two sets of 12 samples collected over 4-6 h. Four samples of each of three methods (P&CAM 318, P & C A M 354, and 2,4-DNP) were used in each set for the first two evaluations. The position of samples in each device was randomized with at least one tube of each method in each quadrant of the sampler to eliminate any bias that might be due to the collection device. Al l samples were collected at 0.05 L/min to eliminate differences in flow between the methods as a variable in the study for the first two evaluations.

The protocol for the evaluation in the fiberglass production facility was slightly modified to study the effect that particulate material might have on formaldehyde monitoring. For this study only two methods were used: P & C A M 125 and P & C A M 354. At this time these were the only two methods recommended by NIOSH for use on their industrial hygiene surveys because sample instability problems had been experienced with P & C A M 318. Samplers were configured both with and without prefilters to study the effect of potential formaldehyde-containing particulates on the sampling results. Again the sample holder device shown in Figure 1 was used. Cellulose ester membrane prefilters were used on half of the samplers in this field evaluation in the fiberglass production facility. After sampling, the prefilters were placed in Nalgene CPE sample bottles with 10 mL of 1 % so-

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dium bisulfite solution. These samples were analyzed for formaldehyde by method P & C A M 125 described earlier. In this instance samplers were run at their recommended flow rates for 4 h (P&CAM 125, 1.0 L/min; P & C A M 354, 0.05 L/min). Although this sampling rate and time exceeded the recommended sample volume of P & C A M 125, it allowed the collection of a greater amount of particulate material and a better chance to see contribution to overall formaldehyde levels from formaldehyde adsorbed on or hydrolyzed from this material. Prefilters were analyzed by the method described earlier, and their contribution to the overall sample was reported separately. Analysis of variance was used to study differences between the method configurations. Samples were collected over 2 days in two 4-h sets each day.

Several assumptions were made in the basic design of these studies. These included the following: differences in position in the sample holder are not statistically significant; a 10 % coefficient of variation for each method is assumed; levels will be above the limit of detection; and no run-method interaction occurs. Previous evidence from NIOSH studies indicated no statistically significant differences between positions when this type of sample collection device was used. Two runs (48 total samples) were required to detect with 80 % confidence a 10 % true difference between any two methods with the significance level fixed at 0.05. Analysis of variance and Duncan's test were used to determine if means of the methods were statistically different (10).

Included as an additional experiment, a sample stability study was performed on the P & C A M 125 samples. Because the analytical method requires that only 4 mL of sample be used in the actual analysis, it was possible to preserve the sampling solutions for later analysis. This analysis was done as a check on sample stability and also as an indicator of formaldehyde generation from particulate. Samples were analyzed immediately upon receipt in the laboratory as well as 10 and 30 days following receipt.

Results and Discussion Before the field evaluation of the methods was attempted, a laboratory test of the sample holder was undertaken. Six samples of both P & C A M 354 and P & C A M 318 were taken in a formaldehyde atmosphere generated by vaporization of formaldehyde in a heated injection block and diluted with clean air. Results from the six P & C A M 354 samples and three of the P & C A M 318 samples and their associated relative standard deviations (RSD) were 1.70 mg/m3 (11%) and 1.68 mg/m3 (11%), respectively. This experiment confirmed our assumption of an RSD of 10 % for the methods under study. The second set of three samples from P & C A M 318 was retained for quality control samples for submission with the field samples to be collected. This second set of samples was submitted for analysis approximately 6 weeks after collection. The result from this set of samples was 0.55 mg/m3 (RSD = 29 % ). These results were the first indication that a sample instability problem existed with method P & C A M 318.

Site 1. The first field evaluation took place in a formaldehyde production facility. The methods used were the DNP method, P & C A M 354, and P & C A M 318. These methods were chosen because they were all sorbent tube methods and could be used at 0.05 L/min with no apparent problems. The results of the samples taken over 2 days are shown in Table I.

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11. K E N N E D Y E T A L . Field Evaluations 155

Table I. Formaldehyde Production Facility Field Data

Sample DNP P&CAM 354 P&CAM 318

Day 1 Sample holder #1 Sample holder #2

Day 2

4 .58 ± 1.55 4 . 1 7 ± 0.44

4 .07 ± 1.79 4 .26 ± 0 .66

2.74 ± 5.6 2 .07 ± 4.44'

Sample holder #1 Sample holder #2

1.34 ± 0 .56 1.33 ± 0.04

0 .97 ± 0 .05 1.18 ± 0 .07

0.62 ± 0 .62° 0.79 ± 0 .35

NOTE : Concentrations are the average of four samples except where noted and are expressed in parts per million with their 9 5 % confidence limits. Averages of the blank values are as follows: 2 , 4 - D N P , 3.1 μg/sample; P & C A M 318, 6.0 Mg/sample; and P & C A M 354, 2.7 ^g/ sample.

flValues are the average of three samples.

Samples were collected for 6 h each day. With some of the samples the pumps stopped working before the end of the 6-h sampling period. Although the sampling pumps were fully charged before use, the conditions of high humidity and temperature (25-30 °C and 80-90% rh) may have adversely affected pump battery life. These low-volume samples contribute to the variability observed in the samples because the low-volume samples are included in the data table. In the statistical analysis, these low-volume samples were treated as outliers, and the DNP method and P&CAM 354 were found to give statistically equivalent results. With P&CAM 318, the nonoutlier results were low and significantly different from the other two methods. Also the RSD with this method was larger than the results obtained during the preliminary laboratory work with the sampler holder. These findings led to further study of sampling and storage parameters of P&CAM 318. The results of that study indicated sample instability when samples were stored for periods longer than 1 week (II).

Site 2 . The second field evaluation took place in a hospital dialysis unit. Formalin solutions (5% and 37%) were used to sterilize the peritoneal dialysis machines by pumping the solution into the machines and letting them sit for 2 h. The time required for the filling of two machines with formalin was approximately 1 h. Samples were collected over this 1-h period. Environmental conditions during this time were approximately 25 °C and 50% rh. Methods used were the DNP method, P&CAM 318, and P&CAM 354. At this time the instability problem of P&CAM 318 was defined, and the analysis request for these samples was cancelled. Results for the DNP method and P&CAM 354 are shown in Table II. A total of two sets of four replicates of each method were collected. In this study formaldehyde levels were quite low. These low levels were also confirmed by a C E A 555 continuous formaldehyde monitor. This monitor gave a time-weighted average concentration during the sampling period of 0.15 ppm. The levels measured by the DNP method and P&CAM 354 were only slightly larger than the blank amounts, which were 3.1 and 3.4 ^g/sample,

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Table II. Hospital Dialysis Unit Field Data

Sample P&CAM 354 DNP

Sample holder 1 0.14 ± 0.03 0.28 ± 0.06° Sample holder 2 0.11 ± 0.20 0.30 ± 0.1

NOTE : Concentrations are the average of four samples except where noted and are expressed in parts per million with their 95 % confidence limits. Averages of the blank values are as follows: 2,4-DNP, 3.1 μg/sample; and P & C A M 354, 3.4 ^g/sample.

a Values are the average of three samples.

respectively. This fact contributes to the high variability of each set of samples. Although a statistically significant difference between the two methods was observed, these differences are probably unimportant because the actual amounts of formaldehyde measured are at the bottom of the analytical range for each method.

Site 3. The third field evaluation took place in a fiberglass insulation production facility. At this sampling site, fiberglass was blown, resin coated, and shaped, all within a single structure. The potential existed for free formaldehyde from the resin system as it was sprayed onto the fiberglass, for particulate-bound formaldehyde from its adsorption onto airborne materials, and for form aldehyde-generating particulate from the resin system chemically degrading in the sampling systems.

Formaldehyde can be trapped in dust as either an adsorbed species or in a chemically bound state (12). During sample workup, the formaldehyde can be released either by desorption or hydrolysis. To attempt to study this problem, a field evaluation was undertaken in a fiberglass insulation production facility. Samples were collected by using methods P&CAM 354 and P&CAM 125 with and without prefilters on each method, to give a total of four sampler combinations. The samplers were arranged in the sample holders in the four configurations in triplicate.

Samples were collected in two 4-h sample sets per day over 2 days. Environmental conditions were 25 - 30 °C and 80 - 90% rh. Results from the sample analysis are shown in Table III. Good agreement was found between impingers with and without prefilters, and the amount of formaldehyde found on the prefilters was minimal. The P&CAM 125 data demonstrate a rather consistent formaldehyde concentration ranging from 0.1 to 0.2 ppm. One significant observation was that glass fibers were found to have passed through the unfiltered P&CAM 125 samples and were collected on the prefilters before the critical orifices. Without the critical orifice prefilters, significant clogging and reduction of flow might have occurred. This problem was not observed with the prefiltered P&CAM 125 samples.

A red color and absorption maximum shift to 520 nm was noted with the desorbed impinger prefilter samples. Possible explanations include the extraction of organics from the filter media or the presence of the phenol in

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11. K E N N E D Y E T A L . Field Evaluations

Table III. Fiberglass Production Facility P & C A M 125 Data

157

Sample Impinger

with Prefilter Impinger Alone

Day 1 Sample holder 1 Sample holder 2

Day 2

0.19 ± 0.02 0.10 ± 0.01

0.20 ± 0.02 0.11 ± 0.0

Sample holder 1 Sample holder 2

0.13 ± 0.02 0.14 ± 0.01

0.12 ± 0.03 0.13 ± 0.01

NOTE : Concentrations are the average of three samples and are expressed in parts per million with their 95% confidence limits. Averages of the blank values are as follows: prefilter, 0.8 /xg/sample; and P & C A M 125, 0.7 μg/sample.

the resin system. Certain organic compounds and phenol, in particular, are negative interferences in P&CAM 125 (7). If phenol were present, then the true amount of particulate-bound formaldehyde determined from the prefilters would be different from the reported values.

The results for the P&CAM 354 tubes, both with and without prefilters, were below the limit of detection for the method. The results for the prefilters for the tubes were also below the limit of detection.

To study the stability of samples collected with P&CAM 125, impinger samples were transferred to Nalgene CPE bottles and analyzed immediately on receipt in the laboratory, 10 days after receipt, and 30 days after receipt. A second purpose for this study was to see if any formaldehyde-generating particulate had been captured by the impingers. If any of this particulate were present, then formaldehyde concentrations should have increased with time. As can be seen from the data in Table IV, the levels appeared to remain constant for at least 10 days. Statistical analysis of the results verified this observation. After storage for 30 days, significant differences were observed between day 1 and day 30 analyses. The stability of P&CAM 125 samples for 10 days is in conflict with the reported instability problems found with this method when evaluated under the joint OSHA-NIOSH Standards Completion Program (13).

Conclusions The results from the first field evaluation in a formaldehyde production facility indicate that good correlation is found between the DNP method and P&CAM 354. Problems of sample instability were discovered with P&CAM 318 and have been defined in other work (II). The discovery of this problem with P&CAM 318 demonstrates once again the need for field evaluation of sampling and analysis methodology. In the second field evaluation in the hospital dialysis unit, the sensitivity and precision of the methods were found to be questionable at low levels. The last field evaluation once again confirmed the lack of sensitivity of P&CAM 354 at low formaldehyde levels.

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Table IV. P & C A M 125 Storage Stability Study

Recovery (μ§1 sample)0

Sample 1 day 10 days 30 days

301 49.7 49.9 (100.5) 48.6 (97.8) 302 48.6 48.1 (99.0) 46.4 (95.4) 303 42.0 41.0 (97.5) 35.5 (84.5) 304 30.3 30.6 (100.9) 29.7 (98.0) 305 21.2 20.6 (97.1) 16.2 (76.4) 306 29.8 30.2 (101.3) 24.2 (81.6) 307 41.5 40.6 (97.7) 39.2 (94.5) 308 29.9 29.1 (97.4) 24.4 (81.6) 309 31.6 30.2 (95.6) 26.1 (82.6) 310 29.7 29.1 (98.0) 30.2 (101.7) 311 27.3 25.9 (94.8) 24.0 (87.9) 312 29.4 28.7 (97.6) 27.9 (94.9)

aPereent recoveries enclosed in parentheses are relative to quantity of formaldehyde found on day 1.

This last study also demonstrated the ability of P&CAM 125 to measure formaldehyde in the 0.1- to 0.2-ppm range with a high degree of precision. Situations in which airborne particulate might be present, especially particulate that might potentially decay and release formaldehyde, warrant the use of a prefilter when P&CAM 125 impinger samples are collected. A second reason for using prefilters is that particulate can pass through the impinger and be trapped in the sample pump or vacuum source. The sample stability study done on P&CAM 125 samples collected during this evaluation indicated good sample stability for up to 10 days after sample collection when stored in Nalgene CPE bottles.

Acknowledgments We acknowledge the assistance of Julia R. Okenfuss for the analysis of the 2,4-DNP-coated silica gel tubes, the UBTL Division, University of Utah Research Institute for the P&CAM 318 and P&CAM 354 analyses, Southern Research Institute for the P&CAM 125 and prefilter analyses, Larry Elliot for assistance in dialysis unit field evaluation, Pierre L . Bélanger for assistance in the fiberglass production facility field evaluation, and Richard Hornung for statistical assistance in the preparation of the sampling protocol.

Mention of company names or products does not constitute endorsement by NIOSH.

Literature Cited 1. Hill, R. H. , Jr.; Arnold, J. E. Arch. Environ. Contam. Toxicol. 1979, 8,

621-28.

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11. K E N N E D Y ET A L . Field Evaluations 159

2. Beasley, R. K . ; Hoffmann, C. E . ; Rueppel, M. L.; Worley, J. W . Anal. Chem. 1980, 52, 1110-14.

3. Kennedy, E . R.; H i l l , R. H., Jr. Anal. Chem. 1982, 54, 1739-42. 4. “National Institute for Occupational Safety and Health Manual of Analytical

Methods”; Taylor, D . G., E d . ; NIOSH: Cincinnati, 1981; DHHS(NIOSH) Publication No. 82-100, P & C A M 354.

5. “National Institute for Occupational Safety and Health Manual of Analytical Methods”; Taylor, D . G., E d . ; NIOSH: Cincinnati, 1980; DHHS (NIOSH) Publication No. 80-125, P & C A M 318.

6. Kim, W . S.; Geraci, C. L.; Kupel, R. Am. Ind. Hyg. Assoc. J. 1980, 41, 334-39.

7. “National Institute for Occupational Safety and Health Manual of Analytical Methods”; Taylor, D . G., E d . ; NIOSH: Cincinnati, 1977; DHHS (NIOSH) Publication No. 77-157-A, P & C A M 125.

8. Intersociety Committee on Methods of Air Sampling and Analysis “Methods of Air Sampling and Analysis,” Method 111; American Public Health Association: Washington, D . C . , 1972; pp. 194-98.

9. Intersociety Committee on Methods of Air Sampling and Analysis “Methods of Air Sampling and Analysis,” 2d ed., Method 116; Katz, Morris, Ed . ; American Public Health Association: Washington, D . C . , 1977; pp. 303-7.

10. Miller, I.; Freund, J. E. “Probability and Statistics for Engineers”; Prentice-Hall: Englewood Cliffs, New Jersey, 1977; Chap. 12.

11. Smith, D . L.; Bolyard, M.; Kennedy, E . R. Am. Ind. Hyg. Assoc. J. 1983, 44, 97-99.

12. Cocalis, C. L.; Beaulieu, H . J., presented at the Am. Ind. Hyg. Conf., Houston, Tex., 1980.

13. National Institute for Occupational Safety and Health-Occupational Safety and Health Administration Standards Completion Program Failure Report for Formaldehyde, S327, NIOSH contract report, 1976.

RECEIVED for review September 28, 1984. A C C E P T E D January 7, 1985.

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[Advances in Chemistry] Formaldehyde Volume 210 (Analytical Chemistry and Toxicology) || Field...

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