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Method number: PV2047
Matrix: Air
Target Concentration: 2 mg/m3 ACGIH TWA TLV
Procedure: Samples are collected by drawing a known volume of air through a glass fiber filter. Samples are desorbed with Carbon Disulfide and analyzed by gas chromatography using a Flame Ionization Detector.
Air volume and studied: 100L at 1 Lpm.
Status of method: Stopgap method. This method has been only partially evaluated and is presented for information and trial use.
Date: 6-9-88 Chemist: Brett Besser


1. General Discussion

1.1. Background

1.1.1. History of procedure

The OSHA Laboratory recently received samples collected on glass fiber filters requesting paraffin wax fume analysis. Although this collection method has been recommended for many years, the supporting documentation had not been collected. Since there is a TLV and samples were received, it was decided to perform the laboratory work needed to evaluate this sampling and analytical procedure.

1.1.2. Toxicity

Pure paraffin wax is widely regarded as non toxic, but may possess some carcinogenic properties.(Ref 5.3) These properties are largely believed to be due to polycyclic aromatic hydrocarbons, but most processed waxes in use in America today do not possess any measurable levels of polycyclics. (Ref 5.1) Work around molten paraffin, especially if it is overheated is more uncomfortable and nauseating than dangerous. (Ref 5.4)

1.1.2. Potential workplace exposure

Workers are exposed to paraffin wax fumes in a variety of industries. Any time that paraffin solid is heated a fume may be produced. Paraffin is ideal for use as a sealer or waterproofing agent. Coating of paper for use as containers for milk is one of the largest uses of paraffin. (Ref 5.1) It is also used in the candle making industry and as an original mold in the casting industry.

1.1.3. Physical properties:

Compound: Paraffin Wax is macrocrystalline and is composed mostly, (40%-90%), of straight chain alkanes Cl8 - C36. The remainder is composed of Cl8 - C36 isoalkanes and cycloalkanes. Paraffin wax contains very little oil. (less than 0.1%)
Odor: none
Color: white
CAS: 8002-74-2
IMIS: 2000
RTECS: RV0350000

1.2. Limit defining parameters

1.2.1. The detection limit of the analytical procedure is 6.8 ng per injection. This is the smallest amount of paraffin that will give a characteristic chromatographic pattern. (Figure 1)

1.2.2. The overall detection limit is 0.034 mg/m3 based on a 100 liter air volume and a 2 mL desorption volume. Air concentrations given throughout this procedure are based on a 100 liter air volume and 2 mL desorption volume.

1.3. Advantages

1.3.1. The sampling procedure is convenient.

1.3.2. The analytical method is reproducible and sensitive.

1.3.3. Reanalysis of samples is possible.

1.4. Disadvantages

1.4.1. Paraffin produces a characteristic fingerprint pattern. Integration generally is done by using the total area of all peaks. An interfering peak counted as part of the total area would produce inaccurate results.

2. Sampling procedure

2.1. Apparatus

2.1.1. A calibrated personal sampling pump, the flow of which can be determined within + 5% at the recommended flow.

2.1.2. A three piece plastic sampling cassette capable of holding a 37 mm glass fiber filter.

2.2. Sampling technique

2.2.1. The glass fiber filter is placed in the cassette and the inlet and outlet plugs are removed.

2.2.2. Connect the sampling cassette to the sampling pump with flexible tubing.

2.2.3. Air being sampled should not pass through any hose or tubing before entering the sampling cassette.

2.2.4. Replace the inlet half of the cassette. Seal the cassette with plastic plugs immediately after sampling. Seal each sample covering the plugs with OSHA Form-21.

2.2.6. With each batch of samples, submit at least one blank. This cassette should be subjected to exactly the same handling as the samples, except no air is drawn through it.

2.2.7. Send the samples and corresponding paperwork to the lab for analysis.

2.2.8. Bulks submitted for analysis must be shipped in a separate container from the air samples.

2.3. Extraction efficiency

2.3.1 Eighteen filters were spiked with a solution of Parowax in carbon disulfide. The solution was 6.26 mg/mL. Six filters were spiked with 6 uL (37 ug, six with 32 uL (200 ug) and the final six with 120 uL (751 ug). This corresponds to approximately 0.1, 0.5 and 2 times the target concentration. The tubes were refrigerated overnight, extracted the next day, and analyzed by gas chromatography using a flame ionization detector. The average extraction efficiency is 95.3%. (Table 1)

Table 1
Extraction Efficiency

Number 2x 0.5x 0.1x
7.51 mg 2.0 mg 0.37 mg

1 95 98 99
2 97 104 95
3 92 96 91
4 94 92 90
5 102 102 86
6 98 95 94
average 96 98 92
std. dev. 3.2 4.1 4.4
overall average 95.3

2.4. Retention efficiency

2.4.1. Six glass fiber filters were spiked with 60 uL of a 6.26mg/mL solution of Parowax in carbon disulfide. This was equivalent to a loading of 372 ug of paraffin wax which is approximately the target concentration. They were stored overnight. Eighty, 100 and 125 liters of humid air (70%) were drawn through the filters the next day. The filters were extracted with carbon disulfide and analyzed. The average result including all air volumes is 101%. (Table 2)

Table 2
Retention Study

Sample Air Amount % Retained
Number Volume Spiked

1 80 372 99
2 " " 109
3 100 " 97
4 " " 97
5 125 " 97
6 " " 106
average 101

2.5. Storage

2.5.1. Five glass fiber filters were spiked with 60 uL of a 6.26 mg/mL solution of Parowax in carbon disulfide. This was equivalent to a loading of 372 ug of paraffin wax which is approximately the target concentration. They were stored in the refrigerator for five days, extracted with carbon disulfide and analyzed. The average recovery after five day storage is 95%. (Table 3)

Table 3
Storage Study

Sample Amount Days % Recovered
Number Spiked Stored

1 372 5 94
2 " " 91
3 " " 101
4 " " 95
5 " " 93
average 95

2.6. Air volume and sampling rate studied

2.6.1. The air volume studied is 100 liters.

2.6.2. The sampling rate studied is 1 liter per minute.

2.7. Interferences

Suspected interferences should be listed on sample data sheets.

2.8. Safety precautions

2.8.1. Sampling equipment should be placed on an employee in a manner that does not interfere with work performance or safety.

2.8.2. Safety glasses should be worn at all times.

2.8.3. Follow all safety practices that apply to the workplace being sampled.

3. Analytical method

3.1. Apparatus

3.1.1. Gas chromatograph equipped with a flame ionization detector (FID).

3.1.2. GC column capable of separating the analyte and an internal standard, if used, from any interferences. The column used in this study was a DB-1 fused silica capillary having the following dimensions; 6 meter length, 0.32 mm ID, 1 u film.

3.1.3. An electronic integrator or some other suitable method of measuring peak areas.

3.1.4. Two milliliter vials with Teflon lined caps.

3.1.5. A 10 uL syringe or other convenient size for sample injection.

3.1.6. Pipettes for dispensing the desorbing solution. The Glenco 1 mL dispenser was used in this method.

3.1.7. Volumetric flasks - 10 mL and other convenient sizes for preparing standards.

3.2. Reagents

3.2.1. Purified GC grade nitrogen, hydrogen, and air.

3.2.2. Carbon disulfide, Reagent grade.

3.3.3. Parowax paraffin used as the analytical standard.

3.3. Sample preparation

3.3.1. Sample cassettes are opened and the filter is placed in a 4 mL vial.

3.3.2. Each filter is extracted with 2 mL carbon disulfide.

3.3.3. The vials are sealed immediately and extracted for 30 minutes with occasional shaking.

3.4. Standard preparation

3.4.1. Standards are prepared by diluting a known quantity of Parowax in carbon disulfide. One thousand ug of Parowax in 10 mL of carbon disulfide will give a standard equivalent to the TLV assuming 100 liter air volume and 2 mL extraction.

3.4.2. A range of separate standards should be made so that the sample results are bracketed.

3.5. Analysis

3.5.1. Gas chromatograph conditions.

Flow rates (mL/min) Temperature (deg.C)
Hydrogen carrier: 1 Injector: 250
Hydrogen flame: 50 Detector: 300
Air: 300 Column: 250
Nitrogen makeup: 25

Injection size: 4 uL
Elution time: Fingerprint from 2 to 12 min.
Chromatogram: Figure 2
Attenuation: 2

3.5.2. Peak areas are measured by an integrator or other suitable means.

3.5.3. Precision was measured by by making 6 consecutive injections of 4 different standards containing Parowax concentrations of 37, 200, 372, and 751 ug/mL. The pooled coefficient of variation is 0.016. (Table 4)

Table 4

Injection 2.0x 1.0x 0.5x 0.1x
Number 750 ug/ml 372 ug/ml 200 ug/ml 37 ug/ml

1 3852800 1939300 1056200 224100
2 3831200 1866400 1082500 219920
3 4044400 1902900 1059100 221010
4 4065500 1906900 1065500 227370
5 3686100 1074300 218380
6 3694700 1071900 205610
Average = 3862450 1903875 1068250 219398
Deviation = 30425 25855 8963 6952
CV = .0079 .014 .0084 .032
Pooled CV = .016

formula for pooled coefficient of variation

A(1), A(2),A(3),A(4) = # of injections at each level
CVl, CV2, CV3, CV4 = Coefficients at each level

3.6. Interferences (analytical)

3.6.1. Any compound having the general retention time of the analyte or the internal standard used is an interference. Possible interferences should be listed on the sample data sheet. GC parameters should be adjusted if necessary so these interferences will pose no problems.

3.6.2. Retention time data on a single column is not considered proof of chemical identity. Samples over the target concentration should be confirmed by GC/Mass Spec or other suitable means.

3.7. Calculations

3.7.1. To calculate the mg/m3 of analyte in samples, the following equation should be used:

(L)(2 mL)(EE)
=  mg 

2 mL
100 L
  =   micrograms
  =   Desorption volume
  =   100 liter air sample
  =   Extraction efficiency

3.8. Safety precautions

3.8.1. All handling of solvents should be done in a hood.

3.8.2. Avoid skin contact with all solvents.

3.8.3. Wear safety glasses at all times.

4. Recommendations for further study

The method seems adequate for both collection and analysis. The only thing that is left to look at is actual quantitative collection of fumes. Paraffin fumes have been produced by heating Parowax in a bubbler tube and collecting them on a filter attached to the exit port. The collection appeared to be good with no breakthrough to the backup pad. But no quantitative check has been performed using an actual dynamic atmosphere of paraffin fumes.

Much of the analytical work could possibly be avoided by the use of pre- and post-weighings. It is unusual to have other contaminates in areas where paraffin wax fumes are being emitted. By using weighings to determine the total mass present on the filter it may be possible to eliminate the chromatographic determination of samples with little or no contamination. Most samples received at the lababoratory fall into this category. This is an area that may warrant further study.

Figure 1

Figure #l Parowax detection limit (1.708 g/mL )

Figure 2

Figure #2 Parowax standard in Carbon Disulfide.(l5.8 g/mL )

5. References

1) P. Shubik et al; "Studies on the Toxicity of Petroleum Waxes"; Toxicology and Applied Pharmacology; Aug. 2 1962.

2) "Encyclopedia of Chemical Toxicology", vol #24, Third Edition, Kirk-Othmer.

3) R. Prosser White "The Dermatergoses or Occupational Affections of the Skin" London H.K. Lewis & Co. 1934.

4) "Queries and Minor Notes" Journal of American Medical Assoc. 110:2102 1938.


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