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Sampling and Analytical Method for Ethylene Oxide
This appendix contains details for the method which has been tested at the OSHA Analytical Laboratory in Salt Lake City. Inclusion of this method in the appendix does not mean that this method is the only one which will be satisfactory.
Employers who note problems with sample breakthrough using the OSHA or other charcoal methods should try larger charcoal tubes. Tubes of larger capacity are available. In addition, lower flow rates and shorter sampling times should be beneficial in minimizing breakthrough problems.
ETHYLENE OXIDE METHOD NO. : 30
Target Concentration: 1.0 ppm (1.8 mg/m3).
Procedure: Samples are collected on two charcoal tubes in series and desorbed with 1% CS2 in benzene. The samples are derivatized with HBr and treated with sodium carbonate. Analysis is done by gas chromatography with an electron capture detector.
Recommended Air Volume and Sampling Rate: 1 liter and 0.05 Lpm.
Detection Limit of the Overall Procedure: 13.3 ppb (0.024 mg/m3) (Based on 1.0 liter air sample).
Reliable Quantitation Limit: 52.2 ppb (0.094 mg/m3) (Based on 1.0 liter air sample).
Standard Error of Estimate: 6.59%.
Special Requirements: Samples must be analyzed within 15 days of sampling date.
Status of Method: The sampling and analytical method has been subjected to the established evaluation procedures of the Organic Method Evaluations Branch.
1. General Discussion.
1.1.1 History of Procedure.
In studies to develop a method for the analysis of EtO at very low concentrations, it was found that the reaction of EtO with HBr (hydrobromic acid) gave a derivative, 2-bromoethanol, readily detectable by an ECD (electron capture detector) due to the presence of the bromine. Of solvents tested for their response on the ECD and their ability to desorb EtO from the charcoal, benzene was the only solvent tested that gave a suitable response on the ECD and a high desorption. The desorption efficiency was improved by using 1% CS2 (carbon disulfide) with the benzene.
1.1.2 Physical Properties.
See Section 5220, Appendix B.
1.2 Limit Defining Parameters.
1.2.1 Detection Limit of the Analytical Procedure.
The detection limit of the analytical procedure is 12.0 picograms of ethylene oxide per injection. This is the amount of analyte which will give a peak whose height is five times the height of the baseline noise.
1.2.2 Detection Limit of the Overall Procedure.
The detection limit of the overall procedure is 24.0 nanograms of ethylene oxide per sample. This is the amount of analyte spiked on the sampling device which allows recovery of an amount of analyte equivalent to the detection limit of the analytical procedure.
1.2.3 Reliable Quantitation Limit.
The reliable quantitation limit is 94.0 nanograms of ethylene oxide per sample. This is the smallest amount of analyte which can be quantiated within the requirements of 75% recovery and 95% confidence limits.
It must be recognized that the reliable quantitation limit and detection limit are based upon optimization of the instrument for the smallest possible amount of analyte. When the target concentration of an analyte is exceptionally higher than these limits, they may not be attainable at the routine operating parameters. The limits reported on analysis reports must be based on the operating parameters used during the analysis of the samples.
The sensitivity of the analytical procedure over a concentration range representing 0.5 to 2 times the target concentration based on the recommended air volume is 34105 area units per µg/mL. The sensitivity is determined by the slope of the calibration curve.
The sensitivity will vary somewhat with the particular instrument used in the analysis.
The recovery of analyte from the collection medium must be 75% or greater. The average recovery from spiked samples over the range of 0.5 to 2 times the target concentration is 88.0%. At lower concentrations the recovery appears to be non-linear.
1.2.6 Precision (Analytical Method Only).
The pooled coefficient of variation obtained from replicate determinations of analytical standards at 0.5X, 1X and 2X the target concentration is 0.036.
1.2.7 Precision (Overall Procedure).
The overall procedure must provide results at the target concentration that are 25% or better at the 95% confidence level. The precision at the 95% confidence level for the 15-day storage test is plus or minus 12.9%.
This includes an additional plus or minus 5% for sampling error.
1.3.1 The sampling procedure is convenient.
1.3.2 The analytical procedure is very sensitive and reproducible.
1.3.3 Reanalysis of samples is possible.
1.3.4 Samples are stable for at least 15 days at room temperature.
1.3.5 Interferences are reduced by the long GC retention time of the derivative.
1.4.1 Two tubes in series must be used because of possible breakthrough and migration.
1.4.2 The precision of the sampling rate may be limited by the reproducibility of the pressure drop across the tubes. The pumps are usually calibrated for one tube only.
1.4.3 The use of benzene as the desorption solvent increases the hazards of analysis because of the potential carcinogenic effects of benzene.
1.4.4 After repeated injections there can be a buildup of residue formed on the electron capture detector which decreases sensitivity.
1.4.5 Recovery from the charcoal tubes appears to be nonlinear at low concentrations.
2. Sampling Procedure.
2.1.1 A calibrated personal sampling pump whose flow can be determined within plus or minus 5% of the recommended flow.
2.1.2 Charcoal tubes: glass tube with both ends flame sealed, 7 cm long with a 6-mm O.D. and a 4-mm I.D., containing 2 sections of coconut shell charcoal separated by a 3-mm portion of urethane foam. The adsorbing section contains 100 mg of charcoal, the backup section 50 mg. A 3-mm portion of urethane foam is placed between the outlet end of the tube and the backup section. A plug of silylated glass wool is placed in front of the adsorbing section.
2.2.1 None required.
2.3 Sampling Technique.
2.3.1 Immediately before sampling, break the ends of the charcoal tubes. All tubes must be from the same lot.
2.3.2 Connect two tubes in series to the sampling pump with a short section of flexible tubing. A minimum amount of tubing is used to connect the two sampling tubes together. The tube closer to the pump is used as a backup. This tube should be identified as the backup tube.
2.3.3 The tubes should be placed in a vertical position during sampling to minimize channeling.
2.3.4 Air being sampled should not pass through any hose or tubing before entering the charcoal tubes.
2.3.5 Seal the charcoal tubes with plastic caps immediately after sampling. Also, seal each sample with OSHA seals lengthwise.
2.3.6 With each batch of samples, submit at least one blank tube from the same lot used for samples. This tube should be subjected to exactly the same handling as the samples (break, seal, transport) except that no air is drawn through it.
2.3.7 Transport the samples (and corresponding paperwork) to the lab for analysis.
2.3.8 If bulk samples are submitted for analysis, they should be transported in glass containers with Teflon-lined caps. These samples must be mailed separately from the container used for the charcoal tubes.
2.4.1 The breakthrough (5% breakthrough) volume for a 3.0 mg/m3 ethylene oxide sample stream at approximately 85% relative humidity, 22° C and 633 mm is 2.6 liters sampled at 0.05 liters per minute. This is equivalent to 7.8 µg of ethylene oxide. Upon saturation of the tube it appeared that the water may be displacing ethylene oxide during sampling.
2.5 Desorption Efficiency.
2.5.1 The desorption efficiency, from liquid injection onto charcoal tubes, averaged 88.0% from 0.5 to 2.0 x the target concentration for a 1.0-liter air sample. At lower ranges it appears that the desorption efficiency is non-linear.
2.5.2 The desorption efficiency may vary from one laboratory to another and also from one lot of charcoal to another. Thus, it is necessary to determine the desorption efficiency for a particular lot of charcoal.
2.6 Recommended Air Volume and Sampling Rate.
2.6.1 The recommended air volume is 1.0 liter.
2.6.2 The recommended maximum sampling rate is 0.05 Lpm.
2.7.1 Ethylene glycol and Freon 12 at target concentration levels did not interfere with the collection of ethylene oxide.
2.7.2 Suspected interferences should be listed on the sample data sheets.
2.7.3 The relative humidity may affect the sampling procedure.
2.8 Safety Precautions.
2.8.1 Attach the sampling equipment to the employee so that it does not interfere with work performance.
2.8.2 Wear safety glasses when breaking the ends of the sampling tubes.
2.8.3 If possible, place the sampling tubes in a holder so the sharp end is not exposed while sampling.
3. Analytical Method.
3.1.1 Gas chromatograph equipped with a linearized electron capture detector.
3.1.2 GC column capable of separating the derivative of ethylene oxide (2-bromoethanol) from any interferences and the 1% CS2 in benzene solvent. The column used for validation studies was: 10 ft x 1/8-inch stainless steel 20% SP-2100, 0.1% Carbowax 1500 on 100/120 Supelcoport.
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 Gas tight syringe--500 L or other convenient sizes for preparing standards.
3.1.6 Microliter syringes--10 L or other convenient size for diluting standards and 1 L for sample injections.
3.1.7 Pipets for dispensing the 1% CS2 in benzene solvent. The Glenco 1 mL dispenser is adequate and convenient.
3.1.8 Volumetric flasks--5 mL and other convenient sizes for preparing standards.
3.1.9 Disposable Pasteur Pipets.
3.2.1 Benzene, reagent grade.
3.2.2 Carbon disulfide, reagent grade.
3.2.3 Ethylene oxide, 99.7% pure.
3.2.4 Hydrobromic acid, 48% reagent grade.
3.2.5 Sodium carbonate, anhydrous, reagent grade.
3.2.6 Desorbing reagent, 99% benzene/1%CS2.
3.3 Sample Preparation.
3.3.1 The front and back sections of each sample are transferred to separate 2-mL vials.
3.3.2 Each sample is desorbed with 1.0 mL of desorbing reagent.
3.3.3 The vials are sealed immediately and allowed to desorb for one hour with occasional shaking.
3.3.4 Desorbing reagent is drawn off the charcoal with a disposable pipet and put into clean 2-mL vials.
3.3.5 One drop of HBr is added to each vial. Vials are resealed and HBr is mixed well with the desorbing reagent.
3.3.6 About 0.15 gram of sodium carbonate is carefully added to each vial. Vials are again resealed and mixed well.
3.4 Standard Preparation.
3.4.1 Standards are prepared by injecting the pure ethylene oxide gas into the desorbing reagent.
3.4.2 A range of standards are prepared to make a calibration curve. A concentration of 1.0 µL of ethylene oxide gas per 1 mL desorbing reagent is equivalent to 1.0 ppm air concentration (all gas volumes at 25°C and 760 mm) for the recommended 1-liter air sample. This amount is uncorrected for desorption efficiency.
3.4.3 One drop of HBr per mL of standard is added and mixed well. 3.4.4 About 0.15 grams of sodium carbonate is carefully added for each drop of HBr (a small reaction will occur).
3.5.1 GC Conditions.
Nitrogen flow rate--10mL/min.
Injection size--0.8 µL
Elution time--3.9 minutes
3.5.2 Peak areas are measured by an integrator or other suitable means.
3.5.3 The integrator results are in area units and a calibration curve is set up with concentration vs. area units.
3.6.1 Any compound having the same retention time of 2-bromoethanol is a potential interference. Possible interferences should be listed on the sample data sheets.
3.6.2 GC parameters may be changed to circumvent interferences.
3.6.3 There are usually trace contaminants in benzene. These contaminants, however, posed no problem of interference.
3.6.4 Retention time data on a single column is not considered proof of chemical identity. Samples over the 1.0 ppm target level should be confirmed by GC/Mass Spec or other suitable means.
3.7.1 The concentration in g/mL for a sample is determined by comparing the area of a particular sample to the calibration curve, which has been prepared from analytical standards.
3.7.2 The amount of analyte in each sample is corrected for desorption efficiency by use of a desorption curve.
3.7.3 Analytical results (A) from the two tubes that compose a particular air sample are added together.
3.7.4 The concentration for a sample s calculated by the following equation:
EtO, mg/m3 = (A x B) / C
A = µg/mL
B = desorption volume in milliliters
C = air volume in liters.
3.7.5 To convert mg/m3 to parts per million (ppm) the following relationship is used:
EtO, ppm = (mg/m3 x 24.45) / 44.05
mg/m3 = results from 3.7.4
24.45 = molar volume at 25°C and 760 mm Hg
44.05 = molecular weight of EtO.
3.8 Safety Precautions
3.8.1 Ethylene oxide and benzene are potential carcinogens and care must be exercised when working with these compounds.
3.8.2 All work done with the solvents (preparation of standards, desorption of samples, etc.) should be done in a hood.
3.8.3 Avoid any skin contact with all of the solvents.
3.8.4 Wear safety glasses at all times.
3.8.5 Avoid skin contact with HBr because it is highly toxic and a strong irritant to eyes and skin.
NOTE: Authority cited: Sections 142.3, 9020, 9030 and 9040, Labor Code. Reference: Sections 142.3, 9004(d), 9009, 9020, 9030 and 9040, Labor Code.
1. Editorial correction moving Note and Histories 1-7 to precede Appendix A of section 5220 (Register 99, No. 28). For prior history of Appendices, see section 5220.