Reference method for measuring emissions of vinyl chloride from manufacturing: part II A-1
Part II - Analysis: Method A-1
Analysis for Vinyl Chloride in Gaseous Samples
- A-1.1 Principle and Applicability
- A-1.2 Range and Sensitivity
- A-1.3 Accuracy and Reproducibility
- A-1.4 Interferences
- A-1.5 Apparatus
- A-1.6 Reagents
- A-1.7 Procedure
- A-1.8 Calibration
- A-1.9 Calculations
A-1.1 Principle and Applicability
A sample of gaseous effluent containing vinyl chloride taken in a plastic bag is analyzed for vinyl chloride by gas chromatography using a flame ionization detector.
The method can be used to measure the concentration of vinyl chloride in gaseous samples of effluent streams from vinyl chloride monomer and polyvinyl chloride manufacturing processes.
A-1.2 Range and Sensitivity
The lower detectable limit will vary according to the chromatograph used and the operating conditions. A lower detectable limit of 0.5 ng of vinyl chloride is attainable with a flame ionization detector. The detector is linear in the range 0.5 to >1000 ng. Under the analytical conditions described and using a 1-ml sampling loop, concentrations of vinyl chloride as low as 500 jμg/m3 (0.2 ppm) can be detected.
A-1.3 Accuracy and Reproducibility
Using a heated gas sampling valve with a 1-ml loop, analyses of standard mixtures of vinyl chloride in nitrogen or air in the range of 5 to 1000 ppm can be repeated to a coefficient of variation of less than 2%.
Tests carried out under laboratory conditions using standard 20- and 50-ppm vinyl chloride mixtures and the sampling techniques of Methods S-1 and S-2 indicate an expected vinyl chloride recovery of between 90 and 99% from Tedlar bags.
Certain volatile hydrocarbons, halogenated hydrocarbons and other organic compounds have elution characteristics similar to vinyl chloride and also give flame ionization detector response. These compounds can cause interferences in the analysis for vinyl chloride. Among the possible interferences, acetaldehyde is the compound most likely to be found in gaseous streams from vinyl chloride sources. In most sources there should not be any interference and the chromatographic separation column specified in this method can be used as described.
If there is reason to believe that another compound is present in the sample and unresolved from vinyl chloride, a secondary column, 2.0 m x 3.2 mm stainless steel packed with 20% SF-96 on Chromosorb P AW 60/80 mesh, may be connected in series with the Chromosorb 102 column. If resolution of the vinyl chloride peak remains unsatisfactory the vinyl chloride peak should be confirmed by mass spectroscopy or some other absolute analytical technique.
A-1.5.1 Sample Recovery And Analysis (Figure A-1-1)
Figure A-1-1: Sample Recovery and Analysis Train
A-18.104.22.168 Gas chromatograph
A gas chromatograph equipped with an oven, having isothermal temperature control of ± l°C, flame ionization detector, potentiometric strip chart recorder, automatic integrator and a heated, temperature-controlled, gas sampling valve fitted with a sampling loop of between 1.0 and 5.0 ml shall be used to analyze the gaseous samples.
A-22.214.171.124 Chromatographic column
The separation column shall be of stainless steel, 2.5 m × 3.2 mm OD (outside diameter) packed with 80/100 mesh Chromosorb 102. The column must be conditioned before initial use at 200°C for 24 hours with about 10 ml/min flow of zero nitrogen.
A-126.96.36.199 Gas controls
Gases used by the gas chromatograph (carrier and fuel supplies) shall be reproducibly flow-adjustable by either pressure or flow regulation and monitored by rotameters or other flow measuring devices.
A manometer (range -200 to +200 mm Hg) accurate to at least 5 mm Hg, is required to monitor the pressure in the sampling loop during sample injection.
A leak-free pump with a minimum capacity of 200 ml/min is required to withdraw the sample from the sample bag.
A-188.8.131.52 Rotameter with Flow-Control Valve
A rotameter with a flow-control valve capable of measuring flows in the range of 0 to 1.5 litres/min is required.
A barometer accurate to 5 mm Hg is required to measure the atmospheric pressure.
A-184.108.40.206 Nitrogen gas
The carrier gas shall be nitrogen, zero grade.
A-220.127.116.11 Hydrogen gas.
The detector hydrogen gas shall be zero grade.
The detector air supply shall be zero grade.
A-18.104.22.168 Standard vinyl chloride cylinders.
Standard commercial gas mixtures in cylinders shall be used. Recommended concentrations are 10, 50 and 1000 ppm vinyl chloride in UHP nitrogen. The 1000-ppm standard mixture is required when reactor opening samples are to be analyzed. Cylinder concentrations are to be certified by analysis traceable to the National Bureau of Standards (NBS).
A-1.7.1 Sample Recovery (Figure A-1-1).
Using a new piece of Teflon tubing, connect the bag to the gas chromatograph sample valve. Plumb the equipment as in Figure A-1-1 so the sample gas passes from the sample valve to the pump, followed by a 0-1500 ml/min rotameter with flow-control valve, and then outside through an exhaust vent or to a charcoal tube.
Set the column temperature to 150°C, the detector temperature to 275°C and the sample loop temperature to 90°C. When optimal hydrogen and air flow rates have been determined, maintain these flow rates during all chromatographic operations. Using zero nitrogen as the carrier gas, establish a flow rate of approximately 30 ml/min, which should produce the required chromatographic separations. Observe the base line periodically and determine that the noise level has stabilized and that base line drift has ceased.
Since gases are compressible, all analyses using a gas sampling valve must be done at a known or constant pressure. The easiest approach is to analyze at atmospheric pressure by purging the sample line and sample loop, then shutting the sample gas flow and allowing sufficient time for the pressure in the valve to equilibrate at atmospheric pressure before injecting. A low pressure manometer on the sample inlet line of the gas sampling valve should be used to establish the stabilization time required after the flow through the valve is stopped. Injection is done when the pressure has stabilized.
To analyze the gas sample contained in a bag, connect the bag to the inlet of the gas sampling valve with a new piece of Teflon tubing as shown in Figure A-1-1. Rotate the sample valve to withdraw gas from the bag through the loop, the pump, the rotameter with the flow-control valve and out to exhaust or through a charcoal tube.
When sufficient sample has been withdrawn to completely purge the sample loop, interrupt the flow at the pump and allow the pressure in the loop to stabilize to atmospheric pressure. Rotate the sample valve to inject the sample.
Record the injection time (the position of the pen on the chart at the time of sample injection), the sample number, the sample loop temperature, the column temperature, carrier gas flow rate, chart speed and the amplifier gain and the attenuator settings. Also record the barometric pressure. From the recorder chart, select the peak having a retention time corresponding to vinyl chloride. Measure the peak area, Am, using the automatic integrator. Record Am and the retention time. Repeat the injection at least twice or until two consecutive vinyl chloride peaks do not vary in area by more than 5%. The average value for these two areas will be used to compute the vinyl chloride concentration in the sample.
A-1.8.1 Calibration of the Gas Chromatograph
The gas chromatograph should be calibrated using chromatographic conditions identical to those in Section A-1.7.2. Fill the 12-litre Tedlar bags with the calibration gas mixtures and analyze the calibration gases as described in section A-1.7.2. Ensure that the bags have been well purged. Flush the gas sampling loop with zero nitrogen, equilibrate and then inject a sample of the zero nitrogen. Record the sample loop temperature, the column temperature, the carrier gas flow rate, the chart speed and the amplifier gain and attenuator settings. Record any peaks or detector responses that occur in the absence of vinyl chloride. Maintaining the same instrumental conditions and with the equipment plumbing arranged identically to Figure A-1-1 and Section A-1.7.2, analyze each of the calibration gas mixtures. Select the peak that corresponds to vinyl chloride and record the retention time, the concentrations of vinyl chloride injected, the attenuator and amplifier gain settings, chart speed, peak area, sample loop temperature, column temperature, carrier gas flow rate and sample loop volume. Record the barometric pressure in the laboratory.
Calculate Ac, the peak area measured by the integrator multiplied by the amplifier gain setting. Repeat this operation until two consecutive injections produce integrated area values for the vinyl chloride peak that are within 5%. Plot the peak areas against the concentation of vinyl chloride in the calibration mixtures on linear graph paper. Draw a straight line through the points. Calibrate daily, or before and after each set of bag samples, whichever is more frequent.
A-1.9.1 Sample Peak Area Determination.
Determine the sample peak area as follows:
- Ac = the sample peak area
- Am = the measured peak area
- Af = the amplifier gain factor
A-1.9.2 Vinyl Chloride Concentrations.
From the calibration curve described in Section A-1.8.1 select the vinyl chloride concentration, Cc, that corresponds to the sample peak area, Ac. Calculate Cb as follows:
- Cb = the concentration of vinyl chloride in the bag sample, ppm
- Cc = the concentration of vinyl chloride indicated by gas chromatograph, ppm
- Pr = the reference pressure, the laboratory pressure recorded during calibration, mm Hg
- Ti = the sample loop temperature at the time of analysis, °K
- Pi = the laboratory pressure at time of analysis, mm Hg
- Tr = the reference temperature, the sample loop temperature recorded during calibration, °K
A-1.9.3 Analysis Report.
For each sample analyzed record the chromatograph operating conditions, calculated concentrations and other pertinent data on Figure A-1-2. Also use Figure A-1-2 to report analysis of calibration mixtures.
Figure A-1-2: Sample Analysis Report
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