Reference methods: releases of vinyl chloride from plants, chapter 4


Part 2: Analysis

Method A-1: Analysis of vinyl chloride in gaseous samples

A-1.1 Principles and Application

A sample of gaseous effluent containing VC taken in a sampling bag is analyzed for VC by gas chromatography using a flame ionization detector (FID), photoionization detector (PID), or Hall electro-conductivity detector (HED) capable of heating, sampling, and analyzing the gas sample. This method is used to measure the concentration of VC in gaseous samples of releases to the atmosphere from VC and PVC plants.

A-1.2 Range and Sensitivity

The lower detectable limit will vary according to the chromatograph used and the operating conditions. The chromatographic system shall demonstrate a lower detectable limit of VC at a concentration of 20% or less of the regulatory limit. The detection limit is defined as the minimal concentration of VC which produces a signal to noise ratio of at least three to one.

A-1.3 Interferences

Certain volatile hydrocarbons, halogenated hydrocarbons, and other organic compounds have elution characteristics similar to those of VC and may also give detector response. Among the possible interferences, acetylaldehyde is the compound most likely to be found in gaseous streams from VC sources. These compounds can cause interferences in the analysis for VC. If there is reason to believe that another compound is present in the sample, which is unresolved from VC, then the VC peak shall be confirmed using an alternative column or by a more specific analytical technique, such as mass spectrometry.

A-1.4 Apparatus

A-1.4.1 Gas Chromatograph (GC)

A GC shall be equipped with an oven having isothermal temperature control of ±1°C and an FID or other detector demonstrating equal or better sensitivity. In support of the GC, a peak area integrator and a temperature controlled gas sampling valve fitted with a sampling loop of known volume (typically ranging from 0.1 to 5.0 mL) shall be used to analyze the gaseous samples.

A-1.4.2 Chromatographic Column

The separation column shall be an open tubular capillary column, 25 m x 0.53 mm internal diameter, and amenable to volatile organic analysis (e.g. PoraPLOT Q or Al2O3 / KCl) meeting the following criteria:

  • provide adequate resolution of the VC peak from neighbouring peaks. Adequate resolution is defined as when the overlap of any neighbouring peak does not exceed 25% of the VC peak;
  • provide reproducibility in the retention time of the VC peak not to exceed a 3% variation from the retention time of the verification standard.

A-1.4.3 Gas Controls

Gases used by the GC (in the carrier, makeup, and detector components of the GC) shall be reproducibly flow-adjustable by either pressure or flow regulation and monitored by a rotameter or another flow-measuring device.

A-1.4.4 Pressure Gauge

A gauge (range +200 to -200 mmHg), a pressure transducer, or a downstream bubbler is required to monitor the pressure in the sampling loop during sample injection. The pressure gauge shall have a measurement accuracy of within ±1% of full scale.

A-1.4.5 Pump or Vacuum

A leak-free pump with a minimum capacity of 200 mL/min or a bench vacuum is required to withdraw the sample from the sampling bag.

A-1.4.6 Flow Monitoring Device

A rotameter with a flow-control valve (flow range 0-1.5 L/min) or other flow monitoring device (e.g. downstream bubbler) is required to monitor flow through the sampling loop. The rotameter shall have a measurement accuracy of within ±5% of full scale.

A-1.4.7 Barometer

A barometer accurate to 2.5 mmHg is required to measure the atmospheric pressure.

A-1.4.8 Thermometer

A thermometer ranging from 0°C to 100°C, accurate to within ±1°C, is required to measure the laboratory ambient temperature.

A-1.5 Reagents

A-1.5.1 Gases

All gases (e.g. helium, nitrogen, hydrogen, air, etc.) shall be zero grade as a minimum requirement.

A-1.5.2 Standard Vinyl Chloride Cylinders

Cylinders of known concentrations of VC in nitrogen gas shall be used. The concentration requirements of VC in nitrogen will vary in accordance with the sampling site and sample loading and shall bracket the expected sample concentration range.

A-1.6 Procedures

A-1.6.1 Calibration of the Gas Chromatograph

The GC shall be calibrated using chromatographic conditions identical to those used in sample analysis, the procedure for which is set out in A-1.6.2. Fill a sampling bag with the calibration gas mixture, and analyze each calibration gas mixture as described in A-1.6.2. Verify that all sampling bags have been purged by flushing with nitrogen or air at least two times. After flushing the gas sampling loop with nitrogen or air, inject a sample of the nitrogen or air blank. Record any peaks or detector responses that occur in the absence of VC.

Maintaining the same instrumental conditions and with the equipment plumbed as mentioned in A-1.6.2, analyze in duplicate each of the calibration gas mixtures to construct a calibration curve with a minimum of three standard gas mixtures bracketing the expected sample concentration range.

For sample concentrations near or below the detection limit, the lowest concentration of calibration gas used shall be at least 10 times the detection limit. The response of the VC peaks for each duplicate analyses shall fall within 5% of the mean or the calibration shall be repeated. When the required calibration range exceeds three orders of magnitude in concentration, then a four-point calibration curve is required as a minimum. The calibration curve is used to determine each sample concentration. An average response factor may be used for sample quantification, as long as the relative standard deviation of the response factors over the working range is ≤5%.

Identify the VC peak and record the retention time, the concentration of VC injected, peak area, sampling loop temperature, carrier gas, sampling loop volume and the temperature and barometric pressure in the laboratory. Record the analytical parameters listed at Form A-1.1.

The calibration shall be confirmed by analyzing a verification standard with a concentration mid-range to the calibration curve once before and after each set of samples within a 12-hour period. The calculated concentration of the verification standard shall lie within 10% of its actual value.

The calibration of the GC, and calculation of the average response factor shall be carried out weekly when VC samples are being analyzed.

A-1.6.2 Analysis

All samples shall be analyzed within 24 hours of collection.

Set the column temperature to achieve separation of sample analytes (as defined in A-1.4.2). Also, set the temperature of the sampling loop, (on the basis that monitoring the temperature of the sampling valve accurately reflects the temperature of the sampling loop) at a constant temperature at least 10°C above ambient temperature (e.g. to minimize condensation and carry over, a temperature of 90- 95°C shall be used). The temperature of the sampling loop shall be consistent and is validated through the calibration process. The temperature shall remain within that range. The temperature of the detector is set for optimal sensitivity, as are detector flow rates (makeup gas, hydrogen, and air if required). Column flow rate (typical flow for a column 25 m x 0.53 mm internal diameter is between 5 and 10 mL/min) is optimized to produce the required chromatographic separation. Observe the baseline periodically and determine that the noise level has stabilized and that baseline drift has ceased.

Since gases are compressible, all analyses using a gas sampling valve shall be performed at a known and constant pressure. One approach is to analyze at atmospheric pressure by purging the sample line and sampling loop, then shutting the sample gas flow and allowing sufficient time for the pressure in the valve to equilibrate at atmospheric pressure before injection of the sample. A low pressure gauge, downstream bubbler, or pressure transducer is used to monitor the sampling loop pressure at time of injection of the sample. Injection of the sample is done once the pressure has stabilized.

To analyze the gas sample contained in a sampling bag, connect the bag to the inlet of the sampling valve on the GC with a clean piece of Teflon® tubing, or stainless steel tubing. Rotate the sampling valve to withdraw gas from the bag through the loop by vacuum or by pushing the sample through and out to exhaust or through a charcoal tube.

When sufficient sample has been withdrawn to completely purge the sampling loop (the volume of a minimum of three sampling loop volumes), interrupt the flow and allow the pressure in the loop to stabilize to atmospheric pressure. Rotate the sampling valve on the GC to inject the sample.

Record all information set out at Form A-1.4, and any other GC conditions which differ from those of the established calibration.

From the chromatogram, select the peak having a retention time corresponding to VC and record the peak area Ac as well as the retention time. Repeat the injection at least twice, until two consecutive VC peaks do not vary by more than 5% of the mean of the two peaks or 1 ppm, whichever is greater. Use the mean value for these two areas to compute the VC concentration in the sample.

A blank sample, consisting of a sampling bag filled with nitrogen or air, shall be run with each set of samples or every 12-hour period to identify any possible interferences or sample carry-over.

A-1.6.3 Calculations

From the calibration curve or the average response factor (see A-1.6.1) determine the concentration of VC in the sample (Cc). Determine the average response factor as follows:

Average Response Factor

Equation A-1.1

Click to enlarge

where:

Rf = average response factor, area counts/ppm

Ai = standard peak area

Ci = concentration of standard, ppm

n = number of calibration points (n ≥3)

Concentration of Vinyl Chloride as Indicated by Gas Chromatography

Equation A-1.2

Click to enlarge

where:

Ac = sample peak area

Rf = average response factor, area counts/ppm

Vinyl Chloride Concentration

Equation A-1.3

Click to enlarge

where:

Cb = the concentration of VC in the bag sample, ppm

Cc = the concentration of VC indicated by gas chromatography, ppm

Pr = the reference pressure, the laboratory pressure recorded during calibration, mmHg

Ti = the sampling loop temperature at the time of analysis, °K

Pi = the laboratory pressure at the time of analysis, mmHg

Tr = the reference sampling loop temperature recorded during calibration, °K

A-1.6.4 Analysis Report

For each sample analyzed, report the information listed below:

  • the instrumental operating conditions (Form A-1.1);
  • the calibration data (Form A-1.2);
  • the analysis data of the verification standard (Form A-1.3); and
  • the calculated sample concentrations (Form A-1.4).

Form A-1.1: Gas chromatograph operating conditions

Date:

____________________________

Instrument identification (Model, Serial Number):

____________________________

Oven Temperature (Isothermal) / Profile of Programmed Temperature:

____________________________

Detector Type / Operating Temperature:

____________________________

Sampling Look Temperatrue and Sample Loop Size (mL):

____________________________

Carrier Gas Type:

____________________________

Detector Operating Parameters (e.g. Gas(es), Gas Flows, Detector Temperature):

____________________________

Laboratory Ambient Temperature /Laboratory Atmospheric Pressure:

____________________________

Column Specification (e.g. Type, Length, Inside Diameter, Film Thickness):

____________________________

Analyzed by:

____________________________

Street address of site where sample was analyzed:

____________________________

Plant name and street address where sample was collected:

____________________________



Form A-1.2: Calibration report

Date analyzed:

____________________________

Time of Analysis:

____________________________

Sample Number:

____________________________

Standard Analysis
 Standards Injection Retention Time
(min)
Response (A i)
(area counts)
Concentration
(Ci) (ppm)
Injections 1 & 2 are within
5% of the mean
(Y or N)
Standard 1 Injection 1        
Injection 2
Standard 2 Injection 1        
Injection 2
Standard 3 Injection 1        
Injection 2
Standard 4 Injection 1        
Injection 2


Comments:



____________________________

Analyzed by:

____________________________

Street address of site where sample was analyzed:

____________________________

Plant name and street address of site where sample was collected:

____________________________



Form A-1.3: Verification standard analysis report

Date Analyzed:

____________________________

Time of Analysis:

____________________________

Standard Gas Composition:

____________________________

Standard Analysis
Verification Standard Analysis Retention Time (min) Response (Ac) (area counts) Concentration (ppm) Calculated value is within 10% of the actual value (Y or N)
Actual Value (Ci) Calculated Value(Cc)
Before Sample(s)        
After Sample(s)        


Comments:



____________________________

Analyzed by:

____________________________

Street address of site where sample was analyzed:

____________________________

Plant name and street address of site where sample was collected:

____________________________



Form A-1.4 Sample analysis report

Date Analyzed:

____________________________

Time of Analysis:

____________________________

Sample Number:

____________________________

Sample Analysis
Sample Retention Time
(min)
Response (Ac) (area counts) Concentration (Cc) (ppm) Injections 1 & 2 are within
5 % of the mean
(Y or N)
Injection 1        
Injection 2        
Average indicated concentration
(Cc) (ppm):
       
Average sample concentration
(Cb) (ppm):
       


Comments:



____________________________

Analyzed by:

____________________________

Street address of site where sample was analyzed:

____________________________

Plant name and street address of site where sample was collected:

____________________________



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