Reference methods: releases of vinyl chloride from plants, chapter 5


Part 2: Analysis

A-2.1 Principles and Application

Method A-2 relates to the vapour equilibrium established between VC, PVC resin, water, and air in a closed system. Residual VC in a PVC resin will equilibrate in a closed vessel rapidly, as long as the temperature of the PVC resin is maintained above the glass transition temperature of that specific resin.

This procedure is suitable for determining the residual VCM content of PVC resins, wet cake, slurry and latex samples.

All samples shall be analyzed within 24 hours of collection.

A-2.2 Range and Sensitivity

(See Section A-1.2)

A-2.3 Apparatus

A-2.3.1 Sample Vials

Crimp top glass vials of known volume (e.g. 22 to 23 mL) with Teflon®-coated seals are required.

A-2.3.2 Vial Sealer

A vial sealer for capping of sample vials is required.

A-2.3.3 Analytical Balance

An analytical balance with an accuracy of ±1 mg for sample weight determination is required.

A-2.3.4 Syringe

A 100 µL syringe is required to inject a small amount of distilled or deionized water into the sample vials.

A-2.3.5 Pliers

Hand pliers, such as the DEKAPITatorTM, are required to open sample vials after headspace analysis.

A-2.3.6 Headspace Analyzer

A headspace analyzer interfaced to a GC shall be used to analyze the resin sample for residual VC. The GC shall be equipped with at least the following features: FID or another detector that is at least as suitable for the analysis of VC as an FID, area integrator, isothermal detector and injector temperature controls, and a programmable oven with an accuracy of ±0.5°C. The headspace analyzers shall be equipped with at least the following features: an automatic head space sampling and injection system capable of analyzing a constant amount of headspace gas from a sealed vial; a thermostat equipped sampling turntable capable of maintaining the sample vials at 90°C ±0.5°C; and pressure regulators that are equipped with gauges and that control the flow of carrier and detector gas.

A-2.3.7 Chromatographic Column

(See A-1.4.2.)

A-2.3.8 Gases

(See A-1.5.1.)

A-2.3.9 Standard Vinyl Chloride Cylinders

(See A-1.5.2.)

A-2.4 Procedures

A minimum of two samples shall be run consecutively. The two highest headspace concentrations of VC shall be used for determining the residual VC concentration in each sample, as long as the difference between these two values is within 5% of the mean or within 1 ppm, whichever is greater.

A-2.4.1 Suspension, Bulk, and Dispersion Resins (Dry)

The weight of the resin shall be a minimum of 0.1 g. An exact weight shall be obtained (±0.001 g) for each sample. Weigh the sample into a tared sample vial. Obtain the accurate sample weight and immediately seal the vial. Record this value using Form A-2.4 or another format of your choice, as this value is required for calculation of the residual VC concentration. For resin samples with a water content < 0.3% by weight, after sealing and weighing the vial, inject 100 µL of distilled or deionized water into the vial, using a 100-µL syringe. Place the sample vial in the headspace analyzer and condition for one hour at 90°C ±1°C.

A-2.4.2 Suspension and Dispersion Homopolymer and Copolymer Slurries

Slurry samples of homopolymer suspension resins shall be suction filtered through a büchner funnel. The filtering process shall be continued only if a steady stream of water is exiting from the funnel. Do not filter beyond this point. The wet cake is then transferred immediately into a plastic bag and twisted shut. Three sample aliquots are to be taken, using a disposable syringe with the tip removed, by inserting the syringe into the resin and packing to a given calibration mark to obtain a wet cake sample weight between 0.2 and 5.0 g. This procedure minimizes contact with air. Transfer the sample aliquot to a tared empty vial. Obtain the exact sample wet weight and immediately seal the vial. Record this value in Form A-2.4. The sample is to be placed in the headspace analyzer and conditioned for a minimum of 1 hour but not to exceed 5 hours at 90°C ±1°C.

Slurry samples of homopolymer dispersion resins or copolymer resins shall not be filtered. The sample shall be thoroughly mixed for a minimum of ten seconds. Using a tared vial add 0.25 to 0.35 g of the sample immediately after mixing. Obtain the exact sample weight and seal the vial as soon as possible. Record this value in Form A-2.4. The sample weight shall not exceed 0.50 g. Condition the vial in the head space analyzer for a minimum period of one hour not to exceed 5 hours at a temperature of 90°C , ±1°C. Determine the dry weight of the slurry samples after the samples have been analyzed on the head space analyzer. After analysis, remove the caps and place the vials in a ventilated oven maintained at a temperature between 100°C and 105°C for 3 hours. The samples shall be dried to constant weight. Reweigh the samples at 1-hour intervals until there is no change in weight. Obtain the sample weight on a dry basis by subtracting the initial weight of the tared empty vial.

A-2.4.3 Gas Chromatograph

Optimize carrier flow according to column type, internal diameter and column length, and record the flow rate. Optimize detector flow rates to yield most sensitive response (without extinguishing the flame in the case of the FID). Check flows with a flow monitoring device and record the flow rate using Form A-2.2 or another format of your choice.

The temperatures must be as follows:

  • GC oven: the temperature must achieve optimal chromatographic resolution of the VC peak, dependent upon the column used.
  • Dosing line: the temperature must be maintained at least 10-20°C above the GCoven temperature.
  • Injection block: the temperature must be maintained at least 10°C above the dosing line temperature.
  • Sample turntable: the temperature must be maintained at 90°C ±0.5°C.
  • Detector: the temperature must be maintained at 250-275°C for the FID.

If the sample being tested contains a substance with a boiling point at or higher than the maximum operating GC oven temperature, this can interfere with the VCpeak during analysis.

In cases of interference, adjust the analysis time to eliminate the interference.

A-2.4.4 Headspace Analyzer with Sampling Loop

Pressurize the sample vial and then purge the sampling loop with the headspace volume of the vial. The analyzer is an automated sampler for the headspace vials. The headspace vials contain the sample and headspace volume. Set flow control and purging time to allow for the flushing of the sampling loop with a volume equal to at least three times the sampling loop volume. Prior to injection of the sample into the analyzer, allow the sample to stabilize using the parameters specified below. It is essential that these parameters remain constant for the analysis of both the sample and the calibration standards. Set the headspace analyzer conditions according to the recommendations of the manufacturer of the headspace analyzer. The GC conditions, listed in A-2.4.3, and headspace analyzer conditions (listed below) shall be the same for both standard and sample analyses.

The headspace analyzer conditions for each parameter are given below:

  • Vial pressurization: 10-15 psi
  • Pressurization time: 0.5 min
  • Flow control: 5-10 cm3/min
  • Loop fill time: 0.3-0.5 min
  • Loop stabilization time: 0.2 min
  • Sampling loop injection time: 0.5-1.0 min
  • Sample turntable temperature: 90°C ±0.5°C

A-2.4.5 Headspace Analyzer with Direct Injection Capability

The analyzer conditions are given below:

  • Dosing time: 2 sec
  • Analysis time: Dependent upon the type of resin to be analyzed and analysis conditions
  • Flushing time: 0.2 min
  • Stabilization time: 0.2 min
  • Sample turntable temperature: 90°C ±0.5°C

A-2.4.6 Preparation of Standards

Prepare calibration standards by filling the vials with the VC/nitrogen gas cylinder standard mixtures of known concentration, rapidly seating the septum and sealing with an aluminum cap. Use a stainless steel tubing line (" to " outside diameter) from the cylinder to the vial. The stainless steel line shall be purged in a fume hood for a minimum of two minutes before filling the vials. After purging, set the flow rate of the calibration gas to 500-1000 mL/min. Hold the vial in the upright position; inject 100 µL distilled or deionized water into the vial. Place the end of the stainless steel line into the vial near the bottom with the septum and cap seated on top, maintaining only a narrow opening for insertion of the stainless steel line. Gradually raise the stainless steel line and, after one minute, remove the line and immediately seal to minimize mixing air with the sample.

Alternatively, the vial may be filled in the inverted position. Pre-purge the stainless steel line and, after one minute of purging remove the stainless steel line gradually. Immediately, seal the vial to minimize mixing air with the standard. After sealing, inject 100 µL of deionized water into the vial.

A-2.4.7 Calibration

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 analysis shall fall within 5% of the mean. If not, the calibration shall be repeated. When the required calibration range exceeds three orders of magnitude in concentration of standard gas mixtures then a four-point calibration curve is required as a minimum. The calibration curve is used to determine each sample's 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 information set out at Form A-2.2. The standard VC calibration curve or the average response factor shall be re-established weekly.

The established calibration shall be verified 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. If the calculated concentration falls outside of this range, then the tester shall take measures to correct the problem. Those measures shall include:

  • diagnostics to identify and correct any chromatographic problems followed by re-verifying the calibration curve;
  • changing the column;
  • using new calibration standards;
  • cleaning the detector; or
  • re-calibration.

The tester shall record every measure taken to correct the problem.

A-2.4.8 Sample Preparation

Samples, including calibration standards, shall be processed under identical analytical conditions. Record the injection time, sample number and any GC operating conditions which differ from the conditions used for the calibration. You may use Form A-2.4 or another format of your choice to do so. Program the headspace analyzer according to the manufacturer's instructions.

A-2.4.9 Calculations

Determine the concentration of VC in the headspace (Cc) by using the calibration curve or the average response factor as mentioned in A-2.4.7. Determine the average response factor as follows:

Average Response Factor

Equation A-2.1

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 in the Headspace (Cc)

Equation A-2.2
Click to enlarge

where:

Ac = sample peak area

Rf = average response factor, area counts/ppm

Residual Vinyl Chloride Concentration

Calculate Crvc, as follows:

Equation A-2.3
Equation A-2.4

Click to enlarge

Crvc = concentration of VC in the sample, ppm by weight, dry basis

Cc = concentration of VC in headspace, ppm by weight, dry basis

Pa = laboratory atmospheric pressure, mmHg

Tl = laboratory temperature, °K

Mv = molecular weight of VC (62.5), g/mole

TS = total solids expressed as a decimal fraction (dry weight / wet weight)

mw = wet sample weight, g

R = gas constant (6.236 x 104mL·mmHg·°K--1·mol--1)

Kp = Henry's law constant for VCM in PVC at 90°C, 6.52 x 10--6
g.g-1mmHg-1

Kw = Henry's law constant for VCM in water at 90°C, 7 x 10--7
g.g-1mmHg-1

T2 = equilibration temperature, °K

Vg = volume of vapour phase (vial volume less sample volume), mL

Vv = vial volume, cm3

1.36 = density of PVC at 90°C, g/cm3

0.9653 = density of water at 90°C, g/cm3

For samples with water volumes of less than 3% of the total headspace volume, calculate Crvc as follows: where:

Equation A-2.5
Equation A-2.6

Click to enlarge

where:

Crvc = concentration of VC in the sample, ppm by weight, dry basis

Cc = concentration of VC in headspace, ppm by weight, dry basis

Pa = laboratory atmospheric pressure, mmHg

Tl = ambient laboratory temperature, °K

Mv = molecular weight of VC (62.5), g/mole

Vg = volume of vapour phase (vial volume less sample volume), mL

md = dry sample weight; g

R = gas constant (6.236 x 104mL·mmHg·°K--1·mol--1)

Kp = Henry's law constant for VCM in PVC at 90°C, 6.52 x 10--6
g.g-1.mmHg-1

T2 = equilibration temperature of vials, °K

Vv = vial volume, cm3

1.4 = density of PVC at 90°C, g/cm3

A-2.4.10 Analysis Report

For each sample analyzed, report:

  • the instrumental operating conditions (Form A-2.1);
  • the calibration data (Form A-2.2);
  • the analysis data of the verification standard (Form A-2.3); and
  • the calculated sample concentrations (Form A-2.4).

Form A-2.1 Headspace analyzer and gas chromatograph operating conditions

Date:

____________________________

Instrument ID:

____________________________


Gas Chromatograph

Model:

____________________________

Serial Number:

____________________________


Headspace Analyzer

Model:

____________________________

Serial Number:

____________________________

Column Specifications: (i.e. type, length, inside diameter, film thickness)

____________________________


Temperatures:

Gas Type and Flow(s):

____________________________

GCOven:

____________________________

Carrier Gas:

____________________________

Injection Block:

____________________________

Detector Makeup Gas (if applicable):

____________________________

Sampling Loop:

____________________________

Other Detector Gas(es):

____________________________

Detector:

____________________________

Cycle Times:

____________________________

Dosing Line:

____________________________

Dosing Time:

____________________________

Sample Turntable:

____________________________

Flushing Time:

____________________________

Laboratory Temperature / Pressure:

____________________________

Analysis Time:

____________________________

Stabilization Time:

____________________________

Analyzed by:

____________________________

Street address of site where sample was analyzed:

____________________________

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

____________________________



Form A-2.2: Calibration report

Date analyzed:

____________________________

Time of Analysis:

____________________________

Sample Number:

____________________________

Gas Composition:

____________________________

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


Analyzed by:


____________________________

Street address of site where sample was analyzed:

____________________________

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

____________________________



Form A-2.3: 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-2.4: Sample analysis report

Date analyzed:

____________________________

Time of Analysis:

____________________________

Sample Number:

____________________________

Standard Analysis
  Vial 1 Vial 2
Vial Weight (g):    
Sample Weight (wet, g):    
Sample Weight (dry, g):    
Vinyl Chloride in Headspace (Cc, ppm):    
Calculated Residual Vinyl Chloride (Crvc)
(Equation A-2.2 and A-2.3):
   


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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