Reference method for measuring emissions of vinyl chloride from manufacturing: part II A-2

Part II - Analysis: Method A-2

Analysis for Residual Vinyl Chloride in Polyvinyl Chloride Resins and Resin Slurries

A-2.1 Principle and Applicability

The basis for this method relates to the vapour equilibrium established between vinyl chloride, polyvinyl chloride resin, water and air in a closed system. It has been demonstrated that residual vinyl chloride monomer in a polyvinyl chloride resin will equilibrate in a closed vessel quite rapidly, provided that the temperature of the polyvinyl chloride resin is maintained above the glass transition temperature of that specific resin.

This procedure is suitable for determining the residual vinyl chloride monomer content of polyvinyl chloride resins, wet cake, slurry and latex samples. If there is reason to believe that some other hydrocarbon with an identical retention time is present in the sample, then supplemental confirmation of the vinyl chloride peak through an absolute analytical technique, such as mass spectroscopy, should be performed.

A-2.2 Sensitivity

The lower limit of detection of the head space method for vinyl chloride may vary according to the chromatographic conditions and sample weight. Using the method described, residual vinyl chloride monomer may be detected in resins at concentrations of 0.5 ppm by weight dry resin.

A-2.3 Precision and Reproducibility

Seven laboratories have participated in a round robin interlaboratory test of three resin samples having residual vinyl chloride concentrations of 1.6 ppm, 2.1 ppm and 62.6 ppm The analytical data resulting from this study indicate that the coefficient of variation of the head space technique lies in the range of 2 to 5%.

A-2.4 Safety

Do not release vinyl chloride to the laboratory atmosphere during preparation of standards. Venting or purging with vinyl chloride/air mixtures must be held to a minimum. When venting or purging is required, the vapour must be routed to outside air. Vinyl chloride, even at low ppm levels, must never be vented inside the laboratory. Always handle vinyl chloride or vinyl chloride mixtures under adequate fume hoods. After vials have been analyzed, the pressure within the vial must be vented prior to removal from the instrument turntable. Vials must be vented into an activated charcoal tube using a hypodermic needle or in a fume hood to prevent release of vinyl chloride into the laboratory atmosphere. The charcoal must be replaced before vinyl chloride breakthrough.

A-2.5 Apparatus

A-2.5.1 Sample Recovery.

A- Simple vials.

Sample vials complete with rubber septa and aluminum sealing caps are required to hold the sample for analysis. Use Perkin-Elmer part number 105-0118, or equivalent.

A- Vial Sealer.

A hand crimper, Perkin-Elmer part number 105-0106, or equivalent, is required to seal the sample vials.

A- Analytical balance.

An analytical balance accurate to ±1 mg is required to weigh the sample vials with and without the sample.

A- Syringe, 100 μl.

A 100 μl syringe is required to inject a small amount of water into the sample vials.

A- Pliers for sample opening.

A special hand plier, Perkin-Elmer part number 105-0107, or equivalent, is required for opening safely the sample vials after head space analysis.

A-2.5.2 Analysis.

A- Head space analyzer.

A gas chromatographic head space analyzer, Perkin-Elmer model F-42, part number 105-0006, or equivalent, shall be used to analyze the resin samples for residual vinyl chloride. The head space analyzer shall be equipped, as a minimum, with the following features: single flame ionization detector and amplifier; isothermal detector and injector temperature controls to ± 0.5°C; automatic head space sampling and injection system; thermostatted sampling turntable with circulatory system for thermostatting capable of maintaining the sample bottles at a minimum of 90°C ± 0.50°C; carrier and detector gases pressure regulators with gauges for flow control. Non-essential but highly desirable options are dual FID detectors and backflush system.

A- Chromatographic column.

The separation column shall be of stainless steel, 3.7 m × 3.2 mm OD packed with 0.2% Carbowax 1500 on Carbopak C HT 60/80 mesh. The column must be conditioned before initial use at 125°C for 24 hours with about 10 ml/min flow of zero nitrogen.

A- Integrator or recorder.

A multi-range single pen recorder is required, as a minimum, to record the detector signal and sample identification code. An automatic computing printer integrator, Perkin-Elmer Model Sigma 10, or equivalent, is much more useful and is recommended for data recording.

A-2.6 Reagents

A-2.6.1 Analysis.

A- Nitrogen gas.

The carrier shall be nitrogen, zero grade.

A- Hydrogen gas.

The detector hydrogen gas shall be zero-grade hydrogen.

A- Air.

The detector air supply shall be zero grade.

A-2.6.2 Calibration.

A- Standard vinyl chloride cylinders.

Standard commercial gas mixtures in cylinders shall be used. Recommended concentrations are 50, 500, 2000 and 4000 ppm vinyl chloride in nitrogen. Cylinder concentrations are to be certified by analysis traceable to NBS.

A-2.7 Procedure.

A-2.7.1 Sample Recovery.

It is recommended that two sample vials be prepared for every resin or resin slurry sample being analyzed. The residual vinyl chloride is determined using both vials and the results from measurements are averaged. If the two results differ by more than 10%, the sample should be analyzed again.

A- Suspension, bulk and dispersion resins (dry).

The weight of the resin used must be between 0.1 and 1.0 g. An exact weight must be obtained (±0.001 g) for each sample. The sample is weighed approximately in an aluminum dish and transferred to a tared sample vial. The exact sample and vial weight is then obtained and the vial is immediately sealed. Record this value on the data sheet as it is required for calculation of the residual vinyl chloride monomer. In the case of relatively dry resin samples (water content <0.3% by weight), 100 μl of distilled water must be injected into the vial, after sealing and weighing, using a 100-μl syringe. The sample vial is then placed in the Perkin-Elmer head space analyzer and conditioned for 1 hour at 90°C.

A- Suspension and dispersion homopolymer and copolymer resin slurries.

Slurry samples of homopolymer suspension resins must be filtered using a small Buchner funnel with vacuum to yield wet cake. The filtering process must be continued only as long as a steady stream of water is exiting from the funnel. Excessive filtration time could result in some loss of vinyl chloride. Approximately 0.2 g of sample are added to a tared vial. The exact sample weight is then obtained and the vial is immediately sealed. Record this value on the data sheet. The sample is then placed in the Perkin-Elmer head space analyzer and conditioned for 1 hour at 90°C.

Slurry samples of homopolymer dispersion resins or copolymer resins should not be filtered. The sample must be thoroughly mixed. Using a tared vial add 0.3 g (approximately 8 drops) of slurry using a medicine dropper. This should be done immediately after mixing. Obtain the exact sample weight and seal the vial as soon as possible. Record this value on the data sheet. Total sample weight must not exceed 0.50 g. Condition the vial for 2 hours at 90°C in the analyzer.

The total solids of the slurry samples are determined after the samples have been analyzed on the head space analyzer. After analysis, retain the sample vials and, after venting the pressure, carefully remove the cap and seal using the special pliers, and place the vials in an oven maintained at between 100°C and 105°C for 3 hours. The samples must be dried to a constant weight. Reweigh the samples at 1-hour intervals until there is no change in weight. The sample weight on a dry basis is then obtained by subtracting the initial weight of the tared empty vial.

A-2.7.2 Analysis.

A- Preparation of the gas chromatograph.

Install the chromatographic column and condition overnight at 125°C. Do not connect the exit end of the column to the detector while conditioning.

A- Flow rate adjustments.

Adjust flow rates as follows:

  1. Nitrogen carrier gas. Adjust the regulator on the gas chromatograph to a pressure of at least 3.2 bar. This will prevent double injections due to sample vial blow back.
  2. Burner air supply. Set the regulator on the chromatograph to supply air to the burner at the rate suggested by the manufacturer for optimum detector operation.
  3. Hydrogen supply. Set the regulator on the chromatograph according to the manufacturer's recommendation. Optimize hydrogen flow to yield the most sensitive detector response without extinguishing the flame.

Check the flows with a bubble meter and record them. Note and record the carrier gas pressure.

A- Temperature adjustments.

Set temperatures as follows:

Oven (chromatographic column)
Dosing line
Injection block
Sample turntable, water
90°C, ± 0.5°C

A- Ignition of flame ionization detector.

Ignite the detector according to the manufacturer's instructions.

A- Amplifier balance.

Balance the amplifier according to the manufacturer's instructions.

A- Programming the chromatograph.

Program the chromatograph as follows:

  1. I - Dosing time: the normal setting is 2 seconds.
  2. A - Analysis time: the normal setting is 8 minutes.

Certain types of samples contain materials with high boiling points, which can cause interference with the vinyl chloride peak on subsequent analyses. In these cases the analysis time must be adjusted to eliminate the interference. An automated backflush system can also be used to solve this problem. If the backflush system is used the analysis time setting "A" can be reduced and the flushing time setting "BF" below increased as required.

  1. BF - Flushing time: the normal setting is 0.2 minutes.
  2. S - Stabilization time: the normal setting is 0.2 minutes.
A- Preparation of the sample turntable.

The numbered sample bottles should be placed in the corresponding numbered positions in the turntable. Insert samples in the following order:

Positions 1 and 2
- old 2000 ppm standard for conditioning.
These are necessary only after the analyzer has not been used for 24 hours or longer.
Position 3
- 500 ppm standard, freshly prepared.
Position 4
- 500 ppm standard, freshly prepared.
Position 5
- 2000 ppm standard, freshly prepared.
Position 6
- 4000 ppm standard, freshly prepared.
Position 7
- Sample No. 7 (This is the first sample of the day, but is given as 7 to be consistent with the turntable integrator printout).

After all samples have been positioned, insert the second set of 50, 500, 2000 and 4000 ppm standards. Samples, including standards, must be conditioned in the bath at 90°C for at least 1 hour (not to exceed 5 hours).

A- Start chromatograph program.

When all samples, including standards, have been conditioned at 90°C for 1 hour, start the analysis program according to the manufacturer's instructions. These instructions must be carefully followed when starting and stopping the program to prevent damage to the dosing assembly.

A-2.8 Calibration

Calibration is to be performed each 8-hour period that the instrument is used. Each day, before running samples, the column should be conditioned by running two of the previous day's 2000 ppm standards.

A-2.8.1 Preparation of Standards.

Calibration standards are prepared by filling the vials with the certified vinyl chloride/nitrogen standards, rapidly seating the septum and sealing with the aluminum cap. Use a stainless steel line from the cylinder to the vial. Do not use rubber or Tygon tubing. The sample line from the cylinder must be purged (into the hood) for several minutes before filling the vials. After purging, reduce the flow rate to approximately 500-1000 ml/min. Hold the vial in an inverted position, place the end of the tubing into the vial near the bottom and after 1 minute slowly remove the tubing. Place the septum in the vial as soon as possible to minimize mixing air with the sample. After the standard vials are sealed, inject 100 μl of distilled water.

A-2.8.2 Preparation of Chromatograph Calibration Curve.

Prepare two 50-ppm two 500-ppm two 2000-ppm and two 4000-ppm standard samples. Run the calibration samples in exactly the same manner as regular samples as given in A-2.7.2. Plot As, the integrator area count for each standard sample, against Cc, the concentration of vinyl chloride in each standard sample. Draw a straight line through the points.

A-2.9 Calculations

A-2.9.1 Response Factor.

From the calibration curve described in section A-2.8.2 above, select the value of Cc that corresponds to As for each sample. Compute the response factor, Rf, for each sample, as follows:

Response Factor Equation

A-2.9.2 Residual Vinyl Chloride Monomer Concentration.

Residual Vinyl Chloride Monomer Concentration Equation
  • Crvc = concentration of vinyl chloride in the sample, ppm by weight
  • Pa = laboratory atmosphere pressure, mm Hg
  • Tl = room temperature, °K
  • Mv = molecular weight of vinyl chloride (62.5)
  • Vg = volume of vapour phase (vial volume less sample volume), ml
  • mt = weight of sample, g, dry basis
  • R = gas constant (6.236 x 104)
  • K = Henry's Law constant for vinyl chloride in PVC at 90°C, K = 6.52 x 10-6
  • T2 = equilibration temperature, °K

if the following conditions are met:

  1. T1 = 22°C (295°K)
  2. T2 = 90°C (363°K)
  3. Pa = 750 mm Hg
  4. volume of vapour phase Equation

    • Vv = vial volume, cc (23.5)
    • 1.4 = density of polyvinyl chloride, g/cm3

  5. Sample contains less than 0.5% water. Equation A-2-2 can be simplified as follows:
Residual Vinyl Chloride Monomer Concentration Equation

Note: Equations A-2-2 and A-2-3 should only be used if the total wet sample volume is less than 0.5 ml. Precise use of these equations with wet samples requires a correction term for the water present. This term is negligible if the water volume is of the order of 1% of the total head space volume.

A-2.9.3 Analysis Report.

For each sample analyzed report the chromatograph operating conditions, calculated concentrations and other pertinent data on Figure A-2-1. Also use Figure A-2-1 to report analysis of calibration mixtures.

Figure A-2-1: Residual Vinyl Chloride Analysis Report

Residual Vinyl Chloride Analysis Report
Report a problem or mistake on this page
Please select all that apply:

Thank you for your help!

You will not receive a reply. For enquiries, contact us.

Date modified: