Methods for the determination of vinyl chloride

Transcription

1 Federation of the Employment Accidents Insurance Institutions of Germany (Hauptverband der Berufsgenossenschaften) Centre for Accident Prevention and Occupational Medicine Alte Heerstraße 111, Sankt Augustin Expert Committee Chemistry Carcinogenic substances Order number: ZH 1/120.12E Established methods Issue: October 1992 Methods for the determination of vinyl chloride Methods tested and recommended by the Berufsgenossenschaften for the determination of vinyl chloride in working areas. Continous sampling 1 Process gas chromatography for stationary measurements 2 Instrument equipped with a galvenic measuring cell for stationary measurements Discontinous sampling For the assessment of working areas, both personal or stationary sampling are possible: 1 Sampling with a pump and adsorption on activated carbon, gas chromatography after desorption. Vinyl chloride-1-gc (Issue: December 1983, revised October 1992) 2 Sampling with a pump and adsorption on activated carbon, headspace gas chromatography after desorption. Vinyl chloride-2-hsgc (Issue: October 1992) IUPAC name: CAS No: vinyl chloride AirMonitoringMethods,Vol.4

2 Analytical Methods AirMonitoringMethods,Vol Continuous sampling For monitoring the concentrations in working areas stationary process gas chromatographs or instruments equipped with a galvanic measuring cell may be used. Portable flame ionization detectors (FID) or photoionization detectors (PID) can be used for the detection of leaks in plants, for control measurements during cleaning processes and repair and also for screening tests. 1 Process gas chromatography for stationary measurements Principle: Technical data: Minimum measuring range: 0 5 ml/m 3 (ppm) Quantification limit: Selectivity: A measured air volume is injected into a carrier gas flow and conducted through a chromatography column. In the column vinyl chloride is separated from accompanying substances in the air sample and determined with a flame ionization detector (FID). 0.1 ml/m 3 (ppm) ^= 0.3 mg/m 3 vinyl chloride in air The method is selective if appropriate columns are used. Measuring time for 1 determination: 1 3 minutes (depending on the accompanying substances). Advantages: Working materials: Manufacturers: Indication of local and temporal concentration changes is possible, rapid and direct response. Pneumatic auxiliary energy, air of highest purity or synthetic air, hydrogen of highest purity, carrier gas. e.g. Asea Brown Boveri, Mannheim, Mannesmann Hartman & Braun, Frankfurt, Siemens AG, Karlsruhe.

3 195 AirMonitoringMethods,Vol.4 Vinyl chloride 2 Instrument equipped with a galvanic measuring cell for stationary measurements Principle: Technical data: Minimum measuring range: 0 10 ml/m 3 (ppm) Quantification limit: Selectivity: Transient response: Advantages: Working material: Manufacturer: Chlorine and hydrogen chloride are released from vinyl chloride at temperatures above 800 C. The components are absorbed in an electrolyte solution and determined potentiometrically with halogen-specific electrodes. 0.2 ml/m 3 (ppm) ^= 0.5 mg/m 3 vinyl chloride in air The method is not selective. (Halogen-specific determination, with selective filter, specific for halogenated hydrocarbons). T 90 2 minutes Indication of local and temporal concentration changes is possible, rapid and direct response. Electrolyte solution. e. g. BASF AG, Ludwigshafen.

4 Analytical Methods AirMonitoringMethods,Vol Discontinuous sampling 1 Sampling with a pump and adsorption on activated carbon, gas chromatography after desorption. Principle: Technical data: With a pump a measured air volume is drawn through activated carbon. After desorption with carbon disulfide the adsorbed vinyl chloride is determined by gas chromatography. Quantification limit: Under the given operating conditions the relative quantification limit is 0.2 ml/m 3 (ppm) ^= 0.5 mg/m 3 vinyl chloride. Selectivity: Advantages: Disadvantages: Apparatus: As a result of interfering substances the concentrations determined may be too high. Interference can generally be eliminated by selecting another column. Personal and selective measurements are possible. No indication of peak concentrations, time-consuming. Pump equipped with gas meter or flow meter, activated carbon tubes, gas chromatograph equipped with flame ionization detector (FID).

5 197 AirMonitoringMethods,Vol.4 Vinyl chloride Detailed description of the method Contents 1 Summary 2 Equipment, chemicals and solutions 2.1 Equipment 2.2 Chemicals 2.3 Solutions 3 Sampling and sample preparation 4 Operating conditions for gas chromatography 5 Analytical determination 6 Calculation of the analytical result 6.1 Calibration curve 6.2 Evaluation of the results by the external standard method 7 Reliability of the method 7.1 Accuracy 7.2 Quantification limit 8 Discussion 9 Manufacturers 1 Summary This method permits the determination of the concentration of vinyl chloride in working areas averaged over the sampling time after personal or stationary sampling. With a pump, which is carried by a person or installed in a stationary position, a measured air volume is drawn through a glass tube containing activated carbon. After the adsorbed vinyl chloride has been desorbed with carbon disulfide it is determined by gas chromatography. Under the conditions found in practice, the absolute quantification limit is 1 ng vinyl chloride. The relative quantification limit is 0.2 ml/m 3. This corresponds to 0.5 mg/m 3 vinyl chloride for a 20 L air sample.

6 Analytical Methods AirMonitoringMethods,Vol Equipment, chemicals and solutions 2.1 Equipment For sampling and sample preparation: Pump Adsorption tubes with activated carbon, Type NIOSH, standardised, consisting of two sections each filled with activated carbon weighing about g which are separated by a porous polymeric material. 10 ml Volumetric flasks with ground glass stoppers For analysis: Gas chromatograph with flame ionization detector 2.2 Chemicals Carbon disulfide, analytical grade Vinyl chloride, purity >99% Gases for gas chromatography: Nitrogen, hydrogen, synthetic air 2.3 Solutions Vinyl chloride stock solution: 2.58 mg vinyl chloride dissolved in 10 ml carbon disulfide. 10 ml carbon disulfide in a vial equipped with septum and screw cap are cooled with dry ice. 1 L vinyl chloride is introduced into an evacuated plastic vessel. At 20 C and 1013 hpa 1 ml of this volume is removed with a gastight syringe and injected through the septum into the vial containing the cooled carbon disulfide. Then the vial is shaken thoroughly. Vinyl chloride calibration solutions: From the vinyl chloride stock solution calibration solutions are prepared containing e.g. 1290, 516 and 51.6 µg vinyl chloride in 10 ml carbon disulfide. 3 Sampling and sample preparation An activated carbon tube is opened and connected to the pump. During working hours the pump and tube are carried by a person or used in a stationary position. For two hours air is drawn through the sampling tube at a flow rate of 10 L/h. The loaded activated carbon is transferred to a 10 ml volumetric flask. 10 ml carbon disulfide is added and the solution is allowed to stand with occasional shaking for 30 minutes (sample solution).

7 199 AirMonitoringMethods,Vol.4 Vinyl chloride 4 Operating conditions for gas chromatography The method was characterized under the following experimental conditions: Apparatus: Perkin-Elmer gas chromatograph F 22, equipped with flame ionization detector Column: Material: Length: Glass column 3 m Internal diameter: 2.2 mm Stationary phase: 10 % DC 200 on Chromosorb W/HP µm or 25 m Marlophen glass capillary column Temperatures: Injector block: 200 C Column: Detector: 75 C isothermal 200 C Carrier gas: Nitrogen: 20 ml/min 5 Analytical determination After half an hour 1 µl of the sample solution (cf. Sect. 3) is injected into the injector block of the gas chromatograph. The area or the height of the vinyl chloride peak is determined. 6 Calculation of the analytical result 6.1 Calibration curve Depending on the concentration of the vinyl chloride calibration solution (cf. Sect. 2.3) 1 4 µl is injected into the gas chromatograph. Using the baseline method the peak areas or the peak heights are taken from the chromatogram and plotted against the vinyl chloride weights. 6.2 Evaluation of the results by the external standard method By means of the calibration curve the vinyl chloride weight in the sample solution is determined from the peak areas or the peak heights taking the blank value into consideration.

8 Analytical Methods AirMonitoringMethods,Vol The vinyl chloride concentration in the air sample c w in mg/m 3 is calculated as follows: c w w V For the calculation of the concentration by volume c v in ml/m 3 (ppm) at 20 C and 1013 hpa from c w : c v = 0.38 c w (2) Legend: c w Vinyl chloride concentration by weight in the air sample in mg/m 3 c v Vinyl chloride concentration by volume in the air sample in ml/m 3 w Vinyl chloride weight in the sample solution in µg, taken from the calibration curve and corrected by the blank value V Air sample volume in L (1) 7 Reliability of the method 7.1 Accuracy The relative standard deviation is ± 4%, determined from calibration measurements by loading of activated carbon tubes with vinyl chloride calibration solutions. 7.2 Quantification limit Under the experimental conditions the absolute quantification limit is 1 ng vinyl chloride. The relative quantification limit is 0.2 ml/m 3 (ppm). This corresponds to 0.5 mg/m 3 vinyl chloride for 20 L air sample, 10 ml sample solution and 1 µl injection volume. 8 Discussion The selection of the chromatography column depends on any additional measuring and interfering components.

9 201 AirMonitoringMethods,Vol.4 Vinyl chloride 9 Manufacturers Pump: e.g. Compur Electronic GmbH, München, Du Pont Instruments, Supplier in Germany: DEHA-Haan & Wittmer GmbH, Friolzheim Activated carbon tubes: e. g Drägerwerk AG, Lübeck Gas chromatograph: e.g. Carlo Erba Supplier in Germany: Erba Science, Hofheim/Ts., Bodenseewerk Perkin-Elmer & Co GmbH, Überlingen, Siemens AG, Karlsruhe, Varian GmbH, Darmstadt

10 Analytical Methods AirMonitoringMethods,Vol Sampling with a pump and adsorption on activated carbon, headspace gas chromatography after desorption This method permits the determination of vinyl chloride concentrations in working areas averaged over the sampling time after personal or stationary sampling. Principle: Technical data: With a pump a measured air volume is drawn through activated carbon. The adsorbed vinyl chloride is desorbed with dimethylacetamide/water (3:1) and analysed by headspace gas chromatography (HSGC). Evaluation is carried out according to the internal standard method (diethyl ether) using a flame ionization detector (FID). Quantification limit: relative: 0.03 mg/m 3 vinyl chloride for 7 L air sample. This corresponds to 0.2 µg vinyl chloride per activated carbon tube. Selectivity: Advantages: Disadvantages: Apparatus: As a result of interfering substances the concentrations may be too high. Interference can generally be eliminated by selecting another column. Personal and selective measurements are possible. No indication of peak concentrations, only one measurement possible. Pump equipped with gas meter or flow meter, activated carbon tubes, headspace gas chromatograph equipped with flame ionization detector (FID).

11 203 AirMonitoringMethods,Vol.4 Vinyl chloride Detailed description of the method Contents 1 Equipment, chemicals and solutions 1.1 Equipment 1.2 Chemicals 1.3 Solutions 2 Sampling 3 Analytical determination 3.1 Sample preparation 3.2 Operating conditions for gas chromatography 4 Evaluation 4.1 Calibration Implementation Determination of the amount of vinyl chloride in the calibration gas 4.2 Calculation of the analytical result 5 Reliability of the method 5.1 Accuracy 5.2 Quantification limit 5.3 Selectivity 5.4 Recovery 6 Discussion 7 References 1 Equipment, chemicals and solutions 1.1 Equipment For sampling and sample preparation: Pump with gas meter or flow meter (e. g. Compur 4903 or Du Pont S 30) Gas collection vessel (gas sampling tube containing some pieces of polytetrafluoroethylene (PTFE) tubing) about 300 ml with PTFE screw taps and side ports Manometer 20 ml Injection bottles (effective volume about 23 ml) with PTFE coated septa and aluminium caps Adsorption tubes with activated carbon, (standardized, consisting of two sections containing about 100 and 50 mg activated carbon which are separated by a porous polymeric material) Caps for the opened activated carbon tubes

12 Analytical Methods AirMonitoringMethods,Vol For analysis: Headspace gas chromatograph with flame ionization detector and sample thermostat with constant mode setting, autosampling from the headspace and back flush (e. g. Sigma 2000 with HS 100 from Perkin Elmer) Continuous-line recorder and/or laboratory data system (e.g A from Hewlett- Packard) Microliter syringes, gastight (e.g. Hamilton 1001 LTN, 1750 N and 1725 N) 1.2 Chemicals Vinyl chloride, purity > 99,95% N,N-Dimethylacetamide, analytical grade Diethyl ether, analytical grade (internal standard) De-ionized water Gases for gas chromatography: Nitrogen, hydrogen, synthetic air 1.3 Solutions Desorption solution: Dimethylacetamide/water mixture (3:1). 250 ml water is added to a 1 L volumetric flask, the flask is filled to the mark with dimethylacetamide and shaken. Diethyl ether stock solution: Solution of 100 mg diethyl ether in 100 ml desorption solution. 5 ml of the desorption solution is added to a 25 ml volumetric flask and about 25 mg diethyl ether weighed to the nearest 0.1 mg is added. The flask is filled to the mark with desorption solution. Diethyl ether standard solution: Solution of 0.5 mg diethyl ether in 100 ml desorption solution. 500 µl of the stock solution is added to a 100 ml volumetric flask which is filled to the mark with desorption solution. Vinyl chloride-diethyl ether stock solution: Solution of 250 mg vinyl chloride and 250 mg diethyl ether in 100 ml desorption solution. 20 ml of the desorption solution are pipetted into a 20 ml injection bottle. 50 mg diethyl ether are weighed to the nearest 0.1 mg and added. Then the injection bottle is closed with septum and crimp cap. With a gastight syringe 20 ml vinyl chloride (about 50 mg) are injected through the septum and weighed to the nearest 0.1 mg. Note! The tip of the needle must not dip into the desorption solution. Vinyl chloride-diethyl ether calibration solution: Solution of 500 µg vinyl chloride and 500 µg diethyl ether in 100 ml desorption solution. 100 µl of the stock solution is added to a 50 ml volumetric flask which is filled to the mark with desorption solution.

13 205 AirMonitoringMethods,Vol.4 Vinyl chloride Vinyl chloride calibration gas: Gas mixture with 4 to 5 µg vinyl chloride in 1 ml gas (at 100 kpa). In an evacuated 300 ml gas sampling tube connected to a manometer, 1 ml vinyl chloride is injected with a microliter syringe via the side ports. Then an overpressure of about 100 kpa is produced with nitrogen. The gas phase is mixed with the pieces of PTFE tubing contained in the gas sampling tube. When the calibration gas is removed, the pressure in the syringe returns to atmospheric pressure. 2 Sampling An activated carbon tube is opened and connected to the pump. During working hours the pump and tube are carried by a person or used in a stationary position. The flow rate can be varied between 0.6 L/h and 0.9 L/h. The air sample volume should not exceed 7 L. 3 Analytical determination 3.1 Sample preparation The contents of the loaded activated carbon tube (separated in measuring and safety zones) are each transferred to a 20 ml injection bottle and 1 ml diethyl ether standard solution is added. Then the injection bottle is sealed with septum and aluminium cap and thermostatted at 70 C in the sample thermostat for 30 minutes. Then samples are automatically taken from the headspace and a gas chromatogram is recorded (operating conditions cf. Sect. 3.2). To ensure that the desorption solution used, the diethyl ether and activated carbon do not contain any interfering impurities, a chromatogram is recorded with the contents of an unloaded activated carbon tube and 1 ml of the diethyl ether standard solution as described for the analytical determination. 3.2 Operating conditions for gas chromatography The method was characterized under the following experimental conditions: Apparatus: Perkin-Elmer Sigma 2000 gas chromatograph with temperature programmer and flame ionization detector, HS 100 headspace autosampler, back-flush device. Column: Material: Stainless steel tube Length: 3 m

14 Analytical Methods AirMonitoringMethods,Vol Internal diameter: Stationary phase: 2.4 mm Carbopack B (60 80 mesh) coated with 1% SP 1000 To apply the back-flush mode the column is divided into sections of 1.0 and 2.0 m. The shorter piece is on the injection side. Carrier gas: Nitrogen: 40 ml/min, 380 kpa Back flush: 270 kpa Detector gases: Hydrogen: 42 ml/min, 250 kpa Synthetic air: 250 ml/min, 270 kpa Temperatures: Column: Temperature controlled from 80 C to 90 C at 3 C/min, then from 90 C to 170 C at 5 C/min Detector: 220 C Sample thermostat: 70 C Transfer line: 100 C Times: Sample thermostatting: 30 min Injection: 0.15 min Pressure stabilization: 0.5 min Back-flush after: 10 min Analysis cycle: 21 min 4 Evaluation Quantitative evaluation is carried out according to the internal standard method via the peak areas. 4.1 Calibration Two calibration factors are determined for quantification and evaluation of the method. Calibration factor f c : Vinyl chloride-diethyl ether and desorption solution without activated carbon (2-phase equilibrium). The calibration factor f c serves to determine the exact amount of vinyl chloride in the calibration gas; f c is determined using the vinyl chloride/diethyl ether calibration solution. Calibration factor f a : Vinyl chloride-diethyl ether with 100 mg activated carbon and desorption solution (3- phase equilibrium). The calibration factor f a is needed to determine the weight of vinyl chloride on the activated carbon. A known weight of vinyl chloride from the calibration gas (cf. Sect. 1.3) is adsorbed on the activated carbon and then desorbed with the diethyl ether standard solution.

15 207 AirMonitoringMethods,Vol.4 Vinyl chloride Implementation Calibration factor f c (2-phase equilibrium): An injection bottle is sealed with septum and aluminium cap, then 1 ml of the vinyl chloride-diethyl ether calibration solution is added and the solution analysed as described in Sect Using the vinyl chloride and diethyl ether peak areas, the calibration factor f c is calculated according to the formula (1): A. st w1 fc (1) A. w 1 st Legend: f c Calibration factor of vinyl chloride A 1 Peak area of vinyl chloride from the calibration solution A st Peak area of diethyl ether from the calibration solution w 1 Weight of vinyl chloride in mg in 1 ml of the calibration solution w st Weight of diethyl ether in mg in 1 ml of the calibration solution Calibration factor f a (3-phase equilibrium): An injection bottle is filled with the 100 mg section of an activated carbon tube. This is sealed with septum and aluminium cap and 1 ml of the vinyl chloride calibration solution and 1 ml of the diethyl ether standard solution are added. The solution is then analysed according to Sect 3.2. Using the vinyl chloride and diethyl ether peak areas, the calibration factor f a is calculated according to the formula (2): A. st w2 fa (2) A. w 2 st Legend: f a Calibration factor of vinyl chloride in 3-phase equilibrium A 2 Peak area of vinyl chloride from the calibration gas A st Peak area of diethyl ether from the standard solution w 2 Weight of vinyl chloride in mg in 1 ml of the calibration gas w st Weight of diethyl ether in mg in 1 ml of the diethyl ether standard solution Determination of the amount of vinyl chloride in the calibration gas An injection bottle is sealed with septum and aluminium cap. 1 ml of the vinyl chloride calibration gas and 1 ml of the diethyl ether standard solution are added. The solution is then analysed according to Sect The vinyl chloride weight in µg in 1 ml of the calibration gas is calculated using diethyl ether as internal standard taking into consideration the calibration factor f c according to the formula (3):

16 Analytical Methods AirMonitoringMethods,Vol f c. A 3. w 3 A st w st (3) Legend: f c Calibration factor of vinyl chloride w 3 Weight of vinyl chloride in µg in 1 ml of the calibration gas w st Weight of diethyl ether in µg in 1 ml of the standard solution A 3 Peak area of vinyl chloride A st Peak area of diethyl ether 4.2 Calculation of the analytical result The concentration by weight of vinyl chloride in the sample air in mg/m 3 is calculated according to the formula (4): c w f. A. w A. V a i st st (4) For the calculation of the concentration by volume c v in ml/m 3 (ppm) at 20 C and 1013 hpa from c w : c v = c w (5) Legend: c w Vinyl chloride concentration by weight in the air sample in mg/m 3 c v Vinyl chloride concentration by volume in the air sample in ml/m 3 f a Calibration factor of vinyl chloride in 3-phase equilibrium A i A st Peak area of vinyl chloride Peak area of diethyl ether w st V Weight of diethyl ether in µg in 1 ml of the standard solution Air sample volume in L 5 Reliability of the method 5.1 Accuracy The relative standard deviation of the whole measuring procedure was determined from 14 measurements to be about 3% for the weights 0.2 µg to 4.5 µg vinyl chloride per activated carbon tube (100 mg).

17 209 AirMonitoringMethods,Vol.4 Vinyl chloride 5.2 Quantification limit The relative quantification limit is 0.03 mg/m 3 vinyl chloride for a 7 L air sample; this corresponds to about 0.2 µg vinyl chloride per activated carbon tube using 100 mg activated carbon and 1 ml of the diethyl ether standard solution. 5.3 Selectivity The selectivity of the procedure depends above all on the type of chromatography column used. In practice the described column has proved suitable. When there are interfering components a column with other separation characteristics must be selected. 5.4 Recovery Determination of the recovery rate was carried out according to the operating conditions named in Sect Mixtures of calibration gases were produced according to Sect. 1.3 and known volumes injected directly into the activated carbon tubes with a gastight syringe. Then 3 to 4 L synthetic air was drawn through the activated carbon tubes with a pump. In the range from 0.2 µg to 4.5 µg vinyl chloride recovery was found to be > 95 %. 6 Discussion The whole procedure has been tested under laboratory conditions up to vinyl chloride concentrations of max. 140 mg/m 3. The shelf life of adsorbed vinyl chloride is limited. After 2 to 3 days migration begins from the measuring section to the safety section. With separate preparation of the safety section it must be borne in mind that the calibration factor for the safety section is slightly smaller than that for the measuring section. The calibration factor for the measuring section can, however, be used to evaluate the results. If more than 25 % of the vinyl chloride is found in the safety section, sampling must be repeated. For the shelf life of loaded tubes cf. e.g. [1]. If the safety section of the activated carbon tube is quantitatively evaluated, it must be borne in mind that this only contains 50 mg activated carbon and the calibration factor f a cannot be used. If needed this calibration factor must be determined as described in Section 4.1. Under the operating conditions described it is possible to determine 1,2-dichloroethane (procedure ZH 1/ E) simultaneously with vinyl chloride.

18 Analytical Methods AirMonitoringMethods,Vol References [1] Vandendriessche S, Griepink B (1989) The certification of benzene, toluene and m-xylene sorbed on tenax in tubes-crm 112. Community Bureau of Reference, Commission of the European Communities, EUR