Method for the determination of 1,3-butadiene

Federation of the Employment Accidents Insurance Institutions of Germany (Hauptverband der Berufsgenossenschaften) Centre for Accident Prevention and Occupational Medicine Alte Heerstraße 111, 53757 Sankt Augustin Expert Committee Chemistry Carcinogenic substances Order number: BGI 505-26E Established methods Issue: May 1985 Method for the determination of 1,3-butadiene Method tested and recommended by the Berufsgenossenschaften for the determination of 1,3-butadiene in working areas. 1 CONTINUOUS PROCEDURE Stationary process gas chromatographs can be used to monitor the concentration of 1,3-butadiene in working areas. 2 DISCONTINUOUS PROCEDURE For the assessment of working areas, both personal and stationary sampling are possible. Sampling with a pump and adsorption on activated carbon, head-space gas chromatography. Air MonitoringMethods,Vol. 7

Analytical Methods Air MonitoringMethods,Vol. 7 32 1 CONTINUOUS PROCEDURE Process gas chromatography for stationary sampling Principle: A measured air volume is added to a stream of carrier gas and drawn through a GC column. Depending on the number and type of accompanying components, some of which may also be determined, further columns are necessary to separate the 1,3-butadiene. To shorten the time needed for analysis, the stream of carrier gas is diverted onto these columns in a suitable manner. The 1,3-butadiene is determined with a flame ionisation detector (FID). Technical data: Smallest measuring range: 0 ¼ 20 ml/m 3 (ppm). Quantification limit: 1.0 ml/m 3 (ppm) = 2.3 mg/m 3 1,3-butadiene. Selectivity: Selective determination possible, if a suitable column is used. Time needed for each determination: Materials: Supplier: 3 ¼ 10 minutes (depending on the accompanying components such as acrylonitrile and styrene) source of pneumatic energy, purified or synthetic air, hydrogen, carrier gas: nitrogen. Siemens AG, Karlsruhe.

33 Air MonitoringMethods,Vol. 7 1,3-Butadiene 2 DISCONTINUOUS PROCEDURE Sampling with a pump and adsorption on activated carbon, headspace gas chromatography Principle: With a pump a measured air volume is drawn through an adsorption tube with activated carbon. The adsorbed 1,3-butadiene is desorbed with a non-volatile solvent and determined by headspace gas chromatography (HSGC). Technical data: Quantification limit: Under the conditions found in practice, the relative quantification limit is 0.5 ml/m 3 (ppm) = 1.1 mg/m 3 1,3-butadiene for a 16-litre air sample. This corresponds to 18 µg 1,3-butadiene per activated carbon tube. Selectivity: When interfering components are present, the values determined may be too high. Interferences can generally be eliminated by selecting a different column. Advantages: Personal sampling and selective determination possible. Disadvantages: No indication of peak concentrations, time-consuming. Apparatus: Pump, gas meter or flow meter, adsorption tubes with activated carbon, head-space gas chromatograph with flame ionisation detector (FID).

Analytical Methods Air MonitoringMethods,Vol. 7 34 Detailed description of the method Contents 1 Summary 2 Equipment, chemicals and solutions 2.1 Equipment 2.2 Chemicals 2.3 Solutions 3 Sampling 4 Analytical determination 4.1 Sample preparation and analysis 4.2 Operating conditions for gas chromatography 5 Evaluation 5.1 Calibration 5.2 Calculation of the analytical result 6 Reliability of the method 6.1 Accuracy 6.2 Quantification limit 6.3 Selectivity 6.4 Recovery 7 Discussion 8 Suppliers 9 References 1 Summary This method permits the determination of 1,3-butadiene concentrations in working areas averaged over the sampling time after personal or stationary sampling. With a pump carried by a person or used in a stationary position, a measured air volume is drawn through a glass tube filled with activated carbon. The butadiene is then eluted with a non-volatile solvent and determined by head-space gas chromatography according to the internal standard method. Under the conditions found in practice, the relative detection limit is 1.1 mg/m 3 = 0.5 ml/m 3 (ppm) 1,3-butadiene for a 16-litre air sample. This corresponds to 18 µg 1,3- butadiene per activated carbon tube.

35 Air MonitoringMethods,Vol. 7 1,3-Butadiene 2 Equipment, chemicals and solutions 2.1 Equipment For sampling and sample preparation: Pump with gas meter or flow meter Sample vials with PTFE* 1 -coated septa and aluminium caps 30 ml, 10 ml Crimper Adsorption tubes filled with activated carbon (standardized, consisting of two zones filled with activated carbon separated by porous polymeric material; see Section 7 discussion) Caps for the opened activated carbon tubes For analysis: Head-space gas chromatograph with flame ionisation detector, automatic injection from the head-space chamber, perhaps with back-flush device Evaluation unit Injection of the sample can also be carried out manually instead of injecting automatically. Gas-tight syringes are required for this. 2.2 Chemicals Butadiene, purity 6 99% Methyl acetate, purity 6 98% (internal standard) N,N-Dimethylacetamide (DMA), GC grade Gases for operating the gas chromatograph: Nitrogen Hydrogen Synthetic air 2.3 Solutions Methyl acetate standard solution: Butadiene/methyl acetate calibration solution: Solution of 50 mg methyl acetate in 100 ml DMA. 50 mg methyl acetate is placed in a 100 ml volumetric flask which is then filled to the mark with DMA. Solution of about 11 mg 1,3-butadiene and 10 mg methyl acetate in 20 ml DMA. About 5 ml gaseous 1,3-butadiene is injected with a gas syringe slowly into the liquid through the septum of a sample vial filled with 20 ml methyl acetate standard solution. 1,3-Butadiene bubbles should not appear at the tip of the * Polytetrafluoroethylene.

Analytical Methods Air MonitoringMethods,Vol. 7 36 needle. It should be prevented that 1,3-butadien escapes at the puncture site of the septum. The amount of added 1,3- butadiene is determined by weighing to the nearest 0.1 mg. 3 Sampling An activated carbon tube is opened and connected to the pump. The pump and tube are carried by a person during working hours or used in a stationary position. The flow rate is set at about 2 l/hour. 4 Analytical determination 4.1 Sample preparation and analysis The two zones of the loaded activated carbon tube are each placed in a 10 ml sample vial. 1 ml methyl acetate standard solution and 1 ml DMA are added to each and the sample vials are closed tightly. The closed sample vial with the loaded activated carbon, 1 ml methyl acetate standard solution and 1 ml DMA are heated in the sample thermostat for 30 minutes at 70 8C. The same volume as for calibration (see Section 5.1) is then injected from the headspace chamber into the gas chromatograph and a gas chromatogram is recorded (for operating conditions see Section 4.2). Quantitative evaluation is performed according to the internal standard method using the peak areas or peak heights. To ensure that the DMA, methyl acetate and activated carbon used do not contain any interfering impurities, a gas chromatogram is recorded with the filling of an unloaded activated carbon tube, 1 ml methyl acetate standard solution and 1 ml DMA as described above. 4.2 Operating conditions for gas chromatography. The method was characterized under the following experimental conditions: Apparatus: Head-space gas chromatograph Carlo Erba model 2900 with flame ionisation detector, automatic sampling from the head-space chamber, back-flush device Column: Material: Quartz capillary Length: 30 m Internal diameter: 0.25 mm Stationary phase: Carbowax 20 M

37 Air MonitoringMethods,Vol. 7 1,3-Butadiene Temperatures: Sample thermostat: 70 8C Injection device: 90 8C Injector block: 200 8C Column: 70 8C, isothermal Detector: 200 8C Carrier gas: Helium, flow rate 2 ml/min Detector gases: Hydrogen, flow rate 35 ml/min Synthetic air, flow rate 350 ml/min 5 Evaluation 5.1 Calibration The vapour-space of a sample vial containing the filling of an unloaded activated carbon tube, 1 ml butadiene/methyl acetate calibration solution and 1 ml DMA, is analysed under the given GC conditions (see Section 4.2). The calibration factor for butadiene is calculated using the butadiene and methyl acetate peak areas according to equation (1): f ˆ A0 is w0 A 0 w 0 is 1 Where: f calibration factor for butadiene A' is Peak area for methyl acetate A' Peak area for butadiene w' Weight of butadiene in mg in 1 ml of the calibration solution Weight of methyl acetate in mg in 1 ml of the calibration solution w' is 5.2 Calculation of the analytical result The concentration by weight of 1,3-butadiene in the air sample in mg/m 3 is calculated according to equation (2): c w ˆ A w is f 1000 A is V 2 For 20 8C and 1013 mbar the concentration by volume in ml/m 3 is calculated from c w according to the following equation (3): c v ˆ 0:44 c w Where: c w Concentration of 1,3-butadiene in the air sample in mg/m 3 c v Concentration of 1,3-butadiene in the air sample in ml/m 3 (ppm) 3

Analytical Methods Air MonitoringMethods,Vol. 7 38 A Peak area for 1,3-butadiene from the sample A is Peak area for methyl acetate from the methyl acetate standard solution w is Weight of methyl acetate in 1 ml of the methyl acetate standard solution V Air sample volume in l f calibration factor for 1,3-butadiene Evaluation using the peak heights can also be carried out as described above. 6 Reliability of the method 6.1 Accuracy For the whole procedure, with a concentration range of 3 ml/m 3 to 8 ml/m 3, the relative standard deviation was calculated from measurements in practice to be 6% with a range of scatter of 12%. 6.2 Quantification limit The quantification limit depends on the type of gas chromatographic detector and the quality of the device. Under the conditions in practice, 18 µg 1,3-butadiene per activated carbon tube can be detected. This corresponds to a 1,3-butadiene concentration of 1.1 mg/m 3 = 0.5 ml/m 3 (ppm) for a 16-litre air sample. 6.3 Selectivity The selectivity of the procedure depends above all on the type of column used. In practice the given capillary column has proved reliable. If there is interference, a column with a different separation phase must be used. 6.4 Recovery Desorption of the 1,3-butadiene with DMA is reproducible. As shown by comparison with calibration solutions, 1,3-butadiene was recovered from test gases almost completely. 7 Discussion Activated carbon tubes (SKC catalogue No. 226±01, filling 100 mg + 50 mg activated carbon) can be used under the given conditions up to a 1,3-butadiene concentration of

39 Air MonitoringMethods,Vol. 7 1,3-Butadiene 100 ml/m 3 (ppm). At higher concentrations or high humidity, activated carbon tubes with a greater filling of activated carbon (about 1 g) should be used. These activated carbon tubes can also be used for greater flow rates during sampling. The loaded activated carbon tubes closed with caps can be stored at room temperature for 5 days. The peak area correction factor is constant over a wide range of weight ratios of 1,3-butadiene: methyl acetate (0.5 :1 to 50 : 1) under the conditions described in Section 4. The determination of 1,3-butadiene has also proved reliable with the use of ± benzyl alcohol as elution agent (instead of N,N-dimethylacetamide) and ± head-space gas chromatography with a packed column (instead of capillary column). Column: stainless steel, length 2 m, internal diameter 3 mm, filled with GP 80/100 Carbopack C coated with 0.19% picric acid. 8 Suppliers Pump: Activated carbon tube, NIOSH: Dråger, type B Head-space gas chromatograph: e. g. Du Pont Instruments, supplier in Germany: DEHA-Haan & Wittmer GmbH, Friolzheim e. g. Chrompack Deutschland, Mçllheim Compur Electronic GmbH, Munich Fleischhacker KG, Schwerte/Ruhr Gçnter Karl ohg, Geisenheim e. g. Drågerwerk AG, Lçbeck e. g. Bodenseewerk Perkin Elmer & Co GmbH, Ûberlingen Carlo Erba, supplier in Germany: Erba Science, Hofheim/Ts Siemens AG, Karlsruhe 9 References Hachenberg H, Schmidt AP (1979) Gas chromatographic head space analysis. London, Philadelphia, Rheine: Heyden and Sons.