Hexane isomers (except n-hexane) and methylcyclopentane

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1 1 Hexane isomers (except n-hexane) and methylcyclopentane Method number 1 Application Air analysis Analytical principle Gas chromatography Completed in July 2010 Summary This analytical method permits the determination of hexane isomers, such as 2- methylpentane, 3-methylpentane, 2,2-dimethylbutane, 2,3-dimethylbutane and methylcyclopentane, in a concentration range from to one times the currently valid Occupational Exposure Limit (OEL) according to TRGS 900 and the air limit value (MAK value) proposed by the Deutsche Forschungsgemeinschaft (DFG) [1, 2] A suitable sampling pump draws ambient air through two charcoal tubes connected in series for sampling; the hexane isomers and methylcyclopentane are adsorbed on the charcoal. After sampling, both adsorption tubes loaded with the hexane isomers and methylcyclopentane are covered with a ternary solvent mixture, and after desorption of the analytes the sample solutions are analysed by means of gas chromatography. Quantification is performed with a flame ionisation detector (FID). Characteristics of the method Precision: Standard deviation (rel.): s = % Expanded uncertainty: U = % in the concentration range from 1to1500 mg/m 3 for n=6determinations Limit of quantification: Absolute: 4ng for the hexane isomers and methylcyclopentane, which is equivalent to 1.0 mg/m 3 at an injection volume of 1 μl, asample solution of 10 ml as well as an air sample volume of 40 L. Recovery: η = (96 to 99%) Sampling recommendation: Sampling time: 2h Air sample volume: 40 L The MAK-Collection Part III, Air Monitoring Methods 2013 DFG, Deutsche Forschungsgemeinschaft 2013 Wiley-VCH Verlag GmbH & Co. KGaA

2 2 Analytic Methods The air sample volume of 40 Lmay not be exceeded; in the case of longer sampling times the flow rate must be appropriately reduced. Description of the substances 2-Methylpentane [ ], 3-methylpentane [ ], 2,2-dimethylbutane [ ], 2,3-dimethylbutane [ ], methylcyclopentane [ ] The hexane isomers and methylcyclopentane are colourless liquids with odours similar to petrol or phenol. They are not miscible with water, but are readily miscible with alcohol, benzene, acetone and chloroform. Substance Synonym Density at 20 C [g/cm 3 ] Molar mass [g/mol] Boiling point [ C] Melting point [ C] 2-Methylpentane 3-Methylpentane Isohexane Dimethylpropylmethane Diethylmethylmethane Neohexane ,2-Dimethylbutane 2,3-Dimethylbutane Methylcyclopentane Hexane isomers: 1mL/m 3 (ppm) ¼b 3.58 mg/m 3,1mg/m 3 ¼b 0.28 ml/m 3 (ppm) Methylcyclopentane: 1mL/m 3 (ppm) ¼b 3.50 mg/m 3,1mg/m 3 ¼b 0.29 ml/m 3 (ppm) According to TRGS 900 as well as the List of MAK and BAT Values the currently valid Occupational Exposure Limit (OEL) is 1800 mg/m 3 (500 ml/m 3 )for the hexane isomers and methylcyclopentane. For short-term exposures they are classified in Peak Limitation Category II with an excursion factor of 2[1, 2]. Hexane isomers are contained, normally as diluents, in organic solvents, adhesives, coatings and paints. Moreover, they are used in the fuel and lubricant industries and can also occur as intermediate products in refining processes. Thus, for example, 2,2-dimethylbutane is utilised in automotive and aviation fuels to raise the octane rating. Methylcyclopentane is used as asolvent in organic synthesis. Detailed information on the toxicity of the hexane isomers and methylcyclopentane is found in the MAK Value Documentations [3]. Authors: D. Breuer, C. Friedrich Examiner: U. Lewin-Kretzschmar

3 Hexane isomers and methylcyclopentane 3 Hexane isomers and methylcyclopentane Method number 1 Application Air analysis Analytical principle Gas chromatography Completed in July 2010 Contents 1 General principles 2 Equipment, chemicals and solutions 2.1 Equipment 2.2 Chemicals 2.3 Solutions 2.4 Calibration standards 3 Sampling and sample preparation 4 Operating conditions for chromatography 5 Analytical determination 6 Calibration 7 Calculation of the analytical result 8 Reliability of the method 8.1 Precision and expanded uncertainty 8.2 Recovery 8.3 Capacity of the adsorbent 8.4 Limit of quantification 8.5 Storage stability 8.6 Influence of the humidity 8.7 Interference 8.8 Blank values 8.9 Remarks

4 4 Analytic Methods 1 General principles This analytical method permits the determination of hexane isomers, such as 2- methylpentane, 3-methylpentane, 2,2-dimethylbutane, 2,3-dimethylbutane and methylcyclopentane, in a concentration range from to one times the currently valid Occupational Exposure Limit (OEL) according to TRGS 900 and the air limit value (MAK value) proposed by the Deutsche Forschungsgemeinschaft (DFG) [1, 2] A suitable sampling pump draws ambient air through two charcoal tubes connected in series for sampling; the hexane isomers and methylcyclopentane are adsorbed on the charcoal. After sampling, both adsorption tubes loaded with the hexane isomers and methylcyclopentane are covered with a ternary solvent mixture, and after desorption of the analytes the sample solutions are analysed by means of gas chromatography. Quantification is performed with a flame ionisation detector (FID). 2 Equipment, chemicals and solutions 2.1 Equipment Pump for personal sampling, suitable for aflow rate of 20 L/h Gas meter Tube holder, suitable for accommodating the tubes used Charcoal tubes, sampling section 300 mg and back-up section 600 mg, for example BIA type, Dräger Safety AG &Co. KGaA, Lübeck, Germany Gas chromatograph with liquid injector, autosampler, and a polar and a nonpolar separation column as well as two flame ionisation detectors (FID) Volumetric flasks 1, 5, 10 and 1000 ml Volumetric pipettes of glass, 2.5 ml and 10 ml Microlitre syringes, 1, 2, 5, 10, 25, 50, 100, 250, 500 and 1000 μl Disposable syringes, 2mLwith disposable PTFE filters, pore size 0.45 μm Screw-capped vials, sealable, nominal volume approx. 20 ml Autosampler vials, sealable, nominal volume approx. 2mL

5 Hexane isomers and methylcyclopentane Chemicals 2-Methylpentane (purity GC >99%) 3-Methylpentane (purity GC ³ 99.9%) 2,2-Methylpentane (purity GC >99.5%) 2,3-Methylpentane (purity GC >98%) Methylcyclopentane (purity GC ~99%) Carbon disulphide p.a., free of benzene (purity GC ³ 99.8%) Dichloromethane p.a. Methanol, p.a. n-undecane, reference substance for GC 2-Methylheptane, reference substance for GC Gases for operation of the gas chromatograph: Helium 5.0 Hydrogen 5.0 Synthetic air, free of hydrocarbons 2.3 Solutions Extraction solution: Ternary mixture (CH 2 Cl 2 /CS 2 /MeOH) =60/35/5 600 ml of dichloromethane are mixed with 350 ml of carbon disulphide in a 1000 ml volumetric flask and then the flask is filled to the mark with 50 ml of methanol. Internal standard (IS): (2-Methylheptane/undecane) =50/ μl of 2-Methylheptane and 800 μl of undecane are dosed into a 2 ml autosampler vial that is then shaken. 2.4 Calibration standards All stock and calibration solutions are prepared in two groups. The two components 2-methylpentane and 2,3-dimethylbutane have the same retention times on

6 6 Analytic Methods the non-polar separation column, and 2-methylpentane and 2,2-dimethylbutane have the same retention times on the polar column. In addition, 2,2-dimethylbutane is not separated from the solvent peak on the non-polar column. For these reasons aseparate calibration must be carried out. It is important to ensure that the volumetric flask only remains open for as brief a period as possible and that the hexane isomers and methylcyclopentane are directly added to the ternary mixture that has been previously placed in the flask. Stock solution I: c(2-methylpentane) =39.0 mg/ml c(3-methylpentane) =39.6 mg/ml To prepare stock solution I, approximately 3 ml of the ternary solvent solution are placed in a 5 ml volumetric flask and then 300 μl each of 2-methylpentane (195 mg) and 3-methylpentane (198 mg) are added. The volumetric flask is then filled to the mark with the ternary mixture and shaken. Stock solution II: c(2,2-dimethylbutane) =38.4 mg/ml c(2,3-dimethylbutane) =39.6 mg/ml c(methylcyclopentane) =40.5 mg/ml To prepare stock solution II, approximately 3 ml of ternary solvent solution are placed in a 5 ml volumetric flask and then 300 μl each of 2,2-dimethylbutane (192 mg) and 2,3-dimethylbutane (198 mg) as well as 270 μl of methylcyclopentane (203 mg) are added. The volumetric flask is then filled to the mark with the ternary mixture and shaken. The prepared stock solutions are transferred to sealable screw-capped vials. The two stock solutions are stable for up to four months when stored in the refrigerator at approx. 4 C. Calibration solutions: c(hexane isomers and methylcyclopentane) = 4 to 1600 μg/ ml Approx. 7 ml of the ternary mixture are placed in separate 10 ml volumetric flasks and the volumes of stock solutions Iand II stated in Table 1are added in each case. Then the flasks are filled to the mark with the ternary solvent mixture, 5 μl of the internal standard solution are added and the flasks are shaken. A calibration standard of medium concentration is used for quality control each working day. The calibration solutions must be freshly prepared before each calibration.

7 Hexane isomers and methylcyclopentane 7 Table 1 Dosing scheme of the calibration solutions in the concentration range from 4 to 1600 μg/ml. Calibration solution No. Stock solution Iand II [μl] [μg/10 ml] [μg/10 ml] 2-Methylpentane 3-Methylpentane 2,2-Dimethylbutane [μg/10 ml] 2,3-Dimethylbutane [μg/10 ml] Methylcyclopentane [μg/10 ml] Sampling and sample preparation Suitable flow-controlled pumps are used for sampling. Immediately before sampling is started, the fused glass ends of two charcoal tubes are opened and connected to each other by asmall piece of tubing (e.g. silicone tubing, PE or PTFE tubing). The charcoal tubes, connected in series, are connected to the pump and the flow rate is adjusted to 20 L/h (0.333 L/min). The recommended sampling time is 2h.The flow rate must be reduced to 5L/h (0.083 L/min) if sampling is to be prolonged to 8 hours. Immediately after sampling has been completed, the charcoal tubes must be sealed with the pertinent caps and sent to the analytical laboratory without delay. The sequence in which the tubes were connected to the pump must be marked. Moreover, the most important parameters for the evaluation, such as temperature, air pressure and relative humidity, must be noted in the sampling record. The tubes are opened in the laboratory and the contents of each tube are transferred completely into separate 20 ml screw-capped vials. Then the charcoal loaded with the analyte is covered with 10 ml of the ternary mixture, 5 μl ofthe internal standard mixture are added and the vial is sealed and shaken. After 30 minutes the solutions must be filtered through disposable filters into autosampler vials and then analysed. 4 Operating conditions for chromatography Apparatus: Gas chromatograph, e.g. Agilent 6890 with two flame ionisation detectors

8 8 Analytic Methods Separation columns: Double capillary technique; both capillary columns are connected in parallel to the injector with acapillary connector (e.g. GRAPHPACK-2M adapter). Capillary column A: Rtx-5 from Restek Stationary phase: 5% diphenyl/95% dimethyl polysiloxane Length: 60 m Inner diameter: 0.25 mm Film thickness: 0.5 μm Capillary column B: HP-INNOWax Stationary phase: Polyethylene glycol (PEG) Length: 60 m Inner diameter: 0.25 mm Film thickness: 0.5 μm Detector: Flame ionisation detector (FID) Temperatures: Columns (A and B): 50 C (11 min isothermal); heating rate 4 C/min to 154 C; analysis time: 37 min Injector: 250 C, split 47.6 ml/min (20:1) Carrier gas: Helium 5.0 Flow rate: 1.2 ml/min, constant flow Injection volume: 1 μl Chromatograms obtained under the stated conditions are shown in Figure 1and Figure 2. FID1 A, (D:\HPCHEM\GC_NEU\DATA\GC2IA\6PU10016.D) pa Methylpentane 3-Methylpentane pa FID2 B, (D:\HPCHEM\GC_NEU\DATA\GC2IA\6PU10016.D) Methylpentane 3-Methylpentane Fig. 1 Example of achromatogram for the gas chromatographic separation of 2-methylpentane and 3-methylpentane on two different columns (Rtx-5 above and HP-INNOWax below) (for the chromatographic conditions see Section 4) min min

9 Hexane isomers and methylcyclopentane 9 FID1 A, (D:\HPCHEM\GC_NEU\DATA\GC2IA\6PU10035.D) pa Methylcyclopentane ,3-Dimethylbutane FID2 B, (D:\HPCHEM\GC_NEU\DATA\GC2IA\6PU10035.D) pa 300 2,2-Dimethylbutane min ,3-Dimethylbutane Methylcyclopentane Fig. 2 Example of achromatogram for the gas chromatographic separation of 2,2-dimethylbutane, 2,3-dimethylbutane and methylcyclopentane on two different columns (Rtx-5 above and HP- INNOWax below) (for the chromatographic conditions see Section 4) min 5 Analytical determination To analyse the samples processed as described in Section 3, 1 μl each of the sample solution is injected into the gas chromatograph and analysed under the conditions stated in Section 4. If the measured concentrations are above the calibration range, then a suitable dilution must be prepared and the analysis must be repeated. 6 Calibration The calibration solutions described in Section 2.4 are used to obtain a calibration function (see also Table 1). 1 μl each of the calibration solutions is injected into the gas chromatograph and analysed in the same manner as the sample solutions. The resulting peak area quotients (ratio of the peak areas of the individual hexane isomers or methylcyclopentane to the peak areas of both internal standards, i.e. 2-methylheptane and undecane) are plotted versus the respective concentration. The calibration curve is

10 10 Analytic Methods linear in the investigated concentration range. A control sample must be analysed each working day to check the calibration function. The calibration must be performed anew if the analytical conditions change or the quality control results indicate that this is necessary. 7 Calculation of the analytical result The concentration of individual hexane isomers and of methylcyclopentane in the workplace air is obtained from the concentration of the substance in the sample solution calculated by the data evaluation unit. The following equation (1) (6) are used for the calculations: ¼ ðfl aþ b V Air F 273 þ t g ½mg=m 3 Š ð1þ 273 þ t a Equation (2) serves to calculate the value at 20 C and 1013 hpa (standard conditions): O ¼ 273 þ t a p a ½mg=m 3 Š ð2þ The corresponding volume concentration (independent of the pressure and temperature) is: ¼ O V m M ð3þ ¼ 273 þ t a 1013 p a 293 V m M ð4þ The following applies to 2-methylpentane, 3-methylpentane, 2,2-dimethylbutane and 2,3-dimethylbutane and methylcyclopentane at t a =20 C and p a =1013 hpa (standard conditions): ðhexan IsomerÞ ¼0;279 ml m 3 ð5þ ðmcpþ ¼0;286 ml m 3 ð6þ

11 Hexane isomers and methylcyclopentane 11 where: is the mass concentration of ahexane isomer or methylcyclopentane in the ambient air on the basis of t a and p a in mg/m 3 o is the mass concentration of ahexane isomer or methylcyclopentane in the ambient air on the basis of 20 C and 1013 hpa in mg/m 3 a is the intercept of the calibration function with the yaxis b is the slope of the calibration graph η is the recovery (to be taken into consideration if necessary) Fl is the peak area of the sample signal F is the conversion factor for the volume of the measured sample (in this case 0.01 L) V Air is the air sample volume in m 3 t g is the temperature in the gas meter in C t a is the temperature during sampling in C p a is the air pressure at the sampling location in hpa is the concentration by volume in the ambient air in ml/m 3 V m is the molar volume of ahexane isomer or methylcyclopentane in L/mol M is the molar mass of ahexane isomer or methylcyclopentane in g/mol 8 Reliability of the method The characteristics of the method were calculated as stipulated in EN 482 [4], EN 1076 [5] and DIN [6]. 8.1 Precisionand expanded uncertainty To determine the precision and expanded uncertainty, five solutions in a concentration range from approx to one times the MAK value of the hexane isomers or methylcyclopentane were evaporated in a dynamic test gas facility at a relative humidity of approx. 50%. Six separate adsorption tubes for 2-methylpentane and 3-methylpentane as well as six separate adsorption tubes for 2,2-dimethylbutane, 2,3-dimethylbutane and methylcyclopentane for each concentration were loaded and prepared as described in Section 3, and analysed under the operating conditions stated in Section 4. The results are shown in Table 2.

12 12 Analytic Methods Table 2 Standard deviation (rel.) and expanded uncertainty Ufor n=6determinations Substance Concentration [mg/m 3 ] Standard deviation (rel.) [%] Expanded uncertainty U [%] 2-Methylpentane Methylpentane ,2-Dimethylbutane ,3-Dimethylbutane Methylcyclopentane Recovery The recovery of the individual hexane isomers and methylcyclopentane was calculated during the determination of the precision in the measurement range (see Section 8.1). The recovery for the hexane isomers and methylcyclopentane was constant over the entire range. The results are shown in Table 3.

13 Hexane isomers and methylcyclopentane 13 Table 3 Mean recovery of the hexane isomers and methylcyclopentane Substance Mean recovery [%] 2-Methylpentane 98 3-Methylpentane 98 2,2-Dimethylbutane 99 2,3-Dimethylbutane 96 Methylcyclopentane Capacity of the adsorbent Experiments on the breakthrough behaviour of the hexane isomers and methylcyclopentane were carried out at arelative humidity of 80%. Abreakthrough for 2,2-dimethylbutane was ascertained when the total concentration of approx mg/m 3 was exceeded at an air sample volume of 40 L(2hat 20 L/h). A breakthrough of all the hexane isomers and methylcyclopentane was observed at asampling time of 3hand aflow rate of 20 L/h. However, in order to rule out a breakthrough during sampling, two adsorption tubes connected in series must always be used. In addition, the flow rate must be appropriately reduced if the sampling time is greater than 2hours so that the maximum air sample volume does not exceed 40 litres. 8.4 Limit of quantification The limit of quantification was determined from a 10-point calibration in the concentration range from 3.2 to 32 μg/ml for the hexane isomers and 3.8 to 38 μg/ ml for methylcyclopentane as stipulated in DIN [6] The limit of quantification for all the hexane isomers and methylcyclopentane was 4.0 μg/ml (absolute 4ng), which is equivalent to arelative limit of quantification of 1mg/m 3 based on an air sample volume of 40 Land asample solution of 10 ml. 8.5 Storagestability The storage stability of the loaded adsorption tubes was checked for concentrations of approx. 70 mg/m 3 and approx mg/m 3 over aperiod of 28 days. The tubes were spiked at arelative humidity of approx. 50% for this purpose.

14 14 Analytic Methods Twelve adsorption tubes per concentration were loaded with 2-methylpentane and 3-methylpentane and twelve adsorption tubes were loaded with 2,2-dimethylbutane, 2,3-dimethylbutane and methylcyclopentane, and they were stored at room temperature. 3 samples from each series were investigated after 1, 7, 14 and 28 days. No changes in the concentration were detected within the stated period. 8.6 Influence of the humidity The influence of the relative humidity was checked for two concentrations on a dynamic test gas facility at two different relative humidity levels. The experiment was carried out on all the hexane isomers and methylcyclopentane at relative humidity levels of approx. 20% and approx. 80% for concentrations of approx. 70 mg/ m 3 and approx mg/m 3. No influence of the humidity was detected. 8.7 Interference 2-Methylpentane and 2,3-dimethylbutane have the same retention times on the non-polar separation column (Rtx-5) and 2-methylpentane and 2,2-dimethylbutane have the same retention times on the polar separation column (HP-INNOWax). In addition, the solvent peak overlaps with the peak of 2,2-dimethylbutane on the non-polar column so that no peak separation is achieved. As a rule the use of two separation columns of different polarity ensures sufficient selectivity of the method. Nevertheless, it should be checked whether other solvents, such as n-hexane, may possibly cause interference. If sufficient separation cannot be ensured, the separation conditions must be appropriately modified. 8.8 Blank values No blank values were detected.

15 Hexane isomers and methylcyclopentane Remarks In addition, tests were performed as part of the experimental check of the method to establish whether carbon disulphide can serve as an alternative extraction agent to the ternary mixture. However, the characteristics of the method, such as the recovery rates, have to be determined anew by the user if the extraction agent is changed. References 1 TRGS 900 (2006) Arbeitsplatzgrenzwerte. Recently revised and supplemented: GMBl 2011 pp [No. 10]. 2 Deutsche Forschungsgemeinschaft (2013) List of MAK and BAT Values Commission for the Investigation of Health Hazards of Chemical Compounds in the Work Area, Report No. 49, Wiley-VCH,Weinheim. 3 Henschler D (ed.) (1992) Hexane (all isomers except n-hexane). Occupational Toxicants: Critical Data Evaluation for MAK Values and Classification of Carcinogens, Volume 4. Wiley-VCH, Weinheim. 4 EN 482 (2012) Workplace atmospheres General requirements for the performance of procedures for the measurement of chemical agents. Beuth Verlag, Berlin 5 EN 1076 (2010) Workplace exposure Procedures for measuring gases and vapours using pumped samplers Requirements and test methods.beuth Verlag, Berlin 6 DIN (2008) Chemical analysis Decision limit, detection limit and determination limit under repeatability conditions Terms, methods, evaluation. Beuth Verlag, Berlin Authors: D. Breuer, C. Friedrich Examiner: U. Lewin-Kretzschmar