Determination Of Dimethylsulfate In Workplace Air By Gas Chromatography With Pre-Column Derivatization

[Objective]Dimethylsulfate(DMS)was a methylation reagent commonly used in medicine,cosmetics,printing and dyeing industries,and organic synthesis,and has a great impact on the environment.It was chemically unstable,which are highly toxic substances.Because its methylation effect was stronger than other reagents and its price were low,it was widely used in organic synthesis industry.If the worker was exposed to the occupational environment of DMS,it cause to irritate the eyes and nose,causing acute symptoms such as headache,dizziness,edema,cough,and high fever.At the same time,it has a burning effect on eyes and skin,and can cause death in severe cases.Therefore,the rapid and accurate determination of DMS of workplace air is great significance in this research.At present,DMS was sampled in silica gel tube for occupational health detection in China,and DMS was derivatized into p-nitroanisole by liquid chromatography.The derivatization method was complicated,the operation was cumbersome and the reaction time was long.The index of the test cannot meet the requirement of the actual work.In this paper,using the derivatization agent aniline and the sodium hydroxide and dispersing agent isopropanol to derivative DMS into N-methylaniline in the air of the workplace directly,and the gas chromatography(GC)separation flame ionization detector(FID)was used for detection.The sample collection and derivation were completed in one step,the operations were reduced,the detection efficiency was improved,and the instrument reagents used were relatively easy to obtain,which was suitable for the occupational health grassroots monitoring unit in China.[Methods]1)The DMS in the workplace air was collected by the small air bubble absorption containing the sodium hydroxide solution,aniline,isopropyl alcohol(volume ratio 1:1:8)absorption liquid.Utilizing the chemically active nature of DMS was derivatized N-methylaniline in which was separated with DB-5chromatographic column analyzed by GC-FID.2)The qualitative and the quantitative analysis of DMS were carried out based on the retention time and peak area of N-methylaniline respectively.Derivatization reagents and dispersants were determined by pre-experiment.The ratio,amount and reaction time range of derivatization reagents and dispersants were determined by single factor rotation method.Optimum conditions were determined by orthogonal test.The reaction product was used characterizes by different columns,spikes and gas chromatography-mass spectrometry(GC-MS).3)The methodological indicators such as the sampling method,sample processing method,sample stability,sample storage time,precision and accuracy were studied and discussed according to the requirements of the"Guidelines for the Development of Occupational Hygiene Standards".4)A total of 24 samples was collected and tested by the developed method by filling,offline and loading process positions in a DMS chemical works.Sampling and testing analysis were carried out at the offline position of DMS by using the developed method and the analytical methods of national standard,and a paired t-test was performed.5)The uncertainty of the air sample was evaluated to determine the reliability of the test method and the comparability of the test results.[Results]1)Absorbent(derived reagent):0.5g/L sodium hydroxide,isopropanol,aniline(volume ratio 1:1:8);absorption tube:small bubble absorption tube of brown;collection conditions:0.3L/min,15min;water bath temperature:60℃;derivative time:30 min;injection volume:1μL;column:HP-5(30m×250μm×0.25μm);heating program:programmed temperature,initial temperature 80℃,hold for 3 min,heat up to 185℃at 15℃/min,hold for 2 min,constant flow rate 0.4 mL/min;mode of injection:automatic injection;inlet temperature 250℃,split ratio 5:1;FID temperature 300℃,hydrogen 30mL/min,air 300mL/min.2)N-methylaniline which a derivative of DMS,Isopropanol and aniline were completely separated without the interference peak under the above conditions.The retention time of DMS was 10.175min,and the correlation coefficient was greater than 0.999.The linear equation was y=0.950x-0.100.The correlation coefficient was 0.9998 in the range of0.36μg/mL~133.20μg/mL,the relative standard deviation was less than 6.35%,and the detection limit was 0.12μg/mL(S/N=3),the minimum detection concentration was0.05mg/m~3(4.5Lairsample);thestandardrecoverieswere100.98%~104.48%.The sample could be kept for at least 7 days at room temperature.3)Twenty-four actual samples were tested and the results showed a concentration range of 0.05 to 0.12 mg/m~3.4)There was no statistical difference between the analytical methods of national standard and the development method.5)The most important factor affecting the test results were the uncertainty component of standard solution preparation and working calibration curve fitting.[Conclusions]1)In this study,the pre-column derivatization-gas chromatography method was used to determine the DMS in the workplace air.Pre-experiment was determined by the derivatization reagent and dispersant.The amount of the derivatizing reagent and the reaction time range were determined by single factor rotation.The test conditions such as column selection,injection volume,column temperature,inlet temperature,split ratio,and detector temperature in gas chromatography were optimized.A rapid,simple,accurate and reliable method for pre-column derivatization gas chromatography of DMS in workplace was established.2)The method has no steps of pretreatment,digestion,extraction,constant volume,etc.,and the instruments and equipment used are easy to obtain,and the sample can be measured after being collected.Since the sampling was completed in one step,there was no need to worry about the sample storage time was too long,resulting in the loss of DMS,which greatly improves the sample storage time.3)Aniline was found to be specific derivative of DMS.4)The derivative product of DMS,N-methylaniline,was completely separated from aniline and isopropanol,and has a high peak area.It was suitable for daily monitoring analysis and batch monitoring of DMS in the workplace air of the occupational health monitoring unit.