College of Medicine, Wuhan University of Science and Technology, Wuhan 430065, China

[Abstract] Objective To establish a method for determination of difluorochloromethane in the air of workplace by direct injection -gas chromatography. Method The difluorochloromethane in air was sampled by syringes and injected directly. The analyte was separated in a30m × 0.32mm ×0.25μm QC3/AC-1 capillary column with flame ionization detection. Results The method showed good linearity in a range from 0.48μg/ml to 7.72μg/ml with a correlation coefficient of 0.9996 and the linear equation was Y=10281x+981.73. The limit of detection for difluorochloromethane was 0.16μg/ml and the limit of concentration value was 160mg/m³when the sample was directly injected. ConclusionThe method was suitable and qualified according to GBZ/T 210.4-2008Guide for Establishing Occupational Health Standards and could be wildly used for determination of difluorochloromethane in workplace.

[Keywords] Difluorochloromethane; Workplace air; Gas chromatography.

1． Introduction

Difluorochloromethane（F22）is one of the raw materials of organo-fluorin industry. F22 is not only widely used in producing tetrafluoroethylene and fluorocarbon, but also is a familiar refrigerant. However, F22 has adverse effects to human health such as acute inhalation toxicity and lung toxic reactions. According to Chinese GBZ2.1-2007 Occupational Exposure Limits for Hazardous Chemicals in the Workplace, PC-TWA value^[1]of F22 in workplace air is 3500 mg/m³. However, up to now, the determination of F22 has not been reported. As a consequence, it is necessary and significant to establish a method for determination of F22 in workplace to protect health of workers. The method was suitable and qualified according to GBZ/T 210.4-2008Guide for Establishing Occupational Health Standards^[2]

2． Experiment

2.1 Reagents

The standards of difluorochloromethane,chlorodifluoromethane and hexafluoropropylene were purchased from Juhuacomp (Zhejiang,China) with a purity of not less than 99.99%.

2.2 Equipment

Analysis of difluorochloromethane was performed by gas chromatography with flame ionization detector (FID),the machine producted nitrogen hydrogen air from Ke Jie Analysis Instrument Co.,Ltd and the chromatography data system developed by Zhejiang university. Syringes were gas-tight and the size of 1.0ml, 100ml were used.

2.3 Sampling

Air samples were collected directly by syringes. According to standard sampling method of GBZ159-2004 (China), the 100ml syringe was pumping with air samples three times before taking air samples, then the syringe inlet was closed immediately. The samples were preserved vertically in a clean container and determined as soon as possible on that day.

2.4 gc conditions

F22 was injected and analyzed in the capillary column (QC3/AC-1, 30m × 0.32mm ×0.25μm) provided by College of Chemistry and Chemical Engineering Nanjing University of Technology (Nanjing, China). The oven temperature, injector temperature and detector temperature were set at 35℃, 200℃ and 260℃,respectively. The flow rate of carrier gas (ultrapure nitrogen,99.999%) was 1.5ml/min in the analytical column and split ratio was 20:1.

2.5 Working standards

Standard stock gas was prepared by adding 1ml (vial 1ml syringe) of pure F22 to a syringe of 100ml diluted in clean air. After mixing adequately, 20ml of this stock gas was injected to another syringe of 100ml as the applied gas and also needed mix fully. This applied gas was further diluted with clean air to obtain F22 standards range from 0.48μg/ml to 7.72μg/ml refer to the above method. All standards were freshly prepared on the day of use. Each concentration level was injected and measured for three times and injection volume was 1.0ml.

2.6 Measurement and calculations

The samples were injected 1.0ml into the capillary column for determination in the given conditions. If the peak area was above the linear range of the working standards, then the gas was needed to be diluted with clean air in an appropriate dilution factor.

Concentrations of the analyte were calculated by formula:

C = 1.0 10⁶m/V ；mg/ m³

Where m was the mass (mg) of the analyte contained in the 1ml injected sample and V was the injective air sampled (ml).

3. Results and discussion

3.1 Linearity and sensitivity

A series of working standards range from 0.48μg/ml to 7.72μg/ml were repeatedly tested for 5 days. The study showed a good linear behavior with correlation coefficient (r) of 0.9996 in this linearity range. The limit of detection (LOD) was determined applying a signal-to-noise ratio which was 3. The method was conducted by subsequent dilutions of the working standards gas. The LOD values for F22 was 0.16μg/ml and the limit of concentration value was 160mg/m³if the sample was directly injected.

3.2 Precision and accuracy

To evaluate precision and accuracy of method, three concentration levels of low, middle and high for F22 which were 0.48μg/ml 1.93μg/ml and 7.73 μg/ml were prepared in 100ml syringes. The three concentrations were repeatedly determined six times during 3~5 days and the precision were individual 4.9%，3.7% and 8.2%. The RSD of measured values was within 10% and complied with the requirement.

Table 1 RSD value for F22 in three levels (n=6)

Added F22 (μg)	Measured F22 (μg)						RSD (%)
Added F22 (μg)	1	2	3	4	5	6	RSD (%)
0.48	0.369	0.422	0.416	0.377	0.371	0.380	4.9
1.93	0.720	0.777	0.783	0.770	0.775	0.779	3.7
7.73	4.446	4.713	4.196	4.117	4.929	4.177	8.2

3.3 Samples stability

The stability of samples storage was evaluated by analysing 6 groups of syringes (three syringes per group) with the same amount of F22(7.72mg/ml).The first group were analysed immediately on that day. The rest five groups stored at room temperature were determined on the 1^st, 3^rd, 5^th and 7^th day. The determination results were compared with the result of the first group. As a result, storage losses of every group stored at room temperature were over 10%. The results show that the samples should not be stored overnight.

3.4 Interference experiment

Compounds used in the workplace, if they have the same or nearly the same retention time as difluorochloromethane on the column, are potential interference. Such compounds as chlorodifluoromethane and hexafluoropropylene (HFP) existed in manufacture of organo-fluorin industry with F22. The study showed that analysis of F22 was not affected by the compounds(Fig.1).

Fig. 1. gc chromatogram for F22 Peak 1: HFP; Peak 2: F22

4. Conclusions

A simple and accurate method based on direct injection -gas chromatography has been successfully developed for the determination of F22 in workplace. The linearity of the method was very good in the F22 range from 0.48μg to 7.72μg. The limit of detection of the method was 0.16μg and the limit of concentration value for F22 was 160mg/m³when the sample volume was directly injected. All the test results for precision，accuracy and so on were qualified and met the request of GBZ/T 210.4-2008 Guide for Establishing Occupational Health Standards—Part 4: Determination Methods of Air Chemicals in Workplace. The samples should not be stored overnight. The present study indicated that this precise and reproduceable method was suitable for the determination of F22 in workplace.

References
[1] Standards of the People’s Republic of China, GBZ2.1-2007

[2] Standards of the People’s Republic of China, GBZ/T 210.4-2008

[3] Banghua Wu, Yuxuan Xie, Panqiao Yu, etal. The method of detecting difluorochloromethane in workplace air by gas chromatographic [J]. CHINESE JOURNAL OF INDUSTRIAL HYGIENE AND OCCUPATIONAL DISEASES, 2009,27 (5) :288-289.
[4] Zhaolin Liu, Leping Qiu, Michael, etal. The method of detecting difluorochloromethane in workplace air by solvent desorption gas chromatographic [J]. CHINESE JOURNAL OF INDUSTRIAL HYGIENE AND OCCUPATIONAL DISEASES, 2007,25 (11) :686-688.
[5] Standards of the People’s Republic of China, GBZ159-2004

[6] NIOSH. Manual of Analytical Methods (NMAM), Difluorochloromethane: 1018 Fourth Edition. 1994.

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