Determination of 54 Volatile Organic Compounds in Drinking Water by Gas Chromatography-Mass Spectrometry with Purge and Trap Based on Response Surface Method

The method mentioned by the title was proposed, and single-factor test was used to determine the ranges of five conditions of purge and trap, such as purging flow, purging time, purging temperature, desorption temperature and desorption time, and the regression model was established by response surface method for obtaining the optimum results of the above 5 conditions. The 20 μL of 2.0 mg·L^-1 fluorobenene internal standard solution was added into a 40 mL-brown glass bottle which was filled with water sample. After purge and trap, the 54 volatile organic compounds (VOCs) were separated on the HP-VOC column by temperature-programming, detected by mass spectrometer with electron impact ion source, and quantified by internal standard method. As shown by the results, the regression model established by the five-factor three-level test using Design-Expert 8.0.6 software was a five-element quadratic equation on the basis of the test results of single-factor method and the center group design principle of response surface method. The regression model had statistical significance (P<0.000 1), the fitting degree was good (P of the misfit term was 0.292 6) and the confidence was high (coefficient of variation was less than 10%). The order of influence degree of single-factor significance was desorption time, purging temperature, purging flow, desorption temperature and purging time, and the order of influence degree of interactive-factor significance was purging flow and purging time, purging temperature and purging flow, purging temperature and purging time and desorption time and desorption temperature. Using Design-Expert 8.0.6 software to solve the regression model, and the purging flow was 40 mL·min^-1, the purging time was 9.0 min, the purging temperature was 20 ℃, the desorption time was 2.2 min, and the desorption temperature was 240 ℃. Under these conditions, the total mass concentrations (30.00±0.41)μg·L^-1 of the 6 typical VOCs (dichloromethane, trichloroethylene, 1,3-dichloropropane, isopropylbenzene, 1,3-dichlorobenzene and naphthalene) was basically consistent with the predicted value (30.36 μg·L^-1). Linear relationships between values of the mass concentration of 52 VOCs and the peak area ratio of VOCs to internal were kept in the range of 0.05-10.00 μg·L^-1 (the linear range of m-xylene/p-xylene was 0.10-20.00 μg·L^-1), with detection limits (3S/N) in the range of 0.01-0.03 μg·L^-1. Using tap water as the blank matrix, test for recovery was made by standard addition method, and values of recovery were found between 87.1% and 107%, with RSDs (n=7) of the determined values in the range of 1.2%-9.2%. The proposed method was applied to the analysis of water samples from urban pipe network in Lanzhou city, and 23 VOCs were detected, and the detection amounts were not more than 45.7 μg·L^-1, lower than the limits specified in the GB 5749-2022.