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Drinking water can be easily contaminated by volatile organic compounds such as halogenated hydrocarbons and benzene derivatives, which can affect the central nervous system and cause anesthesia. According to the Drinking Water Hygiene Standard, these volatile pollutants are included in the monitoring list. However, due to their low concentrations in drinking water (typically in the range of μg/L), traditional methods like liquid-liquid extraction, static headspace, purge and trap, or solid-phase micro-extraction are required. These techniques are time-consuming, complex, and often limit the number of compounds that can be analyzed. In this study, a method was developed for the simultaneous determination of multiple common volatile organic compounds in drinking water using headspace-capillary gas chromatography.
A headspace gas chromatography-hydrogen flame ionization detector (GC-FID) method was successfully applied for the simultaneous detection of 12 volatile organic compounds in drinking water. This approach provided excellent separation and high sensitivity. Compared to the current standard testing method [8], the proposed method offers better separation efficiency, simpler operation, and no need for organic solvents, thus avoiding secondary environmental pollution. It fully meets the requirements of water quality sanitation standards and is suitable for the simultaneous analysis of various trace volatile organic compounds in drinking water.
**1 Materials and Methods**
**1.1 Instruments**
GC-2010 Gas Chromatograph (Shimadzu, Japan); Hydrogen Flame Ionization Detector (FID); TELEDYNE TEKMAR HT3TM Headspace Autosampler System (USA); VIAL LAS Headspace Bottles (USA); AUW220 Analytical Balance (Shimadzu, Japan).
**1.2 Reagents**
Chromatographically pure 1,1,1-trichloroethane, dichloromethane, benzene, trichloroethylene, tetrachloroethylene, toluene, 1,2-dichloroethane, ethylbenzene, p-xylene, m-xylene, o-xylene, styrene, and methanol were obtained from Tianjin Guangfu Fine Chemical Research Institute. Sodium chloride (analytical grade) was dried at 550°C for 2 hours and stored in a desiccator.
**1.3 Test Methods**
**1.3.1 Chromatographic Conditions**
An HP-5 quartz capillary column (30 m × 0.25 mm × 0.25 μm) was used. The temperature program started at 50°C for 8 minutes, then increased to 120°C at 10°C/min, with a total run time of 15 minutes. Carrier gas (nitrogen, 99.999%) flow rate was set at 80 kPa. Hydrogen flow: 40 ml/min; air flow: 400 ml/min; injection port temperature: 200°C; detector temperature: 230°C; split ratio: 1:15.
**1.3.2 Headspace Sampling Conditions**
Furnace temperature: 65°C; quantitative tube temperature: 80°C; transfer line temperature: 80°C. Pressure: transfer line pressure = 80 kPa, headspace bottle pressure = 40 kPa. Time: high-speed oscillation = 2 min; sample equilibration = 10 min; charging time = 110 min; filling time = 110 min; tube balance time = 115 min; injection time = 110 min; injection volume = 110 ml.
**1.3.3 Preparation of the Standard Curve**
Standard stock solutions of 12 compounds were prepared in methanol with concentrations ranging from 6.314 mg/ml to 12.104 mg/ml. The stock solution was diluted 20 times with methanol and then 50 times with pure water to obtain working concentrations between 6.314 μg/ml and 12.104 μg/ml. A mixed standard solution was prepared by combining 10.00 ml of each intermediate solution in a 250 ml volumetric flask. Six series of standard use solutions were prepared according to Table 1. Each solution was injected into a headspace vial containing 4.15 g of sodium chloride, followed by headspace-GC analysis. The retention time was used for qualitative analysis, and peak area vs. concentration was plotted to create the calibration curve.
**1.3.4 Sample Pretreatment**
A 15.10 ml water sample was placed in a headspace vial containing 4.15 g of sodium chloride, rapidly mixed, and analyzed via headspace-GC.
**1.3.5 Sample Determination**
Under optimized chromatographic conditions, the concentrations of 1,1,1-trichloromethane, dichloromethane, benzene, trichloroethylene, tetrachloroethylene, toluene, 1,2-dichloroethane, ethylbenzene, p-xylene, m-xylene, o-xylene, and styrene were quantified using an external standard method based on retention time and peak area.
**2 Results and Discussion**
**2.1 Optimization of Chromatographic Conditions**
Comparative studies were conducted using different capillary columns (HP-5, HP-INNOWAX, DB-1, DB-1701, Rtx-WAX). The HP-5 column provided the best separation performance. With a column temperature program, all 12 compounds were separated within 15 minutes, with good peak shape and resolution.
**2.2 Selection of Headspace Conditions**
**2.2.1 Effect of Equilibrium Temperature**
Equilibrium temperature significantly affects the results. At 65°C, the water vapor content was minimized, leading to stable chromatographic peaks and high sensitivity.
**2.2.2 Effect of Equilibrium Time**
At 65°C, equilibrium time was varied from 5 to 15 minutes. After 10 minutes, the gas-liquid equilibrium was reached, and the peak area stabilized.
**2.2.3 Effect of Sodium Chloride Concentration**
Sodium chloride increases the ionic strength and reduces the solubility of organic compounds. A concentration of 300 g/L was found to be optimal, as further increases did not improve the peak area.
**2.3 Linear Range and Detection Limit**
Under optimized conditions, the linear range of the method was wide, with high correlation coefficients and good sensitivity. The detection limit was calculated as twice the instrument noise, while the quantification limit was 10 times the noise level.
**2.4 Water Sample Analysis and Spike Recovery Test**
The method was applied to 38 tap water and groundwater samples. No detectable levels of the 12 compounds were found. Spiking experiments showed recovery rates between 89.12% and 110.13%, with relative standard deviations (RSD) ranging from 2.14% to 5.17%, meeting the methodological requirements.
**3 Conclusion**
This study successfully established a headspace-GC-FID method for the simultaneous determination of 12 volatile organic compounds in drinking water. The method is simple, sensitive, and environmentally friendly, offering a reliable alternative to traditional techniques. It meets the requirements of water quality sanitation standards and is suitable for the analysis of trace volatile organic compounds in drinking water.
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