GB5750.8-2023 Analysis of 11 Volatile Organic Compounds in Drinking Water Headspace &GC

Abstract

Based on the automatic headspace sampler HS-25 developed by Panyu and the 1949 gas chromatograph, 11 haloalkane are analyzed in this paper. With FID detector, linearity, detection limit and spiked recovery rate meet relevant requirements. The establishment of standard curves and validation of methods are described in detail below. 

Introduction

Drinking water is closely related to each of us. The new revised version of drinking water standard "GB 5749-2022 Hygienic Standard for drinking Water" was officially released on March 15, 2022, and the standard will be officially implemented on April 1, 2023.The inspection standard GB/T 5750, which is compatible with GB 5749 standard, is also being revised.The newly revised "GB/T 5750.8 -2023 standard test method for drinking water Part 8: Organic Indicators" includes 5 conventional indicators, 21 extended indicators and 4 appendix indicators related to VOC in GB 5749-2022 standard.

According to comparison, 27 kinds of halogenated hydrocarbons were determined by Headspace Sampler + capillary column (DB-1701) +ECD, and 11 kinds of volatile organic compounds were determined by Headspace Sampler+ capillary column (DB-WAX) +FID. The combination of these two solutions can cover the analysis of organic matter in conventional projects and most organic matter in extended projects.

This article uses the Panyu headspace sampler HS-25 and the Panno gas chromatograph 1949 (equipped with a split and non split injection port and a hydrogen flame ionization detector) to analyze dichloromethane, benzene, toluene, 1,2-dichloroethane, ethylbenzene, p-xylene, m-xylene, isopropyl benzene, o-xylene, in accordance with the "GB/T 5750.8-2023 Standard Test Methods for Drinking Water Part 8: Organic Matter Indicators" Chlorobenzene and styrene are 11 volatile organic compounds.

Method principle 

Place the sample in a sealed headspace vial, and at a certain temperature and pressure, the volatile components of the sample in the headspace vial evaporate into the liquid space, generating vapor pressure. The gas-liquid phase reaches thermodynamic dynamic equilibrium, and within a certain concentration range, the concentration of the substance to be tested in the gas phase is directly proportional to the concentration in the water phase. Quantitative extraction of the gas phase was performed using a gas chromatograph for separation, followed by detection by a hydrogen flame ionization detector. Qualitative analysis was performed based on retention time, and the standard curve external standard method was used for quantification. 

Instruments and reagents

Gas chromatograph: PANNA 1949 gas chromatograph with FID detector 

Chromatographic column: - wax capillary column 30m × 0.32mm × 0.25 µ m 

Headspace device: Fully automatic headspace sampler HS-25 (Changzhou Panyu Instrument Co., Ltd.) 

Single standard and its concentration: 

Analysis steps 

1. Analysis conditions:

Headspace: Heating balance temperature of 80 ℃, valve/quantitative ring temperature of 90 ℃, transmission line of 150 ℃, heating balance time of 30 minutes, injection time of 1 minute, pressurization pressure of 15 psi, quantitative pressure of 2 psi, low flow blowing of 50ml/min before injection, high flow blowing of 200ml/min after injection, blowing time of 1 minute, sample disk oscillation level of 0.

Gas chromatography:

Chromatographic column DB-wax column 30m * 0.32mm * 0.25 μ M; Injection port 250 ℃, constant flow 1ml/min. The initial temperature of the column box is 40 ℃, maintained for 5 minutes, increased from 5 ℃/min to 45 ℃, maintained for 1 minute, increased from 15 ℃/min to 90 ℃, maintained for 2 minutes, and increased from 100 ℃/min to 150 ℃, maintained for 2 minutes. Split injection, split ratio 5:1, detector 250 ℃, hydrogen 30ml/min, air 300ml/min, tail blowing 25ml/min.

2. Calibration curve drawing: 

The original solution consists of 9 benzene series compounds such as 1000mg/L benzene and toluene, 2000mg/L dichloromethane, and 5000mg/L 1,2-dichloroethane.

Prepare 10ml of 50mg/L benzene series, 40mg/L dichloromethane and 1,2-dichloroethane, and 20mg/L styrene intermediate solution from the original solution (take 500ul of 1000mg/L benzene series, 1000ul of 2000mg/L dichloromethane, and 400ul of 5000mg/L 1,2-dichloroethane to prepare 1000mg/L styrene).

Then take 1ml of intermediate solution and put it into a 100ml volumetric flask to prepare eight benzene series of 100ug/L, dichloromethane and 1,2-dichloroethane of 400ug/L, and styrene standard liquid of 200ug/L. 

Take 6 20ml headspace vials and fill them with 3.7g of NaCl:

vial 1: Take 0.5ml of standard liquid and 9.5ml of pure water and put them into a headspace vial. Seal with a capper and gently shake well for testing. 

vial 2: Take 1ml of standard liquid and 9ml of pure water and put them into a headspace vial. Seal with a capper and gently shake well for testing. 

vial 3: Take 2ml of standard liquid and 8ml of pure water and put them into a headspace vial. Seal with a capper and gently shake well for testing.

vial 4: Take 4ml of standard liquid+6ml of pure water and put it into a headspace vial. Seal with a capper and gently shake well for testing. 

vial 5: Take 6ml of standard liquid and 4ml of pure water and put them into a headspace vial. Seal with a capper and gently shake well for testing. 

vial 6: Take 8ml of standard liquid and 2ml of pure water and put them into a headspace vial. Seal with a capper and gently shake well for testing.

The specific concentrations of the six configured concentrations are shown in the table below: 

Place 6 concentrations of samples into the instrument and measure them according to the aforementioned analysis conditions. The typical spectra of 11 benzene series compounds are shown in Figure 1: 

Figure 1 Typical spectra of 11 volatile substances 

Repeatability spectrum: 

The repeatability spectrum (n=6) of benzene series compounds is within 3%, except for dichloromethane. 

Figure 4 Repeatability Spectrum of 40ug/ml