GB/T 5750.10-2006Standard examination methods for drinking Water -- Disinfection by-products parameters (English PDF)

5.1 Headspace gas chromatography

5.1.1 Scope

This standard specifies the use of headspace gas chromatography for the

determination of dichloromethane, 1,1-dichloroethane and 1,2-dichloroethane

in drinking water and its source water.

This method applies to the determination of dichloromethane, 1,1-

dichloroethane and 1,2-dichloroethane in drinking water and its source water.

The minimum detection mass concentration of this method. dichloromethane 9

µg/L, 1,1-dichloroethane 8 µg/L, 1,2-dichloroethane 13 µg/L.

Under the operating conditions of this method, other halogenated hydrocarbons

do not interfere.

5.1.2 Principle

In a closed headspace bottle, volatile halogenated hydrocarbon molecules

escape from the liquid phase into the gas in the headspace. At a certain

temperature, the molecules of the halogenated hydrocarbon reach a dynamic

equilibrium between the gas and liquid phases, at this time the concentration of

the halogenated hydrocarbon in the gas phase is proportional to its

concentration in the liquid phase. By measuring the concentration of the

halogenated hydrocarbon in the gas phase, it can calculate the mass

concentration of the halogenated hydrocarbon in the water sample.

5.1.3 Reagents and materials

5.1.3.1 Carrier gas and auxiliary gas

5.1.3.1.1 Carrier gas. High purity nitrogen (99.999%).

5.1.3.1.2 Gas. Pure hydrogen ( > 99.6%).

5.1.3.1.3 Combustion supporting gas. Oil-free compressed air, which is purified

by a purge tube containing 0.5 nm molecular sieves.

5.1.3.2 Reagents for preparing standard samples and reagents

5.1.3.2.1 Pure water (fresh deionized water).

5.1.3.2.2 Chromatographic standards (chromatographically pure).

dichloromethane, 1,1-dichloroethane, 1,2-dichloroethane.

5.1.3.3 Reagents and materials for preparing columns

5.1.3.3.1 Columns and fillings are as shown in the relevant contents of 5.1.4.1.3.

5.1.3.3.2 The solvent used for the coating fixative solution. chloroform + butanol

(1 + 1).

5.1.4 Instruments

5.1.4.1 Gas chromatograph

5.1.4.1.1 Hydrogen flame ionization detector.

5.1.4.1.2 Logger or workstation.

5.1.4.1.3 Column

5.1.6 Analytical procedures

5.1.6.1 Instrument adjustment

5.1.6.1.1 Gasification chamber temperature. 200 °C.

5.1.6.1.2 Column temperature. 85 °C.

5.1.6.1.3 Detector temperature. 200 °C.

5.1.6.1.4 Gas flow. Carrier gas 50 mL/min; hydrogen 52 mL/min; air 700 mL/min.

5.1.6.1.5 Attenuation. ADJUST the recorder attenuation in accordance with the

content of the measured component in the sample.

5.1.6.2 Calibration

5.1.6.2.1 Calibration method in quantitative analysis. external standard method.

5.1.6.2.2 Standard samples

A. Number of uses. Each time the sample is analyzed, USE the new standard

use solution to draw the standard curve or USE the response factor to make

calculation.

B. Preparation of standard samples. TAKE three 10 mL volumetric flasks, ADD

a few milliliters of distilled water, accurately WEIGH it, respectively ADD one

drop of dichloromethane, 1,1-dichloroethane, and 1,2-dichloroethane.

Accurately WEIGH it, the mass increased is the mass of dichloromethane, 1,1-

dichloroethane, and 1,2-dichloroethane. USE pure water to make the volume

reach to the mark. After calculating the content, respectively TAKE appropriate

amount of this solution, DILUTE it to rho (dichloromethane) = 5 µg/mL, rho (1,1-

dichloroethane) = 7.5 µg/mL, rho (1, 2-dichloroethane) = 7.5 µg/mL, PREPARE it

before use.

C. Conditions for use of standard solutions in gas chromatography.

a The standard solution injection volume is the same as the specimen

injection volume. When measured by the single standard method, the

standard solution response value shall be close to the specimen response

value.

b When the relative standard deviation is less than 10% within the working

range, the instrument is considered to be in a stable state.

c Standard samples and specimen are injected for analysis as far as

possible at the same time.

Under selected chromatographic conditions, formaldehyde, propionaldehyde,

acetone, and butyraldehyde do not interfere with the determination.

7.1.2 Principle

Acetaldehyde and acrolein in water can be directly separated and measured by

gas chromatography with a hydrogen flame ionization detector. The peak order

is acrolein and acetaldehyde.

7.1.3 Reagents and materials

7.1.3.1 Carrier gas and auxiliary gas

7.1.3.1.1 Carrier gas. High purity nitrogen (99.999%).

7.1.3.1.2 Combustion gas. Pure hydrogen ( > 99.6%).

7.1.3.1.3 Combustion supporting gas. Oil-free compressed air, which is purified

by a purge tube fitted with a 0.5 nm molecular sieve.

7.1.3.2 Reagents for preparing standard samples and specimen

pretreatments

7.1.3.2.1 Sodium bisulfite solution [c(NaHSO3) = 0.05 mol/L]

7.1.3.2.2 Iodine standard solution [c (1/2 I2) = 0.10 mol/L], to be calibrated.

7.1.3.2.3 Sodium thiosulfate standard solution [c (Na2S2O3) = 0.10 mol/L], to be

calibrated.

7.1.3.2.4 Starch solution (5 g/L).

7.1.3.2.5 Sulfuric acid solution (1 + 1).

7.1.3.2.6 Standard. Acrolein and acetaldehyde solution [omega(CH3CHO) = 40%].

7.1.3.3 Reagents and materials for preparing columns

7.1.3.3.1 Columns and fills are described in 7.1.4.1.3.

7.1.3.3.2 Solvent used for coating fixative. dichloromethane.

7.1.4 Instruments

7.1.4.1 Gas chromatograph

7.1.4.1.1 Hydrogen flame ionization detector.

7.1.4.1.2 Logger or workstation.

DRY it naturally, PREPARE for use.

8.1.4.5 PTFE membrane or aluminum foil.

8.1.4.6 Constant temperature water bath. Control temperature ± 1 °C.

8.1.5 Samples

8.1.5.1 Sampling method and storage method. TAKE two headspace bottles

containing 0.1 g of sodium thiosulfate to the site, FILL it with water samples,

immediately USE overturn rubber plugs which are wrapped with aluminum foil

(or PTFE membrane) to seal it, BRING it back to the laboratory. If it cannot be

determined immediately, it must be kept in the refrigerator.

8.1.5.2 Water sample pretreatment. After the water sample is sent to the

laboratory, POUR some water sample in the environment without chloroform to

make the water sample in the bottle to 50 mL mark, immediately COVER the

bottle stopper. PLACE one bottle directly in a constant temperature water bath

at 40 °C as the bottle l, USE the injection needle to inject 0.2 mL of sodium

hydroxide solution (8.1.3.2.2) into another bottle, SHAKE it uniformly, PLACE it

into a constant temperature water bath at 40 °C as a bottle II, both of which are

equilibrated in a 40 °C water bath for 2.5 h.

8.1.6 Analytical procedures

8.1.6.1 Instrument adjustment

8.1.6.1.1 Gasification chamber temperature. 200 °C.

8.1.6.1.2 Column chamber temperature. 150 °C.

8.1.6.1.3 Detector temperature. 250 °C.

8.1.6.1.4 Carrier gas flow. 80 mL/min.

8.1.6.2 Calibration

8.1.6.2.1 Calibration method in quantitative analysis. external standard method.

8.1.6.2.2 Standard samples

A. Number of uses. Each time the sample is analyzed, USE the newly prepared

standard use solution.

B. Preparation of standard samples

a. Preparation of standard stock s...

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