1、 Scope:
Determination of trichloromethane and carbon tetrachloride in drinking water and its source water by headspace capillary column gas chromatography;
Determination of trichloromethane and carbon tetrachloride in drinking water and its source water;
The minimum detectable mass concentrations are: trichloromethane 0.2ug/l and carbon tetrachloride 0.1ug/l.
2、 Principle:
The tested water sample is placed in a sealed headspace bottle, and after a period of equilibrium at a certain temperature, trichloromethane and carbon tetrachloride in the water escape to the upper space of the headspace bottle and reach dynamic equilibrium in the gas-liquid phase. At this point, the concentrations of trichloromethane and carbon tetrachloride in the gas phase are proportional to their concentrations in the liquid phase. By measuring trichloromethane and carbon tetrachloride in the gas phase, the concentrations of trichloromethane and carbon tetrachloride in the liquid phase can be calculated.
3、 Reagents and materials:
1. Carrier gas: high-purity nitrogen gas (purity above 99.999%)
2. Pure water: no analyte detected by chromatography
3. Chromatographic standards: Trichloromethane (99.9%) and carbon tetrachloride (99.9%), both of which are chromatographically pure.
4. AHS-20A Plus Fully Automatic Headspace Sampler (Beijing Beifen Third Spectrum)
5. GC-7900 gas chromatograph with ECD detector, capillary split flow non split injection system
6. Chromatography column: HP-5 (30m × 0.32mm × 0.25um) quartz capillary chromatography column
7. Headspace bottle 20ml.
4、 Sample:
1. Stability of the sample: The components to be tested in the sample are prone to volatilization and need to be stored at low temperatures for testing as soon as possible.
2. Sample collection: During sampling, add 0.3g-0.5g ascorbic acid to the headspace bottle, take water to fill the bottle, seal and store at low temperature, and complete the measurement within 24 hours after collection.
3. Sample processing: In a laboratory where there is no chloroform or carbon tetrachloride in the air, transfer the water sample to a 10ml headspace bottle and equilibrate at 60 degrees for 40 minutes.
4. Sample determination: Use AHS-20A plus headspace sampler to extract gas from the upper part of the headspace bottle for injection.
5、 Main conditions of the instrument:
1. GC vaporization chamber temperature: 200 ℃,
2. GC column box temperature: 60 ℃,
3. GC detector temperature: 200 ℃,
4. GC carrier gas flow rate: 2ml/min,
5. GC split ratio: 20:1,
6. GC tail blowing flow rate: 60ml/min,
7. Headspace equilibrium temperature: 60 ℃,
8. Headspace injection valve temperature: 100 ℃,
9. Headspace pipeline temperature: 100 ℃,
10. Headspace equilibration time: 40 minutes,
11. Injection time: 20 seconds
6、 Preparation of standard reserve solution:
1. Trichloromethane: Accurately weigh 0.8008g of trichloromethane (99.9%) and place it in a 100ml volumetric flask containing a small amount of methanol. Make up to the mark, and the solution is ρ (CHCL3)=8.00mg/ml.
2. Carbon tetrachloride: Accurately weigh 0.4004g of carbon tetrachloride (99.9%) and place it in a 100ml volumetric flask containing a small amount of methanol. Make up to the mark, and the solution is ρ (CCL4)=4.00mg/ml.
3. Preparation of mixed standard solution: Add about 100ml of methanol to a 200ml volumetric flask, and then add 1.0ml of each single standard solution of chloroform and carbon tetrachloride separately. Then add methanol to make up to the volume. The mass concentrations of each component in the mixed standard solution are ρ (CHCL3)=40.0ug/ml and ρ (CCL4)=20.0ug/ml
4. Preparation of standard solution: Take 1.0ml of mixed solution standard solution into a 100ml volumetric flask, dilute with pure water, and the mass concentrations of the standard solution are: ρ（CHCL3)=0.40ug/ml，ρ（CCL4)=0.20ug/ml.
5. Preparation of working curve: Take 6 200ml volumetric flasks and add standard solution of 0.10ml, 0.50ml, 1.00ml, 2.00ml, and 5.00ml at once, dilute with water to the mark, and mix well. The mass concentrations of trichloromethane after configuration are: 0, 0.20, 1.0, 2.0, 4.0, 10.0 ug/L, and the mass concentrations of carbon tetrachloride are: 0, 0.1, 0.5, 1.0, 2.0, 5.0 ug/L. Import 6 additional 20ml headspace bottles to the 10ml mark, seal with caps, equilibrate at 60 degrees for 40 minutes, and perform headspace analysis and curve plotting.
Standard diagram: