Water Quality — Determination of TOC by Nondispersive — Infrared Absorption Method
This standard has been redrafted and modified adoption of International Standard ISO 8245-1987 Water Quality — Guidelines for the Determination of Total Organic Carbon (TOC).
1 Subject Content and Application Scope
1.1 This standard specifies the non-dispersive infrared absorption method for the determination of total organic carbon (TOC) in surface water.
1.2 Determination range
This standard is applicable to the determination of total organic carbon in surface water. The concentration range is 0.5 to 60 mg/L and the lower detection limit is 0.5 mg/L.
1.3 Interference
When the common coexisting ions in the surface water exceed the following content (mg/L), there is interference with the determination, and appropriate pretreatment shall be performed to eliminate the interference effect on the determination: SO42- 400; Cl- 400; NO3- 100; PO43- 100; S2- 100. When the water sample contains large particle suspensions, due to the limitation of the pinhole of the water sample syringe, the determination results usually do not include all granular organic carbon.
2 Principle
2.1 Difference method for determination of total organic carbon
The sample together with the purified air (dried and removed carbon dioxide) are respectively introduced into a high temperature combustion tube (900 °C) and a low temperature reaction tube (160 °C), and the water sample of the high temperature combustion tube is subjected to high temperature catalytic oxidation to make the organic compound and inorganic carbonic acid converted into carbon dioxide; and the water sample in the low temperature reaction tube is acidified to decompose the inorganic carbonate into carbon dioxide, and the carbon dioxide formed is sequentially introduced into the non-dispersive infrared detector. Since a certain wavelength of infrared light is selectively absorbed by carbon dioxide, the infrared absorption intensity of carbon dioxide in a certain mass concentration range is proportional to its mass concentration, whereby the total carbon (TC) and inorganic carbon (IC) of the water sample may be quantitatively determined.
The difference between the contents of total carbon and inorganic carbon is that of the total organic carbon.
2.2 Direct method for determination of total organic carbon
The total organic carbon can be directly determined by aerating the water sample after acidification, decomposing the inorganic carbonate to generate carbon dioxide and then injecting it into the high-temperature combustion tube.
3 Reagents
Unless otherwise specified, reagents used are all analytically pure and the water used shall be distilled water without carbon dioxide.
3.1 Distilled water without carbon dioxide: The distilled water is boiled in a beaker (10% evaporation), slightly cooling, and placed in a lower mouth bottle with a soda lime tube.
3.2 Potassium hydrogen phthalate (KHC8H4O4): guaranteed reagent.
3.3 Anhydrous sodium carbonate (Na2CO3): guaranteed reagent.
3.4 Sodium bicarbonate (NaHCO3): guaranteed reagent; stored in a desiccator.
3.5 Organic carbon standard stock solution: c = 400 mg/L.
Weigh potassium hydrogen phthalate (3.2) (previously dried at 110-120 °C for 2 h, placed in a desiccator to cool to room temperature) 0.8 500 g, dissolved it in water (3.1), transferred into a 1 000 mL volumetric flask. Dilute to the scale with water (3.1), mix, and store for 48 days at low temperature (4 °C).
3.6 Organic carbon standard solution: c = 80 mg/L.
Accurately pipette 10.00mL of organic carbon standard solution (3.5) and transfer to a 50 mL volumetric flask, dilute it to the scale with water, and mix well. This solution is prepared immediately before use.
3.7 Inorganic carbon standard stock solution: c = 400 mg/L.
Weigh sodium hydrogencarbonate (3.4) (previously dried in a desiccator) 1.400 g and anhydrous sodium carbonate (3.3) (previously dried at 105 °C for 2 h, placed in a desiccator, cooled to room temperature) 1.770 g, dissolved them in water (3.1), transfer to a 1 000 mL volumetric flask, dilute to the scale with water (3.1), and mix well.
3.8 Inorganic carbon standard solution: c=80 mg/L.
Accurately pipette 10.00mL of inorganic carbon standard solution (3.7) and transfer to a 50 mL volumetric flask, dilute it to the scale with water (3.1), and mix well. This solution is prepared immediately before use.
4 Apparatus
General laboratory apparatus and the following:
4.1 Non-dispersive infrared absorption TOC analyzer. Working conditions:
4.1.1 Ambient temperature: 5 to 35℃.
4.1.2 Working voltage: instrument rated voltage and alternating current.
4.1.3 Total carbon combustion tube temperature selection: 900 °C; inorganic carbon reaction tube temperature control: 160 ± 5 °C.
4.1.4 Carrier gas flow rate: 180 mL/min.
4.2 Single-pen recorder: Matches the instrument. Working conditions:
4.2.1 Working voltage: instrument rated voltage and alternating current.
4.2.2 Recording paper speed: 2.5 mm/min;
4.3 Microinjector: 50.00 μL.
4.4 Colorimetric tube with stopper: 10 mL.
5 Sampling and Samples
After the water sample is collected, it must be stored in a brown glass bottle.
The water sample can be stored for 24 hours at room temperature. If it cannot be analyzed in time, the water sample can be adjusted to pH ≤ 2 by adding sulfuric acid, and stored at 4 °C for 7 days.
1 Subject Content and Application Scope
2 Principle
3 Reagents
4 Apparatus
5 Sampling and Samples
6 Procedures
7 Expression of Analysis Result
Annex A General Explanation of This Standard (Informative)
Additional Explanation:
