Analysis of total organic carbon in domestic drinking water

author: Otis，cily

2023-01-03

The comprehensive index of organic matter pollution in the domestic and drinking water monitoring project provides a scientific basis for protecting water sources, controlling pollution and improving water quality, and ensuring the health of people's drinking water. At present, it is no longer a technical problem to realize the detection of TOC content in drinking water through TOC analysis technology, but it is the goal that many departments pursue to transform the test in offline scenarios to online monitoring. After the release of the GB 5749-2006 version, China has revised the latest version of the Drinking Water Sanitation Standard again for 16 years. Water quality indicators were adjusted from 106 in version 06 to 97, and water quality reference standards were adjusted from 28 to 55. Total organic carbon is used as the reference index of drinking water quality, and the reference limit is 5mg / L in GB 5749-2022 Sanitary Standard for Drinking Water. In this experiment, the Optosky TOC-3000 total organic carbon analyzer was used as an analytical instrument to conduct the TOC analysis in domestic drinking water. TOC-3000 is an off-line detection equipment based on the digestion principle of ultraviolet persulfate oxidation method. It is mainly used in the detection of total organic carbon in surface water, groundwater, tap water, industrial sewage and other water bodies.

Experimental part

Instruments and reagents
1. Instrument: Optosky TOC-3000 total organic carbon analyzer

1.2 Reagent:
Potassium hydrogen phthalate (reference reagent)
Sodium persulfate (grade pure)
Phosphoric acid (grade pure)
Decarbon 2 distilled water (blank)

empirical method

2.1 Allocation of the standard solution
2.1.1 Standard solution configuration of organic carbon
2.1.1.1 Organic carbon (TOC) standard storage solution: (ρ TOC = 1000 mg/L) Accurately weigh potassium hydrogen phthalate (predried at 110℃ ~120℃ to constant weight) 2.1255 g, place in a beaker, dissolve in pure water, transfer the solution to a 1000 mL volumetric flask, dilute to the line with pure water, and mix well.
2.1.1.2 Inorganic carbon (TIC) standard storage solution: (ρ TIC = 1000 mg/L) accurately weigh the anhydrous sodium carbonate (dried at 105℃ to constant weight) 4.4085 g and sodium bicarbonate (dried in dryer) 3.5000 g, place in a beaker, dissolve in pure water, transfer the solution to 1000 mL volumetric flask, dilute with pure water to the line, mix well.
2.1.1.3 Total carbon standard use solution: (ρ TC = 100 mg/L, ρ T IC = 50 mg/L) to absorb 10.00 mL of inorganic carbon standard storage solution (2.1.1.2) and organic carbon standard storage solution (2.1.1.1) in 200 mL volumetric bottles, dilute to the marking line with pure water, and mix well.
2.1.1.4 Inorganic carbon standard use solution: (ρ TIC = 50 mg/L), respectively absorb 10.00 mL of inorganic carbon standard storage solution (2.1.1.2) into a 200 mL volumetric bottle, dilute to the marking line with pure water, and mix well..1.
2.2 Drawing of the standard curve
2.2.1 The organic carbon concentration is 0.0, 1.0, 2.0, 5.0, 10.0, 20.0, 50.0mg/L standard solution series, using the sample with different concentrations of the same volume, drawing the sample with the carbon mass as the abscissa and the integrated area signal as the ordinate to draw the calibration curve;
2.2.2 Prepare the inorganic carbon concentration as 0.0, 0.5, 1.0, 2.5, 5.0, 10.0, 25.0mg/L standard solution series, adopt the sample with different concentrations of the same volume, take the mass of carbon as the abscissa, and take the integrated area signal as the ordinate to draw the calibration curve;
3. Sample test
Select the difference subtraction test mode and test the blank page, standard point and sample successively.

Table 1 Results of TOC determination of 3 samples

Sample name	order number	TC mg/L	mean mg/L	TIC mg/L	mean mg/L	TOC mg/L
Sample No. 1	1	3.38	3.28	2.37	2.41	0.87
	2	3.27		2.43
	3	3.19		2.44
Sample No. 2	1	1.59	1.56	1.32	1.31	0.25
	2	1.56		1.33
	3	1.53		1.27
Sample No. 3	1	1.88	1.88	1.15	1.17	0.71
	2	1.88		1.17
	3	1.87		1.19

As can be seen from the results in Table 1, each of the three drinking water samples collected has undergone three parallel tests, and the TOC content of samples 1-3 is 0.87mg/L, 0.25mg/L, 0.71mg/L respectively, which is lower than the TOC limit requirements in GB 5749-2022. Whether to meet the drinkable standard requires comprehensive consideration of other indicators. TOC-3000 total organic carbon analyzer is not used in the detection process, with fast detection speed and sensitive response. The automatic sampler can realize the efficient analysis of the total organic carbon in drinking water.

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