Total Organic Carbon (TOC) analyzer is a crucial equipment in water quality monitoring, used to accurately determine the total organic carbon content in water samples, and its results directly reflect the degree of organic pollution in water bodies.Widely used for water quality control and compliance testing in industries such as pharmaceuticals, chemicals, environmental protection, and electricity. Standardized measurement steps are the cornerstone of ensuring data accuracy, reproducibility, and instrument stability. This article will systematically explain the standardized measurement process of TOC analyzer.

　　1、 Overview of Measurement Principle

At present, the mainstream TOC analysis adopts high-temperature catalytic oxidation method or ultraviolet persulfate oxidation method. The core principle is to first acidify and remove inorganic carbon (IC) from the water sample or measure it separately, then oxidize organic carbon to generate carbon dioxide, and finally quantitatively calculate the total organic carbon content by detecting the amount of CO2 generated. The determination follows the subtraction method (TOC=TC-IC) or the direct method.

　　2、 Preparation before measurement

1. Instrument preparation:

① Power on preheating: Start the host, detector, and automatic sampler, preheat for at least 30 minutes to achieve thermal and electronic stability of the system.

② Gas source inspection: Confirm that the high-purity oxygen and carrier gas pressure are sufficient, the gas purity should be ≥ 99.995%, and check that there are no leaks in the gas circuit.

③ Reagent preparation: Prepare sufficient acidic reagents, oxidants, and high-performance carbon free consumables.

2. Calibration and Quality Control:

① Standard solution preparation: Accurately prepare carbon standard solutions of different concentrations.

② Draw calibration curve: Follow the instructions of the instrument operating software to sequentially measure the series of standard solutions. The system will automatically generate the calibration curve for TOC/TC/IC, requiring a correlation coefficient (R2) ≥ 0.999.

③ Quality control sample verification: Before sample determination, run a known concentration quality control sample (QC) to ensure that the measurement results are within its tolerance range, in order to verify the reliability of the instrument status.

　　3、 Sample determination steps

1. Sample pretreatment:

① For turbid or particulate matter rich water samples, they need to be filtered through a 0.45 μ m membrane first to prevent blockage of the injection pipeline or contamination of the oxidation reactor.

The sample bottle should be a dedicated carbon free glass bottle, and the TOC value should be measured as soon as possible after sampling to prevent microbial activity from causing changes.

2. Sample injection and measurement:

① Subtraction method (common):

TC measurement: Inject an appropriate amount of sample (usually tens of microliters) into a high-temperature combustion tube (680 ℃ -1200 ℃), and under the action of a catalyst, all carbon (TC) in the sample is oxidized to CO2, which is quantified by an NDIR detector.

IC measurement: Inject another equal amount of sample into the acidification tank, convert inorganic carbon into CO2 by adding acid and blow it away to detect its content. Or directly measure the TOC of acidifiedsample.

② Direct method (NPOC method):

Acid the sample (usually pH<3) and blow with inert gas for 5-10 minutes to remove IC.

Inject the processed sample into the oxidation reactor, and the carbon measured at this time is non blowable organic carbon (NPOC), which can approximately represent TOC in most water samples.

3. Data collection and processing:

① The instrument software automatically collects the peak signal of the NDIR detector and calculates the concentration of TOC in the sample (mg/L) based on the calibration curve.

② Each sample should be measured in parallel at least twice, the average value should be calculated, and the relative deviation (RSD) should be ensured to meet the method requirements (usually<5%).

　　4、 Operation after measurement

1. System cleaning: After the measurement is completed, it is necessary to rinse the injection needle, reactor, and pipeline multiple times with carbon free water (such as ultrapure water) to prevent cross contamination.

2. Shutdown: First turn off the temperature of the heating furnace, wait for it to cool down, and then turn off the gas and main power.

3. Record and report: Detailed record of sample information, instrument conditions, calibration data, measurement results, and any abnormal situations, and issue a formal testing report.

　　5、 Precautions

1. Blank value control: The blank value of carbon free water must be extremely low and stable, which is the key to ensuring the accuracy of low concentration samples.

2. Salt influence: High salt samples may damage catalysts or combustion tubes, and appropriate dilution or selection of high salt resistant models should be made according to instrument requirements.

3. Regular maintenance: Regularly replacing the injection pad, checking catalyst activity, and cleaning the NDIR detection cell are necessary measures to maintain the optimal performance of the instrument.

Following the above standardized steps can ensure that the TOC analyzer provides accurate and reliable data, providing a solid scientific basis for water quality evaluation and process control. Rigorous operation is not only a requirement for laboratory quality management, but also the fundamental guarantee of data value.