The formaldehyde detector in water is an important tool for evaluating the degree of water pollution, widely used in environmental monitoring, industrial production, and public health fields. The precision of its operation directly affects the reliability of the detection results. The following will analyze the usage details from the key links:
1、 Preparation and Sampling Standards in the Initial Stage
1. Instrument pretreatment
All containers (colorimetric tubes, pipette tips) that come into contact with the sample must be soaked in chromic acid solution and rinsed with pure water at least 3 times to avoid interference from residual organic matter. It is recommended to prepare blank control samples 24 hours in advance to verify the purity of the reagents.
2. Key points for water sample collection
-When sampling surface water, floating objects on the water surface should be avoided, and when using submersible pumps to extract deep water samples, coarse particles and impurities should be filtered out;
-Industrial wastewater sampling should select representative time periods based on the production cycle, and label the sampling point location, temperature, and pH value;
-If the water sample contains a lot of suspended solids, it needs to be filtered through a 0.45 μ m filter membrane, otherwise it will block the optical path of the colorimetric cell.
2、 Core steps of detection operation
1. Accurate addition of reagents
Strictly follow the instructions to add color reagents (such as acetylacetone) in proportion, and use a micropipette to control the error<1%. The order of dropwise addition should not be reversed, especially when adding buffer solution to the reaction system under acidic conditions.
2. Constant temperature color control
Place the mixed sample in a constant temperature water bath (60 ± 1 ℃) and let it stand for color development, with a time error controlled within ± 30 seconds. During this period, avoid strong light exposure to prevent photolysis reactions from occurring.
3. Instrument calibration and reading
-After preheating for 10 minutes, first perform zero point calibration with standard solution, and then measure the blank sample and the test sample in sequence;
-Digital instruments need to wait for the reading to stabilize (fluctuation<0.01mg/L), while analog pointer instruments should look up at the scale line to avoid parallax;
-Each batch of samples needs to be calibrated repeatedly before and after testing to eliminate systematic errors caused by electrode drift.
3、 Key precautions
1. Exclusion of interference factors
-Water samples with residual chlorine>0.1mg/L need to be pre treated with ascorbic acid for dechlorination, otherwise false positives may occur;
-High concentrations of aromatic hydrocarbons can cause an abnormal increase in absorbance, which can be pretreated using activated carbon adsorption columns;
-Avoid directly detecting volatile samples in the fume hood to prevent gas from escaping and changing the liquid phase concentration.
2. Safety protection measures
Operators must wear nitrile gloves and goggles, and the experimental platform should be equipped with anti-corrosion pads. Waste reagents should be classified and collected, and direct discharge without treatment is strictly prohibited.
4、 Data processing and equipment maintenance
1. Parallel sample analysis
At least 3 sets of parallel measurements should be conducted for each water sample, with a relative deviation of less than 5%. If the deviation is exceeded, retesting is required. The raw data record includes information such as sampling time, instrument number, environmental temperature and humidity.
2. Key points of daily maintenance
-Rinse the colorimetric cell with deionized water after daily testing, and wipe the optical lenses with anhydrous ethanol every week;
-When not in use for a long time, remove the battery and store it in a dryer. Perform a self check once a month when powered on;
-Send to the metrology department annually for photometric calibration and replacement of aging photosensitive components.