Talk about the principle of measuring water quality hexavalent chromium by spectrophotometry

Chromium usually exists in water polluted by industrial wastewater such as electroplating, smelting, tanning, textiles, and pharmaceuticals. Chromium usually exists in water in the form of trivalent and hexavalent, hexavalent chromium is more toxic than trivalent chromium, and has carcinogenic hazards. Therefore, my country stipulates that the content of hexavalent chromium in drinking water shall not exceed 0.05mg/L. The specific parameters of chromium in water quality can be detected by spectrophotometry. The principle is as follows: diphenylcarbazide (DPCI) is often used as a color developer when spectrophotometric determination of hexavalent chromium is used. Under slightly acidic conditions (1.0mol/LH2SO), a purple-red complex is formed. Its color depth is proportional to the content of hexavalent chromium, and its maximum absorption wavelength is 540nm. The content of hexavalent chromium can be measured by the standard curve method or related water quality testing instruments. The water quality hexavalent chromium analyzer is developed and designed based on the certification method - GB7467-87 'Determination of water quality hexavalent chromium diphenylcarbohydrazide spectrophotometric method'. The color developer directly reacts with hexavalent chromium to form a purple complex The absorbance is measured by spectrophotometry through imported cold light source and narrow-band interference technology, and the hexavalent chromium content is directly displayed after being processed and calculated by the microcomputer chip, expressed in units of mg/L. The instrument is compact in design, equipped with finished reagents, fast in detection, and simple in operation. It is widely used in emergency monitoring, sewage treatment, chemical, pharmaceutical, hospital wastewater, food, printing and dyeing industries, etc. Wastewater detection.