The invention provides an automatic analyzing method for trace trivalent
chromium in a
water sample. An analyzing instrument comprising a low-pressure pump, a sample
inlet valve, a mixer, a reactor, an optical circulating tank, an
optical detector, a
computer processing system, a sample flow passage, a pushing liquid flow passage, a
masking agent flow passage, an oxidation liquid flow passage and a developing liquid flow passage is used. The automatic analyzing method includes the following steps that firstly, a
base line is measured; secondly, a
spectrogram of the trivalent
chromium in the sample is measured; thirdly, a working curve is drawn; fourthly, the peak height value of the
spectrogram of the trivalent
chromium in the sample is brought into a regression equation of the working curve, and the concentration of the trivalent chromium, to be measured, in the sample is calculated. Pushing liquid is an HNO3 water solution, a
masking agent is a mixed water solution of
ethylenediaminetetraacetic acid and tween-20, oxidation liquid is mixed liquid of
periodate potassium,
sodium tripolyphosphate, water and a
phosphate buffer, and developing liquid is an
indigo carmine water solution. By means of the automatic analyzing method, the trace trivalent chromium in a
water sample is directly measured, the analyzing operation is simplified, and the analyzing sensitivity is improved.