YSI 9300 Photometer User Manual
Page 133
PHOTOMETER TEST INSTRUCTIONS
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Chromium may be present in certain industrial waste waters, such as those from
the tanning, plating and coating industries. Chromium may occur in hexavalent
form as chromates and dichromates, or in trivalent form as chromium salts. In
water supplies hexavalent chromium is a particularly objectionable constituent.
Trivalent chromium, although relatively inert, is also regarded as undesirable.
The YSI Chromicol test provides a means of measuring chromium over the
range 0 - 1.0 mg/l. The test is particularly useful since it can be used to
differentiate between the concentrations of trivalent (Cr
III
) and hexavalent (Cr
VI
)
chromium present.
Method
In the YSI Chromicol method, hexavalent chromium salts in acidic conditions
react with diphenylcarbazide to give a purple colored complex. This provides a
measure of the hexavalent chromium (Cr
VI
) present in the sample. The reagents
are provided in tablet form and the test is simply carried out by adding tablets
to a sample of the water.
To determine total chromium (Cr
III
) plus (Cr
VI
) a fresh sample of the solution is
oxidised using a powder reagent to convert the trivalent chromium to the
hexavalent form. The test is then repeated to give a measure of the total
soluble chromium content of the water. The difference between the two
readings gives a measure of trivalent chromium
The intensity of color produced in the tests is proportional to the chromium
concentrations and is measured using a YSI Photometer.
Photometer Method
AUTOMATIC
WAVELENGTH
SELECTION
0 – 1.0 mg/l
PHOT.55.AUTO