EM Quant® Chromate Test, Catalog No. 10012
Test strips and reagent for the detection
and semi-quantitative determination of chromate ions
General
The Chromate Test can be used to monitor waste
water discharged from electroplating and pickling plants, tanneries,
etc. and for rapidly and reliably determining chromium salts in many
industrial processes.
In gravure printing, the Chromate Test can be
used to check chromate concentrations in chroming and sensitizing
baths to allow optimum values to be maintained. In tanning baths a
protective layer of foam prevents the formation of chromate-containing
alcohols, which are a hazard to health. The effectiveness of this
protective foam layer can be checked with the Chromate Test.
It can also be employed to conjunction with the EM Quant®
Nickel Test as a means of rapidly identifying various grades of steel
(see Nickel Test).
The Chromate Test may also be used to determine
chromium (III) ions, provided that these are oxidized with sodium
peroxide or potassium peroxydisulfate, as described under "Note."
Principle of the Method
The basis of the test is a redox reaction
between chromate ions and diphenylcarbazide. In an acidic solution,
chromate ions oxidize diphenylcarbazide to diphenylcarbazone and this
in turn to diphenylcarbadiazone. Chromium(III) ions thus formed react
with the enol form of diphenylcarbazone to produce a red-violet
complex.
Graduation
0 - 3 - 10 - 30 - 100mg/l (ppm) CrO42-
Directions
- Rinse the measuring vessel several times with some of the sample
and fill to the 5ml mark.
- Add reagent (25% sulfuric acid) dropwise to
bring the pH to below 1 (check the pH with pH indicator strips, for
instance).
- Immerse the reaction zone in the solution
for 1 second, remove excess liquid by stroking the edge of the strip
against the rim of the vessel, wait 15 seconds and compare the
reaction zone with the color scale.
Note
Cr3+ ions can also be determined
with the chromate (Cr6+) test if they are oxidized to
chromate by the following method:
Add 1 spatula-tip of sodium peroxide or potassium peroxydisulfate to 5ml
of solution (pH 5), boil for 5-10 minutes, adjust to below pH 1 with 25%
sulfuric acid and make up to ml with water.
1mg/l CrO42- = 0.45mg/l Cr3+ =
1.31mg/l Cr203
Safety Precautions
Keep the reagent (25% sulfuric acid) away from
the skin. In the event of contact, rinse well immediately with plenty
of water. Seek immediate medical attention of substance enters the
eye.
Influence of Anions
The determination is not disturbed by less than
1000mg/l Br-, BrO3-, Cl-,
ClO3-, ClO4-, CN-,
F-, I-, N3-, NO2-,
NO3-, OCN- , PO43-,
SCN- , SeO32- , SO42-,
S2O82-, WO42-,
acetate, citrate, oxalate, succinate or tartrate. [Fe(CN)6]4-,
S2-, SO32-, S2O42-,
S2O52- and ascorbate reduce CrO4O2-
to Cr3+ (see Note).
Interfering colorations are produced by more than
10mg/l IO3- or IO4-
(pink to brown)
10mg/l MnO4- (gray-pink)
5mg/l VO3- (brown to ruby colored)
25mg/l molydbdate (pink to violet)
50mg/l [Fe(CN)6]3- (gray to grayish-pink)
Influence of Cations
The determination is not disturbed by less than
1000mg/l Ag+, Al3+, Ba2+, Be2+,
Ca2+, Cd2+, Ce3+, Co2+,
Cr3+, Mg2+, Mn2+, Ni2+,
Ni2+, Rb+, Sr2+, Ti4+,
Ti+, Zn2+, or Zr4+
As3+, Fe2+, Sb3+,
Sn2+, VO2+ and molybdenum blue reduce CrO42-
to Cr3+.
Sparingly soluble lead chromate is formed in the presence of Pb2+;
therefore, less or no chromate is detected.
More than 10mg/l Au3+; 100 mg/l Bi3+,
Ce4+ or Cu2+; 25 mg/l Fe3+ colors
the paper pink or brown.
More than 25mg/l Hg+ or 100mg/l Hg2+
colors the paper blue.
Molybdenum blue interferes with the test due to its intrinsic color.
Elimination of Interference
Proceed as follows with 5ml of the solution to be tested:
IO3-, IO4-: adjust to pH 0-1
with 25% hydrochloric acid, add 1 spatula tip of Titriplex® III and
shake well.
Molybdate: adjust to pH 0-1 with 25%
hydrochloric acid, add 1 spatula-tip of oxalic acid and shake well.
MnO4-: adjust to pH 0-1
with 25% sulfuric acid and heat to boiling with a few grains of sodium
azide. Test for chromate immediately after the solution decolorizes.
[Fe(CN)6]3-: adjust to
pH 8-9 with 32% sodium hydroxide solution or 25% sulfuric acid, add 1
spatula-tip of zinc sulfate, shake well, filter, adjust to below pH 1
with 25% sulfuric acid and measure.
Au3+: add 1 spatula-tip of potassium
cyanide, shake and adjust the pH to below 1 with 25% hydrochloric acid
(in a fume cupboard).
Bi3+: add 1 spatula-tip of Titriplex®III and shake.
Cu2+: fill a glass tube with a diameter of 8-10mm with 2g dry
Amberlite® IR-2120 ion exchanger and allow the strong mineral
acid solution (pH ~0) to run through dropwise (1 drop/second).
Fe3+: add 20% sodium hydroxide
solution until the pH is at least 9, filter and then adjust the pH to
below 1 with 25% hydrochloric acid.
Hg+, Hg2+: add 1
spatula-tip of sodium chloride and filter if necessary.
Ce4+: add 1 spatula-tip of potassium
fluoride and filter. Check the pH; if necessary, adjust to below 1
with 25% sulfuric acid.
In the presence of As3+, Sb3+,
Sn2+, S2-, SO32-, S2O42-,
S2O32- or ascorbate,acidify
strongly with 25% sulfuric acid (pH~0), add a few crystals of
potassium permanganate and boil for approximately 1 minute. Decolorize
the hot solution by adding a little sodium azide and shaking. Adjust
the pH to less than 1 with 25% sulfuric acid and test immediately for
chromate.
Standard (1000 mg/l)
19780 Chromate Standard Solutions, 500ml
Package Size
10012 EM Quant® Chromate Test
Chromate Test for 100 determinations; test
strips and reagents included.
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MSDS
(Material Safety Data Sheet)
