EM Quant® Cobalt Test, Catalog No. 10002
Test strips and reagent for the detection
and semi-quantitative determination of cobalt(II) ions
General
Interesting applications for the cobalt rapid
test are to be found in the testing of waste water, electroplating
baths, in the electronics industry, metal industry, in the assaying
and refining of ores, and for checking pigments and other colorants in
the glass and ceramic industries.
Principle of the Determination
The test is based on the formation of a complex
between cobalt(II) and thiocyanate ions which displays a brilliant
blue color in the presence of a high molecular ether. As the reaction
zone contains a buffer, the complexing reaction is not influenced by
the hydrogen ion concentration of the solution between pH 1 and pH 7.
Even in highly acidic solutions (pH 0 to 1) there is only a very
slight color shift to green.
Graduation
0 - 10 - 30 - 100 - 300 - 1000mg/l (ppm) Co2+
Directions
- Immerse a test strip in the solution for 1
second so that the reaction zone is thoroughly wetted.
- Remove the test strip, gently shake to
remove excess liquid, wait 15 seconds and compare the reaction zone
with the color scale.
Notes
The pH of the sample solution should be between
1 and 7. Alkaline solutions must be buffered with sulfuric acid.
Detection is normally disturbed by iron(III) ions, which produce a
blood-red thiocyanate complex, and by copper ions, which produce a
green to brown color. The reaction zone of the strip contains a
special masking agent to suppress these interfering secondary
reactions. This makes the test so selective that as little as 10mg/l
of cobalt(II) can still be detected in the presence of 7500mg/l of
copper(II) and 5000mg/l of iron(III).
Influence of Anions
There is no interference at less than:
| 1000mg/l |
Br, BrO3,
Cl, ClO3, ClO4,
F, I, IO3,
IO4, MnO4
Mo7O246, N3,
NO3, OCN, PO43,
SCN, SO32, SO42,
S2O32, S2O42,
S2O52, S2O82+,
SeO32, WO42,
acetate, ascorbate, citrate, oxalate, succinate or tartrate. |
| 250mg/l |
NO2 |
| CN,
[Fe(CN)6]3 form complexes with Co2+ |
Influence of Cations
There is no interference at less than:
| 1000mg/l |
Ag+, Al3+,
Au3+, Ba2+, Be2+, Bi3+,
Ca2+, Cd2+, Ce4+, Cr3+,
Cu2+, Fe2+, Fe3+, K+,
Li+, Mg2+, NH4+, Na+,
Ni2+, Pb2+, Rb+, Sb3+,
Sn2+, Sr2+, ,Ti4+, VO2+,
Zn2+, Zr4+ |
| 500mg/l |
Mo2+/5+ |
| 300mg/l |
Hg+ |
Elimination of Interference
NO2 interferes by
producing a pink tint (eliminate by adding amidosulfuric acid until
effervescence ceases).
CrO42 and VO32
interfere due to their intrinsic colors (eliminate by adding 1
spatula-tip of ascorbic acid).
If the color of the reaction zone gradually changes to orange, interference
by more than 1000mg/l SeO32 is indicated;
in this event record the value within 30 seconds.
CN, [Fe(CN)6]3
form complexes with Co2+ which can be destroyed in the
usual manner by fuming off with concentrated sulfuric acid.
Interference by cations can be prevented by
masking (see table below).
Add 1 spatula-tip of the specified masking agent
to 5ml sample solution, shake and then test for cobalt(II) ions with
a test strip.
| Color |
In the presence of |
Mask with |
| Brown |
5000mg/l Fe3+ |
potassium
fluoride |
| Brown |
7500mg/l Cu2+ |
sodium thiosulfate |
| Green |
2000mg/l Bi3+ |
potassium fluoride |
| Pink/orange |
500mg/l Mo2+/5+ |
potassium permanganate* |
| Gray |
300mg/l Hg+ |
sodium chloride |
*Add KMnO4 crystals until the pink
color persists.
Standard (1000 mg/l)
Cobalt standard solution, 500ml.
Package Size
10002 EM Quant® Cobalt Test
Cobalt Test for 100 determinations, strips and reagents included.
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