Cobalt thiocyanate test

Scott s test (cobalt thiocyanate test Ruybal test) A presumptive test for cocaine. Scott s reagent has an initial solution of 2% cobalt thiocyanate (Co(SCN)2) in glycerine and water. This is followed by concentrated hydrochloric acid, and then chloroform. A positive test is indicated by a blue colour in the chloroform layer. 

Key to the current discussion is the ability of transition metab to form charged complexes. As charged and relatively stable entities, complex ions can act as cations or anions and form coordination compounds or tightly associated ion pairs. These ion pairs may be solids, or they may form stable neutral species that can be extracted into an organic solvent such as chloroform. Thb b indeed the basb of the cobalt thiocyanate test for cocaine, in which a pink solution of aqueous cobalt thiocyanate is added, along with hydrochloric acid, to the unknown powder. If cocaine or a related substance, such as procaine, b present, a blue color results. In one modification of the test, thb blue ion pair b extracted into a chloroform layer as further evidence for the formation of a tightly associated ion pair. ... 

Figure 7.24 An acidic solution is required for the cobalt thiocyanate test, since the cocaine must be soluble.

Source Deakin, A. L. "A Study of Acids Used for the Acidified Cobalt Thiocyanate Test for Cocaine Base." Microgram Journal, 1 2003,40-44. 

Cocaine drug testing kits either manufactured for law enforcement purposes or produced by the underground. These testing kits are simply presumptive color tests. The basic color test used for cocaine is cobalt thiocyanate. The cocaine or any of the other substances from the caine family will form a brilliant blue flaky precipitate in the cobalt thiocyanate. This is an indication that the product is cocaine, procaine, tetracaine, etc. In order to determine whether there is actually any cocaine and not all procaine, stannous chloride is added to the precipitate causing all of the caines except cocaine to dissolve. 

The apparatus used is the same as that adopted by Conway et al(13). The test was conducted over long periods at higher concentration of surfactants than in any previous studies. In the test, biodegradation was followed by measuring COD(Cr), COD(Mn), cobalt thiocyanate active substances (CTAS) and TOC(Figure 16). 

Colorimetric Methods have frequently been suggested,1 but of these, that originated by Skey and studied by several others 2 appears to be the most useful. It hinges on the fact that potassium thiocyanate yields a blue colour with solutions of cobalt salts, due to the formation of cobalt thiocyanate. On adding alcohol and ether to the liquid, a blue layer is produced. This is destroyed by mercuric chloride, sodium acetate, or sodium thiosulphate, and is masked by the presence of iron salts in consequence of the intense red colour of ferric thiocyanate consequently these substances should not be present when the colorimetric test is applied. 

Ammonium thiocyanate test (Vogel reaction) adding a few crystals of ammonium thiocyanate to a neutral or acid solution of cobalt(II) a blue colour appears owing to the formation of tetrathiocyanatocobaltate(II) ions ... 

Cobalt(II) thiocyanate test to the test solution add an equal volume of the reagent (about 10%, freshly prepared), and stir the wall of the vessel with a glass rod. A deep-blue crystalline precipitate of cobalt tetrathio-cyanatomercurate(II) is formed ... 

Analytical chemists have developed simple chemical tests that can identify the presence of illegal drugs within seconds. Law enforcement officers routinely use these when they are unsure whether someone is in possession of an illegal narcotic. A common field test for cocaine, for example, uses a cobalt thiocyanate complex that turns blue in the presence of cocaine. 

Transition Metal Complexes Related to the Simon test is a family of color-producing reactions based on transition metal complexes (coordination complexes) and tightly associated ion pairs. Coordination complexes arise from a Lewis acid-base interaction between a metal cation, such as cobalt, and an atom with unshared electrons, such as water or, in the case of drugs, basic nitrogen found in alkaloids and amines. Metals that have been used in these reagents include copper, vanadium, bismuth, and cobalt Cobalt, as part of two common reagents (cobalt thiocyanate and Dilli-Koppanyi) is perhaps the most versatile. Cobalt has an electron structure of 3d 4s, while ttie cation has a 3d (2 ) or 3d (3 ") structure. 

Cobalt thiocyanate A reagent used for a color test for cocaine and related tropane alkaloids. 

The thiocyanate ion SCN forms an intensely red-coloured complex (most simply represented as [Fe(SCN)(H20)5] ) which is a test for iron(III). However, unlike cobalt(III), iron(lll) does not form stable hexammines in aqueous solution, although salts containing the ion [FefNHj) ] can be obtained by dissolving anhydrous iron(III) salts in liquid ammonia. 

The formation of the blue complex cobalt salt serves as a sensitive test for the detection of either cobaltous or mercuric ions with a sensitivity of ly Co or lOy of Hg in solution. Depending on the cation to be tested for, the test reagent consists of a concentrated solution of either mercuric chloride or cobaltous acetate containing alkali thiocyanate. The test may be carried out in one drop of liquid on a slide under a microscope (50-100X). Agitation of the drop with... 

In dicyanocobalt(III) a,b,c,d,e,g-hexamethyl-f-stearylamide cobyrinate (derivative 3) the six peripheral amide groups of vitamin B12 have been replaced with methyl ester groups, and the proximal base of the vitamin at the f-position with a stearylamide group (11). Electrodes prepared with this ionophore and DOS as the plasticizer were also selective for thiocyanate and nitrite over the rest of the anions tested. The main anionic interferent was salicylate. In all cases, the response of the electrodes to the preferred anions was sub-Nemstian. Overall, the selectivity pattern obtained with ionophore 3 is similar to that of 2 and to that of the hydrophobic cobyrinate-based electrodes reported previously (5, 12, 13). This observation suggests that in all cobyrinate ionophores the anions interact with the cobalt(III) center, and that the side chains of the corrin ring have a small effect on the selectivity of this interaction. 

In carrying out the test a small quantity of standard cobalt sulphate solution is taken, and acidulated with dilute sulphuric acid. Ammonium thiocyanate is then added and the volume of the liquid made up to 10 c.c. A mixture of alcohol and ether is now added until the total bulk is 20 c.c. and the blue colour of the supernatant ethereal layer is compared with that from a solution of the liquid to be tested, and which has been treated in a precisely similar manner.3... 

Drop test Place a drop of the test solution on a spot plate, add a small crystal of ammonium thiocyanate followed by a little solid cobalt(II) acetate. A blue colour is produced in the presence of mercury(II) ions. 

The spot-test technique is as follows. Mix a drop of the test solution in a micro crucible with a very small drop (0-02 ml) of 0-5m solution of cobalt nitrate and evaporate to dryness. The residue, whether thiocyanate is present or not, is... 

Thiocyanate, (i) Iron(III) chloride solution test colour discharged by HgCl2 solution or by NaF solution, but not by dilute HC1 (IV.10,6). (ii) Cobalt nitrate solution test (IV.10, 9). (iii) Copper sulphate-pyridine test (IV.10, 11). 

Procedure. A drop of the test solution is mixed with 6 drops of a saturated acetone solution of ammonium thiocyanate on a spot plate. According to the cobalt content, a green to blue color appears. 

When nickel salts are to be tested for cobalt, the concentration of the solution should not exceed 0.2 % nickel. A solution of this strength, when it contains nickel alone, gives only a yellowish-green color with an acetone solution of thiocyanate. If as little as 0.5 y cobalt is present in a drop (corresponding to a proportion Co Ni = 1 200), a definite blue-green color develops on addition of thiocyanate. 

Procedure. One or two drops of the sHghtly acid test solution is mixed with a few milligrams of ammonium fluoride on a spot plate then 5 drops of 10 % ammonium thiocyanate solution in acetone are added. In this way, 1 y cobalt in 3 drops of a cobalt solution (1 60,000) can be detected by the blue color in the presence of 1000 times the amount of iron. 

The following procedure, based on the interaction between cuprous thiocyanate and alkaline l,2-diaminoanthraquinone-3-sulfonic acid, is recommended when considerable quantities of accompanying materials, particularly cobalt and nickel salts, are present. A drop of the test solution is placed on filter paper and dried (oven). The spot is then treated with a drop of potassium thiocyanate solution containing sulfur dioxide, and dried again. This treatment produces insoluble white cuprous thiocyanate, which remains fixed in the capillaries of the paper. Manganese, cobalt, nickel, or other heavy metal salts can be removed by bathing the paper repeatedly in potassium thiocyanate solution and finally in distilled water. The dried paper is then spotted with the alkaline dye solution. 

Cobalt, nickel, chromium and copper salts reduce the sensitivity of the iron test because of the color of their ions, or of their reaction products with thiocyanate. However 1.25 y iron can be detected in the presence of 320 times the amount of cobalt or chromium, and 0.025 y iron in the presence of 640 times the amount of nickel or copper. ... 

The formation of (II) provides a quite selective spot test for palladium. Gold must be removed prior to the test because it will cause the development of a deep ruby red in the spot plate test and a diffused violet spot on the paper, apparently due to the reduction of the gold ions to the colloidal metal. Interference may also arise from 0s04 , Os+, Ru+, and RuCle ions because they have distinct self-colors. Mercurous ion causes partial interference by the reduction of part of the palladium to the elementary state, but a positive response can still be seen. It is possible to detect I part of palladium in the presence of 200 parts of platinum or 100 parts of rhodium. Less favorable ratios should be avoided because of the color of these salts. No interference is caused by mercuric and iridic chloride, but free ammonia, ammonium ions, stannous, cyanide, thiocyanate, fluoride, oxalate, and tetraborate ions do interfere. Lead, silver, ferrous, ferric, stannic, cobaltous, nickel, cupric, nitrite, sulfate, chloride, and bromide ions do not interfere. 

Cobalt i salts give a blue solution with thiocyanates in the presence of acetone. This color reaction applied for the detection of cobalt (see page 200) may be used as a test for thiocyanate. 

Procedure. A drop of the acid test solution is mixed in a micro crucible with a small drop (about 0.02 ml) of 1 % cobalt sulfate solution, and evaporated to dryness. The residue is red-violet. The color fades on the addition of a few drops of acetone if no thiocyanate is present, whereas the acetone becomes blue-green to green in the presence of thiocyanates. 

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