Presumptive tests colour

This is easily achieved by undertaking positive controls when the presumptive test is attempted on the sample material. Such controls provide direct reference points against which colour changes can be matched. 

The classical presumptive test for LSD is the Ehrlich s reagent test. In this, I g of the reagent (/ -dimethyIaminobenzaldehyde) is dissolved in 10 ml of orthophos-phoric acid. A small amount of the reagent solution is then added either directly to the test substrate or to the extract to be tested and any colour change observed. 

Following the possible identification of the presence of LSD, the next stage in the analysis is the use of thin layer chromatography (TLC). This is employed because although it cannot be used to prove the identity of LSD, it can be used as a rapid, cost-effective method to eliminate those samples which gave a positive colour reaction in the presumptive tests but which do not contain this drug. These will be rarer when blotter acids are suspected, but may be more common where other substrates have been used as the carrier medium for the LSD itself. 

Presumptive tests for cannabis products are used to test for the presence (or otherwise) of phenolic cannabinoids. The principle one that is used is the Duquenois-Levine test. An alternative which is available and can also be used is the Corinth IV salt test. Both involve a reaction between the cannabinoids and a test reagent to form coloured products. Positive and negative control tests should also be carried out. 

Table 5.1 Colour reactions observed on reacting opiates with common presumptive test reagents (see Appendix 1)...

A number of difficulties are associated with colour tests on fresh and dried plant material, in addition to those associated with analysing a primary amine such as mescaline. These include the fact that the plant material itself may obscure the colour reaction that takes place. Furthermore, a wide range of primary phenethy-lamines and amphetamines may yield similar colour reactions. The presumptive test which can be satisfactorily used is the Marquis test (see Appendix 1). Positive and negative control tests should also be carried out. An orange-red colour will develop if mescaline is present. However, due to the difficulties associated with interpretation of such results, further confirmation of the presence of mescaline, by using chromatographic and spectroscopic techniques, is required. 

Presumptive tests are a series of colour tests that can provide an indication as to the class of drugs that might be present however, because these tests are subjective, confirmatory analysis must also be carried out. A general unknown screen is commonly carried out using GC-MS, although EC-MS has also recently found an application in screening. 

Froehde s tast A presumptive test for opioids. Froehde s reagent consists of 0.5 gram of sodium molybdate (Na2Mo04) dissolved in 100 ml of concentrated sulphuric acid. Opioids give a pink to purple colour. 

Kastle Meyer test (phenolphthalein test) A presumptive test used to indicate blood. Phenolphthalein and hydrogen peroxide are used reaction with haemoglobin in the blood gives a pink colour. 

Mandalin tast A presumptive test for amphetamines and alkaloids. The Mandelin recent is a 1% solution of ammonium vanadate (NH4VO3) in concentrated sulphuric acid. Different substances j e different colours. Mescaline, for example, produces an orange colour, heroin abrown colour, and amphetamine ablue-green colour. 

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. 

If the specimen provided is a trace sample, sufficient material should be recovered to allow an instrumental analysis directly. The nature of the sample will often provide a clue as to the drug(s) involved and direct comparison can be made by using gas chromatography-mass spectrometry (GC-MS), for example. If the specimen is a bulk sample, presumptive (colour) tests are undertaken to determine the class or classes of drugs which the sample contains. Thin layer chromatography (TEC) is used to determine which members of the classes are present and it might also be possible to make a semi-quantitative estimate of the amount(s) of drug(s) present. Standard mixes can then be prepared for use in the confirmatory techniques. 

Typical drug identifications based on chemical analysis depend upon presumptive (colour) test techniques, followed by chromatographic separation. However,... 

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