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Johns SH, Wist AA, Najam AR. 
“Spot Tests: A Color Chart Reference for Forensic Chemists”. 
J. Forensic Sci. 1979;24(3):631-649.
Spot tests, the most common of preliminary screening tests, have been of long-standing use in forensic analysis. With the advent of technological instrumentation, the importance of this utilitarian, albeit basic, test procedure has diminished. In the early development of currently accepted laboratory technique, the spot test (also referred to as the color test) was often employed as a conclusive method for substance identification. Advanced technology has demonstrated that color tests alone indicate nothing but the possible presence or absence of a particular molecular grouping. Consequently, the color test must be considered inconclusive for purposes of positive identification. Thus the main purpose of the spot test is to narrow the list of substances possibly present in any given unknown.

This paper proposes to consolidate the diverse information that has been compiled concerning the color test and to present it in tabular form to foster more effective use of the spot test [1]. Table 1 illustrates a series of nine spot tests applied to each of more than 200 compounds. Although not exhaustive, this table may serve to organize pertinent data and facilitate both manual and computer searches. Each compound has been assigned a numerical code keyed to the specific spot test. Properly applied, the spot test can provide a rapid and highly accurate tool for drug screening.
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