Presumptive tests

One standard test used to determine the presence of the coliform group is called the multiple-tube fermentation technique (sometimes called the presumptive test). If this test indicates the presence of these bacteria, then a confirmed test must be done. If only negative colonies or no colonies develop during this test, it is considered negative otherwise, a completed test must be undertaken. Positive results obtained in the completed test are evidence for the presence of coliform bacteria. Testing methods have been given by the APHA, and the detailed procedures contained therein should be consulted (20). 

Fecal Goliforms. Eecal coliforms are those originating from the intestines of warm-blooded animals. Eecal coliforms can be deterrnined by a multiple-tube procedure, which must be appHed to a positive presumptive test for optimum recovery of fecal coliforms (20). Incubation must be at 44.5 0.2°C for 24 2 h. Gas production during incubation is positive evidence of fecal coliform poUution. 

Tuberculocidal Test. The tubercle bacillus is resistant to disinfectants because the cells are protected with a waxy coating that is not readily penetrated. The tuberculocidal test is a use dilution practical type test that employs porcelain cylinders. The bacteria are different from those in the use dilution method (Table 10), the incubation time is longer, and the details of the procedure are different. For example, in the tuberculocidal test the test is divided into two parts, a presumptive test and a confirmatory test. The former employs Mycobacterium smegmatis and the latter employs Mycobacterium bovis (BCG). For the presumptive test the incubation time is 12 days, as against 48 hours for other bacteria used in the use-dilution method. For the confirmatory test the incubation time is 60 days, with an additional 30 days in case there is no growth. As shown in Table 10, the concentrations of the phenol standard are higher than used with other bacteria. 

The continued impact of afiatoxin on food safety and on economies has motivated the development of new technologies in afiatoxin monitoring. In particular, several research groups have developed biosensors for detection of the toxins, as well as presumptive tests for fungal infection. The biosensor platforms that have been tested range from hand-held to bench-top devices and employ many technologies, such as fiber optics, liposomes, small particles... 

The conclusion is that a positive Griess test on hands cannot constitute evidence of the hands having had contact with explosives. The Griess test should be a presumptive test, to be used only as a preHminary tool for the investigation. Its results should be confirmed in the laboratory before being presented in court. 

However, it cannot be overemphasized that the test is a preliminary, presumptive test, and its results can be presented in court only after they have been confirmed by generally accepted laboratory methods. The point is that when used properly, color tests could significantly assist the investigation and should not be discarded just because there are better, more accurate laboratory techniques. 

Analysis of On-Site Wastewaters for Pesticides by Thin-Layer Chromatography. A field method to identify qualitatively and semi-quantitatively the pesticide constituents of a pesticide-laden wastewater was developed. The field method was developed using thin-layer chromatography (TLC). TLC gives a presumptive test for the presence of specific pesticides and within 30 minutes an estimate of their concentrations. TLC may also reveal the presence of unknown substances. The field application of thin-layer chromatography requires a skilled chemist, but no expensive equipment. The following protocol describes the on-site use of TLC. 

Forensic presumptive tests for blood and semen - whole blood typing... 

Once the samples to be analysed have been identified, physical descriptions, homogenization and sampling, presumptive testing, TEC and confirmatory testing should be undertaken. 

Having recorded all of the physical data, the items to be examined chemically should be chosen. At the time of writing, there is no agreed best-practice protocol for undertaking this and the analyst should work within the requirements of the judicial system in which he/she is operating. The theory applied to powdered amphetamines can be equally applied to amphetamine tablets. The latter should be sampled and presumptive tests, TLC and confirmatory tests then carried out. 

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. 

Although when using this combination of presumptive tests and TLC it is possible to discriminate within this group of compounds, due to the extremely large number of amphetamines available, it is necessary to carry out a confirmatory analytical technique. The foremost of these, for amphetamine identification, is gas chromatography-mass spectrometry (GC-MS). 

The process of analysis of LSD blotter acid follows the same general principles and sequence as for other controlled substances, namely physical description, presumptive testing, TLC and confirmatory analysis. These processes are discussed below. 

The presumptive tests for LSD involve a fluorescence test and a chemical test. 3.23.1 Fluorescence Testing for LSD... 

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. 

This is also true for hash oil, and all three materials wifi be considered in the following sections. This involves the identification of the principle drugs which characterize the plant, namely A -tetrahydrocannabinol (THC), CBD and CBN. For bulk samples, the analysis follows the sequence, presumptive test, TLC and... 

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. 

Other presumptive tests are available for the tentative identification of cannabis [8] but these are not specific to this controlled substance because a wide range of plant materials also contain phenolic compounds which result in similar reactions to those obtained from cannabis. As a consequence, further methodologies must be used to identify the materials. 

Heroin samples, often identified in a preliminary way on the basis of their smell, comprise a large number of opiate drugs which are frequently adulterated with a wide variety of other drugs and pharmacologically inactive materials. Some of the drugs present in this way are themselves controlled substances and so a wide variety of presumptive tests need to be performed to identify all of the classes of drug that might be present. 

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

Bulk samples are analysed by physical description, presumptive tests and thin layer chromatography, followed by confirmation using GC-MS. HPLC is generally used for sample quantification. Trace samples are analysed by the direct examination of recovered materials employing GC-MS. 

In terms of gross morphology, characteristically, coca leaf has two lines which run parallel to the mid-rib on the underside of the leaf. Taxonomically, however, it is difficult to identify leaf and plant material to species on the basis of morphology (leaf and fiower structure) alone and indeed hybridization between species is common [5]. In order to establish that the material comes from the genus Erythroxylon and contains controlled substances, it is therefore necessary to demonstrate the presence of cocaine. In bulk (those which can be seen by the naked eye) samples, this is achieved through a good physical description of the materials and packaging, followed by a combination of presumptive tests, TLC and a tandem technique, usually GC-MS. 

There are a number of presumptive tests for cocaine available from the literature. These are described below. 

Although there are several presumptive tests available for cocaine and related compounds, none alone is specific to cocaine itself. A very simple test for cocaine... 

If positive tests are obtained in the presumptive tests, the next stage in the analysis is to undertake TLC or to proceed directly to a spectroscopic evaluation. The use of TLC will allow a rapid, inexpensive means of discriminating samples containing cocaine from the false positives and a determination of what should be used in the standard mixtures for GC-MS analyses. 

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