Sample Preparation and Analysis

The shipping package containing the pad, is checked for its authenticity and custody documents, upon reaching the laboratory. For the analysis of the sample, the absorbent pad is extracted using a 2.5mL solution of mixed aqueous and methanolic acetate buffer. Traditional laboratory techniques are used to analyze the extract, initially by immunoassay, and then confirming any presumptive-positive results by chromatography [that is, by liquid chromatography (LC)-MS-MS or by gas chromatography-mass spectrometry (GC-MS)] (refer to Table 8-1). The results of the Tests are normally reported as ngdrug/mL of extract buffer and sometimes, presented as the total amount in the sweat patch (that is, 10ng/mL in extract buffer = 25 ng/patch).

Drugs Commonly Analyzed in Sweat and Cutoff Concentrations.

The actual amount of collection of sweat made by the inner pad during the wear period needs to be determined accurately in order to report drug concentrations in the form of ng drug/mL sweat. The volume of collection of sweat made by the pad is marked by potassium, lactate and sodium concentrations, each of which has been considered to be practically adaptable for their variability. However, using concentrations of sodium ion for the test results in promising outcomes, a recent study reported.

Parent drug is generally the main analyte in the sweat that is detected during the test; however metabolites if detected may provide additional evidence of drug usage. In order to declare a sweat patch as affirmative for methamphetamine and cocaine use, the federal courts of US requires that its respective metabolites [amphetamine and benzoylecgonine (BE)] must be detected as well. But, in 2004’s Proposed Revisions, the presence of metabolite is only required to report for methamphetamine, according to SAMHSA. Table 8-1

Generally after usage of cocaine, the results of sweat patch show of BE concentrations less then concentrations of cocaine (normally about 5 to 40 percent on cocaine concentration). However, at times concentrations of sweat patch BE exceed that of cocaine, and there are also examples when, under controlled cocaine dosing circumstances, BE is not detected. The comparative concentrations of cocaine and BE are unpredictable and depends on the length of patch wear period, time since intake or use, dosage and other various features. As the duration of patch wear increases, the ratio of BE to cocaine rises too, signifying a direct relationship. A document regarding sweat patch testing reported that a ratio of BE: Cocaine more than 1:5 indicates usage rather than just an exposure. Also found in the patch testing is the use of amphetamine (a metabolite of methamphetamine), secondary to the use of methamphetamine, usually at 5 to 10 percent of methamphetamine concentrations.

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