Window of detection

Plasma is the main biological sample used in clinical and toxicological analysis, as concentrations found in this matrix are correlated to the pharmacological effect, as well as to the side and toxic effects. However, oral fluid has also been employed in some specific applications because of the advantages associated to this alternative specimen easy, painless, and noninvasive collection, which does not require qualified personnel, it represents the free analyte fraction, and it has a window of detection similar to that in plasma. Within the possible applications of oral fluid analysis, two are of special relevance ... 

Hair analysis may remedy the disadvantages of currently used methods with a wide window of detection ranging from weeks to months and may provide information concerning the severity and pattern of an individual s drug use, when a maternal drug history is not available or is in doubt. 

Urine is currently the most common specimen for detection of drugs of abuse. Hovrever, the window of detectability in urine is generally limited to a few days following drug use. In addition, the collection of urine may require some invasion of privacy and loss of dignity, and urine specimens are subject to adulteration or manipulation to evade detection. For these reasons, alternate biological specimens that may avoid some of these limitations have been investigated/ ... 

From the standpoint of sensitivity to antagonist, a receptor stimulation level of 50% is optimal for functional studies. However, in view of signal-to-noise factors and the need for a clear window of inhibition, an 80% level of stimulation often is employed. In this regard, binding may hold some advantages since the window of detection for a binding assay with a low level of nsb may be... 

Fig. 23.5 Window of detection of dmg use or absence, measured in days. Sweat patches can detect dmg use for up to a week whiist they are worn sweat swabs wiil detect dmg use for up to 24 hours. (Reproduced with permission from Tricho-tech, Cardiff)...

These expressions for the S/N, corresponding to only the shot noise in the ion beam itself (i.e. ignoring contributions from the components of the detection chain. Figure 7.1), reflect the intuitive appreciation that these statistical variations should become relatively less important as the total number of ions actually recorded increases, i.e. as either or both of the average ion current and time window of detection are increased. Of course the value of 4 is primarily determined by the size of the original analytical sample and the concentration of analyte within it, and is thus not within the control of the analyst other than via efficient extraction and clean-up procedures (Chapter 4). Increasing (S/N)j by increasing... 

It can also identify the presence of drugs in hair, which increases the window of detection from hours and days (after which body fluids are no longer useful) to months and even years. It was employed for the first time at an athletic event in 1955 to detect drugs in athletes at a cycling competition in France. (Twenty percent of those tests were positive.) Mass spectrometry is also used to identify residues of arson fires and explosives from post-explosion residues, and to analyze paints, adhesives, and fibers. 

Kiniz P, Villain M, Cirimele V, Pepin G, Ludes B. Windows of detection of lorazepam in urine, oral fluid and hair, with a special focus on drug-facilitated crimes. Forensic Sci Int 2004 145 131-5. 

Finally, the timescale of the ionization is an essential feature of the approach since it must match the time window of detectable ions by a given mass analyser. The time evolution of the Dl process is assumed to include two distinct phases. The schematic picture in Figure 5 shows the that the ion-generation process comprises two consecutive contributions. An initial intense ion current is produced during the first 10- 25 ns, compatible with detection in TOF LMMS. However, selvedge ionization may already start in that initial period but will reach its maximum later and finally continues for microseconds after the end... 

To increase the window of detection for LSD use, because it is rapidly metabolized, recent methods target the metabolites that have longer half-lives. Half-life of nor-LSD is 10 h in urine, compared with that of LSD at about 5 h. The diastereomer iso-LSD is formed during the production of illicit LSD from lysergic acid but also if LSD is exposed to basic aqueous solution and high temperatures. 

Blood testing is believed to produce the most accurate results, but is also the most invasive. Also, drugs and alcohol leave the blood stream rapidly, providing a short window of detection. Employee concerns about the use of needles and the spread of disease have led many employers away from blood testing. 

Hair testing is a more recently developed method. It is the least invasive, but has several drawbacks. Recent drug use (within 7-10 days) is difficult to determine, but the window of detection can stretch as far as 90 days. It is also the most expensive method of testing. 

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