Drugs may be absorbed or
otherwise adhere to certain materials or surfaces during OF collection and handling—such as the collection pad on the device.
Recovery of the drug from the device can be calculated as: % Recovery = [50 ng/mL/100 ng/mL] X 100% Recovery = 50%
Recovery of drugs from the collection
device affects the laboratory’s ability to detect, quantify and report the presence of the drugs. In the example just given, if the laboratories limit of detection was 75 ng/ mL, the drug would have escaped detection (measured concentration 50 ng/mL). Simi- larly, if the laboratory’s limit of quantitation was 75 ng/mL, the drug could not have been accurately quantified. Importantly, if the program’s testing cutoff concentra- tion was 75 ng/mL the sample would be reported “negative”. Te atached table shows experimentally
determined drug recoveries from various devices. Recoveries of > 80 percent should be considered acceptable and > 90 percent desirable. Results for devices 1 through 5 are from an earlier publication and repre- sent previous versions of some devices, or devices that may no longer be commer- cially available. However, the data demon- strates that the recoveries only consistently exceeded 80 percent for benzoylecgonine. Most drug recoveries from the devices were < 60 percent. Marijuana (THC) and its metabolite (THC-COOH) are among the most commonly detected drugs in virtually all testing programs. However, as shown in the table, THC-COOH was poorly or oſten simply not recovered. Results for devices 6 through 14 are from a more recent publication and represent newer devices, or in some cases, improved versions of existing devices. Te data show consistent recoveries for most drugs of greater than 80 percent for devices 6, 7, 9, 10 and 14. Interestingly, devices 1 and 12 are the same device and show essentially no improvement between the studies. Devices 2 and 9 are also the same device; but in contrast, there is a marked improvement
12 datia focus
for the recovery of most drugs. Recovery of marijuana (THC) from most devices remained problematic even in the second study. In part because of the poor recovery of drugs like THC and THC-COOH, some commercial collection device kits incorporate a stabilizing buffer (discussed above). Experimental data from devices using buffers shows promise. Devices 6, 7, 8 and 9 all incorporate transport buffers in their collection methods and have among the best drug recoveries. Recovery of THC from devices 7 and 8 and in separate stud- ies device 6 approached or exceeded 80 percent (Quintela 2006).
How stable are drugs in OF? An advantage of OF is that collections can
be performed on site. However, on-site col- lections risk subjecting the specimen to un- controlled handling and temporary storage conditions. Under uncontrolled and likely variable conditions, drugs in the OF may not be always be stable. Loss of drug because of instability adversely affects detection, quantitation and confounds interpretation. Under controlled conditions, such as frozen storage, most common drugs are reason- ably stable in OF. However, depending on the collection device, THC stability may be problematic even when OF specimens are frozen. Laboratory evaluations have demonstrated poor stability of THC using collection devices that do not incorporate a stabilizing buffer (Langel 2008). Use of a stabilizing buffer improved stability of THC when specimens were stored at room tem- perature, refrigerated and frozen (Crouch 2005 Langel 2008 Moore 2006). Once placed in the buffer, freezing OF sample tended to stabilize THC for 4 to 6 weeks (Crouch 2005 and Langel 2008). Depend- ing on the device, refrigerated sample stor- age may delay degradation of THC at least two weeks (Moore 2006). Under ambient conditions, THC stability is likely affected by device material, buffer characteristics, temperature and exposure to light.
spring 2013
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