The analysis of drugs of abuse in urine can be complicated by matrix components, drug metabolites, and isobaric compounds. In the method developed here, 70 drugs of abuse, including novel psychoactive substances, were analyzed in urine following a simple enzyme hydrolysis sample preparation step. The fast, 8-minute LC-MS\/MS method separated all isobars and generated accurate quantitative results at trace levels for all compounds.<\/p>\n\n\n\n
Testing for drugs of abuse is a necessary task, whether it be for postmortem toxicology, pain management, workplace testing, or a host of other reasons. A variety of biological specimens can be used, but urine is often preferred because it is relatively easy to collect, sample volumes typically exceed what is needed, and target analyte concentrations tend to be higher than in other matrices [1]. In addition, detection windows in urine are typically 1\u20137 days for most drugs of abuse and can be even longer in samples from chronic users [2]. For these reasons, urine has been used for decades to test for drugs of abuse.<\/p>\n\n\n\n
While urine is a common matrix for drugs of abuse analysis, salt concentrations and matrix effects can present analytical challenges. Dilute-and-shoot methods are one approach, but low-level detection can be difficult to achieve because target analytes are diluted along with matrix components. In addition to matrix issues, drugs of abuse analysis can be complicated by the transformation of some drug compounds into glucuronide metabolites. Through this metabolic pathway, which occurs primarily in the liver, glucuronic acid binds to the parent drug, which increases its solubility in water and enables more efficient urinary excretion [3]. The glucuronide forms can be analyzed directly, but because it can be difficult and expensive to source glucuronide standards, LC-MS\/MS methods that target the parent drug instead of the glucuronide forms may be advantageous, although effective chromatographic separation is essential when isobars are present.<\/p>\n\n\n\n
In order to measure parent drugs directly, a hydrolysis step is required prior to analysis to release glucuronic acid from the drugs of interest [3]. One way of achieving this is through enzymatic hydrolysis using \u03b2-glucuronidase, and an example of this reaction is shown in Figure 1. The method developed here employs a simple enzyme hydrolysis sample preparation using \u03b2-glucuronidase and LC-MS\/MS analysis on a Raptor Biphenyl column in order to accurately quantify 70 drugs of abuse, including isobars, at trace levels in urine.<\/p>\n\n\n