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Drug screening is an important part of a thorough toxicologic workup. Urine, in particular, is an excellent specimen to use for this purpose because almost all drugs or their metabolites are excreted and concentrated in urine [1]. Originally, the most common extraction method was liquid-liquid extraction (LLE). (3) However, in recent years, particularly as drug testing has become more common in the workplace and in the athletic arena, solid-phase extraction (SPE) has become an increasingly popular extraction method. One study from 1991 surveyed several Department of Health and Human Services Certified Drug Testing laboratories and found that up to 50% of all extractions done in those laboratories were done by SPE [2]. The modern technology of SPE was first commercially introduced in the 1970s by Waters Associates [2]. Initially, all SPE methods were manual [3-5]. By the late 1970s, commercially prepared SPE columns were being marketed by Analytichem International, now known as Varian Sample Preparation Products [2]. Soon after, multiple phase resins were put on the market. These resins, because they contained many classes of sorbent that were copolymerized on a solid silica support, were able to be used for the separation of many different classes of compounds that had chemical and physical properties markedly different from one another. Since that time, SPE has been a widely used extraction technique in forensic toxicology and the urine drug-testing market. The type of copolymer specifically designed for the urine drug-testing market is a cation-exchange/reversed-phase copolymer. This resin uses a combination of ion exchange and hydrophobic properties that allows for very clean extracts with high extraction efficiencies [2]. The literature has shown that copolymers used in SPE have been useful in extracting the full range of acidic, basic, and neutral drugs of abuse [5,6]. The advantages of SPE have become even more pronounced in recent years with the advent of semiautomated and automated SPE instruments [2,3,7-10]. One study found that, in general, SPE was 12-fold less time-consuming and fivefold less expensive than LLE [11]. Most semiautomated systems facilitate the aspiration of fluid through the columns by a vacuum system or vacuum box. These vacuum boxes often have some way to adjust and control the amount of vacuum. Today, most, if not all, laboratories that use SPE utilize some form of semiautomation but few utilize computer-controlled robot arms to fully automate some or all of the steps. The automated methods have been shown to offer higher drug recoveries and greater precision, usually because in manual procedures flow rates, sample application, and elution are much more variable [8]. The automated systems also have the advantage of decreasing the amount of repetitive work done by laboratory staff. Overall, SPE has been shown to offer many advantages over traditional LLE, including automation, higher selectivity, improved reproducibility, and cleaner extracts [1-17].

Science & Nature
November 1
American Association for Clinical Chemistry, Inc.

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