Zucchella Alessandra, Stramesi Cristiana, Politi Lucia, Morini Luca, Polettini Aldo
Department of Legal Medicine & Public Health, University of Pavia, Via Forlanini 12, 27100, Pavia, Italy.
Forensic Sci Med Pathol. 2007 Jun;3(2):93-100. doi: 10.1007/s12024-007-0011-8. Epub 2007 May 9.
Recently, some of the hair samples that we routinely analyse for drugs of abuse did not produce valid results for cocaine and metabolites. A series of very intense interfering peaks with ion fragments common to cocaine (CO), and benzoylecgonine (BE) were found to cover up the "cocaine" region of the chromatogram. In one of these cases the subject declared he had used a lotion containing Minoxidil in order to prevent hair loss. Starting from this observation we found that the interfering peaks belonged to four different TMS derivatives of Minoxidil. Minoxidil interference was further investigated by applying Tricoxidil(®), a Minoxidil solution, to the hair of CO-free volunteers and to a CO-positive hair strand dipped into Tricoxidil. Hair were analysed before and after treatment. In both cases interfering peaks were absent in the chromatograms of untreated hair and appeared in treated hair. In the CO-positive hair detection of CO, BE and internal standard was completely hindered after treatment with Minoxidil. Attempts to separate interfering peaks from CO and metabolites by modifying the temperature programme failed. None of the hair washing methods tested (methanol; dichloromethane; sodium dodecyl sulphate water solution, 1% w/v followed by methanol; phosphate buffer 0.1 M, pH 6 followed by methanol) succeeded in removing Minoxidil interference. However, a simple solution to partially overcome the problem was to dry up the derivatised extract, reconstitute it in methanol (in order to switch back Minoxidil derivatives to the native molecule), and re-inject it: owing to the higher polarity, underivatised Minoxidil does not interfere any more with the chromatography of CO, at the expense of the disappearance of BE and ecgonine methyl ester both producing TMS derivatives. This strategy was applied to four real cases where Minoxidil interference was recognised: in two of these cases CO was detected. The problem of Minoxidil interference on CO detection may be limited to procedures involving trimethylsilylation, which is probably the most commonly adopted derivatisation in laboratories performing hair analysis for drugs of abuse.
最近，我们在对滥用药物进行常规分析时所检测的一些毛发样本，并未得出可卡因及其代谢物的有效结果。结果发现，一系列与可卡因（CO）和苯甲酰爱康宁（BE）常见离子碎片相同的极强干扰峰，掩盖了色谱图中的“可卡因”区域。在其中一个案例中，受试者宣称他使用了含有米诺地尔的洗剂来防止脱发。基于这一观察结果，我们发现这些干扰峰属于米诺地尔的四种不同的三甲基硅烷（TMS）衍生物。通过将米诺地尔溶液Tricoxidil(®)涂抹于不含CO的志愿者毛发以及一根浸入Tricoxidil的CO阳性毛发上，对米诺地尔干扰进行了进一步研究。在处理前后对毛发进行了分析。在这两种情况下，未处理毛发的色谱图中均无干扰峰，而处理后的毛发中出现了干扰峰。在用米诺地尔处理后，CO阳性毛发中CO、BE和内标的检测完全受到阻碍。通过修改温度程序来分离CO和代谢物的干扰峰的尝试失败了。所测试的毛发清洗方法（甲醇；二氯甲烷；1% w/v十二烷基硫酸钠水溶液，随后用甲醇；0.1 M pH 6的磷酸盐缓冲液，随后用甲醇）均未能成功消除米诺地尔干扰。然而，部分克服该问题的一个简单方法是将衍生化提取物干燥，用甲醇重新溶解（以便将米诺地尔衍生物转换回天然分子），然后重新进样：由于极性较高，未衍生化的米诺地尔不再干扰CO的色谱分析，但代价是产生TMS衍生物的BE和爱康宁甲酯均消失。该策略应用于四个识别出米诺地尔干扰的实际案例：其中两个案例检测到了CO。米诺地尔对CO检测的干扰问题可能仅限于涉及三甲基硅烷化的程序，这可能是在进行滥用药物毛发分析的实验室中最常用的衍生化方法。
