Mastovska Katerina, Lightfield Alan R
US Department of Agriculture, Agricultural Research Service, Eastern Regional Research Center, 600 East Mermaid Lane, Wyndmoor, PA 19038, USA.
J Chromatogr A. 2008 Aug 22;1202(2):118-23. doi: 10.1016/j.chroma.2008.07.009. Epub 2008 Jul 11.
A previously reported multiresidue method for the analysis of 11 important beta-lactams (amoxicillin, ampicillin, cefazolin, cephalexin, cloxacillin, desfuroylceftiofur cysteine disulfide (DCCD), deacetylcephapirin, dicloxacillin, nafcillin, oxacillin, and penicillin G) in bovine kidney has been further streamlined. The method is based on a simple extraction using acetonitrile-water (4:1, v/v), followed by dispersive solid-phase extraction clean-up with C(18) sorbent, concentration of an extract aliquot, and filtration of the final extracts using syringeless filter vials, which are used for the sample introduction in the liquid chromatographic-tandem mass spectrometric (LC-MS/MS) analysis. The recoveries have been improved by adding the internal standard [(13)C(6)]sulfamethazine to the homogenized sample before the extraction step, which enabled a proper control of the volume changes during the sample preparation. Average recoveries of fortified samples were 87-103% for all beta-lactams, except for DCCD, which had an average recovery of 60%. Based on the results of the stability study and LC mobile phase tests, methanol has been eliminated from the entire method, including the LC-MS/MS analysis. The best overall LC-MS/MS (electrospray positive ionization) performance was achieved by using 0.1% formic acid as an additive in both parts of the mobile phase, in water and in acetonitrile. To prevent carry-over in the LC-MS/MS analysis, the LC method was divided into two parts: one serving as an analytical method for injection of the sample and elution of the analytes and the other one, starting at a highly organic mobile phase composition, being dedicated for injection of a solvent, washing of the system, and equilibration of the column to the initial conditions of the analytical method. In this way, a blank solvent is injected after each sample, but these in-between injections contribute minimally to the overall sample throughput.
先前报道的用于分析牛肾中11种重要β-内酰胺类药物（阿莫西林、氨苄西林、头孢唑林、头孢氨苄、氯唑西林、去呋喃甲酰头孢噻呋半胱氨酸二硫化物（DCCD）、脱乙酰头孢匹林、双氯西林、萘夫西林、苯唑西林和青霉素G）的多残留方法已进一步简化。该方法基于使用乙腈 - 水（4:1，v/v）进行简单萃取，随后用C(18)吸附剂进行分散固相萃取净化，对萃取液等分试样进行浓缩，并使用无针滤瓶对最终萃取液进行过滤，该滤瓶用于液相色谱 - 串联质谱（LC - MS/MS）分析中的样品引入。通过在萃取步骤之前向匀浆样品中添加内标物[(13)C(6)]磺胺二甲嘧啶，回收率得到了提高，这使得在样品制备过程中能够适当控制体积变化。除DCCD外，所有β-内酰胺类药物加标样品的平均回收率为87 - 103%，DCCD的平均回收率为60%。基于稳定性研究和LC流动相测试的结果，甲醇已从整个方法中去除，包括LC - MS/MS分析。通过在流动相的水相和乙腈相中均使用0.1%甲酸作为添加剂，实现了最佳的整体LC - MS/MS（电喷雾正离子化）性能。为防止LC - MS/MS分析中的交叉污染，LC方法分为两部分：一部分用作进样和洗脱分析物的分析方法，另一部分从高有机流动相组成开始，专门用于进样溶剂、清洗系统以及将色谱柱平衡至分析方法的初始条件。通过这种方式，在每个样品之后注入空白溶剂，但这些中间进样对整体样品通量的贡献最小。
