Wood G M, Patel S, Entwisle A C, Boenke A
Leatherhead Food Research Association, Surrey, UK.
Food Addit Contam. 1996 Jul;13(5):519-39. doi: 10.1080/02652039609374438.
The European Commission, Measurements and Testing Programme (BCR) has undertaken a project to improve methodology and to prepare certified reference materials for ochratoxin A determination. The first phase of this project, an intercomparison of procedures for the determination of ochratoxin A in wheat, at a content of approximately 13 micrograms/kg, has already been reported. The second intercomparison study, described in this paper, involved 26 European laboratories, from 11 countries, which analysed wheat naturally contaminated at a level of approximately 7 micrograms/kg, and a 'blank' wheat sample (ochratoxin A content < 0.2 microgram/kg). The participants used a variety of procedures which involved different extraction solvents and clean-up procedures. All laboratories used HPLC as the determinative step. Some laboratories also used immunoaffinity column clean-up in comparison with their normal method. Recoveries of the normal methods used by laboratories ranged from 58 to 114%; only three laboratories obtained recoveries outside the accepted range of 70 to 110%. Recoveries of the immunoaffinity column methods, using two sources of column, ranged from 58 to 114% for one and from 4 to 86% for the other. The between-laboratory reproducibility coefficient of variation for all results was 34% for the normal methods, and 34 and 42% for the two types of immunoaffinity columns. It was noted that, after the results were corrected for spike recovery, some laboratories became outliers owing to low spike recoveries. Further investigations of the spiking protocols used by each laboratory showed that the time left for evaporation of the spiking solvent was crucial to the recovery obtained.
欧盟委员会测量与测试计划（BCR）开展了一个项目，旨在改进方法并制备用于赭曲霉毒素A测定的认证参考物质。该项目的第一阶段，即对含量约为13微克/千克的小麦中赭曲霉毒素A测定程序的比对，已经有过报道。本文所述的第二项比对研究涉及来自11个国家的26个欧洲实验室，这些实验室分析了天然污染水平约为7微克/千克的小麦以及一个“空白”小麦样品（赭曲霉毒素A含量<0.2微克/千克）。参与者使用了多种程序，这些程序涉及不同的提取溶剂和净化程序。所有实验室都将高效液相色谱法作为测定步骤。一些实验室还将免疫亲和柱净化与其常规方法进行了比较。各实验室使用的常规方法回收率在58%至114%之间；只有三个实验室获得的回收率超出了70%至110%的可接受范围。使用两种柱来源的免疫亲和柱方法，一种的回收率在58%至114%之间，另一种在4%至86%之间。所有结果的实验室间再现性变异系数，常规方法为34%，两种免疫亲和柱分别为34%和42%。值得注意的是，在对加标回收率进行校正后，一些实验室由于加标回收率低而成为异常值。对每个实验室使用的加标方案的进一步调查表明，加标溶剂蒸发所留时间对获得的回收率至关重要。
