请教有关内标物的类型

另外，我对上段中提到的the mean recovery +/- 2x %RSD 及beyond +/-20 %RSD也感到很模糊，是不是什么地方印错了，是正负20 %的RSD？

补充：上述两个词是我在翻译欧盟最新农残质量控制程序中遇到的，为方便讨论，我将整段摘录如下，另附其英文版全文：Acceptable limits for a individual recovery result should normally be in the range of the mean recovery +/- 2x %RSD and may be adjusted using repeatability (validation) and intra-laboratory reproducibility (routine on-going recovery) data. Recoveries outside this range usually require re-analysis of the batch but may be acceptable in certain justified cases. Where the individual recovery is unacceptably high and no residues are detected, it is not necessary to re-analyse the samples to prove the absence of residues. However, consistently high recovery should be investigated. If a significant trend occurs in recovery, or potentially unacceptable (beyond +/-20 %RSD) results are obtained, the cause(s) must be investigated. In order to assure the correct execution of the whole procedure for each individual sample and the correct injection of each final sample extract in the GC- or LC-system, the use of one or? more quality control (QC-) internal standards, so-called procedurale? and instrument? internal standards, is recommended. These compounds, which are added to the samples prior to extraction and to the final sample extract just before injection, should be chosen to be outside of the target pesticide scope and should preferably represent the entire spectrum of pesticides in terms of polarity and susceptibility to degradation. The recovery of these QC-standards should be within the limits specified by the laboratory but at least within the abovementioned range for individual recovery. 欧盟农残质量控制程序