Many of the methods contained in Part 4000 include specific quality control (QC) procedures. These are considered to be the minimum quality controls necessary to successful performance of the method. Additional quality control procedures can and should be used. Section 4020B describes a number of QC procedures that are applicable to each of the methods in Part 4000. The QC in 4020 should be considered an integral part of each method. The section also references Part 1000 for guidance. This section was reviewed by the Standard Methods Committee in 2009.