Pre-digested and purified protein (QC1) and proteome (QC2) digests are convenient as materials for LC-MS/MS QC as they are quickly prepared for injection. Lyophilized digests are also shelfstable for long time periods and easy to distribute between labs. Commercially available digests of proteins and proteomes are listed in Table . Of specific note are whole proteome digests that can be purchased along with the undigested version, thus an additional opportunity for checking experimental QC. For example, Promega's mass spectrometry-compatible protein extracts of yeast and human K562 cells, and PolyQuant's RePLiCal QconCAT protein . The 2022 sPRG study mixed proteomes of human liver (NIST RM 8461), cow liver (NIST SRM 1577c), and trout tissue (NIST SRM 1947) in different ratios with plans to make both digested and lysate mixes available in the near future (note this mix is no longer considered NIST materials and their use in proteomics is beyond the original intent of the materials). Moreover, there are isotopically labeled proteomes such as the Pierce TMT11 yeast digest and the TKOpro9 and TKOpro16 standards created to evaluate relative quantitation using tandem mass tags (TMT).