The 6 x 5 LC-MS/MS Peptide Reference Mix is a unique reagent designed to monitor liquid chromatography (LC) and mass spectrometry (MS) instrument performance and assist in method development and optimization. The product is a mixture of 30 peptides; 6 sets of 5 isotopologues of the same peptide sequence. The isotopologues differ only by the number of stable, heavy-labeled amino acids incorporated into the sequence. The labels consist of uniform 13C and 15N atoms. Chromatographically, each of the isotopologues is indistinguishable; however, since they differ in mass, they are clearly resolved by mass spectrometry. The isotopologues of each peptide are present in a series of tenfold dilutions. This format allows assessment of instrument dynamic range and sensitivity from a single run. Peptides with a wide range of hydrophobicities were chosen to enable reporting of LC column performance. In addition, the peptides were chosen for maximal stability. Amino acids prone to artificial post-translational modification (i.e., methionine, asparagine, etc.) were excluded from the sequences. None of the peptides have internal lysines or arginines and will therefore not be affected by trypsin or Lys-C. In addition there is a mass separation of at least 4 Daltons between the isotopologues, so that even low-resolution instruments can distinguish the masses. PReMiS Software Tool: The 6 x 5 LC-MS/MS Peptide Reference Mix is accompanied by a complementary PReMiS Software tool (available by download) that reports on key liquid chromatography and mass spec parameters (see table). The parameter reports can be exported to CSV or saved as .pdf files. In addition to the general reporting feature, performance parameters can be tracked over time, allowing a clear assessment of trends to pinpoint poor performance and maintenance needs. For those laboratories that have multiple instruments, the ability to compare parameters across instruments will also be available. Thermo (.raw) and ABSCIEX (.wiff) formats are available for direct importing. Other vendor formats can be imported after conversion to .mzml format. Data reports are rapidly generated (usually in less than 2 minutes), with clear presentation of the XIC of all 30 masses available for immediate viewing.
