R. Lord October 4, 2011 Advantages of LC/MS-MS Over GC/MS for Organic Acid Profiles Summary Table Aspect Sample prep. - Details Chromatographic flexibility Detector specificity Overall variability Run time Instrument cost LC/MS-MS GC/MS Minimal – low variability; high recovery Dilute urine into injection vial containing solution with appropriate internal standards and inject on LC/MS-MS. Extensive – high variability; low recovery Acidify urine; Extract organic acids into non-polar solvent*; Derivitize keto groups*; Derivitize all other functional groups (hydroxyl, carboxylic acid, amine, thiol, phosphate)*; Reduce volume and transfer to GC/MS injection vial*; Inject on GC/MS * steps contributing to variable analyte recoveries Limited – all analytes must be volatilized; limited choices of stationary phases Great – analytes may be grouped by optimal resolution conditions for parallel runs on multiple instruments; highresolution chiral separations Great due to tandem ionization conditions and multiple ion transition settings Low 5-20 min High Limited to daughter ion selection without parent ion identification High > 40 min Moderate RUGGED Performing large profile analysis of urinary organic acids is a complex challenge for clinical laboratories. The ultimate requirement is to achieve rugged, reliable assays of each of the 40 or more analytes reported. That means the methods must deliver high accuracy under conditions of heavy volume independent of the operator. RELIABLE The ultimate criteria for success are low variability with high flexibility in assay conditions. The flexibility requirement is important because of the highly variable chemical nature of the various compounds to be measured. Low variability means that the accurate results are produced routinely. The combination of these dual requirements is achieved much more effectively by using LC/MS-MS than GC/MS. ACCURATE This critical improvement derives from the far simpler sample preparation in LC/MS-MS technology that insures 100% recoveries of all analytes. This greatly reduces the overall variability of the assays yielding more consistent and accurate results with greater sensitivity and specificity.