Calibration curves showed good linear regression for mostorganic acids, with R2being within the range 0.97–0.99. The limitof detection (LOD) values was calculated by considering a signal-to-noise ratio (S/N) value of 3. They ranged from 0.03 mmol glutaricacid/mol creatinine to 0.34 mmol glycolic acid/mol creatinine, indi-cating satisfactory sensitivity of the developed GC-MS method fororganic acids in human urine.The accuracy (recovery, %) of the method was found to rangefrom 79% for methylsuccinic acid to 125.3% for malonic acid. Preci-sion (RSD, %) values were low and ranged from 0.1% for glycolic acidto 5.3% for 3-hydroxy-propionic acid. These values are much lowerFig. 2.than the tolerance limits (20%). Measurements of organic acids inurine samples have been reported to vary among laboratories byalmost 50% [25].The QC urine control samples were used to determine themethod’s precision/repeatability. Precision was high, the RSD val-ues ranged from 0.4% for pimelic acid to 4.5% for malonic acid.Intermediate precision was estimated by analyzing the QC urinesamples on 3 different days, three analyses for each sample andeach day. RSD values ranged from 2.0% for succinic acid to 20% formalonic acid, showing acceptable day-to-day imprecision.