HIPPURIC and METHYL HIPPURIC ACIDS in urine: METHOD 8301, Issue 3, dated 15 March 2003 - page 4 of 5 EVALUATION OF METHOD: LOD/LOQ studies were p erform ed u sing standard s in synthetic u rine, standards in pooled urine, and standards in water. Standards dissolved in synthetic urine gave LODs of 4 µg/mL, 5 µg/mL, 6 µg/mL for hippuric acid, 2-methyl hippuric acid, 3-methyl hippuric acid, and 4-m eth yl hippuric acid, respectively. W ater proved to be a poor m atrix for hippuric acids, giving a high variability. Pooled urine also gave a high variability due to an initial background. Endogenous hippuric acids in pooled urine will skew the calibration curve. Reco very study data shows greater than 96% overall recovery for all analytes from spiked synthetic urine. Overall recovery rates were slightly lower (93% ) for spike d po oled urine, possibly due to variability in natu rally occurring hippuric acids. Precision, Accuracy, and Bias data (Table 1) were obtained for synthetic urine using 7 replica tes at 6 different c onc entra tion leve ls from 10 µ g/m L to 1000 µg/L. Results using pooled urine were similar. A 30-day stability study showed that the hippuric acids in synthetic urine were stable for 7 days at 22 oC and 30 days at 4 oC. In a single synthetic urine sample, hippuric acid was stable through temperature changes from -20 oC to 30oC for 24 hours. Sonication did not affect hippuric acid stability in the samples.
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METHOD UPDATED BY: George T. Motock, James B. Perkins, and John M. Reynolds, DataChem Laboratories, Inc., Salt Lake City, Utah 84123, under NIOSH contract CDC-200-2001-08000. Previous Issues Frederick C. Phipps, NIOSH/DBBS
NIOSH Manual of Analytical Methods (NMAM), Fourth Edition
