Pediatric concentrations of S100B protein in blood: age- and sex-related changes.

retention time. At the evaluated concentration of 5000 ␮g/L, prednisolone produced a signal equivalent to 20 ␮g/L cortisol, representing a 0.4% interference. Fenofi-brate generated parent ions at m/z 361 and 363 in an abundance ratio of 3:1, a distinctive pattern related to the presence of chlorine in the chemical composition. In MS/MS mode, fenofibrate produced a m/z 3633121 transition that interfered with the quantitative transition of cortisol, but it did not produce the m/z 363397 transition. Thus, switching to the secondary transition for quantifi-cation eliminated interference from this drug. In addition, the elution time of the drug was ϳ30 s longer than that of cortisol. Taylor et al. (1) noted isotopic exchange between the deuterated IS and hydrogen-containing vapors in an APCI ion source. Unlike the observations of Taylor et al., we have not observed isotopic exchange with our APCI interface. The reason for this difference is unclear, but it may be related to ion source conditions. The good agreement obtained between our method and the comparison LC-MS/MS method suggests that isotopic exchange did not affect the proposed method. Apparently healthy adult volunteers (25 males and 25 females; age range, 19 –53 years) collected 24-h urine samples without preservative. The volunteers were asked to keep samples under refrigeration during the collection. Statistical results for this study are presented in Table 1. To evaluate agreement between the established reference interval with UFC values in the population, we evaluated results for 2089 random 24-h urine specimens analyzed with the proposed method (Fig. 1). The mean (SD) value for log-transformed UFC excretion in 24 h was 1.26 (0.24) log ␮g/24 h (minimum and maximum, 0.3 and 3.84 log ␮g/24 h, respectively), and skewness and kurto-sis for the distribution were 1.51 and 5.57, respectively. The stability of cortisol in urine was evaluated in the presence of acetic (15 mmol/L), boric (15 mmol/L), and hydrochloric (30 mmol/L) acid. Two samples without added acid were stored and analyzed under the same conditions as the samples stored with the acids. Samples were stored at room temperature, 4 °C, and Ϫ20 °C and analyzed every 4 –7 days during 1 month of storage. Cortisol concentrations in samples stored with the acids were higher by ϳ30% than in samples stored without acid, possibly as a result of partial hydrolysis of sulfate and glucuronide conjugates. In conclusion, the rapid LC-MS/MS method for UFC analysis appears to be free from interference …