Effects of Storage and Handling Conditions on

CLIN. CHEM. 34/1, 44-48

(1988)

Effects of Storage and Handling Conditions on Concentrations of Individual Carotenoids, Retinol, and Tocopherol in Plasma Neal

E. Craft,13 Ellen D. Brown,2 andJ. Cecil Smith, Jr.2’4

We investigated the effects of storage and handling on measured values for carotenoids, retinol, and tocopherol in plasma. We found no significant differences in the concentrations of these analytes measured in plasma samples that were frozen immediately after separation as compared with replicate samples maintained at room temperature in the dark for 24 h. Analytes were stable in solvents for at least 18 h at 23 #{176}C after extraction. Purging samples with nitrogen gas before freezing had no detectable beneficial effects. All analytes were stable in plasma stored at -70 #{176}C for at least 28 months or at -20#{176}C for five months. By 15 months the concentrations of carotenoids were significantly less (P 0.05) alteration in the concentrations of Iz retinol, tocopherol, or individual carotenoids after 18 h in w solvent at room temperature in the dark (Table 2). C., Effect of duration of storage on analyte stability. We maintained plasma samples at -70 #{176}C, to determine whether storage duration influenced vitamin stability. Using regression analysis, we saw no correlation between storage time and measured retinol, tocopherol, or carotenoid concen0 7 28 61 90 150 210 390 450 850 trations during a 28-month period (Figures 1, 2 and 3, TIME (DAYS) respectively). Fig. 1. Effecton measured concentration of retinolof storing plasma at Effect of storage temperature on analyte stability. Plasma -70#{176}C for as longas 28 months The dashed line representsthe mean for the 28-month period. Numbers above samples stored at -20 #{176}C were occasionally analyzed in the bars indicate n determinations at that time point. The lines keping the bars conjunction with plasma samples stored at -70 #{176}C. For as are equivalent to 1 SD long as five months, we could see no significant difference (P >0.05) in analytes in plasma stored at -20 #{176}C compared with -70 #{176}C (Figure 4). However, we saw a significant (P