Department of Clinical Biochemistry, The Royal Liverpool and Broadgreen University Hospitals, Liverpool, UK.
Clin Chem Lab Med. 2010;48(1):81-7. doi: 10.1515/CCLM.2010.017.
The goal of our study was to test the relative stability of urine, unconjugated, free catecholamines and the methyl derivatives. We measured the change in concentrations in commercially available urines after storage at various pH values, temperatures and time, from days up to 10 weeks.
Samples of commercial control urines were adjusted to pH 2.0, 4.0, 6.0 and 8.0 and aliquots stored at ambient temperature (20-26 degrees C), 4 degrees C and -18(o)C. The free catecholamines (cats) and the free methyl derivatives (mets) were measured after 1, 2, 3 and 6 days and 1, 2, 3 and 10 weeks using the automated sample trace enrichment dialysis (ASTED) procedure with reversed phase ion pair high performance liquid chromatography (HPLC) and coulometric detection.
Free catecholamines were relatively stable, with <15% loss of concentration, when stored at pH 6.0 or less for at least 4 days and up to 10 weeks at pH 2.0 at either 4(o)C or -18(o)C. At pH 8.0, the concentration fell to <60% after 48 h and at a pH of 6.0 or 8.0, up to 90% was lost within the first week at 4(o)C and 25(o)C. More than 40% of free normetadrenaline and metadrenaline were lost after 1-2 weeks when stored at 20-25(o)C and pH 8.0. After 10 weeks at pH 4.0, 6.0 and 8.0, up to 90% loss was observed at 25(o)C. Free cats were stable at pH 2.0 and 4.0 at -18(o)C and the free mets were stable at -18(o)C over the entire time period studied and at all pHs.
In the analysis of free catecholamine and the free methyl derivatives, urine samples should be acidified to a pH range 2.0-3.0 to ensure stability and hence the correct analysis.
我们研究的目的是测试尿中非结合、游离儿茶酚胺及其甲基衍生物的相对稳定性。我们测量了在不同 pH 值、温度和时间下（从几天到 10 周），商业上可获得的尿液中浓度的变化。
将商业对照尿液样品调节至 pH 值 2.0、4.0、6.0 和 8.0，并将等分试样储存在环境温度（20-26°C）、4°C 和-18°C。使用自动样品痕量富集透析（ASTED）程序，采用反相离子对高效液相色谱（HPLC）和库仑检测，在 1、2、3 和 6 天以及 1、2、3 和 10 周后测量游离儿茶酚胺（cats）和游离甲基衍生物（mets）。
当在 pH 值 6.0 或更低时储存至少 4 天，在 pH 值 2.0 时储存长达 10 周，游离儿茶酚胺的浓度相对稳定，损失率<15%。在 pH 值 8.0 时，48 小时后浓度降至<60%，在 pH 值 6.0 或 8.0 时，4°C 和 25°C 下第一周内损失高达 90%。在 20-25°C 和 pH 值 8.0 下储存 1-2 周后，游离去甲肾上腺素和去甲肾上腺素的比例超过 40%。在 pH 值 4.0、6.0 和 8.0 下储存 10 周后，在 25°C 下观察到高达 90%的损失。在-18°C 时，游离儿茶酚胺在 pH 值 2.0 和 4.0 下稳定，游离甲基衍生物在-18°C 下在整个研究期间和所有 pH 值下稳定。
在游离儿茶酚胺和游离甲基衍生物的分析中，尿液样品应酸化至 pH 值 2.0-3.0 范围，以确保稳定性，从而得到正确的分析。
