固相萃取-液相色谱-串联质谱法测定水稻中17种细胞分裂素

建立了利用固相萃取-液相色谱-串联质谱同时测定水稻中17种细胞分裂素含量的分析方法。水稻样品经冷冻研磨,用甲醇-水(80 : 20, v/v)溶液浸提,经聚合物阳离子交换树脂(PCX)纯化,采用ZORBAX Extend-C18色谱柱,以甲醇和5 mmol/L甲酸铵水溶液为流动相进行梯度洗脱。采用电喷雾正离子模式电离,选择反应监测模式扫描,外标法定量。优化了色谱分离条件,研究了不同提取溶剂对17种细胞分裂素的提取效率,并考察了PCX固相萃取柱的纯化效果。结果表明,17种细胞分裂素在线性范围内的相关系数(r)均大于0.9984,方法检出限为0.01~0.05 ng/g。水稻根、茎和叶基质在0.2、1和5 ng/g 3个添加水平的平均回收率为60.2%~125.4%(n=6),相对标准偏差(RSD)为5.4%~29.7%。在水稻样品中检出5种细胞分裂素,其含量为0.02~0.93 ng/g。本方法纯化效果好、灵敏度高,可用于水稻中多种痕量细胞分裂素的同时分析。

Analysis of 17 cytokinins in rice by solid phase extraction purification and liquid chromatography-tandem mass spectrometry

A method was developed for the determination of 17 cytokinins in rice by solid phase extraction and liquid chromatography-tandem mass spectrometry. The rice samples were cryogenically ground under liquid nitrogen and extracted with methanol-water (80 : 20, v/v) at 4 ℃ for 16 h. The supernatant was purified on a column packed with polymer cation exchange resin (PCX). The samples were transported and eluted on an analytical column ZORBAX Extend-C18 (100 mm×2.1 mm, 1.8 μm) by methanol and 5 mmol/L ammonium formate aqueous solution. All the analytes were detected in selected reaction monitoring (SRM) mode under positive electrospray ionization (ESI⁺) and quantified by external standard method. The separation conditions were optimized in order to achieve the sufficient separation for the several isomers of cytokinins, such as trans-zeatin-7-glucoside (tZ7G), trans-zeatin-9-glucoside (tZ9G), and trans-zeatin-O-glucoside (tZOG). Moreover, the extraction efficiency of different extraction solvents and clean-up effects of PCX cartridge for each analyte were further investigated. The results showed that the correlation coefficients were not less than 0.9984 in the linear range, and the limits of detection were ranged from 0.01 to 0.05 ng/g. The mean recoveries of the 17 cytokinins at three spiked levels of 0.2, 1 and 5 ng/g were from 60.2% to 125.4% with the relative standard deviations (RSDs) of 5.4%-29.7% (n=6). Finally, five endogenous cytokinins were successfully quantified in real sample, and their contents were between 0.02 and 0.93 ng/g. It means that this method is reliable for quantitative analysis of cytokinins in rice.