Corso Gaetano, Paglia Giuseppe, Garofalo Daniela, D'Apolito Oceania
Clinical Biochemistry, Department of Biomedical Sciences, Faculty of Medicine, University of Foggia, Viale L. Pinto 1, 71100 Foggia, Italy.
Rapid Commun Mass Spectrom. 2007;21(23):3777-84. doi: 10.1002/rcm.3280.
A new method to analyze free amino acids using desorption electrospray ionization (DESI) has been implemented. The method is based on the neutral loss mode determination of underivatized amino acids using a tandem quadrupole mass spectrometer equipped with an unmodified atmospheric interface. Qualitative and quantitative optimization of DESI parameters, including ESI voltage, solvent flow rate, angle of collection and incidence, gas flow and temperatures, was performed for amino acids detection. The parameters for DESI analysis were evaluated using a mixture of valine, leucine, methionine, phenylalanine and tyrosine standards. A few microliters of this mixture were deposited on a slide, dried and analyzed at a flow rate of 2 microL/min. The optimal ionization response was obtained using laboratory glass slides and an equivalent solution of water/methanol doped with 2% of formic acid. The method specificity was evaluated by comparing product ion spectra and neutral loss analysis of amino acids obtained either by DESI or by electrospray ionization flow injection analysis (ESI-FIA). To evaluate the quantitative response on amino acids analyzed by DESI, calibration curves were performed on amino acid standard solutions spiked with a fixed amount of labelled amino acids. The method was also employed to analyze free amino acids from blood spots, after a rapid solvent extraction without other sample pretreatment, from positive and negative subjects. The method enables one to analyze biological samples and to discriminate healthy subjects from patients affected by inherited metabolic diseases. The intrinsic high-throughput analysis of DESI represents an opportunity, because of its potential application in clinical chemistry, for the expanded screening of some inborn errors of metabolism.
一种利用解吸电喷雾电离（DESI）分析游离氨基酸的新方法已得到应用。该方法基于使用配备未改性大气接口的串联四极杆质谱仪对未衍生化氨基酸进行中性丢失模式测定。对包括电喷雾电离（ESI）电压、溶剂流速、收集和入射角、气流及温度等DESI参数进行了定性和定量优化，以用于氨基酸检测。使用缬氨酸、亮氨酸、蛋氨酸、苯丙氨酸和酪氨酸标准品混合物对DESI分析参数进行了评估。将几微升该混合物滴在载玻片上，干燥后以2微升/分钟的流速进行分析。使用实验室载玻片和掺杂2%甲酸的水/甲醇等效溶液可获得最佳电离响应。通过比较DESI或电喷雾电离流动注射分析（ESI-FIA）获得的氨基酸的产物离子谱和中性丢失分析来评估该方法的特异性。为评估DESI分析氨基酸的定量响应，对添加固定量标记氨基酸的氨基酸标准溶液绘制校准曲线。该方法还用于在无需其他样品预处理的快速溶剂萃取后，分析阳性和阴性受试者血斑中的游离氨基酸。该方法能够分析生物样品，并区分健康受试者和患有遗传性代谢疾病的患者。DESI固有的高通量分析是一个机遇，因为其在临床化学中的潜在应用，可用于扩大某些先天性代谢缺陷的筛查。
