Quantification of <i>o,o</i><i>‘</i>-Dityrosine, <i>o</i>-Nitrotyrosine, and <i>o</i>-Tyrosine in Cat Urine Samples by LC/Electrospray Ionization-MS/MS Using Isotope Dilution
作者:Laure Féline Marvin、Thierry Delatour、Isabelle Tavazzi、Laurent Bernard Fay、Carolyn Cupp、Philippe Alexandre Guy
DOI:10.1021/ac020309w
日期:2003.1.1
Quantification of o-tyrosine, o-nitrotyrosine, and o,o‘-dityrosine from cat urine samples was achieved by LC/electrospray ionization-MS/MS (LC/ESI-MS/MS) using an isotope dilution technique in multiple reaction monitoring mode before butylation of o,o‘-dityrosine and after butylation of o-tyrosine and o-nitrotyrosine. This novel approach of amino acids butylation enhanced the MS response by a factor of 7-fold for o-tyrosine and 6-fold for o-nitrotyrosine and decreased the overall chemical background noise. Butylation of o,o‘-dityrosine resulted in a lower MS response as a result of the formation of both mono- and doubly butylated species. The mean recovery for the oxidized amino acids was estimated at 73 ± 2%. The limits of quantitation of NO2-Tyr butyl ester, o-Tyr butyl ester, and di-Tyr in cat urine samples were calculated at 14.5, 28.2 and 140.9 nM, respectively. The oxidized amino acids levels in cat urine extracts ranged from 157 to 250 ng/day for o-Tyr and from 3289 to 11 803 ng/day for di-Tyr. NO2-Tyr was found in only two urine extracts at levels below 58 ng/day. A certain trend of correlation was observed between o,o‘-dityrosine and o-tyrosine when comparing these values against their respective creatinine amounts. A comparison of the data gathered from the ThermoFinnigan TSQ 7000 and Micromass Q-TOF instruments revealed several advantages of using the Q-TOF regarding the exact mass measurement, a lower ion suppression effect and the possibility to perform analyses in full scan product ion mode. These results demonstrate that a Q-TOF instrument can be a good alternative to classical triple quadrupole for quantitative purposes on a relatively small linear dynamic range (4 orders of magnitude for the Q-TOF, as compared to 6 for the triple quadrupole).
通过液相色谱/电喷雾电离-质谱/质谱(LC/ESI-MS/MS)结合同位素稀释技术,在多反应监测模式下,对猫尿样中的o-酪氨酸、o-硝基酪氨酸和o,o'-二酪氨酸进行了定量分析。在o,o'-二酪氨酸丁基化之前,以及o-酪氨酸和o-硝基酪氨酸丁基化之后。这种新的氨基酸丁基化方法增强了质谱响应,o-酪氨酸增强了7倍,o-硝基酪氨酸增强了6倍,并降低了整体的化学背景噪音。o,o'-二酪氨酸的丁基化导致质谱响应降低,这是由于形成了单丁基化和双丁基化的物种。氧化氨基酸的平均回收率估计为73±2%。猫尿样中NO2-Tyr丁酯、o-Tyr丁酯和di-Tyr的定量限分别计算为14.5、28.2和140.9 nM。猫尿提取物中氧化氨基酸的水平在o-Tyr为157至250 ng/天,在di-Tyr为3289至11,803 ng/天。NO2-Tyr仅在两个尿液提取物中被发现,水平低于58 ng/天。在比较这些值与各自的肌酐量时,观察到o,o'-二酪氨酸和o-酪氨酸之间存在一定的相关趋势。从ThermoFinnigan TSQ 7000和Micromass Q-TOF仪器收集的数据比较显示,使用Q-TOF在精确质量测量、较低的离子抑制效应和全扫描产物离子模式分析的可能性方面有几个优势。这些结果表明,在相对较小的线性动态范围内,Q-TOF仪器可以作为经典三重四极杆的替代品,用于定量目的(Q-TOF的动态范围为4个数量级,而三重四极杆为6个数量级)。