Response to Comment on "Laser Desorption/Ionization Coupled to FTICR Mass Spectrometry for Studies of Natural Organic Matter".
Response to Comment on "Laser Desorption/Ionization Coupled to FTICR Mass Spectrometry for Studies of Natural Organic Matter".
复制标题
回应“激光解吸/电离与 FTICR 质谱联用用于天然有机物研究”的评论。
DOI：
10.1021/acs.analchem.8b00332
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发表时间：
2018
影响因子：
7.4
通讯作者：
Kew W
中科院分区：
文献类型：
--
作者：
Kew W
采用三种电离技术--负电喷雾、电喷雾离子注入(−)、负基质辅助激光解吸电离(MALDI)和负激光解吸电离(LDI)，对天然有机物(NOM)进行了质谱分析。1在这项工作中，我们发现(I)MALDI和LDI电离类似类别的化合物；(Ii)MALDI，也就是隐含的LDI，似乎不会导致NOM化合物的不适当碎裂；以及(Iii)ESI和LDI电离很大程度上不同类别的化合物。基于这些观察，我们得出结论，当试图完全表征复杂的NOM样品的分子多样性时，LDI是一种有用的附加电离技术。我们使用了两个国际腐植酸协会(IHSS)标准--苏万尼河黄腐酸(SRFA)和苏万尼河名(SR-NOM)来证明这一点。在他们的回应中，他等人。我已经调查了我们原文的一个方面。2他们注意到，目前的可持续发展能力指数(−)FTICR谱呈双峰分布(200−400m/z和400−800m/z)，而且这两个分布的两部分都不是以350m/z为中心，预计可持续发展能力呈正态分布，在200和700m/z之间延伸。3−5 He等人。评论说，他们以前没有见过这种双峰分布。2他们假设我们观察到的较高的质量分布可能是由于化合物的二聚化，并暗示我们没有优化我们的实验条件。他们进一步指出，从我们的电喷雾谱中的O2−O24，大范围的氧类物种与他们自己的结果不匹配。这些都是值得评论的有趣的观点。为了解决提出的问题，我们使用与以前相同的条件进一步获得了SRFA的ESI谱(−)，但调整了光谱仪以产生“正态”分布。我们还获得了旨在诱导二聚化的额外光谱以及为替代的低质量范围优化的光谱。新获得的SRFA的FTICR MS光谱(图1a；参见实验参数的支持信息)从200 m/z延伸到1000 m/z，最大值约为380 m/z，因此更类似于He等人提供的光谱。为了检验先前获得的双峰数据(图1b)的有效性，比较了从双峰光谱和“正态分布”光谱获得的分子式。对两者整体的直接比较
(FTICR) mass spectra of Natural Organic Matter (NOM) by three ionization techniques, negative electrospray, ESI-(−), negative matrix assisted laser desorption ionization, MALDI, and negative laser desorption ionization, LDI. 1 In that work, we found that (i) MALDI and LDI ionize similar classes of compounds;(ii) MALDI, and by implication LDI, does not appear to cause undue fragmentation of NOM compounds; and (iii) ESI and LDI ionize largely different classes of compounds. Based on these observations, we concluded that LDI is a useful additional ionization technique when attempting to fully characterize the molecular diversity of complex NOM samples. We demonstrated this by using two International Humic Substances Society (IHSS) standards, Suwannee River fulvic acid (SRFA) and Suwannee River NOM (SR-NOM). In their response, He et al. have investigated one side-aspect of our original paper. 2 They noted that the presented ESI-(−) FTICR spectrum of SRFA had a bimodal distribution (200− 400 m/z and 400− 800 m/z) and that neither part of the distribution was centered at around 350 m/z, where SRFA is expected to display a normal distribution, extending between 200 and 700 m/z. 3− 5 He et al. commented that they had not seen this bimodal distribution before. 2 They hypothesized that the higher mass distribution we observed may be due to dimerization of compounds and suggested that we had not optimized our experimental conditions. They further noted that the large range of oxygen class species, from O2− O24 in our ESI spectrum, did not match their own results. These are interesting points worth commenting upon. In order to address the issues raised, we have acquired a further ESI-(−) spectrum for SRFA using the same conditions as before but tuned the spectrometer to produce a “normal” distribution. We have also acquired additional spectra aiming to induce dimerization as well as spectra optimized for alternative, low mass ranges.The newly acquired FTICR MS spectrum of SRFA (Figure 1 a; see the Supporting Information for experimental parameters) extends from 200 to 1000 m/z, with a maximum around 380 m/z, and is thus more similar to the spectrum presented by He et al. that spanned the 220− 650 m/z range with a maximum at 350− 400 m/z. To test the validity of the previously acquired bimodal data (Figure 1 b), a comparison of the molecular formulas obtained from the bimodal and “normally distributed” spectra was made. A direct comparison of the entirety of both