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首页> 外文期刊>Analytical chemistry >Direct Detection of Inorganic Nitrate Salts by Ambient Pressure Helium-Plasma Ionization Mass Spectrometry
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Direct Detection of Inorganic Nitrate Salts by Ambient Pressure Helium-Plasma Ionization Mass Spectrometry

机译：常压氦等离子体电离质谱法直接检测无机硝酸盐

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Inorganic nitrates in solid deposits were detected directly by ambient-pressure helium-plasma ionization-mass spectrometry (HePI-MS), without the need for extensive sample preparation. Nitrates were detected even from complex matrices such as meats and fruit juices. Any electrospray-ionization mass spectrometer can be modified to perform ambient-pressure HePI-MS by simply passing helium through the metal capillary intended for liquid-sample delivery. Nitrates on paper strips, glass slides, or cotton swabs (sometimes wetted with a mineral acid) were inserted directly into the ambient-pressure HePI source. The spectra acquired under negative-ion generating conditions showed a peak at m/z 62 for the nitrate ion, along with a lower-intensity peak at m/z 125 for the nitrate adduct of nitric acid. Apparently, it is nitric acid that is initially transferred to the gas phase, forming an ion-molecule complex with hydroxyl anions present in the plasma. The ion-neutral complex then dissociates by eliminating water to produce gaseous NO_3~- ions. This hypothesis was supported by the observation that certain solid nitrate salts, which were not readily amenable to HePI (notably the alkali nitrates), were immediately detected as m/z 62 and 125 ions upon acidification by a strong acid. Quantitative evaluations showed that the nitrate-signal response versus the deposited mass is linear for over 3 orders of magnitude. With the use of ~(15)N-labeled nitrate (m/z 63), the limit of detection was determined to be as low as 200 fg.
机译：固体沉积物中的无机硝酸盐可通过常压氦等离子体电离质谱（HePI-MS）直接检测，而无需进行大量样品制备。甚至从复杂的基质（例如肉和果汁）中也检测到了硝酸盐。任何电喷雾电离质谱仪都可以修改为通过使氦气简单地通过用于液体样品输送的金属毛细管来执行环境压力HePI-MS。将纸条，载玻片或棉签（有时用无机酸浸湿）上的硝酸盐直接插入常压HePI离子源中。在产生负离子的条件下获得的光谱在硝酸根离子的m / z 62处显示一个峰，在硝酸硝酸根的m / z 125处显示一个较低的强度峰。显然，是硝酸首先转移到气相中，与血浆中存在的羟基阴离子形成离子分子复合物。然后，离子中性络合物通过消除水而解离，生成气态NO_3-。该假设得到以下观察的支持，即某些不易被HePI接受的固体硝酸盐（特别是碱式硝酸盐）在被强酸酸化后立即被检测为m / z 62和125离子。定量评估表明，硝酸盐信号响应与沉积质量的关系在三个数量级以上都是线性的。使用〜（15）N标记的硝酸盐（m / z 63），检测限被确定为低至200 fg。

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