AXYS Analytical Services Ltd., 2045 Mills Road West, Sidney, British Columbia V8L 5X2, Canada.
J Chromatogr A. 2013 Jun 7;1293:36-43. doi: 10.1016/j.chroma.2013.03.040. Epub 2013 Mar 25.
A method for quantitative characterization of naphthenic acid (NA) isomer groups by carbon number and extent of cyclization was developed and validated with water samples from northern Alberta. Following solid phase extraction, NAs undergo derivatization with N-(3-dimethylaminopropyl)-N'-ethylcarbodiimide (EDC) allowing detection by positive electrospray ionization tandem mass spectrometry (+ESI)-MS/MS. NA-EDC derivatives produce a common product ion by MS/MS, regardless of structure of the starting NA. Thus, approximately constant relative response factors (RRFs) were assumed for the various isomer groups that elute at a given point in the elution gradient (supported by calculated RRFs for individual model NAs), facilitating quantification using a single standard (1-pyrenebutyric acid). To reduce the impact of major background fatty acids on NA data, the method employed an optimized liquid chromatography method that separated straight chain (Z=0) analytes from other NAs. Method validation was performed at two spiking levels (7.72μg and 38.6μg total refined Merichem per 500mL of reagent water) and good accuracy (mean recoveries of 82.4±2.5% and 93.0±2.6%, respectively; range ~50-130%) and precision (<17% RSD) were achieved at both spiking levels for all 60 NA isomer groups. The method also performed well in an independent method comparison study in which method accuracy values of 107%, 120%, and 121% were obtained for 2 spiked reagent waters (1mg/L and 50mg/L NAs) and spiked Athabasca River water (0.035mg/L NAs), respectively. Application of the method to samples from northern Alberta revealed that NA concentrations decreased in the order: process water (52.8mg/L)>tailings pond water (30.6mg/L)>well water (0.086mg/L)>surface water (0.007mg/L), and that samples were distinguishable by NA isomer profile using Principal components analysis.
一种基于碳数和环化程度定量表征环烷酸（NA）异构体组的方法已经开发并通过阿尔伯塔省北部的水样进行了验证。水样经过固相萃取后，用 N-(3-二甲氨基丙基)-N'-乙基碳二亚胺（EDC）进行衍生化，然后通过正电喷雾串联质谱（+ESI）-MS/MS 进行检测。无论起始 NA 的结构如何，NA-EDC 衍生物通过 MS/MS 都会产生一个共同的产物离子。因此，假定在洗脱梯度中给定洗脱点洗脱的各种异构体组具有近似恒定的相对响应因子（RRF）（通过对单个模型 NA 的计算 RRF 得到支持），这有利于使用单个标准品（1-苊丁酸）进行定量。为了减少主要背景脂肪酸对 NA 数据的影响，该方法采用了一种优化的液相色谱方法，将直链（Z=0）分析物与其他 NAs 分离。在两个加标水平（7.72μg 和 38.6μg 总精制 Merichem 加标于 500mL 试剂水中）进行了方法验证，在两个加标水平下，所有 60 个 NA 异构体组的准确度（平均回收率分别为 82.4±2.5%和 93.0±2.6%；范围为 50-130%）和精密度（<17%RSD）都很好。该方法在一项独立的方法比较研究中也表现良好，在该研究中，对于 2 种加标试剂水（1mg/L 和 50mg/L NA）和加标阿萨巴斯卡河水（0.035mg/L NA），方法准确度值分别为 107%、120%和 121%。该方法在阿尔伯塔省北部的水样中的应用表明，NA 浓度的顺序为：工艺水（52.8mg/L）>尾矿池水（30.6mg/L）>井水（0.086mg/L）>地表水（0.007mg/L），并且可以通过主成分分析（PCA）根据 NA 异构体图谱来区分样品。
