National Metrology Institute of Japan (NMIJ), National Institute of Advanced Industrial Science and Technology (AIST), Central 3, 1-1-1 Umezono, Tsukuba, Ibaraki 305-8563, Japan.
Innovative Molecular Materials Group, School of Chemistry and Chemical Engineering, Queen's University Belfast, David Keir Building, Stranmillis Road, Belfast BT9 5AG, UK.
Analyst. 2017 Mar 13;142(6):994-998. doi: 10.1039/c6an02286c.
The rise in popularity of electronic cigarettes and the associated new legislation concerning e-liquids has created a requirement for a rapid method for determining the nicotine content of e-liquids in the field, ideally at the point of sale. Here we have developed a rapid method based on surface-enhanced Raman spectroscopy (SERS) with Au colloids and an isotope-labeled nicotine (d-nicotine) internal standard for the measurement/quantification of samples which contain 10s of mg mL nicotine in a complex viscous matrix. This method is novel within the area of SERS because it uses high dilution (ca. 4000×) in the sample preparation which dilutes out the effects of the viscous glycerin/glycerol medium and any flavouring or colouring agents present but still allows for very accurate calibration with high reproducibility. This is possible because the nicotine concentration in the e-liquids (≤24 mg mL) is of several orders of magnitude above the working range of the SERS measurement. This method has been tested using a portable Raman spectrometer and a very large set of 42 commercial e-liquids to check that there is no matrix interference associated with different manufacturers/flavourings/colouring agents etc. Finally, as an alternative to determining the nicotine concentration by measuring peak heights in the spectra, the concentration was also estimated by comparing the sample spectra with those of a set of standard samples which were prepared at known concentrations and held in a spectral library file in the spectrometer. This simple approach allows the concentration to be estimated without any complex data analysis and lends itself readily to a handheld Raman system which is typically designed to carry out library searching using the internal software for materials identification. Library searching against standards correctly classified 41 of the 42 test liquids as belonging to the correct concentration group. This high dilution SERS approach is suitable for the analysis of sample types that have reasonably high concentrations of analytes but suffer from matrix problems, and it therefore has broad potential for applications across food, pharmaceutical and nutraceutical areas.
电子烟的普及以及相关的电子液体新法规的出台，使得人们需要一种能够快速测定现场电子液体尼古丁含量的方法，最好是在销售点进行。在这里，我们开发了一种基于金胶体的表面增强拉曼光谱（SERS）的快速方法，以及一种同位素标记的尼古丁（d-尼古丁）内标，用于测量/定量包含数十毫克毫升尼古丁的复杂粘性基质样品。该方法在 SERS 领域是新颖的，因为它在样品制备中使用高稀释度（约 4000×），可以稀释粘性甘油/丙三醇基质以及任何存在的调味剂或着色剂的影响，但仍可以通过高重复性进行非常准确的校准。这是因为电子液体中的尼古丁浓度（≤24 毫克毫升）比 SERS 测量的工作范围高几个数量级。该方法已使用便携式拉曼光谱仪和非常大的 42 种商业电子液体进行了测试，以检查不同制造商/调味剂/着色剂等与基质干扰无关。最后，作为通过测量光谱中的峰高来确定尼古丁浓度的替代方法，还通过将样品光谱与一组已知浓度并保存在光谱库文件中的标准样品的光谱进行比较来估计浓度。这种简单的方法允许在没有任何复杂数据分析的情况下估计浓度，并且易于与手持式拉曼系统配合使用，该系统通常设计为使用内部软件进行材料识别来执行库搜索。针对标准的库搜索正确地将 42 种测试液体中的 41 种归类为属于正确浓度组。这种高稀释 SERS 方法适用于分析具有合理高浓度分析物但受基质问题影响的样品类型，因此在食品、制药和营养保健品领域具有广泛的应用潜力。
