IDENTIFICATION OF ADULTERATION IN OLIVE OIL: PROBLEMATIZING THE INTRODUCTION TO MASS SPECTROMETRY

This work propose the development of an experiment that may be used for the teaching of chemistry for undergraduate students in general, using the analysis of olive oil and soybean oil toward the direct injection electrospray ionization Mass Spectrometry - DI-MS/MS with 18-crown-6 as organic modifier. Firstly, olive oil was analyzed from two different brands, one of reputed brand and the other of popular brand and lower price. Soybean oil of popular brand was also analyzed in order to search possible similarities in the components of these oils and to search adulterations of olive oil with soybean oil. The mass spectra were obtained in positive ion mode of analysis, and allowed us to observe characteristic ions of soybean oil, olive oil, and identify the adulterated olive oil. This simple experiment of easy development may be applied in any institution which has a mass spectrometer with electrospray ionization. In addition, with the use of the experiment, the teacher can illustrate general chemistry concepts such as: molecular mass, preparation of solutions, oxidation, and acid-base reactions.

本研究提出并开发了一款适用于普通本科化学教学的实验方案，该方案以18-冠-6（18-crown-6）作为有机改性剂，采用直接注入式电喷雾电离串联质谱（direct injection electrospray ionization Mass Spectrometry - DI-MS/MS）对橄榄油与大豆油进行分析。
首先，选取两款不同品牌的橄榄油开展分析：一款为知名品牌，另一款为大众平价品牌；同时还对一款大众品牌的大豆油进行分析，以探究两类油脂的成分相似性，并检测以大豆油掺假橄榄油的情况。
实验采用正离子模式采集质谱数据，可分别观测到橄榄油与大豆油的特征离子峰，实现掺假橄榄油的有效识别。本实验操作简便、易于开展，可在任何配备电喷雾电离质谱仪的教学科研机构中实施。
此外，借助该实验，教师可直观讲解普通化学相关概念，包括相对分子质量、溶液配制、氧化反应以及酸碱反应等。