Identification and Quantification of Arsenolipids Using Reversed-Phase HPLC Coupled Simultaneously to High-Resolution ICPMS and High-Resolution Electrospray MS without Species-Specific Standards

• Published in: Analytical chemistry (Washington) Vol. 83; no. 9; pp. 3589 - 3595
• Main Authors: Amayo, Kenneth O, Petursdottir, Asta, Newcombe, Chris, Gunnlaugsdottir, Helga, Raab, Andrea, Krupp, Eva M, Feldmann, Jörg
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 01.05.2011
• Subjects: Analytical chemistry; Animals; Arsenic - analysis; Arsenic - metabolism; Arsenic content; Chemical compounds; Chemistry; Chromatographic methods and physical methods associated with chromatography; Chromatography, High Pressure Liquid - methods; Chromatography, High Pressure Liquid - standards; Chromatography, Reverse-Phase - methods; Chromatography, Reverse-Phase - standards; Exact sciences and technology; Fatty acids; Fish; Hydrophobic and Hydrophilic Interactions; Lipids; Lipids - analysis; Lipids - chemistry; Lipids - isolation & purification; Molecular structure; Osmeriformes; Other chromatographic methods; Quality Control; Spectrometric and optical methods; Spectrometry, Mass, Electrospray Ionization - methods; Spectrometry, Mass, Electrospray Ionization - standards; Tandem Mass Spectrometry; Time Factors; High resolution; On line; Arsenic; Molecular structure; HPLC chromatography; Arsenic compound; Fragmentation pattern; Standard; Identification; Inductive coupling plasma spectrometry; Retention time; Electrospray; Lipophilic compound; Signal; Sample preparation; Pisces; Hexane; Molecular mass; Quantitative analysis; Methanol; Fractionation; Gradient; Hydrocarbon; Coupled method; Use; Concentration; Fatty acids; Carbon; Vertebrata; Reversed phase chromatography; Acid number; Mass spectrometry MS/MS; Fat; Soluble compound; Mass spectrometry
• DOI: 10.1021/ac2005873
• ISSN: 0003-2700

Although it has been known for decades that arsenic forms fat-soluble arsenic compounds, only recent attempts to identify the compounds have been successful by using a combination of fractionation and elemental and molecular mass spectrometry. Here we show that arsenolipids can directly be identified and quantified in biological extracts using reversed-phase high-performance liquid chromatography (RP-HPLC) simultaneously online-coupled to high-resolution inductively coupled plasma mass spectrometry (ICPMS) and high-resolution electrospray mass spectrometry (ES-MS) without having a lipophilic arsenic standard available. Using a methanol gradient for the separation made it necessary to use a gradient-dependent arsenic response factor for the quantification of the fat-soluble arsenic species in the extract. The response factor was obtained by using the ICPMS signal of known concentration of arsenic. The arsenic response was used to determine species-specific response factors for the different arsenic species. The retention time for the arsenic species was utilized to mine the ES-MS data for accurate mass and their tandem mass spectrometry (MS/MS) fragmentation pattern to give information of molecular formula and structure information. The majority of arsenolipids, found in the hexane phase of fish meal from capelin (Mallotus villosus) was in the form of three dimethylarsinoyl hydrocarbons (C23H38AsO, C17H38AsO, C19H42AsO) with minor amounts of dimethylarsinoyl fatty acids (C17H36AsO3, C23H38AsO3, C24H38AsO3). One of the dimethylarsinoyl fatty acids (C24H38AsO3), with an even number of carbon in the fatty acid chain, was identified for the first time in this work. This molecular formula is unusual and in contrast to all previously identified arsenic-containing fatty acids with odd numbers of carbon.