Development of selective materials and methods for analytical techniques combined with mass spectrometry

Abstract

Mass spectrometry (MS) is a powerful detection technique that has become very important in several chemical disciplines for detection of both small molecules (environmental pollutants, small metabolites) and large biomolecules (proteins, peptides). The "heart" of the mass spectrometer is the analyzer, that uses electrical or magnetic fields, or combination of both, from the region where they are produced, to a detector, where they produce a signal which is amplified. This element separates the gas phase ions according to their m/z (mass to charge ratio) value. MS is mostly used coupled to high performance liquid chromatography (HPLC) or ultra- high performance liquid chromatography (UHPLC) with an atmospheric pressure ionization (API) interface between the LC and MS. The most important API technique is electrospray ionization (ESI), with a wide range of application from small molecules to large molecules such as proteins or polymers. Complex matrix, as environmental samples, biological fluids, food or tissue extracts, are not usually compatible with MS detection without extensive sample preparation. In facts, complex matrix could contains substances that can cause the detector signal to decrease or increase for a selected analyte compared to the signal from the same compound in a standard solution. ESI is the ionization technique in which this phenomenon is most common because in the ESI process ions compete for ionization/desorption. Matrix effect is observed in ESI when compounds co-elute with the analyte of interest: this affects sensitivity, linearity, accuracy, precision and the limit of detection (LOD). Furthermore, the target compound(s) are often present at concentrations lower than their detection limits and require a preliminary concentration step. Therefore, the first step of an analysis is usually some kind of sample pretreatment to improve both the selectivity and sensitivity of the subsequent detection. Many techniques are available for this purpose, the suitability of which depends primarily on the physical state of the sample, e.g. solid-phase extraction (SPE) for liquid and pressurized-liquid extraction for solid samples. Proper sample preparation is critical for MS analysis, because the quality and reproducibility of sample extraction and preparation significantly impact results from MS instruments... [edited by Author]