Derivatization in Mass Spectrometry—8. Soft Ionization Mass Spectrometry of Small Molecules

Abstract

This is the first of two reviews devoted to derivatization approaches for "soft" ionization mass spectrometry (FAB, MALDI, ESI, APCI) and deals, in particular, with small molecules. The principles of the main "soft" ionization mass spectrometric methods as well as the reasons for derivatizing small molecules are briefly described. Derivatization methods for modification of amines, carboxylic acids, amino acids, alcohols, carbonyl compounds, monosaccharides, thiols, unsaturated and aromatic compounds etc. to improve their ionizability and to enhance structure information content are discussed. The use of "fixed"-charge bearing derivatization reagents is especially emphasized. Chemical aspects of derivatization and "soft" ionization mass spectrometric properties of derivatives are considered.

Quantitative Profiling of Major Neutral Lipid Classes in Human Meibum by Direct Infusion Electrospray Ionization Mass Spectrometry

“…12 Among the various types of ionization methods including atmospheric pressure chemical ionization (APCI), electrospray ionization (ESI) is the most suitable for comprehensive analysis of intact lipids since it is the least energetic. 13,14 Due to the lack of acidic and basic groups, neutral lipids including TGs, WEs, CEs, and DEs are typically detected by ESI-MS using ammonium salts of acetate or fluoride [15][16][17][18][19][20][21][22][23][24][25][26][27] as additives and, less frequently, lithium salts of hydroxide or chloride [28][29][30][31] or sodium salts of acetate or iodide. 6,17,19 With the aid of these additives, the detection of TGs, 6,[15][16][17]19,21,22,[25][26][27][28][29] WEs, 6,16,20,30 CEs, 6,16,18,21,23,24,27 and DEs …”

An introduction to liquid chromatography–mass spectrometry instrumentation applied in plant metabolomic analyses

“…Ionisation of the vaporised sample is achieved by applying a high charge (typically ∼5 kV) to the corona pin located at the exit of the heated tube. The corona discharge around the pin causes the vaporised solvent molecules to ionise and form a reagent gas plasma; in turn the vaporised sample molecules are ionised by proton transfer either forming (Zaikin and Halket, 2006). ESI is also achieved (Fig.…”

The use of hydrazine-based derivatization reagents for improved sensitivity and detection of carbonyl containing compounds using MALDI-MSI

“…Derivatization has been proposed as a solution to this problem by introduction of groups with fixed charges or with high proton affinity. An additional benefit of the use of derivatization in "soft" ionisation mass spectrometry techniques such as MALDI-MS is that it can help prevent matrix-related ion suppression and isobaric overlay between matrix and analyte peaks by the introduction of groups with fixed charges or easily ionisable groups [1].…”

“…The most common derivatization reactions of carbonyl compounds reported for analysis by "soft" ionisation mass spectrometry methods are based on the formation of oximes and hydrazones [1]. Other published methods involve the formation of Schiff's bases, semicarbazones and thiosemicarbazones [2].…”

“…Thus the choice is usually determined by experimentation. There are several requirements to consider when choosing the ideal derivatization reagent for use: 1) the reagent should be pre-charged or include a group having high proton affinity, 2) it must contain a suitable reactive group and 3) preferably it should be commercially available or synthesised using inexpensive reagents [1,3]. Careful consideration should be made when selecting the derivatization reagent for example smaller reagents are suited for sterically hindered functional groups, the addition of a larger reagent can have the desired effect of moving the mass of the derivative into the higher mass region of the mass spectrum [2].…”