Design and Synthesis of Labeling Reagents (MS Probes) for Highly Sensitive Electrospray Ionization Mass Spectrometry and Their Application to the Detection of Carbonyl, Alcohol, Carboxylic Acid and Primary Amine Samples

Abstract

Liquid-MS systems, including liquid chromatography-MS instruments (LC/MS), have been used as the most promising qualitative and quantitative analytical methods for a number of substances, including nonvolatile or high molecular-weight substances. [1][2][3][4][5] In this context, electrospray ionization (ESI) is rapidly developing as a method for producing gas-phase ions from analyte species in solution for subsequent analysis by mass spectrometry. The combination of ESI with mass spectrometry, first demonstrated by Fenn and co-workers, 6 has proven to be useful in the analysis of nonvolatile, polar and thermally labile compounds, especially in high-molecular-weight biopolymer analysis, in large part (peptides, proteins, DNA) because these analytes give multi-charged molecular ions, which are observed in the modest m/z range (i.e., m/z < 4000) in mass analyzers. [7][8][9][10][11] However, not all analytes are suitable for ESI-MS measurements due to limitations in the transfer of analytes from solution to the gas phase as ions via the electrospray ionization process. 12-14In order to achieve effective ionization of the sample analyte to be detected by an ESI-MS system, a protic solvent acting via Brφnsted or Lewis acid chemistry (formic acid, acetic acid, trifluoroacetic acid, etc.) or an inorganic salt (ammonium acetate, sodium salt, potassium salt, etc.) is often added to the mobile phase (methanol, water and acetonitrile, etc.) to produce an ionic species [M+H] + , a molecular ion with a proton. However, these solvents and salt additives often result in poor ionization for neutral and nonpolar molecules, and cause problems in the ESI-MS system, such as the following: [15][16][17] i) In the positive ion MS mode, an acid additive such as trifluoroacetic acid lowers the sensitivity due to pairing of the Novel labeling reagents, called MS probes, which possess a positively charged quaternary amine moiety and can transform a neutral analyte into a charged compound by simply mixing with the analyte and allowing the mixture to stand from several minutes to 30 min at room temperature or while heating to 50˚C, were designed and synthesized for the highly sensitive detection of carbonyl, alcohol, carboxylic acid and primary amine samples by electrospray ionization mass spectrometry (ESI-MS). The positively charged products can be detected with high sensitivity in an ESI-MS system, which is the most popular liquid MS instrument. All of the labeled products showed a remarkably large increase in the molecular-ion peak abundance detection sensitivity of over 500-fold at picomolar concentration levels compared to that of unlabeled analytes in an ESI-MS system. These MS probes, used together with liquid MS detection, are widely applicable as a convenient method for the highly sensitive detection of less than picomolar levels of analytes, and therefore greatly enhance the power of ESI-MS analysis.

Newly Developed Chemical Probes and Nano-Devices for Cellular Analysis

“…First of all, we have developed mass probes for specific functional groups. 10,11 The chemical structures of KAP-CHO01, KAP-OH01, KAP-CA01 and KAP-NH01 are shown in Fig. 4.…”

Synthesis of the isotope‐labeled derivatization reagent for carboxylic acids, 7‐(N,N‐dimethylaminosulfonyl)‐4‐(aminoethyl)piperazino‐2,1,3‐benzoxadiazole (d6) [DBD‐PZ‐NH2 (D)], and its application to the quantification and the determination of relative amount of fatty acids in rat plasma samples by high‐performance liquid chromatography/mass spectrometry

“…So far, several derivatization reagents for carboxylic acids in LC/MS have been reported and fatty acids have been derivatized to anilides (Kusaka et al, 1988), n-propylamide (Ikeda and Kusaka 1992), 3-methyl-7methoxy-1,4-benzoxazin-2-one (Kusaka and Ikeda, 1993), methyl esters (Rezanka, 2000), phenacyl esters (Nichols and Davies, 2002;Zaitseva et al, 1999) and esters containing tertiary amino group (Suzuki et al, 2004). However, isotope-labeled reagents have not been used in these studies.…”

Cationic Xylene Tag for Increasing Sensitivity in Mass Spectrometry

“…The cationic (or precationic) groups in these tags have been tertiary amines including pyridine [1-5] (which forms a cation by protonation), quaternary amines (either pyridinium [6-12] or tetraalkylammonium) [1,9,13-20] and phosphonium [20,21]. The functional groups employed in these tags have been as follows: hydrazide [7,13,14,16,17], hydroxy [11,12,15], pyridine [6], acyl chloride [5,16], bromomethyl [16,18], thiocyanate [16], amino [1,2,3,8], o -diamine [2], sulfonyl chloride [2], N-hydroxysuccinimide [18,20,21], anhydride [5], secondary amine [3], carboxylic acid [4,9], fluoropyridinium [4], and 1,2,4-triazolone-3,5-dione [19]. Two kinds of mass spectrometers in terms of ion source mostly have been employed: ESI and MALDI.…”