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A series of natural amino acid (alanine, valine, phenylalanine, and isoleucine) amides have been synthesized and fully characterized. They have been used as supporting ligands in the Ru(II)-catalyzed asymmetric transfer hydrogenation (ath) of acetophenone in the presence of i-PrOH/KOH. Secondary amides impart high reactivity to the corresponding Ru(II) complexes, with TOFs up to 1680 h -1 and ee's up to 47%. The amino acid and the substituents of the amide nitrogen govern the activity and the enantioselectivity of the catalytic processes. The precatalysts obtained by reacting (L)-phenylalanine p-anisidineamide and (L)-valine o-anisidineamide with [Ru(p-cymene)Cl 2 ] 2 have been isolated and characterized as the half-sandwich complexes [(η 6 -p-cymene)Ru(κ 2 -N,N′-aminoamidato)Cl] (10 and 11, respectively). An ESI-MS study conducted on the acetophenone reduction catalyzed by 11 has led to the detection of the organometallic intermediates involved in the catalytic cycle: the precatalyst 11, the 16ecomplex [(η 6 -p-cymene)Ru(κ 2 -N,N′-diamide)] 12, and the hydride [(η 6 -p-cymene)Ru(κ 2 -N,N′-aminoamidato)H] 13.

A new rapid and sensitive method based on matrix solid-phase dispersion (MSPD) followed by liquid chromatography-electrospray-tandem mass spectrometry was devised for the determination of biogenic amines at trace levels in cheese samples. The method required 0.25 g of sample, CN-bonded silica as a dispersant sorbent, and a formic acid aqueous solution/methanol mixture as an eluting solvent. Extraction recoveries from soft cheese products were calculated in the 98 +/- 4-110 +/- 6% range. A procedure based on solid-phase extraction was also evaluated for the extraction of these compounds in cheese. Chromatographic separation was performed using a C18 column with an aqueous ammonium acetate/methanol mixture as the mobile phase under gradient conditions. The method was validated in terms of detection limits (LOD), quantitation limits (LOQ), linearity, recovery, precision, and trueness. Results in the 0.05-0.25 mg kg(-1) range were obtained for the LOD of histamine, tyramine, and beta-phenylethylamine in soft cheese samples. Linearity was established over 2 orders of magnitude. Excellent precision in terms of intra-day repeatability was calculated (RSD% < 5). The applicability of the method to the determination of biogenic amines in cheese products was demonstrated.

Liquid chromatography (LC) with high-resolution mass spectrometry (HRMS) represents a powerful technique for the identification and/or confirmation of small molecules, i.e. drugs, metabolites or contaminants, in different matrices. However, reliability of analyte identification by HRMS is being challenged by the uncertainty that affects the exact mass measurement. This parameter, characterized by accuracy and precision, is influenced by sample matrix and interferent compounds so that questions about how to develop and validate reliable LC-HRMS-based methods are being raised. Experimental approaches for studying the effects of various key factors influencing mass accuracy on low-molecular weight compounds (MW < 150 Da) when using a quadrupole-time-of-flight (QTOF) mass analyzer were described. Biogenic amines in human plasma were considered for the purpose and the effects of peak shape, ion abundance, resolution and data processing on accurate mass measurements of the analytes were evaluated. In addition, the influence of the matrix on the uncertainty associated with their identification and quantitation is discussed. A critical evaluation on the calculation of the limits of detection was carried out, considering the uncertainty associated with exact mass measurement of HRMS-based methods. The minimum concentration level of the analytes that was able to provide a statistical error lower than 5 ppm in terms of precision was 10 times higher than those calculated with S/N = 3, thus suggesting the importance of considering both components of exact mass measurement uncertainty in the evaluation of the limit of detection.

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