Based on our previous report on N-alkylpyridinium isotope quaternization (NAPIQ) for the analysis of alcoholic and α,β-unsaturated ketone compounds, we have further applied NAPIQ method in the screening of hair lipids in drug abusers. Relative isotopic quantification was used for comparison of fatty alcohols between normal and drug abuse group. The NAPIQ strategy was proven to be a high-throughput method in the metabolic comparison studies of different group samples. The attached N-cationic pyridinium significantly improved the detection sensitivity for these fatty alcohols in matrix-assisted laser desorption/ionization Fourier transform ion cyclotron resonance mass spectrometric (MALDI-FTMS) analysis. The experimental results showed that the levels of fatty alcohols in the hair of heroin abuse group decreased significantly compared with the normal groups, which may be the results of the inducing of peroxidation enzyme. NAPIQ was proven to be an effective and alternative method in the research of fatty alcoholic metabolism for drug abuse monitoring.

Based on a 4,6-dimethoxy-2-(methylsulfonyl)pyrimidine (DMMSP) labeling reagent, a sensitive method to determine acidic catecholamine metabolites homovanillic acid (HVA), vanillymandelic acid (VMA), 3,4-dihydroxymandelic acid (DOMA) and 3,4-dihydroxyphenylacetic acid (DOPAC) has been developed using simple chemical derivatization with liquid chromatography/electrospray ionization-tandem mass spectrometry (LC/ESI-MS/MS). Acidic catecholamine metabolites were converted to stable 4,6-dimethoxypyrimidinyl (DMP) derivatives by one-step derivatization. Because of bulky DMP group(s) introduced into the structures of these metabolites, subsequent analysis by LC/ESI-MS/MS in positive ionization with multiple reaction monitoring (MRM) allowed specific detection of DMP derivatives of these metabolites with a wide linear relationship range. The limits of detection were in the range of 1–5 ng/mL. The mean recoveries determined were 100.2% –104.4%. Both relative standard deviation and error for intra- and inter-day measurements were less than 10% for acidic catecholamine metabolites. This strategy enabled accurate and specific determination of acidic catecholamine metabolites in human urine.

For an ion of known formula, there are some ambiguous formulas with respect to its product ions in tandem mass spectrometry in many cases. Researchers determined them mainly by high resolution mass spectrometer combing database searching. Here, we presented an innovative method to enhance the assignment possibility of the elemental composition of the product ion by exploiting the tandem mass spectra of isotopic peaks from the precursor ion such as [M+H+1]⁺, [M+H+2]⁺ and [M+H+3]⁺. This approach involved a process of excluding low match formulas for product ion stepwise until the final formula with the highest match. It also facilitated the deduction of the fragmentation pathway for the precursor ion in tandem mass spectrometry. The isotopic proportions of product ions possessed a good repeatability. Additionally, this method could be performed fast and conveniently on variety of instruments, which offers an alternative determination tool for the elemental composition of product ion in tandem mass spectrometry.

The gas-phase rearrangement reactions of compound 1, 2-dimethoxypyrimidinyloxybenzylaminoben- zenedipropylurea, were studied by ESI-MS/MS. The experimental results showed that introduction of dipropylurea moiety into the molecule initiated various interesting gas-phase chemistries and the mechanisms were proposed on the basis of hydrogen/deuterium (H/D) exchange experiments and theoretical computations. Moreover, product 2, the solution-phase rearrangement product of compound 1, was synthesized and its gas-phase chemistries were also studied to support the propos gas-phase rearrangement reactions of compound 1.

The volatile components in the leaves of C. camphora were analyzed by static headspace-gas chromatography/mass spectrometry (HS-GC-MS) combined with accurate weight measurement. Accurate weight measurement obtained by Time-of-Flight mass spectrometry (TOF-MS) helped to confirm the identification of volatiles in the analysis. 59 volatile components in the leaves of C. camphora were identified, which mainly included cis-3-hexen-1-ol (5.6%), 3-hexen-1-ol, acetate (Z) (11.1%), β-caryophyllene (15.4%), bicyclogermarene (8.4%), trans-nerolidol (19.5%) and 9-oxofarnesol (7.7%). The results show that method using HS-GC-MS combined with accurate weight measurement achieves reliable identification and has extensive application in the analysis of volatile components present in complex samples.

As an extension of our previous work, here a strategy was demonstrated for protein identification and quantification analyses utilizing a combination of stable isotope chemical labeling with subsequent denaturation, enzymatic digestion and matrix assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS). Using [d₀]- and [d₆]-4,6-dimethoxy-2-(methylsulfonyl)pyrimidine ([d₀]-/[d₆]-DMMSP), stable isotopic labels were incorporated before digestion. The comparative samples were combined before labeling after digestion, thus biases resulting from differences in sample digestion were avoided and the higher accuracy of quantification could be attained. The labeling was spatial-selective to particular residues of cysteine, lysine, and tyrosine before denaturation, which could lead to a better universality of the strategy for cysteine-free proteins. In addition, some lysine residues were blocked after labeling, the partly destroyed recognition sites could simplify the trypsin hydrolysates and hence facilitate the MS complexity. Together, our one-step labeling strategy combined several desirable properties such as spatial-selective labeling, reliability of quantitative results, simplification of analysis of complex systems and direct analysis with minimum sample handling. Our results demonstrate the usefulness of the method for analyzing lysozyme in egg white. The method was expected to provide a new powerful tool for comparative proteome research.

The intramolecular cyclization of o-alkynylphenylphosphonamide and N-(o-alkynylphenyl)acetamide was monitored by electrospray ionization mass spectrometry (ESI-MS) and its tandem version (ESI-MS/MS). The proposed intermediates were successfully intercepted and characterized. In addition, the intermediates composed of the substrate coordinated to the palladium(II) center in the reaction of o-alkynylphenylphosphonamide were unexpected before, and this interesting phenomenon of the substrate coordination seems associated with the unique structure of substrates.

A new kind of MALDI matrix, termed paraffin wax immobilized matrix, was used to study peptide mixtures and proteins. During the preparation process, the paraffin wax was heated and coated on the stainless-steel target plate, and then 2,5-dihydrobenzoic acid (DHB) was deposited on the paraffin layer and stainless-steel target plate to obtain different kinds of matrix spots. The morphology of matrices on different supports and peptide-matrix co-crystallization were observed by a high resolution digital-video microscopy system. Peptide mixtures and bovine serum albumin (BSA) digests were used to investigate the performance of the immobilized matrices on the paraffin target. The MALDI-FTMS analysis results also showed that the detection sensitivity of matrices immobilized in the paraffin sample support was better than that on other sample supports.

A chemical method of changing the protecting group was coupled to MS, deuterium-labeled and NMR methods to characterize the intermediates in the palladium(II)-catalyzed cycloisomerization of trifluoromethyl-substituted enynols. It was demonstrated that the method of changing the protecting group of substrates not only caused a decrease in reaction speed, but also provided long-lived reaction intermediates detectable by conventional spectroscopic techniques. In this sense, two assumed reaction intermediates were intercepted and detected by electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI-FTICRMS). For further characterization of these intermediates, the gas-phase behavior of these intermediates was studied by sustained off-resonance irradiation collision-activated dissociation (SORI-CAD) experiments. On the basis of the detailed, spectral interpretation of the palladium-containing species, the fragmentation pathways of the intermediates have been proposed. The deuterium-labeled experiment helped confirm the nature of the intermediates.