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A large number of polyphenols are consumed with the diet and may contribute to the prevention of chronic diseases such as cardiovascular diseases, diabetes, cancers, and neurodegenerative diseases. More comprehensive methods are needed to measure exposure to this complex family of bioactive plant compounds in epidemiological studies. We report here a novel method enabling the simultaneous measurement in urine of 38 polyphenols representative of the main classes and subclasses found in the diet. This method is based on differential 12C-/13C-isotope labeling of polyphenols through derivatization with isotopic dansyl chloride reagents and on the analysis of the labeled polyphenols by tandem mass spectrometry. This derivatization approach overcomes the need for costly labeled standards. Different conditions for enzyme hydrolysis of polyphenol glucuronides and sulfate esters, extraction, and dansylation of unconjugated aglycones were tested and optimized. Limits of quantification varied from 0.01 to 1.1 μM depending on polyphenols. Intrabatch coefficients of variation varied between 3.9% and 9.6%. Interbatch variations were lower than 15% for 31 compounds and lower than 29% for 6 additional polyphenols out of the 38 tested. Thirty seven polyphenols were validated and then analyzed in 475, 24 h urine samples from the European Prospective Investigation on Cancer and Nutrition (EPIC) study. Thirty four polyphenols could be detected and successfully estimated and showed large interindividual variations of concentrations (2-3 orders of magnitude depending on the compound), with median concentrations spanning from 0.01 to over 1000 μM for all 34 compounds. [ABSTRACT FROM AUTHOR]

Contaminants from various sources including medical devices, laboratory materials and the environment, and analytical apparatus may contribute to their endogenous congeners at different stages of the analytical process. Here, an approach is reported for the identification and quantification of contaminating analytes in biological fluids by stable-isotope dilution gas chromatography/mass spectrometry (GC/MS) and gas chromatography/tandem mass spectrometry (GC/MS/MS) methods. This approach is based on the analysis of different sample volumes and determination of the peak area ratio (PAR) of the endogenous analyte to the stable-isotope labeled analogue serving as the internal standard. The PAR is obtained by selected-ion monitoring or selected-reaction monitoring of appropriate ions. Generation of PAR values that correlate inversely with the sample volume subjected to analysis reveals the existence of contamination. The extent of contamination is obtained by plotting the PAR of endogenous analyte to internal standard versus the reciprocal of the sample volume analyzed. Examples are given for uncontaminated and contaminated endogenous analytes in biological samples, including nitrite and nitrate analyzed by GC/MS, and the fatty acid metabolites oleic acid oxide, oleic acid ethanol amide, and arachidonic acid ethanol amide analyzed by GC/MS/MS. Dependence of the PAR of endogenous analyte to its internal standard upon derivatization dine reveals a unique kind of contamination that was identified in the GC/MS analysis of nitrate in plasma as pentafluorobenzyl ester. This kind of contamination occurs at the latest stage of GC/MS analysis and cannot be controlled by reference to the internal standard. [ABSTRACT FROM AUTHOR]

The solid phase isobaric mass tagging (SP1MT) approach is presented for simultaneous protein quantitation and identification. The novelty of the SP1MT strategy relies on a CID-based differentiation of regioisomeric species for quantitalion of tagged proteolytic peptides. SPIMFs are unlabeled mass-tagging reagents, which consist of a reporter group, a mass balance group, and a spacer with a amine-specific reactive group, able to be linked to any N-terminal peptide. Therefore SPIIWF-llnked peptides from a two-plex set appear as a single unresolved precursor ion in MS, whereas the reporter groups lead to quantitation signals of m/z 168.2 and 182.2 Da upon tandem mass specUvimetiy (MS/MS) analysis with matrixassisted laser desorption time-of-flight/time-of-flight (MAh Dl TOF/TOF). This strategy allows ease protein identification by direct submission of MS and MS/MS data to the MASCOT database. SPIMf approach showed an excellent quantitation linearity, detecting any relative concentration differences of peptides in two solutions over a 5-fold concentration range without losing sequencing informadon. Therefore, SPIMT's are an attractive, simple, and low cost alternative for two-plex quantitation of proteins and offer possibilities of tuning the two-plex signal mass window by replacing the spacer. [ABSTRACT FROM AUTHOR]

A total of 14 tetra- to deca-PBDE congeners were separated on a C18 reversed phase liquid chromatographic column. PBDEs 47, 85, 99, 100, 153, 154, 183, 196, 197, 203, 206, 207, 208, and 209 were eluted using a gradient methanol/water/toluene mobile phase system at a flow rate of 0.5 mL min-1. 13C-BDE-47, 13C-BDE-99, 13C-BDE-153, BDE-128, and 13C-BDE-209 were used as internal standards, while 13C-BDE-100 was used as a syringe standard. Separated analytes were ionized using an atmospheric pressure photoionization (APPI) source equipped with a 10 eV krypton lamp and operated in negative ion mode. [M-Br + 0]- ions were monitored as precursor ions for all studied PBDEs, except for BDE-208 and BDE-209 which produced higher intensity at the [C6Br5O]- ion cluster. [Br]- ions were monitored as fragment ions for all target compounds. Method detection limits ranged from 12 to 30 pg. The method was applied to determination of PBDEs in standard reference material (SRM 2585), and favorable results were obtained. Unlike GC methods, no thermal degradation was encountered in the analysis of higher brominated PBDEs. This rendered the method useful for quantification of BDE-209 debromination products. The method also allows the use of 13C-labeled internal standards, which compensate for instrumental fluctuations and matrix-related ion suppression or enhancement. [ABSTRACT FROM AUTHOR]