Analytica Chimica Acta (v.731, #C)

Display Omitted► We discuss progress of MDLC–MS systems in qualitative and quantitative proteomics. ► Both “Top-down” and “bottom-up” strategies are discussed in detail. ► On-line integrations of stable isotope labeling process are highlighted. ► This review gives insights into further directions for higher level integration.With the acceleration of proteome research, increasing attention has been paid to multidimensional liquid chromatography–mass spectrometry (MDLC–MS) due to its high peak capacity and separation efficiency. Recently, many efforts have been put to improve MDLC-based strategies including “top-down” and “bottom-up” to enable highly sensitive qualitative and quantitative analysis of proteins, as well as accelerate the whole analytical procedure. Integrated platforms with combination of sample pretreatment, multidimensional separations and identification were also developed to achieve high throughput and sensitive detection of proteomes, facilitating highly accurate and reproducible quantification. This review summarized the recent advances of such techniques and their applications in qualitative and quantitative analysis of proteomes.
Keywords: Multidimensional liquid chromatography; Qualitative analysis; Quantitative analysis; Proteomics;

Multivariate curve resolution combined with gas chromatography to enhance analytical separation in complex samples: A review by Leandro Wang Hantao; Helga Gabriela Aleme; Marcio Pozzobon Pedroso; Guilherme Post Sabin; Ronei Jesus Poppi; Fabio Augusto (11-23).
Display Omitted► An insight on advantages and pitfalls of CR and GC data since 2000. ► GC–MS and GC × GC applications will be addressed. ► The state-of-art of new algorithms will be presented.This review describes the major advantages and pitfalls of iterative and non-iterative multivariate curve resolution (MCR) methods combined with gas chromatography (GC) data using literature published since 2000 and highlighting the most important combinations of GC coupled to mass spectrometry (GC–MS) and comprehensive two-dimensional gas chromatography with flame ionization detection (GC × GC-FID) and coupled to mass spectrometry (GC × GC–MS). In addition, a brief summary of some pre-processing strategies will be discussed to correct common issues in GC, such as retention time shifts and baseline/background contributions. Additionally, algorithms such as evolving factor analysis (EFA), heuristic evolving latent projection (HELP), subwindow factor analysis (SFA), multivariate curve resolution-alternating least squares (MCR-ALS), positive matrix factorization (PMF), iterative target transformation factor analysis (ITTFA) and orthogonal projection resolution (OPR) will be described in this paper. Even more, examples of applications to food chemistry, lipidomics and medicinal chemistry, as well as in essential oil research, will be shown. Lastly, a brief illustration of the MCR method hierarchy will also be presented.
Keywords: Multivariate curve resolution; Gas chromatography; Mass spectrometry; Comprehensive two-dimensional gas chromatography; Factor analysis; Chemometrics;

Display Omitted► LC–MS metabolite profiles are investigated with ANOVA–PCA and ASCA. ► Growth stage and tissue sample factors were found to affect wheat culture. ► DIMBOA-Glc, DMBOA, HMBOA and MBOA proved to be significant metabolites.Different chemometric techniques have been used to evaluate the effect of distinct experimental conditions and factors on Triticum aestivum L. plant development. The study was conducted using three wheat varieties, Astron, Ritmo and Stakado. These varieties were grown under organic and conventional cultivation systems. Samples were collected at five growth stages. Shoots and roots of each plant at these stages were analysed. Three replicates of each analysed sample were performed to improve representativeness and to allow for the evaluation of natural variability and interaction effects. All samples were analysed using Liquid Chromatography Mass–Spectrometry (LC–MS), and the Total Ion Current (TIC) profiles of benzoxazinone derivatives obtained for each sample were investigated. Qualitative and quantitative assessments of these TIC profiles and of their changes in the analysed samples were carried out using different chemometric techniques. Estimation of main effects, and of their possible interaction, was performed by means of Analysis of Variance combined to Principal Component Analysis (ANOVA–PCA) and of Analysis of Variance combined to Simultaneous Component Analysis (ASCA).
Keywords: Chemometrics; Triticum aestivum L.; Benzoxazinone derivatives; LC–MS; ANOVA–PCA; ASCA;

Display Omitted► A multi-residue analytical method has been developed for antibiotics. ► Oasis HLB SPE is the best cartridge for sample extraction. ► SPE flow rate should not exceed 10 mL min−1. ► Sample acidification enhances recovery. ► Zorbax column performs better than C18 column in antibiotic separation.This paper describes the development of an optimized method based on solid-phase extraction (SPE) followed by liquid chromatography–electrospray ionization tandem mass spectrometry (LC–MS/MS) for the simultaneous analysis of ten antibiotic compounds including tetracyclines, sulfonamides, macrolides and quinolones. LC–MS/MS sensitivity has been optimized by alterations to both LC and MS operations. Of the two high resolution columns tested, Waters Symmetry C18 endcapped and Agilent Zorbax Bonus-RP, the latter was found to show better performance in producing sharp peaks and clear separation for most of the target compounds. Optimization of the MS fragmentation collision and cone energy enhanced the peak areas of the target analytes. The recovery of the target compounds from water samples was most efficient on Waters Oasis HLB SPE cartridge, while methanol was shown to be the most suitable solvent for desorbing the compounds from SPE. In addition, acidification of samples prior to SPE was shown to enhance the recovery of the compounds. To ensure a satisfactory recovery, the flow rate through SPE should be maintained at ≤10 mL min−1. The method was successfully applied to the analysis of antibiotics from environmental water samples, with concentrations being <LOD in tap water, between <LOD to 28 ng L−1 in river water and between <LOD to 230 ng L−1 in sewage effluent.
Keywords: Antibiotics; LC–MS/MS; Solid-phase extraction; Water; Sewage;

Display Omitted► Surface RAFT polymerization was firstly applied to MIP-coated fiber preparation. ► Ultra-thin MIP coating of about 0.55 μm was obtained with homogenous structure. ► MIP-coated fiber showed improved selectivities to Sudan I–IV dyes. ► MIP-coated SPME–LC–MS/MS method was used for monitoring of trace Sudan dyes.Surface reversible addition-fragmentation chain transfer (RAFT) polymerization method was firstly applied to the preparation of molecularly imprinted polymer (MIP) coated silicon solid-phase microextraction (SPME) fibers. With Sudan I as template, an ultra-thin MIP coating with about 0.55-μm thickness was obtained with homogeneous structure and controlled composition, due to the controllable radical growing and chain propagation in surface RAFT polymerization. The MIP-coated fibers were found with enhanced selectivity coefficients (3.0–6.5) to Sudan I–IV dyes in contrast with those reported in our previous work. Furthermore, the ultra-thin thickness of MIP coating was helpful to the effective elution of template and fast adsorption/desorption kinetics, so only about 18 min was needed for MIP-coated SPME operation. The detection limits of 21–55 ng L−1 were achieved for four Sudan dyes, when MIP-coated SPME was coupled with liquid chromatography (LC) and mass spectrometry (MS) detection. The MIP-coated SPME–LC–MS/MS method was tested for the monitoring of ultra trace Sudan dyes in spiked chilli tomato sauce and chilli pepper samples, and high enrichment effect, remarkable matrix peaks-removing capability, and consequent high sensitivities were achieved to four Sudan dyes.
Keywords: Molecularly imprinted polymer; Coating; Solid-phase microextraction; Reversible addition-fragmentation chain transfer polymerization;

Quantitative selenium speciation in human urine by using liquid chromatography–electrospray tandem mass spectrometry by Ying Lu; Alice Rumpler; Kevin A. Francesconi; Spiros A. Pergantis (49-59).
Display Omitted► Development of a selected reaction monitoring mass spectrometric method for the identification of Se species in human urine. ► A selenosugar was detected as the major human urinary metabolite of selenium in the samples analysed. ► The trimethylselenonium ion was detected in the urine of one volunteer before and after receiving a selenium supplement. ► Strict quality control measures were applied to validate identification. ► Quantitation was conducted using an isotopically labelled internal standard and the standard additions methodology.A liquid chromatography–electrospray-tandem mass spectrometry (ES-MS/MS) method was developed for the speciation analysis of four organic selenium species of relevance to human urinary metabolism, namely trimethylselenomium ion (TMSe+), selenomethionine (SeMet) and the two selenosugars, methyl 2-acetamido-2-deoxy-1-seleno-β-d-galactos/-glucos-amine (SeGalNAc and SeGluNAc, respectively). Their chromatographic separation was achieved by using a cation exchange pre-column coupled in-series with a reversed-phase high-performance liquid chromatography column, along with an isocratic mobile phase. Online detection was performed using ES-MS/MS in selective reaction monitoring mode. SeGalNAc was detected as the major human urinary metabolite of selenium in the samples analysed, whereas TMSe+ was detected in the urine of one volunteer before and after receiving a selenium supplement. SeMet was not detected as a urine excretory metabolite in this study. Spiking experiments performed with the urine samples revealed significant signal suppression caused by coeluting matrix constituents. To overcome such interferences, isotopically labelled 13CD3 82SeGalNAc was used as an internal standard, whereas in the absence of an isotopically labelled internal standard for TMSe+, the standard addition method was applied. Quality control for the accurate quantitation of TMSe+ and SeGalNAc was carried out by analysing spiked human urine samples with appropriate selenium standards over a concentration range of 10–50 μg Se L−1. The method has achieved a limit of detection in the presence of urine matrix comparable to that of HPLC-inductively coupled plasma-mass spectrometry for the four selenium species: 1.0 μg Se L−1 for TMSe+, 5.6 μg Se L−1 for SeMet, and 0.1 μg Se L−1 for both SeGalNAc and SeGluNAc.
Keywords: Selenium speciation; Selenosugars; Urine analysis; Electrospray mass spectrometry; Selected reaction monitoring; Isotopically labelled internal standard;

Integrated rapid resolution liquid chromatography–tandem mass spectrometric approach for screening and identification of metabolites of the potential anticancer agent 3,6,7-trimethoxyphenanthroindolizidine in rat urine by Yaping Tian; Jiuming He; Ruiping Zhang; Haining Lv; Shuanggang Ma; Yanhua Chen; Shishan Yu; Xiaoguang Chen; Yan Wu; Wenyi He; Zeper Abliz (60-67).
Display Omitted► A RRLC–MS/MS approach was developed for metabolite analysis. ► MSE and mpMS/MS were integrated to improve throughput and sensitivity. ► The metabolites of a potential anticancer agent CAT were detected in rat urine. ► Demethylated, N-oxidized and hydroxylated metabolites were identified.An integrated approach combining data acquisition using MSE and multi-period product ion scan (mpMS/MS), with high-resolution characteristic extracted ion chromatograms (hcXIC) as a data mining method, was developed for in vivo drug metabolites screening and identification. This approach is illustrated by analyzing metabolites of a potential anticancer agent, 3,6,7-trimethoxyphenanthroindolizidine (CAT) in rat urine based on rapid resolution liquid chromatography combined with tandem mass spectrometry (RRLC–MS/MS). Untargeted full-scan MSE enabled the high-throughput acquisition of potential metabolites, and targeted mpMS/MS contributed to the sensitivity and specificity of the acquisition of molecules of interest. The data processing method hcXIC, based on the structure of CAT, was shown to be highly effective for the metabolite discovery. Through the double-filtering effect of the characteristic ion and accurate mass, conventional extracted ion chromatograms that contained a substantial number of false-positive peaks were simplified into chromatograms essentially free of endogenous interferences. As a result, 21 metabolites were detected in rat urine after oral administration of CAT. Based on the characteristic fragmentation patterns of the phenanthroindolizidine alkaloid, the structures of 9 metabolites were identified. Furthermore, the interpretation of the MS/MS spectra of these metabolites enabled the determination of demethylation position as well as the differentiation between N-oxidized and hydroxylated metabolites.
Keywords: Metabolite; Rapid resolution liquid chromatography–tandem mass spectrometry; Integrated analytical approach; Phenanthroindolizidine alkaloid; Potential anticancer agent;

Display Omitted► The GO-based probe consisted of FITC labeled T-rich ssDNA, GO and Hg2+ ions. ► The method was based on a competitive ligation of Hg2+ by GSH/Cys and T–T mismatches. ► Good sensitivity and selectivity were obtained for the determination of GSH/Cys. ► Biothiols in serum and cell extract samples were detected with satisfactory results.A fluorometric method for quantity analysis of biothiols was developed using a graphene oxide (GO)-based “molecular beacon”-like probe, which consisted of FITC labeled thymine (T)-rich single-stranded DNA (ssDNA), GO and Hg2+ ions. The labeled ssDNA containing T–T mismatches would self-hybridize to duplex in the presence of Hg2+, which can avoid its adsorption on GO and the fluorescence of this GO-based probe was recovered. The fluorescence of the probe quenched after the addition of biothiols such as glutathione (GSH) and cysteine (Cys) owing to thiol groups can selectively competitive ligation of Hg2+ ions with T–T mismatches. In the present work, the GO-based probe was used for the determination of GSH and Cys. Under the optimal conditions, a linear correlation was established between fluorescence intensity ratio I 0/I and the concentration of GSH in the range of 2.0 × 10−9–5.0 × 10−7  mol L−1 with a detection limit of 1.0 × 10−9  mol L−1. The linear range for Cys is from 5.0 × 10−9 to 4.5 × 10−7  mol L−1 with a detection limit of 2.0 × 10−9  mol L−1. The proposed method was applied to the determination of GSH in human serum and cell extract samples with satisfactory results.
Keywords: Biothiols; Glutathione; Cysteine; Graphene oxide; Thymine–thymine mismatch;

Display Omitted► Functional gold nanoparticles are demonstrated as a sensitive Cr(III) probe. ► It is simple, rapid, sensitive and field-portable. ► The method allows a detection concentration as low as 31 ppb. ► Cr(VI) in waste water also can be detected, in line with our expectations.A simple, rapid, sensitive and field-portable colorimetric technique for the determination of Cr(III) in aqueous solution based on an aggregation-induced color transition of gold nanoparticles (AuNPs) has been developed. AuNPs were first functionalized with a dithiocarbamate-modified N-benzyl-4-(pyridin-4-ylmethyl)aniline ligand (BP-DTC). Chelation of Cr(III) by several of these ligands, bound to different nanoparticles, led to nanoparticle aggregation in solution. This gave rise to a color change from wine-red to blue that was discernible by the naked eye and an easily measurable alteration in the extinction spectrum of the particles. The method could be used to determine Cr(III) with a detection limit of 31 ppb. Furthermore, selective detection of trace Cr(III) in aqueous solution in the presence of 12 other transition metal ions has been achieved. Toward the goal of practical applications, the sensor has been further evaluated with a view to monitoring Cr(III) in nutritional supplements and the blood of diabetes patients and also applied in the indirect determination of Cr(VI) in waste water.
Keywords: Colorimetric assay; Gold nanoparticles; Chromium detection; Aqueous solution;

Dynamic properties of the polyethylene glycol molecules on the oscillating solid–liquid interface by Minoru Yoshimoto; Yukiko Yuda; Hidenobu Aizawa; Hiroaki Sato; Shigeru Kurosawa (82-87).
Display Omitted► QCM is used for investigating the dynamic properties of the PEG molecules on the solid–liquid interface oscillating at MHz. ► The number-average molecular weights (M n) of the PEG molecules are systematically varied over 4 orders of magnitude. ► The value of ΔF slope against M n indicates the Debye process. ► The resonant length of the PEG molecule moving with the oscillating plate of 9 MHz is estimated at 54.2 Å.The dynamic properties of polyethylene glycol (PEG) molecules on the solid–liquid interface oscillating at MHz were investigated using the quartz crystal microbalance (QCM). The number-average molecular weights (M n) of the PEG molecules were systematically varied over 4 orders of magnitude. This study makes it clear that the series-resonant frequency shift, ΔF, of the QCM against the square root of the density–viscosity product of the PEG solution is linear and has the intercept. Moreover, systematical analysis reveals that the ΔF slope rapidly decreases with M n and that the ΔF intercept becomes constant above 4.0 × 103  g mol−1. As a result, those reveal that the resonant length of the PEG molecule moving with the oscillating plate of 9 MHz is 54.2 Å. We also find that the behaviors of ΔF due to M n are mainly caused by the length of the PEG molecule.
Keywords: Quartz crystal microbalance; Polyethylene glycol; Solid–liquid interface; Resonant length;

High-performance closed-tube PCR based on switchable luminescence probes by Ari Lehmusvuori; Ulla Karhunen; Antti-Heikki Tapio; Urpo Lamminmäki; Tero Soukka (88-92).
Display Omitted► Real-time PCR based on switchable lanthanide luminescence probes. ► Nonfluorescent probes form a highly fluorescent lanthanide chelate complex. ► Self-assembly of the lanthanide ion carrier chelate and the light absorbing antenna. ► Very low background fluorescence and high specific signal generation. ► Improved DNA detection sensitivity leading to diminished PCR threshold cycles.We introduce a switchable lanthanide luminescence reporter technology based closed-tube PCR for the detection of specific target DNA sequence. In the switchable lanthanide chelate complementation based reporter technology hybridization of two nonfluorescent oligonucleotide probes to the adjacent positions of the complementary strand leads to the formation of a highly fluorescent lanthanide chelate complex. The complex is self-assembled from a nonfluorescent lanthanide chelate and a light-harvesting antenna ligand when the reporter molecules are brought into close proximity by the oligonucleotide probes. Outstanding signal-to-background discrimination in real-time PCR assay was achieved due to the very low background fluorescence level and high specific signal generation. High sensitivity of the reporter technology allows the detection of a lower concentration of amplified DNA in the real-time PCR, resulting in detection of the target at the earlier amplification cycle compared to commonly used methods.
Keywords: PCR; Switchable sensors; Lanthanide chelate; Time-resolved measurement; Diagnostics;