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Analytica Chimica Acta (v.772, #)

Editorial Board (pp. iii).

Use of isotope ratio mass spectrometry to differentiate between endogenous steroids and synthetic homologues in cattle: A review by Geert Janssens; Dirk Courtheyn; Sven Mangelinckx; Stéphanie Prévost; Emmanuelle Bichon; Fabrice Monteau; Geert De Poorter; Norbert De Kimpe; Bruno Le Bizec (pp. 1-15).

Scheme: Representation of the observed isotope ratios and the relation to exogenous and endogenous natural steroids. AS stands for “amount of steroid”.Display Omitted► The difference between endogenous and exogenous steroids is thoroughly laid out. ► Factors influencing the carbon ratio and the use of Δ¹³C-values are explained. ► Implementation of GC/C/IRMS to detect steroid abuse in cattle is reviewed. ► Alternative methods and upcoming techniques are discussed. ► The differences and similarities with sports doping control are highlighted.Although substantial technical advances have been achieved during the past decades to extend and facilitate the analysis of growth promoters in cattle, the detection of abuse of synthetic analogs of naturally occurring hormones has remained a challenging issue. When it became clear that the exogenous origin of steroid hormones could be traced based on the¹³C/¹²C isotope ratio of the substances, GC/C/IRMS has been successfully implemented to this aim since the end of the past century. However, due to the costly character of the instrumental setup, the susceptibility of the equipment to errors and the complex and time consuming sample preparation, this method is up until now only applied by a limited number of laboratories. In this review, the general principles as well as the practical application of GC/C/IRMS to differentiate between endogenous steroids and exogenously synthesized homologous compounds in cattle will be discussed in detail, and will be placed next to other existing and to be developed methods based on isotope ratio mass spectrometry. Finally, the link will be made with the field of sports doping, where GC/C/IRMS has been established within the World Anti-Doping Agency (WADA) approved methods as the official technique to differentiate between exogenous and endogenous steroids over the past few years.

Keywords: Gas chromatography linked to combustion/isotope ratio mass spectrometry; Steroid; Cattle; Natural hormone; Doping; Urine

Multivariate curve resolution-particle swarm optimization: A high-throughput approach to exploit pure information from multi-component hyphenated chromatographic signals by Hadi Parastar; Heshmatollah Ebrahimi-Najafabadi; Mehdi Jalali-Heravi (pp. 16-25).

•A new MCR method based on particle swarm optimization (PSO) is developed.•Multi-component simulated GC–MS and HPLC–DAD data are successfully resolved.•Performance of MCR-PSO algorithm is compared with MCR-ALS and MCR-FMIN.•MCR-PSO is used for high-throughput analysis of real chromatographic data.Multivariate curve resolution-particle swarm optimization (MCR-PSO) algorithm is proposed to exploit pure chromatographic and spectroscopic information from multi-component hyphenated chromatographic signals. This new MCR method is based on rotation of mathematically unique PCA solutions into the chemically meaningful MCR solutions. To obtain a proper rotation matrix, an objective function based on non-fulfillment of constraints is defined and is optimized using particle swarm optimization (PSO) algorithm. Initial values of rotation matrix are calculated using local rank analysis and heuristic evolving latent projection (HELP) method. The ability of MCR-PSO in resolving the chromatographic data is evaluated using simulated gas chromatography–mass spectrometry (GC–MS) and high-performance liquid chromatography–diode array detection (HPLC–DAD) data. To present a comprehensive study, different number of components and various levels of noise under proper constraints of non-negativity, unimodality and spectral normalization are considered. Calculation of the extent of rotational ambiguity in MCR solutions for different chromatographic systems using MCR-BANDS method showed that MCR-PSO solutions are always in the range of feasible solutions like true solutions. In addition, the performance of MCR-PSO is compared with other popular MCR methods of multivariate curve resolution-objective function minimization (MCR-FMIN) and multivariate curve resolution-alternating least squares (MCR-ALS). The results showed that MCR-PSO solutions are rather similar or better (in some cases) than other MCR methods in terms of statistical parameters. Finally MCR-PSO is successfully applied in the resolution of real GC–MS data. It should be pointed out that in addition to multivariate resolution of hyphenated chromatographic signals, MCR-PSO algorithm can be straightforwardly applied to other types of separation, spectroscopic and electrochemical data.

Keywords: Chemometrics; Multivariate curve resolution; Particle swarm optimization; Hyphenated chromatography; Rotational ambiguity

Aptamer based strategy for cytosensing and evaluation of HER-3 on the surface of MCF-7 cells by using the signal amplification of nucleic acid-functionalized nanocrystals by Shaoping Lv; Yong Guan; Dong Wang; Yifeng Du (pp. 26-32).

An electrochemical strategy based on aptamers and nanoprobes was developed for the rapid collection and detection of MCF-7 cells and HER-3 on the surface of MCF-7 cells.Display Omitted► Nanoparticles were used for the amplification of electrochemical detection. ► Magnetic beads (MBs) were used for the separation tool. ► High-affinity DNA aptamers were used for signal recognition.The electrochemical detection of cell lines of MCF-7 (human breast cancer) has been reported, using magnetic beads for the separation tool and high-affinity DNA aptamers for signal recognition. The high specificity was obtained by using the magnetic beads and aptamers, and the good sensitivity was realized with the signal amplification of DNA capped CdS or PbS nanocrystals. The ASV (anodic stripping voltammetry) technology was employed for the detection of cadmic cation and lead ions, for electrochemical assay of the amount of the target cells and biomarkers on the membrane of target cells, respectively. This electrochemical method could respond to as low as 100cellsmL⁻¹ of cancer cells with a linear calibration range from 1.0×10² to 1.0×10⁶cellsmL⁻¹, showing very high sensitivity. Moreover, the amounts of HER-3 which were overexpressed on MCF-7 cells were calculated correspond to be 3.56×10⁴ anti-HER-3 antibody molecules. In addition, the assay was able to differentiate between different types of target and control cells based on the aptamers and magnetic beads used in the assay, indicating the wide applicability of the assay for early and accurate diagnose of cancers.

Keywords: Electrochemical; Magnetic beads; Aptamer; MUC1 nanocrystal; Cancer cell; HER-3

Cork as a new (green) coating for solid-phase microextraction: Determination of polycyclic aromatic hydrocarbons in water samples by gas chromatography–mass spectrometry by Adriana Neves Dias; Vanessa Simão; Josias Merib; Eduardo Carasek (pp. 33-39).

Display Omitted► Cork as a new coating for solid-phase microextraction was proposed. ► Good results were achieved, demonstrating the applicability of the cork as coating for SPME. ► The efficiency of cork fiber was very similar to commercially available fibers.A new fiber for solid-phase microextraction (SPME) was prepared employing cork as a coating. The morphology and composition of the cork fiber was evaluated by scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR), respectively. The proposed fiber was used for the determination of polycyclic aromatic hydrocarbons (PAHs) in river water samples by gas chromatography–selected ion monitoring–mass spectrometry (GC–SIM–MS). A central composite design was used for optimization of the variables involved in the extraction of PAHs from water samples. The optimal extraction conditions were extraction time and temperature of 60min and 80°C, respectively. The detection and quantification limits were 0.03 and 0.1μgL⁻¹, respectively. The recovery values were between 70.2 and 103.2% and the RSD was ≤15.7 ( n=3). The linear range was 0.1–10μgL⁻¹ with r≥0.96 and the fiber-to-fiber reproducibility showed RSD≤18.6% ( n=5). The efficiency of the cork fiber was compared with commercially available fibers and good results were achieved, demonstrating the applicability and great potential of cork as a coating for SPME.

Keywords: Solid-phase microextraction; Cork; PAHs; Water samples; GC–MS

Peptides trapping cocaine: docking simulation and experimental screening by solid phase extraction followed by liquid chromatography mass spectrometry in plasma samples by Marcello Mascini; Camilla Montesano; Manuel Sergi; German Perez; Maristella De Cicco; Roberta Curini; Dario Compagnone (pp. 40-46).

Display Omitted► Two peptides were computationally designed as selective SPE sorbent for cocaine. ► The hexapeptide–cocaine complex was docked with different scoring functions. ► The extraction procedure for SPE was optimized for human plasma. ► QHWWDW was found to have good recovery in agreement with docking simulation.Two different hexapeptides were computationally designed and tested as selective SPE sorbent for cocaine. The amino acid residues used for designing the two hexapeptides, tested in SPE experiments, were, according to chemical function and interatomic distances, the most (QHWWDW) and the lowest (ESSIDH) preserved sequences in 4 proteins binding cocaine. The hexapeptide–cocaine complex was docked with different scoring functions combinations and resulting binding scores were compared with the SPE results. The extraction procedure for SPE was optimized considering volume loading, pH effect, and human plasma matrix interferences. Cocaine was loaded onto the modified resin cartridge at 10ngmL⁻¹ and the peptide QHWWDW was found to have the highest recovery with the best retention at pH 7.5, in agreement with docking simulation. Retention experiments were carried out also on cocaine metabolites nor-cocaine, benzoylecgonine and ecgonine methyl ester. Except for nor-cocaine the retention of metabolites on resin modified with peptide QHWWDW decreased drastically confirming the peptide selectivity, and validating the simulation data. Compared to standard solutions, only a slight decrease in cocaine recovery was observed loading human plasma samples after a partial protein precipitation.

Keywords: Cocaine; Biomimetic ligands; SPE; LC-MS/MS; Plasma

Correlation of precursor and product ions in single-stage high resolution mass spectrometry. A tool for detecting diagnostic ions and improving the precursor elemental composition elucidation by S. Borràs; A. Kaufmann; R. Companyó (pp. 47-58).

Display Omitted► We are describing a technique to spot ions which are derived from each other. ► Single stage high resolution data is used. ► This “in silicon” technique is compared to conventional precursor scan. ► Some applications for this technique are presented.Monitoring of common diagnostic fragments is essential for recognizing molecules which are members of a particular compound class. Up to now, unit resolving tandem quadrupole mass spectrometers, operating in the precursor ion scan mode, have been typically used to perform such analysis. By means of high-resolution mass spectrometry (HRMS) a much more sensitive and selective detection can be achieved. However, using a single-stage HRMS instrument, there is no unequivocal link to the corresponding precursor ion, since such instrumentation does not permit a previous precursor selection. Thus, to address this limitation, an in silico approach to locate precursor ions, based on diagnostic fragments, was developed. Implemented as an Excel macro, the algorithm rapidly assembles and surveys exact mass data to provide a list of feasible precursor candidates according to the correlation of the chromatographic peak shape profile and other additional filtering criteria (e.g. neutral losses and isotopes). The macro was tested with two families of veterinary drugs, sulfonamides and penicillins, which are known to yield diagnostic product ions when fragmented. Data sets obtained from different food matrices (fish and liver), both at high and low concentration of the target compounds, were investigated in order to evaluate the capabilities and limitations of the reported approach. Finally, other possible applications of this technique, such as the elucidation of elemental compositions based on product ions and corresponding neutral losses, were also presented and discussed.

Keywords: Diagnostic fragment; Elemental composition elucidation; High-resolution mass spectrometry; Ion correlation; Precursor location; Orbitrap

Absolute quantification of NAD(P)H:quinone oxidoreductase 1 in human tumor cell lines and tissues by liquid chromatography–mass spectrometry/mass spectrometry using both isotopic and non-isotopic internal standards by Zhiyuan Tang; Mengqiu Wu; Yingchun Li; Xiao Zheng; Huiying Liu; Xuefang Cheng; Lin Xu; Guangji Wang; Haiping Hao (pp. 59-67).

Display Omitted► The peptide fingerprint map of NQO1 has been defined by using TripleTOF. ► Signature peptide of NQO1 can be quickly quantified within 10min. ► Analysis is performed with non-isotopic analog and compared with isotopic method. ► This method is adequate for NQO1 quantitation from human cancer cells and tissues.NAD(P)H:quinone oxidoreductase 1 (NQO1, DT-diaphorase) is a prognostic biomarker and a potential therapeutic target for various tumors. Therefore, it is of significance to develop a robust method for the absolute quantification of NQO1. This study aimed to develop and validate a LC–MS/MS based method and to test the appropriateness of using non-isotopic analog peptide as the internal standard (IS) by comparing with a stable isotope labeled (SIL) peptide. The chromatographic performance and mass spectra between the selected signature peptide of NQO1 and the non-isotopic peptide were observed to be very similar. The use of the two internal standards was validated appropriate for the absolute quantification of NQO1, as evidenced by satisfactory validation results over a concentration range of 1.62–162fmolμL⁻¹. This method has been successfully applied to the absolute quantification of NQO1 expression in various tumor cell lines and tissues. NQO1 expression in human tumor tissues is much higher than that in the neighboring normal tissues in both the cases of lung and colon cancer. The quantitative results obtained from the isotopic and non-isotopic methods are quite similar, further supporting that the use of non-isotopic analog peptide as internal standard is appropriate and feasible for the quantification of NQO1. By comparing with a classical isotopic IS, the present study indicates that the use of a non-isotopic peptide analog to the proteotypic peptide as the internal standard can get equal accuracy and preciseness in measuring NQO1. The universal applicability of the non-isotopic IS approach for the quantification of proteins warrants further research.

Keywords: Abbreviations; NQO1; NAD(P)H:quinone oxidoreductase 1; MRM; multiple reaction monitoring; ELISA; enzyme-linked immunosorbent assay; IS; internal standard; SIL; stable isotope labeled; SPE; solid phase extraction; FA; formic acid; MPA; mobile phase A; MPB; mobile phase B; ESI; electrospray ionization; CE; collision energy; IDA; information dependent acquisition; NSCLC; non-small-cell lung cancer; QC; quality control; RE; relative error; CV; coefficient of variance; SD; standard deviation; LLOQ; lower limit of quantification; TSA; tanshinone IIALC–MS/MS; TripleTOF; Non-isotopic; NQO1; Cancer

Hyphenation of ionic liquid albumin glassy carbon biosensor or protein label-free sensor with differential pulse stripping voltammetry for interaction studies of human serum albumin with fenoprofen enantiomers by Deia Abd El-Hady; Ahmed K. Youssef (pp. 68-74).

Display Omitted► New wearable ionic liquid (IL) biosensor for chiral discrimination of fenoprofen. ► Proving the ability of IL as a mediator and promoter of activity of protein on GCE. ► Simple voltammetric estimation of binding constants of HSA–fenoprofen enantiomers. ► Performing the displacement and reciprocal competitive binding studies on the biosensor.A new biosensor or protein label-free sensor composed of 1-butyl-3-methylimidazolium hexafluorophosphates (BMIMPF₆)-human serum albumin (HSA) film on glassy carbon electrode (GCE) was produced. Unfortunately, the native proteins themselves are often unstable in physiological conditions. Here, we introduced conjugation with ionic liquid (IL) such as BMIMPF₆ which improved the stability and binding affinity of protein onto GCE. A rapid, simple and reliable method for the chiral discrimination and real time protein binding studies of fenoprofen enantiomers with HSA was developed by hyphenating ionic liquid albumin glassy carbon (ILAGC) biosensor with differential pulse cathodic stripping voltammetry under physiological conditions. The electrochemical behavior of chiral fenoprofen was monitored by cyclic voltammetry, from which large response was obtained froml-fenoprofen. The surface coverage of fenoprofen enantiomers was calculated by double potential-step chronocoulometry. The binding constants of chiral fenoprofen with HSA were estimated to be 3.2×10⁵±0.3Lmol⁻¹ and 0.8×10⁴±0.4Lmol⁻¹ forl- andd-fenoprofen, respectively giving acceptable precision (SD ≤ 0.4) and good agreement with the literature values. The competitive interactions of ibuprofen with fenoprofen enantiomers–HSA were studied giving a significant decreasing in the binding degrees of analytes to HSA. The reciprocal competitive experiments indicated thatl-fenoprofen replacedd-fenoprofen from HSA. The proposed electrochemical biosensor holds great potential for chiral discrimination and real time binding studies of drugs with protein.

Keywords: Chiral biosensor; Ionic liquid; Protein; Glassy carbon electrode; Fenoprofen

Optimization of a lateral flow immunoassay for the ultrasensitive detection of aflatoxin M₁ in milk by Laura Anfossi; Claudio Baggiani; Cristina Giovannoli; Flavia Biagioli; Gilda D’Arco; Gianfranco Giraudi (pp. 75-80).

Display Omitted► The development of a high sensitive lateral flow immunoassay is described. ► The developed assay allowed aflatoxin M₁ detection in milk at level required by EU regulations. ► Article describes advances in lateral flow technology towards high sensitivity. ► A simple and rapid sample pre-treatment was proposed to overthrow matrix interference.A high sensitive immunoassay-based lateral flow device for semi-quantitatively determine aflatoxin M₁ (AFM₁) in milk was developed. Investigation and optimization of the competitor design and of the gold-labelling strategy allowed the attainment of the ultra-sensitive assessment of AFM₁ contamination at nanograms per litre level (LOD 20ngL⁻¹, IC₅₀ 99ngL⁻¹), as requested by European regulations. A one order of magnitude detectability enhancement in comparison to previously reported gold colloid immunochromatographic assays for this toxin was obtained.Direct detection of the target toxin in milk could be obtained by acquiring images of the strips and correlating intensities of the coloured lines with analyte concentrations. The one-step assay can be completed in 17min, including a very simple and rapid sample preparation, which allowed the application of the assay to milk samples which differ in fat and protein contents. Although imprecise (mean RSD about 30%), the method proved to be accurate and sensitive enough to allow the correct attribution of sample as compliant or non-compliant according to EU legislation in force. Agreeing results to those of a reference ELISA were obtained on 40 milk samples by matrix-matched calibration in pasteurized milk.

Keywords: Immunochromatographic assay; Gold colloid; Mycotoxins; Food analysis

Glucose oxidase-functionalized fluorescent gold nanoclusters as probes for glucose by Xiaodong Xia; Yunfei Long; Jianxiu Wang (pp. 81-86).

Display Omitted► A glucose oxidase/gold nanocluster conjugates formed by etching chemistry. ► Integration of the bioactivities and fluorescence properties within a single unit. ► These conjugates serve as novel fluorescent probe for glucose.Creation and application of noble metal nanoclusters have received continuous attention. By integrating enzyme activity and fluorescence for potential applications, enzyme-capped metal clusters are more desirable. This work demonstrated a glucose oxidase (an enzyme for glucose)-functionalized gold cluster as probe for glucose. Under physiological conditions, such bioconjugate was successfully prepared by an etching reaction, where tetrakis (hydroxylmethyl) phosphonium-protected gold nanoparticle and thioctic acid-modified glucose oxidase were used as precursor and etchant, respectively. These bioconjugates showed unique fluorescence spectra ( λ_{em max}=650nm, λ_{ex max}=507nm) with an acceptable quantum yield (ca. 7%). Moreover, the conjugated glucose oxidase remained active and catalyzed reaction of glucose and dissolved O₂ to produce H₂O₂, which quenched quantitatively the fluorescence of gold clusters and laid a foundation of glucose detection. A linear range of 2.0×10⁻⁶–140×10⁻⁶M and a detection limit of 0.7×10⁻⁶M (S/N=3) were obtained. Also, another horseradish peroxidase/gold cluster bioconjugate was produced by such general synthesis method. Such enzyme/metal cluster bioconjugates represented a promising class of biosensors for biologically important targets in organelles or cells.

Keywords: Gold nanocluster; Glucose oxidase; Etching chemistry; Glucose; Fluorescence

Quantitative detection of well-based DNA array using switchable lanthanide luminescence by Ulla Karhunen; Minna Soikkeli; Susanne Lahdenperä; Tero Soukka (pp. 87-92).

Display Omitted► Oligonucleotide hybridization switches on lanthanide luminescence. ► The binary probe technology enables wash-free nucleic acid array. ► Detection of both synthetic targets and PCR-amplified E. coli DNA is demonstrated.In this report a novel wash-free method for multiplexed DNA detection is demonstrated employing target specific probe pairs and switchable lanthanide luminescence technology on a solid-phase array. Four oligonucleotide capture probes, conjugated at 3′ to non-luminescent lanthanide ion carrier chelate, were immobilized as a small array on the bottom of a microtiter plate well onto which a mix of corresponding detection probes, conjugated at 5′ to a light absorbing antenna ligand, were added. In the presence of complementary target nucleic acid both the spotted capture probe and the liquid-phase detection probe hybridize adjacently on the target. Consequently the two non-luminescent label molecules self-assemble and form a luminescent mixed lanthanide chelate complex. Lanthanide luminescence is thereafter measured without a wash step from the spots by scanning in time-resolved mode. The homogeneous solid-phase array-based method resulted in quantitative detection of synthetic target oligonucleotides with 0.32nM and 0.60nM detection limits in a single target and multiplexed assay, respectively, corresponding to 3× SD of the background. Also qualitative detection of PCR-amplified target from Escherichia coli is described.

Keywords: Lanthanide; Luminescence; Nucleic acid; Array; Homogeneous

Practical considerations for preparing polymerized phospholipid bilayer capillary coatings for protein separations by Seid M. Adem; Elisabeth Mansfield; John P. Keogh; Henry K. Hall Jr.; Craig A. Aspinwall (pp. 93-98).

Display Omitted► We investigated the stability of polymerized lipid bilayer capillary coatings. ► Effects of pH and capillary inner diameter on stability of coating were studied. ► Smaller inner diameter capillaries provide a very stable coating. ► The polymerized lipid bilayer coatings are stable across a wide range of pH values. ► The polymerized lipid bilayer coatings are stable for an extended period of time.Phosphorylcholine (PC) based phospholipid bilayers have proven useful as capillary coating materials due to their inherent resistance to non-specific protein adsorption. The primary limitation of this important class of capillary coatings remains the limited long-term chemical and physical stability of the coatings. Recently, a method for increasing phospholipid coating stability in fused silica capillaries via utilization of polymerized, synthetic phospholipids was reported. Here, we expand upon these studies by investigating polymerized lipid bilayer capillary coatings with respect to separation performance including run-to-run, day-to-day and column-to-column reproducibility and long-term stability. In addition, the effects of pH and capillary inner diameter on polymerized phospholipid coated capillaries were investigated to identify optimized coating conditions. The coatings are stabilized for protein separations across a wide range of pH values (4.0–9.3), a unique property for capillary coating materials. Additionally, smaller inner diameter capillaries (≤50μm) were found to yield marked enhancements in coating stability and reproducibility compared to wider bore capillaries, demonstrating the importance of capillary size for separations employing polymerized phospholipid coatings.

Keywords: Phospholipids; Capillary coating; Polymerized lipid bilayer; Bis-SorbPC

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Analytica Chimica Acta (v.772, #)

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Analytica Chimica Acta (v.772, #)