Analytica Chimica Acta (v.623, #2)
Editorial Board (i).
Mass spectrometry of the fifth nucleoside: A review of the identification of pseudouridine in nucleic acids by Anita Durairaj; Patrick A. Limbach (117-125).
Pseudouridine, the so-called fifth nucleoside due to its ubiquitous presence in ribonucleic acids (RNAs), remains among the most challenging modified nucleosides to characterize. As an isomer of the major nucleoside uridine, pseudouridine cannot be detected by standard reverse-transcriptase-based DNA sequencing or RNase mapping approaches. Thus, over the past 15 years, investigators have focused on the unique structural properties of pseudouridine to develop selective derivatization or fragmentation strategies for its determination. While the N-cyclohexyl-N′-β-(4-methylmorpholinium)ethylcarbodiimide p-tosylate (CMCT)-reverse transcriptase assay remains both a popular and powerful approach to screen for pseudouridine in larger RNAs, mass-spectrometry-based approaches are poised to play an increasingly important role in either confirming the findings of the CMCT-reverse transcriptase assay or in characterizing pseudouridine sequence placement and abundance in smaller RNAs. This review includes a brief discussion of pseudouridine including a summary of its biosynthesis and known importance within various RNAs. The review then focuses on chemical derivatization approaches that can be used to selectively modify pseudouridine to improve its detection, and the development of mass-spectrometry-based assays for the identification and sequencing of pseudouridine in various RNAs.
Keywords: N-Cyclohexyl-N′-β-(4-methylmorpholinium)ethylcarbodiimide p-tosylate derivatization; Cyanoethylation; Pseudouridine-synthase; Matrix-assisted laser desorption/ionization-mass spectrometry; Liquid chromatography–mass spectrometry; Modified nucleosides;
High-accuracy determination of iron in seawater by isotope dilution multiple collector inductively coupled plasma mass spectrometry (ID-MC-ICP-MS) using nitrilotriacetic acid chelating resin for pre-concentration and matrix separation by Jeroen de Jong; Véronique Schoemann; Delphine Lannuzel; Jean-Louis Tison; Nadine Mattielli (126-139).
In the present paper we describe a robust and simple method to measure dissolved iron (DFe) concentrations in seawater down to <0.1 nmol L−1 level, by isotope dilution multiple collector inductively coupled plasma mass spectrometry (ID-MC-ICP-MS) using a 54Fe spike and measuring the 57Fe/54Fe ratio. The method provides for a pre-concentration step (100:1) by micro-columns filled with the resin NTA Superflow of 50 mL seawater samples acidified to pH 1.9. NTA Superflow is demonstrated to quantitatively extract Fe from acidified seawater samples at this pH. Blanks are kept low (grand mean 0.045 ± 0.020 nmol L−1, n = 21, 3× S.D. limit of detection per session 0.020–0.069 nmol L−1 range), as no buffer is required to adjust the sample pH for optimal extraction, and no other reagents are needed than ultrapure nitric acid, 12 mM H2O2, and acidified (pH 1.9) ultra-high purity (UHP) water. We measured SAFe (sampling and analysis of Fe) reference seawater samples Surface-1 (0.097 ± 0.043 nmol L−1) and Deep-2 (0.91 ± 0.17 nmol L−1) and obtained results that were in excellent agreement with their DFe consensus values: 0.118 ± 0.028 nmol L−1 (n = 7) for Surface-1 and 0.932 ± 0.059 nmol L−1 (n = 9) for Deep-2. We also present a vertical DFe profile from the western Weddell Sea collected during the Ice Station Polarstern (ISPOL) ice drift experiment (ANT XXII-2, RV Polarstern) in November 2004–January 2005. The profile shows near-surface DFe concentrations of ∼0.6 nmol L−1 and bottom water enrichment up to 23 nmol L−1 DFe.
Keywords: Iron; Mass spectrometry; Seawater; Weddell Sea;
Bromine determination in polymers by inductively coupled plasma-mass spectrometry and its potential for fast first screening of brominated flame retardants in polymers and paintings by Auristela Solà Vázquez; José M. Costa-Fernandez; Jorge Ruiz Encinar; Rosario Pereiro; Alfredo Sanz-Medel (140-145).
The impact of brominated flame retardants (BFRs) on the environment and their potential risk in animal and human health is a present concern. Therefore, existing legislation in the European Union demands that polymers with BFRs are identified and eliminated from the recycling process due to their potential health hazard.In this work, a flow-injection (FI) system coupled to inductively coupled plasma-mass spectrometry (ICP-MS) was optimized for the detection of traces of bromine in polymers, plastic paints and enamels containing BFRs. Sample preparation requires a microwave-assisted digestion in order to transfer bromine in polymeric samples to solution. After appropriate optimization of the digestion procedure and the ICP-MS detection, a detection limit (DL) of 4.2 mg kg−1 was obtained for synthesized polyurethane standards containing known concentrations of bromine. The precision of the proposed method, evaluated as the R.S.D. of signals obtained for three replicates of polymeric standard BFRs at the normative EU level, was as low as 3.6%.This simple developed methodology was characterized for the screening of bromine in polymeric matrices. The proposed system provides rapid binary yes/no overall responses, being appropriate for the screening of bromine above a pre-set concentration threshold. The unreliability region (UR), given by the probability of false positives and false negatives (set at 5% in both cases), was in the range between 442 and 678 mg kg−1 of bromine (at a cut-off level of 0.1% in BFRs by weight of homogeneous material fixed by the EU normative). Finally, the applicability of the proposed screening system was tested for the reliable control of bromine in different commercial samples including flame-retardant paints and enamels.
Keywords: Bromine; Polymers; Inductively coupled plasma-mass spectrometry; Brominated flame retardants; Screening;
Quality control and original discrimination of Ganoderma lucidum based on high-performance liquid chromatographic fingerprints and combined chemometrics methods by Yi Chen; Shang-Bin Zhu; Ming-Yong Xie; Shao-Ping Nie; Wei Liu; Chang Li; Xiao-Feng Gong; Yuan-Xing Wang (146-156).
In this paper, the feasibility and advantages of employing high-performance liquid chromatographic (HPLC) fingerprints combined with chemometrics methods for quality control of the cultured fruiting bodies of Ganoderma lucidum were investigated and demonstrated for the first time. In order to compare the HPLC fingerprints chromatograms between G. lucidum from different origins, the similarities of all the 60 samples and relative peak areas of 19 characteristic compounds were firstly calculated respectively. Then different pattern recognition procedures, including hierarchical cluster analysis (HCA), principal component analysis (PCA), partial least squares-discrimination analysis (PLS-DA) and soft independent modeling of class analogy (SIMCA) were applied to classify the G. lucidum samples according to their cultivated origins. Consistent results were obtained to show that G. lucidum samples could be successfully grouped in accordance with the province of origin. Furthermore, four marker constituents were screened out to be the most discriminant variables, which could be applied to accurate discrimination and quality control of G. lucidum by quantitative analysis. Finally, the chemical properties of those samples were also investigated to find out the differences of quality between them. Ranked in decreasing order, the quality of the G. lucidum can be arranged as Jinzhai/Huangshan, Shandong followed by Zhejiang samples. Our results revealed that the developed method has potential perspective for the original discrimination and quality control of G. lucidum.
Keywords: G. lucidum; High-performance liquid chromatography; Fingerprint; Chemometrics;
Assays for serum cholinesterase activity by capillary electrophoresis and an amperometric flow injection choline biosensor by Bo-Chuan Hsieh; Hsien-Yi Hsiao; Tzong-Jih Cheng; Richie L.C. Chen (157-162).
A capillary electrophoresis method and a durable choline biosensor were developed for measuring serum cholinesterase (EC 184.108.40.206) activity, a useful clinical index for liver function. The former is based on separation of benzoate and benzoylcholine (the artificial substrate of cholinesterase) in an uncoated fused-silica capillary. The migration time of benzoylcholine and benzoate was 1.3 min and 5.5 min, respectively. By the peak areas of A 233 signals, the linear dynamic ranges for both analytes were 0.01–50.0 mM, and the relative standard deviations of 1.0 mM benzoylcholine and benzoate were less than 4% and 6%, respectively.The FIA-choline sensor was constructed with the working electrode of the flow cell covered with a natural chitinous membrane purified from Taiwanese soldier crab, Mictyris brevidactylus. The biomembrane served as the supporting material for enzyme immobilization (choline oxidase, EC 220.127.116.11), and also prevented protein adsorption on the electrode surface. The calibration curve was linear between 0.05 and 5.0 mM (r = 0.999). The relative standard deviations for 1.0 mM choline (n = 7) were less than 3%, and the activity of the bioactive membrane lasted for about 2 months. The analytical results of both methods correlated well (r = 0.940).
Keywords: Benzoate; Benzoylcholine; Biosensor; Capillary electrophoresis; Serum cholinesterase;
A novel separation/preconcentration system based on solidification of floating organic drop microextraction for determination of lead by graphite furnace atomic absorption spectrometry by Shayessteh Dadfarnia; Ali Mohammad Salmanzadeh; Ali Mohammad Haji Shabani (163-167).
Solidified floating organic drop microextraction (SFODME) was successfully used as a sample preparation method for graphite furnace atomic absorption spectrometry (GFAAS). 20 μL of 1-undecanol containing dithizone as the chelating agent (2 × 10−4 mol L−1) was transferred to the water samples containing lead ions, and the solution was stirred for the prescribed time. The sample vial was cooled in an ice bath for 5 min. The solidified extract was transferred into a conical vial where it melted immediately, and then 10 μL of it was analyzed by GFAAS.Factors that influence the extraction and complex formation, such as pH, concentration of dithizone, extraction time, sample volume, and ionic strength were optimized. Under the optimized conditions, a good relative standard deviation of ±5.4% at 10 ng L−1 and detection limit of 0.9 ng L−1 were obtained. The procedure was applied to tap water, well water, river water and sea water, and accuracy was assessed through the analysis of certified reference water or recovery experiments.
Keywords: Solidified floating organic drop microextraction; Graphite furnace atomic absorption spectrometry; Preconcentration; Lead analysis; Natural waters;
Analysis of steroids in yeast-mediated cell culture by on-line solid-phase extraction coupled high-performance liquid chromatography electrospray-ionization/mass spectrometry and novel continuous postcolumn infusion of internal standard technique by Cheanyeh Cheng; Hsiang-Rong Tsai (168-177).
The reduction of 17-ketosteroid estrone or androstenedione to corresponding 17α- and 17β-estradiol or testosterone and epitestosterone has been performed with Saccharomyces cerevisiae. In the analysis of the cell culture, the solid-phase extraction (SPE) method was on-line coupled to high-performance liquid chromatography electrospray-ionization/mass spectrometry (HPLC-ESI/MS) for sample pretreatment to eliminate the complicated matrix interference and preconcentrate of the analytes before chromatographic separation. A novel quantification method with the continuous postcolumn infusion of internal standard was developed for the determination of substrate and products. This novel quantitative method can stabilize and enhance the ionization of all analytes during analysis. The HPLC-ESI/MS analysis of estrone, 17α-, and 17β-estradiol was operated with a negative ion mode and the analysis of androstenedione, testosterone, and epitestosterone was operated with a positive ion mode. The optimal concentration of the internal standard progesterone with the continuous postcolumn infusion technique was 3 μg mL−1 for estrogen analysis and 1 ng mL−1 for androgen analysis and both were at a constant infusion rate of 0.5 μL min−1. All of the linear correlation coefficients of the standard calibration curves were over 0.99 and had a linear range from 0 to 50 ng mL−1. The limit of detections (LODs) and the limit of quantitations (LOQs) for steroids analyzed were from 0.12 to 0.36 ng mL−1 and from 0.4 to 1.2 ng mL−1, respectively. The analysis accuracies and precisions were better than 94% and lower than 8.8% R.S.D., respectively. The developed method for the analysis of steroids in the cell culture was successful.
Keywords: Estrogens; Androgens; Saccharomyces cerevisiae; Solid-phase extraction; Liquid chromatography electrospray-ionization/mass spectrometry; Postcolumn infusion of internal standard;
Assessment of hand-held Raman instrumentation for in situ screening for potentially counterfeit artesunate antimalarial tablets by FT-Raman spectroscopy and direct ionization mass spectrometry by Camilla Ricci; Leonard Nyadong; Felicia Yang; Facundo M. Fernandez; Christopher D. Brown; Paul N. Newton; Sergei G. Kazarian (178-186).
Pharmaceutical counterfeiting has become a significant public health problem worldwide and new, rapid, user-friendly, reliable and inexpensive methods for drug quality screening are needed. This work illustrates the chemical characterization of genuine and fake artesunate antimalarial tablets by portable Raman spectroscopy and validation by FT-Raman spectroscopy and ambient mass spectrometry. The applicability of a compact and robust portable Raman spectrometer (TruScan™) for the in situ chemical identification of counterfeit tablets is reported.
Keywords: Counterfeit drugs; Portable Raman spectroscopy; Mass spectrometry; Desorption electrospray ionization; Direct analysis in real-time; Malaria;
Analysis of a coloured Dutch map from the eighteenth century: The need for a multi-analytical spectroscopic approach using portable instrumentation by K. Castro; N. Proietti; E. Princi; S. Pessanha; M.L. Carvalho; S. Vicini; D. Capitani; J.M. Madariaga (187-194).
A Dutch map from the eighteenth century was multi-analytically analysed making use of energy dispersive X-ray fluorescence (EDXRF), Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance (NMR), Raman and scanning electron microscopy coupled to energy dispersive spectrometry (SEM-EDS). The cellulosic support was characterised and its state of conservation was evaluated. Besides, paramagnetic impurities were detected together with copper metallic chips. The colours present in some areas of the map were also analysed. Vermilion, carbon black and organic pigments were found. Surprisingly, in the green areas, the rare presence of the mineral moolooite (copper oxalate) was detected. A possible biological attack is discussed in order to explain the presence of such compound. Almost all of the techniques used in the analysis were portable, non-destructive and non-invasive, which is very desirable when analysing objects belonging to Cultural Heritage. The need for a multi-analytical approach using portable instrumentation is also discussed.
Keywords: Raman; Fourier transform infrared spectroscopy; Nuclear magnetic resonance; X-ray fluorescence spectrometry; Scanning electron microscopy-energy disperse spectrometry; Moolooite;
Development of an optical surface plasmon resonance biosensor assay for (fluoro)quinolones in egg, fish, and poultry meat by A.-C. Huet; C. Charlier; G. Singh; S. Benrejeb Godefroy; J. Leivo; M. Vehniäinen; M.W.F. Nielen; S. Weigel; Ph. Delahaut (195-203).
The aim of this study was to develop an optical biosensor inhibition immunoassay, based on the surface plasmon resonance (SPR) principle, for use as a screening test for 13 (fluoro)quinolones, including flumequine, used as veterinary drugs in food-producing animals. For this, we immobilised various quinolone derivatives on the sensor chip and tested binding of a range of different antibodies (polyclonal and one engineered antibody) in the presence and absence of free (fluoro)quinolones. The main challenge was to detect flumequine in an assay giving good results for the other compounds. One antigen–antibody combination proved satisfactory: polyclonal antibodies raised against a dual immunogen and, on the sensor chip, a fluoroquinolone derivative. It was the first time that this concept of the bi-active antibody was described in the literature.The assay, optimised for detection in three matrices (poultry muscle, fish, and egg), was tested on incurred samples prepared by liquid extraction followed by two washing steps. This rapid, simple method proved adequate for detecting at least 13 (fluoro)quinolones at concentrations below established maximum residue levels (MRLs). The reference molecule norfloxacin could be detected in the range of 0.1–10 μg kg−1 in extracts of egg and poultry meat and in the range of 0.1–100 μg kg−1 in extracts of fish. The determined midpoints of these calibration curves were about 1, 1.5 and 3 μg kg−1 in poultry meat, egg and fish, respectively.
Keywords: Antibiotic; Quinolones; Biosensor; Surface plasmon resonance; Detection;
Approach for non-destructive pigment analysis in model liquids and carrots by means of time-of-flight and multi-wavelength remittance readings by Manuela Zude; Lorenzo Spinelli; Alessandro Torricelli (204-212).
Non-destructive spectroscopy in the visible and near infrared wavelength range has been introduced for analyzing absorbing compounds in fruit and vegetables. A drawback of the method appears due to the measuring principle, where photons detected in the diffusive tissue are influenced by the sample absorption but also scattering properties leading to variation in the photon pathlength. In the present work, distribution of time-of-flight reading was used to calculate the effective pathlength between source and detector. Using this information in addition to the spectral intensities obtained with common continuous wave spectroscopy, Lambert–Beer law was applied for analyzing absolute pigment contents.The method was tested for liquid phantoms mimicking the optical properties of fresh fruit and vegetables. Lambert–Beer law using a constant pathlength as well as combined application of the intensity at a specific wavelength and the effective pathlength resulted in low calibration errors with r 2 > 0.98. Applying the two calibrations on phantoms mimicking changes in the scattering properties resulted in validation results of r 2 = 0.47 and 0.64, respectively.Improved results by using the effective pathlength were confirmed on real-world samples. The carrot carotenoids analysis resulted in validation results of r 2 = 0.66 and 0.74, respectively, while the measuring uncertainty was reduced from 18.10 to 9.62%.Multivariate calibrations using the entire carrot spectra and data pre-processing aiming the reduction of scattering effects resulted in slightly lower measuring uncertainty by comparison. In the sensor fusion approach proposed, however, no expensive spectrophotometer is required and the phenomenon of varying optical properties of the sample is characterized.
Keywords: Carotenoids; Carrots; Effective pathlength; Lambert–Beer law; Phantom; Sensor fusion; Time-of-flight;
An electropolymerized Nile Blue sensing film-based nitrite sensor and application in food analysis by Xiaowei Chen; Fang Wang; Zilin Chen (213-220).
This paper reports a poly-Nile Blue (PNB) sensing film based electrochemical sensor and the application in food analysis as a possible alternative for electrochemical detection of nitrite. The PNB-modified electrode in the sensor was prepared by in situ electropolymerization of Nile Blue at a prepolarized glassy carbon (GC) electrode and then characterized by cyclic voltammetry (CV) and pulse voltammetry in phosphate buffer (pH 7.1). Several key operational parameters affecting the electrochemical response of PNB sensing film were examined and optimized, such as polarization time, PNB film thickness and electrolyte pH values. As the electroactive PNB sensing film provides plenty of active sites for anodic oxidation of nitrite, the nitrite sensor exhibited high performance including high sensitivity, low detection limit, simple operation and good stability at the optimized conditions. The nitrite sensor revealed good linear behavior in the concentration range from 5.0 × 10−7 mol L−1 to 1.0 × 10−4 mol L−1 for the quantitative analysis of nitrite anion with a limit of detection of 1.0 × 10−7 mol L−1. Finally, the application in food analysis using sausage as testing samples was investigated and the results were consistent with those obtained by standard spectrophotometric method.
Keywords: Nitrite sensor; Nile Blue; Chemically modified electrode; Food analysis;
A study of the analytical behaviour of selected new molecular entities using electrospray ionisation ion trap mass spectrometry, liquid chromatography, gas chromatography and polarography and their determination in serum at therapeutic concentrations by Virginia Rodríguez Robledo; W. Franklin Smyth (221-230).
This paper provides analytical chemical information on selected new molecular entities (NMEs) which are drugs that have recently been approved by the FDA. These are the antiretroviral drugs, atazanavir, indinavir and emtricitabine, the antibacterial gemifloxacin, rosuvastatine which is a cholesterol-lowing drug, the anti-cancer drug gefitinib and aprepitant for neurological disorders. Electrospray ionisation-quadrupole ion trap mass spectrometry (ESI-MS n ) was employed to generate tandem mass spectrometric (MS2) data of the drugs studied and structural assignments of product ions were supported by quadrupole time-of-flight mass spectrometry (QToF-MS/MS). These fragmentation studies were then utilised in the development and validation of a specific and sensitive liquid chromatographic method (LC–ESI-MS2) to identify and determine these drugs at therapeutic concentration levels in serum after a single protein precipitation procedure with acetonitrile. In addition, this method was compared to the application of gas liquid chromatography-flame ionisation detection (GLC-FID) and differential pulse polarography (DPP) for the analysis of these NMEs in serum.
Keywords: New molecular entities; Electrospray ionisation-ion trap mass spectrometry; Liquid chromatography–electrospray ionisation-ion trap mass spectrometry; Gas liquid chromatography-flame ionisation detection; Differential pulse polarography; Serum analysis;
Capillary electrophoresis–chemiluminescence determination of norfloxacin and prulifloxacin by Zhongju Yang; Xiaoli Wang; Weidong Qin; Huichun Zhao (231-237).
A capillary electrophoresis (CE)–chemiluminescence (CL) method for determining norfloxacin (NFLX) and prulifloxacin (PFLX) was developed based on the enhanced CL intensity of the cerium(IV)–sulfite–fluoroquinolone (FQ) reaction sensitized by terbium(III). The separation was conducted in buffer composed of 20 mM sodium citrate, 4 mM citric acid and 10 mM sodium sulfite at pH 6.1. The CL reagent solution consisted of 2 mM cerium(IV), 4 mM terbium(III) and 1.1 mM hydrochloric acid. NFLX and PFLX were baseline separated within 11 min with detection limits (S/N = 3) of 0.057 and 0.084 μg mL−1, respectively. The maximum intra- and inter-day relative standard deviations (R.S.D.s) of migration time of the analytes were less than 4.0% and 4.2%, respectively. The proposed method was applied to detect NFLX and PFLX in fortified urine sample and the results were comparable to high-performance liquid chromatography (HPLC)–UV method. Moreover, the high selectivity of the CL detection and the high-separation efficiency of CE render the method the potential of quick analyzing fluoroquinolones in real complex matrix.
Keywords: Capillary electrophoresis; Chemiluminescence; Fluoroquinolones; Urine sample;