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Analytica Chimica Acta (v.633, #1)

Editorial Board (pp. iii).

Recent trends in total reflection X-ray fluorescence spectrometry for biological applications by Norbert Szoboszlai; Zsófia Polgári; Victor G. Mihucz; Gyula Záray (pp. 1-18).

This review is focused on the application of total reflection X-ray fluorescence (TXRF) spectrometry in the field of biological research. In the last decade, most papers were published by authors who applied laboratory-scale TXRF equipments. The application of synchrotron radiation as excitation source (SR-TXRF) shows a slowly increasing tendency. In the cited papers the micro-, trace and multielement capability of these TXRF techniques was demonstrated in the clinical and medical laboratory practice, as well as in various plant physiological studies. For speciation of elements in biological matrices, the TXRF was used as element specific detector following an off-line separation step (e.g., thin layer chromatography, high performance liquid chromatography), however, these off-line methods are not competitive with the on-line coupled HPLC-inductively coupled plasma mass spectrometry.

Keywords: Total reflection X-ray fluorescence (TXRF); Biological samples; Environmental; Human; Clinical; Elemental analysis

Short transient signals, a challenge for inductively coupled plasma mass spectrometry, a review by Martin Tanner; Detlef Günther (pp. 19-28).

The ability to acquire and handle short transient signals is key in order to open new applications for inductively coupled plasma mass spectrometry (ICP-MS), for example, in life sciences. Technological and methodological achievements are reviewed to show challenges and capabilities of short transients in ICP-MS technology or hyphenated techniques. The dynamic processes in the plasma need to be controlled or observed to assure quality of quantitative results. Most precise instrumentation is to date multiple collector sector field MS but drifting isotope ratios are observed in transient signals using these instruments, thus limiting precision of such measurements and leaving unknowns in quantitative results. TOFMS in principle provides fast simultaneous multi-element detection, scanning instruments like quadrupole MS or scanning sector field MS are fundamentally restricted. However, new commercial ICP-MS instruments can be expected in the near future, making short transients more and more attractive to shorten acquisition times and to increase signal to noise ratio of element analyses.

Keywords: Inductively coupled plasma mass spectrometry; Fast transient signals; Plasma robustness; Mass spectrometers; Simultaneous multi-element detection

Matrix effects on the multi-collector inductively coupled plasma mass spectrometric analysis of high-precision cadmium and zinc isotope ratios by Alyssa E. Shiel; Jane Barling; Kristin J. Orians; Dominique Weis (pp. 29-37).

Resin-derived contaminants added to samples during column chemistry are shown to cause matrix effects that lead to inaccuracy in multi-collector inductively coupled plasma mass spectrometry measurement of small natural variations in Cd and Zn isotopic compositions. These matrix effects were evaluated by comparing pure Cd and Zn standards and standards doped with bulk column blank from the anion exchange chromatography procedure. Doped standards exhibit signal enhancements (Cd, Ag, Zn and Cu), instrumental mass bias changes and inaccurate isotopic compositions relative to undoped standards, all of which are attributed to the combined presence of resin-derived organics and inorganics. The matrix effect associated with the inorganic component of the column blanks was evaluated separately by doping standards with metals at the trace levels detected in the column blanks. Mass bias effects introduced by the inorganic column blank matrix are smaller than for the bulk column blank matrix but can still lead to significant changes in ion signal intensity, instrumental mass bias and isotopic ratios. Chemical treatment with refluxed HNO₃ or HClO₄/HNO₃ removes resin-derived organic components resulting in matrix effects similar in magnitude to those associated with the inorganic component of the column blank.Mass bias correction using combined external normalization-SSB does not correct for these matrix effects because the instrumental mass biases experienced by Cd and Zn are decoupled from those of Ag and Cu, respectively. Our results demonstrate that ion exchange chromatography and associated resin-derived contaminants can be a source of error in MC-ICP-MS measurement of heavy stable element isotopic compositions.

Keywords: MC-ICP-MS; Mass bias; Resin; Ion exchange chromatography; Heavy stable isotopes; Transition metals

Real time and in situ determination of lead in road sediments using a man-portable laser-induced breakdown spectroscopy analyzer by J. Cuñat; F.J. Fortes; J.J. Laserna (pp. 38-42).

In situ, real time levels of lead in road sediments have been measured using a man-portable laser-induced breakdown spectroscopy analyzer. The instrument consists of a backpack and a probe housing a Q-switched Nd:YAG laser head delivering 50mJ per pulse at 1064nm. Plasma emission was collected and transmitted via fiber optic to a compact cross Czerny-Turner spectrometer equipped with a linear CCD array allocated in the backpack together with a personal computer. The limit of detection (LOD) for lead and the precision measured in the laboratory were 190μgg⁻¹ (calculated by the 3σ method) and 9% R.S.D. (relative standard deviation), respectively. During the field campaign, averaged Pb concentration in the sediments were ranging from 480μgg⁻¹ to 660μgg⁻¹ depending on the inspected area, i.e. the entrance, the central part and the exit of the tunnel. These results were compared with those obtained with flame-atomic absorption spectrometry (flame-AAS). The relative error, expressed as [100(LIBS result−flame AAS result)/(LIBS result)], was approximately 14%.

Keywords: Portable laser-induced breakdown spectrometry instrument; Traffic pollution; Particulate material; Lead in situ screening; Surface analysis

Pattern recognition of Chinese flue-cured tobaccos by an improved and simplified K-nearest neighbors classification algorithm on near infrared spectra by Li-Jun Ni; Li-Guo Zhang; Juan Xie; Jian-Qun Luo (pp. 43-50).

In tobacco industry of China, tobacco leaves are classified and managed in terms of their cultivation areas and plant parts of tobacco-stalks. However, sometimes intentionally or involuntary mislabeling cultivation areas, blending tobacco plant parts would occur into tobacco market. The error will affect the style and quality of cigarettes. In the present work, more than 1000 Chinese flue-cured tobacco leaf samples, which have 12 genotypes and cultivated from 5 to 10 regions of China in 2003 and 2004, have been discriminated by means of an improved and simplified KNN classification algorithm (IS-KNN) based on near infrared (NIR) spectra. An original method of optimizing number of significant principal components (PCs) based on analysis of error and cross-validation was advanced. Compared with conventional pattern recognition methods KNN, NN, LDA and PLS-DA, IS-KNN exhibits good adaptability in discrimination of complicated Chinese flue-cured tobaccos. The practice in this work shows that optimized number of PCs and performance of classification models are closely relative to complicated extent of samples but not to number of categories or samples. The results demonstrated the usefulness of NIR spectra combined with chemometrics as an objective and rapid method for the authentication and identification of tobacco leaves or other kinds of powder samples.

Keywords: Near infrared; Pattern recognition of multi-categories; Improved and simplified K-nearest neighbors; Optimization of principal component number; Chemometrics; Tobacco

CYP450 2B4 covalently attached to carbon and gold screen printed electrodes by diazonium salt and thiols monolayers by M.A. Alonso-Lomillo; C. Yardimci; O. Domínguez-Renedo; M.J. Arcos-Martínez (pp. 51-56).

An easy covalent immobilization method used to develop enzyme biosensors based on carbon and gold screen printed electrodes (SPCEs and gold SPEs) is described. The linkage of biomolecules through 4-nitrobenzenediazonium tetrafluoroborate, mercaptopropionic acid and thioctic acid monolayers has been attempted using bare SPCEs and gold SPEs, as well as gold nanoparticles (AuNPs) modified SPCEs and gold SPEs. Direct covalent attachment of Cytochrome P450 2B4 (CYP450 2B4) to the transducer has been carried out by carbodiimide and hydroxysuccinimide. Experimental variables in the immobilization process and in the chronoamperometric determination of Phenobarbital (PB) have been optimized by the experimental design methodology. Reproducibility of the different biosensors has been checked under the optimum conditions, yielding values lower than 6%. Their performances have been shown by the determination of PB in pharmaceutical drugs.

Keywords: Screen printed electrodes; Gold nanoparticles; Diazonium salt; Self-assembled monolayer; Biosensor

Polydimethylsiloxane/polypyrrole stir bar sorptive extraction and liquid chromatography (SBSE/LC-UV) analysis of antidepressants in plasma samples by L.P. Melo; A.M. Nogueira; F.M. Lanças; M.E.C. Queiroz (pp. 57-64).

A new polymeric coating consisting of a dual-phase, polydimethylsiloxane (PDMS) and polypyrrole (PPY) was developed for the stir bar sorptive extraction (SBSE) of antidepressants (mirtazapine, citalopram, paroxetine, duloxetine, fluoxetine and sertraline) from plasma samples, followed by liquid chromatography analysis (SBSE/LC-UV). The extractions were based on both adsorption (PPY) and sorption (PDMS) mechanisms. SBSE variables, such as extraction time, temperature, pH of the matrix, and desorption time were optimized, in order to achieve suitable analytical sensitivity in a short time period. The PDMS/PPY coated stir bar showed high extraction efficiency (sensitivity and selectivity) toward the target analytes. The quantification limits (LOQ) of the SBSE/LC-UV method ranged from 20ngmL⁻¹ to 50ngmL⁻¹, and the linear range was from LOQ to 500ngmL⁻¹, with a determination coefficient higher than 0.99. The inter-day precision of the SBSE/LC-UV method presented a variation coefficient lower than 15%. The efficiency of the SBSE/LC-UV method was proved by analysis of plasma samples from elderly depressed patients.

Keywords: Stir bar sorptive extraction; Polypyrrole; Polydimethylsiloxane; Liquid chromatography; Plasma sample

Integrated analysis of serum and liver metabonome in liver transplanted rats by gas chromatography coupled with mass spectrometry by Yi Wang; Yi Tao; Yunjin Lin; Liang Liang; Yi Wu; Haibin Qu; Tingbo Liang; Yiyu Cheng (pp. 65-70).

In this paper, we present a metabonomic method for the investigation of abnormal metabolic process in both serum and liver tissue of liver transplanted rats. Syngeneic transplantation was performed on male Lewis rats. The serum and grafted liver on day 1, 3, and 7 post-transplant were collected to analyze endogenous metabolites using gas chromatography coupled with mass spectrometry (GC–MS). The method was validated with acceptable linearity, precision, and repeatability. Thirty-four metabolites in serum and 29 metabolites in liver were identified. Results of correlation analysis illustrated metabolites with similar function exhibited similar variations in liver and serum. The data processed by principle component analysis (PCA) showed time-dependent biochemical variations. As a consequence, the present study may offer specific putative pathways in the pathophysiological mechanism of orthotopic liver transplantation.

Keywords: Liver transplantation; Metabolomic profile; Gas chromatography–mass spectrometry; Integrated analysis

Selective spectrofluorimetric determination of glutathione in clinical and biological samples using 1,3,5,7-tetramethyl-8-phenyl-(2-maleimide)-difluoroboradiaza-s-indacene by Xiao-Feng Guo; Hong Wang; Yue-Hong Guo; Hua-Shan Zhang (pp. 71-75).

This work reports the development of a selective, sensitive and rapid spectrofluorimetric method for the determination of reduced glutathione (GSH) in the presence of relatively high levels of cysteine (Cys) in clinical and biological samples using 1,3,5,7-tetramethyl-8-phenyl-(2-maleimide)-difluoroboradiaza-s-indacene (TMPAB- o-M). The fluorescence from TMPAB- o-M is strongly quenched by its maleimide moiety, but after reaction with thiol, the fluorescence is restored with a 350-fold intensity increase (fluorescence quantum yield from 0.002 to 0.73). In H₃Cit–Na₂HPO₄ buffer (pH 7.40), the derivatization is completed in just 5min under 37°C. The linear range is 0.005–0.2μmolL⁻¹, with detection limit of 1.1×10⁻¹⁰molL⁻¹ (signal-to-noise ratio=3). Almost all amino acids, including Cys, impose no interference even if present at relatively high concentrations (amino acids:GSH=100:1, Cys:GSH=1:1, molar ratio, C_GSH=3×10⁻⁷molL⁻¹). The sample can be used directly without further treatment after the protein is removed. The developed method is precise with a relative standard deviation (R.S.D.) lower than 5.0% ( n=6) and has been applied to the determination of GSH in human blood and pig’s liver with recoveries between 94.4 and 105.6%.

Keywords: 1,3,5,7-Tetramethyl-8-phenyl-(2-maleimide)-difluoroboradiaza-s-indacene; Glutathione; Human blood; Pig’s liver; Spectrofluorimetry

A high throughput chemiluminescence method for determination of chemical oxygen demand in waters by Hong Yao; Bin Wu; Haibin Qu; Yiyu Cheng (pp. 76-80).

A novel and high throughput chemiluminescence (CL) method for determination of chemical oxygen demand (COD) in water sample was originally developed based on potassium permanganate–glutaraldehyde CL system. With this method, dissolved organic matter in water samples was digested by excess acid potassium permanganate, the reacted mixture solutions containing surplus KMnO₄ were added in wells of a 96-well plate, followed by injection of glutaraldehyde in the wells, and CL was then produced along with the reaction of the added glutaraldehyde with the surplus KMnO₄ and detected by a photomultiplier tube (PMT). The difference (Δ I) between the CL intensity for distilled water and that for sample water was proportional to the COD value of water sample. The calibration graph was linear in the range of 0.16–19.24mgL⁻¹ with a detection limit of 0.1mgL⁻¹. A complete analysis could be performed in 40min including digestion and detection, giving a very high throughput of 3×96 samples in about 60min. Compared with the conventional methods, this method is simple and sensitive and consumes very limited and cheap reagents. Owing to its rapid, automatic, high throughput and low cost characteristics, the presented CL method has been applied successfully to the determination of COD in real water samples ( n=32) with satisfactory results.

Keywords: Chemical oxygen demand; High throughput; Chemiluminescence; Permanganate–glutaraldehyde system

A hydrogel based fluorescent micro array used for the characterization of liquid analytes by A.R. Thete; T. Henkel; R. Göckeritz; M. Endlich; J.M. Köhler; G.A. Groß (pp. 81-89).

A fluorimetric micro spot array using non-specific recognition function is described for the analysis of liquid samples. The array was composed of binary mixtures of various fluorescence dyes which were embedded in a hydrogel matrix. The interactions between the fluorescent dyes and their molecular surrounding inside the hydrogel, influence their fluorescence wave length and intensities. The array was used for the characterization of solvent mixtures. Developed fluorescence patterns of the complete array as well as the fluorescence intensity changes of single spots were analysed. It was proven, that specific analytical information can be gained using this non-specific recognition approach. The identification of some alcoholic beverages is described as an example of the application of this method when used for quality control purposes. Analogous to the appellation “electronic nose” and “electronic tongue” the described micro spot array acts as an “optochemical tongue”.

Keywords: Chemo chips; Sensor array; Fluorescence imaging; Pattern recognition; Analytical array; Optochemical tongue

Biosensor system for continuous glucose monitoring in fish by Yuki Yonemori; Eiji Takahashi; Huifeng Ren; Tetsuhito Hayashi; Hideaki Endo (pp. 90-96).

A biosensor system was developed for continuous estimation of blood glucose in fish. Because it is difficult to measure blood components in real-time due to decreased sensor output resulting from blood coagulation and coalescing blood proteins at the sensor placement site, we used the eyeball scleral interstitial fluid (EISF) as the site of sensor implantation. Evaluation of the relationship between EISF and blood glucose concentrations revealed that the blood glucose concentration correlated closely with the EISF glucose concentration ( y=2.2996+0.9438 x, R=0.960, n=112). To take advantage of the close correlation between blood and EISF glucose, we prepared a needle-type enzyme sensor for implantation in the fish sclera using a flexible wire electrode. The sensor provided a rapid response, good linearity, and reproducibility. Continuous glucose monitoring could be carried out by implanting this needle-type glucose sensor onto the eye. The findings indicated that the glucose concentration increased with sensor output current over time, and that changes in the blood glucose were continuously reflected in the EISF. The glucose concentration was estimated based on the one-point or two-point calibration methods. The two-point calibration method yielded the most accurate glucose monitoring (blood glucose range of 70–420mgdL⁻¹) over 160min. Sensor-estimated glucose and whole blood glucose values were highly correlated ( y=0.4401+0.8656 x, R=0.958).

Keywords: Biosensor; Enzyme sensor; Glucose; Blood; Monitoring; Fish; Interstitial fluid

A label-free fluorescence sensor for probing the interaction of oligonucleotides with target molecules by Xiaohong Cheng; Tao Bing; Xiangjun Liu; Dihua Shangguan (pp. 97-102).

This paper describes a universal, label-free fluorescence sensor that gauges the interaction of oligonucleotides with their targets. The sensor is based on supramolecular assemblies formed by oligonucleotides (polyanions) and small molecule cation surfactant in aqueous solution. The environmentally dependent dye pyrene, encapsulated in the apolar interiors of the assemblies via hydrophobic interactions works as the fluorescence probe. Target binding causes the conformational change of the oligonucleotides, which results in disorganization of supramolecular assemblies, release of pyrene into the aqueous solution and subsequent quenching of its fluorescence. The kinetic processes (including the formation of supramolecular assemblies and the release of pyrenes after adding the targets) were investigated. The fluorescence decreases of pyrenes are proportional to the concentrations of targets within the linear ranges. This label-free fluorescence system is simple, convenient, low cost, and can serve as an alternative tool for interaction studies of oligonucleotides with their targets, especially with small molecular targets.

Keywords: Supramolecular assembly; Fluorescence sensor; Oligonucleotide ligand; Molecular interaction

Multiplex detection of tumor markers with photonic suspension array by Yuanjin Zhao; Xiangwei Zhao; Xiaoping Pei; Jing Hu; Wenju Zhao; Baoan Chen; Zhongze Gu (pp. 103-108).

A novel photonic suspension array was developed for multiplex immunoassay. The carries of this array were silica colloidal crystal beads (SCCBs). The codes of these carriers are the characteristic reflection peak originated from their structural periodicity, and therefore they do not suffer from fading, bleaching, quenching, and chemical instability. In addition, because no dyes or materials related with fluorescence are included, the fluorescence background of SCCBs is very low. With a sandwich format, the proposed suspension array was used for simultaneous multiplex detection of tumor markers in one test tube. The results showed that the four tumor markers, α-fetoprotein (AFP), carcinoembryonic antigen (CEA), carcinoma antigen 125 (CA 125) and carcinoma antigen 19-9 (CA 19-9) could be assayed in the ranges of 1.0–500ngmL⁻¹, 1.0–500ngmL⁻¹, 1.0–500UmL⁻¹ and 3.0–500UmL⁻¹ with limits of detection of 0.68ngmL⁻¹, 0.95ngmL⁻¹, 0.99UmL⁻¹ and 2.30UmL⁻¹ at 3 σ, respectively. The proposed array showed acceptable accuracy, detection reproducibility, storage stability and the results obtained were in acceptable agreement with those from parallel single-analyte test of practical clinical sera. This technique provides a new strategy for low cost, automated, and simultaneous multiplex immunoassay.

Keywords: Suspension array; Multiplex assay; Tumor marker detection; Immunoassay; Colloidal crystal bead

Development of electrochemical sensors for nano scale Tb(III) ion determination based on pendant macrocyclic ligands by Ashok K. Singh; Prerna Singh; Shibdas Banerjee; Sameena Mehtab (pp. 109-118).

The two macrocyclic pendant ligands 3,4,5:12,13,14-dipyridine-2,6,11,15-tetramethyl-1,7,10,16-tetramethylacrylate-1,4,7,10,13,16-hexaazacyclooctadeca-3,13-di ene (L₁) and 3,4,5:12,13,14-dipyridine-2,6,11,15-tetramethyl-1,7,10,16-tetra(2-cyano ethane)-1,4,7,10,13,16-hexaazacyclooctadeca-3,13-diene (L₂) have been synthesized and explored as neutral ionophores for preparing poly(vinylchloride) (PVC) based membrane sensors selective to Tb(III) ions. Effects of various plasticizers and anion excluders were studied in detail and improved performance was observed. The best performance was obtained for the membrane sensor having a composition ofL₁: PVC:1-CN:NaTPB in the ratio of 6: 32: 58: 4 (w/w; mg). The performance of the membrane based onL₁ was compared with polymeric membrane electrode (PME) as well as with coated graphite electrode (CGE). The electrodes exhibit Nernstian slope for Tb³⁺ ions with limits of detection of 3.4×10⁻⁸molL⁻¹ for PME and 5.7×10⁻⁹molL⁻¹ for CGE. The response time for PME and CGE was found to be 10s and 8s, respectively. The potentiometric responses are independent of the pH of the test solution in the pH range 3.0–7.5 for PME and 2.0–8.5 for CGE. The CGE has found to work satisfactorily in partially non-aqueous media upto 30% (v/v) content of methanol, ethanol and 20% (v/v) content of acetonitrile and could be used for a period of 5 months. The CGE was used as indicator electrode in the potentiometric titration of Tb³⁺ ions with EDTA and in determination of fluoride ions in various samples. It can also be used in direct determination of Tb³⁺ ions in tap water and various binary mixtures with quantitative results.

Keywords: Macrocyclic pendant ligands; Terbium selective sensor; Polymeric membrane electrode; Coated graphite electrode

Detection of nicotine based on molecularly imprinted TiO₂-modified electrodes by Cheng-Tar Wu; Po-Yen Chen; Jian-Ging Chen; Vembu Suryanarayanan; Kuo-Chuan Ho (pp. 119-126).

Amperometric detection of nicotine (NIC) was carried out on a titanium dioxide (TiO₂)/poly(3,4-ethylenedioxythiophene) (PEDOT)-modified electrode by a molecular imprinting technique. In order to improve the conductivity of the substrate, PEDOT was coated onto the sintered electrode by in situ electrochemical polymerization of the monomer. The sensing potential of the NIC-imprinted TiO₂ electrode (ITO/TiO₂[NIC]/PEDOT) in a phosphate-buffered saline (PBS) solution (pH 7.4) containing 0.1M KCl was determined to be 0.88V (vs. Ag/AgCl/saturated KCl). The linear detection range for NIC oxidation on the so-called ITO/TiO₂[NIC]/PEDOT electrode was 0–5mM, with a sensitivity and limit of detection of 31.35μAmM⁻¹cm⁻² and 4.9μM, respectively. When comparing with the performance of the non-imprinted one, the sensitivity ratio was about 1.24. The sensitivity enhancement was attributed to the increase in the electroactive area of the imprinted electrode. The at-rest stability of the ITO/TiO₂[NIC]/PEDOT electrode was tested over a period of 3 days. The current response remained about 85% of its initial value at the end of 2 days. The ITO/TiO₂[NIC]/PEDOT electrode showed reasonably good selectivity in distinguishing NIC from its major interferent, (−)-cotinine (COT). Moreover, scanning electrochemical microscopy (SECM) was employed to elucidate the surface morphology of the imprinted and non-imprinted electrodes using Fe(CN)₆³⁻/Fe(CN)₆⁴⁻ as a redox probe on a platinum tip. The imprinted electrode was further characterized by scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR).

Keywords: Amperometry; Biosensor; Nicotine; Molecularly imprinted TiO; ₂; Scanning electrochemical microscopy; Poly(3,4-ethylenedioxythiophene)

Large volume injection for the direct analysis of ionophores and avermectins in surface water by liquid chromatography–electrospray ionization tandem mass spectrometry by T.S. Thompson; D.K. Noot; F. Forrest; J.P. van den Heever; J. Kendall; J. Keenliside (pp. 127-135).

A simple method for the direct determination of residues of ionophore antibiotics and avermectin antiparasitics in surface water is reported. Using a large volume injector, a mixture of methanol and surface water is injected into an analytical liquid chromatography (LC) column and subsequently screened for residues of these veterinary pharmaceuticals using electrospray ionization tandem mass spectrometry. On-line sample enrichment and chromatographic separation are achieved using a single, short (20mm) octadecylsilane LC column. The method permits the detection of four ionophores and two avermectins in surface water samples at low ngL⁻¹ concentrations. Minimal matrix effects were observed for a variety of surface water samples which permitted the use of reagent-based standards for quantitation.

Keywords: Ionophores; Avermectins; Surface water; Liquid chromatography–tandem mass spectrometry; On-line enrichment; Monensin

Multiple compounds determination and fingerprint analysis of Lidanpaishi tablet and keli by high-performance liquid chromatography by Lina Xu; Xu Han; Yan Qi; Youwei Xu; Lianhong Yin; Jinyong Peng; Kexin Liu; Changkai Sun (pp. 136-148).

The objective of this paper was to establish an efficient method for quality control of Lidanpaishi (LDPS) tablet and keli, two famous traditional Chinese medicines. A simple and reliable high-performance liquid chromatography (HPLC) coupled with photodiode array detector (DAD) method was developed both for fingerprint analysis (FA) and quantitative determination. In quantitative analysis, linear regressions, limit of detection (LOD) and quantification (LOQ), intra-day and inter-day precisions, recovery, repeatability and stability were all tested and good results were obtained to simultaneously determine the 15 marker compounds, namely chlorogenic acid, rhaponticin, 6,7-dimethoxycoumarin, naringin, hesperidin, neohesperidin, baicalin, wogonoside, baicalein, wogonin, chrysin, honokiol, magnolol, emodin, and chrysophanol in the herbal drugs. In fingerprint analysis, 34 peaks were selected as the characteristic peaks to evaluate the similarities of different samples collected from different pharmaceutical companies in China according to the State Food and Drug Administration (SFDA) requirements, and two kinds of data, relative retention time (RRT) and relative peak area (RPA) were used to identify the common peaks in 15 samples for investigation. Furthermore, hierarchical cluster analysis (HCA) was also performed to evaluate the variation of the herbal drugs. The present approach, i.e. HPLC coupled with multiple compounds determination (MCD) and FA is a powerful and meaningful tool to comprehensively conduct the quality control of traditional Chinese medicines.

Keywords: Lidanpaishi formula; Quality control; Multiple compounds determination; Fingerprint analysis; High-performance liquid chromatography

Investigation into classification/sourcing of suspect counterfeit Heptodin™ tablets by near infrared chemical imaging by Marta B. Lopes; Jean-Claude Wolff (pp. 149-155).

Near infrared chemical imaging (NIR-CI) analysis was performed on 55 counterfeit Heptodin™ tablets obtained from a market survey and an additional 11 authentic Heptodin™ tablets for comparison. The aim of the study was to investigate whether NIR-CI can be used to detect the counterfeit tablets and to classify/source them so as to understand the possible number of origins to aid investigators and authorities to shut down counterfeiting operations. NIR-CI combined with multivariate analysis is particularly suited to compare chemical and physical properties of samples, since it is a quick and non-destructive method of analysis. Counterfeit tablets were easily distinguished from the authentic ones. Principal component analysis (PCA) and k-means clustering were performed on the data set. The results from both analyses grouped the counterfeit tablets in 13 main groups. The main groups found with both methods were quite consistent. Out of the 55 tablets only 18% contained the correct active pharmaceutical ingredient (API), i.e., the anti-viral drug lamivudine. The remaining 82% of counterfeit tablets contained talc and starch as main excipients. The API containing tablets classified into three main groups, based mainly on the amount of lamivudine present in the tablet. The group which had close to the correct amount of lamivudine sub-classified into three groups. From the analysis carried out, it is likely that the counterfeit tablets originate from as many as 15 different sources.

Keywords: Counterfeit medicines; Near-infrared chemical imaging; Near-infrared spectroscopy; Principal component analysis; k-Means clustering; Classification of counterfeit medicines

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Analytica Chimica Acta (v.633, #1)