Analytica Chimica Acta (v.580, #1)

Contents (v-vi).

An enzyme-linked immunosorbent assay (ELISA) based on polyclonal antibody with enhanced chemiluminescent (ECL) detection of fumonisin B1 (FB1) in food samples has been developed. Assay conditions, including concentrations of antibody and enzyme conjugate, competition time and so on, were optimized. The effects of pH and two different organic solvents were investigated. The optimized ECL-ELISA system allowed FB1 determination in a linear working range of 0.14–0.9 μg L−1 with IC50 value of 0.32 μg L−1 and a limit of detection of 0.09 μg L−1. The ECL-ELISA was about 10 times more sensitive and about 30% time less than that of colorimetric ELISA using the same antibody and HRP-conjugate. Good recoveries with spiked food samples were obtained, and the results correlated well with those obtained using conventional direct competition ELISA assay and HPLC method, which indicated that ECL-ELISA was capable of being applied for the specific detection and routine monitoring of FB1 in food samples.
Keywords: Fumonisin B1; Enhanced chemiluminescence; Enzyme-linked immunosorbent assay (ELISA); Food;

A new post chemiluminescence (PCL) reaction was observed when atropine sulfate was injected into the reaction mixture after the finish of CL reaction of Ce(IV) and sodium sulfite. The possible mechanism for the PCL reaction was discussed via the investigation of the CL kinetic characteristics, the CL spectra, the UV absorption spectra and the fluorescence spectra of some related substances. The flow injection PCL method for the determination of atropine sulfate was established. The relative standard deviation (R.S.D.) was 2.8% (n  = 11, c  = 5.0 × 10−6  g mL−1). The PCL intensity responded linearly to the concentration of atropine sulfate in the range 1.0 × 10−6 to 5.0 × 10−5  g mL−1 with a linear correlation of 0.9947. The detection limit was 4 × 10−7  g mL−1 atropine sulfate. The method had been applied to the determination of atropine sulfate in the tablets and the results were consistent with the method of Chinese pharmacopoeia.
Keywords: Post chemiluminescence; Ce(IV); Sodium sulfite; Atropine sulfate;

In this paper, a novel electrochemiluminescence (ECL) imaging sensor array was developed for determination of hydrogen peroxide (H2O2), which was based on Cu/Zn alloy galvanic cell generated ECL. In alkaline solution, Cu/Zn galvanic cell was formed because of corrosion effect, the galvanic cell could supply stable potential for ECL generation of luminol, and the weak ECL emission could be enhanced by H2O2. The galvanic cell sensor array was designed by putting Cu/Zn alloy in 96-well microtiter plates separately. The relative ECL intensity was proportional with the concentration of hydrogen peroxide in the range of 1.0 × 10−6 to 1.0 × 10−4  mol l−1 and the detection limit was 3.0 × 10−7  mol l−1 (3σ), the relative standard deviation (R.S.D.) for 11 parallel measurements of 1.0 × 10−5  mol l−1 H2O2 was 4.0%.
Keywords: Sensor array; Galvanic cell; Electrochemiluminescence;

A flow cytometric assay technology based on quantum dots-encoded beads by Hai-Qiao Wang; Tian-Cai Liu; Yuan-Cheng Cao; Zhen-Li Huang; Jian-Hao Wang; Xiu-Qing Li; Yuan-Di Zhao (18-23).
A flow cytometric detecting technology based on quantum dots (QDs)-encoded beads has been described. Using this technology, several QDs-encoded beads with different code were identified effectively, and the target molecule (DNA sequence) in solution was also detected accurately by coupling to its complementary sequence probed on QDs-encoded beads through DNA hybridization assay. The resolution of this technology for encoded beads is resulted from two longer wavelength fluorescence identification signals (yellow and red fluorescent signals of QDs), and the third shorter wavelength fluorescence signal (green reporting signal of fluorescein isothiocyanate (FITC)) for the determination of reaction between probe and target. In experiment, because of QDs’ unique optical character, only one excitation light source was needed to excite the QDs and probe dye FITC synchronously comparing with other flow cytometric assay technology. The results show that this technology has present excellent repeatability and good accuracy. It will become a promising multiple assay platform in various application fields after further improvement.
Keywords: Quantum dots; Encode beads; Flow cytometric assay technology;

Carbon and gold microdisc electrodes (30 and 10 μm, respectively) have been tested as substrates for in situ bismuth film plating from unstirred solutions of variable acetate buffer content and were subsequently used in the anodic stripping voltammetry determination of Pb(II) and Cd(II) ions. The effects of Bi(III) concentration, analyte accumulation time, stirring as well as supporting electrolyte content have been studied. Under optimal conditions good voltammetric responses were obtained by means of square wave anodic stripping voltammetry in unstirred analyte solutions of 5 × 10−8 to 10−6  M, even in the absence of added buffer. In an indicative application, Pb(II) ion levels were determined in tap water using bismuth-plated carbon microdisc electrodes.
Keywords: Bismuth film electrodes; Microelectrodes; Carbon fibre electrodes; Gold disc electrodes; Anodic stripping voltammetry;

A comparative study to determine picomolar concentrations of platinum in natural waters was performed using two different analytical techniques. Results obtained by cathodic stripping voltammetry (CSV) were compared with those obtained by isotope dilution-inductively coupled plasma mass spectrometry (ID-ICPMS) combined with anion exchange resin column extraction method. Using successive UV irradiations with low-pressure mercury (L-Hg) lamp for 4 h prior to CSV analysis, the results of both methods were comparable. Without adequate photolytic decomposition, the results obtained using CSV were generally lower than those obtained using ID-ICPMS in the estuarine waters around Tokyo Bay. This difference implies the presence of organically complexed Pt species in the estuarine waters. The Pt enrichment in the middle of the Tokyo Bay estuaries probably reflects the anthropogenic release of Pt from highly populated areas in Tokyo.
Keywords: Platinum; Cathodic stripping voltammetry (CSV); Inductively coupled plasma mass spectrometry (ICPMS); UV irradiation; Natural water; Estuary;

New spectrofluorometric application for the determination of ternary mixtures of drugs by Fawzy A. El-Yazbi; Hassan H. Hammud; Sulaf A. Assi (39-46).
A new spectrofluorometric method was developed for the determination of a ternary mixture of dexamethasone, dexchlorpheniramine maleate, and fluphenazine hydrochloride in dosage forms where the literature did not reveal any method for analysis of this mixture.The method was based on the use of the first and second derivatives of the ratio of the emission spectra with a zero-crossing technique. The ratio spectra were obtained by dividing the emission spectrum of the mixture by that of one of the components. The concentrations of the other components were then determined from their respective calibration graphs treated similarly.The method can resolve the spectral overlapping of the three components and was applied successfully for the determination of these drugs in synthetic mixtures and in commercial dosage forms.
Keywords: Dexamethasone; Dexchlorpheniramine maleate; Fluphenazine hydrochloride; Spectrofluorometry; Derivative ratio; Zero-crossing technique;

The Raman and mass spectra of 1,4-diphenylbuta-1,3-diene and several of its monomethyl and dimethyl homologues are reported and discussed, with a view to developing a spectroscopic protocol for detecting the presence and position of a methyl group in these compounds. Raman spectroscopy and mass spectrometry are shown to provide complementary information, by which the four available monomethyl homologues may be readily distinguished from each other and 1,4-diphenylbuta-1,3-diene itself. The utility of these 1,4-diarylbutadienes as model compounds for carotenoids and related materials, which may serve as indicators of extinct or extant extraterrestrial life, is considered.
Keywords: Diphenylbutadiene; Carotenoids; Raman spectroscopy; Mass spectrometry; Astrobiology;

A surfactant-sensitized spectrophotometric method for determination of trace orthophosphate has been developed using anion surfactant (Ultrawet 60 L) with molybdate and malachite green in low acidic medium (pHT 1.0). The method detection limit (3 × standard deviation of blank, n  = 10) was 8 nM and the calibration curve was linear over a range of 10–400 nM (r 2  = 0.997). The molar absorptivity was 1.26 × 105  L mol−1  cm−1 at 600 nm with the background correction at 530 nm. The precision of method was 3.4% at 50 nM and 2.4% at 100 nM orthophosphate (n  = 10). The hydrolysis of eight organic phosphorus and polyphosphate compounds was less than 2% of the total phosphorus present (5–10 μM). This method showed less arsenate interference than previous methods, with only 3% even in the presence of orthophosphate in the samples. No interference of silicate up to 40 μM was observed. Background anions (in an order of SO4 2−  > NO3  > Cl) have greater effects than cations (Ca2+  > Mg2+  > Na+) on the reagent blank and the molar absorptivity of the color product.
Keywords: Orthophosphate determination; Malachite green; Interference; Organic phosphorus; Hydrolysis; Silicate; Arsenate; Spectrophotometry; Surfactant;

A simple and fast flow injection spectrophotometric method for the determination of bromate in water samples was developed. The detection system is based on the oxidation of prochlorperazine (PCP) with bromate in strongly acidic medium. Large amounts of chloride and bromide was found, for the first time, to act as an activator, and to enhance the sensitivity for bromate detection. The oxidation product of PCP gives pink color, which can be used to monitor the reaction spectrophotometrically at 525 nm. Under the optimal conditions, the method is selective; only nitrite, chlorite and hypochlorite can interfere with the determination of bromate. The elimination of these three ions is discussed. The calibration graph for bromate determination was linear in the range of 10–130 μg L−1 with a detection limit of 2.3 μg L−1. The repeatability was satisfactory, with the relative standard deviation of 1.1% (25 μg L−1, n  = 10). The sample throughput was 44 h−1. The proposed method was found to be highly reliable for screening drinking waters containing bromate, which is above or below legislation limit of 10 μg L−1.
Keywords: Spectrophotometry; Flow injection; Prochlorperazine; Bromate; Drinking water;

Dynamic microwave-assisted extraction coupled with on-line spectrophotometric determination of safflower yellow in Flos Carthami by Ligang Chen; Lan Ding; Huarong Zhang; Juan Li; Yutang Wang; Xiupin Wang; Chenling Qu; Hanqi Zhang (75-82).
A rapid dynamic microwave-assisted extraction and on-line detection by spectrophotometry is proposed for the determination of safflower yellow in Flos Carthami. A high pressure and a peristaltic pump were used to deliver the solvent. A TM010 microwave resonance cavity was applied to concentrate the microwave energy and the forward power about 60 W was enough for the extraction. Other extraction conditions also were examined and optimized. In this work, the extraction process can be monitored by measuring the absorption of safflower yellow in the extract, which would be convenient for rapid optimization of the extraction process. The detection and quantification limits are 8 and 27 μg mL−1, respectively. The within-day and between-day precision (R.S.D.) are 1.6–3.2% and 2.8–4.2%, respectively. Compared with off-line detection, the proposed method may provide more rapid measurement and is more convenient for obtaining continuous measurements.
Keywords: Dynamic microwave-assisted extraction; On-line detection; Safflower yellow; Flos Carthami;

Spectrophotometric determination of 4,6-dinitro-o-cresol (DNOC) in soil and lemon juice by A. Uzer; E. Ercag; H. Parlar; R. Apak; H. Filik (83-90).
Although the use of once widely applied selective herbicide, 4,6-dinitro-o-cresol (DNOC), was cancelled by US-EPA in 1987, it is still found in soil and water due to its slow degradation in the environment. Since solid phase extraction-spectrophotometry combinations are much simpler and cheaper than chromatography/MS based methods and most routine laboratories lack such sophisticated instrumentation, it is desirable to establish novel sensitive, well-established, and field-applicable spectrophotometric methods for the rapid assay of DNOC in water and soil. For this purpose, two distinct spectrophotometric methods utilizing the periodate and copper(II)-neocuproine (Nc) reagents have been developed following Zn/HCl reduction of the pesticide in a microwave oven for 15 s, and validated for DNOC determination at mg L−1 level. The LOD values were 1.6 and 0.2 mg L−1 for periodate and Cu(II)-Nc methods, respectively. Statistical comparison of the developed methods was made with the aid of high performance liquid chromatography (HPLC) equipped with a C18 (5 μm), 250 mm× 4.6 mm ID reversed phase column in conjunction with a UV (264 nm) detector, and a methanol (HPLC grade) +0.1% glacial acetic acid mixture mobile phase. Both spectrophotometric methods were directly applicable to soil since they were not interfered with common soil cations and anions, together with some pesticides. These methods were applied to real samples such as synthetically contaminated montmorillonite and lemon juice, and overall recovery efficiencies at the order of 95% or greater were achieved in the devised adsorption/elution procedures. An 8-hydroxyquinoline (oxine)-impregnated XAD copolymer resin stabilized with Fe(III) salt was used to preconcentrate DNOC at a concentration factor of 20 from lemon juice contaminated with 1 mg L−1 DNOC, and the analyte retained at pH 2.5 was eluted with 0.025 M methanolic NaOH. Both the devised spectrophotometric methods and the proposed preconcentration column with optimized sorption and desorption conditions are novel for DNOC assay in the natural environment.
Keywords: 4,6-Dinitro-o-cresol assay; Spectrophotometry; Copper(II)-neocuproine; Periodate; Solid phase extraction; XAD-oxine resin;

This study presents the use of quaternary ammonium bromides as additives in N-methylformamide (NMF) for the separation and quantification of chelating agents as copper complexes by capillary zone electrophoresis (CZE). The new quaternary ammonium bromides were synthesized in our laboratory and used for the first time for CZE applications performed in NMF media. The methods were developed and optimized for determination of six chelating agents (trans-1,2-diaminocyclohexane-N,N,N′,N′-tetraacetic acid (CDTA), diethylenetriaminepentaacetic acid (DTPA), ethylenediaminetetraacetic acid (EDTA), N-(2-hydroxyethyl)ethylenediamine-N,N′,N′-triacetic acid (HEDTA), nitrilotriacetic acid (NTA) and triethylenetetraaminehexaacetic acid (TTHA)) as copper complexes. Among the tested electrolyte additives in NMF media (pHapp 10.2) dimethyldioctylammonium bromide (DMDOAB), dimethyldinonylammonium bromide (DMDNAB) and dimethyldidecylammonium bromide (DMDDAB), at a concentration of 20 mmol L−1 improved the separation of the copper complexes. The optimized methods require only 12 min for one analysis, and the detection limits for copper complexes of DMDNAB, the best-performing additive, were ≤24 μmol L−1. Relative standard deviations (R.S.D.) for migration times were ≤2.5, ≤2.1, ≤3.1% and for peak areas, ≤3.1, ≤3.0, ≤3.2% for DMDOAB, DMDNAB and DMDDAB used as additives, respectively. All three methods were successfully applied to the analysis of natural and wastewater samples. No matrix effects from these samples were observed. The interaction between quaternary ammonium bromides and copper complexes is discussed.
Keywords: Chelating agents; Copper complexes; Ionic liquids; N-Methylformamide; Quaternary ammonium bromides; Capillary zone electrophoresis;

Modeling of analytical peaks: Peaks properties and basic peak functions by S.V. Romanenko; A.G. Stromberg; T.N. Pushkareva (99-106).
The general approach to the detailed characterizing of peak properties based on the use of characteristic points on a peak contour located at the certain levels is proposed. Three basic functions of peaks have been chosen which are submitted in normalized form on height and width. The ability to characterize a peaks shape of a certain analytical series is shown by an example of series of analytical peaks of thallium obtained by stripping voltammetry at linear and step potential sweep. Also the proposed shape parameters are studied for groups of stripping voltammetry and chromatographic peaks.
Keywords: Chemometrics; Peak model; Peak properties; Peak shape analysis;

Although the modern instrumentation enables for the increased amount of data to be delivered in shorter time, computer-assisted spectra analysis is limited by the intelligence and by the programmed logic tool applications. Proposed tutorial covers all the main steps of the data processing which involve the chemical model building, from calculating the concentration profiles and, using spectra regression, fitting the protonation constants of the chemical model to multiwavelength and multivariate data measured. Suggested diagnostics are examined to see whether the chemical model hypothesis can be accepted, as an incorrect model with false stoichiometric indices may lead to slow convergence, cyclization or divergence of the regression process minimization. Diagnostics concern the physical meaning of unknown parameters β qr and ɛ qr , physical sense of associated species concentrations, parametric correlation coefficients, goodness-of-fit tests, error analyses and spectra deconvolution, and the correct number of light-absorbing species determination. All of the benefits of spectrophotometric data analysis are demonstrated on the protonation constants of the ionizable anticancer drug 7-ethyl-10-hydroxycamptothecine, using data double checked with the SQUAD(84) and SPECFIT/32 regression programs and with factor analysis of the INDICES program. The experimental determination of protonation constants with their computational prediction based on a knowledge of chemical structures of the drug was through the combined MARVIN and PALLAS programs. If the proposed model adequately represents the data, the residuals should form a random pattern with a normal distribution N(0, s 2), with the residual mean equal to zero, and the standard deviation of residuals being near to experimental noise. Examination of residual plots may be assisted by a graphical analysis of residuals, and systematic departures from randomness indicate that the model and parameter estimates are not satisfactory.
Keywords: Spectrophotometric titration; Dissociation constant; Protonation; 7-Ethyl-10-hydroxycamptothecine; Anticancer drug; SPECFIT; SQUAD; INDICES; PALLAS; MARVIN;