Flow systems for precise and accurate coulometric determinations of ions that were developed on the basis of electrolytic ion transfer at the aqueous|organic solution (W|O) interface are reviewed. The electrolysis cell in the system is composed of a porous poly(tetrafluoroethylene) tube (1.0 mm inner diameter), a metal wire (0.8 mm diameter) inserted into the tube, O into which the tube is immersed, a reference electrode in O and a platinum wire counter electrode in O. The electrolysis is carried out by forcing W containing a species of interest to flow through the narrow gap between the tube and the metal wire. The coulometric determination can be performed with an efficiency of more than 99% and a precision of better than 0.2% based on the ion transfer under an optimum condition, even if the ion is redox inert such as Na+, K+, Mg2+, Ca2+, ClO4−, picrate or alkylsulfonates. The system can be applied to selective electrolytic solvent extraction of ions.
Procedures to determine the density of peptides immobilized on a glass surface for the quantitative detection of phosphorylated peptides for phosphoproteomic applications of peptide microarrays are described. Two kinds of representative fluorescent probe molecules, anti-phosphotyrosine antibody (AB) and phos-tag (PT), were examined to compare their ability for the quantitative detection of phosphorylated peptides. PT is a metal complex with a binding specificity to phosphorylated amino acids, and is much smaller in size than AB. Thus, PT is quantitatively bound to the phosphorylated peptides, even at a high immobilization density without steric hindrance, making them highly suited for future microarrays requiring smaller sized peptide spots for much higher throughput.
To generate a new specific recognition module for the enrichment and detection of ricin, galactose-functionalized silanized magnetic iron-oxide nanoparticles (Gal-SiMNPs) were assembled by amino-silanized MNPs (amino-SiMNPs) and a galactose linker. Amino-SiMNPs were produced by a coprecipitation method, and were coated with double layers of silica and aminosilane by hydrolysis of tetraethoxysilane and 3-aminopropyltriethoxysilane, respectively. A galactose with an amido-acid linker was synthesized by four steps of chemical modification from O-acetyl protected galactose. The diameters of Gal-SiMNPs were characterized as being 60 ± 20 nm. The average amount of galactose-loading and ricin-binding on Gal-SiMNPs was 30 ± 2 μg galactose and 29 ± 2 μg ricin toxin on the surface of 1 mg of Gal-SiMNPs, respectively. Furthermore, a rapid, simple and efficient colorimetric assay was established for the detection of ricin based on the Gal-SiMNPs, and the limits of detection (LODs) of 2 and 4 ng/mL for ricin in physiological buffer and serum were obtained, respectively.
It is very important to investigate antimony geochemical behavior in order to identify its source, or reveal contamination processes, since antimony and its compounds are considered to be pollutants of high priority by the Environmental Protection Agency of the United States (USEPA). However, the concentration of antimony in most geological samples is very low, and its stable isotope mass difference is only 1.6%. An antimony preconcentration method for isotope analysis using modified Thiol Cotton Fiber has been developed. Using this new method, the recovery of antimony was 99.5 ± 3.6% (n = 3) and blank values were <0.1 ng. The standard error of the ε123Sb isotope ratios in the proposed method is only 0.4ε, much smaller than those of the previous method. The proposed method is therefore effective in the preconcentration and separation of antimony for antimony isotope analysis.
It is widely recognized that lead (Pb) affects children’s cognitive function, even at relatively low blood lead levels (<10 μg dL−1). The determination of the source of Pb in children is essential for effective risk management. The use of multi-collector ICPMS (MC-ICPMS) for isotope ratio measurements of Pb in environmental and biological samples was examined for this purpose. MC-ICPMS with an instrumental mass fractionation correction by Tl allowed accurate isotope ratio measurements of the Pb isotopic reference material NIST SRM 981. However, the presence of matrix elements (Al, Ca, Fe and Na) at more than 10 mg kg−1 in the sample solution significantly deteriorated the accuracy. The separation of Pb from the matrix is necessary for accurate measurements of the isotope ratio of Pb in environmental and biological samples. Bromide-complexation, followed by anion exchange was found to be satisfactory in terms of the recovery of Pb (90 to 104%) and the efficiency of matrix separation. The procedure was applied to a preliminary source analysis of Pb in the blood of Japanese children, and a significant contribution of indoor dust was demonstrated.
The complex autocatalytic reaction between potassium permanganate (KMnO4) and hydrogen peroxide (H2O2) was studied by online UV-Vis spectra methods. The kinetic profiles of the absorptive components, including KMnO4 and two intermediates, were obtained by resolving the spectra-kinetic matrix with iterative target transformation factor analysis (ITTFA). But for the product Mn(II), which is not absorptive in the monitoring wavelength range, this was not applicable. Therefore, local mass balance region (LMBR) technique was proposed to get all of the scaled profiles, especially the non-absorptive components. Influences of various reaction conditions, such as concentrations of H2O2 and sulfuric acid (H2SO4) and reaction temperatures, were also investigated. Contrary to most other reactions, when initial concentrations of hydrogen peroxide ([H2O2]0) are largely excessive ([H2O2]0/[KMnO4]0 >40), higher [H2O2]0 will decrease the degradation rate, while the higher temperature makes the reaction go much slower.
Here, we report on a procedure in which ultrasonic waves were used to mix a water-ionic liquid two-phase system to simultaneously derivatize amines with dansyl chloride and extract, and the resulting dansyl amines into an ionic liquid (IL) at room temperature within 15 min. The ILs used were room-temperature ionic liquids (RTILs), such as 1-alkyl-3-methylimidazolium hexafluorophosphate ([CnMIM][PF6], n = 4, 6, 8), which are insoluble in water, and can extract more than 88% of the total dansyl amines (Dns-amines) present in aqueous solution. The Dns-amines formed were separated by chromatography in 20 μL of RTIL in a mobile-phase gradient of acetonitrile–water flowing through an Agilent Zorbax SB-C18 column. The eluents were analyzed at 333 nm using a UV detector. The optimal analytical conditions were achieved by using the following: RTILs with a 4-carbon alkyl chain; a 7-mL water sample and 1 mL each of 5 mM dansyl chloride in acetone and 20 mM sodium tetraborate buffer for use with a fixed volume (1 mL) of IL; buffer pH of 10.4; duration of 15 min; and an acetonitrile–water ratio of 50:50 from zero time to 3 min, 80:20 from 4 to 10 min, and 50:50 from 11 to 16 min. In comparison to the single-phase hot-water (70°C) derivatization process reported earlier, the simultaneous process developed here showed a higher derivatization efficiency at the tested concentration. The linear range of analysis (0.14 – 7.14 mg/L) was determined, and the correlation coefficient (R) ranged from 0.9878 to 0.9980. Furthermore, the estimated percentage of recovery from amine-spiked river-water samples ranged from 76 to 108%. The method presented here is simple and fast, and does not involve the use of volatile organic extractants.
Dynamic liquid–liquid–liquid microextraction coupled with ion-pair liquid chromatography (IP-LC) and photodiode array detection was developed and used for the extraction and analysis of chlorinated phenoxyacetic acids (CPAs) and chlorophenols (CPs) from water samples. An organic extraction solvent mixture was chosen to simultaneously and effectively extract both CPAs and CPs from aqueous samples. The method detection limit (MDL) ranged from 0.06 to 0.45 μg L−1 with good reproducibility. The relative standard deviations were in the range of 2.6 – 6.5% at lower spiked concentrations and 3.0 – 4.6% at higher concentrations. Good linearity of analytes was achieved in the range of 0.5 – 500 μg L−1. The acceptable relative recoveries (82.9 – 112.4%) for environmental waters revealed the presence of negligible matrix effects in the case of real samples. The applicability of this newly developed method was illustrated by determinations of CPAs and CPs in environmental water samples.
A novel method for the determination of propranolol hydrochlorid (PRO) in human urine was developed using capillary electrophoresis coupled with electrochemiluminescence detection (CE-ECL). The parameters that affected the separation and detection were optimized. Under the optimal conditions, the linear range for PRO was from 0.003 to 2 μg/mL (r2 = 0.9993), and the detection limit was 1.3 ng/mL (S/N = 3). The method was successfully applied to the study of the pharmacokinetics of PRO in human urine. The relative standard deviations of ECL intensity and migration time were 2.6 and 2.1%, respectively (1.0 μg/mL PRO, n = 6). The recovery was between 96.71 and 97.30%. The peak excretion rate in urine was observed during the 0.5 – 1 h after oral administration of a 10-mg PRO tablet and the urinary excretion ratio of PRO was 13.6% within 12 h. The method was simple, rapid, economical and sensitive, and may improve the detection of PRO as a doping agent in sports.
Alkyl-chain ferrocene cationic surfactants (ACFcCS) can form ion-pair complexes with anions, and are then adsorbed at hydrophobic electrode surfaces or extracted to organic layers. The amount of adsorbed ACFcCS-anion complex is dependent on the anion concentration in a solution, and the anion concentration can be determined from the current intensity of the oxidation wave of the ferrocene part of ACFcCS. In this work, we studied the adsorption behavior of (ferrocenylmethyl)dodecyldimethyl ammonium ion (FcMDDMA) on a carbon-paste electrode, which accompanies the ion-pair formation with an inorganic anion, an organic anion, or heparin molecule. A concentration analysis of a heparin sodium injection sample was carried out using adsorption voltammetry, and the amperometric titration used FcMDDMA as the end-point indicator.
The electrooxidation of acyclovir (ACV) was studied using a gold electrode (GE) modified with a self-assembled monolayer of 2-mercaptobenzothiazol (MBZ) and [5,10,15,20-tetrakis(3-methoxy-4-hydroxyphenyl)porphyrinato]copper(II) (TMHPP Cu(II)) by square wave voltammetry (SWV). The self-assembled films are stable and showed blocking characteristics towards the faradaic processes such as gold surface oxidation and under potential deposition of copper. The optimized conditions obtained for the MBZ/TMHPP Cu(II)-modified GE were 0.1 M phosphate buffer solution (pH 7.0), square wave frequency of 15 Hz and square wave amplitude of 25 mV. Under these optimum conditions, the resultant peak current increases linearly with the concentration of ACV in the range of 1.0 × 10−3 to 1.0 × 10−8 M with a detection limit of 1.0 × 10−8 M. The MBZ/TMHPP Cu(II)-modified GE showed good stability and selectivity and it can be used to quantify ACV in pharmaceutical formulations and urine samples.
A new method for the simultaneous determination of amoxicillin trihydrate (AMT) and sodium diclofenac (DIC) in pharmaceutical formulations is proposed. The resolution of binary mixtures of these drugs has been accomplished by using partial least squares (PLS) regression analysis. The model was obtained from UV spectral data and validated by internal cross-validation; it was used to find the concentration of analytes in some commercial samples. The method was applied in the concentration ranges of 0 – 120.0 mg L−1 for AMT and 0 – 16.0 mg L−1 for DIC, allowing a rapid, accurate and precise simultaneous estimation of the concentration of both analytes of interest in the presence of small amounts of different, unmodelled, absorbing excipients, in spite of their important spectral overlapping. The accuracy, precision and figures of merit (FOM) for AMT and DIC were calculated. This new method proved to be useful for a fast and simultaneous determination of AMT and DIC in pharmaceutical formulations.
The binding properties on alizarin to human serum albumin (HSA) have been studied for the first time using fluorescence spectroscopy in combination with UV-visible absorbance spectroscopy. The results showed that alizarin strongly quenched the intrinsic fluorescence of HSA through a static quenching procedure, and non-radiation energy transfer occurred within the molecules. The number of binding sites was 1, and the efficiency of Förster energy transfer provided a distance of 1.83 nm between tryptophan and alizarin binding site. ΔHθ, ΔSθ and ΔGθ were obtained based on the quenching constants and thermodynamic theory (ΔHθ < 0, ΔSθ > 0 and ΔGθ < 0). These results indicated that hydrophobic and electrostatic interactions are the main binding forces in the alizarin-HSA system. In addition, the results obtained from synchronous fluorescence spectra and three-dimensional fluorescence spectra showed that the binding of alizarin with HSA could induce conformational changes in HSA.
A simple and inexpensive preconcentration technique has been developed for the ultra-trace determination of lead(II) using electrothermal atomic absorption spectrometry (ETAAS). The lead(II) complex with dicyclohexano-18-crown 6-ether (DC18C6) was extracted to a small piece of cellulose acetate-type membrane filter (2 × 5 mm) merely by vigorously eccentric stirring for 120 min under the coexistence of sodium dodecyl sulfate (SDS) at around pH 7. The extraction medium was inserted into a graphite cuvette for the determination of lead(II) by ETAAS. A linear relation was obtained for the range of 0.1 – 5.0 ng in 10 ml of lead(II) standard solution (r = 0.998). The detection limit was found to be 0.03 ng of lead(II) in 10 ml (0.003 μg l−1) of water sample. The proposed method was applied to the ultra-trace determination of lead(II) in river water, underground water, tap water, and snow fall samples.
An anti-fouling ability of diamond-like carbon (DLC) electrodes to biological macromolecules has been investigated from a decrease in the electrochemical redox current of Fe(CN)64−/3−, used as a redox marker. A DLC electrode and a glassy carbon (GC) electrode were immersed in a solution containing bovine serum albumin (BSA) or DNA. The GCs treated with biological macromolecules gave rise to a significant decrease in the currents, while there was no signal decreases from the treated DLCs. The signals from the DLCs remain essentially unchanged for at least 24 h at a 10 mg/mL concentration level of BSA.
The vapor condensation method can be used for forming an alternative flow of liquid masses using a single solvent for alternative plugs flow liquid chromatography (APFLC), described in our previous paper. APFLC is more effective when adopting a T-shaped flow path and aqueous-organic solvents with a liquid-to-gas volume ratio (bulk fraction; β) ranging between 0.0006 and 0.004 in an open tubular GC capillary column at below 70°C. High-density plugs flow by a T-shaped flow path leads to extremely high resolution. Alternative plugs flow is formed when the liquid contact angle to the solid phase is above 75°. An aqueous mixture of the usual HPLC solvent can be readily used for APFLC. An EI-mass spectrum is obtained that is comparable with that in the NIST library, except for the DMF mixture medium. Due to low-pressure loss properties in the column, the system does not require a high-pressure liquid pump. Solid hydrocarbon resin with a contact angle to water of between 75° and 79°, such as polystyrene and olefinic polymers, is anticipated to be applicable to APFLC and hydro-membrane gas chromatography (HMGC) by a consideration of their surface tensions.
Protein identification in polyacrylamide gel electrophoresis (PAGE) requires post-electrophoretic steps like fixing, staining and destaining of the gel, which are time-consuming and cumbersome. We have developed a method for direct visualization of protein bands in PAGE using tetrakis(4-sulfonato phenyl)porphyrin (TPPS) as a dye without the need for any post electrophoretic steps, where separation and recovery of enzymes become much easier for further analysis. Activity staining was done to prove that the biochemical activity of the enzymes was preserved after electrophoresis.
The fluorescent derivatization of tryptophan metabolites (xanthurenic acid, nicotinic acid, picolinic acid, and 3-hydroxyanthranilic acid) by the catalytic activity of horseradish peroxidase (HRP) was investigated in the presence of excess H2O2. Non-fluorescent xanthurenic acid (XA) and nicotinic acid (NA) were converted into a fluorescent compound with maximum excitation and emission wavelengths at 325 and 425 nm, and 318 and 380 nm, respectively. This fluorescent derivatization was developed for the fluorometric determination of trace amounts of XA and NA. The calibration curves were linear from 1.0 to 10.0 nmol XA and from 5.0 to 20.0 nmol NA in a 1.0-mL sample solution. The UV spectra of the reaction solutions suggested that compound III as an intermediate of HRP played an essential role in this fluorescent derivatization with HRP.
From the viewpoint of the phytotoxicity and mobility of Al3+ released from soil minerals due to soil acidification, the interaction between Al3+ and acrylic acid (AA) and polyacrylic acid (PAA) as a model compound of fulvic acid was investigated. The interaction was examined at pH 3 so as to avoid the hydrolysis of Al3+. The interaction between Al3+ and AA was weak. However, the interaction between Al3+ and PAA was strong and depended on the initial (COOH in PAA)/Al molar ratio (RP) of the solution. For the range of 1/RP, the interaction between Al3+ and PAA can be divided into three categories: (1) 1:1 Al-PAA-complex (an Al3+ combines to a carboxyl group), (2) intermolecular Al-PAA-complex (an Al3+ combines to more than 2 carboxyl groups of other Al-PAA-complexes) in addition to the 1:1 Al-PAA-complex and (3) precipitation of intermolecular complexes. In conclusion, RP is an important factor affecting the behavior of Al3+ in acidic soil solution.