We have developed a strategy to detect the DNA-binding affinities of chemical compounds with a real-time PCR analyzer. In this system, the DNA-binding affinities of chemical compounds are efficiency detected by PCR with high sensitivity. To obtain accurate information about the DNA-binding affinities of chemical compounds, primer-dimers prepared in advance are used as templates. The denature temperature is settled to around the melting temperature of the templates.
An on-chip enzyme-linked immunosorbent assay combined with an electrochemical detection method (EC-ELISA) was employed to detect a leptin, one of the most important adipose derived hormones, using gold electrodes modified with a tri(ethylene glycol) terminated short alkanethiol (TEGCnSH, Cn = (CH2)n, n = 2, 4, 6, and 8) monolayer. These TEGCnSH monolayers on gold electrodes can suppress non-specific protein adsorption without affecting the electrochemical activity required for detecting p-aminophenol (PAP), which is an alkaline phosphatase (ALP) product. We measured leptin with a highly sensitive detection range (100 pg mL−1 to 10 ng mL−1 level) and with the desired detection limit (13.6 pg mL−1) by using electrochemical detection. For detecting leptin, the EC-ELISA method using TEGC4SH modified gold electrode with a poly(dimethylsiloxane) based microchannel was superior to the conventional ELISA method. With the EC-ELISA method, we were able to measure leptin with a satisfactory detection range and a pg level detection limit within 30 min, which is a much lower detection level than that obtained with conventional plate based ELISA.
An on-site determination method for trace manganese has been developed using the manganese-catalyzed oxidation of Malachite Green (MG) with potassium periodate. Absorbance measurement of MG was carried out using a laboratory-made palm-top size colorimeter with a red-green-blue light-emitting diode. The reciprocal value (1/τ) of the reaction time at a fixed absorbance value for red light was chosen as a kinetic parameter for simple on-site analyses. The value of 1/τ was proportional to the concentration of manganese in the range of 2 – 20 μg L−1. At a reaction temperature (T) of 20°C or more, manganese was determined within a reaction time of 25 min. The calibration equation was approximated by 1/τ = (aT + b)[Mn] + (cT + d), where a to d were constants in a range of 10 – 40°C. The two equations for 30°C (for the laboratory-preparation of the calibration equation) and T give the value of 1/τ at 30°C as 1/τf = (30a + b)(1/τ – cT – d)/(aT + b) + 30c + d. Without any temperature control, 1/τf can be calculated by this equation and measurements of 1/τ and T. The calculation introduced analytical errors of within 1 μg L−1. The proposed method was successfully applied to tap-, river- and lake-water samples.
An amperometric L-ascorbic acid (AA) biosensor fabricated by immobilizing ascorbate oxidase (AO) in poly(3,4-ethylenedioxythiophene) (PEDOT) and multi-walled carbon nanotubes (MWCNTs) composite films was reported for the first time. The entrapment of AO in PEDOT/MWCNTs composite films was performed during an electrochemical polymerization process. The influence of various experimental conditions was examined for determining the optimum analytical performance. The response of the biosensor towards AA under the optimized conditions is linear from 0.05 to 20 mM with a detection limit of 15 μM (S/N = 3). The biosensor shows a response time of 20 s and a sensitivity of 23.95 mA M−1 cm−2. The apparent Michaelis–Menten constant (Km) and apparent activation energy (Ea) are 19.5 mM and 21 kJ mol−1, respectively. Moreover, the biosensor exhibits good anti-interferent ability, good reproducibility and remarkable storage stability.
High-throughput cupric ion reducing antioxidant capacity (CUPRAC) methods were developed for assessment of total antioxidant capacity (TAC) in urine and serum, based on reduction of Cu(II)-neocuproine complex to highly colored Cu(I)-neocuproine complex, measured spectrophotometrically at 450 nm. The reaction time was significantly reduced from 30 to 4 min by application of a calibration compound (uric acid) with kinetic behavior similar to that shown by urine samples. The method was implemented in a microformat (96 well plates) and also in an automatic fashion (flow injection analysis, FIA). A determination throughput value of 288 h−1 (microplate method) or of 15 h−1 (automatic FIA) was attained. Application of both methods to human serum (SRM 909b, level I) and urines (n = 9) provided TAC values in agreement with those of the end-point batch method.
In order to determine phenolic compounds in water, we propose a method based on the reaction of phenolic compounds with 4-aminoantipyrine in the presence of peroxodisulfate at pH 10 to form antipyrine dye and the solid-phase extraction of dye with a Varian Bond Elut Plexa cartridge. Dye collected on the cartridge is eluted with acetonitrile and the absorbance is measured at 475 nm. In our experiments, recovery ratios of >90% were obtained for phenol, o-aminophenol, m-aminophenol, o-methoxyphenol, m-methoxyphenol, p-methoxyphenol, o-cresol, m-cresol, o-chlorophenol, m-chlorophenol, p-chlorophenol, 2,5-dimethylphenol, and 2,4-dichlorophenol. The calibration curve obeyed Beer’s law in the range 0 – 0.30 μg ml−1 phenol. The precision of repeated tests (n = 4) was 1.7% of the phenol solution (0.10 μg ml−1); the detection limit was 0.0011 μg ml−1. Recovery tests using river water, waste water, and sewage influent gave highly satisfactory results.
For the present study, a tri-wavelength UV/Vis spectrophotometric method for rapid determination of quinoline (Q) and 2-hydroxyquinoline (HQ) during Q biodegradation was developed. Based on the spectral measurements at 289 nm (the isosbestic point of Q and HQ), 326 and 380 nm, the spectral interference of extracellular polymeric substances (EPS) in the process samples could be minimized, and the amounts of Q and HQ could be simultaneously quantified. Our results indicated that the relative standard deviations in the repeatability tests were 2.7 and 1.7% for Q and HQ, respectively. The method validation was conducted by comparing the data obtained using the present method with those generated from high performance liquid chromatography (HPLC). The same set of samples from Q biodegradation process was used. The relative differences between the two methods were within 10%. In conclusion, the present method is simple, rapid, and suitable for the investigation in Q biodegradation processes.
Simultaneous determinations of common inorganic anionic species (SO42−, Cl−, NO3−, phosphate and silicate) and cations (Na+, NH4+, K+, Mg2+ and Ca2+) were conducted using an ion-chromatography system with dual detection of conductivity and spectrophotometry in tandem. The separation of ionic species on a weakly acidic cation-exchange resin was accomplished using a mixture of 100 mM ascorbic acid and 4 mM 18-crown-6 as an acidic eluent (pH 2.6), after which the ions were detected using a conductivity detector. Subsequently, phosphate and silicate were analyzed based on derivatization with molybdate and spectrophotometry at 700 nm. The detection limits at S/N = 3 ranged from 0.11 to 2.9 μM for analyte ionic species. This method was applied to practical river water and wastewater with acceptable criteria for the anion-cation balance and comparisons of the measured and calculated electrical conductivity, demonstrating the usefulness of the present method for water quality monitoring.
We developed an ion-exclusion/adsorption chromatography (IEAC) method employing a polystyrene-divinylbenzene-based weakly acidic cation-exchange resin (PS-WCX) column with propionic acid as the eluent for the simultaneous determination of multivalent aliphatic carboxylic acids and ethanol in food samples. The PS-WCX column well resolved mono-, di-, and trivalent carboxylic acids in the acidic eluent. Propionic acid as the eluent gave a higher signal-to-noise ratio, and enabled sensitive conductimetric detection of analyte acids. We found the optimal separation condition to be the combination of a PS-WCX column and 20-mM propionic acid. Practical applicability of the developed method was confirmed by using a short precolumn with a strongly acidic cation-exchange resin in the H+-form connected before the separation column; this was to remove cations from food samples by converting them to hydrogen ions. Consequently, common carboxylic acids and ethanol in beer, wine, and soy sauce were successfully separated by the developed method.
Porphyrazines possessing non-coordinating alkyl (propyl) and aralkyl (4-tert-butylphenyl) groups in the periphery were studied as optical sensors for a set of mono-, di- and trivalent cations. Investigated porphyrazines in the UV-Vis monitored titrations revealed significant responses towards aluminium and gallium cations, unlike other metal ions studied. Additionally, porphyrazine possessing 4-tert-butylphenyl peripheral substituents showed sensor property towards ruthenium cation and was chosen for further investigation. The presence of isosbestic points in absorption spectra for its titration with aluminium, gallium and ruthenium cations, accompanied by a linear Benesi–Hildebrand plot, proved complex formation. The continuous variation method was used to determine binding stoichiometry in 1:1 porphyrazine-metal ratio. X-Ray studies and density functional theory calculations were employed to investigate octa(4-tert-butylphenyl)porphyrazine structure. The results helped to explain the observed selectivity towards certain ions. Interaction between ion and porphyrazine meso nitrogen in a Lewis acid–Lewis base manner is proposed.
A wireless magnetoelastic sensor has been developed for the determination of 2-naphthol (2-NAP) in human urine. This method is based on the precipitation of 2-NAP with diazonium salts produced by the diazo-reaction of sulfamethoxazole (SMZ) with nitrite under a weak alkaline condition, resulting in a descending of the resonance frequency of a wireless magnetoelastic sensor. The frequence shift values (ΔF) of the sensor were directly proportional to the concentration in the range of 1.13 – 139 μmol L−1 for 2-NAP with a correlation coefficient of 0.997 and a detection limit of 0.340 μmol L−1. The relative standard deviations were 2.38, 2.40 and 2.44%, and the average recovery was 107% (n = 6). The proposed method has additional advantages of being less time-consuming, low cost and remote query, and can be applied for real-time and in situ monitoring of 2-NAP in human urine. It would be a benefit to extend the scope of applications of magnetoelastic sensing techniques.
Tungsten coil atomic emission spectrometry (WCAES) has been evaluated as a potentially portable technique for field applications. The tungsten coil (W-coil) was extracted from a commercially available slide projector bulb and used as both the atomizer and the excitation source. The coil was powered by a small solid-state power supply. A hand-held CCD spectrometer, powered from a laptop computer, collected the signal. Fifteen elements were used to evaluate the portable system. For elements in the UV region, LODs were increased by a factor of 2000 for Cu; 200 for Ag; and 25 for Co through a 400-W solid state power supply compared to a 200-W solid state power supply. Signals for Al, Cr, Ga, Mn, Li and V in the near UV region also increased around a factor of 25. Therefore, the WCAES device could be used for elements in both the visible and UV regions, and the system could be taken into the field to measure elements in various samples.
It was found that a novel iridium complex, [(dpci)2Ir(bvbbi)](PF6) (dpci = 3,4-diphenylcinnoline, bvbbi = N,N′-bivinyester-1H,1′H-[2,2′] bibenzimidazole), with Ce(IV) in the presence of sodium sulfite can induce a great chemiluminescence (CL) emission. More importantly, a rapid and sensitive CL method for the determination of tryptophan coupled with a flow-injection analysis (FIA) technique has been developed based on the inhibition effect of the tryptophan to the CL emission of [(dpci)2Ir(bvbbi)](PF6)-Ce(IV)-SO32− system. Under the optimum conditions, the decreased CL intensity is proportional with the concentration of tryptophan in the range of 5.0 × 10−7 to 2.0 × 10−5 mol L−1, and the detection limit is 8.2 × 10−8 mol L−1 (3σ). The relative standard deviation (RSD) for 11 parallel measurements of 1.0 × 10−5 mol L−1 tryptophan is 2.7%. The proposed method has been applied successfully for the determination of tryptophan in its pharmaceutical formulations. Moreover, the possible inhibition mechanism of tryptophan on [(dpci)2Ir(bvbbi)](PF6)-Ce(IV)-SO32− CL system was briefly discussed.
The anodic voltammetric behavior of tiapride hydrochloride (TiapCl) was studied at carbon paste electrodes in 0.04 M Britton–Robinson buffer pH 7.0 using cyclic and differential pulse voltammetric techniques. The oxidation of TiapCl is an irreversible diffusion-controlled process. A differential pulse anodic voltammetric procedure has been developed for determination of the drug over the concentration range 0.36 – 19.35 μg/ml with detection and quantification limits of 0.12 and 0.40 μg/ml, respectively. The proposed method was successfully applied for the determination of the drug in commercial tablets and in spiked human urine samples.
Qualitative differentiation between natural and enriched chicken eggs through omega (ω) 3 fatty acid profiles by capillary zone electrophoresis (CZE) under direct UV detection at 200 nm is proposed. The electrolyte background consisted of 12.0 mmol L−1 tetraborate buffer (pH 9.2) mixed with 12.0 mmol L−1 Brij 35, 17% acetonitrile (ACN) and 33% methanol (MeOH). Omega 3 fatty acid profile in chicken egg samples were analyzed by CZE system and confirmed by single-quadrupole mass spectrometry with an electrospray ionization probe set to negative ionization mode after sample preparation by the Folch method. The results showed that ω fatty acid profiles analyzed by the CZE approach can be used to chemical markers to monitor fraud, presenting simplicity, short analysis time (10 min) and low cost as advantages.
The extraction efficiency of a dispersive liquid–liquid microextraction (DLLME) method coupled with gas chromatography–microelectron capture detection (GC-μECD) for the simultaneous determination of 20 organochlorine pesticides (OCPs) in water samples was evaluated. The optimum conditions of DLLME for OCP measurement in water sample were determined with 10 μL of carbon tetrachloride (CCl4) and 1.5 mL of acetone as the extraction and dispersive solvents, respectively, all measurements were conducted under room temperature without the addition of salt. OCPs were extracted with good recoveries (60.35 – 107.89%) by the proposed method, except for heptachlor and aldrin due to the specific physico-chemical properties of these chemicals. Quantitative analysis showed that the relative standard deviations (RSDs) were below 9% and rather wider linear ranges (LRs) of 0.1 – 50 μg/L were obtained. The limits of detection (LODs) were in the range of 0.21 – 11.65 ng/L and no significant matrix effects were observed. Obtained results demonstrated that DLLME coupled with GC-μECD was rapid, convenient and efficient for OCP analysis in water samples.
Interactions of the anionic form of C.I. Mordant Blue 29 with cationic and nonionic surfactants have been studied by absorption spectroscopy. The dye interacts strongly with oppositely charged surfactants in the pre-micellar concentration range with an accompanying change in its spectral properties, while its interaction with the polyoxyethylene group of nonionic surfactants does not have such remarkable effects. In ternary mixtures, however, the influence of the polyoxyethylene group on the optical properties of C.I. Mordant Blue 29-tetradecyltrimethylammonium bromide and C.I. Mordant Blue 29-octadecyltrimethylammonium chloride systems is quite different. In addition, the influence of the interaction between the HL3− form of C.I. Mordant Blue 29 and the surfactants on the formation of chelate complexes with iron(III) has been studied. The optimized structures of Fe-Mordant Blue 29 complexes are also reported herein. Geometries have been calculated by the Hartree–Fock method with the cc-pVDZ basis set.