Linear Calibration Range Research Articles

Determination of Nalbuphine Hydrochloride in Pharmaceutical Formulations Using Diperiodatoargentate(III)-Rhodamine-B Chemiluminescence System by Flow Injection Analysis.

A novel method for the analysis of nalbuphine hydrochloride (NAL) is reported based on its enhancement effect on a diperiodatoargentate(III)-rhodamine-B (Ag(III) complex-Rh-B) chemiluminescence (CL) system in an aqueous sulfuric acid medium using flow-injection analysis (FIA). The optimal conditions of the CL reaction were: sulfuric acid, 10-2 M; Ag(III) complex, 2.0 × 10-4 M; Rh-B, 2.0 × 10-5 M; Brij-35, 0.01%; sample loop volume, 300 μL; and flow rate, 3.0 mL/min/stream. The limit of detection (LOD) and limit of quantification (LOQ) were 0.001 and 0.003 mg/L (S/N = 3 and 10); linear calibration range, 5 × 10-3 - 5.0 mg/L (R2 = 0.9999) and injection throughput, 150/h. The relative standard deviation (RSD) was from 0.8 - 3.2% over the range studied. The suggested technique was applied for the determination of NAL in pharmaceutical injections, compared with a reported spectrophotometric method, and obtained results were found to be satisfactory. Based on spectrophotometric studies, the most probable mechanism of the CL reaction has been briefly described and drawn schematically.

The assessment of a method for measurements and lead quantification in air particulate matter using total reflection X-ray fluorescence spectrometers

This paper presents the assessment of a direct method to measure and analyse Pb in air particulate matter (PM) collected on polytetrafluoroethylene (PTFE) filtering membranes prepared by the SMART STORE® procedure. The suitability of grazing incidence X-ray fluorescence technique is verified on a set of continuous and conformal thin film samples created by atomic layer deposition. Different scans changing the angles of incidence are performed and the fluorescence intensity of thin films on PTFE substrate compared with that obtained by similar thin films deposited on Si wafer substrates. The effects of sample preparation, constraints, and limitations of the experimental setup are discussed. The results obtained by three commercial total reflection X-ray fluorescence spectrometers, equipped with Mo or Rh X-ray tubes, are compared. Reference samples with different Pb content are used to define the best measurement conditions, corresponding to the maximum fluorescence intensity. The precision is evaluated in terms of relative standard deviation of the net intensity, taking into account the homogeneity of the PM samples and hardware contributions to the errors. The calibration curves are built on the basis of mono- and multi-elemental Pb loaded PTFE reference samples. The analytical parameters, namely linear calibration and determination range, limits of detection, and quantification, are determined.

Highly sensitive UPLC-MS/MS method for the quantification of paromomycin in human plasma

A highly sensitive method was developed to quantitate the antileishmanial agent paromomycin in human plasma, with a lower limit of quantification of 5 ng/mL. Separation was achieved using an isocratic ion-pair ultra-high performance liquid chromatographic (UPLC) method with a minimal concentration of heptafluorobutyric acid, which was coupled through an electrospray ionization interface to a triple quadrupole - linear ion trap mass spectrometer for detection. The method was validated over a linear calibration range of 5 to 1000 ng/mL (r2≥0.997) with inter-assay accuracies and precisions within the internationally accepted criteria. Volumes of 50 μL of human K2EDTA plasma were processed by using a simple protein precipitation method with 40 μL 20 % trichloroacetic acid. A good performance was shown in terms of recovery (100 %), matrix effect (C.V. ≤ 12.0 %) and carry-over (≤17.5 % of the lower limit of quantitation). Paromomycin spiked to human plasma samples was stable for at least 24 h at room temperature, 6 h at 35 °C, and 104 days at −20 °C. Paromomycin adsorbs to glass containers at low concentrations, and therefore acidic conditions were used throughout the assay, in combination with polypropylene tubes and autosampler vials. The assay was successfully applied in a pharmacokinetic study in visceral leishmaniasis patients from Eastern Africa.

Analysis of β-blocker timolol maleate drug residues in wastewater and biological fluids using differential pulse – anodic stripping voltammetry

ABSTRACT Drug residues in water represent one of the most serious environmental problems because of their high toxicity to the biological system. Thus, this study reports a low-cost strategy for fast and precise analysis of β- blocker timolol maleate (TM) using differential pulse anodic stripping voltammetry (DP ASV) at a bare glassy carbon electrode (GCE). At the optimised solution pH 7.2 and other analytical parameters (accumulation time, deposition potential, scan rate, and pulse amplitude), a well-defined oxidation peak was observed at 0.85 V vs Ag/AgCl electrode. The linear calibration range for TM at 0.85 V vs. Ag/AgCl electrode was found to be 5.0 × 10−7 – 1.3 × 10−4 mol L−1 (0.21–56.2 μg mL−1) (R 2 = 0.9947) with lower limits of detection (LOD) and quantitation (LOQ) of 2.7 × 10−7 (0.12) and 8.99 × 10−7 mol L−1 (0.39 μg mL−1), respectively. The developed assay was satisfactorily applied for trace determination of TM residues in biological fluids (urine), environmental water samples and eye drop with good recoveries (90.5 ± 0.66–106 ± 0.66%), demonstrating good accuracy and applicability of the proposed method as an effective and reliable electrochemical sensor for analysis of TM in complex matrices. Common organic and inorganic compounds did not interfere with TM in its determination. The established strategy was validated using the official HPLC method. Analysis results obtained by the present method were comparable to those obtained using the official method; indicating that the proposed method could be used as an alternative method for the routine quality control of the drug in complex matrices. Chromatographic methods are still more precise, while electrochemical sensors are promising for the analyte determination as they have reduced analytical time, low cost and reproducible. The proposed sensor also demonstrated excellent precision, selectivity, and reproducibility for TM determination.

Development of deep eutectic solvent extraction method for extraction of Zn2+ from powdered milk and baby formula samples and its determination by ICP-OES

In the present study, the deep eutectic solvent-based extraction method has been developed for separation of Zn prior to ICP-OES analysis. Five different choline chloride-based deep eutectic solvents were prepared. The Zn extraction ability of DESs from milk powder and baby formulation samples which contain a high amount of milk protein was investigated. The parameters affecting the extraction efficiency such as the amount and type of solvent, extraction time and ambient temperature were optimized. Oxalic acid-based DES gave the highest yield and reproducible results and appropriate preparation criteria. It is concluded from the results that DES-oxalic can quantitatively extract Zn from milky samples. The analytical parameters such as linear calibration range, limit of detection (4.2 µg L−1) and quantification (14.1 µg L−1) were also calculated. The added-found method is successfully applied to ERM BD 150 standard reference material, and the recovery values and standard deviation values were found between the ranges of 79.4–97.21 µg L−1 and 4.1–6.31 µg L−1, respectively. The method was also applied to real samples, and the recovery values were found between 73 and 106% in the spiked samples.

Amplification Strategy of Silver Nanoclusters with a Satellite-Nanostructure for Substrate-Free Assay of Alkaline Phosphatase by ICP-MS.

Alkaline phosphatase (ALP) plays critical roles in signal transmission and cell growth/apoptosis. Its abnormal level in serum/cell is tightly related to diseases, thus, serum and cellular ALP detection is of great significance for disease diagnosis. Herein, a novel approach for ALP assay based on a satellite-nanostructure is developed by conjugating lanthanide upconversion nanoparticles (UCNPs) with silver nanoclusters (AgNCs) through DNA bridging. UCNPs serve as the cores to conjugate with DNA fragments, followed by assembly of AgNCs as the satellites on UCNPs surface through the AgNCs-cytosine affinity, to produce the satellite-nanostructure of UCNPs@DNA-AgNCs. The presence of ALP converts phosphate groups into hydroxyl groups at DNA helix, weakening the coordination of DNA with UCNPs. As a result, the satellite AgNC labeling on DNA fragments strips off the UCNP surface. Silver is quantified by measuring isotope 107Ag with ICP-MS, which further derives the content of ALP by correlation to the number of AgNCs. A linear calibration range is obtained in 0.005-120 U/L with a detection limit of 1.8 mU/L. The distinct advantage of this strategy, on one hand, is the substrate-free feature that eliminates the intermediate process of substrate reaction, where the substrate activity decrease and its instability may significantly deteriorate the sensitivity. On the other hand, ALP triggers the production of a large number of AgNCs resulting in substantial amplification on ICP-MS signal to give a favorable sensitivity. This is the first attempt for ALP detection by inductively coupled plasma mass spectrometry.

Carbon dots-enhanced chemiluminescence method for the sensitive determination of iodide

The nitrogen doped carbon dots regulated by formaldehyde were synthesized using citric acid and melamine by a simple hydrothermal method. The obtained carbon dots (MFCD) significantly enhanced the weak chemiluminescence (CL) reaction of K2Cr2O7 with NaHSO3 by means of energy transform from the intermediate of excited sulphur dioxide (SO2*) and the radiative recombination of oxidant-injected holes and electrons. Interestingly, it was discovered that iodide was effective in enhancing the CL intensity of this system. Based on this finding, the MFCD-based CL system as a sensitive and selective probe was applied for detection of nM levels of iodide ions. Under optimum conditions, the probe had a linear calibration range from 0.03 to 5.0 μM with a detection limit of 5.6 nM. The developed CL method was applied for the detection of iodide in milk and mineral water samples.

Establishing repeatability and ruggedness of chiral separations in micellar electrokinetic chromatography mass spectrometry: Combined use of covalently bonded capillary column and molecular micelles

Although micellar electrokinetic chromatography-mass spectrometry (MEKC-MS) using bare silica capillary filled with molecular micelles is an advantageous hyphenated technique for chiral analysis, it is still in the developmental stage. This is mainly because of the lower repeatability of retention time and peak area associated with the difficulty in controlling electroosmotic flow on bare silica capillaries. Besides the lower robustness and electrospray erosion of the fused-silica capillary tip, the lifetime is limited for 10–15 runs per capillary column. We have tested a new MEKC-MS method to eradicate this problem using a covalently bonded 2-acrylamido-2-methyl-1-propane-sulfonic acid (AMPS) column filled with free floating molecular micelles, polysodium N-undecenoxy carbonyl-L-leucinate (poly-L-SUCL). Simultaneous enantiomeric separations and MS/MS detection of three β-blockers [atenolol (ATEN), metoprolol (METO) and, pindolol (PINDO)] was achieved within 25 min with improved column lifetime of at least 45–50 runs. Excellent repeatability of retention time was observed for β-blockers, as evidenced by the relative standard deviation of less than 2% and 3% for intra-capillary and inter-capillary column, respectively. The linear calibration range of both β-blockers was simultaneously established using enantiomers of PINDO as an internal standard. The limit of detection and the lower limit of quantitation were 0.2 μg/mL and 0.5 μg/mL, respectively, for both ATEN and METO. Acceptable recovery of the enantiomeric content of the commercial METO tablet (98-99.5%) and ATEN tablet (89-92.5%) were obtained with adequate system suitability for the precision of peak area (≤10% RSD) under optimum conditions. The developed MEKC-MS approach was extended, which provided broader repeatibility of chiral separation to a panel of primary, secondary and tertiary amines as well as one anionic chiral compound.

Ultrasound enhanced solid-phase extraction of ultra-trace arsenic on Fe3O4@AuNPs magnetic particles

Using ultrasound (US) to reduce the agglomeration of magnetic materials has attracted many researchers’ attention in the field of magnetic solid phase extraction (MSPE). This paper showed that even the simple magnetic material (Fe3O4@AuNPs) can stimulate excellent arsenic (As) enrichment performance with the assistance of US. Compared with stirring dispersion, the extraction efficiencies of Fe3O4@AuNPs for 0.2 μg L−1 As(III) and As(V) improved by a factor of about 6.2- and 5.7-times with ultrasonic agitation, respectively. Importantly, when the ultrasonic frequency and power are varied within a certain range, the extraction efficiency was increased by about 50% and 130%, respectively. This effect of ultrasonic frequency and power on the enrichment of arsenic by magnetic materials has never been reported. The number, dispersion uniformity and energy released by the bursting of cavitation bubbles under different conditions are considered to be the main reasons for the above phenomena. Additionally, the As(III) or As(V) can be converted into a gaseous product by in-situ slurry chemical hydride generation (SCHG) technology, and the material adsorbed by the material can be effectively removed, thereby ensuring that the complex is repeated at least 5 times or more. Under the optimized conditions, the whole enrichment process can be shortened from ~1 h to several minutes in the presence of US. At the same time, the linear calibration range was 0.01–3.0 μg L−1 documenting that this US-assisted dispersive MSPE method coupled with a sensitive spectral detector (e.g. atomic fluorescence spectrometer, AFS) is suitable for analysis of inorganic As in natural water samples. The content of arsenic in five kinds of natural water samples ranged from 34 ng L−1 to 2.3 μg L−1.

Measurement of aflatoxin M1 in powder and pasteurized milk samples by using a label–free electrochemical aptasensor based on platinum nanoparticles loaded on Fe–based metal–organic frameworks

In the present study, a sensitive label–free electrochemical aptasensor is introduced to measure aflatoxin M1 (AFM1) by using platinum nanoparticles (PtNPs) decorated on a glassy carbon electrode (GCE) modified with Fe–based metal–organic frameworks, MIL–101(Fe). The MIL–101(Fe) and the PtNP/MIL–101(Fe) are synthesized and characterized by Fourier transform infrared spectroscopy, X–ray diffraction, UV–Visible spectroscopy, and field–emission scanning electron microscopy. Cyclic voltammetry and electrochemical impedance spectroscopy (EIS) are done to monitor the fabrication processes of the aptasensor. In optimum conditions, the linear calibration range of 1.0 × 10−2 to 80.0 ng mL−1 and the detection limit of 2.0 × 10−3 ng mL−1 are obtained to measure AFM1 concentration using the EIS method. Finally, the fabricated aptasensor is successfully applied to measure AFM1 concentration in powder and pasteurized milk samples.

Towards direct analysis of solid and liquid samples exploiting a 3D printed dialysis unit and sequential injection: Application for automated derivatization and determination of gamma-aminobutyric acid in foodstuff and beverages

In this work, a new design of a dialysis unit for direct analysis of solid and liquid samples is presented. The homemade unit was constructed using a 3D printer due to its simple and fast fabrication ability. The dialysis unit is composed of cylindrical-shaped donor and acceptor chambers. A stainless steel sieve is installed inside the donor chamber. SEM images clearly showed that the sieve prevented membrane blockage by suspension particles in the sample. Multiple dialysis units were connected to a sequential injection (SI) system for serial determination of gamma-aminobutyric acid (GABA) in solid and liquid samples. The dialysate from each dialysis unit was consecutively aspirated into the SI flow line for on-line derivatization of GABA with 2-hydroxy-1-naphthaldehyde (3.0% w/v). The derivative was detected spectrophotometrically at 425 nm. The linear calibration range extended to 1000 mg L−1 GABA (r2 > 0.99) with high precision (1.2 %RSD). The developed system was applied to analysis of dietary supplements, grains of germinated brown rice and milk. The samples were directly introduced into the donor chamber either as powder or liquids. The measured GABA content using the developed method was compared using high performance liquid chromatography, with good agreement using Pearson’s correlation (r2 = 0.9999). The method has high accuracy based on recovery studies (99.8 ± 1.5%) and high sample throughput (64 samples h−1).

Selective extraction of cocaine from biological samples with a miniaturized monolithic molecularly imprinted polymer and on-line analysis in nano-liquid chromatography

We report the on-line coupling of a monolithic molecularly imprinted polymer to nano-liquid chromatography for the selective analysis of cocaine and its main metabolite, benzoylecgonine, in complex biological samples. After the screening of different synthesis conditions, a monolithic molecularly imprinted polymer was in situ synthesized into a 100 μm internal diameter fused-silica capillary using cocaine as template, methacrylic acid as functional monomer, and trimethylolpropane trimethacrylate as cross-linker. Scanning electron microscopy was used to assess the homogeneous morphology of the molecularly imprinted polymer and its permeability was measured. Its selectivity was evaluated by nano-liquid chromatography-ultraviolet, leading to imprinting factors of 3.2 ± 0.5 and 2.2 ± 0.3 for cocaine and benzoylecgonine, respectively, on polymers resulting from three independent syntheses, showing the high selectivity and the repeatability of the synthesis. After optimizing the extraction protocol to promote selectivity, the monolithic molecularly imprinted polymer was successfully on-line coupled with nano-liquid chromatography-ultraviolet for the direct extraction and analysis of cocaine present in spiked human plasma and saliva samples. The repeatability of the obtained extraction recovery, between 85.4 and 98.7% for a plasma sample spiked at 100 ng mL−1, was high with relative standard deviation values lower than 5.8% for triplicate analyses on each of the three independently synthesized molecularly imprinted polymers. A linear calibration range was achieved between 100 and 2000 ng mL−1 (R2 = 0.999). Limits of quantification of 14.5 ng mL−1 and 6.1 ng mL−1 were achieved in plasma and urine samples, respectively. The very clean-baseline of the resulting chromatogram illustrated the high selectivity brought by the monolithic molecularly imprinted polymer that allows the removal of a huge peak corresponding to the elution of interfering compounds and the easy determination of the target analyte in these complex biological samples.

In situ Electrochemical Synthesis of a Composite Film Containing Nickel Hexacyanoferrate and Bentonite Clay for the Sensitive Determination of Acetaminophen and Dopamine

AbstractA composite film of nickel hexacyanoferrate (NiHCF) and bentonite (Bt) clay (abbreviated as NiHCF−Bt) is synthesized by an in situ electrochemical method. For this synthesis, nickel ions are immobilized on Bt clay by an ion‐exchange process, equilibrating Bt clay with nickel nitrate. On a glassy carbon electrode (GCE), the nickel ion‐exchanged Bt clay (Ni2+−Bt) is coated to get the modified electrode which is represented as GCE/Ni2+−Bt. The NiHCF−Bt composite film is prepared on the GCE surface using the GCE/Ni2+−Bt and scanning the electrode potentials between −0.10 to 1.00 V continuously in an aqueous solution containing potassium hexacyanoferrate and potassium chloride. This NiHCF−Bt modified GCE (GCE/NiHCF−Bt) exhibits redox peaks due to the oxidation and reduction of the central metal ion, Fe2+. The electro‐generated Fe3+ present in the GCE/NiHCF−Bt, electrocatalytically oxidizes a range of drugs like acetaminophen (AC), dopamine (DA), and tyrosine (TY) at decreased overpotentials with high current. This property is advantageously used for the precise quantification of AC, DA, and TY. Sensitivity, limit of detection, and linear calibration range for the determination of AC are found to be 0.20 μA μM−1 cm−2, 1.5 μM, and 25.0–1000.0 μM, respectively. Further, the amount of AC present in pharmaceutical products is satisfactorily quantified which demonstrated the use of the NiHCF−Bt composite film in electroanalysis.

Ultra-trace sensing of cadmium and lead by square wave anodic stripping voltammetry using ionic liquid modified graphene oxide

The detection of Cd (II) and Pb (II) ions have been done by modifying the glassy carbon electrode (GCE) with graphene oxide (GO) mixed ionic liquid (IL) (BMIM-PF₆) and nafion binder. The developed nanocomposite film combines the advantages of graphene and ionic liquid for enhanced detection. The estimated sensitivity for Cd (II) was 0.0711 µA/ppb and limit of detection found to be 0.33 ppb in the concentration range of 2.4–70 ppb. The effect of deposition potential (Dp), deposition time (Dt) and stirring speed(S) have been carried out for the response of Cd (II) current signal. The estimated sensitivity for Pb (II) was 0.0371 µA/ppb and limit of detection value of 0.42 ppb found in the linear calibration range of 5–15 ppb. Further the study of interaction effect of independent parameters (Dp, Dt, S) has also been studied by designing the experiment based on Box-Behnken design. The RSM modeling and optimization of process parameters for Cd (II) current response by IL/GO/GCE electrode was carried out with suitable empirical model. This developed sensor exhibited selective, good stability and reproducibility that could be explored for environmental, food and pharmaceutical analysis.

Spectrofluorimetry - Cloud point extraction determination of trace arsenic (III) with 2′,7′-dichlorofluorescein

In this work, explains a separation and Preconcentration procedure for the determination of arsenic (III) by spectrofluorimetric method after complexation with the 2′,7′-dichlorofluorescein as a fluorogenic reagent agent presence by the nonionic surfactant Triton X-114 in λex 271 nm and λem 537 nm, after that, the quantitatively isolated into a unimportant volume of the surfactant-rich phase later a centrifugation. The optimum conditions, such as pH, volume of surfactant and reagent (TritonX-114), equilibrium temperature and incubation time on the cloud point extraction procedure, were studied and optimized on the extraction productivity percentage. In this method limits of detection and quantification LOD and LOQ of As(III) ion was (0.102) and (0.525) ng/mL respectively, and a linear calibration range of ( 5.0 -50.0) ng/mL for As(III). The proposed method has been successfully applied to the determination of As(III) ion in water samples with agreeable results.

Placeholder Strategy with Upconversion Nanoparticles-Eriochrome Black T Conjugate for a Colorimetric Assay of an Anthrax Biomarker.

The timely warning of the germination of bacterial spores and their prevention are highly important to minimize their potential detrimental effects and for disease control. Thus, a sensitive and selective assay of biomarkers is most desirable. In this work, a nanoprobe is constructed by conjugating lanthanide upconversion nanoparticles (UCNPs) with sodium tripolyphosphate (TPP) and eriochrome black T (EBT). The nanoprobe, UCNPs-TPP/EBT, serves as a platform for the detection of the anthrax biomarker, dipicolinic acid (DPA). In principle, DPA displaces EBT from the UCNPs-TPP/EBT nanoconjugate, resulting in a color change from magenta to blue because of the release of free EBT into the aqueous solution. The binding sites on UCNPs are partly preblocked with TPP as the placeholder molecule, leaving a desired number of binding sites for EBT conjugation. On the basis of this dye displacement reaction, a novel colorimetric assay protocol for DPA is developed, deriving a linear calibration range from 2 to 200 μM with a detection limit of 0.9 μM, which is well below the infectious dose of the spores (60 μM). The assay platform exhibits excellent anti-interference capability when treating a real biological sample matrix. The present method is validated by the analysis of DPA in human serum, and its practical application is further demonstrated by monitoring the DPA release upon spore germination.

Ultrasensitive colorimetric detection of Hg2+ in urine based on single hairpin DNA-based self-propelled dual-cycle targets recycling amplification strategy

ABSTRACT This work reported a label-free single hairpin DNA-based self-propelled dual-cycle targets recycling strategy for ultra sensitive detection of Hg2+ based on T-Hg2+-T structure, exonuclease Ш (Exo Ш)-assisted self-propelled dual-cycle targets recycling and haemin/G-quadruplex (DNAzyme) signal amplification. The hairpin DNA probe with G-quadruplex fragment and continuously repeated sequences was specially designed for this strategy. Hg2+ could assist the combination between Hg2+ binding probe and free 3ʹ-terminus of hairpin DNA probe by T-Hg2+-T coordination to form the blunt 3ʹterminus that triggered Exo III-assisted digestion, and set free Hg2+, Hg2+ binding probe, and free G-quadruplex fragment. The released Hg2+ and Hg2+ binding probe is recycled through cycle 1. The released free G-quadruplex fragments are recycled through cycle 2. Single hairpin DNA-propelled dual-cycle targets recycling triggered by ultra-trace Hg2+ produce massive G-quadruplex fragments that bind haemin to yield G-quadruplex−haemin DNAzymes, which can efficiently catalyse ABTS-H2O2 system and convert ABTS2- to the coloured products. This ultra-sensitive colorimetric assay successfully achieved Hg2+ analysis in urine as low as 0.07 pmol/L with a linear calibration range from 0.1 pmol/L to 50 pmol/L (R2 = 0.992), and was amenable to quantification of Hg2+ in complex biological matrixes. This proposed single hairpin DNA-propelled signal amplification strategy displayed excellent sensitivity, remarkable specificity, high capacity of resisting disturbance, simplicity, low-cost, and was successfully applied for colorimetric detection of Hg2+ in urine samples with good recovery and accuracy.

Triple functional small-molecule-protein conjugate mediated optical biosensor for quantification of estrogenic activities in water samples

Establishing biosensors to map a comprehensive picture of potential estrogen-active chemicals remains challenging and must be addressed. Herein, we describe an estrogen receptor (ER)-based evanescent wave fluorescent biosensor by using a triple functional small-molecule–protein conjugate as a signal probe for the determination of estrogenic activities in water samples. The signal probe, consisting of a Cy5.5-labelled streptavidin (STV) moiety and a 17β-estradiol (E2) moiety, acts simultaneously as signal conversion, signal recognition and signal report elements. When xenoestrogens compete with the E2 moiety of conjugate in binding to the ER, the unbound conjugates are released, and their STV moiety binds with desthiobiotin (DTB) modified on the optical fiber via the STV–DTB affinity interactions. Signal probe detection is accomplished by fluorescence emission induced by an evanescent field, which positively relates with the estrogenic activities in samples. Quantification of estrogenic activity expressed as E2 equivalent concentration (EEQ) can be achieved with a detection limit of 1.05 μg/L EEQ by using three times standard deviation of the mean blank values and a linear calibration range from 20.8 to 476.7 μg/L EEQ. The optical fiber system is robust enough for hundreds of sensing cycles. The biosensor-based determination of estrogenic activities in wastewater samples obtained from a full-scale wastewater treatment plant is consistent with that measured by the two-hybrid recombinant yeast bioassay.

Sensitive Determination of Acetaminophen in the Presence of Dopamine and Pyridoxine Facilitated by their Extent of Interaction with Single‐walled Carbon Nanotubes

AbstractSingle‐walled carbon nanotubes (SWCNTs) were immobilized on glassy carbon (GC) electrode by drop casting The resulting modified electrode (represented as GC/SWCNTs) efficiently oxidizes acetaminophen (AC), dopamine (DA) and pyridoxine (PY) by decreasing the respective oxidation potentials and increasing peak currents in comparison to bare GC electrode. The extent of lowering of overpotentials is in the order of AC>PY>DA, in agreement with the order of decrease in the HOMO‐LUMO energy gap (ΔE) of these analytes, as determined from Density Functional Theory (DFT) calculations. DFT calculations further reveal that due to the interaction of the analytes on the SWCNT(10,10) there is a negative charge density transfer (higher probability of electron transfer, lower ΔE value) to the frontier molecular orbitals of the analytes, which eases their oxidation. Since AC, DA and PY oxidize distinctly at distinct potential values, the present SWCNTs modified electrodes could be used to simultaneously determine them. Cyclic voltammetry, differential pulse voltammetry and amperometry techniques are utilized to understand the electrochemical characteristics of the analytes (AC, DA and PY) and subsequent sensing of them at the GC/SWCNTs electrode. The electrode is then applied to the determination of AC as a case study. Sensitivity, detection limit and linear calibration range for the AC are found to be 7.9 μA μM−1 cm−2, 1.1 μM and 2.0–100.0 μM, respectively. The increased electroactive surface area of the GC/SWCNTs increases the oxidation peak currents and hence increases the sensitivity of the determination.

Simple flow system with in-line gas-diffusion unit for determination of ethanol employing hypsochromic shift of visible absorbance band of methyl orange

The effect of solvent composition on the uv–visible spectrum of methyl orange was investigated for application to the quantitative determination of ethanol. At fixed pH, there was a hypsochromic shift of the absorbance band of methyl orange with increasing ethanol concentration. Using acetate buffer at pH 3.40 the change of absorbance at 530 nm of a solution of methyl orange containing known concentrations of standard ethanol was measured to provide a calibration curve. In order to apply this method to the analysis of alcoholic samples, such as distilled spirits, blended spirits and liquid herbal medicines, a simple gas-diffusion unit coupled with flow system was employed to separate the ethanol from sample matrices. Using the gas diffusion-flow system and employing an evaporation time of 2 min, a linear calibration range of 5–45% (v/v) ethanol was achieved ((ΔA = (0.0078 ± 0.0002)x(ethanol, %(v/v)) + (0.040 ± 0.005)), r2 = 0.998). The limit of detection (3σ blank/slope) was 2.23% (v/v). The developed gas diffusion-flow system was applied to the analysis of colorless distilled spirits, yellow blended spirits and dark brown herbal medicines that are available in the local markets of Bangkok, Thailand. Validation of the method was carried out by comparing the results with analysis using gas chromatography. There was no statistically significant difference at the 95% confidence level for all alcoholic samples analyzed.