A multi-syringe flow injection system for the spectrophotometric determination of trace levels of iron in waters using a liquid waveguide capillary cell and different chelating resins and reaction chemistries

A method integrating a long waveguide capillary cell with a preconcentration resin in a multi-syringe flow injection analysis (MSFIA) system for iron determination in waters was developed. The determination of iron is based on a colorimetric reaction and two reagents were tested, ferrozine and ammonium thiocyanate. A liquid waveguide capillary cell (1.0 m pathlength, 550 µm i.d. and 250 µL internal volume) with a preconcentration resin were used to improve the sensitivity of the determination. Two different preconcentration resins were also tested, Chelex 100 and NTA Superflow. The developed method employing the NTA Superflow with ferrozine colorimetric reagent provided a detection limit of 0.05 µg L^− 1 with a linear response up to 8 µg L^− 1 and a sample throughput rate of 12 per hour. The developed system presents low reagents/sample consumptions. The accuracy was assessed using a certified reference water sample.     

Electrochemical determination of rosiglitazone by square-wave adsorptive stripping voltammetry method

Square-wave adsorptive stripping voltammetry technique was used to determine rosiglitazone (ROS) on the hanging mercury dropping electrode (HMDE) surface, in Britton Robinson buffer, pH = 5. The voltammetric cathodic peak was observed at ?1520 mV vs. Ag/AgCl reference electrode. The voltammetric peak response was characterized with respect to pH, supporting electrolyte, accumulation potential, preconcentration time, scan rate, frequency, pulse amplitude, surface area of the working electrode and the convection rate. Under optimal conditions, the voltammetric current is proportional to the concentration of ROS over the concentration range of 5 × 10^?8–8 × 10^?7 mol l^?1 (r = 0.9899) with a detection limit of 3.2 × 10^?11 mol l^?1 using 120 s accumulation time. The developed SW-AdSV procedure showed a good reproducibility, the relative standard deviation RSD% (n = 10) at a concentration level of 5 × 10^?7 mol l^?1 was 0.33%, whereas the accuracy was 101% ± 1.0. The proposed method was successfully applied to assay the drug in the human urine and plasma samples with mean recoveries of 90 ± 0.71% and 86 ± 1.0%, respectively.     

Preconcentration procedure trace amounts of palladium using modified multiwalled carbon nanotubes sorbent prior to flame atomic absorption spectrometry: 1st Nano Update

A method for preconcentration of palladium at trace level on modified multiwalled carbon nanotubes columns and determination by flame atomic absorption spectrometry (FAAS) has been developed. Multiwalled carbon nanotubes (MWCNTs) were oxidized with concentrated HNO₃ and the oxidized multiwalled carbon nanotubes were modified with 5-(4′-dimethylamino benzyliden)-rhodanine, and then were used as a solid sorbent for preconcentration of Pd(II) ions. Factors influencing sorption and desorption of Pd(II) ions were investigated. The sorption of Pd(II) ions was quantitative in the pH range of 1.0–4.5, whereas quantitative desorption occurs with 3.0 mL 0.4 mol L^?1 thiourea. The amount of eluted palladium was measured using flame atomic absorption spectrometry. The effects of experimental parameters, including sample flow rate, eluent flow rate, and eluent concentration were investigated. The effect of coexisting ions showed no interference from most ions tested. The proposed method permitted a large enrichment factor (about 200). The relative standard deviation of the method was ±2.73% (for eight replicate determination of 2.0 μg mL^?1 of Pd(II)) and the limit of detection was 0.3 ng mL^?1. The method was applied to the determination of Pd(II) in water, road dust, and standard samples.     

Comparison of palladium and zirconium treated graphite tubes for in-atomizer trapping of hydrogen selenide in hydride generation electrothermal atomization atomic absorption spectrometry

Zirconium treated graphite tubes were investigated and compared with non-treated and palladium coated ones for in situ trapping of selenium hydride generated in a flow injection system. Selenium was effectively trapped on zirconium treated tubes at trapping temperatures of 300–600°C, similar to those observed for palladium, whereas trapping temperatures higher than 600°C had to be used with non-treated tubes. Zirconium treated tubes used in this work showed good stability up to 300 trapping/atomization cycles, with precision better than 5%, characteristic masses of 42 (peak height) and 133 pg (peak area) of selenium were obtained. Sensitivity of zirconium and palladium treatments were similar, but zirconium offered the advantage of a single application per tube. Detection limits were 0.11 (peak height) and 0.23 ng (peak area) for a 1 ml sample volume.     

Temperature controlled ionic liquid-dispersive liquid phase microextraction for determination of trace lead level in blood samples prior to analysis by flame atomic absorption spectrometry with multivariate optimization

This paper described a new approach for the preconcentration of lead (Pb²⁺) by temperature controlled ionic liquid-dispersive liquid phase microextraction (TIL-DLME) prior to analyzing by flame atomic absorption spectrometry (FAAS). An ionic liquid (IL) 1-Butyl-3-methylimidazolium hexafluorophosphate [C₄MIM][PF₆] was used as an extractant solvent. The Pb²⁺ was complexed with ammonium pyrrolidinedithiocarbamate (APDC) and then entered into the infinite IL drops at high temperature (> 70 °C). Important variables affecting the microextraction efficiency such as pH, ligand concentration, amount of IL, temperature and incubation time were investigated. The results showed that the coexistent ions had no obvious negative effect on the determination of Pb²⁺. In the optimum experimental conditions, the limit of detection (LOD) and the enhancement factor (EF) were 0.13 μg L^? 1 and 93, respectively. The relative standard deviation (RSD) of 10 μg L^? 1 Pb²⁺ was 4.3%. The developed method was validated by determining Pb²⁺ in certified reference material (CRM) and the results showed that the determined values of Pb²⁺ were in good agreement with the certified value. The proposed method was applied satisfactorily for the preconcentration of Pb²⁺ in acid digested blood samples of children with different respiratory disorders.     

Ultra-sensitive cholesterol biosensor based on low-temperature grown ZnO nanoparticles

A high-sensitive cholesterol amperometric biosensor based on the immobilization of cholesterol oxidase (ChOx) onto the ZnO nanoparticles has been fabricated which shows a very high and reproducible sensitivity of 23.7 μA mM^?1 cm^?2, detection limit (based on S/N ratio) 0.37 ± 0.02 nM, response time less than 5 s, linear range from 1.0 to 500.0 nM and correlation coefficient of R = 0.9975. A relatively low value of enzyme’s kinetic parameter (Michaelis–Menten constant) ～4.7 mM has been obtained which indicates the enhanced enzymatic affinity of ChOx to Cholesterol. To the best of our knowledge, this is the first report in which such a very high-sensitivity and low detection limit has been achieved for the cholesterol biosensor by using ZnO nanostructures modified electrodes.     

The distribution of dissolved thallium in the different water masses of the western sector of the Ross Sea (Antarctica) during the austral summer

Vertical profiles for total dissolved thallium were obtained at five sites in the western sector of the Ross Sea (Southern Ocean), Antarctica. Thallium is estimated to have a natural mean seawater concentration between 50 and 65 pmol L^− 1 with higher values in the North Pacific (65 ± 5 pmol L^− 1) and lower in the Bay of Biscay and Irish Sea (49 ± 3 pmol L^− 1). Our samples show a concentration varying from 22 to 55 pmol L^− 1 with a mean value of 46 pmol L^− 1, depending on depth, dissolved oxygen, salinity and local topographic characteristics. The analyses were performed using an ICP-SFMS that has enabled us to obtain reliable Tl concentration measurements with a relative standard deviation of better than 2.5% and a detection limit, calculated as three times the standard deviation of the “blank signal” of 0.69 pmol L^− 1 (1.60 pmol L^− 1, obtained analysing four blank solutions (n = 5) prepared with the same water and acid used for the dilution/acidification steps). Thallium appears to have a nearly conservative distribution in seawater as highlighted also from the comparison with the profiles of two seawater conservative elements: molybdenum and uranium; however it also highlights the presence of a reactive component of thallium, which is more influenced by the presence of particulate matter, oxygen content and fluorescence.     

Preconcentration of atrazine and simazine with multiwalled carbon nanotubes as solid-phase extraction disk

A sensitive and selective preconcentration method using solid-phase extraction (SPE) disk, namely multiwalled carbon nanotubes (MWCNTs) disk, is proposed for the determination of atrazine and simazine in water samples. Atrazine and simazine were extracted on MWCNTs disk and then determined by gas chromatography–mass spectrometry (GC/MS). Several parameters on the enrichment factor of the analytes were investigated. The experimental results showed that it was possible to obtain quantitative analysis when the solution pH was 5 using 200 mL of validation solution containing 0.1 μg of triazines and 5 mL of acetone as an eluent. The maximum enrichment factors for atrazine and simazine were 3900 ± 250 and 4000 ± 110, respectively when 200 mL of sample solution volume was used. Relative standard deviations for seven determinations were 6.9% (atrazine) and 3.0% (simazine) under optimum conditions. The linear range of calibration curves were 0.1 to 1 ng mL^− 1 for each analyte with good correlation coefficients. The detection limits (3S/N) were 2.5 and 5.0 pg mL^− 1 for atrazine and simazine, respectively. The proposed method was successfully applied to the determination of atrazine and simazine in environmental water samples with high precision and accuracy.     

Optimization of parameters of sampling and determination of reduced sulfur compounds using cryogenic capture and gas chromatography in tropical urban atmosphere

Reduced sulfur compounds, RSCs (H₂S, COS, CH₃SH, CH₃SCH₃, CS₂ and CH₃S₂CH₃) play a role in global cycle and acid rain formation. At trace levels RSCs in air are difficult to collect, store and analyze because of their highly adsorptive and reactive properties. This work optimizes parameters of sampling and instrumental determination of RSCs for urban measurements. The method used is based on cryogenic sampling and gas chromatography provided with a cryofocusing trap and flame photometric detection.Greater sampling efficiency was obtained with liquid argon as freezing fluid and air flow rate of 150 mL min^? 1 for two hours. Best results have been obtained with preconcentration for 3 min and injection volume of 3 ml. For H₂S, CH₃SH and CH₃S₂CH₃ the method showed a precision of 89%, limit of detection of 0.10 µg m^? 3 and limit of quantification 0.3 µg m^? 3. For CH₃SCH₃ and CS₂ the corresponding values were 89%, 0.15 µg m^? 3 and 0.5 µg m^? 3 and for COS were 75%, 0.18 µg m^? 3 and 0.8 µg m^? 3 respectively. Sampling efficiency varied between 70–80% for all the RSCs. Accuracy of H₂S from field measurements obtained with parallel measurements using a continuous monitor varied between 88 and 98%. The optimized methodology proved to be suitable for field measurements in urban tropical atmospheres with different characteristics.     

Stability-indicating HPLC method for the determination of nicardipine in capsules and spiked human plasma. Identification of degradation products using HPLC/MS

In this stability-indicating, reversed-phase high-performance liquid chromatographic method for nicardipine (NIC), forced degradation has been employed and the formed degradants were separated on a C18 (150 mm × 3.9 mm, 5 μm) analytical column using a mobile phase consisted of 70% methanol: acetic acid containing 0.01 M triethylamine with pH 4. The flow rate was 1.0 mL/min and the photodiode array detection wavelength was 353 nm. Forced degradation of the drug was carried out under acidic, basic, photolytic, and oxidative stress conditions. Chromatographic peak purity data indicated no co-eluting peaks with the main peaks. This method resulted in the detection of seven degradation products. Among these, two major degradation products from basic hydrolysis, one from oxidation by H₂O₂ and four from photolytic stress were identified by mass spectral data. A good linear response was achieved over the range of 0.5–40 μg/mL with a limit of detection (LOD) of 0.011 μg/mL and limit of quantification (LOQ) of 0.036 μg/mL. The suggested method was successfully applied for the analysis of NIC in its commercial capsules, with mean% recovery value of 100.11 ± 2.26%. The method was extended to the in vitro determination on NIC in spiked human plasma samples with mean% recovery of 99.04 ± 5.67%. The suggested method was utilized to investigate the kinetics of photolytic induced degradation.     

Development of an accurate procedure for the determination of arsenic in fish tissues of marine origin by inductively coupled plasma mass spectrometry

High accuracy procedures for the determination of arsenic are needed for assigning reference values to certified reference materials (CRMs). There are a number of problems associated with the determination of total arsenic by inductively coupled plasma–mass spectrometry. Arsenobetaine (AsB) (the major species in fish) gives an enhanced response (9%) when compared to inorganic arsenic(V) and is very difficult to decompose. Chloride causes interference at m/z 75 by the formation of ArCl⁺ and chloride levels can be significant in marine fish. Also residual carbon in digests can lead to enhancement of arsenic signals by charge transfer effects. This can easily lead to erroneous quantification when compared to standards that do not contain carbon.This newly developed procedure overcomes these issues by complete mineralisation of the matrix leaving insignificant amounts of residual carbon and by removal of chlorine by evaporation. A detection limit of 30 ng/g was achieved. Recoveries for the following CRMs: DORM 2 100.1 ± 4.3%, SRM1548 96.1 ± 4.6%, BCR 422 103.6 ± 6.2% and SRM2976 105.9 ± 6.2% were obtained. The digestion procedure uses open vessel wet digestion with a mixture of sulfuric and nitric acid held at 300 °C. The decomposition of AsB was confirmed by speciation analysis of the digest. Carbon (m/z 13) was monitored to demonstrate the efficiency of the digestion. Instrumentation for the reduction of ArCl⁺ interference was not required and this view is supported by the recovery data. Measurements were performed by external calibration using tellurium as an internal standard.     

Determination of Total Tannin of White and Red Rind Pomegranate (Punica Granatum L.) by Colorimetry Method Using Reagent 1, 10 Phenantroline

Determination of the total tannin of white and red rind pomegranate (Punica granatum L.) has been carried out by colorimetry method using reagent 1,10 phenantroline. This method is based on reduction of iron (III) into iron (II) by tannin at temperature 80⁰C for 20 min. Then the formed of iron (II) was reacted with 1,10 phenantroline to form orange red colour complex that could be measured by spectrophotometer visible at maximum absorption wavelength of 508 nm. The limit of detection (LOD) and the limit of quantitation (LOQ) obtained were 0.34 μg/mL and 1.14 μg/mL, respectively. This result was found to be linier with R value of 0.9984; accuracy as percent recovery was 84.69 ± 0.85% and coefficient of variant (KV) was 1.003% for white rind pomegranate while red rind pomegranate percent recovery was 84.38 ± 0,45% and coefficient of variant (KV) was 0.53%. The total tannin of white rind pomegranate was 18.28 ± 0.072%b/b and red rind pomegranate was 17.33 ± 0.081%b/b     

Preparation of boron-doped diamond nanowires and their application for sensitive electrochemical detection of tryptophan

The paper reports on the fabrication and electrochemical investigation of boron-doped diamond nanowires (BDD NWs) electrodes. The nanowires were obtained directly from highly doped polycrystalline diamond substrates using reactive ion etching (RIE) with oxygen plasma. The technique does not require any complicated processing steps such as mask deposition or template removal. The influence of the surface state on the electrochemical characteristics is discussed. The interface with the most favourable electrochemical response is investigated for the detection of tryptophan using differential pulse voltammetry. A detection limit of 5 × 10^?7 M was obtained on oxidized BDD NWs, as compared to 1 × 10^?5 M recorded on planar oxidized boron-doped diamond interfaces.     

Extraction and preconcentration of trace levels of cobalt using functionalized magnetic nanoparticles in a sequential injection lab-on-valve system with detection by electrothermal atomic absorption spectrometry

A new approach to performing extraction and preconcentration employing functionalized magnetic nanoparticles for the determination of trace metals is presented. Alumina-coated iron oxide nanoparticles were synthesized and used as the solid support. The nanoparticles were functionalized with sodium dodecyl sulfate and used as adsorbents for solid phase extraction of the analyte. Extraction, elution, and detection procedures were performed sequentially in the sequential injection lab-on-valve (SI-LOV) system followed by electrothermal atomic absorption spectrometry (ETAAS). Mixtures of hydrophobic analytes were successfully extracted from solution using the synthesized magnetic adsorbents. The potential use of the established scheme was demonstrated by taking cobalt as a model analyte. Under the optimal conditions, the calibration curve showed an excellent linearity in the concentration range of 0.01–5 μg L^?1, and the relative standard deviation was 2.8% at the 0.5 μg L^?1 level (n = 11). The limit of detection was 6 ng L^?1 with a sampling frequency of 18 h^?1. The present method has been successfully applied to cobalt determination in water samples and two certified reference materials.     

A highly stable cylindrical microwave cavity resonator for the measurement of the relative permittivities of gases

We present a new and highly stable cylindrical microwave cavity resonator designed for the measurement of the relative permittivities of gases. The cylinder has an internal volume of just 5.7 cm ³, which makes it the smallest such a resonator reported to date. The equipment and procedure used to measure the resonance frequencies and halfwidths with fractional random errors better than  ±  6 · 10 ^− 7and  ±  4 · 10 ^− 3, respectively, are described. We have developed also an analytical model which describes the cylinder’s resonant behaviour with a fractional accuracy of the order of  ±  10 ^− 6. Our model includes a novel method for determining the perturbation due to the presence of an opening in the boundary wall which is shown to be in excellent agreement with experimental results.     

An isoperibol micro-bomb calorimeter for measurement of the enthalpy of combustion of organic compounds. Application to the study of succinic acid and acetanilide

A micro static-bomb combustion calorimeter, developed from a 1107 Parr semi-micro bomb, has been provided with a new micro-bomb and calorimetric bucket. In the best conditions of operation, the energy equivalent of this calorimetric arrangement is just ε(calor)=(731.82 ± 0.22) J · K⁻¹, which means an uncertainty of 0.03 per cent for the calibration with benzoic acid NIST 39j. This combustion calorimeter has been used in the measurement of the enthalpy of combustion of the succinic acid and acetanilide, giving −(1489.3 ± 1.6) kJ · mol⁻¹ and −(4222.5 ± 1.1) kJ · mol⁻¹, respectively, for these substances.     

Enhanced oxygen evolution at hydrous nickel oxide electrodes via electrochemical ageing in alkaline solution

The effect of electrochemically ageing hydrous nickel oxide films via slow repetitive potential multi-cycling across the main nickel (II/III) redox peak was investigated in an aqueous base environment using cyclic voltammetry and steady state polarisation curves in the oxygen evolution reaction (OER) region. Similarities between hydrous nickel oxide films and electroprecipitated ‘battery type’ nickel oxide were shown due to their similar change in redox and oxygen evolving properties as a result of film ageing. This ageing method was found to significantly enhance the OER performance of the hydrous nickel oxide electrode with the OER overpotential decreasing by 60 ± 2 mV and experiencing a 10 fold increase in OER rate for a fixed overpotential over that of an un-aged electrode. The OER turnover frequency for an aged electrode was found to be 1.16 ± 0.07 s^− 1 in comparison to 0.05 ± 0.003 s^− 1 for a hydrous nickel oxide electrode not subjected to ageing.     

Application of modified multiwalled carbon nanotubes as solid sorbent for separation and preconcentration of trace amounts of manganese ions

In this work, the potential of modified multiwalled carbon nanotubes for separation and preconcentration of trace amounts of manganese ion is studied. Multiwalled carbon nanotubes were oxidized with concentrated HNO₃ and then modified with loading 1-(2-pyridylazo)-2-naphtol. Mn(II) ions could be quantitatively retained by modified multiwalled carbon nanotubes in the pH range of 8–9.5. Elution of the adsorbed manganese was carried out with 5.0 mL of 0.1 mol L^?1 HNO₃. Detection limit is 0.058 ng mL^?1 and analytical curve is linear in the range of 0.1 ng mL^?1–5.0 μg mL^?1 in the initial solution with a correlation coefficient 0.9977 and the preconcentration factor is 100. Relative standard deviation for eight replicate determination of 0.5 μg mL^?1 of manganese in the final solution is 0.41%. The effects of the experimental parameters, including the sample pH, flow rates of sample and eluent solution, eluent type, breakthrough volume and interference ions, were studied for preconcentration of Mn(II) ions in detail to optimize the conditions. The method was successfully applied for separation, preconcentration and determination of manganese in different samples.     

Assessment of a dynamic hollow-fibre liquid phase microextraction system for human blood plasma samples

A dynamic liquid phase microextraction (LPME) system, based on hollow-fibre supported liquid membrane (SLM) extraction, was developed for extracting ionisable xenobiotics from human plasma, and its performance was evaluated (in terms of extraction efficiency, reproducibility, durability and carry-over) using nitrophenolic compounds as model analytes at concentrations of 0.1–0.5 μg mL^?1 in aqueous standards. The efficiency and repeatability were tested also on spiked human plasma. The system is non-expensive, convenient, requires minimal manual handling and enables samples with volumes as small as 0.2 mL to be extracted. For plasma samples extraction efficiencies of between 30 and 58% were achieved within 20 min, including washing steps. The limit of detection (LOD) values were in the range 0.02–0.03 μg mL^?1. The developed system can provide enrichment factors up to eight, based on the injection-to-acceptor volume ratio (in this case 0.2–0.025 mL). The same hollow-fibre membrane was used up to 8 days with no loss of efficiency. Carry-over was lower than detection limit.     

Comparative Study of the Developed Chemiluminescent,ELISA and SPR Immunoassay Formats for the Highly Sensitive Detection of Human Albumin

Chemiluminescent enzyme immunoassay (CLEIA), surface plasmon resonance (SPR) immunoassay and enzyme- linked immunosorbent assay (ELISA) were developed for the highly sensitive detection of human albumin (HA). The bioanalytical procedure, involving the surface modification and antibody immobilization, was the same for all immunoassay formats. The bioanalytical platforms, i.e. microtiter plates (MTP) and SPR gold chips, were initially functionalized with 3-aminopropyltriethoxysilane and then crosslinked to anti-HA antibodies using 1-ethyl-3-[3- dimethylaminopropyl] carbodiimide hydrochloride and sulfo-N-hydroxysuccinimide. The developed HA immunoassay formats were compared on the basis of their analytical performance. CLEIA was found to be the best format for HA detection as it had the highest analytical sensitivity with lowest limit of detection and widest dynamic range. The analytical sensitivity of various immunoassay formats were in the decreasing order of CLEIA > ELISA > SPR. The developed CLEIA for HA detection was 6-fold more sensitive than the widely used commercially-available ELISA. The anti-HA antibody bound MTPs, stored at 4 °C in 0.1 M PBS, pH 7.4, were stable for up to 4 weeks, and can be effectively used for the rapid detection of HA in just 2.5 h.