Flow Injection Mode Research Articles

Efficient Photochemical Vapor Generation from Low Concentration Formic Acid Media.

Herein, we report on surprisingly efficient photochemical vapor generation (PVG) of Ru, Re, and especially Ir, achieved from very dilute HCOOH media employing a thin-film flow-through photoreactor operated in flow injection mode. In the absence of added metal ion sensitizers, efficiencies near 20% for Ir and approximately 0.06% for Ru and Re occur in a narrow range of HCOOH concentrations (around 0.01 M), significantly higher than previously reported from conventionally optimized HCOOH concentrations (1-20 M). A substantial enhancement in efficiency, to around 9 and 1.5%, could be realized for Ru and Re, respectively, when 0.005 M HCOONa served as the PVG medium. The addition of metal ion sensitizers (particularly Cd2+ and Co2+) to 0.01 M HCOOH significantly enhanced PVG efficiencies to 17, 2.2, and 81% for Ru, Re, and Ir, respectively. Possible mechanistic aspects occurring in dilute HCOOH media are discussed, wherein this phenomenon is attributed to the action of 185 nm radiation available in the thin-film flow-through photoreactor. An extended study of PVG of Fe, Co, Ni, As, Se, Mo, Rh, Te, W, and Bi from both dilute HCOOH and CH3COOH was undertaken, and several elements for which a similar phenomenon appears were identified (i.e., Co, As, Se, Te, and Bi). Although use of dilute HCOOH media is attractive for practical analytical applications employing PVG, it is less tolerant toward dissolved gases and interferents in the liquid phase due to the likely lower concentrations of free radicals and aquated electrons required for analyte ion reduction and product synthesis.

Sensitive method for total selenium determination in garlic and nuts by UV–photochemical vapor generation coupled to atomic absorption spectrometry using mild conditions

Photochemical vapor generation (PVG) coupled on–line to atomic absorption spectrometry using a flow injection mode was investigated for the determination of total Se in garlic and nut samples. In the presence of low molecular weight organic acid solutions, Se(IV) is converted by UV irradiation to volatile species which are transported to the heated quartz tube atomizer. Formic and acetic acids were tested as photochemical reagents and a mixture of 1.5 % (v/v) formic and 5 % (v/v) acetic acid was the best alternative. Central composite design was employed for parameters optimization. The effect of potential interfering elements such as hydride–forming elements, transition metals and nitric acid was investigated to ascertain possible effects of the matrix on Se(IV) signal. Under optimized conditions a detection limit (LOD) of 33 ng g–1 (3σ) was reached. Samples of garlic and nuts purchased at a local market were analyzed and Se concentrations spanned the range 0.36–248 µg g–1. These results were compared with ICP–MS measurements utilizing an elliptical joint confidence region (EJCR) with bilinear least squares analysis, and good results were obtained.

Highly Efficient Photochemical Vapor Generation for Sensitive Determination of Iridium by Inductively Coupled Plasma Mass Spectrometry.

Herein, we describe the highly efficient photochemical vapor generation (PVG) of a volatile species of Ir (presumably iridium tetracarbonyl hydride) for subsequent detection by inductively coupled plasma mass spectrometry (ICPMS). A thin-film flow-through photoreactor, operated in flow injection mode, provided high efficiency following optimization of identified key PVG parameters, notably, irradiation time, pH of the reaction medium, and the presence of metal sensitizers. For routine use and analytical application, PVG conditions comprising 4 M formic acid as the reaction medium, the presence of 10 mg L-1 Co2+ and 25 mg L-1 Cd2+ as added sensitizers, and an irradiation time of 29 s were chosen. An almost 90% overall PVG efficiency for both Ir3+ and Ir4+ oxidation states was accompanied by excellent repeatability of 1.0% (n = 15) of the peak area response from a 50 ng L-1 Ir standard. Limits of detection ranged from 3 to 6 pg L-1 (1.5-3 fg absolute), dependent on use of the ICPMS reaction/collision cell. Interferences from several transition metals and metalloids as well as inorganic acids and their anions were investigated, and outstanding tolerance toward chloride was found. Accuracy of the developed methodology was verified by analysis of NIST SRM 2556 (Used Auto Catalyst) following peroxide fusion for sample preparation. Practical application was further demonstrated by the direct analysis of spring water, river water, lake water, and two seawater samples with around 100% spike recovery and no sample preparation except the addition of formic acid and the sensitizers.

Ascorbic acid as an alternative coreactant for luminol reaction and sensitive chemiluminescence determination of ascorbic acid in soft drinks

Ascorbic acid can serve as an efficient coreactant for luminol chemiluminescence (CL) reaction. An observable CL emission is produced when mixing ascorbic acid with luminol in an alkaline condition. The CL signal is further dramatically enhanced by cobalt(II) ions. This CL system was exploited as a new method for direct determination of ascorbic acid with a flow injection mode. A good linear response is acquired between the CL signal and ascorbic acid concentration in 5.0–1000.0 ng/mL range with a detection limit of 1.3 ng/mL. The relative standard deviations are 2.3% for intra–day (n = 11) and 3.7% for inter–day (n = 3) by parallel determination of 0.5 μg/mL ascorbic acid solution. The method has good selectivity for ascorbic acid since no obvious responses are observed for a variety of inorganic ions and biological substances. The practicability of the method has been demonstrated by the analysis of ascorbic acid in some soft drinks.

Elemental Analysis of Environmental Waters by Solution Cathode Glow Discharge—Atomic Emission Spectrometry (SCGD-AES) with a Multifunctional Injection System

A multifunction sample injection system combined with solution cathode glow discharge—atomic emission spectrometry (SCGD-AES) was developed based on several simple devices (six-way valve, peristaltic pump and medical injector). The equipment enables two analytical modes (continuous flow and flow injection), selected according to the sample. Moreover, the equipment can be operated at atmospheric pressure without any inert gas. Under the optimal experimental conditions (1150 V discharge voltage, 2.5 mm discharge gap, 2.32 mL min−1 flow rate and solution pH 1.0), ten elements (Na, K, Mg, Cu, Rb, Ag, Tl, Cd, Zn, and Mn) were determined using SCGD-AES in the continuous flow and flow injection modes. The detection limits for metals were from 0.1 to 264 µg L−1 (continuous flow mode) and 0.9 to 282 µg L−1 (flow injection mode). The relative standard deviations of the spectral intensities were below 2%. The instrumentation was successfully applied to the Yangtze River and reservoir water samples. The accuracy and viability were confirmed by comparison with inductively coupled plasma—atomic emission spectrometry (ICP-AES) measurements.

Spectrophotometric Determination of Vitamin B1 in Dosage forms Using Drugs Compounds as Reagents by Normal and Reverse Flow Injection Methods

Background: Thiamine hydrochloride (THY), also known as vitamin B1, is a water soluble vitamin usually found in food, and considered as a dietary supplement and treatment in case of vitamin deficiency for example in malabsorption and chronic diarrhea. Objective: Rapid, green, and sensitive methods for the assay of vitamin B1 (thiamine hydrochloride, THY) in pharmaceutical forms, using normal and reverse flow injection manifolds and sulfonamide drugs as green and safe reagents were reported. Sulfamethoxazole and sulfadimidine drugs were used rather than toxic and expensive reagents. Methods: nFIA and rFIA manifolds were used for automated the reaction of THY with diazotized sulfamethoxazole (DSMZ) and diazotized sulfadimidine (DSDM) in an alkaline medium, respectively. The absorbance of the resultant red-orange azo dyes was monitored spectrophotometrically at λmax494 and 496nm for both methods, respectively. Results: The linearity of the suggested methods was in the ranges 2–80 µg/mL (LOD 0.69 µg/mL, % RSD 0.32, n=6) for nFIA method and 0.5-70 µg/mL (LOD 0.29 µg/mL, %RSD 0.85, n=6) for rFIA. Sampling frequency was 84 and 51 injections per hour for nFIA and rFIA methods respectively. Chemical and physical variables for both methods were studied carefully. Conclusion: Both flow injection modes were effectively applied in assay of THY in its pharmaceutical forms. The results were compared with those of standard pharmacopeia method and the statistical analysis indicated insignificant differences in accuracy and precision between the methods.

Ultrasensitive Detection of Ruthenium by Coupling Cobalt and Cadmium Ion-Assisted Photochemical Vapor Generation to Inductively Coupled Plasma Mass Spectrometry

An extremely sensitive methodology for the determination of Ru was developed by coupling photochemical vapor generation (PVG) analyte introduction with inductively coupled plasma mass spectrometry (ICPMS). PVG was undertaken with a thin-film flow-through photoreactor in a medium comprising 8 M formic acid in the presence of 10 mg L-1 Co2+ and 25 mg L-1 Cd2+. The volatile product (presumably ruthenium pentacarbonyl) was generated in a flow injection mode, yielding an overall efficiency of 29% at a sample flow rate of 1.4 mL min-1. The presence of both Co2+ and Cd2+ sensitizers enhanced PVG efficiency by 3,200-fold, permitting a 31 s irradiation time. Although enhanced efficiency (≈40%) could be obtained with increased Co2+ concentration, this was not suitable for routine use due to co-generation of cobalt carbonyl. Excellent repeatability (<2.5%) and reproducibility (4%) were achieved for 200 ng L-1 Ru3+. Limits of detection ranged from 20 to 42 pg L-1 (10-21 fg absolute) depending on the measured isotope and operational mode of the ICPMS reaction/collision cell. Interferences from inorganic acids and their anions, several transition metals, and metalloids were investigated. Practical application of the methodology was demonstrated by the analysis of seven water samples of various matrix complexities (well water, spring water, contaminated water, and seawater).

Detailed evaluation of conditions of photochemical vapor generation for sensitive determination of nickel in water samples by ICP-MS detection

Photochemical vapor generation (PVG) of Ni was optimized using inductively coupled plasma mass spectrometry detection and a 19 W high-efficiency flow-through photoreactor operated in a flow injection mode (0.49 mL sample volume). The main aim was to achieve very high sensitivity and low limits of detection (LOD) for determination of Ni in fresh water samples, which necessitated to keep low Ni contamination and rather low dilution of samples by added formic acid as a photochemical agent. With respect to that a reaction medium composed of 30% (m/v) formic acid and a flow rate through the photoreactor of 1.5 mL min−1, which corresponds to an irradiation time of 29 s, were chosen as optimal. These PVG conditions were characterized by 42% overall PVG efficiency and by relative and absolute LOD of 1.9 ng L–1 and 0.9 pg, respectively. Almost double efficiency was achievable when pH was adjusted by an addition of 1.5 M ammonium formate, reflected in the proportional increase in sensitivity. However, no significant benefit to analytical performance was found at those conditions. Interferences from inorganic anions likely to be encountered during analytical application to real samples (i.e., NO3−, Cl−, SO42−) were investigated in detail as well as interferences from several transition metals and metalloids. The accuracy was successfully verified by an analysis of the standard reference material NIST 1643f (fresh water) and certified reference materials SLRS-6 (river water), ERM-CA713 (wastewater) and CTA-FFA-1 (fine fly ash), the last one after simple acid digestion. The applicability of this sensitive methodology was further demonstrated by a direct analysis of three water samples (river and well) that were collected and only acidified with formic acid to 30% (m/v).

Determination of the Fluoroquinolones Levofloxacin and Ciprofloxacin by a Piezoelectric Immunosensor Modified with Multiwalled Carbon Nanotubes (MWCNTs)

Methods for the high-sensitivity determination of fluoroquinolones using a piezoelectric immunosensor based on multi-walled carbon nanotubes (MWCNTs) are developed. The use of MWCNTs in the formation of a stable piezoelectric sensor detection layer increases the active specific surface area which is necessary for receptor molecule binding. The concentrations of hapten-protein conjugates (35/65 serial concentration) and polyclonal antibodies are determined in the direct (15/85 for levofloxacin, 18/82 for ciprofloxacin) and in the competitive immunoassay formats (14/86 for levofloxacin, 10/90 for ciprofloxacin). Conditions for the analysis in the flow-injection mode were studied. The carrier flow rate was 30 and 50 µl/min depending on the detection layer formation method. The characteristics of MWCNTs-based piezoelectric immunosensors were characterized for the determination of fluoroquinolones in the static and in the flow-injection modes. The direct and competitive immunoassay formats (detection limit, linear range of target concentrations, reproducibility) were determined. The detection limits were 9 and 8 ng/ml for levofloxacin and ciprofloxacin in the competitive format and 25 and 21 ng/ml in the direct assay. The piezoelectric immunosensors were employed for the analysis of milk.

Flow injection hydride generation and on-line W-coil trapping for electrothermal vaporization dielectric barrier discharge atomic emission spectrometric determination of trace cadmium

A fast, low-cost and sensitive method for the determination of trace cadmium was developed by using a miniaturized dielectric barrier discharge microplasma atomic emission spectrometer coupled with a tungsten coil (W-coil) for on-line hydride generation trapping-electrothermal vaporization. Total sample throughput can be greatly improved through the adoption of a horizontally fixed W-coil and the flow injection mode. In addition, the horizontally fixed W-coil and an inserted quartz capillary for on-line trapping contributed to stable and good signal even at a high gas flow rate when volatile cadmium species were trapped, and less sample-consuming and time-saving can be realized in this work. Compared to direct injection, the sensitivity and the LOD were improved by 29- and 38-fold, respectively. The proposed method provides a promising approach to develop a miniaturized instrumentation for highly sensitive detection of trace elements.

Flow Injection Electrochemical Quartz Microbalance with ICP-OES Detection

The electrochemical quartz crystal microbalance (EQCM) has been previously reported in flow injection (FI) mode as a microgravimetric sensor for analytes that can be deposited onto an electrode surface through various mechanisms such as adsorption, covalent bond, or electrodeposition. Since this methodology does not provide the composition of the deposited species, it must be coupled with other analytical techniques.In this work, a new hyphenated technique, flow injection – electrochemical quartz crystal microbalance – inductively coupled plasma optical emission spectroscopy (FI-EQCM-ICP-OES), is used to study the deposition and stripping of metallic ions under hydrodynamic conditions in a modified commercially-available EQCM flow cell with a reaction volume of 50 uL. An automatic flow injection valve (FIV) delivers a fixed volume of analyte from a sample loop to the EQCM flow cell, where the electrodeposition reaction occurs, and the current and frequency change corresponding to the mass deposited on the electrode is measured in real time. After a film of the analyte has formed it can be rapidly stripped by changing the potential of the electrode. An ICP-OES connected downstream of the EQCM provides continuous elemental analysis throughout the deposition and stripping processes. One of the advantages is the possibility of sequential deposition-stripping experiments without having to disturb the working electrode in the flow cell.This platform was tested via flow injection of cupric sulfate samples in a sulfuric acid matrix at 200 uL/min, with cathodic electrodeposition and anodic stripping performed at different potentials. We also developed a finite element 3D model of the electrochemical flow cell in COMSOL Multiphysics®, with the simulated results in reasonable agreement to the measured current and mass deposition in the copper experiments. The image below shows the simulated [Cu+2] profile in COMSOL Multiphysics® during cathodic electrodeposition, 62 seconds after the sample enters the reaction chamber of the flow cell. Figure 1

Polymeric Membrane Sensors for Batch and Flow Injection Potentiometric Determination of Procainamide

Three new potentiometric membrane sensors responsive to procainamide hydrochloride (PR) were constructed and their general performance characteristics were determined. The sensors were constructed from PR ion-association complexes with tetraphenylborate (NaTPB) (1), phosphomolybdic acid (PMA) (2) and phosphotungstic acid (PTA) (3) as exchange sites in a polyvinyl chloride (PVC) matrix. The sensors exhibited stable, rapid and near-Nernstian properties for PR at concentrations of $1\times 10^{{-2 }}$ – $4\times 10^{-6}$ , $1\times 10^{-2}- 5\times 10^{-6}$ , $1\times 10^{-2}$ – $6\times 10^{-6}$ M at 25 °C with cationic slopes of 58 ± 0.5, 57 ± 0.5 and 56 ± 0.5 (mV/decade) for sensor 1, 2 and 3 respectively. The response time of the sensors was 20s in the optimum pH range of 4-8. The sensors were used in steady state and flow injection mode (automated system). Method validation revealed the sensors have high selectivity, low detection limits, long life, wide dynamic ranges as well as high accuracy and precision. Direct determination of 5- $2000~\mu \text{g}$ /ml of PR in solution returned average recoveries of 98.5%, 99.0% and 98.5% and mean relative standard deviations of 1.6%, 1.6% and 1.8% at $200.0~\mu \text{g}$ /ml for sensor 1, 2 and 3 respectively. Further, detection of procainamide in spiked urine exhibited favorable relative standard deviation (1.60-1.76%) and high recovery (98.83-99.26%). The sensors were used as end-point indicators for titration of procainamide with NaTPB.

A New Validated Potentiometric Method for Sulfite Assay in Beverages Using Cobalt(II) Phthalocyanine as a Sensory Recognition Element.

A simple potentiometric sensor is described for accurate, precise, and rapid determination of sulfite additives in beverages. The sensor is based on the use of cobalt phthalocyanine as a recognition material, dispersed in a plasticized poly(vinyl chloride) matrix membrane. o-Nitrophenyl octyl ether (o-NPOE) as a membrane solvent and tri-dodecylmethyl- ammonium chloride (TDMAC) as ion discriminators are used as membrane additives. Under the optimized conditions, sulfite ion is accurately and precisely measured under batch and flow injection modes of analysis. The sensor exhibits fast and linear response for 1.0 × 10−2–1.0 × 10−6 M (800–0.08 µg/mL) and 1.0 × 10−1–5.0 × 10−5 M (8000–4 µg/mL) sulfite with Nernstian slopes of −27.4 ± 0.3 and −23.7 ± 0.6 mV/concentration decade under static and hydrodynamic modes of operation, respectively. Results in good agreement with the standard iodometric method are obtained.Validation of the assay method is examined in details including precision, accuracy, bias, trueness, repeatability, reproducibility, and uncertainty and good performance characteristics of the method are obtained. The sensor response is stable over the pH range of 5 to 7 without any significant interference from most common anions. The advantages offered by the proposed sensor (i.e., wide range of assay, high accuracy and precision, low detection limit, reasonable selectivity, long term response stability, fast response, and long life span and absence of any sample pretreatment steps) suggest its use in the quality control/quality assurance routine tests in beverages industries, toxicological laboratories and by inspection authorities.

SEQUENTIAL MULTI-ELEMENT DETERMINATION OF TRACE-METALS IN BIODIESEL SAMPLES USING HR-CS FAAS

In this work the feasibility of sequential multi-element determination of Zn, Fe, Mg, Cu, Na, K, Cr, Al and Ca in biodiesel samples by high-resolution continuum source flame atomic absorption spectrometry (HR-CS FAAS) was investigated. Biodiesel samples obtained from different sources and different chemical processes were analysed. The samples were diluted with n-propanol and water (1.4 mol L-1 HNO3) to form a microemulsion (ME) before its introduction in the HR-CS FAAS using a flow injection mode. The sample B-01 (obtained from soybean oil) was used for optimisation of the instrumental parameters. The accuracy of the proposed method was checked by analysis of certified reference material (CRM) Conostan BDM2A (for K and Na) and BDM2B (for Ca and Mg) and by comparison with acid digestion and recovery tests (for Zn, Fe, Cu, Cr and Al). The obtained results for CRM analysis showed good agreement with certified values within 95% of confidence (Student’s t-test). Recovery tests values ranged from 87-114%. The method developed for the analysis of biodiesel samples is accurate, simple, fast, and suitable for routine application.

Cadmium Assisted Photochemical Vapor Generation of Tungsten for Detection by Inductively Coupled Plasma Mass Spectrometry.

Efficient photochemical vapor generation (PVG) of tungsten has been achieved for the first time using a 19 W thin film flow-through photoreactor. The volatile product (most probably tungsten hexacarbonyl) was generated using a flow injection mode and 40% (v/v) formic acid as the reaction medium. An inductively coupled plasma mass spectrometer was utilized for ultrasensitive detection. The addition of Cd2+ as a sensitizer was critical, enhancing the overall PVG efficiency some 30 000-fold. At an optimal irradiation time of 19 s, a 6.1-fold enhancement factor and an overall PVG efficiency of 43% were determined from a comparison of the response to direct solution nebulization when using a sample flow rate of 2 mL min-1 and 500 mg L-1 Cd2+ as a sensitizer. A limit of detection of 0.9 ng L-1 and repeatability (RSD) of 2% at 100 ng L-1 were achieved. Interference from inorganic acids (HNO3, HCl, H2SO4, and HF) was investigated with respect to analytical application to real samples. The accuracy and practical feasibility of this ultrasensitive methodology was successfully verified by analysis of Certified Reference Material CTA-FFA-1 (Fine Fly Ash) and six natural water samples with low W concentrations.

Constant Potential Amperometric Flow-Injection Analysis of Ions and Neutral Molecules Transduced by Electroactive (Conductive) Polymers.

We first report on constant potential (dc) amperometric flow-injection analysis (FIA) transduced by electroactive (conductive) polymers. Amperometric response is caused by the polymer recharging in order to maintain the electrode potential at a constant level when (i) ions are crossing the film|solution interface and polarizing electrode|film interface or (ii) ions or neutral molecules are specifically interacting with the polymer recharging it. The response under constant solution flow is a current peak and in flow-injection mode is a couple of current peaks directed opposite of the first sharp, analytically valuable peak. In both constant flow and flow-injection regimes, the peak current is dependent on analyte concentrations; obviously, the FIA mode provides more advantageous analytical characteristics. Constant potential amperometric flow-injection analysis is shown for boronate- and sulfate-functionalized polyanilines as well as for Prussian Blue, a member of the inorganic polymer family. As a proof of concept, the successful dc amperometric detection of lactate in human sweat with boronate-functionalized polyaniline has been shown. The proposed approach would revolutionize the field of conductive/electroactive polymer-supported ion sensing with the introduction of reliable and robust amperometry as a valuable alternative to existing potentiometry.

Investigation of the conditions for selenium determination by photochemical vapor generation coupled to graphite furnace atomic absorption spectrometry

In this study instrumental parameters and sample preparation methods for Se determination using photochemical vapor generation (PVG) coupled to graphite furnace atomic absorption spectrometry (GF AAS) were investigated. Coconut water was selected as sample due to its nutritional importance and matrix complexity. The PVG was performed in a flow injection mode. The Se volatile species, generated in the UV reactor, were separated from the condensed phase in a gas-liquid separator and introduced automatically in the graphite furnace. These species were trapped on the integrated graphite platform surface coated with Ir as permanent modifier. The PVG conditions such as concentration of low molecular weight organic compound (LMWC), sample and carrier gas flow rate, effect of reagents frequently used in sample preparation (HNO3 and H2O2) were investigated. Formic acid 0.44 mol L−1 was selected as LMWC. The addition of HNO3 (14 mmol L−1) and H2O2 (145 mmol L−1) increased the sensitivity. Pre-reduction of Se (VI) to Se (IV) was performed on-line in a quartz spiral tube coated with a thin film of TiO2. The insertion of Ar flow rate (115 mL min−1) before the reactor inlet has improved the sensitivity, comparing with the introduction of Ar after the reactor. UV-assisted photo-oxidation of coconut water samples was employed as an alternative sample preparation to avoid the NO3−/NO2−, and H2O2 interference. The figures of merit were: sensitivity 0.0680 s ng−1, limits of detection and quantification 0.65 μg L−1 and 2.2 μg L−1, respectively, and characteristic mass of 62 pg. The PVG efficiency was estimated as 79% when comparing with conventional hydride generation. Furthermore, a mass balance study was accomplished in order to identify possible analyte losses in the PVG system, which the overall recovery was up to 85%. The results of recovery tests accomplished with real samples of coconut waters varied between 80 and 103% for Se (IV), Se (VI), and selenomethionine.

Efficient Photochemical Vapor Generation of Molybdenum for ICPMS Detection.

Photochemical vapor generation (PVG) of Mo was accomplished using a 19 W high-efficiency flow-through photoreactor operating in a flow injection mode using 30-50% (w/v) formic acid as a reaction medium. The generated volatile product (most probably molybdenum hexacarbonyl) was directed by an argon carrier gas to a plastic gas-liquid separator and introduced into the spray chamber of an inductively coupled plasma mass spectrometer for detection. Particular attention was paid to the determination of overall PVG efficiency relative to that for liquid nebulization. Utilizing a sample flow rate of 1.25 mL min-1, corresponding to an irradiation time of 38 s, PVG efficiencies in the range 46-66% were achieved. The efficiency could be further enhanced by the presence of mg L-1 added Fe3+ ions. A limit of detection of 1.2 ng L-1 and precision of 3% (RSD) at 250 ng L-1 were achieved. Interferences from inorganic anions likely to be encountered during analytical application to real samples (NO3-, Cl-, SO42-, NO2-, and ClO4-) were investigated in detail. The accuracy and applicability of this sensitive methodology was successfully verified by analysis of fresh water Standard Reference Material NIST 1643e, two seawater Certified Reference Materials (NASS-7 and CASS-6), and by analysis of two samples of commercial dietary supplements solubilized in formic acid.

Prussian Blue-Based Thin-Layer Flow-Injection Multibiosensor for Simultaneous Determination of Glucose and Lactate

A planar multibiosensor for the simultaneous determination of glucose and lactate is developed by combining the Prussian Blue-based electrocatalyst and the protocol for immobilization of glucose oxidase and lactate oxidase enzymes from solutions with a high content of an organic solvent. High sensitivity coefficients (>80 mA M–1 cm–2 for lactate and >20 mA M –1 cm–2 for glucose) are demonstrated by the multibiosensors operating in the flow-injection mode in a thin-layer measuring cell. The linear range of the analyzed concentration is 1–500 μM for lactate and 5–1000 μM for glucose. A multibiosensor can be used repeatedly (the exhibited operational stability is not less than 100 measurements without the need for recalibration), which allows using it for the analysis of diluted blood samples and blood serum. The electrocatalytic system with a multibiosensor demonstrates performance characteristics that are superior to the commercial analyzers.

Investigation of hydride generation from arsenosugars - Is it feasible for speciation analysis?

Hydride generation (HG) from arsenosugars (dimethylarsinoylribosides) in batch and flow injection modes was studied. Its efficiency was found higher in H2SO4 medium than in HCl and higher in the batch mode than in the flow injection mode. To increase the efficiency in the flow injection mode a new generator with two inlets of NaBH4 solution was designed. This modified generator was interfaced between a HPLC column and an atomic fluorescence detector. The arsenosugars studied yielded HG efficiencies in the range 13–30% most probably due to a complicated mechanism of HG. While the mechanism included a formation of two structures of the analyte-borane-complexes, only one of them can lead to a formation of volatile arsanes (dimethylarsane, methylarsane, and arsane were identified).