Flow Injection Analysis Conditions Research Articles

Novel Disposable Potentiometric Sensor for Determination of Granisetron in Surface Water Samples and Pharmaceutical Formulations

Herein, the fabrication and characterization of novel granisetron (GST) disposable screen-printed potentiometric sensors was described. Different fabrication protocols were introduced including; incorporation of different ions of pairing agents or GST- ion associates as electroactive sensing materials. For sake of simplicity, the dummy blank sensors can be soaked in the GST- ion associates aqueous suspension, where ion associates were extracted within the electrode matrix by the membrane plasticizer. Deep and comprehensive investigations were performed regarding the sensing matrices compositions including the influence of modifier nature and content, plasticizer, and the fabrication protocol. Incorporation of the electrode matrix with SWCNTs improved the sensor performance. Sensors modified with phosphotungstic acid showed Nernstian compliance for the GST concentration range from 10−6 to 10−2 mol L−1, adequate operational shelf lifetime (6 weeks) and fast response time (4s). Moreover, the electrode potential was pH-independent in wide range with improved selectivity. The developed sensors were introduced for GST quantification in surface water samples and pharmaceutical formulations under flow injection analysis (FIA), standard addition and potentiometric titration conditions.

Применение реакции окисления N-метил-п-аминофенола пероксидом водорода, катализируемой ионами Fe(II) и Fe(III) в проточно-инжекционном анализе водопроводной воды

The article presents the results of the application of the oxidation reaction of N-methyl-p-aminophenol with hydrogen peroxide, catalyzed by Fe(II) and Fe(III) ions in the flow injection analysis (FIA) of tap water. Using a commercially available system for FIA with spectrophotometric detection, an optimal scheme for conducting an indicator catalytic reaction in a liquid stream was proposed, which was used to determine the total iron content in tap water. Spectrophotometric detection of colored products of the indicator catalytic reaction of the oxidation of N-methyl-p-aminophenol with hydrogen peroxide is carried out at the absorption maximum of the absorption spectrum in the visible region at λmax = 490 nm. It was shown that, under nonequilibrium FIA conditions, it is possible to significantly minimize the contribution of the noncatalytic reaction to the total analytical signal. The latter is accompanied by the expansion of the range of determined catalyst contents to lower concentrations. Taking into account the proposed FIA scheme for determining the total iron content in tap water by the oxidation of N-methyl-p-aminophenol with hydrogen peroxide, catalyzed by Fe(II) and Fe(III) ions, the linearity range of the analytical signal remains in the range of 0.05-0.4 μg/ml. The lower limit of the determined iron content is 0.02 μg/ml with a productivity of 40 samples per hour. Sample preparation of tap water consists in filtering and maintaining the required pH for the catalytic indicator reaction and subsequent FIA. The cations Al, Zn, Ni, V(V), Pb, Cd, Mn(II), and Cr(VI) do not have a significant interfering effect; only the presence of complexing agents can reduce the rate of the catalytic reaction, which, accordingly, affects the analysis results.

A flow analysis system integrating an optoelectronic detector for the quantitative determination of active ingredients in pharmaceutical formulations

A simple, compact and low-cost optoelectronic detector was developed for complete turbidimetric measurements under continuous flow injection analysis. The device was fabricated by integrating white snow light-emitting diodes as a light source with solar cells as a detector (WLEDs-SCs) of attenuated light that is passed through the analyte. The device is made from ten of WLEDs and three solar cells only without any filters, lenses and fibers. The device operates according to the turbidimetric principle which measures the attenuated light at 180° of the incident light. The developed detector was adapted under flow injection analysis conditions and its real analytical utility has been successfully confirmed by validation and the development of a turbidimetric method for the quantitative determination of Cyproheptadine hydrochloride (CPH) in pure and pharmaceutical formulations. The proposed method is based on forming a turbid, yellow ion-pair association complex in a closed flow system as a result of a reaction between the drug and potassium chromate which was used as a precipitation reagent. Under optimized conditions, the analysis system offers linear range 2.2–160 µg ml−1 with a limit of detection at 0.6 µg ml−1, limit of quantification 1.8 µg ml−1 and correlation coefficient of 0.9986. The intra-day and inter-day precision for two serial estimations of 30 and 60 µg ml−1 of CPH exhibited a relative standard deviation of 0.94%, 0.29 and 0.68%, 0.21% respectively. While the accuracy of the proposed method has expressed as a recovery percentage (Rec %) and error % which were between 100.45–100.67 and 0.45% to 0.67% respectively. The proposed method has been successfully applied for the CPH determination in pharmaceutical preparations with high throughput tests (60 injections per hour) with no interference effect of the common excipients.

Promoting bioanalytical concepts in genetics: A TATA box molecularly imprinted polymer as a small isolated fragment of the DNA damage repairing system

We demonstrate that a new, stable, artificial TATA (T — thymine, A — adenine) box is recognized by amino acids recognizing the natural TATA box. Here, the former mimicked, as a minimal motif, oligodeoxyribonucleotide interactions with amino acids of proteins involved in repairing of damaged dsDNA. By electropolymerization, we molecularly imprinted non-labeled 5′-TATAAA-3′ via Watson-Crick nucleobase pairing, thus synthesizing, in a one-step procedure, the hexakis[bis(2,2′-bithien-5-yl)] TTTATA and simultaneously hybridizing it with the 5′-TATAAA-3′ template. That is, a stable dsDNA analog having a controlled sequence of nucleobases was formed in the molecularly imprinted polymer (MIP). The 5′-TATAAA-3′ was by the X-ray photoelectron spectroscopy (XPS) depth profiling found to be homogeneously distributed both in the bulk of the MIP film and on its surface. The 5′-TATAAA-3′ concentration in the 2.8(±0.2)-nm relative surface area, ~140-nm thick MIP film was 2.1 mM. The MIP served as a matrix of an artificial TATA box with the TATAAA-promoter sequence. We comprehensively characterized this artificial DNA hybrid by the polarization-modulation infrared reflection-absorption spectroscopy (PM-IRRAS) and X-ray photoelectron spectroscopy (XPS). Further, we examined interactions of DNA repairing TATA binding protein (TBP) amino acids with the artificial TATA box prepared. That is, molecules of l-phenylalanine aromatic amino acid were presumably engaged in stacking interactions with nucleobase steps of this artificial TATA box. The nitrogen-to‑phosphorus atomic % ratio on the surface of the MIP-(5′-TATAAA-3′) film increased by ~1.6 times after film immersing in the l-glutamic acid solution, as determined using the XPS depth profiling. Furthermore, l-lysine and l-serine preferentially interacted with the phosphate moiety of 5′-TATAAA-3′. We monitored amino acids interactions with the artificial TATA box using real-time piezoelectric microgravimetry at a quartz crystal microbalance (QCM) and surface plasmon resonance (SPR) spectroscopy under flow injection analysis (FIA) conditions.

Novel Calixarene/Carbon Nanotubes Based Screen Printed Sensors for Flow Injection Potentiometric Determination of Naproxen

AbstractNovel sensitive disposable sensors have been introduced for potentiometric determination of naproxen (NAP) based on single‐walled carbon nanotubes‐polyvinyl chloride (SWNTs‐PVC) composite incorporated of calix[4]arene as host‐guest molecular recognition element. The electrode matrix composition was optimized on the basis of the nature and content of the sensing element, cationic sites, plasticizer and nanomaterial. Remarkable selectivity and sensitivity towards NAP was achieved in the concentration range from 10−8 to 10−2 mol L−1 with anionic Nernstian compliance −61.0±0.0 mV decade−1. Modification with calixarene and carbon nanotubes improved the sensors performance through formation of NAP‐calixarene inclusion complex and promotion of the electron‐transfer processes which enhance the potential stability, response time, and shelf lifetime of the sensor. The proposed sensors were successfully applied for the potentiometric assay of NAP in dosage formulation and biological fluids under batch and flow injection analysis (FIA) conditions with average recoveries agreeable with the reported official methods.

Oligonucleotide Determination via Peptide Nucleic Acid Macromolecular Imprinting in an Electropolymerized CG-Rich Artificial Oligomer Analogue.

We devised and fabricated a chemosensor for determination of the genetically relevant 5'-GCGGCGGC-3' (G = guanine; C = cytosine) oligonucleotide. For that, we simultaneously electrosynthesized and electrode-immobilized a sequence-defined octakis(2,2'-bithien-5-yl) DNA hybridizing probe using both a "macromolecular imprinting in polymer strategy" and a sequence-programmable peptide nucleic acid (PNA) template. With electrochemical impedance spectroscopy (EIS) and surface plasmon resonance (SPR) transductions under stagnant-solution and flow injection analysis (FIA) conditions, respectively, we determined the above oligonucleotide with 200-pM EIS limit of detection. With its EIS-determined apparent imprinting factor of ∼4.0, the chemosensor was discriminative to both mismatched oligonucleotides and Dulbecco's modified Eagle's medium sample interferences.

Flow-Injection Amperometric Determination of DOPA and Tyrosine at a Dual Electrode Modified with the Gold–Cobalt Binary System

The gold–cobalt binary system, electrodeposited on the surface of a screen-printed electrode, exhibits catalytic activity in the electrooxidation of DOPA and tyrosine. The catalytic effect is shown in a multiple increase in current compared with the oxidation current of the modifier and a decrease in the oxidation overvoltage of organic compounds. Methods for the flow-injection amperometric determination of DOPA and tyrosine at the proposed modified electrode are developed. The simultaneous amperometric determination of DOPA and tyrosine at a dual screen-printed electrode modified with an Au–Co binary system the under conditions of flow-injection analysis is demonstrated. The linear dependence of the analytical signal on the concentration of DOPA and tyrosine is observed in the ranges from 1 × 10–9 to 1 × 10–4 M and from 5 × 10–8 to 5 × 10–4 M, respectively.

Selective Sensing of the Biotinyl Moiety Using Molecularly Imprinted Polyaniline Nanowires

A chemosensor for selective recognition of biotinyl moiety has been devised using electropolymerized film and tested against selective biotinylated targets. The sensor comprises biotin molecularly imprinted polymer (MIP) polymeric nanowires, as a recognition element, overlaid on gold-coated quartz transducers. The preparation of nanostructured MIPs and reference systems have been demonstrated using electrochemical copolymerization of the stabilized complex between the template (biotin), the functional monomer (4-aminobenzoic acid), and cross-linker (aniline) and/or sacrificial biotin-modified Al2O3 membrane. Density functional theoretical studies signify formation of a stable hydrogen-bonded complex of biotin with 4-aminobenzoic acid in the pre-polymerization mixture. Scanning electron microscope studies revealed uniformly grown and densely packed polyaniline hierarchical structures. Piezoelectric microgravimetry under flow injection analysis (FIA) conditions revealed selective binding of biotin methyl ester (BtOMe, 4) (79.89 ± 2.17 Hz/mM) with imprinted polyaniline hierarchical structures over 10 fold higher than the non-imprinted counterpart. The detection limit of the MIP is 50 nM under optimized conditions. Particularly, the sensor selectively recognizes BtOMe from structural or functional analogues, such as thiamine (4.87 ± 0.10 Hz/mM) and pyridoxamine (12.08 ± 0.24 Hz/mM). Importantly, the MIP hierarchical structures were shown to be selective for biotinylated targets (biotin moiety labeled cytochrome C, dextran, oxytocin and obestatin).

Altered electrochemistry of oxcarbazepine on cathodically treated boron-doped diamond electrode: Selective detection by pulsed amperometric detection coupled to flow-injection analysis

This work presents a novel electrochemical method for the determination of oxcarbazepine (OXC) in urine and pharmaceutical samples using a flow injection analysis (FIA) system coupled to multiple-pulse amperometric (MPA) detection on a boron-doped diamond electrode (BDDE). The unique voltammetric profile of OXC on the BDDE, consisting of two electrochemical oxidation processes between +1.6 and +1.8 V versus Ag/AgCl/3.0 mol L−1 KCl generating cationic radical species that undergo two electrochemical reduction processes at −0.2 and −1.0 V, was used for the application of MPA detection for the selective detection of OXC in biological samples. Briefly, OXC determination consisted in the application of a three-potential waveform: (1) at +1.7 V/200 ms, generator potential pulse for oxidation of OXC; (2) at −1.1 V/30 ms, collector potential pulse for reduction of the generated product and OXC quantification; (3) at −1.3 V/300 ms, potential pulse for cleaning the BDDE. This strategy enabled OXC determination in urine free from the interference of ascorbic and uric acids. The method showed high repeatability (RSD < 1.0% for injections of 100 μmol L−1 OXC), high analytical frequency (65 determinations per hour), wide working linear range (from 2.0 to 80.0 μmol L−1) with a limit of detection of 0.42 μmol L−1 under optimized FIA conditions (sample loop: 200 μL and flow rate: 3.5 mL min−1), and recovery values close to 100% in all analyses.

Porous boron-doped diamond/CNT electrode as electrochemical sensor for flow-injection analysis applications

Porous boron-doped diamond (p-BDD) electrodes were prepared and explored as a potential electrochemical sensor for applications in flow-injection analysis (FIA) coupled to amperometric detection systems. Porous BDD films were grown by Hot Filament Chemical Vapor Deposition (HFCVD) over oxygen plasma functionalized carbon nanotubes and, morphological and chemical characterizations of the obtained composite material were carried out by Field Emission Gun Scanning Electron Microscopy (FEG-SEM) and Raman spectroscopy. The analytical performance of the designed p-BDD electrode under FIA conditions was investigated using two model electroactive analytes, epinephrine (EP, an important neurotransmitter) and acetaminophen (AC, a commonly consumed analgesic). All experimental parameters, such as applied potential, flow-rate and injection volume for both analytes were optimized. Under the best experimental conditions, the analytical curves for EP and AC were linear from 0.60 to 30.0μmolL−1 (EP) and from 0.80 to 70.0μmolL−1 (AC), with detection limits of 0.50μmolL−1 and 0.70μmolL−1 for EP and AC, respectively. Measurement precision was demonstrated from a number of amperometric measurements performed for successive injections of standard AC and EP solutions. In addition, the applicability of the developed FIA procedure was reported for the AC and EP determination in human serum fluid.

Molecularly Imprinted Polymer Chemosensor for Selective Determination of an N-Nitroso-l-proline Food Toxin.

A molecularly imprinted polymer (MIP)-based chemosensor for the selective determination of a chosen toxin, N-nitroso-l-proline (Pro-NO), was devised and fabricated. By means of DFT, the structure of the pre-polymerization (functional monomer)-template complex was modeled. This complex was then potentiodynamically electropolymerized in the presence of cross-linking monomer to form a MIP-Pro-NO thin film. Next, the Pro-NO template was extracted from MIP-Pro-NO with 0.1 m NaOH. Piezoelectric microgravimetry (PM) on an electrochemical quartz crystal microbalance and electrochemical (differential pulse voltammetry (DPV) and electrochemical impedance spectroscopy (EIS)) techniques were used to transduce binding of Pro-NO to molecular cavities of the MIP-Pro-NO. With DPV and EIS chemosensing, the limits of detection (LODs) were about 80.9 and 36.9 nM Pro-NO, respectively; and the selectivity coefficients for urea, glucose, creatinine, and adrenalin interferences were 6.6, 13.2, 2.1, and 2.0, respectively, with DPV as well as 2.3, 2.0, 3.3, and 2.5, respectively, with EIS. With PM under flow injection analysis conditions, the LOD was 10 μm Pro-NO. The MIP-Pro-NO chemosensor detectability and selectivity with respect to interferences were sufficiently high to determine Pro-NO in protein-providing food products.

Early diagnosis of fungal infections using piezomicrogravimetric and electric chemosensors based on polymers molecularly imprinted with d-arabitol

An elevated concentration of d-arabitol in urine, especially compared to that of l-arabitol or creatinine, is indicative of a fungal infection. For that purpose, we devised, fabricated, and tested chemical sensors determining d-arabitol. These chemosensors comprised the quartz crystal resonator (QCR) or extended-gate field-effect transistor (EG-FET) transducers integrated with molecularly imprinted polymer (MIP) film recognition units. To this end, we successfully applied a covalent approach to molecular imprinting, which involved formation of weak reversible covalent bonds between vicinal hydroxyl groups of arabitol and boronic acid substituents of the bithiophene functional monomer used. The MIP films were synthesized and simultaneously deposited on gold electrodes of quartz crystal resonators (Au-QCRs) or Au-glass slides by oxidative potentiodynamic electropolymerization. With the QCR and EG-FET chemosensors, the d-arabitol concentration was determined under flow-injection analysis and stagnant-solution binding conditions, respectively. Selectivity with respect to common interferences, and l-arabitol in particular, of the devised chemosensors was superior. Limits of detection and linear dynamic concentration ranges of the QCR and EG-FET chemosensors were 0.15mM and 0.15 to 1.25mM as well as 0.12mM and 0.12 to 1.00mM, respectively, being lower than the d-arabitol concentrations in urine of patients with invasive candidiasis (>220μM). Therefore, the devised chemosensors are suitable for early diagnosis of fungal infections caused by Candida sp. yeasts.

Potentiometric chemosensor for neopterin, a cancer biomarker, using an electrochemically synthesized molecularly imprinted polymer as the recognition unit.

With an established procedure of molecular imprinting, a synthetic polymer receptor for the neopterin cancer biomarker was devised and used as a recognition unit of a potentiometric chemosensor. For that, bis-bithiophene derivatized with cytosine and bithiophene derivatized with boronic acid were used as functional monomers. The open-circuit potential (OCP) based transduction under flow-injection analysis conditions (FIA) determined neopterin in the concentration range of 0.15-2.5mM with the 22 µM limit of detection (LOD) and 7.01(±0.15) mVmM(-1) sensitivity indicating its potential suitability in clinical analysis applications. The molecularly imprinted polymer (MIP) film showed an appreciable apparent imprinting factor of ~6. The chemosensor successfully discriminated the interferences including the 6-biopterin and pterin structural analogs of neopterin as well as glucose and creatinine. Moreover, it determined neopterin in synthetic serum samples.

Construction and Application of Flow Enzymatic Biosensor Based of Silver Solid Amalgam Electrode for Determination of Sarcosine

AbstractIn this paper, the flow amperometric enzymatic biosensor based on polished silver solid amalgam electrode for determination of sarcosine in model sample under flow injection analysis conditions is presented. The biosensor works on principle of electrochemical detection of oxygen decrease during enzymatic reaction which is directly proportional to the concentration of sarcosine in sample. The whole preparation process takes about 3 h. The RSD of repeatability of 10 consecutive measurements is 1.6 % (csarcosine=1.0×10−4 mol dm−3). Under optimal conditions the calibration dependence was linear in the range 7.5×10−6–5.0×10−4 mol dm−3 and limit of detection was 2.0×10−6 mol dm−3.

Wide-range screening of psychoactive substances by FIA-HRMS: identification strategies.

Recreational drugs (illicit drugs, human and veterinary medicines, legal highs, etc.) often contain lacing agents and adulterants which are not related to the main active ingredient. Serious side effects and even the death of the consumer have been related to the consumption of mixtures of psychoactive substances and/or adulterants, so it is important to know the actual composition of recreational drugs. In this work, a method based on flow injection analysis (FIA) coupled with high-resolution mass spectrometry (HRMS) is proposed for the fast identification of psychoactive substances in recreational drugs and legal highs. The FIA and HRMS working conditions were optimized in order to detect a wide range of psychoactive compounds. As most of the psychoactive substances are acid-base compounds, methanol-0.1% aqueous formic acid (1:1v/v) as a carrier solvent and electrospray in both positive ion mode and negative ion mode were used. Two data acquisition modes, full scan at high mass resolution (HRMS) and data-dependent tandem mass spectrometry (ddMS/HRMS) with a quadrupole-Orbitrap mass analyzer were used, resulting in sufficient selectivity for identification of the components of the samples. A custom-made database containing over 450 substances, including psychoactive compounds and common adulterants, was built to perform a high-throughput target and suspect screening. Moreover, online accurate mass databases and mass fragmenter software were used to identify unknowns. Some examples, selected among the analyzed samples of recreational drugs and legal highs using the FIA-HRMS(ddMS/HRMS) method developed, are discussed to illustrate the screening strategy used in this study. The results showed that many of the analyzed samples were adulterated, and in some cases the sample composition did not match that of the supposed marketed substance.

Cytosine derivatized bis(2,2'-bithienyl)methane molecularly imprinted polymer for selective recognition of 6-thioguanine, an antitumor drug.

A molecularly imprinted polymer (MIP) was designed and synthesized to serve as a functional material for selective recognition of 6-thioguanine (6TG), an antitumor drug. For that, the newly synthesized functional monomer, cytosine-bis(2,2'-bithienyl)-(4-carboxyphenyl)methane ester (Cyt-S4), revealed Watson-Crick type nucleobase pairing of 6TG. Formation of the Cyt-S4 and 6TG complex of the 2:1 stoichiometry was postulated based on the DFT calculations at the B3LYP/3-21G((⁎)) level and experimentally confirmed by fluorescence titration. The molecularly imprinted polymer (MIP) film was deposited by potentiodynamic electropolymerization on a Pt disk electrode as well as on an Au-coated glass slide and on an Au-quartz crystal resonator. The statistical model of formation of this film was successfully simulated by molecular dynamics. Completeness of the subsequent 6TG template extraction from MIP was confirmed by the UV-visible spectroscopy. An imprinting factor of 2.9 for the MIP film was determined by piezoelectric microgravimetry using ECQM. The double-layer capacity and alternating current measurements under flow-injection analysis (FIA) conditions were selected to transduce the 6TG recognition signal into the change of the double-layer capacity dependence on the 6TG concentration in solution for different supporting electrolyte concentrations. Detectability of the resulting chemosensor was 10 µM 6TG for the 0.5 M KF carrier solution in FIA. Selectivity of the chemosensor with respect to common interferences was high, e.g., it exceeded 130 to 2-amino-6-methylmercaptopurine, a 6TG metabolite.

Nicotine molecularly imprinted polymer: Synergy of coordination and hydrogen bonding

Two new bis(2,2′-bithienyl)methane derivatives, one with the zinc phthalocyanine substituent (ZnPc-S16) and the other with the 2-hydroxyethyl substituent (EtOH-S4), were synthesized to serve as functional monomers for biomimetic recognition of nicotine (Nic) by molecular imprinting. Formation of a pre-polymerization complex of the Nic template with ZnPc-S16 and EtOH-S4 was confirmed by both the high negative Gibbs free energy gain, ΔG=−115.95kJ/mol, calculated using the density functional theory at the B3LYP/3-21G⁎ level, and the high stability constant, Ks=4.67×105M−1, determined by UV–vis titration in chloroform. A solution of this complex was used to deposit a Nic-templated molecularly imprinted polymer (MIP-Nic) film on an Au electrode of a quartz crystal resonator of EQCM by potentiodynamic electropolymerization. The imprinting factor was as high as ~9.9. Complexation of the Nic molecules by the MIP cavities was monitored with X-ray photoelectron spectroscopy (XPS), as manifested by a negative shift of the binding energy of the Zn 2p3/2 electron of ZnPc-S16 after Nic templating. For sensing applications, simultaneous chronoamperometry (CA) and piezoelectric microgravimetry (PM) measurements were performed under flow-injection analysis conditions. The limit of detection of the CA and PM chemosensing was as low as 40 and 12µM, respectively. Among them, the CA chemosensing was more selective to the cotinine and myosmine interferences due to the 1.10V vs. Ag/AgCl discriminating potential of nicotine electro-oxidation applied. Differences in selectivity to the analyte and interferences were interpreted by modeling complexation of Nic and, separately, each of the interferences with a “frozen” MIP-Nic molecular cavity.

Flow-injection and sequential injection determination of hydroxypurines on an electrode modified with mixed-valence ruthenium and iridium oxides

Mixed-valence ruthenium (RuOx) and iridium (IrOx) oxides and composites on their basis (RuOx-IrOx or IrOx-RuOx) electrodeposited onto the surface of a glassy carbon electrode exhibit a catalytic activity in the electrooxidation of uric acid, xanthine, and hypoxanthine. The transition from metal oxides to composites of two mixed-valence metal oxides leads to an increase in the catalytic effect of the oxidation of hydroxypurines. The IrOx-RuOx composite demonstrated the highest catalytic activity. Procedures for the amperometric detection of hydroxypurines on this composite electrode under the conditions of flow-injection analysis (FIA) and sequential injection analysis are proposed. A linear dependence of an analytical signal on the analyte concentration is observed in the range 1 × 10−6 to 5 × 10−3 M for uric acid and xanthine and 5 × 10−7 to 5 × 10−3 M for hypoxanthine under FIA conditions and from 5 × 10−7 to 5 × 10−3 M for uric acid and xanthine and 5 × 10−9 to 5 × 10−3 M for hypoxanthine in sequential injection analysis. Under FIA conditions, the sensitivity, rapidity, and performance of the analysis increase compared to the stationary conditions. The advantages of sequential injection analysis over FIA include a lower consumption of the supporting electrolyte; the absence of pumps and connections; and an increase in sensitivity, reproducibility, and rapidity.

Selective voltammetric and flow-injection determination of guanine and adenine on a glassy carbon electrode modified by a ruthenium hexachloroplatinate film

An inorganic film of ruthenium hexachloroplatinate (RuPtCl6), deposited on the surface of a glassy carbon electrode, exhibits electrocatalytic activity in the oxidation of purine bases, such as adenine and guanine. Appropriate working conditions are found for fabricating a polymer film on the surface of glassy carbon and for recording the maximum electrocatalytic effect for the modified electrode. A method is developed for the selective voltammetric determination of guanine and adenine in their simultaneous presence on an electrode modified by a RuPtCl6 film. A procedure is proposed for the amperometric detection of purine bases with this modified electrode under the conditions of flow-injection analysis. The dependence of the analytical signal on the concentration of guanine and adenine is linear up to 5 × 10−6 and 5 × 10−7 M in the stationary mode and to 5 × 10−7 and 5 × 10−8 M under flow conditions, respectively. The proposed method was tested in the analysis of calf thymus DNA for the concentrations of guanine and adenine.

Fullerene derived molecularly imprinted polymer for chemosensing of adenosine-5′-triphosphate (ATP)

For molecular imprinting of oxidatively electroactive analytes by electropolymerization, we used herein reductively electroactive functional monomers. As a proof of concept, we applied C60 fullerene adducts as such for the first time. For that, we derivatized C60 to bear either an uracil or an amide, or a carboxy addend for recognition of the adenosine-5′-triphosphate (ATP) oxidizable analyte with the ATP-templated molecularly imprinted polymer (MIP-ATP). Accordingly, the ATP complex with all of the functional monomers formed in solution was potentiodynamically electropolymerized to deposit an MIP-ATP film either on an Au electrode of the quartz crystal resonator or on a Pt disk electrode for the piezoelectric microgravimetry (PM) or capacitive impedimetry (CI) determination of ATP, respectively, under the flow-injection analysis (FIA) conditions. The apparent imprinting factor for ATP was ∼4.0. After extraction of the ATP template, analytical performance of the resulting chemosensors, including detectability, sensitivity, and selectivity, was characterized. The limit of detection was 0.3 and 0.03mM ATP for the PM and CI chemosensor, respectively. The MIP-ATP film discriminated structural analogues of ATP quite well. The Langmuir, Freundlich, and Langmuir–Freundlich isotherms were fitted to the experimental data of the ATP sorption and sorption stability constants appeared to be nearly independent of the adopted sorption model.