FIA Conditions Research Articles

Sustainable synthesis of hierarchically grown chloramphenicol‐imprinted poly(caffeic acid) nanostructured films

AbstractHierarchically nanostructured chloramphenicol (CLP) imprinted thin polymer films have been developed using a renewable monomer, the antioxidant caffeic acid (CA), using sacrificial nanostructures to induce porosity into the films. The poly(caffeic acid) (PCA) films were synthesized on Au/quartz resonators via greener polymerization conditions (clean energy electropolymerization in aqueous buffer or a non‐ionic deep eutectic solvent). The sacrificial nanostructures explored included zein‐based protein nanobeads, anodized alumina membrane, and Tween 20‐derived polysorbate micelles, where dissolution of the sacrificial nanostructure templates from the PCA films afforded uniform long‐range hyperporous networks, nanowires and nanoparticles, respectively, as revealed by SEM studies. Selective extraction of the CLP template from PCA films, was monitored by XPS, and afforded CLP selective cavities. The CLP‐imprinted PCAzein films demonstrated eight‐ to 25‐fold higher sensitivity than the other nanostructures in a QCM‐sensor format, the limit of detection (LOD) under optimized FIA conditions was 50 mM. Significant sensitivities for CLP in milk were observed (1.5 μg/ml to 3 mg/ml), covering the clinically relevant concentration range. The PCAzein thin films selectively differentiate CLP from structurally related antibiotics and are robust. Their production from renewable feedstocks of biological origin highlights the potential of this class of nanostructured materials for applications utilizing thin films.

Hierarchical polymeric architectures through molecular imprinting in liquid crystalline environments

The use of liquid crystalline (LC) media as sacrificial templates during the polymer synthesis has been explored. The LC-media introduce morphological features into resultant polymers which when used together with molecular imprinting can produce materials with hierarchical architectures. Bupivacaine (1) imprinted co-polymers of 2-hydroxyethylmethacrylate (HEMA) (2a) and 1,4-divinylbenzene (DVB) (3a) were synthesized using photochemical initiation in lyotrophic liquid crystalline phases of AOT (5) in water/p-xylene and Triton X-100 (6) /water systems. SEM studies revealed the impact of the LC-media on polymer morphology, with polymer brush-like structures, with bristles of ≈30 nm diameter. The polymer morphology reflects that of the hexagonal phase of the LC medium. The rebinding characteristics of polymer films were evaluated quartz crystal microbalance (QCM, under FIA conditions). The influence of the presence of imprinting-derived recognition sites in AOT (5) in water/p-xylene polymer film induced brush-like features which provided a 25-fold enhancement of sensor sensitivity. This chemosensor was shown to be selective for the local anesthetic template, bupivacaine, through studies using the structural analogues ropivacaine and mepivacaine.

Electrochemically synthesized molecularly imprinted polythiophene nanostructures as recognition elements for an aspirin-chemosensor

A chemosensor utilizing electro-polymerized film, as recognition element, has been devised and tested for selective determination of aspirin. The sensor consists of molecularly imprinted polymer (MIP) recognition elements electrodeposited as polymeric nanowires on gold-coated quartz resonator. A nanostructures were prepared by electrochemical co-polymerization of the preformed complex between the template, aspirin, the functional monomers, 3-thienylboronic acid (3-TBA) and 3-thiopheneacetic acid (3-TAA), and thiophene, which was employed as a cross-linker. This nanostructure upon leaching aspirin serve as MIP. Polymerizations were performed in acetonitrile (MIP-org) as well as a micelle-forming medium (MIP-mic). For MIP nanowire (MIP-ano) synthesis, sacrificial alumina templates were used during electro-polymerization in acetonitrile. Scanning electron microscope studies revealed compactly arranged polythiophene nanowires of uniform thickness in MIP-ano film, and MIP-mic film produced aggregated micron sized polymer structures. Density functional theoretical studies indicated a stable hydrogen bond-based complexation of aspirin by 3-TBA and 3-TAA in the pre-polymerization mixture implying that the MIP film thus prepared could selectively rebind the aspirin template. The MIP-ano-based chemosensor was sensitive towards aspirin (0.5–10mM), over clinically relevant range (0.15–0.5mM) under optimized FIA conditions. The sensitivity (20.62Hz/mM) of the MIP-ano was eight and fifteen times higher than the MIP-mic (2.80Hz/mM) and MIP-org (1.10Hz/mM). Notably, the sensor selectively discriminates aspirin from structurally or functionally related interferants and metabolites, such as, salicylic acid, acetylsalicyloyl chloride and ibuprofen.

Programmed Transfer of Sequence Information into a Molecularly Imprinted Polymer for Hexakis(2,2'-bithien-5-yl) DNA Analogue Formation toward Single-Nucleotide-Polymorphism Detection.

A new strategy of simple, inexpensive, rapid, and label-free single-nucleotide-polymorphism (SNP) detection using robust chemosensors with piezomicrogravimetric, surface plasmon resonance, or capacitive impedimetry (CI) signal transduction is reported. Using these chemosensors, selective detection of a genetically relevant oligonucleotide under FIA conditions within 2 min is accomplished. An invulnerable-to-nonspecific interaction molecularly imprinted polymer (MIP) with electrochemically synthesized probes of hexameric 2,2'-bithien-5-yl DNA analogues discriminating single purine-nucleobase mismatch at room temperature was used. With density functional theory modeling, the synthetic procedures developed, and isothermal titration calorimetry quantification, adenine (A)- or thymine (T)-substituted 2,2'-bithien-5-yl functional monomers capable of Watson-Crick nucleobase pairing with the TATAAA oligodeoxyribonucleotide template or its peptide nucleic acid (PNA) analogue were designed. Characterized by spectroscopic techniques, molecular cavities exposed the ordered nucleobases on the 2,2'-bithien-5-yl polymeric backbone of the TTTATA hexamer probe designed to hybridize the complementary TATAAA template. In that way, an artificial TATAAA-promoter sequence was formed in the MIP. The purine nucleobases of this sequence are known to be recognized by RNA polymerase to initiate the transcription in eukaryotes. The hexamer strongly hybridized TATAAA with the complex stability constant KsTTTATA-TATAAA = ka/kd ≈ 106 M-1, as high as that characteristic for longer-chain DNA-PNA hybrids. The CI chemosensor revealed a 5 nM limit of detection, quite appreciable as for the hexadeoxyribonucleotide. Molecular imprinting increased the chemosensor sensitivity to the TATAAA analyte by over 4 times compared to that of the nonimprinted polymer. The herein-devised detection platform enabled the generation of a library of hexamer probes for typing the majority of SNP probes as well as studying a molecular mechanism of the complex transcription machinery, physics of single polymer molecules, and stable genetic nanomaterials.

Chemically Modified Carbon Paste Sensor for Potentiometric Determination of Doxycycline Hydrochloride in Batch and FIA Conditions

Chemically Modified Carbon Paste Sensor for Potentiometric Determination of Doxycycline Hydrochloride in Batch and FIA Conditions

Electrochemically synthesized molecularly imprinted polymer of thiophene derivatives for flow-injection analysis determination of adenosine-5′-triphosphate (ATP)

Two selective chemosensors for adenosine-5′-triphosphate (ATP) determination featuring molecularly imprinted polymer (MIP) film recognition units were fabricated. For imprinting, three different thiophene derivatives were used as functional monomers. That is, the uracil substituent of bis(2,2′-bithienyl)methane 2 complementarily H-bond paired the adenine moiety of ATP, the boronic acid substituent of thiophene 3 covalently bound vicinal diols of the ribofuranose moiety, and amide substituents of bis(2,2′-bithienyl)methanes 4 bound to the pyrophosphate moieties. Different binding motifs adopted for the ATP recognition and the structure of the supramolecular pre-polymerization complex were optimized with the DFT computing at the B3LYP/3-21G(⁎) level. MIP films were prepared by potentiodynamic electropolymerization of this complex with the imprinting factor of 9.47±0.2. An analytical signal was transduced with a 10-MHz resonator of EQCM and a Pt electrode for the piezoelectric microgravimetry (PM) and capacitive impedometry (CI) determination of ATP, respectively, under FIA conditions. Analytical properties of the MIP film were unraveled by spectroscopic ellipsometry, XPS, IRRAS, and DPV. The limit of detection was 0.1 and 0.2μM for the PM and CI chemosensor, respectively, being an order of magnitude lower than the ATP concentration in biological systems. Moreover, cross-selectivity was demonstrated with the adenosine-5′-diphosphate (ADP) imprinting and ATP discrimination.

Molecularly imprinted polymer of bis(2,2′-bithienyl)methanes for selective determination of adrenaline

New chemical sensors for adrenaline Adr were fabricated. For that, a thin film of a molecularly imprinted polymer (MIP) was templated with protonated adrenaline HAdr. Differential pulse voltammetry (DPV), capacitive impedometry (CI), or piezoelectric microgravimetry (PM) was integrated within each chemosensor for analytical signal transduction. First, molecular structure of prepolymerization complex of HAdr with bis(2,2′-bithienyl)methane substituted with the benzo-(18-crown-6) 2 and 4-carboxyphenyl 3 was thermodynamically optimized at the B3LYP/6-31g(d) level. Then, a HAdr-templated MIP film was deposited on the Pt disk electrode and on the Au film electrode of a 10-MHz quartz crystal resonator (QCR) by potentiodynamic electropolymerization from solution of HAdr, 2, 3, and the cross-linking tris([2,2′-bithiophen]-5-yl)methane 4 monomer at the HAdr:2:3:4=1:1:1:2 mole ratio. For determination of Adr, the DPV peak current for the K4[Fe(CN)6] redox probe under batch conditions and the resonant frequency and capacity of the electrical double layer under FIA conditions were measured. The lower limits of detection (LOD) were 2nM, 0.5μM, and 1.5μM for the DPV, PM, and CI chemosensor, respectively, indicating suitability of the DPV chemosensor for Adr determination in biological systems (~50nM). The chemosensors were appreciably selective to Adr in the presence of common interferents.

Potentiometric determination of tolterodine in batch and flow injection conditions

Two new ion-selective electrodes of the plastic membrane type for the determination of Tolterodine (Tol) were prepared. These electrodes depend on the incorporation of the ion-exchangers of the above mentioned drug with phosphotungestic acid (PTA) or Silicotungestic acid (STA) in a PVC matrix. A comparative study is made between the performance characteristics of electrodes containing ion-exchanger in batch and FIA conditions.The usable concentration range of the electrodes was found to be (1.0×10−5–1.0×10−2 and 5.0×10−5–1.0×10−2M) in batch and FIA conditions, respectively. The electrodes have nearly the same usable concentration, pH range and exhibited high selectivity toward Tol in the presence of many inorganic cations and can be used in biological fluids such as urine and plasma. The dissolution profile of the investigated drug as well as its assay in pure and pharmaceutical preparations was performed, and the results were relatively accurate and precise as indicated by the recovery values and coefficients of variation.

Dissolution Testing and Potentiometric Assay of Sertraline Hydrochloride in Batch and FIA Conditions

An electrochemical polyvinyl chloride membrane sensor for sertraline (Ser) was prepared based on the ion associate of sertraline with phosphotungstic acid. The sensor was fully characterized in terms of its membrane composition, life span, effect of soaking, pH, interferences, and temperature and exhibited an average Nernestian response (61.6 ± 0.9 mV/decade) in the concentration range of 1.0 × 10−2 –5.0 × 10−5 M. Sertraline was assayed potentiometrically in its pure solutions and pharmaceutical preparations using the developed electrode under batch and flow injection conditions and the recovery values ranged from 93.44–101.12%, with a relative standard deviation of 0.53–1.27%. The sensor was successfully applied to the determination of the dissolution profile study of (Ser) tablets and the results were validated by comparison with spectrophotometric assays according to the quality control unit of the tablets pharmaceutical company producers. The results obtained from the proposed electrode were statistically analyzed and compared to a reported method. No significant difference was observed regarding both accuracy and precision.

Molecularly imprinted polymer (MIP) based piezoelectric microgravimetry chemosensor for selective determination of adenine

An adenine-templated molecularly imprinted polymer (MIP) film, deposited on a poly(bithiophene) barrier film, served as the recognition element of a piezomicrogravimetric (acoustic) chemosensor. A 10 MHz AT-cut shear-thickness-mode bulk-acoustic-wave quartz crystal resonator with Pt film electrodes was used as the signal transducer. Adenine electrooxidation was prevented by the barrier film. The MIP film was deposited by electrochemical co-polymerization of two functional monomers of bis(bithiophene) derivatives, bearing either the 18-crown-6 or dioxaborinane substituent, in the presence of the adenine template. A strong base solution was then used to extract the template. Completeness of the template removal was substantiated by the UV–vis, XPS, DPV, and EIS measurements. The chemosensor performance was evaluated with the piezoelectric microgravimetry detection at QCM under FIA conditions using a carrier acetonitrile–water (1:1, v: v) mixed solvent solution. The linear dynamic concentration range extended from at least 0.1 to 1 mM for the 35 μL/min flow rate, and 100 μL volume of the injected adenine solution. The chemosensor selectivity allowed for discrimination of the adenine analyte from structurally and functionally related interferants, such as 2-aminopurine, guanine, and ascorbic acid. The determined from the FIA kinetic studies stability constant of the MIP–adenine complex, (18 ± 2.4) × 10 4 M −1, was much higher than that of the MIP–(2-aminopurine), (650 ± 90) M −1, MIP–guanine, (122 ± 11) M −1, and MIP–(ascorbic acid), (92 ± 10) M −1, complexes. The concentration limit of detection was as low as 5 nM adenine for the 35 μL/min flow rate, and 1 mL volume of the injected sample solution.

Application of Oxybutynin Selective Sensors for Monitoring the Dissolution Profile and Assay of Pharmaceutical Dosage Forms

Two ion-selective sensors of the plastic membrane type were prepared for the determination of oxybutynin hydrochloride (OxCl). They depend on the incorporation of the ion-associates with phosphotungestic acid or phosphomolybdic acid in a PVC matrix. A comparative study is made between their performance characteristics in batch and FIA conditions. The sensors have nearly the same usable concentration, temperature and pH range. They have a wide range of selectivity and can be applied for the determination of the relevant drug with nearly the same precision and accuracy in vitro. Dissolution testing was applied using the sensors; this offers a simple, rapid, cheap way out of sophisticated and high cost instruments used in the pharmacopeial method using HPLC. The investigated drug was determined in its pure and pharmaceutical preparations. The results were accurate and precise, as indicated by the recovery values and coefficients of variation.

Molecularly imprinted poly[bis(2,2′-bithienyl)methane] film with built-in molecular recognition sites for a piezoelectric microgravimetry chemosensor for selective determination of dopamine

A piezoelectric microgravimetry (PM) chemosensor, featuring a film of molecularly imprinted polymer (MIP) of poly[bis(2,2′-bithienyl)methane] bearing either a 3,4-dihydroxyphenyl or benzo-18-crown-6 substituent, for selective determination of dopamine was devised and tested. A Pt/quartz resonator and a dopamine-templated MIP film, deposited by electropolymerization onto an underlayer of poly(bithiophene), served as the transducer and recognition element of the chemosensor, respectively. The UV–vis spectroscopic and XPS as well as electrochemical measurements verified completeness of the dopamine template extraction with a strong base solution. The extraction-generated molecular cavities featured recognition sites that served selective dopamine analyte binding. The SECM imaging substantiated the permeability characteristics of the template-free MIP film. The dopamine analyte was determined under FIA conditions with the PM detection. The lower limit of detection was 10 nM dopamine at favorable conditions involving the 35 μL/min carrier solution flow rate and the injected sample volume of 1 mL. The sensitivity of the chemosensor increased almost fivefold when the poly(bithiophene) film coated Pt/quartz electrode was used instead of the bare Pt/quartz electrode as the substrate for deposition of the MIP film. The chemosensor successfully discriminated dopamine from structural and functional analogues, such as 2-phenylethylamine, histamine, and ascorbic acid. The optimum mean thickness of the MIP film was ∼ 220 nm.

Determination of Diphenylpyraline Hydrochloride in Pure Solutions and Pharmaceutical Preparations Using Ion Selective Electrodes Under Batch and FIA Conditions

New diphenylpyraline (Di) ion selective plastic membrane electrodes for both conventional and coated wire types based on the ion associate of Di-HCl with sodium tetraphenylborate (NaTPB) and phosphotungestic acid (PTA) were prepared. The conventional type electrode was fully characterized in terms of membrane composition, plasticizer, filling solution, life span, pH, ionic strength, and temperature. The membranes of optimum compositions were used for the preparation of both graphite and cupper coated wire electrodes. The prepared electrodes were used for the potentiometric determination of the investigated drug in raw material and pharmaceutical preparations under batch and flow injection analysis conditions. The selectivity of the electrodes towards a large number of excipients like inorganic cations, sugars, and amino acids was tested. In addition, the determination of Di-HCl, the solubility product of the ion associate and the formation constant of the precipitation reaction leading to the ion associate formation were carried out using a conductimetric technique based on its ion association with NaTPB and PTA.

Adaptation of a commercial ion selective fluoride electrode to a tubular configuration for analysis by flow methodologies

The determination of fluoride ions in water samples is accomplished by using a tubular flow through detector constructed by drilling a channel through a commercially available LaF 3 crystal electrode in such a way that the original contacts of the non-modified unit are maintained. Its performance when incorporated in both FIA and SIA systems was evaluated and the results show that the tubular unit retains the characteristics of the non-modified electrode. In SIA conditions an extended linear range of response and lower detection limit were achieved when compared with the electrode performance in FIA conditions. These aspects together with the additional advantage of low sample and reagent consumptions in SIA when compared to FIA, makes the incorporation of the proposed tubular ISE in a SIA system the preferred approach for on line determination and monitoring of fluoride content in natural water samples.

Potentialities of pH-electrode modified with alkaline phosphatase

A novel biosensor obtained by immobilization of alkaline phosphatase at the surface of pH-electrode has been developed and its potential applications have been announced. Although the applied enzyme is not specific and exhibits biocatalytic activity towards many substrates, the biosensor reveals high and specific sensitivity only for monofluorophosphate. Moreover, this biosensor can be easily converted into apoenzyme electrode and applied for the enzyme cofactor detection. As the developed biosensor works well under FIA conditions, these transformations can be reversibly and reproducibly performed on-line without any strenuous pretreatments. This opportunity has been illustrated by the detection of zinc cations using the developed biosensor-FIA system.

New automatized method with amperometric detection for the determination of azithromycin

A FIA–amperometric method for azithromycin determination was developed. A working glassy carbon electrode and a Ag/AgCl/NaCl (3 M) reference electrode were used. The determination is based on the electrochemical oxidation of the azithromycin at 0.9 V in Britton–Robinson buffer solution (pH 8.0). Due to the adsorption of the reaction products on the electrode surface, an effective cleaner cycle was implemented. By using the optimum chemical and FIA conditions, a concentration linear range of 1.0–10.0 mg L −1 and a detection limit (LOD) of 0.76 mg L −1 are obtained. The method was validated and satisfactorily applied to the determination of azithromycin in pharmaceutical formulations.

An electrochemical sensor for l-dopa based on oxovanadium-salen thin film electrode applied flow injection system

An oxovanadium-salen complex ( N,N′-ethylene-bis(salicylideneiminato) oxovanadium) thin film deposited on a graphite–polyurethane electrode was investigated with regard to its potential use for detection of l-dopa in flow injection system. The oxovanadium(IV)/oxovanadium(V) redox couple of the modified electrode was found to mediate the l-dopa oxidation before its use in the FIA system. Experimental parameters, such as pH of the carrier solution, flow rate, sample volume injection and probable interferents were investigated. Under the optimized FIA conditions, the amperometric signal was linearly dependent on the l-dopa concentration over the range 1.0 × 10 −6 to 1.0 × 10 −4 mol L −1 ( I anodic μA) = 0.01 + 0.25 [ l-dopa μmol L −1]) with a detection limit (S/N = 3) of 8.0 × 10 −7 mol L −1 and a sampling frequency of 90 h −1 was achieved. For a concentration of 1.0 × 10 −5 mol L −1 l-dopa, the R.S.D. of nine consecutive measurements was 3.7%.

Design of a flow injection method for chlorophyll determination in in vitro plants

A flow injection (FIA) method was designed for the determination of chlorophylls a and b in small in vitro Dieffenbachia maculata “Sublime” plants. In the first step, the pigments from spinach leaves were separated, purified by solvent extraction and freeze–dried, to obtain standards for the FIA optimization. The sample extraction procedure was optimized. Four solvents were tested: diethyl ether, methanol, acetone and ethanol. The ethanol 96% was the optimal solvent for FIA purposes. It allows to the efficient extraction of the pigments and water can be used as carrier. The best FIA conditions found for the quasi-simultaneous quantification of chlorophylls a and b were a flow rate of 10.84 mL min −1, a sample injection volume of 1.45 mL and a reactor length of 63 cm. The detection was performed with the automatic wavelength scanning Cintra 10e spectrometer, at 649 and 665 nm. The results obtained by the FIA method were compared to those obtained by the Arnon method. A deviation less than 5% was found between results for both methods. The concentration (mg g −1) of chlorophylls a and b during three periods of the plants (in vitro, acclimatization, and adult) was determined to evaluate the whole in vitro procedure. It was found an increment of both pigment concentrations since the in vitro step till the adult stage, while the chlorophylls a to b ratio decreases. The designed method is suitable especially for the determination of the pigments at low concentrations in small samples with appropriate analytical quality.

Chemically modified carbon paste electrode for the potentiometric determination of dicylomine hydrochloride in batch and in FIA conditions.

A carbon-paste electrode for dicyclomine hydrochloride (DcCl) was prepared and fully characterized in terms of composition, life span, usable pH range and temperature. The electrode was applied to the potentiometric determination of dicylominium ion in its pure state and in pharmaceutical preparations in batch and flow injection conditions and in biological fluids using standard additions method. The electrode is based on a mixture of two ion-exchangers, namely, dicyclominium-phosphomolybdate and dicylominium-tetraphenylborate, dissolved in dioctyl phthalate as pasting liquid. The modified electrode showed a near-Nernstian slope of 58 +/- 2 mV over the concentration range of 1.2 x 10(-5)-1.6 x 10(-2) M with an average recovery of 97-102% and a RSD of 0.090-1.00. The electrode exhibits good selectivity for DcCl with respect to a large number of inorganic cations, sugars, amino acids and organic substances of biological fluids. Potentiometric titrations of DcCl with several titrants have been monitored using this modified carbon paste electrode as an end-point indicator electrode.

Determination of ambroxol hydrochloride in pure solutions and some of its pharmaceutical preparations under batch and FIA conditions

New ambroxol (Amb) ion selective plastic membrane electrodes of both conventional and coated graphite types based on the ion-pair of ambroxolium tetraphenylborate (Amb–TPB) ion-pair are prepared. The conventional type electrode was fully characterized in terms of membrane composition, life span, pH, ionic strength and temperature. It was applied to potentiometric determination of ambroxol in pure solutions and pharmaceutical preparations under batch and flow injection conditions. The potentiometric determination was used in the determination of ambroxol in muco syrup in four batches of different expiry dates, also the amounts of ambroxol released after 1, 8 and 16 h from the muco sustained release type (S.R.) capsules were also assayed. The selectivity of the electrode toward a large number of excipient like inorganic cations, sugars and amino acids was tested. The solubility product of the ion-pair and the formation constant of the precipitation reaction leading to the ion-pair formation were determined conductimetrically.