Showing papers in "Analytical Letters in 1991"
TL;DR: In this article, a molecularly imprinted polymer was prepared using tert-butyloxycarbonyl-L-phenylalanine as the print molecule and methacrylic acid as the functional monomer.
Abstract: A molecularly imprinted polymer was prepared using tert-butyloxycarbonyl-L-phenylalanine as the print molecule and methacrylic acid as the functional monomer. The bulk polymer obtained was ground, sieved, packed into a column and investigated in the HPLC-mode by frontal chromatography to determine the number of binding sites and dissociation constants for the enantiomers interacting with the polymer. The dissociation constant for the L-enantiomer of the print molecule was lower than for the D-enantiomer (6.3 mM and 8.1 mM, respectively). This means that the affinity for the L-enantiomer was higher than for the D-enantiomer. The number of binding sites in the polymer giving rise to these dissociation constants were determined to be 28 μmol per g dry polymer. (Less)
113 citations
TL;DR: Pesticides as paraoxon and aldicarb have been determined with an amperometric hydrogen peroxide based choline sensor and the use of the enzyme in solution gave the best results with a detection limit of 2 ppb pesticide.
Abstract: Pesticides as paraoxon and aldicarb have been determined with an amperometric hydrogen peroxide based choline sensor. These pesticides inhibit the enzyme acetylcholinesterase which in presence of its substrate, acetylcholine, produces choline. When these pesticides are in presence of acetylcholinesterase, the activity of this enzyme decreases; this causes a decrease of choline production which is monitored by a choline sensor and correlated to the concentration of pesticide in solution. Two different procedures were followed: one with both the enzymes acetylcholinesterase and choline oxidase immobilized, the second one with the acetylcholinesterase in solution and the choline oxidase immobilized. Parameters as pH, buffer, enzyme concentration, substrate concentration and reaction and incubation times were optimized. Results showed that these compounds can be detected in the range 10 – 100 ppb. The use of the enzyme in solution gave the best results with a detection limit of 2 ppb pesticide.
87 citations
TL;DR: In this paper, an enzyme electrode was described for the determination of cholesterol dissolved in chloroform/hexane (1:1), which was shown to be applicable to the detection of cholesterol in samples of butter and margarine.
Abstract: An enzyme electrode is described for the determination of cholesterol dissolved in chloroform/hexane (1:1). The enzyme electrode is shown to be applicable to the determination of cholesterol in samples of butter and margarine.
59 citations
TL;DR: In this paper, a phosphate sensor based on amperometric determination was constructed with immobilized pyruvate oxidase and an oxygen electrode, and the determination time was 7min.
Abstract: A phosphate sensor based on amperometric determination was constructed with immobilized pyruvate oxidase and an oxygen electrode. A rapid, simple and sensitive determination of phosphate was performed with the sensor. The determination time was 7min. The linearity range of this sensor was 12 – 80μM.
51 citations
TL;DR: A second derivative spectroscopic method for the determination of p-aminophenol in paracetamol powder is described in this article, where the second derivative absorbance (d2A/dλ2) values were measured at 223.8 nm (Δ = 4.2 nm).
Abstract: A second derivative spectroscopic method for the determination of p-aminophenol in paracetamol powder is described. Second derivative absorbance (d2A/dλ2) values were measured at 223.8 nm (Δ = 4.2 nm) where p-aminophenol showed derivative responses obeying Beer's Law but paracetamol had negligible derivative absorption. The concentrations of p-aminophenol solutions prepared in 0.1 N HCl (0.12–7.61 mcg/ml), containing constant amounts of paracetamol (20 mcg/ml) related linearly with the d2A/dλ2 values and gave a straight line (r = −0.9999). The method allowed determination of 0.5% to 38% of p-aminophenol in paracetamol without prior separation, it is rapid, precise and accurate.
47 citations
TL;DR: In this article, a triisocyanate cross-linking agent was used to chemically cross-link thionin on the surface of a spectroscopic graphite electrode, resulting in a purple film with an additional reversible redox couple a t E° of +73 mV vs. Ag/AgCl.
Abstract: Thionin, a redox mediator that has been used to study the electrochemical behavior of reduced β-nicotinamide adenine dinucleotide (NADH), was chemically cross-linked on the surface of a spectroscopic graphite electrode by using a triisocyanate cross-linking agent. The electrodes modified in this manner had a purple film with an additional reversible redox couple a t E° of +73 mV vs. Ag/AgCl compared to uncross-linked thionin. The thionin modified electrode mediated oxidation of NADH with response to NADH between 7.0 × 10–7 to 1.8 × 10–3 M, a sensitivity of 113 pAJcmWmM, and a detection limit of 0.5 μM.
42 citations
TL;DR: In this article, a constant potential procedure to pretreat carbon fiber electrodes is described, which essentially consists of two steps: +3.0 V for 30 s and -2 V for 10 s.
Abstract: A constant potential procedure to pretreat carbon fiber electrodes is described. This essentially consists of two steps: +3.0 V for 30 s and -2.0 V for 10 s. The anodic potential treatment enhances sensitivity for catechols, and cathodic potential treatment improves selectivity, which results in a potential shift of AA from catechols. The optimum parameters and experimental conditions for electrochemical treatment were explored. Treated carbon fiber electrode used in rat brain showed well-defined and separated peaks of AA and catechols.
42 citations
TL;DR: In this article, an amperometric enzyme electrode for the analysis of glucose was described, which used adsorbed benzoquinone on a carbon electrode to mediate electron transfer from glucose oxidase.
Abstract: This paper describes an amperometric enzyme electrode for the analysis of glucose. The glucose sensor utilised adsorbed benzoquinone on a carbon electrode to mediate electron transfer from glucose oxidase. A linear response to 0–15 mM glucose was observed. The electrode's response to glucose, its pH profile and the effect of temperature are presented.
41 citations
TL;DR: In this paper, simple and selective spectrophotometric methods for the determination of norfloxacin and nalidixic acid are described. The methods are based on the measurement of the intensity of the orange-red colour produced by the drugs with ferric chloride in dimethylsulphoxide-methanol medium.
Abstract: Simple and selective spectrophotometric methods for the determination of norfloxacin, ciprofloxacin, cinoxacin and nalidixic acid are described. The methods are based on the measurement of the intensity of the orange-red colour produced by the drugs with ferric chloride in dimethylsulphoxide-methanol medium. The methods are highly accurate and have been successfully applied for analysis of bulk drugs and pharmaceutical preparations. The results are in good agreement with the official methods.
39 citations
TL;DR: In this paper, the amperometric response of a mixed-glucose oxidase-redox mediator-carbon paste electrode, permanently poised at the operating potential, was investigated in phosphate buffer as a function of glucose concentration over a period of four weeks.
Abstract: The amperometric response of a mixed-glucose oxidase-redox mediator-carbon paste electrode, permanently poised at the operating potential, has been investigated in phosphate buffer as a function of glucose concentration over a period of four weeks.
38 citations
TL;DR: Biotinylated acetylcholinesterase from Eel was immobilized to a biotinylated cellulose nitrate membrane via a streptavidin bridge and this biosensor was evaluated for its potential to detect organophosphate (OP) anticholineterases (antiChEs).
Abstract: Biotinylated acetylcholinesterase (AChE) from Eel was immobilized to a biotinylated cellulose nitrate membrane via a streptavidin bridge. Using a light addressable potentiometric sensor (LAPS), enzyme activity was determined as a function of substrate concentration (i.e. acetylcholine) and amount of enzyme immobilized to the membrane. This biosensor was also evaluated for its potential to detect organophosphate (OP) anticholinesterases (antiChEs).
TL;DR: In this paper, a simple isocratic HPLC elution method consisting of acetonitrile: 5% phosphoric acid (30:70) was employed for the separation of ramipril from precursors I and II in 15 minutes.
Abstract: A sensitive, accurate and reproducible method for the analysis of ramipril and its two precursors (precursors I and II), which could be present as impurities in bulk material or pharmaceutical preparations, has been described. A simple isocratic HPLC elution method consisting of acetonitrile: 5% phosphoric acid (30:70) was employed for the separation of ramipril from precursors I and II in 15 minutes. The limit of detection under UV 220nm for ramipril was 36 pmole ± 8.20%. A standard curve was constructed for ramipril determination. These chromatographic conditions failed to separate peaks corresponding to precursors I and II. Another mobile phase, acetonitrile: 5% phosphoric acid (20:80), allowed the separation and quantification of precursors I and II in 20 minutes. The limit of detection under UV 220 nm was 67 pmole ± 8.06% and 76 pmole ± 10.04% for precursors I and II respectively. Ramipril peak has a tendency to broaden drastically under these chromatographic conditions.
TL;DR: In this article, the reaction between lead(II) and 2-(2-Thiazolylazo)-p-Cresol (TAC) in the presence of TERGITOL NPX (4 mg/ml) at an apparent pH 9.0-10.0 results in an intensely colored complex which is stable for at least 4 hours.
Abstract: The reaction between lead(II) and 2-(2-Thiazolylazo)-p-Cresol(TAC) in the presence of TERGITOL NPX (4 mg/ml) at an apparent pH 9.0–10.0 results in an intensely colored complex which is stable for at least 4 hr. The composition of the complex is 1:2 cation: TAC and the log of the formation constant is 11.92 ± 0. 40. Beer's law is obeyed up to 6.0μg.ml−1 of lead(II) at 650nm. The apparent molar absorptivity at 650 nm is 2.07 × 104 1. mole−1.cm−1 and the detection limit was obtained as 10.0 ng.ml−1 of lead(II). The method is applied to determination of lead(II) in copper-base alloy.
TL;DR: In this paper, hydrogen peroxide was determined amperometrically in a steady-state arrangement by utilizing a kohlrabi -ferrocene-based carbon paste electrode.
Abstract: Hydrogen peroxide was determined amperometrically in a steady-state arrangement by utilizing a kohlrabi - ferrocene based carbon paste electrode. A very short response time (2.6 seconds) and a relatively large usable pH range (5.0–7.4) were obtained. Several important hydrogen donors were studied as possible interferences.
TL;DR: In this paper, a polymer modified electrode with electrocatalytic properties was used for the detection of nitrite in flowing solutions using an electrodeposited polymer film of the [Ru(bpy)2(vpy) 2+2+2+) complex, where bpy is 2,2′ bypyridyl and vpy is 4-vinylpyridine.
Abstract: The electrochemical detection of nitrite in flowing solutions using a polymer modified electrode with electrocatalytic properties is described. The modifier was an electrodeposited polymer film of the [Ru(bpy)2(vpy)2+2+ complex, where bpy is 2,2′ bypyridyl and vpy is 4-vinylpyridine. The modified electrodes showed the ability to enhance the nitrite response and avoid surface fouling. The electrodeposited films exhibited higher mechanical stability than similar chemisorbed coatings.
TL;DR: The recent development of piezoelectric immunosensors is reviewed in this paper, where the selectivity provided by the biological coatings together with the inherent sensitivity of the PZ devices and the ability to oscillate the crystal in liquid medium have induced a rising interest in this class of sensors.
Abstract: The recent development of piezoelectric immunosensors is reviewed. The selectivity provided by the biological coatings together with the inherent sensitivity of the PZ devices and the ability to oscillate the crystal in liquid medium have induced a rising interest in this class of sensors. Methods of coating and several applications are reported including microgravimetric immunoassays, microbial assays and gas phase immunosensors.
TL;DR: A graphite working electrode was used with 1,1 dimethylferrocene (DMF) as electron mediator for the determination of L-glutamate in various foodstuffs as mentioned in this paper.
Abstract: A mediated enyme electrode was developed for the determination of L-glutamate, based on the immobilization of L-glutamate oxidase from Streptomyces sp. X 119–6. A graphite working electrode was used with 1,1 dimethylferrocene (DMF) as electron mediator. The electrode responded linearly to L-glutamate over the range 0.2 to 2 mM (0.029–0.29 g/l). The enzyme electrode was applied to the measurement of L-glutamate in various foodstuffs.
TL;DR: A simple and sensitive method was described for the determination of formaldehyde and acetaldehyde in methanol and ethanol, respectively and a limit for aldehydes in alcohols is a necessary requiremen...
Abstract: A simple and sensitive method was described for the determination of formaldehyde and acetaldehyde in methanol and ethanol, respectively. A limit for aldehydes in alcohols is a necessary requiremen...
TL;DR: In this paper, the authors investigated the detection limits for the measurement of unconjugated and conjugated bilirubin in aqueous solutions using surfactant fluorescence enhancement and visible laser fluorometry.
Abstract: Improvements on detection limits for the measurement of unconjugated and conjugated bilirubin in aqueous solutions using surfactant fluorescence enhancement and visible laser fluorometry were investigated. To maximize the fluorescence signal, commonly used surfactants were employed to enhance the fluorescence quantum yields of these bilirubin molecules and one of the visible lines of an argon ion laser was used for fluorometric excitation; to minimize optical noise, a unique optical fiber flow-cell was employed. Relative and absolute limits of detection for the micelle-bound unconjugated and conjugated bilirubin were in the sub-micromole per liter and sub-nanogram range, respectively. These capabilities should be important for the potential use of surfactants in flow injection analysis or micellar liquid chromatography for the determination of bilirubin species in biological materials.
TL;DR: In this article, a sensitive voltammetric method is developed for quantitation of the antibiotics tetracycline and oxytetracyCLine (Terramycin), which is based on controlled adsorptive preconcentration of the antibiotic on the hanging mercury drop electrode (HMDE), followed by tracing the voltammogram in a cathodic potential scan.
Abstract: A sensitive voltammetric method is developed for the quantitation of the antibiotics tetracycline and oxytetracycline (Terramycin). The method is based on controlled adsorptive preconcentration of the antibiotic on the hanging mercury drop electrode (HMDE), followed by tracing the voltammogram in a cathodic potential scan. The modes used are direct current stripping voltammetry (DCSV) and differential pulse stripping voltammetry (DPSV). The adsorptive stripping response was evaluated with respect to preconcentration time and potential, concentration dependence and composition of supporting electrolyte. The detection limits found were 5 × 10−8 (2 min. preconcentration) by DPSV and 1 × 10−7M (10 sec.) by DCSV. These values correspond to 25 and 50 ppb respectively. The relative standard deviation (at 1 × 10−7M level) is 1.4%. Successful applications of the method to analysis of urine and pharmaceutical formulations as capsules or ampules, are described.
TL;DR: A flow injection analysis (FIA) method for the determination of hydrogen peroxide by aryl oxalate chemiluminescence detection was studied in this article, where sulforhodamine 101 was used as a new fluorophore and bis[4-nitro-2-(3,6,9-trioxadecyloxycarbonyl)phenyl]oxalate (TDPO) in imidazole buffer.
Abstract: A flow injection analysis (FIA) method for the determination of hydrogen peroxide by aryl oxalate chemiluminescence detection was studied. The analyte was detected by using sulforhodamine 101 as a new fluorophore and bis[4-nitro-2-(3,6,9-trioxadecyloxycarbonyl)phenyl]oxalate (TDPO) in imidazole buffer (pH 7.0)-acetonitrile. The detection limit was 3.0 × 10−9 M. The relative standard deviation (n=6) for 1.0 × 10−6 M hydrogen peroxide was 2.8%. This FIA method was shown to be 20 to 2500 times more sensitive than the previous FIA method with aryl oxalate chemiluminescence.
TL;DR: In this article, a derivative spectrophotmetric procedure for the simultaneous determination of acetaminophen-orphenadrine citrate, ibuprofen, and acyclic acid-chlorzoxazone, binary mixtures is described.
Abstract: A derivative spectrophotmetric procedure for the simultaneous determination of acetaminophen-orphenadrine citrate, acetaminophen-ibuprofen and acetaminophen-chlorzoxazone, binary mixtures is described. The procedure minimises the mutual interference between these drugs in mixtures and allows the determination of these compounds without a previous extraction step. The precision of the method, expressed as the relative standard deviation, is better than 4%. The method has been successfully applied to laboratory mixtures and commercial tablets containing these drugs.
TL;DR: The potential response behavior of a strontium doped poly(dibenzo-18crown-6) film electrode to Strontium ions in solution has been examined in this article and the effect of polymerization conditions on the characteristics of the response is discussed.
Abstract: The potential response behaviour of a strontium doped poly(dibenzo-18-crown-6) film electrode to strontium ions in solution has been examined. The effect of polymerization conditions on the characteristics of the response is discussed. The performance of the electrode with respect to electrode reproducibility, response stability and regeneration is also studied. The calibration plots for electrode have an unexpected slope of 58–59 mv per strontium(II) concentration decade at 25[ddot]C and a detection limit of about 2.9 × 10−5 M. The selectivity coefficients for this polymeric electrode for most of the potential interferants are in the order of 10−3. This polymeric film electrode has a relatively fast response, is easy to prepare and has a reasonable lifetime.
TL;DR: Biosensors for formate and ethanol were prepared by using graphite electrodes chemically modified with NMP+TCNQ−, together with molecular-weight enlarged NAD and the corresponding dehydrogenase, hence it could be entrapped by a dialysis membrane.
Abstract: Biosensors for formate and ethanol were prepared by using graphite electrodes chemically modified with NMP+TCNQ−, together with molecular-weight enlarged NAD and the corresponding dehydrogenase. The molecular-weight of the NAD-PEG was about 20000 g/mol, hence it could be entrapped by a dialysis membrane.
TL;DR: In this article, the potential of using commercially available solid phase extraction membranes and solid-state spectroscopy for monitoring water pollution is brought out, which brings out the potential for at least semiquantitative analysis.
Abstract: Research results are described which bring out the potential of using commercially available solid-phase extraction membranes and solid-state spectroscopy for monitoring water pollution. The membranes are used to preconcentrate pollutants by sorption from aqueous solution followed by nondestructive spectroscopic measurements. Solid-state fluorescence measurements using EmporeTM C18 membranes were employed in the laboratory for concept validation studies. Tabs from the membranes were suspended in solutions containing parts per billion (ppb) concentrations of anthracene for specific periods of time. The tabs were withdrawn, allowed to dry briefly in air, and then examined for fluorescence. The potential exists for at least semiquantitative analysis. The method is relatively simple. Use of extraction membranes in B dip-stick mode is new, as is the use of the membranes with solid-state fluorescence spectroscopy. Limitations are being defined.
TL;DR: In this paper, a high performance liquid chromatographic procedure for simultaneous determination of water-soluble vitamin preparations containing pyridoxine hydrochloride (Vit. B6), cyanocobalamin, thiamine, and folic acid using a cyclobond I column was developed.
Abstract: A high performance liquid chromatographic procedure for simultaneous determination of water-soluble vitamin preparations containing pyridoxine hydrochloride (Vit. B6, cyanocobalamin (Vit. B12), thiamine hydrochloride (Vit. B1) and folic acid using a cyclobond I column was developed. The four vitamins were assayed in multivitamin pharmaceutical formulations not containing minerals. Samples were chromatographed using pH 7 phosphate buffer: methanol (80 : 20 %) mobile-phase. The procedure is rapid and the total chromatographic time does not exceed 6.64 min. The method is accurate, precise and specific.
TL;DR: The Fourier function method has been applied to the independent determination of fluphenazine hydrochloride (FH) and nortriptyline hydrochlorides (KH) (1:20) in both laboratory made mixtures and commercial tablets.
Abstract: The Fourier function method has been applied to the independent determination of fluphenazine hydrochloride (FH) and nortriptyline hydrochloride (KH) (1:20) in both laboratory made mixtures and commercial tablets. The method is based on the absorbance measurement of FE (the minor component) in concentrated mixture solutions, which is then properly diluted prior to NH absorbance measure-
TL;DR: In this paper, a method for simultaneous determination of pharmaceuticals in two-component commercial formulations by first-order derivative UV spectrophotometry was developed, and the average recoveries of the four compounds in the formulations under study were 100.04 ± 1.28% 101.50 ± 2.27 %, 101.59 % 1.24 % and 100.49 ± 2%.
Abstract: Procedures were developed for the simultaneous determination of pharmaceuticals in two-component commercial formulations by first-order derivative UV spectrophotometry. Phenylephrine hydro chloride and carbinoxamine maleate in capsules and diphenhydramine hydrochloride and naphazolixehydro hydrocloride in nasal gelly were succesfully assayed. A simple sensitive method in the usual range for the binary preparations has been developed. Average recoveries of the four compounds in the formulations under study were 100.04 ± 1.28% 101.50 ± 2.27 %, 101.59 % 1.24 % and 100.49 ± 2.59 %.
TL;DR: A micro determination method at μg 1−1 levels for vanadium by solid phase spectrophotometry has been developed in this article, where 5-Bromosalicylhydroxamic acid was used as chromogenic reagent to form a 1:2 violet complex which was easily sorbed and concentrated on a dextran-type anion-exchange resin.
Abstract: A microdetermination method at μg 1−1 levels for vanadium by solid-phase spectrophotometry has been developed. 5-Bromosalicylhydroxamic acid was used as chromogenic reagent to form a 1:2 violet complex which is easily sorbed and concentrated on a dextran-type anion-exchange resin. The resin-phase absorbances at 560 and 850 nm were measured directly. Vanadium can be determined in the 5 - 60 μg 1−1 range with a RSD of 4.3%. The method is applied to the determination of vanadium in pet roleiim crudes and natural water, samples.
TL;DR: In this article, it was demonstrated that a microcolumn (1 mm i.d., 5 cm length) manifold system is described for automatic delivery of eluant (0.12 ml) to a heated atomic absorption graphite atomizer.
Abstract: It is demonstrated that silica gel columns will quantitatively adsorb free Cu2+ and Pb2+ ions at pH > 8. These are eluted with 0.1 M HNO3 but not with methanol. Negatively charged EDTA chelates are not adsorbed. Neutral APDC chelates are partially adsorbed on silica columns, but are quantitatively adsorbed on C18-bonded columns, and are eluted with methanol. The metal ions are partially adsorbed on C18-bonded columns, due to residual silanol groups. A microcolumn (1 mm i.d., 5 cm length) manifold system is described for automatic delivery of eluant (0.12 ml) to a heated atomic absorption graphite atomizer, using either methanol or 0.1 M HNO3 in methanol eluant, allowing speciation and measurement of parts per billion of metals. These studies demonstrate that by using a mixed column or sequential columns of silica gel and C18-bonded silica, cationic and neutral metal species could be adsorbed, followed by sequential elution and measurement using methanol and then 0.1 M HNO. Negatively charged spec...