Spectrophotometric Determination of Some Phenolic Antibiotics in Dosage Forms

 A simple and sensitive spectrophotometric method is described for the determination of some phenolic antibiotics namely: cefadroxil, amoxicillin and vancomycin. The method is based on the measurement of the orange yellow species produced when the drugs are coupled with diazotized benzocaine in triethylamine medium. The method is applicable over the range of 0.8–12 μg/ml for cefadroxil, 2–16 μg/ml for amoxicillin and 2–18 μg/ml for vancomycin. The formed compounds absorb at 455 nm for both cefadroxil and amoxicillin and at 442 nm for vancomycin. The proposed method has detection limits of 0.018 μg for cefadroxil, 0.0034 μg for amoxicillin and 0.0156 μg for vancomycin. The stoichiometric ratio for the studied compounds was found to be 1:1 and a proposal of the reaction pathway was made. The proposed method was applied for the analysis of the cited drugs in their pharmaceutical preparations. The results are in good agreement with those obtained by the official methods. Received February 7, 2000. Revision June 14, 2000.     

Flow-injection solid surface lanthanide-sensitized luminescence sensor for determination of <Emphasis Type="Italic">p</Emphasis>-aminobenzoic acid

A single optosensing device based on lanthanide-sensitized luminescence was developed for determination of p-aminobenzoic acid (PABA). The method is based on the formation of a complex between PABA and Tb(III) immobilized on the solid phase (QAE A-25 resin) placed inside the flow cell. NaCl (1 M) was used as carrier solution and HCl (0.05 M) as eluent. The sample solutions of PABA (100 μL) containing Tb(III) and buffered at pH = 6.0 were injected into the carrier stream and the luminescence was measured at λ _ex = 290 nm and λ _em = 546 nm. The method shows a linear range from 0.2 to 6.0 μg mL⁻¹ with an RSD of 1.2% (n = 10) and a sampling frequency of 22 h⁻¹. A remarkable characteristic of the method is its high selectivity which allows it to be satisfactorily applied to the analysis of PABA in pharmaceutical samples without prior treatment. Figure Typical emission bands of Tb(III) in a solid-phase PABA–Tb(III) luminescence spectrum     

Stabilization of antibodies by haptens

A new, sensitive and very simple spectrofluorimetric biparameter sensor is described for the determination of salicylamide and/or salicylic acid in pharmaceutical preparations. The method integrates the transitory retention and fluorescence detection of both compounds on Sephadex QAE A-25 resin packed into a conventional flow-through cell. A monochannel manifold with two alternative carriers is used. At pH 2.0 (first carrier) salicylic acid is selectively retained on the solid support and after developing the analytical signal it is desorbed. At pH 11.0 (second carrier) both salicylic acid and salicylamide are simultaneously and transitorily retained on the solid, the analytical signal now corresponding to both analytes. The monochromators were tuned at 260 (excitation) and 415 (emission) nm, respectively. The calibration graph for salicylamide is linear over the range 0.01 to 0.32 μg mL^–1 and for salicylic acid from 0.04 to 1.0 μg mL^–1 in the presence of each other. The relative standard deviation and the sampling frequency for the determination of salicylamide (0.20 μg mL^–1) and salicylic acid (0.50 μg mL^–1) were 1.1% and 35 h^–1, and 0.9% and 45 h^–1, respectively. Good results on application to individual determination or mixture resolution in pharmaceutical samples testify to the usefulness of the proposed sensor. Received: 20 April 1999 / Revised: 7 June 1999 / Accepted: 12 June 1999     

A simple solid phase spectrofluorimetric method combined with flow analysis for the rapid determination of salicylamide and salicylic acid in pharmaceutical samples

A new, sensitive and very simple spectrofluorimetric biparameter sensor is described for the determination of salicylamide and/or salicylic acid in pharmaceutical preparations. The method integrates the transitory retention and fluorescence detection of both compounds on Sephadex QAE A-25 resin packed into a conventional flow-through cell. A monochannel manifold with two alternative carriers is used. At pH 2.0 (first carrier) salicylic acid is selectively retained on the solid support and after developing the analytical signal it is desorbed. At pH 11.0 (second carrier) both salicylic acid and salicylamide are simultaneously and transitorily retained on the solid, the analytical signal now corresponding to both analytes. The monochromators were tuned at 260 (excitation) and 415 (emission) nm, respectively. The calibration graph for salicylamide is linear over the range 0.01 to 0.32 μg mL^–1 and for salicylic acid from 0.04 to 1.0 μg mL^–1 in the presence of each other. The relative standard deviation and the sampling frequency for the determination of salicylamide (0.20 μg mL^–1) and salicylic acid (0.50 μg mL^–1) were 1.1% and 35 h^–1, and 0.9% and 45 h^–1, respectively. Good results on application to individual determination or mixture resolution in pharmaceutical samples testify to the usefulness of the proposed sensor. Received: 20 April 1999 / Revised: 7 June 1999 / Accepted: 12 June 1999     

Determination of Active Ingredients of Apocynum Venetum by Capillary Electrophoresis with Electrochemical Detection

 A simple, reliable and reproducible method, based on capillary electrophoresis (CE) with electrochemical detection (ED), for the determination of three active ingredients of both Apocynum Venetum compound tablets and medicinal herbs was described. The active ingredients mainly consist of rutin, d-catechin and quercetin. Operated in a wall-jet configuration, a 300 μm diameter carbon-disk electrode was used as the working electrode, which exhibits good responses at + 950 mV (vs. SCE) for the three analytes. Under the optimum conditions, the analytes were base-line separated within 19 min, and excellent linearity was obtained in the concentration range from 1.0 × 10⁻⁴ g/ml to 1.0 × 10⁻⁶ g/ml. The detection limit (S/N = 3) was 3.0 × 10⁻⁷ g/ml, 5.0 × 10⁻⁷ g/ml, and 4.0 × 10⁻⁷ g/ml for d-catechin, rutin and quercetin, respectively. This work provides a useful method for the analysis of traditional Chinese medicines. Received July 12, 2000. Revision January 3, 2001.     

Determination of copper by anodic stripping voltammetry on a glassy carbon electrode using a continuous flow system

 A successful flow-through system was developed for trace analysis of copper using DPASV with a glassy-carbon electrode. Periodical chemical regeneration of the electrode with a 1 mol/L NaOH solution increased sensitivity and precision. The method was shown to be applicable with a detection limit of 0.56 μg/L, with a determination time of less than 7 min per measurement (without deaeration time). The drawback of the system is the 10 min deaeration time. The system gave an accuracy of 0.090±0.005% for a certified reference material of low alloy steel containing 0.090±0.004% Cu. Applicability to various fresh water samples with a Cu content between 1.57 and 13.11 μg/L with an RSD<2.36% is illustrated. Received: 11 March 1996/Revised: 1 July 1996/Accepted: 4 July 1996     

Determination of copper by anodic stripping voltammetry on a glassy carbon electrode using a continuous flow system

 A successful flow-through system was developed for trace analysis of copper using DPASV with a glassy-carbon electrode. Periodical chemical regeneration of the electrode with a 1 mol/L NaOH solution increased sensitivity and precision. The method was shown to be applicable with a detection limit of 0.56 μg/L, with a determination time of less than 7 min per measurement (without deaeration time). The drawback of the system is the 10 min deaeration time. The system gave an accuracy of 0.090±0.005% for a certified reference material of low alloy steel containing 0.090±0.004% Cu. Applicability to various fresh water samples with a Cu content between 1.57 and 13.11 μg/L with an RSD<2.36% is illustrated. Received: 11 March 1996/Revised: 1 July 1996/Accepted: 4 July 1996     

Determination of Thiosemicarbazones by Means of the Induced Iodine-Azide Reaction

 The iodine-azide reaction induced by eight thiosemicarbazones was investigated. Inducing properties of thiosemicarbazones are different and depend on the parent carbonyl compound used for synthesis. The inductor coefficients of the examined thiosemicarbazones vary from 61 to 176. Optimum conditions for the determination of microamounts of thiosemicarbazones are given. The detection limit for the determination by the back-titration method depends on the inducing activity and is 0.9 μg for phenyl-thiosemicarbazones and 2 μg for diethyl-thiosemicarbazone in a 5-mL sample, and this corresponds to a concentration of 0.9 × 10⁻⁶ mol/L and , respectively. The automatic titration with the diluted iodine solution decreases the detection limit to about 50 ng in a 10-mL sample. Received October 28, 1998. Revision April 9, 1999.     

Determination of ascorbic acid by use of a flow-through solid phase UV spectrophotometric system

A continuous flow-through solid phase spectrophotometric system was developed for the determination of ascorbic acid based on the measurement of its intrinsic absorbance in the UV region when retained on a 1 mm Sephadex QAE A-25 anion exchanger gel layer which is placed into an appropriate quartz flow-through cell, the absorbance exhibited by this solid phase being monitored at 267 nm. A monochannel manifold was used, the sample (300, 600 or 1000 μL) being injected into the carrier solution (acetate buffer). This solution also elutes the analyte after developing the analytical signal, and regenerates the resin layer which, therefore, remains ready for the next sample. The linear dynamic range and other analytical parameters vary according to the sample volume injected. Three calibration lines were established for 300, 600 and 1000 μL sample volume, which ranged from 1.0 to 20.0, 0.5 to 10.0 and 0.2 to 6.0 μg mL^–1, respectively. The detection limits were 0.04 (300 μL), 0.03 (600 μL) and 0.02 μg mL^–1 (1000 μL), the sampling rates 28, 24 and 21 h^–1, and the RSDs (n = 10) 0.87%, 1.08% and 0.90%, respectively. The amount of ascorbic acid in various samples (pharmaceuticals, sweets and urine) were successfully determined with this method. Received: 28 April 1998 / Revised: 3 June 1998 / Accepted: 30 June 1998     

Determination of ascorbic acid by use of a flow-through solid phase UV spectrophotometric system

A continuous flow-through solid phase spectrophotometric system was developed for the determination of ascorbic acid based on the measurement of its intrinsic absorbance in the UV region when retained on a 1 mm Sephadex QAE A-25 anion exchanger gel layer which is placed into an appropriate quartz flow-through cell, the absorbance exhibited by this solid phase being monitored at 267 nm. A monochannel manifold was used, the sample (300, 600 or 1000 μL) being injected into the carrier solution (acetate buffer). This solution also elutes the analyte after developing the analytical signal, and regenerates the resin layer which, therefore, remains ready for the next sample. The linear dynamic range and other analytical parameters vary according to the sample volume injected. Three calibration lines were established for 300, 600 and 1000 μL sample volume, which ranged from 1.0 to 20.0, 0.5 to 10.0 and 0.2 to 6.0 μg mL^–1, respectively. The detection limits were 0.04 (300 μL), 0.03 (600 μL) and 0.02 μg mL^–1 (1000 μL), the sampling rates 28, 24 and 21 h^–1, and the RSDs (n = 10) 0.87%, 1.08% and 0.90%, respectively. The amount of ascorbic acid in various samples (pharmaceuticals, sweets and urine) were successfully determined with this method. Received: 28 April 1998 / Revised: 3 June 1998 / Accepted: 30 June 1998     

Spectrophotometric Determination of Trace Amounts of Vanadium Based on its Catalytic Effect on the Reaction of Diphenylamine and Hydrogen Peroxide

 In this work a kinetic spectrophotometric method for the determination of trace amounts of vanadium is presented. The method is based on the catalytic effect of the vanadium(V) on the reaction between diphenylamine (DPhA) and hydrogen peroxide in a concentrated solution of formic acid. The formation of the deep-blue oxidation product is followed by a filter spectrophotometer, equipped with an optical fiber assembly, on line with a PC provided with the suitable software. The measurements were taken at 583 nm, with an immersed type cell of 1 cm light path length. The optimization of the operating conditions regarding concentrations of the reagents, temperature and interferences are also investigated. The working curve is linear over the concentration range 0.40–4.0 μg/ml vanadium(V). The relative standard deviation for a standard solution of 0.6 μg/ml of vanadium is 0.5% (n = 5). The proposed method proved highly sensitive, selective and relatively rapid for the assay of vanadium, at low level of 0.40 μg/ml without any pre-concentration step. The method was applied to alloys and cosmetics samples. The results were compared to those received with a reference method. Good agreement was attained, with a mean error of 0.5%. Received February 25, 2000. Revision May 15, 2000.     

Simultaneous Voltammetric Determination of Molybdenum and Copper in Manganese Compounds

 Adsorptive voltammetry was employed for the determination of copper and molybdenum in manganese compounds. As working electrode the hanging mercury drop electrode (HMDE) was used. The method was applied in aqueous solutions of MnCl₂ and Mn(NO₃)₂, as well as in pre-treated manganese dioxide and manganese ores. The detection limits are 3 μg/g for copper and 5 μg/g for molybdenum in the sample. The RSDs at concentration level of 8 μg/g are 2.2 and 3.2% for copper and molybdenum, respectively.     

Cyclodextrin-based optosensor for the determination of quinine

 A flow-through optosensor for quinine is described. It has been developed in conjunction with a flow-injection analysis system and uses immobilized β-cyclodextrin as the sensing agent. The detection limit for quinine was 0.20 ng ml^-1 with a relative standard deviation of 2.1% for the determination of 0.05 μg ml^-1 (n=7) of quinine. The method has been successfully tested for the determination of quinine in some pharmaceutical preparations. Received: 4 June 1996 / Revised: 23 August 1996 / Accepted: 24 August 1996     

Determination of Cobalt with a Tungsten Tube Atomizer by Electrothermal Atomic Absorption Spectrometry and its use for the Analysis of Biological Materials

 The determination of cobalt by electrothermal atomic absorption spectrometry with a tungsten tube atomizer has been investigated. The absolute characteristic mass (the mass of element giving 0.0044 abs.) of cobalt by the atomizer was 5.8 pg and the detection limit was 0.65 ng/ml (3S/N). The interferences caused by large amounts of interferents like Al, Ca, Cu, Fe, K, Mg, Na, Pb and Zn were evaluated and most of these elements were found to interfere with the cobalt signal. Ammonium thiocyanate as a chemical modifier was found to be efficient to eliminate the severest interferences. The accuracies of the recommended method were found to be almost satisfactory for the determination of cobalt in biological materials, as shown by a comparison with the reported values of NIST materials at the 0.02–0.4 μg/g level. Received August 24, 1998. Revision February 9, 1999.     

Cyclodextrin-based optosensor for the determination of quinine

 A flow-through optosensor for quinine is described. It has been developed in conjunction with a flow-injection analysis system and uses immobilized β-cyclodextrin as the sensing agent. The detection limit for quinine was 0.20 ng ml^-1 with a relative standard deviation of 2.1% for the determination of 0.05 μg ml^-1 (n=7) of quinine. The method has been successfully tested for the determination of quinine in some pharmaceutical preparations. Received: 4 June 1996 / Revised: 23 August 1996 / Accepted: 24 August 1996     

Flow Injection Chemiluminescence Determination of Pipemidic Acid Using On-Line Electrogenerated Cobalt(III) as Oxidant

 A novel flow injection chemiluminescence (CL) system for the determinati on of pipemidic acid is described. It is based on the direct CL reaction of pipemidic acid and Co(III) in acid medium. The unstable Co(III) was on-line electrogenerated by constant current electrolysis. The CL intensity was linear with pipemidic acid concentration in the range of 0.01∼100 μg/ml, the determination limit was 3.3×10⁻⁹ g/mL. The whole process could be complete d in 1 min with a relative standard deviation of 3.2%. The proposed method is suitable for automatic and continuous analysis and has been applied successfully to the analysis of pipemidic acid in a pharmaceutical preparation. Received November 22, 1999. Revision March 24, 2000.     

Electrochemical solid phase micro-extraction and determination of salicylic acid from blood samples by cyclic voltammetry and differential pulse voltammetry

The electrochemical solid phase micro-extraction of salicylic acid (SA) at graphite-epoxy-composed solid electrode surface was studied by cyclic voltammetry. SA was oxidized electrochemically in pH 12.0 aqueous solution at 0.70 V (vs. saturated calomel electrode) for 7 s. The oxidized product shows two surface-controlled reversible redox couples with two proton transferred in the pH range of 1.0∼6.0 and one proton transferred in the pH range of 10.0∼13.0 and is extracted on the electrode surface with a kinetic Boltzman function of i _p = 3.473–4.499/[1 + e^{(t − 7.332)/6.123}] (χ ² = 0.00285 μA). The anodic peak current of the extracted specie in differential pulse voltammograms is proportional to the concentration of SA with regression equation of i _p = −5.913 + 0.4843 c (R = 0.995, SD = 1.6 μA) in the range of 5.00∼200 μM. The detection limit is 5.00 μM with RSD of 1.59% at 60 μM. The method is sensitive and convenient and was applied to the detection of SA in mouse blood samples with satisfactory results.     

Identification and quantification of pesticides and polycyclic aromatic hydrocarbons in water and food by gas chromatography-mass spectrometry

Chances are examined for the identification and determination of pesticides of different types and polycyclic aromatic hydrocarbons, 46 items, in water and food by means of gas chromatography with time-of-flight mass spectrometry detection. The detection limits make from 0.01 to 0.5 mg/L if the injected volume of samples is 1 μL; the analytical range is 0.02–10 mg/L. In the mode of selective ion registration and preliminary preconcentration by liquid and solid-phase extraction, the detection limits of analytes make from 2 to 100 ng/L in water and from 0.2 to 10 μg/kg for solid samples.     

Determination of cyanide in blood by electrospray ionization tandem mass spectrometry after direct injection of dicyanogold

An electrospray ionization tandem mass spectrometric (ESI-MS-MS) method has been developed for the determination of cyanide (CN^–) in blood. Five microliters of blood was hemolyzed with 50 μL of water, then 5 μL of 1 M tetramethylammonium hydroxide solution was added to raise the pH of the hemolysate and to liberate CN^– from methemoglobin. CN^– was then reacted with NaAuCl₄ to produce dicyanogold, Au(CN)₂^–, that was extracted with 75 μL of methyl isobutyl ketone. Ten microliters of the extract was injected directly into an ESI-MS-MS instrument and quantification of CN^– was performed by selected reaction monitoring of the product ion CN^– at m/z 26, derived from the precursor ion Au(CN)₂^– at m/z 249. CN^– could be measured in the quantification range of 2.60 to 260 μg/L with the limit of detection at 0.56 μg/L in blood. This method was applied to the analysis of clinical samples and the concentrations of CN^– in the blood were as follows: 7.13 ± 2.41 μg/L for six healthy non-smokers, 3.08 ± 1.12 μg/L for six CO gas victims, 730 ± 867 μg for 21 house fire victims, and 3,030 ± 97 μg/L for a victim who ingested NaCN. The increase of CN^– in the blood of a victim who ingested NaN₃ was confirmed using MS-MS for the first time, and the concentrations of CN^– in the blood, gastric content and urine were 78.5 ± 5.5, 11.8 ± 0.5, and 11.4 ± 0.8 μg/L, respectively.     

An integrated reaction-retention and spectrophotometric detection flow system for the determination of nickel

An integrated flow-through photometric sensor for the determination of nickel in real samples of various origins has been developed. The sensor is based on the reaction of Ni(II) with 1-(2-pyridylazo)-2-naphthol (PAN) immobilized on a cationic resin which was placed in a flow-cell using a spectrophotometer tuned at 566 nm as detector. The Ni(II) ion from the sample injected into the carrrier stream (pH = 5.0) of a monochannel continuous flow system reacts with the immobilized chromogenic reagent to form a red chelate which remains on the active solid support and generates the analytical signal. When this reached its maximum value the Ni(II)-PAN chelate was destroyed using 1 M H₂SO₄ as eluents, leaving the sorbed PAN untouched. The response of the sensor was linear in the three concentration ranges assayed: 0.3–4.0, 0.1–1.6 and 0.05–0.8 μg mL^–1 for sample volumes of 100, 400 and 800 μL, respectively, and the R.S.D.(%) (n = 10) were 1.80(100 μL), 3.04(400 μL) and 2.29(800 μL). The sensor showed an excellent selectivity which could also be increased with a simple on-line modification to avoid interference from copper. It was applied to a variety of real samples with very good results in all cases. Received: 15 April 1998 / Revised: 29 June 1998 / Accepted: 3 July 1998