Reversed flow-injection manifold for the spectrophotometric determination of captopril based on its inhibitory effect on the Co(II)-2,2'-dipyridyl-2-pyridylhydrazone complex formation

The present work reports a new, simple and rapid reversed flow-injection (r-FI) method for the accurate and precise spectrophotometric determination of captopril (CPL) in pharmaceutical formulations. The method is based on the inhibitory effect of CPL on the complex formation of Co(II) with 2,2'-dipyridyl-2-pyridylhydrazone (DPPH). The chemical and FI variables were studied and optimized. The calibration graph was linear in the range 0-250 mg l(-1) CPL, at a sampling rate of 60 injections per hour. The method was found to be very precise [s(r)=0.8% at 100.0 mg l(-1) CPL (n=12)] and the 3sigma detection limit (c(L)=2.5 mg l(-1)) was quite satisfactory. Its application to commercially available pharmaceuticals produced excellent results, with a mean relative error of e(r)<1.0%.     

Flow-injection manifold for the simultaneous spectrophotometric determination of Fe(II) and Fe(III) using 2,2''-dipyridyl-2-pyridylhydrazone and a single-line double injection approach

A simple and rapid flow-injection (FI) method is reported for the simultaneous spectrophotometric determination of Fe(II) and Fe(III) in pharmaceutical products. The method is based on the reaction of Fe(II) with 2,2'-dipyridyl-2-pyridylhydrazone (DPPH) in acidic medium to form a water-soluble reddish complex (lambdamax=535 nm). Fe(III) reacts with DPPH under flow conditions only after its on-line reduction by ascorbic acid (AsA). Both analytes were determined in the same run via a double-injection valve, which enabled the simultaneous injection of two sample volumes in the same carrier stream (,,single-line double-injection" approach). The two well-defined peaks produced corresponded to total iron [Fe(II)+Fe(III)] and Fe(II). Speciation of the analytes in their mixtures was achieved by multiple regression analysis. The calibration curves obtained were linear over the ranges 0-30 and 0-50 mg L(-1) for Fe(II) and Fe(II), respectively, and the precision [s(r)=1.0% for Fe(II) and 1.5% for Fe(III)] was satisfactory. The method proved to be selective and adequately sensitive (cL=0.25 and 0.17 mg L(-1) for Fe(III) and Fe(II), respectively, in mixtures). Application of the method to the analysis of pharmaceutical samples resulted in excellent accuracy; the percent mean recoveries were in the range 99.0-102.0% for both Fe(II) and Fe(III) and the mean relative error was e(r)=1.0%.     

Stopped-flow injection liquid-liquid extraction spectrophotometric determination of palladium in airborne particulate matter and automobile catalysts

A stopped-flow injection liquid-liquid extraction (SF-EX-FIA) spectrophotometric method is reported for the determination of palladium(II), using the 2,2'-dipyridyl-2-pyridylhydrazone (DPPH) as a color forming reagent. The colored complex Pd(II)-DPPH was extracted in CHCl(3) and the absorbance was monitored at 560 nm. An injection valve was used as a commutator in order to combine the stopped-flow technique with liquid-liquid extraction FI system. The calibration graph was linear up to 12 mg l(-1) (s(r)=0.27%; r=0.9999) with a detection limit of c(L)=0.007 mg l(-1). The sampling rate was 20 injections per hour. The proposed method has been successfully applied to the determination of palladium in airborne particulate matter (APM) and in automobile exhaust gas converter catalysts.     

Rapid flow injection spectrophotometric determination of monofluorophosphates in toothpastes after on-line hydrolysis by alkaline phosphatase immobilized on a cellulose nitrate membrane

A new, rapid flow injection (FI) method is reported for the spectrophotometric determination of monofluorophosphate (MFP) ions in toothpastes. MFP ions are hydrolyzed on-line by alkalinephosphatase (APase) immobilized on a cellulose nitrate membrane, prior to injection in the FI system. The yielded orthophosphate ions are determined spectrophotometrically (lambda(max) = 690 nm) using the molybdenum blue approach. The chemical and FI variables that affected the enzymatic reaction were studied and optimized. A study of interferences was also carried out. The proposed method is very precise (s(r) = 0.7% at 1.0 x 10(-4) mol l(-1) MFP, n = 12), fast (sampling rate of 72 h(-1)) and allows the determination of MFP ions in the range of 4.0 x 10(-5) to 6.0 x 10(-4) mol l(-1) with a satisfactory 3sigma detection limit of 4.0 x 10(-6) mol l(-1). The application of the proposed FI method to toothpaste samples yielded accurate results (e(r) < 2.0%) compared with a potentiometric reference procedure.     

Kinetic methods for the determination of cadmium(II) based on a flow-through bulk optode

Three kinetic methods based on flow injection, flow, and stopped-flow injection were applied for the determination of Cd(II) using a flow-through bulk optode membrane that incorporates 1-(2-pyridylazo)-2-naphtol (PAN) in a plasticized poly(vinyl) chloride membrane entrapped in a cellulose support. The calibration graphs plotting the reflectance at 560 nm versus [Cd(II)](1/2) for the first two methods and versus [Cd(II)] for the third were linear up to 56.2 mg l(-1). The detection limits of the methods were 0.01, 0.06 and 0.8 mg l(-1), respectively. The FI method was selected for application purposes. The variation coefficient of the sensor response for 11.2 mg l(-1) of Cd(II) was +/-0.31 and +/-0.65% between different membranes. The sensor can be readily regenerated with a carrier (acetic-acetate) buffer of pH 4. The FI method was applied to the determination of cadmium in an alloy and in water.     

Determination of oxolinic acid in cow's milk and human urine by means of a single-use phosphorimetric sensor

A single-use phosphorimetric drop plane sensor for the determination of oxolinic acid (OXA) is proposed. The sensor was formed by a 30x16 mm(2) rectangular strip of Mylar type polyester as solid support that contained a circular sensing zone, 6 mm in diameter and 20 mum in thickness, formed by PVC plasticized with tributylphosphate adhered to its surface. When the strip was introduced for 1 hour into a sample solution, the analyte was retained in the sensing zone, making it possible to directly measure the phosphorescence intensity emitted by the OXA in the solid phase, at lambda(exc)=330 nm and lambda(em)=449 nm. The variables that affect the construction of the sensor have been studied, along with the experimental variables that influence the fixation of the analyte in the sensor. The method's detection limit was 0.01 mg l(-1) with an applicable concentration range from 0.04 to 1.50 mg l(-1) and a repeatability of 2.6% at the concentration range of 0.8 mg l(-1). The method was applied to samples of human urine and cows' milk, with recovery percentages ranging between 97.6 and 108.7%.     

Determination of carbohydrazide at trace and subtrace levels

We developed three analytical methods for the determination of carbohydrazide at different concentration levels. One involves the volumetric titration of the analyte with bromate ion and dead-stop end-point detection, and is applicable to concentrations above 10 mg/l., so it can be used for standardizing carbohydrazide solutions. A second, spectrophotometric method is based on the reduction of FE(III) and measurement of the absorbance of the Fe(II)-ferrozine complex, and features an applicability range of 25-700,mug/l. carbohydrazide. The third method uses differential pulse polarography and the oxidation of carbohydrazide in a basic medium at a dropping mercury electrode to determine the analyte. This last method is the most sensitive of the three and also that offering the widest determination range: from 4 to 3000 mug/l. carbohydrazide.     

Evaluation of a reagent-injection flow injection technique for sample background absorption elimination: determination of chloride in cigarettes

The applicability of reagent-injection flow injection (FI) technique in elimination of background absorption was evaluated by using the FI determination of water-soluble chloride in cigarettes, based on the mercury thiocyanate method, as a model. Some parameters of the proposed reagent-injection FI method were optimized and the proposed procedure had a linear range of 0-7.5 mg l(-1) Cl, a detection limit of 0.02 mg l(-1) Cl, a sampling rate of 60 h(-1) and a relative standard deviation of 0.1% at 5 mg l(-1) Cl. Eight cigarette samples were analyzed by this proposed reagent-injection FI method and the referential membrane dialysis FI procedure. The relative errors were <4.3%, and paired t-test shows that there are no significant differences between these two methods. As no dialysis unit was needed, the reagent-injection FI method has much simpler flow system than the existed CFA and FI methods.     

The determination of trace amounts of tin by flow-injection hydride generation atomic-absorption spectrometry with on-line ion-exchange separation and preconcentration

A hydride generation atomic-absorption spectrometric (AAS) method with flow-injection (FI), aimed at developing a practical routine assay for the determination of tin in food digests, is described. In order to modify the sample matrix and to achieve optimized and reproducible conditions for the hydride generation reaction, the analyte is initially converted into its chlorostannate-complex thereby allowing it to be separated and preconcentrated on-line on an incorporated micro-column packed with a strongly basic anion exchanger and subsequently to be eluted by diluted nitric acid under strictly controlled conditions. Optimum acidic conditions for the FI hydride generation AAS system was found to be 0.01-0.05M nitric acid. At a consumption of 2.7-ml sample volume, aspirated by time-based injection, the procedure resulted in an enrichment factor of 3.5 and yielded a detection limit of 0.08 microg/l. (3sigma) at a sampling frequency of 72/hr. The precision was 2.5% rsd at the 10 microg/l. level. Potential interferents, such as Ni(II), Co(II), Zn(II) and Fe(III) could, at a Sn level of 10 microg/l., be tolerated at an excess of 1000 times without impairing the assay, while a 100-1000-fold excess of Cu(II) decreased the signal by 10-15%. Recoveries in the range 94-102% were obtained for canned food sample digests spiked with 10 microg/l. Sn.     

Flame atomic absorption spectrometric determination of chromium(VI) by on-line preconcentration system using a PTFE packed column

A new, sensitive and robust time-based flow injection (FI) method for on-line preconcentration and determination of ultra trace amounts of chromium(VI) by flame atomic absorption spectrometry (FAAS) has been elaborated. The sample is initially mixed on-line with ammonium pyrrolidine dithiocarbamate (APDC) and the Cr(VI)-PDC chelate is absorbed quantitatively on a mini-column packed with polytetrafluoroethylene (PTFE) turnings at a pH range 0.8-1.4. The complex is subsequently eluted with isobutyl methyl ketone (IBMK) and introduced directly into the nebulizer-burner system. The optimized system offered improved performance characteristics, with unlimited lifetime of the proposed column. The enhancement factor was 80, for a 3-min preconcentration time and the sample frequency was 18 h(-1). The calibration curve was linear over the concentration range 1-40 mug l(-1) with a detection limit of c(L)=0.8 mug l(-1) and a relative standard deviation of s(r)=3.2%, at the 20 mug l(-1) level. The proposed method was evaluated by analyzing samples of certified and spiked water, and it was applied to the analysis of natural water samples and sediments.     

Flow and Sequential Injection Manifolds for the Spectrophotometric Determination of Captopril Based on its Oxidation by Fe(III)

 Two new simple and rapid methods are reported for the accurate and precise spectrophotometric determination of captopril (CPL) using flow (FI) and sequential injection (SI) analysis. The methods are based on the fast oxidation of CPL by Fe(III). The produced Fe(II) reacts with 2,2′-dipyridyl-2-pyridylhydrazone (DPPH) in acidic medium to form a colored complex which is monitored spectrophotometrically at 535 nm. Both methods allow the determination of the analyte up to 1000 mg L⁻¹ at a sampling rate of 120 and 60 injections per hour for FI and SI, respectively. The methods are very precise [s _r=0.8 and 1.2% at 500 mg L⁻¹ CPL (n=12) for FI and SI, respectively] and the 3σ detection limits (c _L=4.0 and 7.0 mg L¹, respectively) are quite satisfactory. Their application to a variety of anti-hypertensive commercial pharmaceutical formulations showed excellent results (relative errors, e _r, < ± 1.6% in all cases compared to an official HPLC method), while common pharmaceutical excipients were found not to interfere. Recovery experiments further verified the accuracy of the developed methods, as the percent recoveries were in the range of 98.1–102.5%. Author for correspondence. E-mail: themelis@chem.auth.gr Received May 9, 2002; accepted January 8, 2003 Published online May 5, 2003     

Rapid determination of dissolved organic phosphorus in soil leachates and runoff waters by flow injection analysis with on-line photo-oxidation

A rapid method suitable for the determination of dissolved organic phosphorus (DOP) in soil leachates and runoff waters is presented. The flow injection (FI) manifold contains an in-line PTFE reaction coil wrapped around a low power UV lamp and is based on the spectrophotometric determination of dissolved reactive phosphorus (DRP) and mineralised DOP at 690 nm after reduction of phosphomolybdate to molybdenum blue with tin(II) chloride. The linear range was 0-1.5 mg 1(-1) PO(4)-P, with a detection limit (3 s) of 7 mug 1(-1) and a sample throughput of 40 h(-1). Tolerance to potential matrix interferences in soil pore waters, particularly Al(III), Si(IV), Fe(II) and Fe(III), was achieved using a combination of on-line sample pre-treatment by a strong acid ion exchange column, low photoreactor pH and acid induced control of the kinetics of the molybdenum blue reaction. The results obtained with this manifold were in good agreement with those obtained by a batch spectrophotometric reference method.     

H-point standard addition method for simultaneous determination of Fe(II), Co(II) and Cu(II) in micellar media with simultaneous addition of three analytes

H-point standard addition method, HPSAM, with simultaneous addition of three analytes is proposed for the resolution of ternary mixtures. It is a modification of the previously described H-point standard addition method that permits the resolution of three species from a unique calibration set by making the simultaneous addition of the three analytes. The method calculates the analyte concentration from spectral data at two wavelengths where the two species selected as interferents present the same absorbance relationship. These wavelength pairs are easily found, and can be selected to give the most precise results. Diethyldithiocarbomate (DDC) in a cationic micellar solution of cetyltrimethylammonium bromide (CTAB) was used for determination of Fe(II), Co(II) and Cu(II) at pH 5.50. The results showed that simultaneous determination of Fe(II), Co(II) and Cu(II) could be preformed in the range of 0.0–6.0, 0.0–8.0 and 0.0–12.0 μg ml⁻¹, respectively. The proposed method was successfully applied to the simultaneous determination of Fe(II), Co(II) and Cu(II) in several synthetic mixtures containing different concentration of Fe(II), Co(II) and Cu(II).     

Trace humic and fulvic acid determination in natural water by cloud point extraction/preconcentration using non-ionic and cationic surfactants with FI-UV detection

A preconcentration and determination method for humic and fulvic acids at trace levels in natural water samples was developed. Cloud point extraction was successfully employed for the preconcentration of humic acid (HA) and fulvic acid (FA) prior to the determination by using a flow injection (FI) system coupled to a spectrophotometric UV-Vis detector. The quantitative extraction of HA and FA within the pH range 1-12 was obtained by neutralization of the anionic charge on the humic substances with a cationic surfactant, hexadecyltrimethylammonium bromide (CTAB). This generated a hydrophobic species that was subsequently incorporated (solubilized) into the micelles of a non-ionic surfactant polyethylene glycol, tert-octylphenyl ether (Triton X-114). The FI method for HA and FA determination was developed by injection of 100 microl of the extracted surfactant-rich phase using an HPLC pump with spectrophotometric detection at 350 nm. A 50 ml sample solution preconcentration allowed an enrichment factor of 167. The limit of detection (LOD) obtained under the optimal conditions was 5 microg l(-1). The precision for ten replicate determinations at 0.2 mg l(-1) HA was 3.1% relative standard deviation (RSD), calculated from the peak heights. The calibration using the preconcentration system for HA and FA was linear with a correlation coefficient (r2) of 0.9997 at levels near the detection limits up to at least 1 mg l(-1). The method was successfully applied to the determination of HA and FA in natural water samples (river water).     

Single-use optical sensor for the determination of iron in water and white wines

A new method, based on the use of a disposable sensor, for the determination of Fe(II) in waters and wines is proposed. The sensor is formed by an inert rectangular strip of polyester (Mylar) and a circular film (6 mm in diameter) adhered on its surface. This film, which contains the required reagents for the fixation of the analyte by means of a complexation reaction, forms the sensing zone of the sensor. When the sensor is introduced in an acidified (pH 2.5) sample solution containing between 4.0 and 300.0 micrograms/L of Fe(II), a violet-red colour develops in the initially colourless sensing zone. The linear range of the method depends on the equilibration time of the sensor with the sample solution. Thus, when the equilibration time was 5 min, the linear range was 41.0-300.0 micrograms/L, while for 60 min the range was 4.0-50.0 micrograms/L. Detection and quantification limits were 12.0 and 41.0 micrograms/L, respectively, for an equilibration time of 5 min. The precision of the method, expressed as relative standard deviation of ten samples of 100.0 micrograms/L of Fe(II), was 4.9%. Interferences produced by other species usually present in waters or wines have been studied. Cu(II) and Co(II) interfered seriously at concentration levels higher than 100.0 and 150.0 micrograms/L, respectively. The method was applied to the determination of Fe(II) in different types of waters and wines, using atomic absorption spectrometry as a reference method.     

Flame AAS and UV-VIS determination of cobalt, nickel and palladium using the synergetic effect of 2-benzoylpyridine-2-pyridylhydrazone and thiocyanate ions

A quantitative synergetic extraction procedure for cobalt, nickel and palladium from thiocyanate aqueous solutions into methyl isobutyl ketone (MIBK), containing 2-benzoylpyridine-2-pyridylhydrazone (BPPH), was studied by flame atomic absorption spectrometry (FAAS) and molecular absorption spectrometry (UV-VIS). Using FAAS, linear calibration graphs were obtained from 0.0-0.5 mg l(-1) Co(II), 0.0-1.5 mg l(-1) Ni(II) and 0.0-2.0 mg l(-1) Pd(II). The reproducibilities were s(r,Co(II))=2.0%, s(r,Ni(II))=1.0% and s(r,Pd(II))=1.3% and the limits of detection were c(L,Co(II))=0.004 mg l(-1), c(L,Ni(II))=0.009 mg l(-1) and c(L,Pd(II))=0.012 mg l(-1). Using UV-VIS method the linear calibration graphs were 0.0-0.5 mg l(-1) for Co(II), 0.0-1.0 mg l(-1) for Ni(II) and 0.0-2.0 mg l(-1) for Pd(II). The reproducibilities were s(r,Co(II))=1.3%, s(r,Ni(II))=1.7% and s(r,Pd(II))=1.0% and the limits of detection were c(L,Co(II))=0.001 mg l(-1), c(L,Ni(II))=0.004 mg l(-1) and c(L,Pd(II))=0.002 mg l(-1). The extraction method is almost free from interferences and has been successfully applied to the determination of cobalt, nickel and palladium in dental alloys.     

Rapid and selective method for the spectrophotometric determination of nickel naphthenate in gasoline in a microemulsion

A new method for the spectrophotometric determination of nickel naphthenate in gasoline in a microemulsion was developed. PAN reacts with nickel(II) forming a red complex with composition 1:2 (metal to ligand) nickel(II)-PAN and absorption maximum at 568 nm. Nickel naphthenate in gasoline can be determined with PAN in a microemulsion, in the pH range 3.0 approximately 10.0 with a molar absorptivity of 4.8x10(4) l mol(-1) cm(-1). Beer's law was obeyed up to 0.8 mg l(-1) of nickel(II) in the microemulsion system. The interference of Cu(2+), Fe(3+), Mn(2+), Pb(2+) and Zn(2+) can be eliminated by adding 0.5 ml of a mixed masking agent. The method is rapid, simple and highly selective.     

Determination of lead by on-line solid phase extraction using a PTFE micro-column and flame atomic absorption spectrometry

A rapid and sensitive time-based flow injection (FI) method for on-line preconcentration and determination of lead by flame atomic absorption spectrometry (FAAS), using polytetrafluoroethylene (PTFE) turnings as packing material in a micro-column, has been developed. The sample was mixed on-line with ammonium pyrrolidine dithiocarbamate (APDC) and the non-charged Pb(II)-PDC complex was absorbed quantitatively on the hydrophobic PTFE material, at a pH range 1.4-3.2. The preconcentrated complex was effectively eluted with isobutyl methyl ketone (IBMK) and introduced into the nebulizer-burner system. A nested coil (NC) is proposed for parking the eluate temporarily, in order to enable different elution and nebulization flow rates. With 180 s preconcentration time the sample frequency was 15 h(-1), and the enhancement factor was 330 at 13.0 ml min(-1) sample flow rate. The detection limit was c(L)=0.8 mug l(-1), the relative standard deviation (R.S.D.) 2.6% at the 30 mug l(-1) level and the calibration curve was linear over the concentration range 1.6-100 mug l(-1). The proposed method was evaluated by analyzing certified reference materials of water, sediments and fish tissue. Finally, it was applied successfully to the analysis of various environmental samples.     

A simple flow injection system with bead injection for trace iron determination

A simple and low cost flow injection (FI) system with bead injection (BI) was developed for determination of low concentration (mumol l(-1)) of iron in water samples. Chelex-100 chelating resin beads, trapped in a jet ring cell, were employed. The intensity of red complex of 1,10-phenanthroline with Fe(2+) was monitored using colorimetric detector with a LED green light source. Amount of total Fe (Fe(2+) and Fe(3+)) and Fe(2+) can be evaluated by with and without reduction of Fe(3+) using ascorbic acid. Lowest detectable levels of Fe(2+) were 0.90 and 0.45 mumol l(-1) for sample loading time of 3 and 5 min, respectively. Working range was up to 3.90 mumol l(-1) using 0.3% w/v 1, 10-phenanthroline. Percent recoveries of spiked water samples (0.90-2.33 mumol l(-1) of Fe(2+)) were 100-110%.     

Flame Atomic Absorption Spectrometric Determination of Cu(II), Co(II), Cd(II), Fe(III) and Mn(II) in Ammonium Salts and Industrial Fertilizers after PrEconcentration/Separation on Diaion HP-20

A sensitive and simple separation-enrichment technique for the determination of trace amounts of Cu(II), Co(II), Cd(II), Fe(III) and Mn(II) was described. Metal ions were complexed with 1-nitroso-2-naphthol at pH 9. Following solid-phase extraction on Diaion HP-20 resin, metals were determined by flame atomic absorption spectrometry. The effect of the matrix ions were investigated. The recoveries of metal ions were greater than 95%. The detection limits of the analyte ions ( k = 3, N = 21) were varying 0.18 µg/l for Cd(II) to 0.44 µg/l for Fe(III). The method was applied to a stream sediment standard reference material (GBW7309), some ammonium salts and industrial fertilizer samples for the determination of copper, cobalt, cadmium, iron and manganese. The relative standard deviations (RSD) of the determinations for analyte ions at µg/g levels varied from 1 to 10%.