Simultaneous determination of propacetamol and paracetamol by derivative spectrophotometry

The present paper describes a procedure that phenols in air were preconcentrated in a membrane cell and their content was determined by adsorptive polarography. First, the phenols in air samples were preconcentrated in a membrane cell using 2.0 M NaOH solution, then in a pH 1.3 buffer solution p-bromophenylamine forms a diazoate with NaNO(2), and into the mixture the collected phenols were added to form azo-compound in a pH 13 buffer solution. The azo-compound can be adsorbed at the mercury electrode and yields a sensitive oscillopolarographic wave. Over the range 2.0x10(-8)-2.0x10(-5) M, the peak currents are linearly proportional to the concentration of phenols. The detection limit is 5.0x10(-9) M.     

Preconcentration with chromatomembrane cell and adsorptive polarographic determination of fluorine in air

The present paper describes a procedure in which fluorine in the air was preconcentrated in a chromatomembrane cell and its content was determined by adsorptive polarography. In a pH 4.90 buffer solution the fluorine ion can form a ternary complex with La(III) and ALC. The complex can be adsorbed at the mercury electrode and yields a sensitive oscillopolarographic wave at -0.67 V, which can be sensitized by Triton X-100. Over the range 3.0x10(-8)-1.60x10(-6) M, the peak currents are linearly proportional to the concentration of the fluoride. The detection limit is 1.0x10(-8) M. First the fluorine in the air samples was preconcentrated in the chromatomembrane cells using 0.10 M NaOH solution, then its content was determined by complex-adsorptive polarography.     

Study on the determination of metronidazole in human serum by adsorptive stripping voltammetry

In Britton-Robinson buffer, metronidazole is preconcentrated on a HMDE at 0.0 V (vs. AgAgCl). An adsorptive stripping peak is observed at -0.62 V. The response is linear from 1 x 10(-8) to 1 x 10(-6)M with 1.5 min accumulation. The method has been successfully applied to the determination of metronidazole in human serum and formulations.     

Development of a Passive Sampler for Long-Term Measurements of Formaldehyde and Total Oxidants in Air

A diffusive sampling device is described that is capable of reliable measurements of formaldehyde and total oxidants (Ox = ozone + nitrogen dioxide) at sub-ppbv concentration levels in ambient air. These species are collected on silica gel particles coated with 1-methyl-1-(2,4-dinitrophenyl)hydrazine (MDNPH) and phosphoric acid. The formaldehyde hydrazone (HCHO-MDNPh) and the N-methyl-2,4-dinitroaniline (MDNA) formed are extracted with acetonitrile and determined by HPLC with UV detection at 365ánm. The measured sampling rate for HCHO, 15.0 mLmin^-1, agrees well with the theoretical value of 16.0, whilst an experimental sampling rate of 10.7 mLmin^-1 (25% lower than the calculated one) is observed for Ox. The sampling rates seem to be independent of the sampling duration up to one month. The precision of the measurements for co-located passive samplers averaged is 7.3% for HCHO and 7.2% for Ox in urban air.     

Differential pulse adsorptive stripping voltammetric determination of dinoseb and dinoterb at a modified electrode.

A sensitive adsorptive stripping voltammetric method for the determination of dinitrophenolic herbicides, dinoseb (DSB) and dinoterb (DTB) at a bare carbon paste electrode (CPE) and a clay modified carbon paste electrode (CMCPE) was developed. A systematic study of various experimental conditions, such as the pH, accumulation variables and composition of a modifier on the adsorptive stripping response, were examined by using differential pulse voltammetry. A significant improvement was observed in the sensitivity by using the present method with CMCPE. When CMCPE was used, a linear response was obtained over the concentration range 2 x 10(-10) to 3 x 10(-7) M and 6 x 10(-10) to 6 x 10(-7) M with lower detection limits of 1 x 10(-10) M and 5.4 x 10(-10) M for dinoseb and dinoterb, respectively, at an accumulation time of 100 s. The interference from other herbicides and ions on the stripping signals of both compounds was also evaluated. The described method was applied to estimate of the dinoseb and dinoterb in environmental samples.     

Development of a Highly Sensitive and Selective Bismuth Optical Sensor Based on (2E,4E)-5-(2,4-Dinitrophenyl Amino)penta-2,4-dienal

Abstract

An optical sensor based on (2E,4E)-5-(2,4-dinitrophenyl amino)penta-2,4-dienal as ionophore has been developed for the determination of bismuth(III) ions in aqueous solutions. This proposed membrane works on the basis of a cation-exchange mechanism and shows a significant absorbance signal change on exposure to 1 M HCl solution of pH 0.0 containing bismuth ions. The optode membrane shows a reproducible and reversible response toward bismuth in the concentration range 0.2 to 60.5 ppm with a detection limit of 0.095 ppm. This sensor has been used for determination of bismuth in real samples.     

Anodic stripping voltammetric determination of mercury by use of a sodium montmorillonite-modified carbon-paste electrode

A sodium montmorillonite (SWy-2)-modified carbon-paste electrode has been examined for determination of trace levels of mercury. Because of its strong cation-exchange and adsorptive characteristics, SWy-2 greatly improves the sensitivity of determination of Hg(2+). Hg(2+) is preconcentrated and reduced on the modified electrode surface at -0.40 V and then stripped from the electrode surface during the positive potential sweep. The conditions used for determination, e.g. supporting electrolyte, pH, amount of SWy-2, accumulation potential, and accumulation time, were optimized. The peak current was linearly dependent on the concentration of mercury from 1 x 10(-9) to 5 x 10(-7) mol L(-1). The detection limit (signal-to-noise ratio=3) was 1 x 10(-10) mol L(-1) after accumulation for 6 min. When the SWy-2-modified carbon-paste electrode was used to detect mercury in water samples the average recovery was 101.11%.     

On-line collection/concentration and detection of sulfur dioxide in air by flow-injection spectrophotometry coupled with a chromatomembrane cell.

A simple and rapid procedure for SO2 determination in air was developed by using a flow injection analysis (FIA) system coupled with a 3-hole chromatomembrane cell (CMC). The CMC was applied for the on-line collection/concentration of SO2 from air into a solution of 2 g l(-1) triethanolamine (TEA) solution as an absorbing solution: SO2 was converted to SO3(2-) in the alkaline absorbing solution. The solution containing absorbed SO2 was introduced into the carrier stream of the FIA system. The amount of SO3(2-) in the absorbing solution was measured by spectrophotometry with a mixed reagent of pararosaniline and formaldehyde, and was converted to the concentration of SO2 in the air sample. A calibration graph prepared by using standard sodium sulfite aqueous solutions was adopted for the determination of SO3(2-) in the absorbing solution. The SO2 concentration in indoor air examined was found to be 22.7 +/- 0.2 ppbv using 20 ml of air sample with the air flow rate of 5 ml min(-1), where the relative standard deviation was 1.7%. The detection limit for aqueous solutions and air samples were 6.9 x 10(-8) M and 0.48 ppbv, respectively. The measuring time for one sample was about 10 min when a 20 ml air sample was used. The interferences from common anionic species, formaldehyde and acetaldehyde, were also examined.     

Reactions of bis(2,4-dinitrophenyl) phosphate with hydroxylamine

For dephosphorylation of bis(2,4-dinitrophenyl) phosphate (BDNPP) by hydroxylamine in water, pH region 4-12, the observed first-order rate constant, k(obs), initially increases as a function of pH, but is pH-independent between pH 7.2 and pH 10. The initial BDNPP cleavage by nonionic NH(2)OH (<0.2 M) involves attack by the OH group and follows first-order kinetics, but the overall initial reaction of BDNPP liberates ca. 1.7 mol of 2,4-dinitrophenoxide ion (DNP). This initial reaction generates a short-lived O-phosphorylated hydroxylamine, 2, followed by three possible reactions: (1) reaction of 2 with hydroxylamine, generating 2,4-dinitrophenyl phosphate (DNPP, 3), which subsequently forms DNP; (2) intramolecular displacement of the second DNP group and rapid decomposition of the cyclic intermediate to form phosphonohydroxylamine and eventually inorganic phosphate; (3) a novel rearrangement with intramolecular aromatic nucleophilic substitution involving a cyclic intermediate and migration of the 2,4-dinitrophenyl group from O to N. Values of k(obs) increase modestly with pH > 10, the reaction is biphasic, and the yield of DNP increases. An increase in [NH(2)OH] also increases the yield of DNP, due largely to accelerated hydrolysis of DNPP.     

Reaction of bis(2,4-dinitrophenyl) phosphate with hydrazine and hydrogen peroxide. Comparison of O- and N- phosphorylation

Nonionic hydrazine reacts with anionic bis(2,4-dinitrophenyl) phosphate (BDNPP), giving 2,4-dinitrophenyl hydrazine and dianionic 2,4-dinitrophenyl phosphate by an S(N)2(Ar) reaction, and at the phosphoryl center, giving 2,4-dinitrophenoxide ion and a transient phosphorylated hydrazine that rearranges intramolecularly to N-(2,4-dinitrophenyl)-N-phosphonohydrazine. Approximately 58% of the reaction at pD = 10 occurs by N-phosphorylation, as shown by (31)P NMR spectroscopy. Reaction of HO(2)(-) is wholly at phosphorus, and the intermediate peroxophosphate reacts intramolecularly, displacing a second 2,4-dinitrophenoxide ion, or with H(2)O(2), giving 2,4-dinitrophenyl phosphate and O(2). Rate constants of O- and N-phosphorylation in reactions at phosphorus of NH(2)NH(2), HO(2)(-), and NH(2)OH and its methyl derivatives follow Bronsted relationships with similar slopes, but plots differ for oxygen and nitrogen nucleophiles. The reaction with NH(2)NH(2) has been probed by using both NMR spectroscopy and electrospray ionization mass and tandem mass spectrometry, with the novel interception of key reaction intermediates in the course of reaction.     

Quantification of terbutaline in pharmaceutical formulation and human serum by adsorptive stripping voltammetry at a glassy carbon electrode

The electrochemical oxidative behavior of terbutaline at the glassy carbon electrode was studied in a series of the Britton-Robinson buffer of pH 2--11. Cyclic and square-wave voltammograms of terbutaline at the pH values 相似文献   

Voltammetric measurement of haloperidol following adsorptive accumulation at glassy-carbon electrodes

A sensitive stripping voltammetric method is reported for trace measurement of the psychotherapeutic drug haloperidol. The method is based on adsorptive preconcentration of haloperidol on the glassy-carbon electrode in an open circuit, followed by medium exchange and voltammetric determination of surface species. Cyclic voltammetry was used to explore the adsorptive behaviour and the results obtained suggest that the adsorption of haloperidol corresponds to the Frumkin-type isotherm. The adsorptive stripping response was evaluated with respect to stripping mode, electrolyte. pH, preconcentration time, concentration dependence, possible interference and other variables. The detection limit was 1.3 x 10(-9)M (10 min preconcentration) and the response was linear. The relative standard deviation (at the 1.3 x 10(-6)M level) was 2.3%. Applicability to a patient's urine sample is illustrated.     

Trace measurements of the antineoplastic agent methotrexate by adsorptive stripping voltammetry

An extremely sensitive voltammetric method is presented for trace measurement of the cancer chemotherapy drug methotrexate. The method is based on controlled adsorptive preconcentration of methotrexate on the hanging mercury-drop electrode, followed by voltammetric determination of the surface species. Cyclic voltammetry was used to explore the interfacial behaviour. The adsorptive stripping response was evaluated with respect to preconcentration time and potential, pH, concentration dependence, stripping mode, possible interferences, and other variables. The detection limit found was 2 x 10(-9)M (5-min preconcentration), the response was linear, and the relative standard deviation (at the 1.6 x 10(-7)M level) 2.2%. Sensitive adsorptive stripping measurements were also obtained by use of a carbon-paste disk electrode. Applicability to urine analysis is illustrated.     

Simultaneous determination of HCHO,CH3CHO and O(x) in ambient air by hydrazine reagent and hplc

Formaldehyde, acetaldehyde, ozone and nitrogen dioxide in ambient air are simultaneously collected on silica gel cartridges coated with 1-methyl-1-(2,4-dinitrophenyl)hydrazine (MDNPH), where the two aldehydes are derivatized to their respective hydrazones, while the two oxidants are converted into N-methyl-2,4-dinitroaniline (MDNA). The three products are then separated and quantified by HPLC with UV detection at 360 nm. The stoichiometric factors of the MDNPH reactions with O3 and NO2 in laboratory tests correspond to 2.0 +/- 0.1 moles of MDNA per mole of O(x) (O3 + NO2). The limits of detection (LOD) are 0.7 ppbv HCHO, 0.8 ppbv CH3CHO and 1.6 ppbv O(x) for 30 L (1 h) air sampled. The sampling performance is insensitive to relative humidities encountered in real atmospheres. When compared with Sep-Pak DNPH silica cartridges as well as with ozone photometric and nitrogen dioxide chemiluminescent analyzers, the proposed chromatographic method demonstrates a very good accuracy (12% for HCHO, 14% for CH3CHO and 7% for O(x), on the average) under field sampling conditions at concentrations lower than 3 and 1 ppbv, for HCHO and CH3CHO, respectively and ranging from 28 to 62 ppbv for O(x).     

Analytical utility of coupled transport across a supported liquid membrane Selective preconcentration of zinc

A liquid membrane comprising 5-10% bis(2,4,4-trimethylpentyl)phosphinic acid in dodecane that is supported between an aqueous sample at pH 4.7-6.0 and a 0.1M HCl receiver results in uphill transport of Zn(II) from the sample into the receiver. With 2 ml of receiver, a 5 cm(2) membrane and 60 min dialysis time, Zn(II) is preconcentrated by a factor of ca. 13 when the initial concentration in the sample is in the range 1.5 x 10(-7)-1.5 x 10(-4)M. The enrichment factor is directly proportional to time up to 30 min since the transport rate of Zn(II) across the membrane is constant over this period. At longer times the flux is slowed as the system begins to approach equilibrium. The presence of other metals such as Cu(II), Co(II), Ni(II), Cd(II), Pb(II) and Fe(II) does not change the enrichment factor for Zn(II), even when the interferent is at a concentration high enough for the rate of transport (nmole/min) of the interferent and Zn(II) to be about the same. The flux of Zn(II) was about 40 times that of Cu(II) and 100 times that of Co(II) when their concentrations in the sample were equal. The other metal ions examined are not significantly transported.     

Using 2,4 DNPH-PVC membrane sensors for indirect determination of formaldehyde in urea glue and wastewater

Three simple, rapid, and sensitive ion-selective electrodes for indirect determination of free formaldehyde in urea glue and wastewater have been developed. The methods are based on the formation of the membrane sensors 2,4-dinitrophenylhydrazine-phosphtungestic acid (DNPH-PTA), 2,4-dinitrophenylhydrazine-phosphomolybdic acid (DNPH-PMA), and 2,4-dinitrophenylhydrazine-tetraphenylborate (DNPH-TPB) as neutral carriers. The sensors are stable and show fast potential responses of 30?s, and near-Nernstian cationic slopes of 56.2?±?0.5, 54.3?±?0.5, and 53.8?±?0.4?mV per decade of activity between pH 0.5 and 3.5 over a wide range of 2,4-dinitrophenylhydrazine concentrations (1?×?10^?5 to 1?×?10^?2?M). These sensors were used for indirect determination of formaldehyde over concentration range (1?×?10^?4 to 1?×?10^?1?M). The selectivity coefficients of the developed sensors indicate excellent selectivity for 2,4 DNPH over a large number of organic and inorganic species. The mediator o-nitrophenyloctyl ether has a significant affect on the lifetime of the fabricated sensors. The analytical applications of the proposed sensors showed good results for indirect determination of formaldehyde in formaldehyde solutions, wastewater solutions, and free formaldehyde in urea-formaldehyde liquid and powder glues. The results were compared favourably with that obtained by ASTM, colorimetric, and British Standard methods.     

Trace measurements of colchicine by adsorptive stripping voltammetry

A highly sensitive voltammetric method for trace measurements of the alkaloid colchicine is described. The method is based on the controlled adsorptive accumulation of the drug at the hanging mercury drop electrode, followed by voltammetric determination of the surface species. The adsorptive stripping response is evaluated with respect to preconcentration time and potential, solution pH, voltammetric waveform and other variables. With a 10-min preconcentration, a detection limit of 1.3 x 10(-10)M is obtained. The relative standard deviation (at the 1 x 10(-7)M level) is 1.1%. Applicability to urine analysis is illustrated.     

An Abnormal Reaction of N-(2,4-dinitrophenyl)-L-proline with Thionyl Chloride

N-(2,4-Dinitrophenyl)-4-amino-n-butyl aldehyde 3 was obtained with high yield of 80% when N-(2,4-dinitrophenyl)-L-proline 1 reacted with SOCl2 at room temperature,However,the anticipated product N-(2,4-dinitrophenyl)-Tetrahydropyrrolyl-2-(4-methylthiophenyl)ketone 2 did not be produced.The mechanism was discussed in this article.     

Electrochemical adsorptive behavior of some fluoroquinolones at carbon paste electrode.

Cyclic voltammetry and differential pulse voltammetry were used to explore the adsorption behavior of three antibacterial agents at a carbon paste electrode. The drugs were accumulated on a carbon paste electrode, and a well-defined oxidation peak was obtained in acetate buffer (pH 5.0). The adsorptive stripping response was evaluated as a function of some variables such as the scan rate, pH and accumulation time. A simple, precise, inexpensive and sensitive voltammetric method has been developed for the determination of the cited drugs (Lomefloxacin (LFX), Sparfloxacin hydrochloride (SFX), and Gatifloxacin (GFX)). A linear calibration was obtained from 2 x 10(-7) M to 4 x 10(-5) M for LFX, 2 x 10(-7) M to 6 x 10(-5) M for SFX, and GFX. The limits of detection (LOD) were 4.2 x 10(-7), 7 x 10(-7) and 6.6 x 10(-7) M, while the limits of quantification (LOQ) were 1.4 x 10(-6), 2.3 x 10(-6) and 2.2 x 10(-6) M for LFX, SFX, and GFX, respectively. The R. S. D. of five measurements at the 1 x 10(-6) M level were 0.4, 0.5 and 0.3 for LFX, SFX and GFX, respectively. The method was applied to the determination of LFX, SFX and GFX in dilute urine samples and dosage forms, and compared with the HPLC method.     

Adsorptive voltammetric behaviour of immunoglobulin M

The adsorptive voltammetric behaviour of immunoglobulin M (IgM) has been investigated at the static mercury drop electrode. The stripping process yields an analytically useful signal and the detection limit is 1.2 x 10(-10)M. The adsorptive voltammetric behaviour of IgM has been compared with that of IgG and streptavidin.