Potentiometric titration of polyhexamethylene biguanide hydrochloride with potassium poly(vinyl sulfate) solution using a cationic surfactant-selective electrode.

A potentiometric titration method using a cationic surfactant as an indicator cation and a plasticized poly(vinyl chloride) membrane electrode sensitive to the cationic surfactant is proposed for the determination of polyhexamethylene biguanide hydrochloride (PHMB-HCl), which is a cationic polyelectrolyte. A sample solution of PHMB-HCl containing an indicator cation (hexadecyltrimethylammonium ion, HTA) was titrated with a standard solution of an anionic polyelectrolyte, potassium poly(vinyl sulfate) (PVSK). The end-point was detected as a sharp potential change due to an abrupt decrease in the concentration of the indicator cation, HTA, which is caused by its association with PVSK. The effects of the concentrations of HTA ion and coexisting electrolytes in the sample solution on the degree of the potential change at the end-point were examined. A linear relationship between the concentration of PHMB-HCl and the end-point volume of the titrant exists in the concentration range from 2.0 x 10(-5) to 4.0 x 10(-4) M in the case that the concentration of HTA is 1.0 x 10(-5) M, and that from 1.0 x 10(-6) to 1.2 x 10(-5) M in the case that the concentration of HTA is 5.0 x 10(-6) M, respectively. The proposed method was applied to the determination of PHMB-HCl in some contact-lens detergents.     

Complex formation constants for the aqueous copper(I)-acetonitrile system by a simple general method

A simple spectrophotometric method for the evaluation of formation constants for aqueous copper(I) has been developed, based on the kinetics of reduction of Co(III)(NH(3))(5)X complexes. The method has been applied to the aqueous copper(I)-acetonitrile system to determine the successive formation constants beta(1), beta(2), and beta(3) as 4.3 x 10(2) M(-)(1), 1.0 x 10(4) M(-)(2), and 2.0 x 10(4) M(-)(3), respectively, in 0.14 M NaClO(4)/HClO(4) at 21 +/- 1 degrees C.     

Anion selective polymeric membrane electrodes based on cyclopalladated amine complexes

The potentiometric anion selectivity of two polymer membrane based electrodes (I and II) formulated with two new cyclopalladated amine complexes as the active components are examined. The electrodes exhibit a non-Hofmeister selectivity pattern with a significantly enhanced response towards thiocyanate, iodide and nitrite. The graph potential versus log c is linear over the concentration range 10(-6)-6x10(-2) M thiocyanate with electrode I and 10(-6)-10(-3) M with electrode II; 10(-5)-10(-2) M iodide with electrode I and 10(-3)-6x10(-2) M with electrode II; and 10(-3)-6x10(-2) M nitrite with both electrodes. The influence of the plasticizer and pH are studied. The potentiometric selectivity coefficients for I, II and blank membrane electrodes are reported. The selective interaction between Pd(II) thiocyanate, iodide and nitrite is postulated to be the reason for its higher response.     

A 9,10-anthraquinone derivative having two propenyl arms as a neutral ionophore for highly selective and sensitive membrane sensors for copper(II) ion.

New polymeric membrane (PME) and coated graphite (CGE) copper(II)-selective electrodes based on 1-hydroxy-2-(prop-2'-enyl)-4-(prop-2'-enyloxy)-9,10-anthraquinone were prepared. The electrodes reveal linear emf-pCu2+ responses over wide concentration ranges (1.0 x 10(-5)-1.0 x 10(-1) M with a slope of 27.3 mV decade-1 for PME and 8.0 x 10(-8)-5.0 x 10(-2) M with a slope of 29.1 mV decade-1 for CGE) and very low limits of detection (8.0 x 10(-6) M for PME and 5.0 x 10(-8) M for CGE). The potentiometric response is independent of the pH of the test solution in the pH range 3.0-6.0. The proposed electrodes possess very good selectivities over a wide variety of other cations, including alkali, alkaline earth, transition and heavy metal ions, the selectivity coefficients for the CGE being much improved over those for the PME. The electrodes were used as indicator electrodes in the potentiometric titration of Cu2+ and in the recovery of copper ions from wastewater.     

Highly sensitive chemiluminescence detection of copper(II) in capillary electrophoresis with field-amplified sample injection

Field-amplified sample injection of copper(II) was investigated using capillary electrophoresis with chemiluminescence detection. The sensitivity of copper(II) has been improved markedly by the field-amplified sample injection technique and the detection limit reaches 2 x 10(-11) M. By injection of a short plug of water before sample introduction, the sensitivity can be further improved 5-fold and the detection limit reaches 4 x 10(-12) M. The relative standard deviations (n = 6) of the migration time and the peak height are 0.61% and 4.7% at 1.0 x 10(-9) M Cu(II), respectively. Parameters affecting the field-amplified sample injection, such as separation voltage and concentration of electrophoretic buffer, have been investigated.     

Determination of copper with neocuproine by thermal-lens spectrometry

Conditions for the spectrophotometric determination of copper with 2,9-dimethyl-l,10-phenan-throline (neocuproine) in the presence of ascorbic acid in a water-ethanol solution (9 : 1) at pH 4.5–5.0 have been found. The detection limit is 3 x 10^-6 M. The concentration range is from 4.4 x 10^-6 to 3 x 10^-4 M. Conditions for the determination of copper(I) with neocuproine by thermal lens spectrometry have been proposed. The detection limit is 4 x 10^-7 M. The concentration range is from 7 x 10^-7 to 6 x 10^-5 M. Iron(II) at concentrations as high asn x 10^-4 M does not interfere with the determination of copper. Changes in the conditions for the photometric reaction associated with passing from spectrophotometric measurements to thermal lensing are discussed.     

Capillary electrophoretic determination of phosphate based on the formation of a Keggin-type [PMo12O40]3- complex.

Based on the formation of a Keggin-type [PMo12O40]3- complex, a sensitive capillary electrophoresis (CE) method was developed for the determination of P(V) with direct UV detection at 220 nm. A mixture of alpha- and beta-Keggin-type [PMo12O40]3- complexes was readily formed in a sample solution consisting of a trace amount of P(V), 2.5 mM Mo(VI), 0.050 M p-C6H3(CH3)-2-SO3H (XSA), and 60% v/v CH3CN. When a 0.05 M HCl and 60% v/v CH3CN solution was used as a migration electrolyte, the Keggin complexes exhibited a sharp and well-defined peak in the electropherogram. The peak area was linearly dependent on the P(V) concentration in the range of 5 x 10(-7)-5 x 10(-5) M; a detection limit of 1 x 10(-7) M was achieved. In comparison with indirect UV detection, the direct UV detection is about ten times more sensitive, because the Keggin complexes possess high molar absorptivities. The developed CE method was applied to the determination of P(V) in river water, and the results were in good agreement with those obtained by ion chromatography (IC) and colorimetry (COL) based on the formation of mixed-valence heteropoly blue species.     

Tetrabenzyl pyrophosphate as a new class of neutral carrier responsive to lead ion

Tetrabenzyl pyrophosphate and diphenylphosphinic anhydride, with two phosphoryl groups (PO) as ligating sites, can be used as novel ionophores to make Pb(2+)-selective membrane electrodes. A good result was obtained with tetrabenzyl pyrophosphate, and the electrode based on this ionophore and bis(1-butylpentyl) adipate as a solvent mediator in a poly(vinyl chloride) membrane matrix exhibited a near-Nernstian response to Pb(2+) in the concentration range of 1x10(-5)-1x10(-2) M with a slope of 28.7 mV per concentration decade in a solution containing 0.1 M Mg(NO(3))(2). The limit of detection was 3x10(-6) M. The selectivity of this electrode to other metal cations was comparable to the best case in many Pb(2+)-selective electrodes so far developed. Addition of potassium tetrakis(p-chlorophenyl)borate (40 mol% relative to tetrabenzyl pyrophosphate) caused a drastic change in the response slope (53.3 mV per concentration decade), probably due to the formation of PbA(+), where A stands for anions present in the sample solution, and decreased significantly the electrode selectivity to other metal cations.     

Photochemistry of neutral isonitrile gold(I) complexes: modulation of photoreactivity by aurophilicity and pi-acceptance ability

This work demonstrates for the first time that aurophilicity and ligand pi-acceptance ability sensitize the photoreactivity of Au(I) complexes. Photolysis of LAu(I)Cl (L = RNC or CO) complexes leads to free L, Au(III), and Au(0) photoproducts. Solutions of (p-tosyl)CH(2)NCAuCl in dichloromethane undergo significant oligomerization leading to dimers and trimers with formation constants of 1.61 x 10(3) and 6.61 x 10(3) M(-1), respectively, representing the highest values reported to date for complexes that exhibit aurophilic association in solution. The photoproduct quantum yield (Phi) varies with the LAu(I)Cl concentration in solution. For (p-tosyl)CH(2)NCAuCl, metallic gold forms with Phi = 0.0065 and 0.032 in 4.0 x 10(-5) and 4.0 x 10(-3) M dichloromethane solutions, respectively. Meanwhile, irradiation of t-BuNCAuCl primarily produces t-BuNCAuCl(3) with Phi = 0.0045 and 0.013 for 5.0 x 10(-5) and 5.0 x 10(-3) M dichloromethane solutions, respectively. For Au(CO)Cl, metallic gold forms with Phi = 0.013 and 0.065 upon irradiation of 8.0 x 10(-5) and 8.0 x 10(-3) M dichloromethane solutions, respectively. Hence, *[LAuX](n) oligomeric species are more photoreactive than monomeric species. The results also demonstrate intuitive control of Phi via modulation of the pi-acceptance ability of L, as both follow CO > (p-tosyl)CH(2)NC > (alkyl)NC in LAuCl, a trend that is also commensurate with the relative long-term photosensitivity of the corresponding solids and solutions. A new method for preparing stable small gold nanoparticles is described based on the fundamental findings above. Thus, photolysis of different concentrations of LAuX in solutions containing a primary amine-terminated dendrimer leads to clear solutions exhibiting tunable visible plasmon absorptions of gold nanoparticles; these solutions maintain their colors and stability indefinitely. TEM measurements for representative samples prepared by photolysis of (p-tosyl)CH(2)NCAuCl solutions give rise to spherical nanoparticles as small as 5 nm.     

Spectrophotometric determination of a nanomolar amount of ascorbic acid using its catalytic effect on copper(II) porphyrin formation

A simple, fast and sensitive flow-injection method is proposed for the determination of nanomolar amounts of ascorbic acid in tea, urine and blood. The procedure is based on the accelerating effect of a nanomolar level of ascorbic acid on the reaction of cooper(II) with 5,10,15,20-tetrakis(1-methylpyridinium-4-yl)porphyrin, H(2)tmpyp(4+). Ascorbic acid reduces Cu(II) to Cu(I) which catalyzes the incorporation of Cu(II) into H(2)tmpyp(4+) to form Cu(II)(tmpyp)(4+). In this method two solutions, one containing ascorbic acid and H(2)tmpyp(4+) and the other containing copper(II) and acetate buffer (pH 5.0), were injected into two flowing streams of water through two sample injectors of 120 mu1 sample volume. The mixture was allowed to react in a 2 m reaction coil and the colored solution of Cu(II)(tmpyp)(4+) was monitored at 550 nm (epsilon = 2.01 x 10(4)M(-1)cm(-1)). The present method was applied to the determination of ascorbic acid in tea, urea and blood. Reducing agents such as sugars and vitamins B(1), B(2), B(6) and B(12) did not give serious errors at a concentration of 10(-6) M for the determination of 1.0 x 10(-8)M ascrobic acid. The relative standard deviation of the present method was 2.8% for the determination of 1.0 x 10(-8)M ascorbic acid. The reaction mechanism was clarified from the kinetic results of the formation of Cu(II)(tmpyp)(4+) in the presence of various concentrations of ascorbic acid, copper(II) and hydrogen ion.     

Fabrication of herbicide biosensors based on the inhibition of enzyme activity that catalyzes the scavenging of hydrogen peroxide in a thylakoid membrane.

A novel herbicide biosensor with a thylakoid modified membrane electrode is presented. Thylakoid, isolated from spinach leaves, was entrapped in a membrane of poly (vinylalcohol) with the styrylpyridinium group (PVA-SbQ). The thylakoid membrane was fixed on the surface of a platinum electrode. It was found that the enzymes in thylakoid kept their activity for several months in the membrane. The oxidative current of hydrogen peroxide in a Tris-HCl buffer solution (pH 7.4) was detected at the modified electrode by a differential pulse voltammetric method. In the presence of herbicides, the oxidation current from the hydrogen peroxide decreased due to an inhibitor effect on the enzymes in thylakoid compared with that in the absence of the herbicides. The changes in the oxidation current at the electrode were proportional to the herbicide concentrations. The sensor could be used to detect herbicides in concentration ranges of 3 x 10(-9) - 1.5 x 10(-7) M for paraquat, 1 x 10(-8) - 3 x 10(-7) M for diuron, 4 x 10(-8) - 3 x 10(-6) M for prometryn, 5 x 10(-8) - 5 x 10(-6) M for atrazine and 1 x 10(-7) - 5 x 10(-6) M for ametryn, respectively. The enzyme activity on scavenging hydrogen peroxide in the modified PVA-SbQ membrane was examined.     

A contribution to the use of chelating agents in anodic stripping voltammetry

The E(p)/(2), values of the ions Pb(2+), Bi(3+), Cu(2+), Cd(2+), Tl(+) were determined by means of cyclic voltammetry in solutions of acetate and Britton-Robinson buffers and in solutions containing EDTA and DCTA. DCTA was then utilized in the determination of small amounts of bismuth, down to 10(-7)M, in the presence of 10(4) times as much lead, and of traces of thallium down to 5 x 10(-9)M in the presence of 2 x 10(5) times as much cadmium by anodic stripping voltammetry. The precision was good. Further, the trace copper concentration in analytical grade DCTA was determined. A new flow-through vessel for stripping analysis with solution exchange is also described and the reproducibility of results without solution exchange, with manual solution exchange, and with the flow-through vessel is evaluated for a model determination of thallium in a DCTA solution.     

Construction and performance characteristics of new tetramisole selective plastic membrane electrodes

New tetramisole (Tm) ion selective PVC membrane electrodes are constructed based on either the ion-pair complex Tm TPB (Electrode I) where TPB is tetraphenylborate or the ion associate Tm(3) PT (Electrode II) where PT is phosphotungstate. The rectilinear concentration ranges of Electrodes I and II are 4 x 10(-5)-10(-2)M (average slope = 55.7 mV/concentration decade) and 5 x 10(-5)-10(-2)M TmCl (average slope = 57.0 mV/concentration decade), at 25 degrees C, respectively. The life time of the two Electrodes I and II are 14 and 49 days of continuous working, respectively. The change in pH does not affect the electrodes performance within the range 3.0-5.5, 3.0-6.0 and 3.0-7.0 for Tm concentrations 10(-2) 5 x 10(-3) and 10(-3)M, respectively. The isothermal coefficients of Electrodes I and II are found to be 0.000667 and 0.001164 V/ degrees C, respectively. The electrodes proved to be highly selective for TmCl towards inorganic cations, sugars and amino acids. The standard addition method and potentiometric titration are used to determine Tm in pure solutions and in tetramisole 10% oral solution. Regeneration process for the exhausted Electrodes I and II is applied successfully by soaking them in a solution of NaTPB and PTA, respectively.     

Preconcentration of iron (III), cobalt (II) and copper (II) nitroso-R complexes on tetradecyldimethylbenzylammonium iodide-naphthalene adsorbent

Iron, cobalt and copper form coloured water soluble anionic complexes with disodium 1-nitroso-2-naphthol-3-6-disulphonate (nitroso R-salt). The anionic complex is retained quantitatively as a water insoluble neutral ion associated complex (M-nitroso R-TDBA) on tetradecyldimethylbenzylammonium iodide on naphthalene (TDBA(+)I(-)-naphthalene) packed column in the pH range of: Fe(III): 3.1-6.5, Co: 3.4-8.5 and Cu 5.9-8.0 when their solutions are passed individually over this adsorbent at a flow rate of 0.5-5.0 ml/min. The solid mass consisting of an ion associated metal complex along with naphthalene is dissolved out of the column with 5 ml dimethylformamide/chloroform and metals are determined spectrophotometrically. The absorbance is measured at 710 nm for iron, 425 nm for cobalt and 480 nm for copper. Beers law is obeyed in the concentration range 9.2-82 mug of iron, 425 nm for cobalt cobalt and 3.0-62 mug of copper in 5 ml of final DMF/CHCl(3) solution. The molar absorptivities are calculated to be Fe: 7.58 x 10(3), Co: 1.33 x 10(4) and Cu: 4.92 x 10(4)M(-1)cm(-1). Ten replicate determinations containing 25 mug of iron, 9.96 mug of cobalt and 3.17 mug of copper gave mean absorbances 0.677, 0.450 and 0.490 with relative standard deviations of 0.88, 0.98 and 0.92%, respectively. The interference of large number of metals and anions on the estimations of these metals has been studied. The optimized conditions so developed have been employed for the trace determination of these metals in standard alloys, waste water and fly ash samples.     

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.     

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.     

New plastic membrane and carbon paste ion selective electrodes for the determination of triprolidine.

Triprolidine (Trip) ion selective electrodes of three types: the conventional polymer membrane (I), graphite coated electrode (II) and carbon paste electrode (III), have been prepared, based on the ion pair of triprolidine hydrochloride with sodium tetraphenylborate. The electrodes exhibit a linear response with a mean calibration graph slope of 56.12, 55.00 and 54.32 mV decade(-1) at 25 degrees C for I, II and III, respectively, within the concentration ranges 1.96 x 10(-5) - 1.00 x 10(-2) M for I and 3.84 x 10(-5) - 1.00 x 10(-2) M for II and III. The detection limits are 1.13+/-0.13 x 10(-5), 1.70+/-0.06 x 10(-5) and 1.78+/-0.05 x 10(-5) M for the three electrodes, respectively. The change of pH within the ranges 4.85 - 8.75 and 4.70 - 8.50 for I and III, respectively, did not affect the electrode performance. The standard electrode potentials were determined at different temperatures and were used to calculate the isothermal coefficient of the electrode. The electrodes showed a very good selectivity for Trip with respect to a large number of inorganic cations and compounds. The standard addition method was applied to the determination of TripCl in pure solution, pharmaceutical preparations, and urine samples.     

Evaluation of coupled transport across a liquid membrane as an analytical preconcentration technique

When two aqueous solutions are separated by a liquid membrane that contains a complexing agent which is a conjugate base of a weak acid, a metal ion can be transported from the solution of the higher pH against its concentration gradient into the more acidic solution. With Cu(II) as the analyte and a liquid membrane consisting of a mixture of oximes dissolved in kerosene, enrichment factors for a prescribed dialysis time in a simple experimental apparatus were nearly independent of Cu(II) concentration over the range 10(-4)-10(-7)M. With 0.1M hydrochloric acid as the receiver, the enrichment factor was independent of ionic strength and of sample pH in the range 4-9. The effect of sample pH on the interference of Fe(III) was examined. With a pH-2.5 formate buffer, the enrichment factor for Cu(II) decreased as the Fe(III) concentration increased, but in a pH-9.3 ammonium buffer, 0.14 mM Fe(III) did not interfere with the transport of Cu(II) from a 16muM copper sample.     

High-resolution determination of H+ by ion chromatography. Application to the simultaneous determination of H+, Na+, NH4+ and K+ in acid rain.

An ion chromatographic (IC) method was developed for the high-resolution determination of a sample's free hydrogen ion concentration (H+). Highly purified lithium dodecyl sulfate was used as the stationary phase, a slightly acidified aqueous LiCl solution was used as the mobile phase and conductivity was used for analyte detection. An electrical double layer (EDL) containing H+ was established on the stationary phase by using a slightly acidified electrolyte solution as the eluent. H+ in the EDL protonated any weak acid groups (i.e., silanols) on the stationary phase so that H+ from the sample could be retained/separated purely by dodecyl sulfate. The optimum molar ratio of H+:Li+ in the EDL for this IC system was obtained by using an aqueous solution containing 40.0 mM LiCl and 0.07 mM H2SO4 as the eluent. After separation, H+ was detected by direct conductimetric measurement. An H+ detection limit of better than 8.2 x 10(-6) M was obtained from the analysis of standard aqueous H2SO4 solutions. Other monovalent cations could also be separated with this method, giving detection limits of 7.4 x 10(-5), 4.3 x 10(-5) and 4.2 x 10(-5) M for Na+, NH4+ and K+, respectively. The method was applied to the simultaneous determination of H+, Na+, NH4+ and K+ in acid rain. The results obtained showed a significant improvement in reproducibility when compared with those from a conventional pH-meter. Acid rain samples with a pH < 5 could be analyzed with this IC system.     

Biosensor based on paraffin/graphite modified with sweet potato tissue for the determination of hydroquinone in cosmetic cream in organic phase

An organic-phase biosensor based on paraffin/graphite modified with sweet potato (Ipomoea batatas (L.) Lam.) tissue as the source of peroxidase was developed and used for determining hydroquinone in cosmetic creams. This enzyme in the presence of hydrogen peroxide catalyses the oxidation of hydroquinone to p-quinone which electrochemical reduction back to hydroquinone was obtained at a peak potential of -0.22 V. The recovery of hydroquinone from two samples ranged from 99.1 to 104.1% and a rectilinear analytical curve for hydroquinone concentration from 7.5x10(-5) to 1.6x10(-3) M (r=0.9991) were obtained. The detection limit was 8.1x10(-6) M and relative standard deviation was <1.0% for a solution containing 7.3x10(-4) M hydroquinone and 1.0x10(-3) M hydrogen peroxide in 0.10 M tetrabutylammonium bromide methanol-phosphate buffer solution (95:5% v/v) (n=10). The results obtained for hydroquinone in cosmetic creams using the proposed biosensor are in close agreement with those obtained using a Pharmacopoeia procedure at the 95% confidence level.