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.     

Selective determination of thiamine (vitamin B(1)) in pharmaceutical preparations by direct potentiometric argentometric titration with use of the silver-silver sulphide ion-selective electrode

A simple and selective argentometric titration method is described for determination of thiamine (vitamin B(1)), based on direct potentiometric titration in alkaline media (0.5M) in which a chemical transformation takes place, creating two acidic groups, the protons of which are replaceable by silver ions. The acidimetric and argentometric potentiometric titration curves display two consecutive potential breaks specific for thiamine. The second break is reproducible and corresponds to a 2:1 reaction ratio of silver to thiamine. No interference is caused by other vitamins, active ingredients and inactive excipients normally present in multivitamin preparations. The results obtained for determination of thiamine in pure powders, pharmaceutical tablets and ampoules showed an average recovery of 98.2% of the nominal values and a mean standard deviation of 0.5%, and agreed fairly well with data obtained by the British Pharmacopoeia procedure.     

Qualitative and quantitative analysis of mixtures of sulfonamides VIII

The quantitative analysis of mixtures of sulfonamides by means of the acidimetric and argentometric titration of the -SO₂NH-group and by means of various determinations of the aromatic -NH₂-group and the amidic -NH-R-group is discussed. The acidimetric titration of the -SO₂NH-group (in two different performances) proved to be well suited. The argentometric titration is acceptable, though less universally applicable.     

Simple instrument for titrimetry without visual indicators. Gasometric titrations: Argentometry

Several argentometric determinations have been worked out to show that the gasometric titration method is applicable not only to acid-base and redox reactions, but also to precipitation and complex-formation reactions. The processes reported allow the direct and indirect determination of iodide and cyanide, as well as the direct titration of silver ion in soluble and slightly soluble silver salts.     

Analysis of polyhexamethylene biguanide in multipurpose contact lens solutions

The objective of this study was to establish a reasonably simple and reliable method to measure very low concentrations of polyhexamethylene biguanide (PHMB) in multipurpose contact lens solutions (MPSs). By using a weak cation exchange solid phase extraction cartridge to extract the PHMB from MPS, followed by HPLC analysis using an evaporative light scattering detector, low levels (0.1 ppm) of PHMB were detected. Application of this method to a series of off-the-shelf MPS with PHMB as the active ingredient demonstrated these solutions contain 1 ppm. The contact lens solution with hydrogen peroxide as the active ingredient gave no peak where the PHMB peak eluted. The Polyquad^® contact lens solution generated a peak close to the retention time of PHMB. Recovery of PHMB from fortified hydrogen peroxide contact lens solution was good at 0.25 ppm and above; 105% with a RSD of 17% or less. The repeatability of the HPLC system ranged from 4 to 11% RSD; the reproducibility of the entire method was less than 17.5% RSD. Storage and stability studies indicated that storage of MPS with PHMB for chemical analysis are not temperature dependent, but are affected by the composition of the container in which the contact lens solution is stored.     

Identification of isothiocyanates (Mustard oils) and liquid primary amines via the formation of 1-substituted 2-tetrazoline-5-thione

The oscillometric method is suggested for the determination of alkali salts of organic acids in non-aqueous media. In the titrations of organic sodium and potassium salts the influence of water content and dielectric constant of non-aqueous solvents on the slopes of the titration curves was investigated. Errors obtained were in the range of±0.6 to 1.5%.     

非水滴定和傅立叶红外光谱在聚丙烯马来酸酐接枝物表征中的应用

采用非水滴定法中的无机碱直接滴定方法测定了马来酸酐在聚丙烯上的接枝率,并对该方法作了可行性验证,讨论了非水滴定中的两个难点：化学计量比的确定和滴定终点的判断。通过傅立叶红外光谱法(FTIR)对聚丙烯马来酸酐接枝物的纯化效果、自由基引发反应对非水滴定的影响及聚丙烯接枝马来酸酐的反应机理作了定性分析,并结合非水滴定的数据绘制了红外定量校准曲线。     

Effect of Structure on Titration Curves of p-Bromoaniline-Formaldehyde-p-Cresol Copolymers in Nonaqueous Media

Copolymers obtained by the condensation of p-bromoaniline, formaldehyde, and p-cresol have been separated into five fractions by a fractional precipitation method. Some of these copolymers showed characteristic titration curves in non-aqueous media. The titration curves indicated a series of breaks which bear integral relations to each other. These features have been interpreted in terms of homoconjugation, intramolecular hydrogen bonding, and composition of the copolymers.     

Thermal decomposition of the biguanide complexes of the 3d-transition metals

The thermal decomposition (TG, DTG and DTA) of the complexes of biguanide with the following metals was studied: V, Cr, Mn, Co, Ni, Cu and Zn. Structural water, when present, is first eliminated at ～100–150°C; this is followed by a main decomposition state at ～300–350°C. Pyrolytic residues are analysed and characterised by their x-ray powder diffraction patterns and are found to be the oxides V₂O₅, Cr₂O₃, Mn₃O₄, Co₃O₄, NiO, CuO and ZnO, respectively. The decomposition curves of the free ligand (biguanide) and biguanide sulphate are also given. The decomposition characteristics are discussed.     

Alkalimetric determination of amoxycillin trihydrate in non-aqueous medium

A simple method for determination of amoxycillin by non-aqueous titration in dimethylformamide medium is described. The relative standard deviation is 0.3%.     

非水光度滴定法测定钢中低碳

研究了非水滴定定碳法中非水吸收液的组成、指示剂的配比及滴定终点时溶液色泽的吸光度变化。结果表明,由乙醇、乙醇胺及不饱和多胺组成的非水体系对钢样燃烧时所释出的二氧化碳能最有效的吸收。试验选择了百里酚酞和茜素黄R的混合液为滴定指示剂,能给出敏锐的终点指示。在此基础上设计了一套非水定碳的自动分析装置。无论自动仪器或手工操作所得的分析结果都与标准值符合。方法应用于低含量碳的测定。     

A combination of synchronous fluorescence spectroscopy with chemometric treatment and internal standards in non-aqueous potentiometric titrations of fulvic acids

The acid properties of a soil fulvic acid (sfua) were characterized by potentiometric titration with tetrabutylammonium hydroxide in two non-aqueous solvents with high acid—base resolution power N,N-dimethylformamide (DMF) and acetonitrile. Synchronous fluorescence spectroscopy (SyF) was also used to monitor directly the sfua status during the potentiometric titration in DMF. The potentiometric titration curves showed no clear end-point and the analysis of the sets of spectra obtained at increasing neutralization degree, with a self-modeling curve resolution method (SIMPLISMA), revealed the existence of two components with featureless concentration profiles. Internal standards (maleic, salicylic and p-hydroxylbenzoic acids) were used to determine the amounts of acid groups with different acid strengths in the two non-aqueous solvents. It was shown that the variations observed in the SyF spectra sets of the internal standards are not correlated with those observed in the sfua data. The splitting of the sfua groups in the non-aqueous titration curves seems to be forced artificially depending on the standards used.     

Coulo-bipotentiometric titrations in the analysis of bromine in bromine-doped cadmium chalcogenides

The detection of bromine in the 60–1300 p.p.m. range in Cd-chalcogenideshas been proved feasible by a d.e.p. version of argentometric titration, where the titrant (silver ions) is coulo-generated. The analytical method described seems to meet the requirements of the simplicity necessary when routine work is needed and when small samples (about 20–100 mg) are available.     

Determination of Mg, Ti and Cl in Ziegler-Natta catalysts by WDXRF

A method for determination of Mg, Ti and Cl in Ziegler-Natta (ZN) catalysts by wavelength dispersive X-ray fluorescence (WDXRF) spectrometry was developed. For comparative reasons, Ti was determined by spectrophotometry, Mg by complexometry and Cl by argentometric titration. Direct pressing was shown to be unsuitable for sample preparation due to catalyst decomposition. For Ti and Mg measurements, catalyst samples were calcinated at 1000 °C and pressed at 275 MPa. Their determination by the fundamental parameters based on the Ti Ka line measurement was shown to be equivalent to those results obtained by univariate calibration or by the classical methods. Cl was determined by aqueous extraction, followed by deposition on a support. Chloride loss was observed. Fixation of Cl as AgCl on polytetrafluoroethylene (FHLC) millipore membrane afforded the best results. Nevertheless, measurements by WDXRF were shown to be inferior to those obtained by argentometric titration.     

Semiconductor gallium arsenide electrodes for the potentiometric titration of mercaptans in raw hydrocarbons

Electrochemically modified electrodes based on gallium arsenide (GaAs) were designed for the potentiometric determination of mercaptans in raw hydrocarbons. The main electrochemical characteristics (linearity range of the electrode function, limit of detection, and slope of electrode function) were studied. The argentometric titration of mercaptans in a gas condensate was performed using the GaAs electrodes prior to and after modification. The use of the electrochemically modified electrode ensures a more reliable determination of the titration end-point.     

非水库仑滴定法测定天然水体中溶解的无机碳

介绍用非水库仑滴定法测定天然水体中溶解的无机碳，对非水库仑滴定方法的关键技术－非水电解液进行了组分选择及优化，并对实验条件进行了优化。用该方法对碳酸钠标准溶液进行测定，测定结果的相对标准偏差为0.18%，测定值与理论值的平均相对误差为0.48%，表明该方法具有较高的精密度与准确度。     

Kinetics and Mechanisms of Reactions of some complexes of Chromium(III). Formation of Oxalatobis(biguanide) chromium(III) Ion from Diaquobis(biguanide) chromium(III) Ion and its Dissociation in Acid Medium

The kinetics of formation of oxalatobis(biguanide)chromium(III) ion from diaquobis(biguanide)chromium(III) ion and oxalate has been studied in aqueous solution (pH ca. 3–4). The results indicate ion-pair formation between the reacting species followed by reaction by an essentially dissociative mechanism (S_N1IP). The kinetics of dissociation of the oxalatobis(biguanide)chromium(III) ion in acid medium has also been studied. The reactions involved are the loss of the two biguanide ligands in stages and by proper choice of acid concentrations and temperature the rates of the two steps could be followed separately. The results indicate S_N2CA mechanism.     

Gravimetric determination of palladium with biguanide sulfate

Biguanides are interesting reagents for the determination of palladium owing to their solubility, chemical resistance, and selectivity in moderately acidic solutions. A procedure for the gravimetric determination of palladium(II) in the form of Pd(HL)₂SO₄, where HL = biguanide, is proposed and the conditions of precipitation, treatment of the precipitate, precision, accuracy, and selectivity of the procedure are discussed.     

Coulometric titration of proteins with silver

The sulfhydryl groups of some proteins were studied by a coulometric argentometric titration; disulfide groups in the presence of sulfite were titrated by the same technique. Direct procedures and a technique utilizing excess coulometrically generated silver(I) were used. The latter method enabled small samples (20–1000 μg of protein) to be titrated with a precision of less than 4%. The proteins were generally titrated in both the native state and the denatured state (8 M urea). Bovine serum albumin, α-chymotrypsin, glutathione reductase, human hemoglobin, insulin, β-lactoglobulin, and ovalbumin were examined and the results compared to those of previous workers.     

Argentometric titration of chloride with dichlorofluoroscein as an adsorption indicator: A useful modification

The addition of excess of ethyl alcohol renders more useful the argentometric titration of chloride with dichlorofluoroscein as adsorption indicator by improving the end-point, both when simple counter-ions are present and also when the presence of adsorbable and/or complexing counter-ions renders the normal technique inadequate.