Photometric determination of micro amounts of thiosulphate by means of its cyanolysis with lanthanum(III) as catalyst

Lanthanum(III) has been found to catalyse the reaction of thiosulphate with cyanide. The effects of pH, reaction time and temperature, amount of cyanide and lanthanum, and order of addition of reagents have been investigated. Temperature has little effect in the range 10–30°, but at both 35° and 40° the rate is noticeably faster. Reaction is complete at room temperature in 1.5 hr at pH 9.3–9.6, and in 3 hr at pH 9.1–9.6. The method can be applied to the determination of 1.0 × 10⁻⁵−6.0 × 10⁻⁴M thiosulphate, with a relative standard deviation of 0.3% for 4 × 10⁻⁴M thiosulphate.     

Applications of enzyme-catalysed reactions in trace analysis-II Determination of cyanide, sulphide, and iodine with invertase

Methods are described for the determination of cyanide (10⁻⁸–10⁻⁵M and sulphide (10⁻⁷–10⁻⁵ M) based on the de-inhibitory effect of these ions on invertase inhibited by mercury(II) or by silver. Iodine (0.1–3 μg) may be determined by its inhibition of invertase.     

Potentiometric titration of sulphate, sulphite and dithionate mixtures, with use of a lead ion-selective electrode

Simple methods are described for the analysis of sulphate, sulphite and dithionate mixtures by potentiometric titration with lead perchlorate (and use of a lead ion-selective electrode). The error and precision are both about 2–5% for the sulphate concentration range 3 × 10⁻³ −6 × 10⁻⁴M. The sulphur content in fuels derived from refuse was determined by potentiometric titration after bomb-combustion and the results compared favourably with those from the standard BaSO₄ gravimetric method.     

Selective potentiometric determination of Bi(III) with a coated-wire electrode

A bismuth-selective electrode based on the chlorobismuthate(III) salt of Aliquat 336 is described. The electrode gives nearly linear response in the bismuth concentration range 10⁻¹–10⁻⁴M. The optimum solution conditions for operation of the electrode have been determined together with possible interference effects. The application of the electrode to analysis of samples containing large amounts of other metals is illustrated by the determination of bismuth in pharmaceuticals. The electrode is shown to give results by direct potentiometry and the standard-addition method which differ from atomic-absorption results by not more than 2%.     

Selektive Bestimmung in verdünnter Lösung befindlicher Säuren von verschiedener Stärke durch oszillometrische titration

The stronger of a pair of weak acids may be selectively titrated in aqueous solution when the conjugate base of a third acid of intermediate strength is used as titrant. Titrations of 10⁻²–10⁻³M solutions can be followed by high-frequency oscillometric measurements with an error of about 1%, when the strengths of the two acids differ by a factor of 10² or more, and of the acid and titrant by 10^1,3 or more.

Résumé

On peut titrer sélectivement en solution aqueuse le plus fort d'une paire d'acides faibles lorsque la base conjuguée d'un troisième acide de force intermédiaire est utilisée comme agent de titrage. On peut suivre les titrages de solutions 10⁻²–10⁻³M par mesures osdilométriques de haute fréquence avec une erreur d'environ 1%, lorsque les forces des deux acides diffèrent d'un facteur de 10² ou plus, et celles de l'acide et de l'agent de titrage de 10^1,3 ou plus.     

Determination of Ag(I) with chemically modified carbon paste electrode based on 2,3-dicyano 1,4-naphthoquinone

The utility of carbon paste modified with 2,3-dicyano 1,4-naphthoquinone (CYNQ) for the voltammetric determination of Ag(I) is demonstrated. The method is based on the formation of Ag(I) complex with CYNQ by accumulation from the aqueous solution to the electrode surface without an applied potential. Using the medium exchange technique, the electrode was transferred to another media followed by linear-scan voltammetric measurements. The reduction peak of the Ag(I)-CYNQ complex was observed at +0.22 V (vs. SCE). The silver response is studied with respect to paste composition, pH of the measurement solution, reproducibility, interference and other variables. A detection limit of 5 × 10⁻⁸M was obtained and the calibration curve was linear over the range 1 × 10⁻⁶−8 × 10⁻⁵M.     

Polarographic catalytic nickel prewave induced by some cysteine-containing dipeptides

The catalytic nickel prewave produced by Cys-Gly, Cys-Tyr and Cys-Phe was studied in acetate buffer at pH 4–6.5. These peptides are more active than cysteine, especially the last two. The catalytic activity is depressed by decrease of pH owing to protonation of the catalyst. However, Cys-Phe and Cys-Tyr are still active at pH < 5, in contrast to Cys-Gly and Cys. This difference is accounted for by the interaction of the aromatic ring with the electrode surface at potentials more positive than the potential of zero-charge. This effect enhances the surface concentration of the catalyst in the case of Cys-Phe or Cys-Tyr. At pH < 5, a catalyst concentration 10⁻⁵M and large excess of nickel, the current is controlled by the rate of accumulation of catalyst in the adsorbed state. Under these conditions the reducible complex is a 1:1 Ni²⁺-catalyst chelate. The catalytic wave recorded at pH 4.8 allows the determination of Cys-Phe or Cys-Tyr (10⁻⁶−10⁻⁴M) in the presence of the constituent amino-acids.     

A lead(II) ion selective electrode via a metal complex of poly(hydroxamic acid)

A new lead(II) electrode has been constructed with poly(hydroxamic acid) (PHXA) as the active material and silicone rubber as the supporting material. The electrode gave near Nerstian response over the concentration range 4 × 10⁻⁵−1 × 10⁻²M lead(II). The detection limit of the electrode is approximately 4 × 10⁻⁶M and the electrode works well in the pH range 4.5–6.0. The response time was 50–120 sec over the whole concentration range and the electrode has a working life of at least 4 weeks. Iron(III) severely poisoned the electrode membrane. Nickel(II) and mercury(II) gave very strong interference compared to copper(II), silver(I), cobalt(II), sodium(I), potassium(I), zinc(II) and cadmium(II) which gave some or little interference. Values determined with atomic absorption (AAS) and a commercial lead(II) electrode were in good agreement with those measured with the lead(II) electrode reported here.     

In Process Citation

A method for the quantitative determination of cationic and non-ionic surfactants which is based on their inhibiting effect on certain electrochemical reactions has been developed. This technique enables one to determine, with a precision of 2–3%, these substances at concentrations of the order of 10⁻⁶M.

Zusammenfassung

Wir haben eine Methode eingestelt, um oberflächenaktiven kationischen und nicht ionischen Substanzen zu dosieren. Diese Methode ist auf ihren Inhibitoreffekt gewissen elektrochemischen Reaktionen gegenüber gegründet. So ist es möglich, diesen Substanzen mit einer guten Genauigkeit (2–3%) bei Konzentrationen von ungefähr 10⁻⁶M zu dosieren.     

Applications of enzyme-catalysed reactions in trace analysis-III Determination of silver and thiourea by their combined inhibition of invertase

Thiourea has been found to enhance the inhibition of invertase by silver ions. The effect is applied to the determination of 1–5 × 10⁻⁷ M silver and of 10⁻⁷–10⁻⁸ M thiourea. A mechanism is suggested for the enhancement.     

Determination of pK(a)'s for thymol blue in aqueous medium: evidence of dimer formation

Formation constants for recrystallized thymol blue were determined in water, using the SQUAD and SUPERQUAD programs. The best model correlating spectrophotometric, potentiometric and conductimetric data was fitted with the dissociation of HL⁻=L²⁻+H⁺−log K=8.918±0.070 and H₃L₂⁻=2L²⁻+3H⁺−log K=29.806±0.133 with the SUPERQUAD program at variable low ionic strength (1.5×10⁻⁴–3.0×10⁻⁴ M); and HL=L²⁻+H⁺−log K=8.9±0.000, H₃L₂⁻ =2L²⁻+3H⁺−log K=30.730±0.032, H₄L₂=2L²⁻+4H⁺−log K=32.106±0.033 with SQUAD at 1.1 M ionic strength.     

Separation of trans-1,2-cyclohexanediaminetetra-acetic acid chelates of bismuth(III), iron(III) and copper(II) by reversed-phase paired-ion chromatography

Trans-1,2-cyclohexanediaminetetra-acetic acid (DCTA) chelates of bismuth(III), iron(III) and copper(II) have been separated by two techniques using reversed-phase paired-ion chromatography. In one, the chelates in aqueous solution were separated within 20 min on a 6.0 × 300 mm ERC-ODS column with 10⁻²M tetrabutylammonium ion (TBA⁺) in methanoi-water mixture (45:55 v/v) as eluent. In the other, the metal ions in aqueous solution were separated within 10 min by direct injection into an ERC-ODS column with 10⁻²M TBA⁺/10⁻³M DCTA in methanoi-water mixture (40:60 v/v) as eluent.     

Simultaneous determination of selenium and lead in whole blood samples by differential pulse polarography

The polarographic reduction of lead in the presence of selenite gives rise to an additional peak corresponding to the reduction of lead (Pb) on adsorbed selenium (Se) on mercury at −0.33 V. The selenium and lead content can be determined using this peak by the addition of a known amount of one of these ions first and then the second ion. The linear domain range of lead is 5.0×10⁻⁷–2.0×10⁻⁵ M and for selenium 5.0×10⁻⁷–1.0×10⁻⁵ M. Using this method 4.90×10⁻⁷ M Se(IV) and 1.47×10⁻⁶ M Pb(II) in a synthetic sample could be determined with a relative error of +2.0% and 1.8%, respectively (n=4). A recovery test after acid digestion for a synthetic sample was 97% for selenium and 96.5% for lead. The method was applied to 1 ml of digested blood, and 328±23 μg l⁻¹ Se(IV) and 850±62 μg l⁻¹ Pb(II) could be determined with a 90% (n=5) confidence interval.     

Glycopyrronium-selective electrodes

Liquid-membrane and PVC-membrane glycopyrronium-selective electrodes have been developed. They are based on the ion-pair complexes of glycopyrronium with dicyclohexylnaphthalenesulphonate, di-isopentylnaphthalenesulphonate, di-isobutylnaphthalenesulphonate and tetraphenylborate. Their response is nearly Nernstian over the pH-range 4–8, and the detection limits range from 10⁻⁶M to 10⁻⁵M. For the liquid-membrane electrodes, with homologous membrane solvents, the response slopes are linearly related to the inverse of the dielectric constant of the membrane solvent, according to the formula S = C_o − C₁/ε. A similar relation exists between the slopes for both types of electrode and the dielectric constants of mixed-solvent backgrounds. The electrodes can be used in the potentiometric determination of glycopyrrolate.     

The effect of trace levels of cyanide on the formation of mercury-iodide complexes

The interference of trace levels of cyanide with the formation of iodo-mercury complexes is made the basis of a method of trace analysis for cyanide. The decrease in absorbance of the iodo-mercury complexes is a linear function of total cyanide concentration up to about 5 × 10⁻⁵M in 0.1M sodium hydroxide medium when the iodide and mercury total concentrations are 0.05M and 3 × 10⁻⁵M respectively. Several cyano-mercury complexes are formed simultaneously, and quite a large fraction of the cyanide remains uncomplexed.     

Simultaneous potentiometric determination of ClO(3)(-)-ClO(2)(-) and ClO(3)(-)-HClO by flow injection analysis using Fe(III)-Fe(II) potential buffer

A rapid potentiometric flow injection technique for the simultaneous determination of oxychlorine species such as ClO₃⁻–ClO₂⁻ and ClO₃⁻–HClO has been developed, using both a redox electrode detector and a Fe(III)–Fe(II) potential buffer solution containing chloride. The analytical method is based on the detection of a large transient potential change of the redox electrode due to chlorine generated via the reaction of the oxychlorine species with chloride in the potential buffer solution. The sensitivities to HClO and ClO₂⁻ obtained by the transient potential change were enhanced 700–800-fold over that using an equilibrium potential. The detection limit of the present method for HClO and ClO₂⁻ is as low as 5×10⁻⁸ M with use of a 5×10⁻⁴ M Fe(III)–1×10⁻³ M Fe(II) buffer containing 0.3 M KCl and 0.5 M H₂SO₄. On the other hand, sensitivity to ClO₃⁻ was low when a potential buffer solution containing 0.5 M H₂SO₄ was used, but could be increased largely by increasing the acidity of the potential buffer. The detection limit for ClO₃⁻ was 2×10⁻⁶ M with the use of a 5×10⁻⁴ M Fe(III)–1×10⁻³ M Fe(II) buffer containing 0.3 M KCl and 9 M H₂SO₄. By utilizing the difference in reactivity of oxychlorine species with chloride in the potential buffer, a simultaneous determination method for a mixed solution of ClO₃⁻–ClO₂⁻ or ClO₃⁻–HClO was designed to detect, in a timely manner, a transient potential change with the use of two streams of potential buffers which contain different concentrations of sulfuric acid. Analytical concentration ranges of oxychlorine species were 2×10⁻⁵–2×10⁻⁴ M for ClO₃⁻, and 1×10⁻⁶–1×10⁻⁵ M for HClO and ClO₂⁻. The reproducibility of the present method was in the range 1.5–2.3%. The reaction mechanism for the transient potential change used in the present method is also discussed, based on the results of batchwise experiments. The simultaneous determination method was applied to the determination of oxychlorine species in a tap water sample, and was found to provide an analytical result for HClO, which was in good agreement with that obtained by the o-tolidine method and to provide a good recovery for ClO₃⁻ added to the sample.     

Polarographic determination of proguanil and chlorhexidine

The method is based on the cathodic wave obtained for chlorhexidine and proguanil in buffered aqueous dimethylformamide media. Concentrations up to 8 × 10⁻⁵ and 6 × 10⁻⁴M, respectively, can be determined. The difference in behaviour at various pH values or in the presence of surface-active agents, is useful for characterization of both biguanides.     

Time measurement-visual analysis of nickel(II) using autocatalytic reaction with sodium sulfite/hydrogen peroxide system and its application to the length detection-flow analysis

Trace amounts of nickel(II) can function as a trigger (=reaction initiator) in an autocatalytic reaction with the sodium sulfite/hydrogen peroxide system. Based on this finding, sub-μg L⁻¹ levels of nickel(II) were determined by a time measurement using the autocatalytic reaction. The detection range using the above method was 10⁻⁹–10⁻⁵ M, the detection limit (3σ) was 8.1 × 10⁻¹⁰ M (0.047 μg L⁻¹), and the relative standard deviation was 2.66% at nickel(II) concentration of 10⁻⁷ M (n = 7). This method was applied to length detection-flow injection analysis. The detection range for the flow injection analysis was 2 × 10⁻⁹–2 × 10⁻³ M. The detection limit (3σ) was 1.4 × 10⁻⁹ M (0.082 μg L⁻¹), and the relative standard deviation was 1.86 at initial nickel(II) concentration of 10⁻⁶ M (n = 7).     

Studies on the extraction and determination of metals-I Extraction of hafnium into methyl isobutyl ketone and tributyl phosphate

The effect of various factors on the distribution of hafnium ( 5.60 × 10⁻⁴M) between different acids and methyl isobutyl ketone (MIBK) or tributyl phosphate (TBP) was studied by using ^{176 + 181} Hf as a tracer, when the extraction is made from 7.5–11M hydrochloric acid with an equal volume of IM TBP in benzene, hafnium is extracted quantitatively (>99%). The hafnium can be stripped with 1–3M hydrochloric acid.     

The decomposition of hypobromite solutions

The stability of 10⁻¹–10⁻³N hypobromite solutions, stored in brown or colourless bottles at room temperature, has been investigated. A reaction mechanism of decomposition has been proposed and some practical conclusions have been drawn concerning the optimal method of preparation and the required frequency of control of hypobromite solutions used as an analytical reagent.