The coulometric titration of acids and bases in m-cresol medium

A method is described for the coulometric titration of acids and bases in the solvent m-cresol. The method is suitable for bases with pK_a values greater than 11 in m-cresol, or for acids with pK_a values below 13 in m-cresol. Amounts of 5–50 μeq of acid or base can be determined with a relative accuracy of ±1%.     

Coulometric titration of zinc with ferrocyanide

A method has been developed for the automatic coulometric titration of zinc ion with ferrocyanide ion generated by the reduction of ferricyanide ion at a platinum cathode. The composition of the zinc precipitate was found to depend on the pH. Over the pH range from about 1 to 3 it corresponds exactly to K₂Zn₃[Fe(CN)₆]₂, but at higher pH values the precipitate contains a smaller proportion of ferrocyanide to zinc. At the optimum pH of 2 quantities of zinc from 0.3 to 30 mg in 8o ml were titrated automatically with an average error smaller than ± 1% The ferriferrocyanide couple should be applicable to other coulometric titrations involving both redox and precipitation reactions.     

Determination of Total Selenium in Human Urine and Serum by Graphite-Furnace Atomic-Absorption Spectrophotometry with Palladium-Nickel-Ammonium Nitrates as a Matrix Modifier

After human urine or serum was diluted (1 + 9) with HNO₃ (0.2%, v/v) and standard additions of Se solution (100 μ L^?1), the diluted sample (10 μL) was introduced into the graphite cuvette. The matrix modifier [10μL, containing Pd (0.6 μg) + Ni (25 μg) + NH₄NO₃ (80 μg) in HNO₃ (0.2%, v/v) for urine, or Pd (0.3 μg) + Ni (30 μg) + NH₄NO₃ (80 μg) + Triton X-100 (0.04%) in HNO₃ (0.2%, v/v) for serum, respectively] was added and the mixture was heated according to a temperature program. The matrix modifier containing NH₄NO₃ in a suitable amount and a small amount of Pd enhanced the sensitivity for Se. The method detection limits (3σ) after dilution were about 4.9 ± 0.8 and 2.36 ± 0.18 μg L^?1 for urine and serum, respectively. The accuracy of this method was tested with SRM #2670 human urine Se and Seronorm Trace Elements #116 human serum Se, respectively, and the results of 97.6 – 101% and 100 – 104% were obtained with precision ± 0.3% and ± 2%, respectively. This method can be applied easily and accurately to the determination of concentration of total Se in human urine and serum.     

Controlled-potential coulometric determination of platinum in americium—platinum alloys

A controlled-potential coulometric method for the determination of platinum in americium—platinum alloys is described. Platinum in the hexachloroplatinate complex is reduced to the metal at —0.3 V vs. the saturated silver chloride electrode on a mercury pool electrode. For quantities up to 5 mg, the standard deviation was 6.4 μg.     

Coulometric determination of dissolved oxygen in water

The oxygen content of air-saturated distilled water has been determined at between 10 and 40 degrees by using a controlled-potential coulometric method based on an earlier published method for the iodometric determination of nitrite. The maximum error for the determinations was +/- 0.3% over the whole range, and the time of analysis about 3 min. An equation is given for the solubility in the measured range, and some thermodynamic functions are calculated.     

Chronopotentiometric and controlled-potential electrolytic studies of the formation of intermetallic compounds in copper-zinc,platinum-zinc,and other amalgams

The behaviors of amalgams containing: copper and zinc; platinum and zinc; platinum and cadmium; silver and zinc; silver and cadmium; cadmium and copper; cadmium, copper and platinum; and silver, nickel and zinc were investigated by controlled-potential electrolysis and chronopotentiometry. Copper-zinc amalgams contain the compound CuZn, for which the solubility product at 25°C is equal to (3.8±0.6)×10^?6M², and also a soluble but sparingly dissociated compound that is richer in zinc. Platinum-zinc amalgams contain PtZn₂, PtZn₃ and PtZn₄ in metastable equilibrium. Gold-cadmium amalgams contain the compound AuCd, whose solubility product at 25°C is equal to (1.7±0.1)×10^?5M². Compound formation could not be detected in silver-zinc, silver-cadmium, cadmium-copper, platinum-copper or cadmium-copper-platinum amalgams, but there was an uncertain indication that silver-nickel-zinc amalgams might contain the first ternary intermetallic compound found in amalgams.     

Simultaneous determination of 10 kinds of biogenic amines in rat plasma using high‐performance liquid chromatography coupled with fluorescence detection

We describe a simple, rapid, selective and sensitive HPLC method coupled with fluorescence detection for simultaneous determination of 10 kinds of biogenic amines (BAs: tryptamine, 2‐phenethylamine, putrescine, cadaverine, histamine, 5‐hydroxytryptamine, tyramine, spermidine, dopamine and spermine). BAs and IS were derivated with dansyl chloride. Fluorescence detection (λ_ex/λ_em = 340/510 nm) was used. A satisfactory result for method validation was obtained. The assay was shown to be linear over the ranges 0.005–1.0 μg/mL for tryptamine, 2‐phenethylamine and spermidine, 0.025–1.0 μg/mL for putrescine, 0.001–1.0 μg/mL for cadaverine, 0.25–20 μg/mL for histamine, 0.25–10 μg/mL for 5–hydroxytryptamine and dopamine, and 0.01–1.0 μg/mL for tyramine and spermine. The limits of detection and the limits of quantification were 0.3–75.0 ng/mL and 1.0–250.0 ng/mL, respectively. Relative standard deviations were ≤5.14% for intra‐day and ≤6.58% for inter‐day precision. The recoveries of BAs ranged from 79.11 to 114.26% after spiking standard solutions of BAs into a sample at three levels. Seven kinds of BAs were found in rat plasma, and the mean values of tryptamine, 2‐phenethylamine, putrescine, cadaverine, histamine, spermidine and spermine determined were 52.72 ± 7.34, 11.45 ± 1.56, 162.56 ± 6.26, 312.75 ± 18.11, 1306.50 ± 116.16, 273.89 ± 26.41 and 41.51 ± 2.07 ng/mL, respectively.     

Controlled potential lodometric determination of nitrate after reduction to nitrite by coppered cadmium

A controlled-potential coulometric iodometric method previously developed for the accurate determination of small amounts of nitrite has been extended for the determination of nitrate after its reduction on a coppered cadmium reductor. The conditions for quantitative reduction have been investigated with respect to type of reductor and pH. Nitrate-nitrogen in the range 0.01-100 mug ml may be determined with high accuracy in less than 10 min, including the reduction step. The method has been applied with good results to a large variety of samples such as meat products, juices and waste waters.     

The determination of microgram quantities of fluoride: The use of the aluminium-chromeazurol-s complex

A spectrophotometric method for determining fluoride using the aluminium chromeazurol complex is described. Fluoride in solution free from interfering ions or obtained by distillation as hydrofluosilicic acid is determined by destruction of the complex, the amount destroyed being directly proportional to the fluoride present. The method will detect as little as 0.02 μg/ml of fluoride and with 0–20 μg in the final solution fluoride can be determined with an accuracy of ± 0.6 μg.     

Optimierung der Kjeldahl-Methode zur Bestimmung von Stickstoff in Reinstmetallen

The Kjeldahl principle has been modified for improvement in the detectibility of nitrogen in high-purity metals (e.g. Cu, Fe, Zr, Nb, Ta, etc.), and also for the exact determination of smallest amounts of nitrogen in many inorganic and organic matrices. After decomposition of the sample with acid mixtures (HF/HClO₄ or HCl/HClO₄) under pressure in a PTFE bomb, the ammonium produced is separated via ammonia by steam distillation in a special micro circulating distillation apparatus, and absorption in dilute sulphuric acid. The determination is performed directly in the absorption vessel on only 2 ml of solution by coulometric titration with OBr^? and biamperometric end-point detection. With the exception of the decomposition, the whole procedure is program-controlled. The construction of the electronic control device is described in general principle. Determining amounts of 0.1 to 1000 μg N, the coefficients of variation were found to be from ± 10 to < ± 1 %, respectively. One determination can be carried out within 30 min.     

The determination of microgram quantities of fluoride: The use of the aluminium-eriochromecyanin complex

A spectrophotometric method for determining fluoride using the aluminium-eriochromecyamn complex is described. Fluoride in solutions free from mterfering ions,or obtained by distillation as hydrofluosilicic acid is determined by its destruction of the complex, the amount destroyed being directly proportional to the fluoride content. The method will detect as little as 0.02 μg/ml of fluoride and with 0–20 μg in the final solution fluoride can be determined with accuracy of ± 0.6 μg.A preliminary study of the aluminium-eriochromecyanin-fluoride system, has been carried out and a tentative reaction mechanism suggested.     

Anodic Stripping Potentiometric Determination of Cu,Pb, Cd and Zn In Natural Waters on a Novel Combined Electrode System

Abstract

A method is described for the reliable determination of copper, lead, cadmium and zinc in natural waters by anodic stripping potentiometry with the use of a novel combined electrode. The method involves two stripping cycles during which copper is initially determined on its own, followed by simultaneous determination of lead, cadmium and zinc after addition of gallium (III) ions. The optimum conditions include 0.01 M HCl as supporting electrolyte, 10 mg/L Hg (II) as chemical oxidant; E_dep(Cu) -700 mV vs Ag/AgCl; E_{dep(Pb,Cd,Zn)} -1200 mV vs Ag/AgCl; t_dep 10s; 150 μg/L Ga (III); sample rotation rate 5 and rest period 30s. Under these conditions, as low as 0.06 μg/L Cu (0.7% RSD); 0.2 μg/L Pb (13% RSD); 0.04 μg/L Cd (7.8% RSD) and 0.06 μg/L Zn (5.5% RSD) can be determined reliably. A linear concentration range of 0–110 μg/L was obtained for the four metals. The successful application of the method to reference fresh water, creek water and tap water is demonstrated.     

A silicon sensor for measurement of liquid flow and thickness of fouling biofilms

A silicon sensor for the measurement of the flow velocity and thickness of a flouling biofilm was designed and fabricated. Using micro-machining in silicon, small and thermally-insulated sensor areas could be constructed. A physical model was worked out showing that with a double-chip method, both flow velocity and biofilm thickness can be measured. Experiments showed that this method gave a smaller accuracy in thickness measurements compared to a single-chip method at constant flow velocity. The accuracy in thickness measurement was ±0.5 for the single-chip method at ±3.5 μm for the double-chip method. The accuracy in flow velocity measurement decreased at increased film thickness, from about ±10% of the measured value at zero film thickness to about ±30% of the measured value at 20μm film thickness. A pilot experiment studying biofilm development in sea water over a period of 48 days is also presented.     

Controlled-potential back-titration with electrogenerated iodine as an intermediate: application to the determination of thiols

A controlled-potential electroanalytical method has been devised for the accurate determination of small amounts of thiols. An adequate excess of iodine is generated, the sample is added and the unreacted iodine is then electrolytically reduced. The iodine consumed is calculated from the measured number of coulombs. Amounts of thiols in the range 0·2–5 mg may be determined with an error of ± 0.05 %. A coulometric cell has been constructed which permits very high electrolysis rates, owing to efficient stirring by a large rotating platinum electrode combined with a high electrode-area to solution-volume ratio. A constant of 0·11 sec⁻¹ is found for the reduction of iodine. The necessity of careful control of background currents and current efficiency in coulometric determinations is discussed.     

Extraction-spectrophotometric determination of mercury with 1,2,4,6-tetraphenylpyridinium perchlorate

The characteristics of 1,2,4,6-tetraphenylpyridinium perchlorate (TPPP) as a reagent for the formation of ion-pair complexes with metal-bromide anions, and its application to the spectrophotometric determination of mercury are described. This reagent forms a 1:1 complex with bromomercurate(II) ions that is slightly soluble in water and can be extracted with isopentyl acetate. The optimum conditions are about 0.5 M sulphuric acid and 0.03 M potassium bromide. Mercury can be determined at 310 nm in the range 0.04–0.5 μg ml^?1; the apparent molar absorptivity is 2.63 × 10⁴ l mol^?1 cm^?1, and the conditional stability constant is log K - 4.7 ± 0.1 at 20°C. The main interferences are easily removed. Mercury can be determined in sphalerites and zinc amalgams.     

The coulometric titration of acids and bases in dimethylsulfoxide media

The coulometric titration of 20–200 μeq of acids and bases in DMSO media is described. In the titration of bases, the electro-oxidation of hydrogen at a platinized platinum electrode is used as the source of protons. The conditions for 100 % current efficiency at this electrode are low current density to avoid passivity and regular treatment of the electrode with potassium dichromate—sulfuric acid to remove a poisoning sulfide layer. The accuracy of the titrations is better than ±1 %. Very weak acids like phenols (pK_a (DMSO) ≈16) can be titrated successfully. Tris(hydroxymethyl)aminomethane is the weakest base titrated.     

Kinetic spectrophotometric determination of antimony(III) based on induced oxidation of tris(1,10-phenanthroline)iron(II) by chromium(VI)

The method involves the measurement of the extent of the induced reaction, which ceases a few seconds after initiation. Antimony(III) can be determined in the range 0.4–10 μg ml^-1. The standard deviation is ±0.25 μg. The method is applied to marine sediments.     

New method for determining small concentrations of chloride ion

A new method has been devised for the determination of concentrations of chloride ion from approximately 10^-6 to 2·10^-4 M. The test solution is equilibrated with solid silver chloride, the silver ion concentration is determined by potentiometric titration with iodide ion, and the chloride concentration is calculated by the solubility product principle. Chloride concentrations near 10^-6 M can be determined with an accuracy of about ±5%, and at 10^-5 M the error is within ±0.5%. Chloride concentrations above 2-3· 10^-4 M cannot be accurately determined because of the formation of AgCl₂^-.     

Extract–filter–shoot liquid chromatography with mass spectrometry for the analysis of vitamin D2 in a powdered supplement capsule and standard reference material 3280

An “extract–filter—shoot” method for the analysis of vitamin D₂, ergocalciferol, in a dry powdered dietary supplement capsule containing rice flour excipient and in a National Institute of Standards and Technology standard reference material 3280 is reported. Quantification of vitamin D₂ was done by atmospheric pressure chemical ionization mass spectrometry using selected ion monitoring, two transitions of selected reaction monitoring, and extracted ion chromatograms from full scans. UV detection was used for the quantification of Vitamin D₂ in the dry powder capsule, whereas interfering species rendered UV detection unreliable for standard reference material 3280. Average values for standard reference material 3280 ranged from 8.27 ± 0.58 to 8.33 ± 0.57 μg/g using internal standard calibration and response factor approaches, compared to the previous National Institute of Standards and Technology internal value for vitamin D₂ of 8.78 ± 0.11 μg/g, and the recently updated reference value of 8.6 ± 2.6 μg/g. The powdered supplement capsule was found to contain 28.19 ± 0.35 to 28.67 ± 0.90 μg/capsule for a capsule labeled to contain 25.00 μg. The triacylglycerol composition of the rice flour excipient in the powdered supplement capsule determined by atmospheric pressure chemical ionization mass spectrometry is also reported.     

Atomabsorptionsspektralphotometrische bestimmung von zink in galliumarsenid und galliumaluminiumarsenid

The determination by atomic-absorption spectroscopy of zinc in gallium arsenide and gallium aluminium arsenide is described. In 5–20 mg of sample, 0·1–3 μg of zinc can be determined. The coefficient of variation is 4·5%. The influence of the matrix is described and discussed.