Indirect determination of fluoride by EDTA back-titration of lanthanum

Semimicro to macro amounts of fluoride ion (0.4-100 mg) are determined rapidly and accurately by precipitation with an excess of lanthanum at pH 2.5-2.8 by digestion on a water-bath, cooling to room temperature, addition of excess of EDTA and back-titration of the excess with zinc solution to the Xylenol Orange end-point at ph 5.8-5..9. Large amounts of chloride, acetate and perchlorate, and small amounts of sulphate and silicate do not interfere, but phosphate does. This method is much superior to the usual thorium nitrate titration method and can be applied after preliminary separation of fluorine by steam distillation or pyrolysis.     

Substoichiometric separation of indium by extraction with 8-hydroxyquinoline and its application to the determination of indium in semiconductor grade silicon

A substoichiometric extraction method of indium with 8-hydroxyquinoline and its application to the determination of indium in semiconductor silicon are described.     

Substoichiometric precipitation of fluoride with lanthanum

The substoichiometric precipitation of fluoride with lanthanum was studied by using¹⁸F and¹⁴⁰La tracers and it was found that fluoride could be precipitated substoichiometrically with lanthanum and the reaction ratio between fluoride and lanthanum was 3∶1. The pH range at which fluoride can be separated substoichiometrically with lanthanum is between 2 and 8. Barium and indium interfere in the precipitation of fluoride, sodium, copper and manganese, however, not. Fluorosilicate can also be precipitated substoichiometrically by using lanthanum as a precipitant and the reaction ratio between fluorosilicate and lanthanum was 1∶2. This separation was applied for the determination of oxygen in silicon crystals. The concentration of oxygen measured in some silicon crystals was between 5 and 27 ppm and in good agreement with those by non-destructive method and infrared spectrophotometry.     

Spectrophotometric determination of halogenated 8-hydroxyquinoline derivatives

A spectrophotometric method is proposed for the determination of 8-hydroxyquinoline and three of its iodinated derivatives: 5-chloro-7-iodo-8-hydroxyquinoline (clioquinol), 5,7-di-iodo-8-hydroxy-quinoline (iodoquinol) and 8-hydroxy-7-iodo-quinolone-5-sulphonic acid (chinoform). The suggested method depends on the reaction with 4-aminoantipyrine in the presence of an alkaline oxidizing agent. A red antipyrine dye with an absorption peak at 500 nm is produced in all cases. The reacting ratio has been determined and a reaction mechanism is presented. The proposed method can be applied to the analysis of pharmaceutical preparations containing the compounds studied, and the results obtained compare favourably with those obtained with the standard methods.     

Substoichiometric determination of manganese by neutron-activation analysis

A simple and rapid method for the substoichiometric determination of traces of manganese in various materials by neutron-activation analysis has been developed. After dissolution of the irradiated test sample, manganese(II) carrier is added and subsequently oxidised by peroxodisulphate to the heptavalent state. The permanganate thus formed is finally extracted into chloroform as tetraphenylarsonium permanganate using a substoichiometric amount of tetraphenylarsonium chloride. This single separation step isolates radiochemically pure manganese-56 in the analysis of a relatively simple material in which interfering elements (gold, rhenium, etc.) are absent. When this is not true, a preliminary separation of manganese from the irradiated sample, based on the extraction of manganese diethyldithio-carbamate into chloroform and followed by stripping of the manganese with dilute sulphuric acid, must be used. A simultaneously irradiated standard containing manganese must be treated in exactly the same way as a test sample. In the materials analysed by the new method 10(-5) to 10(-3)% of manganese has been determined.     

Substoichiometric determination of phosphorus

Phosphorus in orchard leaves (NBS SRM-1571) and spinach (SRM-1570) was determined by various substoichiometric analytical methods such as the direct method, GRASHCHENKO's method and the method of carrier amount variation. All samples were labelled with³²P radioisotope. The data obtained by the method of carrier amount variation were also treated by the method of least squares instead of De VOE's method. Phosphorus concentration in orchard leaves was 0.206±0.011% by the direct method, 0.219±0.011% by GRASHCHENKO's method, 0.211±0.011% by the method of carrier amount variation and 0.207±0.007% by the method of least squares, respectively. These values agree with the value reported by NBS (0.21±0.01%). Furthermore, these concentrations obtained by various substoichiometric methods were compared with those by radioactivation reported in a prevoius paper.     

Substoichiometric determination of copper by neutron-activation analysis

A rapid and selective method has been developed for the determination of Cu in complex matrices by thermal neutron-activation analysis employing substoichiometric extraction with 1,2,3-benzotriazole /1,2,3-BT/ into chloroform. The time required for radiochemical purification and counting of two samples was 2 h. 1.015 g Cu can be determined with an accuracy of 6.40% and a purification of 5.26%.     

Substoichiometric determination of chromium

The present work deals with the determination of Cr/III/ by means of the substoichiometric isotope dilution method, using PAN, 1-/2-pyridylazo/-2-naphthol as a complexing agent. Chromium forms a 12 complex with PAN. Heating to 90°C for 3 min was necessary for complete complexation. The complex was extracted into chloroform at pH 3.5 /acetate buffer/. Tens of micrograms of chromium could be determined. Effect of diverse metal ions was also studied.     

Substoichiometric determination of iridium using PAN as a reagent

Conditions are established for the substoichiometric determination of iridium employing 1-/2-pyridylyzo/-2-naphthol /PAN/ as a chelating agent. Iridium forms a red coloured complex /12/ with PAN at pH 5 /acetate buffer/, on heating for 60 min in a boiling water bath. The complex was extracted with chloform. Tens of micrograms of iridium were determined with an accuracy of ±0.38%. Effects of diverse metal ions on the determination of iridium were studied and methods for suppression of interferences were developed.     

Substoichiometric determination of zinc by the isotope-dilution method using a chelating agent-loaded resin

A substoichiometric method for the determination of zinc has been developed. Zinc can be separated from other cations by using an anion-exchanger loaded with a substoichiometric amount of 8-quinolinol-5-sulphonic acid. Interfering metals can be removed beforehand by dithizone extraction. The feasibility of this method for water analysis was also examined.     

Substoichiometric determination of tungsten by neutron activation analysis

A method for the substoichiometric determination of tungsten by thermal neutron activation analysis has been developed based on the selective extraction of the tungsten dithiol complex into amyl acetate. The method is simple, rapid and accurate. It has been used in the determination of tungsten in alloy steel, meteorites and biological standard kale.     

Substoichiometric determination of palladium by neutron activation analysis

A method is described for the substoichiometric determination of traces of palladium by neutron activation analysis involving the extraction of palladium with isonitrosoacetophenone. The sensitivity of the method is 0.005 μg of Pd. With 200 mg of silver alloy containing 0.0005% palladium, the average of three determinations of Pd is 0.98 μg, which varies between 1.07 μg and 0.91 μg at 95% confidence limit. The time required for radiochemical purification and counting of the sample does not exceed 12 minutes. Part of this work was presented at the International Conference on Modern Trends Activation Analysis, held in Gaithersburg, Maryland, USA, October 7–11, 1968.     

Substoichiometric determination of chromium by neutron activation analysis

A method of radioactivation analysis has been developed for the determination of chromium. It is based on the substoichiometric extraction of chromium diethyldithio-carbamate into methyl-isobutyl-ketone from acetate buffer solution in the presence of EDTA and potassium cyanide. The method has been applied for the determination of chromium in high-purity calcium carbonate and NBS glasses as standard reference materials.     

Substoichiometric determination of mercury by neutron activation analysis

A method has been developed for the substoichiometric determination of mercury by thermal neutron activation analysis, based on the selective extraction of the Hg(II)—Bindschedler's Green complex into 1,2-dichloroethane. The method has been applied for the determination of trace amounts of mercury in geological standards such as W-1, GR, Sye-1, and T-1, meteorite Allende de Publito, and biological materials such as kale, IR1 standard tobacco, and human blood serum.     

Substoichiometric determination of Cd by neutron activation analysis

A rapid method has been developed for the determination of cadmium in environmental samples by thermal neutron activation analysis involving substoichiometric extraction with 1,2,3-benzotriazole /1,2,3-BT/. Cd was radiochemically separated as CdS using 1-amidino-2-thiourea. The time required for radiochemical purification containing two samples and a standard was about 2 h. 4.63 g of Cd can be determined with an accuracy of 6.69% and precision of 6.25%. Mash potatoes, animal bones, raw sludge and cattle manure have been analyzed by this method.     

Substoichiometric determination of silver by Neutron Activation Analysis

A rapid and selective method has been developed for the determination of Ag in biological samples and mineral ores by thermal neutron activation analysis employing substoichiometric extraction with 1,2,3-benzotriazole /1,2,3-BT/ into chloroform. The time required for the radiochemical purification and counting of two samples was 1 h. 4.84 g Ag can be determined with an accuracy of 7.44% and a precision of 3.57%.