Donatella Ferri

Determination of some inorganic species in edible vegetable oils and fats by ion chromatography

Abstract A procedure has been developed for the ion chromatographic determination of total chlorine, phosphorus and sulphur and of iron, copper, nickel, zinc, cobalt, lead and cadmium in edible vegetable oils and fats. The organic matrix which strongly interferes in analytical procedures, is completely removed by saponification followed by oxidative UV photolysis. This method is simpler and requires less reagents compared with other sample pretreatment procedures. To oil and fats, ethanol and potassium hydroxide were added, and they were saponified for half an hour. Hydrogen peroxide was added and the sample was subjected to UV photolysis at 85±5°C. In less than 1 h organic constituents were completely degraded, while inorganic constituents, except nitrates, iodides and manganese, remained unaffected by UV radiation. Chlorine, phosphorus and sulphur, present in different organic compounds, can be quantified as total amounts only, without speciation. The clear sample solutions were directly injected on to an ion chromatograph equipped both with a conductivity detector, for the determination of total chloride, phosphate and sulphate ions using a carbonate–hydrogencarbonate eluent, and a post-column reactor and a variable-wavelength UV–Vis detection system, for the determination of lead and cadmium using an oxalate eluent and iron, copper, nickel, zinc and cobalt using a pyridine-2,6-dicarboxylic acid eluent. The method has been tested on spiked and unspiked samples of vegetable oils and fats and was found to be satisfactory for the determination of the previously cited elements. Ion chromatographic responses were compared to voltammetric ones and were found to be in good agreement (±3%).

Differential-pulse polarographic determination of molybdenum in steel

A method for the determination of molybdenum in steel, based on catalytic electroreduction by the molybdate ion, is described. After a suitable sample dissolution, iron is removed by cation exchange and molybdenum is eluted with 0.5 M nitric acid. The eluate is diluted 1 + 1 with 4 M ammonium nitrate solution, and polarographic analysis carried out over the range from 0 to –1.0 V versus a saturated calomel electrode. The method is applicable to the determination of molybdenum in the 0.001–5% of molybdenum range and good agreement is reported for a number of certified British Chemical Standard and commercial steels.

Determination of total phosphorus in soaps/detergents by ion chromatography

Abstract The quantitative determination of phosphorus in soaps and detergents is a classical analytical problem owing to the complexity of the matrix containing a variety of chemical species (i.e., surfactants, complexones and/or zeolites, optical whiteners, perfumes, etc.). A new method has been developed for the analysis of total phosphorus in soaps and detergents which employs UV photolysis of the analyte. It has the advantages that it is a simple procedure and has very low blank values because of the small amount of reagent required for the sample pretreatment. Different types of soaps and detergents were subjected to oxidative UV photolysis. It was found that the organic matrix was degraded in about 60 min, thereby permitting the quantitative analysis of various inorganic species, especially the phosphate ion. Soaps and detergents of different “types and brands” were found to contain phosphate from a few mg/l or mg/kg to the 1% level. The results were compared with those obtained by conventional alkaline fusion followed by reduction to molybdenum blue, and were found to be in good agreement.

Differential pulse polarographic determination of traces of phosphorus in semiconductor silicon

Abstract A method for the indirect determination of phosphorus in semiconductor silicon is presented. After silicon dissolution with hydrofluoric and nitric acids and matrix volatilization, molybdophosphoric acid is formed in 0.25 M hydrochloric acid and then extracted into n-butyl acetate. Back-extraction with 2 M ammonium nitrate—1 M ammonia solution and addition of nitric acid gives a suitable supporting electrolyte for measurement of the catalytic molybdenum wave. Differential pulse polarography provides a detection limit of ca. 5 ng g - with a precision of about ±2%, with linear calibration curves up to at least 0.1 μg P ml -1 .

Differential pulse polarographic determination of traces of molybdenum in solar-grade silicon

Abstract After dissolution of silicon with hydrofluoric and nitric acids and matrix volatilization as hexafluorosilicic acid, 0.2 M nitric acid and 1.8 M ammonium nitrate are added to the residue. Molybdate is then determined by means of its catalytic wave in nitrate media. The limit of determination is ca. 0.1 μg g-1 and calibration graphs are linear up to 0.2 μg Mo(VI) ml-1.

Determination of the stoicheiometry of uranium dioxide by differential-pulse polarography

Uranium dioxide is widely used as a nuclear fuel and usually it exists as a non-stoicheiometric hyperstate UO2+x because of the oxygen interstitial arrangement. The proposed method for determining the oxygen to uranium ratio in uranium oxides is based on the dissolution of the nuclear fuel in concentrated phosphoric acid under an inert atmosphere, to preserve the uranium oxidation states. After complete dissolution, sulphuric acid is added in order to obtain a 1.47 M H3PO4–1.5 M H2SO4 supporting electrolyte. Differentialpulse polarographic determination of uranium(VI) directly follows at –0.09 V versus S.C.E. An aliquot of this solution is then oxidised with an almost equivalent amount of cerium(IV) sulphate solution, converting all uranium(IV) into uranium (VI); the total uranium content is then determined in the same way. The proposed method permits determinations of uranium(VI) levels as low as 0.2 µg ml–1 with a relative standard deviation of about 2%.The oxygen to uranium ratio is calculated by the equation O/U = 2.000 0 + U(VI)/total U and a result of 0.001 unit is obtainable with a coefficient of variation of about ±0.1%.

Potentiometric determination of boron in graphite microspheres for nuclear engineering

Abstract The well-known acidimetric determination of boron via the boric acid-mannitol complex is applied to the analysis of boron-loaded graphite microspheres used in nuclear engineering. After the sample is accurately ground, it is fused with an oxidizing alkaline flux. The melt is dissolved with warm water, the solution is acidified to completely remove carbon dioxide and the boric acid is titrated potentiometrically with carbonate-free sodium hydroxide after its complexing with mannitol. The determination of at least 0.2% boron in graphite is carried out with an average error of less than 1%.

Determination of tungsten in composite nuclear fuels by differential-pulse polarography

Nuclear reactor fuels must comply with stringent composition requirements in order to guarantee safe operation and neutron economy.In this work, differential-pulse polarography was investigated as a means for the determination of tungsten impurities in composite nuclear fuels. The concentration range studied was 0.001–0.005% of tungsten. The proposed method is based on the dissolution of the sample in concentrated orthophosphoric acid under an inert atmosphere. No matrix separation is required and a suitable amount of sulphuric acid is added directly to the sample solution in order to obtain a 7.4 M H3PO4-4.5 M H2SO4 supporting electrolyte solution. After de-aeration of the solution, differential-pulse polarographic determination of tungsten(VI) was carried out at –0.250 V versus an Ag-AgCl reference electrode. The detection limit was found to be 1 µg ml–1 of tungsten(VI) with a relative standard deviation of about 5%.More than 25 elements were tested and only AsIII, MoVI, RuIII and SbV were found to interfere in the determination of tungsten(VI).

Differential-pulse polarographic determination of traces of titanium in solar grade silicon@@@Differentialpuls-polarographische Bestimmung von Titanspuren in Silicium vom Reinheitsgrad fr Solarzellen

ZusammenfassungDie vorgeschlagene Methode beruht auf der katalytischen Aktivität von Ti(IV) in Gegenwart von Chlorationen. In chlorathaltiger saurer Oxalatlösung ergibt Ti(IV) infolge seiner katalytischen Elektroreduktion einen besonders großen polarographischen Strom und die gut ausgebildete polarographische Stufe ist zur Spurenanalyse geeignet.Nach Auflösung des Siliciums mit Fluß- und Salpetersäure und Verflüchtigung der Matrix als Hexafluorkieselsäure werden 0,1 M KClO3-Lösung und 0,2 M Oxalsäure in 0,25 M Schwefelsäure direkt zum Rückstand zugegeben. Die differentialpuls-polarographische Analyse dieser Lösung ergibt eine Nachweisgrenze von etwa 50 ng/g mit einer relativen Standardabweichung von ± 4–5% und einer reproduzierbaren Eichkurve bis zu 0,8 μg Ti(IV)/ml. Das Verfahren gestattet ebenfalls die gleichzeitige Bestimmung von Ti und Cu mit einer Nachweisgrenze für Cu von weniger als 10 μg/g. In Abwesenheit von Schwefelsäure ist auch eine gleichzeitige Bestimmung von Ti und Fe mit einer Nachweisgrenze für Fe von etwa 1,5 μg/g möglich.SummaryThe proposed method for the determination of Ti in solar grade silicon is based on the catalytic activity of titanium(IV) in presence of chlorate ions. In acidic oxalate solution containing chlorate, titanium(IV) gives an exceptionally high polarographic current owing to its catalysed electroreduction and the well-shaped polarographic wave is suitable for trace analysis.After dissolution of silicon with hydrofluoric and nitric acids and matrix volatilization as hexafluorosilicic acid, 0.1 M potassium chlorate and 0.2 M oxalic acid in 0.25 M sulphuric acid are directly added to the residue. Differential pulse polarography of this solution provides a detection limit of about 50 ng g−1, with a relative standard deviation of ±4–5% and a reproducible calibration curve up to at least 0.8 μg Ti(IV) ml−1. This method also permits the simultaneous determination of titanium and copper with a detection limit for copper of less than 10 μg g−1. In absence of sulphuric acid, the simultaneous determination of titanium and iron is also possible, with a detection limit for iron of about 1.5 μg g−1.

Differential pulse polarographic determination of inorganic and organic arsenic in natural waters

SummaryAs(III), As(V) and organic arsenic in water are determined by differential pulse polarography. As (III) is directly determined in 2M HCl as supporting electrolyte. Total inorganic arsenic [As (III) + As(V)] is measured after reduction of electro-inactive As(V) with sodium sulphite. Total arsenic is determined after oxidative treatment of the water residue with potassium permanganate and magnesium nitrate, and reduction of arsenic with sodium sulphite. Organic arsenic is evaluated by difference. The efficiency of the whole procedure is 78–80% and its detection limit is 1μg/l. The relative standard deviation is better than ±1.5% at 50μg/l. Interferences due to heavy metals are overcome by removing them by anionexchange or pre-electrolysis with a mercury cathode.ZusammenfassungAs (III), As(V) und organisches Arsen in Wässern wurden differentialpuls-polarographisch bestimmt. As (III) wurde direkt in 2 M HCl als Trägerelektrolyt bestimmt. Das anorganische Gesamtarsen [As(III) und As(V)] wurde nach Reduktion des elektro-inaktiven As(V) mit Natriumsulfit gemessen. Nach der oxydativen Behandlung des Wasserrückstandes mit KMnO4 und Magnesiumnitrat und nach Reduktion des Arsens mit Natriumsulfit wurde das Gesamtarsen bestimmt, und das organisch gebundene Arsen durch Differenzbildung ermittelt. Die Ausbeute des gesamten Verfahrens beträgt 78–80%, seine Erfassungsgrenze 1μg/l Die relative Standardabweichung ist besser als ±1,5% bei 50μg/l. Störungen durch Schwermetalle werden entweder durch deren Entfernung mittels Anionen-austauscher oder durch vorhergehende Elektrolyse mit einer Quecksilberelektrode beseitigt.