K. Dash

Determination of traces of As, B, Bi, Ga, Ge, P, Pb, Sb, Se, Si and Te in high-purity nickel using inductively coupled plasma-optical emission spectrometry (ICP-OES).

A method has been developed for the determination of traces of arsenic, boron, bismuth, gallium, germanium, phosphorus, lead, antimony, selenium, silicon and tellurium in nickel matrix. The sample was dissolved in HClO4 (~ 150°C) and nickel was settled as crystalline nickelperchlorate [Ni(ClO4)2] on cooling. The mixture was ultrasonicated and after the separation of Ni(ClO4)2, analytes of interest were determined in the supernatant using ICP-OES. Similarly, it was also found that, after the dissolution of nickel in perchloric acid, when the solution temperature was maintained at ~ 100°C, long needle like crystals of nickel perchlorate were formed. The crystals were separated from the mixture and trace elements in the supernatant were determined using ICP-OES. In both methods the matrix removal was >99% and the recoveries of analytes were in the range 92-97%. The limits of detection for As, B, Bi, Ga, Ge, P, Pb, Sb, Se, Si and Te were found to be 0.18, 0.21, 0.07, 0.06, 0.25, 0.11, 0.09, 0.10, 0.17, 0.20 and 0.07 μg g(-1) respectively. The procedure was applied for the analysis of a standard reference material nickel oxide (SRM 761, Nickel Oxide No.1, NBS, USA) and the values obtained are in close agreement with the certified values.

Procedure for determination of trace ions in boric acid by matrix volatilization–ion chromatography

A method for determination of anions and cations in boric acid is proposed by matrix volatilization. The boric acid matrix was eliminated as trimethyl borate ester in a vapour phase matrix elimination (VPME) system using a mixture of glycerol-methanol. In this VPME system, in situ reagent purification, sample decomposition and digest evaporation were achieved in a single step. Trace anions were separated on anion-exchange column (IonPac AS17) by an isocratic elution with 15 mM sodium hydroxide and the cations on a cation-exchange column (IonPac CS12) by 20 mM hydrochloric acid as eluents. Method detection limits (3sigma) for most ions ranged from 0.3 to 8 ng/g (ppb). Recovery experiments combined with comparison of data obtained by other methods were employed to verify the accuracy of the proposed method. Application of the method to determine trace levels of anions like acetate, oxalate, sulfate, phosphate and cations such as lithium, sodium, potassium, magnesium and calcium in two highly pure grades of boric acid using ion chromatography is demonstrated.

Ultrasound-assisted analyte extraction for the determination of sulfate and elemental sulfur in zinc sulfide by different liquid chromatography techniques.

The speciation and determination of sulfate (SO4(2-)) and elemental sulfur (S degree) in zinc sulfide (ZnS) using ion-chromatography (IC) and reversed-phase liquid chromatography (RPLC) respectively is described. Three sample pretreatment approaches were employed with the aim of determining sulfate: (i) conventional water extraction of the analyte; (ii) solid-liquid aqueous extraction with an ultrasonic probe; and (iii) elimination of the zinc sulfide matrix via ion-exchange dissolution (IED). The separation of sulfate was carried out by an anion-exchange column (IonPac AS17), followed by suppressed conductivity detection. Elemental sulfur was extracted ultrasonically from the acid treated sample solution into chloroform and separated on a reversed phase HPLC column equipped with a diode array detector (DAD) at 264 nm. The achievable solid detection limits for sulfate and sulfur were 35 and 10 microg g(-1) respectively.

Determination of trace levels of boron in graphite powder by inductively coupled plasma-optical emission spectrometry (ICP-OES)

A method has been developed for the determination of traces of boron in graphite powder. The graphite powder was made into a paste using Na2CO3 solution (flux). The paste form of graphite powder was fused in a muffle furnace and was mixed in a glycerol solution. The flux was separated from the glycerol solution as a solid residue by heating over a water bath. The boron present in the glycerol solution was measured by ICP-OES. Compared to conventional Na2CO3 fusion, the amount of flux and fusion time were reduced by a factor of 32 and 8, respectively. Due to the extraction of boron from the flux into glycerol solution, the preconcentration was increased by a factor of 200. The separation of flux was >92% with the recovery of analyte in the range of 92–96%. The detection limit was found to be 90 ng g−1.

Determination of indium in high purity antimony by electrothermal atomic absorption spectrometry (ETAAS) using boric acid as a modifier.

The use of boric acid as a modifier for the determination of trace amount of indium in high purity antimony by electrothermal atomic absorption is described. It was found that the negative influence of the hydrofluoric acid, used for the digestion could not be eliminated by using stabilized temperature platform furnace (STPF) alone. Due to the high dissociation energy (D(0)=506kJmol(-1)) of indium fluoride, it is difficult to dissociate in the gas phase and hence is lost. In presence of HF (used for the dissolution of antimony), the universal Pd-Mg modifier does not work satisfactorily. Additionally, rising corrosion and reduced tube lifetime were observed when the acid digested (HF-HNO(3)) antimony solution was injected in to the platform. Improvement in platform life and elimination of interferences were achieved by the addition of boric acid as a chemical modifier together with ruthenium coating of the platform. Corrosive changes of the transversely heated graphite atomizer (THGA) platform surface were examined by scanning electron microscopy. The standard addition method was applied. A characteristic mass of 36pg was obtained. The detection limit of the proposed method is around 0.04mugg(-1). The developed method was applied to the determination of indium in real samples. The data obtained by this method were in good agreement with those obtained by ICP-MS.

Traceable quantitation of cyanocobalamin (vitamin B12) via measurement of cobalt and phosphorus: a comparative assessment using inductively coupled plasma atomic emission spectrometry (ICP-AES) and ion chromatography (IC)

Traceable and precise quantitative measurements of cyanocobalamin (CN-Cbl) have been hampered by the lack of well characterized standards and pure materials of this bio-inorganic analyte that belongs to the water-soluble vitamins of the B-group known as vitamin B12. Measurement of cobalt and/or phosphorus content of vitamin B12 offer an approach for its quantitation that is traceable to the International System of Units (SI) with low measurement uncertainty. Cobalt and phosphorus measurements of CN-Cbl were carried out by Inductively Coupled Plasma-Atomic Emission Spectrometry (ICP-AES) and Ion Chromatography (IC). Use of a mixed bed ion exchange column coupled with post column reaction, IC provides a means to differentiate free cobalt from the cobalt complexed inside the corrin ring of the CN-Cbl molecule. In the case of ICP-AES and IC, a prerequisite for quality measurement is the purity of the starting vitamin B12 material. The relative expanded uncertainties (% U) expressed at 95% confidence for these analyses range from 0.3 to 1%.

Accurate quantitation standards of glutathione via traceable sulfur measurement by inductively coupled plasma optical emission spectrometry and ion chromatography

The quantitative analysis of glutathione (GSH) is important in different fields like medicine, biology, and biotechnology. Accurate quantitative measurements of this analyte have been hampered by the lack of well characterized reference standards. The proposed procedure is intended to provide an accurate and definitive method for the quantitation of GSH for reference measurements. Measurement of the stoichiometrically existing sulfur content in purified GSH offers an approach for its quantitation and calibration through an appropriate characterized reference material (CRM) for sulfur would provide a methodology for the certification of GSH quantity, that is traceable to SI (International system of units). The inductively coupled plasma optical emission spectrometry (ICP-OES) approach negates the need for any sample digestion. The sulfur content of the purified GSH is quantitatively converted into sulfate ions by microwave-assisted UV digestion in the presence of hydrogen peroxide prior to ion chromatography (IC) measurements. The measurement of sulfur by ICP-OES and IC (as sulfate) using the “high performance” methodology could be useful for characterizing primary calibration standards and certified reference materials with low uncertainties. The relative expanded uncertainties (% U) expressed at 95% confidence interval for ICP-OES analyses varied from 0.1% to 0.3%, while in the case of IC, they were between 0.2% and 1.2%. The described methods are more suitable for characterizing primary calibration standards and certifying reference materials of GSH, than for routine measurements.