Microdetermination of Mn, Fe, Co, Ni, Cu, Zn, Ag, Cd, Hg, Pb, Bi and U in inorganic and organometallic compounds with morpholinium morpholine-N-dithiocarboxylate

The chelates of morpholinium morpholine-N-dithiocarboxylate with manganese(II), iron(II), iron(III), cobalt(II), nickel, copper(II), zinc, silver, cadmium, mercury(II), lead, bismuth and uranium(VI) have been prepared and their compositions elucidated. Simple, accurate and relatively rapid procedures for the gravimetric and titrimetric microdetermination of these metals in inorganic and organometallic compounds are presented.     

Quantitative separation of traces of lead,cadmium and many other elements from gram amounts of thallium by cation-exchange chromatography

Traces of lead and minor amounts up to 20 mg, can be separated from gram amounts of thallium by cation-exchange chromatography on a column containing only 2 g of AG50W-X4 resin. Thallium passes through the column in 0.1 M HCl in 40% acetone. The retained lead can be eluted with 3 M HCl or HNO₃. Other elements, including Cd, Zn, In, Ga, Cu(II), Fe(III). Mn(II), Co(II). Ni(II), U(VI) and Al, are retained quantitatively with lead. Only Hg(II), Au(III), the platinum metals, bismuth and elements forming oxyanions accompanying thallium. Results for the determination of trace elements in 99.999% pure thallium are presented.     

Simultaneous determination of Cr(III) and Cr(VI) with prechelation of Cr(III) using phthalate by ion interaction chromatography with a C-18 column

Ion interaction chromatography has been successfully used for the simultaneous determination of Cr(III) and Cr(VI) in waste water. A C-18 column which had been dynamically coated with octylamine was used for the separation of Cr(III) and Cr(VI) based on anionic interaction. Cr(III) was chelated with potassium hydrogen phthalate (KHP) before injecting into the column since the Cr(III) did not exist in an anionic form like the Cr(VI) (Cr₂O₇²⁻) presented at the optimum condition. The analytes were detected at 200 nm and linear relationship between absorption with the concentration of Cr(III) or Cr(VI) was 0.1-50 mg/L. Most of the interested interferences including alkali metals, heavy metals and organic materials have no significant effect on Cr(III)-KHP complexation and Cr(VI) stability, only NH₄⁺ and ascorbic acid yielded the serious effect on the Cr(VI) stability. The relative standard deviations calculated from both of peak area and retention time were 0.75-2.20%. The sensitivity of the method at the level concentration of sub mg/L enabled the simultaneous determination of Cr(III) and Cr(VI) contents in waste water samples without any special sample preparation step.     

Oscillopolarographic adsorptive wave determination of microamounts of orthophosphate

In the system HCl-Sb(III)-ammonium molybdate-acetone-butanone, PO(3-)(4), Sb(III) and Mo(VI) form a ternary heteropoly acid, which can be adsorbed on a dropping mercury electrode and reduced to a heteropoly blue. The electrochemical reaction produces a sensitive polarographic wave with peak potential of -0.42 V vs. SCE. The limit of determination of phosphate is 6 x 10(-8)M. The coefficients of variance are 10 and 3% for 0.1 and 1muM phosphate, respectively.     

Quantitative separation of gold from cadmium, indium, zinc and other elements by cation-exchange chromatography in hydrochloric acid-acetone medium

Gold(III) can be separated from Cd, In. Zn, Ni, Cu(II), Mn(II), Co(II), Mg, Ca, Al, Fe(III), Ga and U(VI) by adsorbing these elements on a column of AG50W-X8 sulphonated polystyrene cation-exchange resin from 0.1M HCl containing 60% v v acetone, while Au(III) passes through and can be eluted with the same reagent. Separations are sharp and quantitative. The amounts of gold retained by the resin are between 1 and 2 orders of magnitude lower than encountered during adsorption from aqueous 0.1M HCl. Recoveries for mg amounts of gold are 99.9% or better and for ng amounts are still better than 99%, as shown by radioactive tracer methods. Hg(II), Bi, Sn(IV), the platinum metals and some elements which tend to form oxy-anions in dilute acid accompany gold. All other elements, though not investigated in detail, should be retained, according to their known distribution coefficients. Relevant elution curves, results of quantitative separations of binary mixtures and of recovery tests are presented.     

Determination of plutonium by secondary coulometric titration with internally generated iron(II)

The method for plutonium determination based on secondary controlled-potential coulometry, as described by SHULTS, is applied for analysis in the range of 0.1–5 mg plutonium. The method involves the oxidation of plutonium to Pu(VI) with perchloric acid followed by its reduction by an internally generated ferrous mediator. This is a two step procedure, involving the reduction of Pu(VI) and Fe(III) to a mixture of Pu(III) and Fe(II), followed by the oxidation of Pu(III) and Fe(II) to Pu(IV) and Fe(III), respectively. The net results is the reduction of Pu(VI) to Pu(IV), measured as the difference between the currents consumed during the reduction and oxidation steps. The original method of SHULTS involves 10–25 mg plutonium for each determination. Since the present method is intended for the analysis of smaller amounts of plutonium, the oxidation procedure described in the original version had to be modified. The method is found to work satisfactorily with a precision better than 0.1% at 5 mg level and 1.2% for 0.1 mg plutonium.     

Diphenic acid as a selective reagent for the amperometric determination of thorium(IV)

Th(IV) has been titrated amperometrically at an applied e.m.f of −1.0 V (dropping mercury electrode vs. SCE) with diphenic acid (neutralized with sodium hydroxide). Th(IV) in the range 8.0–60.0 mg/100ml can be determined with an error of ±0.5%. A number of foreign ions including Ce(IV), Zr(IV), La(III), U(IV), U(VI) do not interfere even if present in excess but traces of Ti(IV) do. The method is rapid and selective and has been used for the determination of Th(IV) in monazite sand.     

Refreshable mercury film silver based electrode for determination of chromium(VI) using catalytic adsorptive stripping voltammetry

The refreshable mercury film silver based electrode Hg(Ag)FE applied for determination of Cr(VI) traces using catalytic adsorptive striping voltammetry (CAdSV) will be presented. The film electrode is characterized by its very good surface reproducibility (not less than 2%) and long-term stability (1500–2000 measurement cycles). The mechanical refreshing of mercury film is realized in the specially constructed device, in a time shorter than 1–2 s.

In the paper, it will be proved that a mechanically weak hanging mercury drop electrode (HMDE) may be substituted by mercury film Hg(Ag)FE electrode with a surface area adjustable from 1.5 to 12 mm². For the electrode surface 4 mm² the detection limit obtained for Cr(VI) was 0.19 nM, while the linearity range measured for a 20 s accumulation time was between 0.5 and 50 nM. The relative standard deviation (R.S.D.) in determination of Cr(VI) varied from 1 to 5%. The influence of the excess of Cr(III) on determination of Cr(VI) was analyzed using samples from the Dobczyce reservoir spiked with known amounts of Cr(VI) and Cr(III).     

Spectrophotometric determination of germanium with Catechol Violet and cetyltrimethylammonium bromide

A ternary complex between germanium, Catechol Violet (CV) and cetyltrimethylanunoniuni bromide is proposed for the determination of germanium. The stoichiometric ratio Ge:CV is 1:2. Beer's law is obeyed from 0.1 to 1.0 ppm of Ge. The method is highly selective. Interference from Sn(IV), Fe(III), Bi(III), Cr(VI), Mo(VI), V(V) and Sb(III) in mg amounts is eliminated by extracting the germanium into carbon tetrachloride from 9M HC1 and then stripping into water before the photometric determination.     

The micro-heterometric determination of silver with p-dimethylamino-benzylidene-rhodanine: Direct determination of traces of silver in alloys and solutions

A heterometric method was presented for the direct determination of 0.05–0.1 mg silver in 20 to 30 ml solution. The solution contained, besides complexing agents, 99.7 to 99. 9% of the following metals Ca, Ba, Mg, Zn, Mn, Ni, Co, Al, Cr (99%). Fe(III). Pb, Cu, Sb, Bi, U, Hg, Zr, Ce, Th, Tl. The error was 0.0–2.0% It was possible to determine the same amount of silver in solutions of Pd (~ 95%). Au(III) (~ 90%) or Pt(IV) (~ 97%) with an error of 0.0–3.0%.A full titiation always lasted ca. five minutes.     

Test analysis method using ion pairs of pyrocatechol azo derivatives and trihydroxyfluorones with cetylpyridinium and their chelates with metal ions immobilized on paper

A two-stage procedure is proposed for the immobilization of ion pairs of pyrocatechol azo derivatives and trihydroxyfluorones and their chelates with metal ions on paper. It is demonstrated that ion pairs of phenylfluorone and thiazolylazopyrocatechol with cetylpyridinium can be used for the test determination of 0.01-10 mg/L Ti(IV), 0.05-20 mg/L Mo(VI), and 0.1–20 mg/L W(VI) and V(V) by the length of the colored zone of test strips after their contact with a test solution and for the determination of 0.01-0.5 mg/L Al and Mo(VI) and 0.001-0.1 mg/L Ti(IV) by the color intensity of reactive papers after passing a test solution. Chelates of Mo(VI) with tiazolylazopyrocatechol and of Sb(III) with phenylfluorone are used for the test determination of 0.01-1000 mg/L cationic surfactants. The selectivity of reactions is studied, and procedures are proposed for the determination of the above elements in different materials. The relative standard deviation of the results of analysis is no higher than 50%.     

Inorganic polarography in organic solvents-III Analytical applications of metal-acetylacetonate complexes in toluene

Indium and palladium are determined polarographically with a dropping mercury electrode in a toluene phase, following extraction as the acetylacetonates from aqueous solutions containing 2-10 ppm of the metals (or 0.1-0.5 ppm with a greater ratio of sample volume to solvent volume). Of 31 elements examined, only Co(III), Cr(III), Cu(II), Fe(III), In, Mo(VI), Pd and Ti(IV) gave extractable complexes with reduction waves in the available potential range. Specificity for palladium is obtained by extraction at pH 0.5, and for indium at pH 9 m the presence of cyanide and ascorbic acid as masking agents.     

Adsorptive stripping voltammetric determination of chromium in gallium

The electroanalytical chemistry of trace metals has progressed strongly with the development of cathodic stripping voltammetry (CSV) preceded by adsorption collection of organic metal complexes. A sensitive method for the determination of trace amount of chromium in gallium is described. Gallium is dissolved in sodium hydroxide containing hydrogen peroxide. The method is based on the catalytic activity of nitrate ions on the reduction of Cr(III)TTHA (triethylene tetramine-N,N,N',N',N',N'-hexaacetic acid) complex. The sensitivity of this method is further improved by adsorption preconcentration of Cr(III)TTHA complex at a hanging mercury drop electrode (HMDE). The Cr(III) formed at the electrode surface by the reduction of Cr(VI), which is present in the bulk solution, is immediately complexed by TTHA. The adsorbed complex is then reduced at a peak potential of - 1.26 V, and the peak height of Cr(III) reduction is measured. The determination limit was restricted by the amount of chromium present in the reagent blank solution. The method is suitable for the determination of chromium at level as low as 0.2 mug g(-1) (with about 50 mg of sample) and a relative standard deviation of 15%.     

Application of a renewable silver based mercury film electrode to the determination of Cr(VI) in soil samples

The design and experimental results of the application of a renewable mercury film silver based electrode to the determination of Cr(VI) in soil samples are presented. The main feature of this procedure is that it can be used in field measurements. The procedure is based on the extraction of total Cr(VI) exploiting the complexation property of diethylenetriaminepentaacetic acid (DTPA) followed by electrochemical reduction of Cr(VI) to Cr(III) with the formation of Cr(III)-H₂DTPA complex adsorbed on mercury film electrode. The voltammetric signal is caused by reduction of this complex. The validation of the proposed procedure was made by Cr(VI) determination in the certified reference material “Chromium VI in soil”. The protocol for Cr(VI) determination has also been applied to the analysis of Rendoll soil samples with satisfying precision.

     

Determination of trace molybdenum in vegetable and food samples by spectrophotometry with p-carboxyphenylfluorone

A new highly sensitive and selective chromogenic reagent, p-carboxyphenylfluorone (p-CPF), was studied for spectrophotometric determination of trace molybdenum. In 0.36 mol L(-1)phosphoric acid medium, p-CPF reacts with molybdenum(VI) to form a 1:3 red complex, which has a sensitive absorption peak at 531 nm. Under optimal conditions, the reaction of molybdenum(VI) with p-CPF completed rapidly and absorbance remains almost constant for at least 24 h. Molybdenum(VI) obeyed Beer's law in the range 0-2.0 microg mL(-1); the apparent molar absorption coefficient, Sandell's sensitivity and the limit of detection were found to be 1.03 x 10(5) L mol(-1) cm(-1), 1.028 ng cm(-2)and 0.73 ng mL(-1) respectively; the effect of various foreign ions were examined in detail. It was found that most coexisting ions can be tolerated in considerable amounts, especially 800 mg of Mn(II), 200 mg of Mg(II), Fe(II), Co(III), Ni(II) and Cd(II), 50 mg of Ca(II) and Al(III), 25 mg of Cu(II) and Fe(III), 10 mg of Hg (II), La(III), Bi(III), Pb(II) and Zn(II) don't interfere with the determination of molybdenum(VI). The proposed method is very simple, sensitive and selective, it has been applied to determine molybdenum in vegetable and food samples with a very high precision and accuracy. Moreover, the synthesis of the reagent and the conditions of the colour reaction were also studied in detail.     

Extractive separation and spectrophotometric determination of palladium and platinum with dithizone in the presence of stannous chloride

The conditions [acid used, presence of chloride and tin(II)] for the extractive separation and spectrophotometric determination of palladium and platinum as the dithizonates Pd(HDz)(2) and Pt(HDz)(2) have been examined. In the absence of stannous chloride platinum does not undergo extraction. Conditions for the separation and determination of these metals in the presence of mercury, gold and copper, which are also extracted with dithizone into carbon tetrachloride or chloroform under the conditions suitable for palladium (1M sulphuric acid/0.1M hydrochloric acid), have been defined. The mercury and gold dithizonates are formed quickly and can be removed before the palladium and platinum compounds have had time to form. They can be decomposed with iodide. Copper dithizonate is decomposed by reduction with tin(II). The proposed procedure has been applied to the determination of palladium in technical platinum metal.     

Determination of trace chromium(VI) by an inhibition-based enzyme biosensor incorporating an electropolymerized aniline membrane and ferrocene as electron transfer mediator

A novel inhibition-based glucose oxidase (GOx) biosensor for environmental chromium(VI) detection is described. An electropolymerized aniline membrane has been prepared on a platinum electrode containing ferrocene as electron transfer mediator, on which GOx is cross-linked by glutaraldehyde. The mechanism of the redox reaction on the electrode and the performance of the sensor are studied. The sensor's response to glucose decreases when it is inhibited by chromium(VI), with a lower detection limit of 0.49?µg?L^?1, and the linear response range is divided into two parts, one of which is 0.49–95.73?µg?L^?1 and the other is 95.73?µg^?1 to8.05?mg?L^?1. The enzyme membrane is shown to be completely reactivated after inhibition, retaining 90% activity over more than forty days. Interference to chromium(VI) determination from lead(II), copper(II), cadmium(II), chromium(III), cobalt(II), tin(II) and nickel(II) is found to be minimal, while high concentrations of mercury(II) and silver(I) may interfere with the determination of trace chromium(VI). The sensor has been used for chromium(VI) determination in soil samples with good results.     

Sequential injection analysis for Cr(VI) and Cr(III) with renewable surface reflection spectrophotometry.

On the basis of the chromogenic reaction of chromium(VI) with 1,5-diphenylcarbohydrazide (DPC) on the surface of Polysorb C-18 beads and the sequential injection renewable surface technique (SI-RST), a highly sensitive reflect spectrophotometric method for the determination of chromium(III) and chromium(VI) was proposed. Considerations of system and flow cell design, and factors that influence the determination performance were discussed. With 300 microl of sample loaded and 0.6 mg of beads trapped, the linear response range was 0.02 - 0.5 mg l(-1) Cr(VI) with a detection limit (3 sigma) of 2.4 microg l(-1) Cr(VI). The method achieves a precision of 1.3% RSD (n = 11) and a throughput of 53 samples per hour. The determination of Cr(III) was based on the same reaction for the determination of Cr(VI) after being oxidized by (NH4)2S2O8. The precision of the oxidation method was evaluated using a 0.2 mg l(-1) Cr(III) standard, yielding an RSD of 2.5% (n = 11). The average recovery of Cr(III) oxidized was tested to be 99.1%. The proposed method was used in the simultaneous determination of Cr(VI) and Cr(III) in water samples, and the error was less than 3%.     

Redox titrations at millimolar concentration in n,n-dimethylformamide media

Potentiometric oxidation-reduction titrations in N,N-dimethylformamide (DMF) have been shown to be valid at millimolar concentrations of titrand. Forward and reverse titrations that involve the oxidants copper(II), chromium(VI), iron(III), and mercury(II) with the reductants titanium(III), cobalt(II), ascorbic acid, cysteine, and thiolactic acid have been examined. Some preliminary results of titanium(III) in DMF titrimetry in the determination of copper and iron in alloys are presented.     

The chromatography of metals on DEAE-cellulose layers in phosphoric acid media

The adsorption behaviour of forty-eight metals on DEAE-cellulose thin layers has been examined in aqueous phosphoric acid media. R_F values are given as a function of phosphoric acid concentration over the range 0.01–1.0 M and are compared with those obtained in a similar manner with a crystalline cellulose, Avicel SF. Particularly strong retention on DEAE-cellulose occurred for Mo(VI), W(VI), Re(VII), the platinum group metals, Au(III) and Bi(III). Weak to moderate retention was also observed for several metals, such as V(V), Fe(III), Se(IV), In(III), the rare earths and U(VI), at lower concentrations of phosphoric acid (<0.1 M).