Complexometric determination of mercury(II) with 2-imidazolidinethione as a selective masking agent

A simple, rapid and selective complexometric method is proposed for the determination of mercury(II). Mercury(II) is first complexed with a known excess of EDTA and the surplus EDTA is back-titrated at pH 5.0-6.0 with lead nitrate, Xylenol Orange being used as indicator. 2-Imidazolidinethione is then added to displace EDTA from the Hg-EDTA complex quantitatively and the EDTA released is titrated with lead nitrate. Reproducible and accurate results are obtained for 2-75 mg of mercury, with a relative error of less than 0.3% and standard deviation of less than 0.04 mg.     

Quantitative complexometric determination of mercury(II) in synthetic alloys and complexes using 2-thiazolinethiol as a masking agent

A simple, rapid and selective complexometric method is proposed for the determination of mercury(II). Mercury(II) and other related metal ions are first complexed with an excess of EDTA and the surplus EDTA is back-titrated with a standard lead nitrate solution at pH 5.0–6.0 (hexamine buffer) using xylenol orange as an indicator. A 0.2% solution of 2-thiazolinethiol in acetone is then added to displace EDTA from the Hg(II)-EDTA complex. The released EDTA is titrated with a standard lead nitrate solution as before. Reproducible and accurate results are obtained in the range of 0.8 g l^?1?15.8 g l^?1 of mercury with a relative error less than ±0.25% and a coefficient of variation (n = 6) not higher than 0.28%. The interference of various ions was studied and the method was employed for the analysis of mercury in its synthetic alloy mixtures and in complexes.     

Determination of palladium(II) using thiosemicarbazide as a replacing reagent

A simple, rapid, accurate, and selective complexometric method is proposed for the determination of palladium(II). Palladium(II), with associated diverse metal ions, is first complexed by adding a known excess of EDTA, and the uncomplexed EDTA is back titrated with lead nitrate solution in acetic acid-sodium acetate buffer (pH 5.0–6.0) until the end-point. Thiosemicarbazide (1%) solution in water is added to displace EDTA from the Pd-EDTA complex. The released EDTA is then titrated with the lead nitrate solution. Reproducible and accurate results are obtained in the concentration range of 1–10 mg of palladium with a relative error of less than 0.4% and a standard deviation of less than 0.02. The interference of many commonly associated metal ions was also studied. Advantages of this method over other complexometric methods of palladium determination are high-lighted.     

Complexometric determination of palladium(II) using thioacetamide as a selective masking agent

A simple, rapid and accurate complexometric method for the determination of palladium(II) is proposed, based on the selective masking property of thioacetamide towards palladium(II). In the presence of diverse metal ions, palladium(II) is complexed with excess of EDTA and the surplus EDTA is back titrated at pH 5-5.5 (acetic acid-sodium acetate buffer) with standard lead nitrate solution using xylenol orange as indicator. An excess of a 0.5% aqueous solution of thioacetamide is then added to displace EDTA from Pd(II)-EDTA complex. The released EDTA is titrated with the same standard lead nitrate solution as before. Reproducible and accurate results are obtained in the concentration range 0.5 mg - 17.80 mg of palladium with relative error of +/- 0.16% and coefficient of variation not exceeding 0.26%. The effect of diverse ions is studied. The method is used for the determination of palladium in its complexes, catalysts and synthetic alloy mixtures.     

Determination of sulpha-drugs with ion-selective membrane electrodes

A liquid-membrane mercury(II)-sensitive electrode is used for determination of various sulpha drugs by addition of excess of mercuric nitrate and potentiometric back-titration of the surplus mercury(II) with EDTA. The performance of the electrode is compared with that of an Ag(2)S crystal-membrane electrode. Attempts to prepare a sulphamethoxazole-sensitive electrode failed.     

Back titration with mercuric nitrate in alkaline medium

Summary A rapid, reliable and accurate method for the determination of trivalent chromium, based on back titrating excess EDTA solutions in the presence of chromium versenate, with mercuric nitrate in alkaline media is given. By its aid amounts of chromium in the order of 50 micro- to 15 milligrams can be determined with fair accuracy. The method is applied for analysis of binary mixtures of chromium with thorium, copper(II), bismuth or mercury(II).     

Selective complexometric determination of mercury, using thiourea as masking agent

A method is described for selective complexometric determination of mercury, thiourea being used as masking agent. An excess of EDTA is added and the surplus EDTA is back-titrated with lead nitrate, with Xylenol Orange or Methylthymol Blue as indicator (pH 5-6). Thiourea is then added to decompose the mercury-EDTA complex and the liberated EDTA is again back-titrated with lead nitrate. The interference of various cations has been studied.     

Microdetermination of nitrates and nitramines-II Gasometric methods based on reduction with mercury, iron(II), titanium(III) and hydroquinone

Four gasometric micro-methods based on the reduction of nitrates or nitramines to nitric oxide with mercury, iron(II), titanium-(III) and hydroquinone in acid media are described. The mercury method is recommended for nitrate esters and secondary nitramines in the absence of aromatic compounds. The iron(II) method is advocated for primary nitramines and nitrate salts in the presence of aromatic compounds. Reductions with titanium(III) and hydroquinone are also successful with the nitrate salts in the presence of an aromatic moiety but the former gives less accurate results. The reduction conditions, mechanism, applications and limitations are described.     

Bismuthiol as an analytical reagent

Summary Lead can be determined from its Bismuthiol II complex volumetrically by dissolving it in an excess of EDTA at a p_H of about 10 and titrating the excess of the EDTA against a magnesium or lead solution. In the same way silver can be determined by dissolving the complex in an excess of cyanide and back titrating the excess against a standard silver nitrate with iodide as the indicator. The results of the former are fairly accurate while those due to latter are highly satisfactory with silver less than 20 mg. With higher amounts of silver, however, the results are within +2%.Part VIII see Z. analyt. Chem. 156, 103 (1957).     

Complexometric determination of cadmium using 2-Mercaptoethanol as masking reagent

A complexometric method for the determination of cadmium(II) in presence of other metal ions is described based on the selective masking ability of 2-mercaptoethanol towards cadmium(II). Cadmium and other ions in a given sample solution are initially complexed with excess of EDTA and the surplus EDTA is titrated with lead nitrate solution at pH 5.0–6.0 (hexamethylentetramine), using xylenol orange as indicator. A known excess of 2-mercaptoethanol solution (10% alcoholic) is then added, the mixture is shaken well and the released EDTA from the Cd-EDTA complex is titrated against standard lead nitrate solution. The interferences of various ions are studied and the method is applied to the determination of cadmium in its complexes. Reproducible and accurate results are obtained for 3.5–25mg of Cd with relative errors 0.65% and standard deviations 0.06 mg.     

Selective complexometric determination of copper in ores and alloys using 2,2′-bipyridyl as masking agent

An EDTA titration method is described for the determination of copper(II) in the presence of other ions based on the selective masking ability of 2,2′-bipyridyl. Copper and other ions in a given sample solution are initially complexed with an excess of EDTA and the surplus EDTA is titrated with lead nitrate solution at pH 5.0–6.0 (hexamine), using xylenol orange as an indicator. A known excess of 2,2′-bipyridyl solution (1% in 50% alcohol) is then added, the mixture is shaken well and the released EDTA from the Cu–EDTA complex is titrated against standard lead nitrate solution. The interference of various ions are studied and the method is applied to the determination of copper in its ores and alloys. Reproducible and accurate results are obtained for 2.54–25.40 mg of copper with S.D. values <0.04 mg.     

Anodic a.c. polarography of methylthymol blue

The anodic a.c. polarographic properties of methylthymol blue (MTB) were investigated in the supporting electrolyte of potassium nitrate containing buffer. The difference in the peak potentials of MTB and EDTA is a good measure of the difference in the stabilities of both chelates. The stability constant of mercury(II)-MTB complex was successfully determined on the basis of that reported for the mercury(II)-EDTA complex.     

Selective complexometric determination of mercury with thiocyanate as masking agent

A method is proposed for selective complexometrie determination of mercury, thiocyanate being used as masking agent. An excess of EDTA is added and the surplus is back-titrated at pH 5-6 with lead nitrate, Xylenol Orange or Methylthymol Blue being used as indicator. Thiocyanate is then added to decompose the mercury-EDTA complex and the liberated EDTA is titrated with lead nitrate. The interference of various cations has been studied.     

Iodimetric determination of hydrazine and hydroquinone with thallium(III) solutions

SeIenium(IV) at trace levels can be determined in hydrochloric and perchloric acid solutions by alternating current and differential pulse polarography. The use of a hanging mercury drop electrode with accumulation of elemental selenium followed by cathodic stripping gives detection limits in the range 0.1–1 p.p.b. With a dropping mercury electrode the detection limit is 8 p.p.b. The possible interferences of Te(IV), Ge(IV), Cu(II), Cd(II) and Pb(II) are discussed. The serious interference of lead(II) can be prevented by addition of EDTA.     

Determination of Mercury(II) with Dithizone by Diffuse Reflectance Spectrometry on a Fibrous Anion Exchanger

The possibility of the determination of mercury(II) with dithizone on the solid phase of a fibrous ion-exchange material filled with the AV-17 anion exchanger was studied. Mercury is adsorbed as an anionic complex. The sorption of mercury as chloride, iodide, sulfate, thiosulfate, nitrate, and EDTA complexes was studied. A procedure was proposed for the sorption–spectrometric determination of mercury with dithizone on a solid phase after sorption as the chloride complex. For improving the selectivity of the method, EDTA is added to the solution. The determination is affected only by Pd(II). The time of analysis is 15 min. The procedure was tested in the analysis of tap and river water and a solution modeling natural water.     

Determination of micromolar concentrations of iodide by electrothermal atomic absorption spectrometry

When a solution (at pH 3.4–4.8) containing iodide and mercury(II) nitrate in a graphite tube is heated by increasing the temperature at a uniform rate, two mercury absorption peaks appear because the decomposition temperature of mercury(II) iodide is higher than that of mercury(II) nitrate. Measurement of the second peak allows 1 × 10^-6–5 × 10^-5 M iodide to be determined with good reproducibility. Equimolar concentrations of cyanide, sulfide and thiosulfate interfered, but these anions could be destroyed with hydrogen peroxide. Interfering cations were removed by extraction of 8-quinolinol complexes.     

A collaborative study of four methods of assay of benzylpenicillin

The assay of benzylpenicillin by iodimetric titration, spectrophotometry with a mercury(II) chloride—imidazole reagent, titration with mercury(II) nitrate in acetate buffer solution, and titration with mercury(II) perchlorate in aqueous pyridine solution, was examined in four laboratories. The first two methods were applied to two samples (the third one being the reference sample), the mercury(II) nitrate titration to three, and the mercury(II) perchlorate method to two samples. The four methods gave very similar results, but the purity obtained with the mercury(II) perchlorate method was slightly lower, and this procedure is less desirable because pyridine is used as solvent. There were no great differences in the relative standard deviations of the four methods. The titration with mercury(II) nitrate is preferred because it is an absolute method.     

Indirect Complexometric Determination of Mercury(II) Using Potassium Bromide as Selective Masking Agent

 A complexometric method for the determination of mercury in presence of other metal ions based on the selective masking ability of potassium bromide towards mercury is described. Mercury(II) present in a given sample solution is first complexed with a known excess of EDTA and the surplus EDTA is titrated against zinc sulfate solution at pH 5–6 using xylenol orange as the indicator. A known excess of 10% solution of potassium bromide is then added and the EDTA released from Hg-EDTA complex is titrated against standard zinc sulfate solution. Reproducible and accurate results are obtained for 8 mg to 250 mg of mercury(II) with a relative error ± 0.28% and standard deviations ≤0.5 mg. The interference of various ions is studied. This method was applied to the determination of mercury(II) in its alloys. Received April 18, 2001 Revision October 10, 2001     

Complexometric Determination of Mercury(II) Using 2-Mercaptopropionylglycine as a Selective Masking Reagent

 A selective complexometric method for the determination of mercury(II) in the presence of associated metal ions is reported, based on the selective masking ability of 2-mercaptopropionylglycine (MPGH₂) towards mercury. Mercury, along with other associated metal ions, is first complexed with excess of EDTA and the surplus EDTA is back titrated at pH 5–6 (hexamine buffer) with standard zinc sulfate solution using xylenol orange as indicator. An aqueous 1% solution of MPGH₂ is then added to displace EDTA selectively from the Hg-EDTA complex and the released EDTA is titrated with the same standard zinc sulfate solution. Reproducible and accurate results are obtained for 4–85 mg of mercury with a relative error of ≤ 0.26% and coefficient of variation not exceeding 0.42%. The interferences of various cations and anions are studied. The method is used for the analysis of mercury in its complexes and alloy samples. Received August 30, 2000. Revision January 15, 2001.     

Natural pyrite as an electrochemical sensor for potentiometric titrations with EDTA, mercury(II) and silver(I)

The results obtained in potentiometric titrations of copper(II), mercury(II) and iron(III) with standard EDTA solutions are presented. The titration of copper(II) at pH values in the range from 8.11 to 10.99 (ammonia buffer) and the titration of mercury(II) and iron(III) at pH values from 3.59 to 5.65 (acetate buffer) were performed. The titration end-point (TEP) was detected with an indicator electrode made from natural crystalline pyrite as an electrochemical sensor. The results obtained in potentiometric titration with the pyrite electrode were compared with those obtained using a platinum electrode (Fe³⁺), a Cu ion selective electrode (Cu²⁺) and a Hg electrode (Hg²⁺). Accurate and reproducible results with good agreement were obtained, but higher potential changes at the TEP were obtained using the pyrite electrode. In the course of the titration the potential was established within less than 1 min, whereas at the TEP it was within about 2–3 min. The potential changes at the TEP were in the range from 60 to 200 mV per 0.1 ml EDTA, according to the stability constant of the complex formed. The highest potential changes, ranging from 160 to 200 mV, were obtained in the titration of iron(III) at pH 3.59. Reverse titration was also performed and accurate and reproducible results were obtained. Moreover, titration of halogenide and thiocyanate with standard mercury(II) solutions, as well as cyanide with silver(I) solution, were performed and accurate and reproducible results were again obtained. Received: 20 February 1998 / Accepted: 19 November 1999