Titrimetric microdetermination of isoniazid by amplification reactions

An amplification method for the determination of (0.01–2.0 mg) isoniazid is described. It depends on oxidation of the isoniazid sample solution with a chloroform solution of iodine and removed of its excess, oxidation of the resulting iodide with bromine, and iodometric titration of the liberated iodate after 6-fold amplification. Alternatively, the liberated iodine is reduced to iodide, and again oxidized to yield 36 iodide ions for every iodide ion originally present. The coefficient of variation does not usually exceed 1.5% for above 0.5 mg of isoniazid but increases to 3.6% at the 0.01-mg level.     

Titrimetric Microdetermination of chloral hydrate by amplification reactions

A simple titrimetric method for estimation of 0.1–5 mg of chloral hydrate is presented. It depends on oxidation of an alkaline solution of chloral hydrate with a chloroform solution of iodine, removal of excess of iodine, oxidation of the resulting iodide with bromine, and iodometric titration of the iodate produced, giving 6-fold amplification. Alternatively, the iodide formed is oxidized with periodate, masking of the excess of periodate with molybdate at pH 3, and iodometric titration of the iodate, giving 24-fold amplification. The coefficient of variation does not usually exceed 2%, for above 1 mg of chloral hydrate but increases to 3.8% at the 0.1-mg level.     

A new fully automated on-line digestion system for ultra trace analysis of mercury in natural waters by means of FI-CV-AFS

A fully automated flow injection (FI) system utilizing the extraordinary oxidation power of bromine monochloride (BrCl) for the transformation of dissolved mercury species to Hg(2+) and oxidation of dissolved organic carbon (DOC) has been developed and coupled to cold vapor (CV) atomic fluorescence spectrometry (AFS) for highly sensitive mercury detection. The system can be applied to natural waters, sea water as well as freshwater and provides a detection limit as low as 16 pg Hg l(-1) from a sample volume of 7 ml. The relative standard deviation is about 4-10%. A 3-fold measurement of one sample is completely processed within 15 min. Dissolved organic carbon, chloride and iodide ions are tolerated in concentrations of 15 mg DOC l(-1), >21 g Cl(-)l(-1), and 10 mg I(-)l(-1). Validation of the proposed method yielded a good recovery of total mercury in a moorland water sample and in the certified reference material ORMS-3, river water. Investigation of eight real water samples with mercury concentrations in the range of 0.3-1.4 ng l(-1) also confirmed the suitability of the proposed method.     

Titrimetric microdetermination of salicylic, acetylsalicylic, and p-hydroxybenzoic acids by amplification reactions

A novel titrimetric method with amplification has been developed for the determination of 0.05–2.0 mg of salicylic, acetylsalicylic, or p-hydroxybenzoic acid. It depends on bromination of these compounds by bromine to tribromophenylhypobromite, which liberates iodine when treated with iodide. The liberated iodine is extracted with chloroform, reduced to iodide, oxidation of the resulting iodide with bromine, and iodometric titration of the iodate produced gives the sixfold amplification method. The coefficient of variation does not exceed 1% for above 0.5 mg of the studied compounds, but increases to 2.8% at the 0.05-mg level.     

Indirect amplification method for determining mercury by direct-current polarography. Application to organomercury compounds

An amplification method for the determination of 0.5–70 ppm (2.5 × 10⁻⁶ to 3.5 × 10⁻⁴ M) of Hg(II) is described. Hg(II) is reacted with a slight excess of KI, and the excess iodide is oxidized by bromine water and measured polarographically as iodate with sixfold amplification. Alternatively, the iodate formed is reacted to liberate iodine which is then reduced to iodide, and again oxidized to yield six iodate ions for every iodide ion originally present;

2. Microdetermination of Mercury in Organomercurial Compounds

polarographic reduction requires 36 electrons. Oxidation of the excess iodide with periodate yields four iodate ions for every iodide ion and therefore allows 24-fold amplification.Microdetermination of mercury in organomercurials is achieved using the sixfold method following closed flask combustion: the average percentage error for 10 determinations is ±0.40 and the time required for one sample run is 45 min.     

Micro and submicro iodometric determination of arsenite and sulphite ions by amplification reactions

Two methods are described for the micro and submicro iodometric determination of arsenite and sulphite ions involving 3- and 6-fold amplification reactions, respectively. The arsenite method is based on oxidation with an excess of periodate, masking of the unreacted periodate with molybdate, and final iodometric titration of the iodate released. The sulphite method depends upon oxidation with iodine and removal of its excess by extraction with chloroform, and oxidation of the iodide formed to iodate, which is determined iodometrically as usual. The two methods are simple, rapid, and accurate. The average recoveries obtained are 99.9 and 99.3% for arsenite and sulphite, respectively.     

Titrimetric microdetermination of uric acid and thioglycollic acid by amplification reactions

A simple amplification method for determination of 0.05-2 mg of uric acid or thioglycollic acid has been worked out. It depends on iodine oxidation of the uric acid or thioglycollic acid solutions, removal of the excess of iodine, oxidation of the resulting iodide with bromine, and iodometric titration of the resulting iodate. The coefficient of variation ranges from 0.7 to 2.4% for uric acid and from 0.5 to 1.9% for thioglycollic acid, depending on the amount of the acid.     

Iodometric microdetermination of hydrazines by amplification reactions

Two new, simple, rapid, and accurate iodometric amplification methods are described for the micro and submicro determination of hydrazine. The first depends on oxidation with a chloroform solution of iodine and removal of its excess, oxidation of the resulting iodide with bromine, and iodometric titration of the liberated iodate. The second method is based on oxidation with periodate at pH 8, masking of the excess of periodate with molybdate at pH 3, and iodometric titration of the iodate. The order of amplification involved in the two methods is 6- and 3-fold, respectively. Micro amounts of hydrazine sulphate and dihydrochloride were determined satisfactorily by both methods, the average recoveries being 98.6 and 99.4%.     

Titrimetric determination of chloramine-T and some aldoses by amplification reactions

A titrimetric method with amplification has been worked out for the determination of chloramine-T and certain aldoses. It is based on Leipert determination of iodide produced in the case of chloramine-T by reduction of the determinand with excess of iodide, and extraction and subsequent reduction of the iodine liberated. In the other case, the aldoses are oxidized with iodine, the surplus oxidant is extracted, and the residual iodide is determined. The method is applicable to chloramine-T in the range 0.01-3 mg, with a relative error between -3.0 and -0.4% and a relative standard deviation of 0.6-0.8%, depending on the amount present, and to 0.05-1 mg of glucose, galactose or arabinose, or 0.1-2 mg of lactose or maltose, with a relative standard deviation of 1.4% for > 0.5 mg of aldose.     

Chemical amplification methods for the sequential determination of trace amounts of ruthenium by titrimetric and spectrophotometric procedures

Two simple, inexpensive and rapid iodometric and spectrophotometric procedures were developed for trace amount determination of ruthenium. The proposed methods were based on the oxidation of ruthenium(II or III) with sodium periodate at pH 2.4-3.6, masking the excess periodate with sodium molybdate. The released iodate was then allowed to react with KI at pH 3, with subsequent determination of the released iodine spectrophotometry as triiodide at 350 nm or iodometry with 0.005 M sodium thiosulphate. This procedure offers an 18- and 15-fold amplification per Ru(II) or Ru(III) ion, respectively. Alternatively, the produced iodine was extracted with CHCl(3), shaken with an aqueous solution of sodium sulphite and the produced iodide ion was then allowed to react with bromine (or sodium periodate). The released iodate was subsequently determined by iodometry or spectrophotometry after addition of KI. The bromine and sodium periodate oxidation procedures offered 90- and 360-fold amplification per ruthenium(III) ion, and 108- and 432-fold amplification per ruthenium(II) ion. Ruthenium(IV) content was determined by these procedures after prior reduction to Ru(III) with sulphurous acid. The binary mixtures Ru(II)-Ru(III); Ru(III)-Ru(IV) and Ru(II)-Ru(IV) in aqueous solution at concentration 0.05 mug ml(-1) were successfully analyzed by the developed procedures. The utility of the proposed methods for the analysis of ruthenium in its complexes was demonstrated. Natural seawater and seawater spiked with ruthenium were analyzed satisfactorily.     

Titrimetric determination of phenol resorcinol and phloroglucinol

A new and sensitive titrimetric method with an amplification procedure has been worked out for the determination of 10-1000 mug of phenol, resorcinol or phloroglucinol. The method is based on reaction of the phenols with an excess of bromine to form bromosubstituted aryl hypobromites. After removal of excess of bromine with formic acid, the hypobromites are treated with iodide to liberate an equivalent amount of iodine, which is extracted into chloroform, then reduced to iodide and determined by the Leipert procedure with 6-fold amplification. The coefficient of variation does not exceed 0.4% for amounts of determinand > 100 mug, but increases to 1.5% at the 10-mug level.     

Chemical enhancement method for the determination of mercury by spectrophotometry after iodide extraction

A selective and sensitive spectrophotometric method for the determination of 0.08-2.5 ppb of mercury(II) is described. Mercury is extracted as tetraiodomercury(II)-Cd-phenanthroline ion-pair into benzene and selectively stripped into EDTA. The iodide associated with mercury present in the stripping is oxidized to iodate and then treated with excess iodide to give iodine. The iodine formed is extracted into benzene and equilibrated with iodate in acidic medium in the presence of chloride and Rhodamine 6G for the formation of ICI(-)(2) species and its extraction as ion-pair with Rhodamine 6G. Determination is completed by measuring the absorption of the extract at 535 nm. The coefficient of variation is 1.5% for 10 determinations of 200 ng of mercury. The method has been applied to establish the mercury content of natural waters and chloralkali plant effluent.     

Iodometric microgram determination of Mn(II) in aqueous media by an indirect chemical amplification reaction

A rapid, simple and highly sensitive iodometric amplification method is described for the determination of microgram amounts of Mn(II). The method is based on oxidation of Mn(II) with an excess of periodate in acetate buffer (pH 2.8-3.0), masking of the unreacted periodate with molybdate, and after addition of iodide, titration of the liberated iodine is with thiosulphate. The proposed method offers 20-fold amplification for Mn(II) and was found suitable for the determination of Mn(II) in the presence of permanganate ions. Mn(II) in tap water and an industrial waste water has been successfully determined by the proposed method.     

Voltammetric determination of mercury(II) at a carbon paste electrode in aqueous solutions containing tetraphenylborate ion

The determination of mercury(II) ions can be achieved by monitoring the decrease in the oxidation peak of the tetraphenylborate ion in the presence of this metal ion at a carbon paste electrode. The reaction between mercury(II) and the tetraphenylborate ion results in the formation of diphenylmercury, thus providing the method with good selectivity over other metal ions. Using anodic stripping voltammetry in a neutral electrolyte, a linear dependence of the decrease of peak height was observed on increasing the mercury(II) concentration in the range 1 x 10(-6)-8 x 10(-9)M mercury(II). Zinc(II), cadmium(II), lead(II), nickel(II), cobalt(II), tin(II), potassium(I) and ammonium(I) ions did not interfere at a 1000-fold concentration excess. Iron(III) and chromium(III) did not interfere at a 250-fold and 50-fold concentration excess, respectively. Following masking procedures, copper(II), bismuth(III) and silver(I) did not interfere at a 100-fold concentration excess. The method can be used to determine the concentration of mercury(II) in natural waters contaminated by this metal.     

碘的阴极溶出伏安法研究

本文研究了碘在悬汞电极上的阴极溶出行为。提出了直接以络合剂(EDTA,DTPA,DCTA)为电解底液便可有效地消除铅、镉、铜等重金属元素的干扰。测定检出限为6.3×10^-9M。方法可不经分离富集直接测定饮用水和食盐中的痕量碘。     

Titrimetric and spectrophotometric methods for the determination of cerium(IV) in aqueous solution

A titrimetric and spectrophotometric methods for cerium(IV) determination have worked out. The first method relies upon the treatment of cerium(IV) solution with an excessive amount of iodide; the liberated iodine is extracted into chloroform, then reduced to iodide. The latter is iodometrically determined after 6- or 36-fold amplification. The spectropho-tometric finish is based upon the reaction of the titled ion with iron(II), in the presence of hexacyanoferrate(II), to form an intense prussian blue color suitable for the trace determination of cerium(IV) ion.     

Simple and rapid determination of iodide in table salt by stripping potentiometry at a carbon-paste electrode

A simple and rapid procedure, utilising constant-current stripping analysis (CCSA) at a carbon-paste electrode containing tricresyl phosphate as a pasting liquid (TCP-CPE), has been developed for the determination of iodide in table salt. Because of a synergistic accumulation mechanism based on ion-pairing and extraction of iodide in combination with electrolytic pretreatment of the TCP-CPE, the method is selective for iodide and enables direct determination of iodide in samples of table salt containing anti-caking agents such as K(4)[Fe(CN)(6)] (food additive "E 536") or MgO. The iodide content (calculated as KI) can be determined in a concentration range of 2 to 100 mg kg(-1) salt, with a detection limit (S/N=3) of 1 mg kg(-1), and a recovery from 90 to 115%. The proposed method has been used to determine iodide in several types of artificially iodised table salt and in one sample of natural sea salt. The results obtained agreed well with those obtained by use of three independent reference methods (titration, spectrophotometry, and ICP-MS) used to validate the CCSA method, indicating that the developed method is applicable as a routine procedure for rapid testing in salt production process control and in the analysis of marketed table salts.     

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.     

Simple and Equipment-Free Paper-Based Device for Determination of Mercury in Contaminated Soil

This work presents a simple and innovative protocol employing a microfluidic paper-based analytical device (µPAD) for equipment-free determination of mercury. In this method, mercury (II) forms an ionic-association complex of tetraiodomercurate (II) ion (HgI₄²⁻_(aq)) using a known excess amount of iodide. The residual iodide flows by capillary action into a second region of the paper where it is converted to iodine by pre-deposited iodate to liberate I_2(g) under acidic condition. Iodine vapor diffuses across the spacer region of the µPAD to form a purple colored of tri-iodide starch complex in a detection zone located in a separate layer of the µPAD. The digital image of the complex is analyzed using ImageJ software. The method has a linear calibration range of 50–350 mg L⁻¹ Hg with the detection limit of 20 mg L⁻¹. The method was successfully applied to the determination of mercury in contaminated soil and water samples which the results agreed well with the ICP-MS method. Three soil samples were highly contaminated with mercury above the acceptable WHO limits (0.05 mg kg⁻¹). To the best of our knowledge, this is the first colorimetric µPAD method that is applicable for soil samples including mercury contaminated soils from gold mining areas.     

Mercury speciation in sea food by flow injection cold vapor atomic absorption spectrometry using selective solid phase extraction

An on-line inorganic and organomercury species separation, preconcentration and determination system consisting of cold vapor atomic absorption spectrometry (CV-AAS or CV-ETAAS) coupled to a flow injection (FI) method was studied. The inorganic mercury species was retained on a column (i.d., 3 mm; length 3 cm) packed to a height of 0.7 cm with a chelating resin aminopropyl-controlled pore glass (550 A) functionalized with [1,5-bis (2 pyridyl)-3-sulphophenyl methylene thiocarbonohydrazyde] placed in the injection valve of a simple flow manifold. Methylmercury is not directly determined. Previous oxidation of the organomercurial species permitted the determination of total mercury. The separation of mercury species was obtained by the selective retention of inorganic mercury on the chelating resin. The difference between total and inorganic mercury determined the organomercury content in the sample. The inorganic mercury was removed on-line from the microcolumn with 6% (m/v) thiourea. The mercury cold vapor generation was performed on-line with 0.2% (m/v) sodium tethrahydroborate and 0.05% (m/v) sodium hydroxide as reducing solution. The determination was performed using CV-AAS and CV-ETAAS, both approaches have been used and compared for the speciation of mercury in sea food. A detection limit of 10 and 6 ng l(-1) was achieved for CV-AAS and CV-ETAAS, respectively. The precision for 10 replicate determinations at the 1 microg l(-1) Hg level was 3.5% relative standard deviation (R.S.D.), calculated from the peak heights obtained. Both approaches were validated with the use of two certified reference materials and by spiking experiments. By analyzing the two biological certified materials, it was evident that the difference between the total mercury and inorganic mercury corresponds to methylmercury. The concentrations obtained by both techniques were in agreement with the certified values or with differences of the certified values for total Hg(2+) and CH(3)Hg(+), according to the t-test for a 95% confidence level. It is amazing how this very simple method is able to provide very important information on mercury speciation.