Sulfate barium titration

Determination of the level of total sulfur in a rubber can give information on the type of cure system used, for example, elemental sulfur plus accelerator or sulfur donor system, etc. The ISO 6528-1 1992 method — Rubber — Determination of total sulfur content — Part 1 Oxygen combustion flask method is often employed. The principle of the method is oxidation by ignition in an atmosphere of oxygen in the presence of hydrogen peroxide, conversion of sulfur to sulfuric acid and determination of the sulfate by titration with barium perchlorate. The method is... 

Place 25 mL of the decolorized filtrate obtained from the Sodium Chloride test (above) into a 125 mL Erlenmeyer flask, and add 1 drop of a 0.5% phenolphthalein solution in 50% ethanol. Add 0.05 N sodium hydroxide, dropwise, until the solution is alkaline to pH paper, and then add 0.002 N hydrochloric acid until the indicator is decolorized. Add 25 mL of ethanol and about 0.2 g of tetrahydroquinone sulfate indicator. Titrate with 0.03 N barium chloride solution to a red endpoint. Make a blank determination. 

Sulfate can be determined by titrating with barium ion, to precipitate BaS04. As in the gravimetric determination of sulfate by precipitation of barium sulfate, this titration is subject to errors by coprecipitation. Cations such as K", Na", and NHU" " (especially the first) coprecipitate as sulfates ... 

Sulfate in soil on Mars, A barium sulfate precipitation titration described at the opening of this chapter is shown in the figure. The initial concentration of Cl" before adding BaCl2 was 0.000 19 M in 25 mL of aqueous extract of Martian soil. At the end point, when there is a sudden rise in Ba, [cr] = 0.009 6 M. 

Barium sulfate precipitation titration from Phoenix Mars Lander. [Data from Reference 1, courtesy S. Kounaves, Tufts University.)... 

Barium Perchlorate Titration—The sulfate is titrated with barium perchlorate using a thorin-methylene blue mixed indicator. 

Determination of Soluble Sulfate by Titration Using a Barium ISE... 

The slow and more acciuute determination of the sulfate by titration was fortuitous. It was noticed early on that the Cl in the first two WCL units slowly increased during the analysis. Initially this was thought to be due to a slow release of Q from the added soil. However, during the Sol 96 analysis no sample was added to the WCL, but the same increase in Cl was present. It thus became clear that there was a slow and constant titration of the solution with the barium in the reagent crucibles. The increase in Cl was also independently confirmed by chrmiopotentiometiy. Figure 6.5 shows the results of this unintended titration. 

Analytical Methods. The official NIOSH recommended method for determining sulfur dioxide in air consists of drawing a known prefiltered volume of air through a bubbler containing hydrogen peroxide, thus oxidising the sulfur dioxide to sulfuric acid. Isopropyl alcohol is then added to the contents in the bubbler and the pH of the sample is adjusted with dilute perchloric acid. The resultant solution is then titrated for sulfate with 0.005 M. barium perchlorate, and Thorin is used as the indicator. 

Sodium thiosulfate is determined by titration with standard iodine solution (37). Sulfate and sulfite are determined together by comparison of the turbidity produced when barium chloride is added after the iodine oxidation with the turbidity produced by a known quantity of sulfate iu the same volume of solution. The absence of sulfide is iadicated when the addition of alkaline lead acetate produces no color within one minute. 

Impurities in bromine may be deterrnined quantitatively (54). Weighing the residue after evaporation of a bromine sample yields the total nonvolatile matter. After removing the bromine, chloride ion may be deterrnined by titration with mercuric nitrate, and iodide ion by titration with thiosulfate water and organic compounds may be detected by infrared spectroscopy sulfur may be deterrnined turbidimetricaHy as barium sulfate and heavy metals may be deterrnined colorimetricaHy after conversion to sulfides. 

It is convenient to titrate the suspended barium salt with 18 N sulfuric acid (approx. 12-14 ml.) to a pH. of 1.5 using a pH meter. After removal of the barium sulfate the slight excess of sulfate ion may be precipitated using barium chloride solution. The end point is taken when several drops of filtrate show no turbidity either upon addition of sulfuric acid or barium chloride solution. 

Other detection methods are based on optical transmittance [228-231], Alcohol sulfates have been determined by spectrophotometric titration with barium chloride in aqueous acetone at pH 3 and an indicator [232] or by titration with Septonex (carbethoxypentadecyltrimethylammonium bromide) and neutral red as indicator at pH 8.2-8.4 and 540 nm [233]. In a modified two-phase back-titration method, the anionic surfactant solution is treated with hyamine solution, methylene blue, and chloroform and then titrated with standard sodium dodecyl sulfate. The chloroform passing through a porous PTFE membrane is circulated through a spectrometer and the surfactant is analyzed by determining the absorbance at 655 nm [234]. The use of a stirred titration vessel combined with spectrophotometric measurement has also been suggested [235]. Alternative endpoint detections are based on physical methods, such as stalag-mometry [236] and nonfaradaic potentiometry [237]. 

Barium perchlorate colorimetric titration. This colorimetric titration procedure is used in the determination of inorganic sulfate impurities in complex systems of water-soluble sulfonates and sulfonic acids. Sulfonates are precipi-... 

Cesium is determined as the tetraphenylborate, total cobalt as the anthranilate, sulfate as barium sulfate, and cobalt(III) by addition of the alum to excess of potassium iodide solution followed by titration with thiosulfate- Anal. Calcd. -for CsCo(S04)2-12H20 Cs, 22.2 Co, 9.82 S04, 32.0. Found Cs, 22.2 Co, 9.83 S04, 32.3 Co(III), 9.80. 

Lebel [224] has described an automated chelometric method for the determination of sulfate in seawater. This method utilises the potentiometric end-point method for back titration of excess barium against EDTA following precipitation of sulfate as barium sulfate. An amalgamated silver electrode was used in conjunction with a calomel reference electrode in an automatic titration assembly consisting of a 2.5 ml autoburette and a pH meter coupled to a recorder. Recovery of added sulfate was between 99 and 101%, and standard deviations of successive analyses were less than 0.5 of the mean. 

The bomb method for sulfur determination (ASTM D129) uses sample combustion in oxygen and conversion of the sulfur to barium sulfate, which is determined by mass. This method is suitable for samples containing 0.1 to 5.0% w/w sulfur and can be used for most low-volatility petroleum products. Elements that produce residues insoluble in hydrochloric acid interfere with this method this includes aluminum, calcium, iron, lead, and silicon, plus minerals such as asbestos, mica, and silica, and an alternative method (ASTM D1552) is preferred. This method describes three procedures the sample is first pyrolyzed in either an induction furnace or a resistance furnace the sulfur is then converted to sulfur dioxide, and the sulfur dioxide is either titrated with potassium iodate-starch reagent or is analyzed by infrared spectroscopy. This method is generally suitable for samples containing from 0.06 to 8.0% w/w sulfur that distill at temperatures above 177°C (351°F). 

An Ion Chromatograph has been successfully automated by interfacing it to an automatic sampler (7). Continuous unattended analysis was possible, the actual number of samples analyzed being limited by the ionic capacity of the suppressor column. The automated Ion Chromatograph was used to analyze soluble sulfates, ammonia and alkyl amines in stack and automobile exhqust samples. Excellent agreement between IC and automated barium chloroanilate titration for sulfate was obtained with a relative standard deviation less than 5%. 

The normality or molarity of the acid can be determined by titration with a standard solution of sodium hydroxide using a color indicator, or by potentio-metric titration using a pH meter or a millivoltmeter. The sulfate anion in dilute acid can be measured by precipitation with barium chloride or by ion chromatography. 

The precipitation as barium sulfate requires boiling in the absence of air to remove sulfur dioxide. (The residue from the distillation procedure for sulfur dioxide may be used.) Some skill in handling the precipitate is required for accurate results. Complexometric titration after precipitation as lead sulfate (4) is possible. By using three solutions containing different amounts of barium chloride, it is possible to rapidly determine from the clouding whether a wine contains more or less than 0.7, 1.0, or 2.0 grams/liter of potassium sulfate. 

Recently there has been considerable interest on the subject of chemical test reactions for isothermal microcalorimeters. Chemical test reactions allow a user to check if an instrument is functioning correctly because they reflect more accurately the processes under study in a real experiment. Indeed, the ideal case would be to have a universally accepted chemical test reaction for each type of experiment (perfusion, titration, etc.) one may wish to investigate. Examples of systems that have been proposed as chemical test reactions include 18-crown-6/barium sulfate (2) for titration calorimetry... 

Such methods are wet oxidation of pulp followed by estimation of sulfate by precipitation of barium sulfate (Canadian Pulp and Paper Association Standard G28 1970), X-ray fluorescence spectroscopy (Rivington 1988, Kibblewhite et al. 1987), and combustion of pulp followed by analysis of sulfur as sulfur dioxide or as sulfate. The sulfur dioxide evolved is determined by iodometric titration (Canadian Pulp and Paper Association useful method G.7U, March 1959). Sulfate can be determined by titration with barium chloride (Ora 1960), back-titration with sulfuric acid after addition of barium perchlorate (Aldrich 1974), potentiometric titration with lead perchlorate using an ion-selective electrode (Ross and Frant 1969), or ion chromatography (Douek and Ing 1989). 

If both products of the reaction are sparingly soluble, as for example in the titration of sulfates by barium hydroxide, viz.,... 

Wolfrom and coworkers have summated their analytical data on the barium acid salt of heparin, and have expressed the data in terms of a tetrasaccharide unit which comprises two molecular proportions each of 2-amino-2-deoxy-D-glucose residue and D-glucuronic acid residue, and 5 (rather than 6) ester sulfate groups, in an N S ratio of 2 5. The barium sulfur ratio was 1 2, which indicated that the sulfur is essentially present as ester sulfate, and hence the acidity must be due to the carboxyl group, in accordance with the shape of the titration curve. " ... 

For detailed explanations of the chemistry of specific prreipitation titrations the reader is referred to other sources. These include methods such as the Mohr method for halides using the silver chromate end point, the Fajans adsorption indicator method, the Volhard method for FeSCN end point, the titration of halide mixtures with the attendant solid-solution and adsorption effects, the titration of fluoride with thorium(IV), and the titration of sulfate with barium ion. 

Indirect determinations of several types can be carried out. Sulfate has been determined by adding an excess of standard barium(II) solution and back-titrating the excess. By titrating the cations in moderately soluble precipitates, other ions can be determined indirectly. Thus sodium has been determined by titration of zinc in sodium zinc uranyl acetate, and phosphate by determination of magnesium in magnesium ammonium phosphate. Quantitative formation of tetracyano nickel-ate(II) has been used for the indirect determination of cyanide. ... 

An iron-selective electrode based on a glass Fe-1173 (Ge2sSbx2Seeo) has been reported to respond to xmcomplexed iron(ni) in sulfate solutions. It was used to evaluate formation constants of iron(III)-sulfate complexes and as an indicator for titrations of sulfate with barium. The mechanism of the sensing action is obscure. 

Sodium oxalate has been used as a primary standard substance for Ce(IV) in sulfuric acid. In the absence of a catalyst a temperature of 70 to 75°C is necessary. Smith and Getz found that in 1 to 2 M perchloric acid solution, sodium oxalate can be titrated at room temperature with Ce(IV) perchlorate or nitrate but not with sulfate. Rao, Rao, and Rao carried out the titration at room temperature in the presence of barium chloride to remove sulfate, which retards the reaction between oxalate and Ce(IV) and between oxalate and oxidized ferroin. Alternatively, some Fe(III) was added, and the trace of Fe(II) produced photochemically then reacted with the indicator. Rao, Rao, and Murty carried out the titration in 0.5 M HNOj with ammonium hexanitratocerate(IV) instead of the sulfate. With a small amount of KI and KIO3, a satisfactory end point was obtained at room temperature with ferroin as indicator. 

The concentration of sodium ions was determined by flame photometry. Analysis of nickel, calcium, and magnesium ion concentration was carried out by atomic absorption spectrophotometry (Pye Unicam 8800, United Kingdom). The concentration of sulfate ions was determined by titration with barium chloride (BaCl2) solution in the presence of rhodizonate as indicator. Chloride ions were determined using ion-selective electrodes (manufacmred by Radelkis, Hungary). 

Part 13 of ISO 787 determines water-soluble sulfates, chlorides and nitrates. The sample extract can be prepared by either cold or hot extraction method described in Section 4.28. The sulfates in the extract are determined by precipitation with barium chloride, the chlorides are determined by titration with silver nitrate, and the nitrates are determined by a colorimetric method using Nessler reagent." Part 19 gives an alternative method of determination of nitrates by a salicylic acid method. 

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