Barium gravimetric analysis

Wil Kastning of the Nebraska State Agriculture Laboratory filters barium sulfate precipitates using filtering crucibles and a vacuum system while performing a gravimetric analysis of fertilizers for sulfate content. 

As an example, gravimetric analysis can be used to determine the amount of water in hydrated barium chloride. 

Water of crystaUization in hydrated salts can be measured by thermo-gravimetric analysis. Zinc can be analyzed in an aqueous solution by AA or ICP. Sulfate can be identified by precipitation with barium chloride solution or by ion chromatography. The zinc content in the heptahydrate is determined by AA, ICP and other instrumental methods. 

Microwave laboratory ovens are currently quite popular. Where applicable, these greatly shorten drying cycles. For example, slurry samples that require 12 to 16 hours for drying in a conventional oven are reported to be dried within 5 to 6 minutes in a microwave oven. The time needed to dry silver chloride, calcium oxalate, and barium sulfate precipitates for gravimetric analysis is also shortened significantly. ... 

We take advantage of the common ion effect to decrease the solubility of a precipitate in gravimetric analysis. For example, sulfate ion is determined by precipitating BaS04 with added barium chloride solution. Figure 10.3 illustrates the effect of excess barium ion on the solubility of BaS04. 

A student proposes to analyze barium gravimetrically by precipitating Bap2 with NaF. Assuming a 200-mg sample of Ba " in 100 mL is to be precipitated and that the precipitation must be 99.9% complete for quantitative results, comment on the feasibihty of the analysis. 

The barium form of zeolite A is of moderate stability, unlike other alkali metal and alkaline earth forms which can be stable to about 1000°C. This work uses the techniques of differential thermal analysis (DTA) and thermo gravimetric analysis (TGA) in conjunction with isotopic labelling and x-ray powder photography to investigate the thermal stability of heteroionic forms of zeolite A. Reasons for the instability of BaA and Na/BaA zeolites are suggested and comparisons made with A zeolites containing Na and Sr cations. 

Barium is also notable for the very low solubility of the sulfate, which permits its application to gravimetric analysis for either barium or sulfate. Barium compounds give a characteristic green color to flames which is used in qualitative analysis. Barium salts are all highly toxic with the exception of the most insoluble materials. Metallic barium has the body-centered cubic structure. 

In gravimetric analysis, the solution-preparation step has its own special significance. The analyte must be separated from interfering species, or the interferents must be masked. For example, if iron(III) is to be estimated as its hydrated oxide in the presence of chromium(III), then the mixture is initially treated with perchloric acid so as to oxidize chromium(III) to chromate (chromium(VI), Cr04 ), followed by addition of ammonia to precipitate the hydrated iron oxide. Sometimes it is necessary to remove interferents, for example, when calcium is to be estimated as calcium sulfate in the presence of barium. The barium is removed as its chromate and the calcium is precipitated quantitatively as its sulfate. 

Most barium salts are quite insoluble and gravimetric analysis is very accurate. However, flame spectroscopic methods may be used if the sample can be dissolved. Flame atomic absorption spectroscopy (FAAS) is the best method though the sensitivity of flameless (electrothermal) atomization in an atomic absorption spectrometer is significantly greater than the flame method and this may be essential for biological or clinical specimens [21]. Specially coated electrothermal AAS furnace tubes are required to avoid the formation of barium carbide. 

Using this chemical phenomenon, heavy-metal fluoride glasses were prepared using trifluoroacetates of zirconium, barium, lanthanum, aluminum and sodium [21]. Eigure 10.2 shows thermal gravimetric analysis of the ZBLAN powder in this process. A drastic decrease in weight (47.4%) was observed in the range of 220-300 °C, which was attributed to the decomposition from the trifluoroacetate to the sohd ZBLAN fluoride. 

If the nonionic surfactant is extracted from water into an organic solvent as its potassium tetrathiocyanatozincate(II) complex, its original concentration can be related to the concentration of zinc in the extract, as determined by atomic absorption spectrometry (117) or visible spectrophotometry (118). The gravimetric barium chloride/molybdophosphoric acid method for determination of nonionics has also been adapted to an atomic absorption finish, with the residual molybdenum being determined in the supernate after centrifugation (45). Similarly, the bismuth in the barium/ethoxylated surfactant/tetraiodobismuthate precipitate can be determined by AAS (52). This procedure is discussed with gravimetric analysis. 

Gravimetric and volumetric methods are practicable for the quantitative determination of the a-sulfo fatty acid esters. Using gravimetric methods the surfactant is precipitated with p-toluidine or barium chloride [105]. The volumetric determination method is two-phase titration. In this technique different titrants and indicators are used. For the analysis of a-sulfo fatty acid esters the quaternary ammonium surfactant hyamine 1622 (p,f-octylphenoxyethyldimethyl-ammonium chloride) is used as the titrant [106]. The indicator depends on the pH value of the titration solution. Titration with a phenol red indicator is carried out at a pH of 9, methylene blue is used in acid medium [106], and a mixed indicator of a cationic (dimidium bromide) and an anionic (disulfine blue VN150) dye can be used in an acid and basic medium [105]. 

Analytical methods employed in soil chemistry include the standard quantitative methods for the analysis of gases, solutions, and solids, including colorimetric, titrimetric, gravimetric, and instrumental methods. The flame emission spectrophotometric method is widely employed for potassium, sodium, calcium, and magnesium barium, copper and other elements are determined in cation exchange studies. Occasionally arc and spark spectrographic methods are employed. 

Section 12 of ASTM Chemical Analysis of Gypsum and Gypsum Products (C 471) deals with the determination of sulfur trioxide in gypsum gravimetrically. Basically, gypsum is dissolved in dilute hydrochloric acid, and sulfate is precipitated as barium sulfate by addition of hot/boiling barium chloride solution. 

A standard wet chemical analysis (ASTM D-811) is available for determination of aluminum, barium, calcium, magnesium, potassium, silicon, sodium, tin, and zinc. The procedure involves a series of chemical separations with specific elemental analysis performed by using appropriate gravimetric or volumetric analyses. 

Species analysis is performed with various analytical methods, and some examples are described in the following section. Sulfate can be determined depending on the amount in various waters (drinking, surface, waste and saline waters), either colorimetri-cally after reaction with chloranilate in forming the colored acid chloranilate ion, automated as methylthymol blue, as barium sulfate either gravimetrically or nephelometri-cally (turbidimetric) and directly with IC... 

Like cements, the elemental composition is determined by XRF or AAS techniques. The XRF bead is made using lithium tetraborate at 1050°C. Sulfide content cannot be determined by XRF. Sulfite, SO3 , and sulfate, S04 , are safely analyzed by XRF. Na2C03 -I- K2CO3 fusion is carried out for Ca, Mg, Fe, and A1 analysis by AAS. Lanthanum chloride is used as a sulfate interference suppressant. Gravimetric sulfate determinations are also carried out by precipitation as barium sulfate. The Leco Carbon-Sulfur Analyzer can also be used for quality control purposes. The fluoride is determined by XRF or a pyrohydrolysis method. The measurement of particle size distribution is carried out in a manner similar to that for cements and clays. 

The total sulfur content may be determined by one of several methods that convert it to sulfate by wet chemical analysis. One of these, the Eschka method, involves combustion of coal at 800°C in the presence of alkaline/oxidant medium (e.g., two parts of calcined MgO and one part anhydrous sodium carbonate) all sulfur is converted to sulfate that by the addition of barium chloride precipitates as barium sulfate, which is calcined to BaO and measured gravimetrically (see ASTM D3177). This is a standard method in many countries. Another is the high-temperature method where the coal is burned in oxygen at 1350°C, converting all sulfur present into SO2. The SO2 is then converted to sulfuric acid for titrimetric determination. 

Precipitation. Sulfate can be precipitated by either the barium or calcium ion, and both are used commercially. Turning first to barium, we note that the solubility of BaS04 is so low that its precipitation is the standard gravimetric technique for analysis for the sulfate ion. In a brine loop, the precipitation step could be located anywhere, but it is most convenient to combine it with the precipitation of metals in the brine treatment tanks (Section 7.S.2.2) and not to add another step to the process. 

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