Zirconium-alizarin solution

Procedure. A strip of quantitative filter paper is impregnated with the red zirconium-alizarin solution. The dried paper is moistened with a drop of 50 % acetic acid and then a drop of the neutral test solution is placed on the moist fleck. A yellow spot appears in the presence of fluorides. When only small amounts of fluorine are present, it is advisable to hasten the reaction by warming the paper in steam. 

Reagents Zirconium-alizarin paper Commercial zirconium oxide (ZrOg) is digested with warm dilute hydrochloric acid and filtered. The solution should contain about 0.5 mg zirconium per ml. Several ml of the zirconium solution is treated with a slight excess of an alcoholic solution of alizarin. Excess of alizarin may be recognized by extracting a portion of the solution with ether, which becomes yellow. The zirconium-alizarin solution thus prepared is warmed for ten minutes in the water-bath. Filter paper is bathed in the warm solution and dried. 

Precipitated tertiary calcium phosphate, under the same conditions, reacts after a few minutes due to production of acid-insoluble zirconium phosphate. The decomposition of the zirconium-alizarin lake is not instantaneous as in the case of calcium fluoride probably because the color lake is adsorbed by zirconium phosphate, which is the initial product. This supposition is supported by the finding that zirconium phosphate is reddened immediately by contact with an acid zirconium-alizarin solution. 

The fact that solid calcium fluoride reacts immediately with zirconium alizarinate renders it possible to detect fluoride in a mixture with phosphates and oxalates. These salts interfere with the detection of fluoride in aqueous solution, because they form either insoluble or complex zirconium phosphates (or oxalates) and thus destroy the red zirconium-alizarin compound and also produce the yellow color. The fluoride in such mixtures may be isolated by treating the alkaline or neutral test solution with calcium chloride the precipitate is ignited and digested with dilute acid. The residue then may easily be tested for fluoride by the zirconium-alizarin solution. ... 

Procedure, A few mg of the sample are taken, or a drop of the solution is evaporated to dryness in an ignition tube. A piece of potassium the size of a pin head is added. The tube is heated, gently at first, and then strongly for 1 minute. The molten metal thus comes into intimate contact with the sample. After cooling, 0.5 ml of water is placed in the tube and then a few drops of a strongly acid (hydrochloric) red zirconium-alizarin solution. It is not necessary to filter off particles of carbon. The red color changes to yellow when the response is positive. 

Strongly acidify about 2 ml of the fusion filtrate with glacial acetic acid, and boil until the volume is reduced to about one-half. Cool. Place one drop of the solution upon zirconium-alizarin red S test paper (2). A yellow colour on the red paper indicates the presence of fluoride. Large amounts of sulphates and phosphates may interfere with this test. 

Prepare the zirconium-alizarin red S paper as follows. Soak dry filter paper in a 5 per cent solution of zirconium nitrate in 5 per cent hydrochloric acid and, after draining, place it in a 2 per cent aqueous solution of sodium alizarin sulphonate (BDH Alizarin Red S ). The paper is coloured red-violet by the zirconium lake. Wash the paper until the wash water is nearly colourless and then dry in the air. 

Zirconium-alizarin lake test Hydrochloric acid solutions of zirconium salts are coloured reddish-violet by alizarin-S or by alizarin (see under Aluminium, Section III.23, reactions 8 and 9 and under Zirconium, Section VII.18, reaction 8) upon adding a solution of a fluoride the colour of such solutions changes immediately to a pale yellow (that of the liberated alizarin sulphonic acid or alizarin) because of the formation of the colourless hexafluorozirconate(IV) ion... 

The most sensitive method of carrying out the spot test is as follows. Impregnate some quantitative filter paper or drop-reaction paper with the zirconium-alizarin-S reagent, dry it and moisten with a drop of 1 1 (v/v) acetic acid. Place a drop of the neutral test solution upon the moist red spot the spot will turn yellow. 

Use may be made of the fact that even solid calcium fluoride reacts with the zirconium-alizarin-S reagent (compare Section IV. 17, reaction 6) and, in consequence, the fluoride test may be carried out in the presence of oxalate and phosphate, which interfere in aqueous solution. The calcium salts are precipitated in neutral or faintly basic solution. The precipitate is ignited and digested with dilute acid. The residue is then tested for fluoride by the zirconium-alizarin-S test the red hue of the reagent disappears and a yellow colouration results (see Section IV.17, reaction 6). 

In Inorganic Chemistry, typical spray reagents for cations include potassium iodine (0.2%, aqueous), hydrogen sulphide (saturated aqueous solution), ammonium sulphide (0.2 N, aqueous), quercetin (0.1%, alcoholic), l-(2-pyridylazo)-2-naphthol (PAN) (0.2%, methanolic), oxine (8-hydroxyquinoline) (1% methanolic, view under visible and UV light), and sodium rhodizonate (0.5%, aqueous). Reaction with dithizone to produce coloured dithizonate chelates of many metals is particularly suitable if quantitative spectrometric analysis (in situ or after elution) is to be carried out. Anions are detected with bromocresol purple (0.1%, alcoholic), 1% ammoniacal silver nitrate + 0.1% alcoholic fluorescein/UV light, zirconium alizarin lake (0.1% in HC1 solution), and ammonium molybdate (1%, aqueous) followed by SnCl2 (1%) and HC1 (10%). Typical detection limits range from 10 ng (10 9g) to several pg (10 6g). 

When the HF crystals were prepared the quartz tube was protected by a thin layer of paraffin wax. Triply distilled water was degassed by shaking and evacuation to remove most of the 02 and C02 and then some tenth of a ml. of a 0.5M HF solution was added. The solution was saturated with H2, degassed, resaturated, and degassed again. Finally the solution was saturated with H2 and frozen in the same way as the pure water samples. A piece of the top and the bottom of the crystal was cut away, and the concentration of HF in the two samples was determined spectrophotometrically by the zirconium-alizarin method (14). The crystal was discarded if a concentration gradient was detected. The concentration of HF in the irradiated part of the crystal was also determined. 

Direct detection of even insoluble fluorides is also possible by means of the zirconium-alizarin test. Use is made of the fact that in the presence of small amounts of acid, precipitated or native calcium fluoride is readily soluble in warm aqueous solutions of salts that form complex fluorides. Pure calcium fluoride gives a clear solution impure products leave only the " gangue behind. 

A hydrochloric acid dispersion of the zirconium-alizarin lake also dissolves calcium fluoride with formation of [ZrFg]-, Ca+2, and free alizarin. The test can be carried out on a microscope slide by stirring a very small amount of the powdered fluoride with a drop of the violet reagent solution. A yellow color is formed at once. 

Fluorides can be detected with high sensitivity through their reaction with zirconium alizarinate . This test (page 221) is based on the facts that, in mineral acid solution, zirconium salts yield a red-violet color with alizarin and that this color changes to yellow (the color of acid alizarin solution) on the addition of excess fluoride because of the production of complex zirconium hexafluoride ions. The reactions can be represented by ... 

The zirconium alizarinate does not correspond precisely to an inner complex zirconium salt of alizarin rather, it is the hydrosol of a violet zirconium-alizarin lake, i.e. a colored adsorption compound of hydrolysis products of aqueous zirconium salt solutions with alizarin (compare Vol. II page 347). 

Procedure. A drop of the test solution, which should be as nearly neutral as possible, is mixed in a micro crucible with a drop of an alcoholic alizarin solution, and boiled once. Zirconium and also the other metals give red to violet adsorption compounds. A drop of 1 iV hydrochloric acid is then added. Only the zirconium compound remains unaffected. Much zirconium gives a deep red-violet color and precipitate a little gives red flakes. 

Fluorine ions are evidenced by the destruction of the zirconium-alizarin complex (see Chap. 30). Revealing bromide ions in the presence of chloride ions is trickier. It is carried out with chloramine T and phenol red. The reaction is performed at pH = 5.2. The bromide ions are oxidized by chloramine T into bromine, which reacts by substitution with phenol red. A purple color appears. Normally, a pure solution of phenol red is yellow. 

Mix together on a spot plate 2 drops each (equal volumes) of a 0-1 per cent aqueous solution of alizarin-S (sodium alizarin sulphonate) and zirconyl chloride solution (0-1 g solid zirconyl chloride dissolved in 20 ml concentrated hydrochloric acid and diluted to 100 ml with water) upon the addition of a drop or two of the fluoride solution the zirconium lake is decolourized to a clear yellow solution. 

If both Tiand Zr are present, the precipitate of zirconium phosphate may be filtered off (best in the presence of a little macerated filter paper, or a Whatman filtration accelerator), and the filtrate treated with Na2S03 or with Na2S203 solution and warmed. The peroxotitanic acid is reduced and titanium phosphate precipitates. It may be necessary to reduce the acidity of the solution somewhat to precipitate the titanium completely. Zr may also be identified by the alizarin-S reaction. 

Alizarin S 0.05% aqueous solution. Dissolve 50 mg of the reagent in 100 ml of water. Standard zirconium solution 1 mg/ml. 

Intorre and Martell (237) have also studied the formation of mixed chelate species in which the zirconium 1 1 complex with the hexa-dentate chelating ligands, ethylenediaminetetraacetic acid, iV-hydroxy-ethylethylenediaminetriacetic acid, and m7 s-cyclohexanediaminetetra-acetic acid, are shown to take up one mole of the bidentate ligands, l,2-dihydroxybenzene-3,5-disulfonate l,8-dihydroxynaphthalene-3,6-disulfonate 8-hydroxyquinoline-5-sulfonate, and acetylacetone (except ZrHEDTA), to form 8-coordinate 1 1 1 species. At least for the zir-conium-EDTA-l,2-dihydroxybenzene-3,5-disulfonate species, there is evidence for dimerization (230). Additionally, the Zr EDTA complex reacts with one mole of the bidentate ligands, 5-sulfosalicyclic acid, alizarin sulfonate, citric acid, and lactic acid to form 1 1 1 complexes tartaric acid and pyrophosphate ions form complexes which could not be identified. The zirconium-nitriloacetic acid complex in the presence of two moles of oxalic acid or l,2-dihydroxybenzene-3,5-sulfonate also forms 1 1 1 complexes in solution. 

Fluorides with zirconium ions form a colourless complex [ZrFg] which is more stable than Zr with alizarine (red), therefore, an equivalent amount of this dye is destroyed when F solutions are added. Reduction of the intensity of the solution colour measures the concentration range from 0.05-2.5 mg [14, 15]. 

When solutions of beryllium salts are brought together with red-violet solutions of quinalizarin [1,2,5,8-tetrahydroxyanthraquinone (I)] in am-moniacal or caustic alkali solution, a blue-violet precipitate or color appears. Although quinalizarin, as a derivative of alizarin, is a lake-forming dyestuff, which produces red to red-violet adsorption compounds with oxyhydrates of aluminum, zirconium, thorium, etc., its beryllium reaction product seems to be a stoichiometrically defined compound rather than an adsorption complex. In conformity with the fact that the blue product contains two atoms of beryllium combined with one molecule of quinalizarin, it seems proper to view the material as a basic beryllium salt with the structure (II) or (Ila) ... 

The addition of alizarin or alizarin sulfonate to dilute solutions of zirconium chloride containing hydrochloric acid results in a red-violet color due to the formation of hydrosols of a zirconium lake with these dyestuffs (see page 518). The dispersions turn yellow as soon as they are treated with excess fluoride. The zirconium combines with the latter to form colorless complex [ZrFanions and is withdrawn from the alizarin lake. Consequently, only the yellow color of the alizarin remains. 

Reagent 0.05 g zirconium nitrate is dissolved in 60 ml water and 10 ml concentrated hydrochloric acid. The solution is mixed with a solution of 0.05 g sodium alizarin sulfonate in 50 ml water. 

Zirconium salts, in not too strong acid solution, give a red to dark violet precipitate on the addition of an alcoholic solution of alizarin or an aqueous solution of alizarin sulfonic acid. Other polyhydroxyanthraquinones behave similarly. The precipitation is accelerated by warming. 

The precipitability by polyhydroxyanthraquinones from weakly acid solution is specific for zirconium (and hafnium). The precipitate is an adsorption compound (lake) of zirconium hydroxide and alizarin (compare Al-alizarin lake, page 97). The production of the lake involves the binding, through chemical adsorption, of alizarin on the surface of the Zr(OH)4 sol particles, which are present in solutions of zirconium salts as a result of the hydrolysis Zr+ -f- 4 HgO- Zr(OH)4 -f 4 H+. The hydrolysis equilibrium is constantly disturbed by the removal of Zr(OH)4, so that, in a not too acid solution, there is extensive precipitation of zirconium in the form of the alizarin lake. This lake is also produced by precipitating solutions of zirconium salts with ammoniacal solutions of alizarin. The lake is stable against dilute hydrochloric acid. In strong hydrochloric acid solutions of zirconium salts, alizarin produces a fairly stable hydrosol of the lake (compare the test for fluoride, page 221). 

The complex between zirconium and alizarine red S (sodium 3,4-dihydroxy-9,10-dioxo-2-anthracene sulfonate. Figure 6.2) gives red-brown color in acid solution if alizarine red S is in excess and violet color if the zirconium is in excess. The complex is decolorized by fluoride ions. Phosphate, arsenate, sulfate, thiosulfate, and oxalate as well as organic hydroxy acids interfere with this reaction. 

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