Sulphur, detection estimation

Detection and Estimation.—Sulphurous acid is usually detected by its reducing action, for instance on potassium diehromate solution, the acid being warmed in order that the test may be effected with the evolved gas the odour of sulphur dioxide is also a fairly trustworthy indication. For special purposes9 many of the reactions already mentioned may be applied. 

Detection and Estimation of Sulphuric Acid.—The usual dry test for a sulphate is reduction on charcoal in the presence of sodium or potassium carbonate alkali sulphide in the fused product can easily be detected by moistening on a clean silver coin or by the application of other suitable tests. 

Detection and Estimation.—Pure solutions of permonosulphuric acid give no yellow coloration with a solution of titanium dioxide in sulphuric acid and so may be distinguished from similar solutions owing their oxidising power to the presence of hydrogen peroxide. 

Detection and Estimation.—The decomposition of thiosulphates by means of hydrochloric acid to yield sulphur dioxide with separation of sulphur serves as a primary identification test, the limit of sensitiveness being about 0-1 mg. S203 per c.c.3 The alkali thiosulphates produce with silver nitrate solution a white precipitate of thiosulphate which gradually turns yellow, then brown, and finally black, due to the formation of sulphide the change is accelerated by warming 4... 

The Detection and Estimation of Thiocyanates.—A thiocyanate may be detected by its behaviour with sulphuric acid (p. 281) and by the blood-red colour produced with ferric chloride, which colour is dis-... 

The detection and estimation of selenium in the mother-liquors from the preparation of sulphite-cellulose is rendered difficult by the colour of these liquors, due to the organic substances present. The presence of the element is indicated by the fact that a red deposit is formed on the sides of the combustion tube when the organic matter is being burnt off. Estimation may be carried out by evaporating the liquor until all the free sulphur dioxide has been evolved, acidifying with hydrochloric acid and boiling to remove the last traces of sulphur dioxide. After allowing to stand in a warm place for a few days the selenium settles to the bottom of the container and may be estimated as described.4... 

Occurrence, Extraction, Refining, Applications—The Allotropy of Sulphur Changes in tho Vaporous State, Allotropy in tho Liquid. State, Allotropy in the Solid Stato, Crystalline Forms of Sulphur, Amorphous Sulphur— Colloidal Sulphur—General Physical Properties of Sulphur—Chemical Propertius—Valency—Atomic Weight—Detection and Estimation. 

There is a very simple and quick method that can be used to detect the reducing power of sulphur dioxide, developed in the last century and often called the Ripper titration (Ough, 1988). In this method, sulphur dioxide is titrated against iodine or potassium iodate/potassium iodide solution in the presence of starch. When all the sulphur dioxide has been oxidised, a blue colour is produced by the reaction of free iodine with the starch. This is a very quick method but will give only an estimate of the level of sulphur dioxide as other reducing substances, such as ascorbic acid, will interfere consequently, this method is not particularly appropriate for juices with high ascorbate levels. 

Sugar is detected in these waters by treating 2 c.c. of the liquid with 5 drops of 20% alcoholic a-naphthol solution and then carefully adding 10 c.c. of concentrated sulphuric acid (absolutely free from nitric acid) so that the two liquids do not mix. In presence of sugar, a violet ring forms at the surface of separation. A few comparative tests will indicate if the quantity of sugar is estimable the reaction is very sensitive and detects even o ooi% of sugar. 

Separation of mono- and di-ester pyrrolizidine alkaloids has been achieved by ion-pair adsorption t.l.c., using chloride (or iodide) as the counter-ion.48 Chloranil has been used to oxidize pyrrolizidine alkaloids on t.l.c. The pyrrole derivatives that were formed were then detected with Ehrlich s reagent49 or sulphuric acid.50 Mixtures of pyrrolizidine alkaloids have been separated by h.p.l.c. on a reversed-phase styrene-divinylbenzene resin.51 In a sensitive method for the detection of pyrrolizidine alkaloids, the protonated alkaloids were complexed with aqueous methyl orange. The dye was then released from the complex and estimated spectrophotometrically.52... 

Other methods depend upon reduction of the chlorate with sulphurous acid, iron, etc., and estimation of the chloride formed, and upon precipitation as nitron chlorate. Methods for the detection of small quantities of chlorate have been given under potassium nitrate. 

Fusel oil may be detected by adding water, shaking out with chloroform, separating, and allowing the chloroform to evaporate. The residue wifh addition of dilute sulphuric acid should give no smelt of fusel oil. Fusel oil may he estimated quantitativdy by oxidation to valeric arid. 

In general, all the above-mentioned methods, employing concentrated sulphuric acid, have common drawbacks which may lead both to under- and over-estimation of carbohydrate content. During dehydration of individual sugars, non-detectable by-products such as 7-pyrones or benzene derivatives may be formed. No distinction is made between mono- and polysaccharides and since the different methods have different responses towards the various sugars, comparison of results obtained by the different authors is difficult. 

The presence of rosin may be detected by the Liebermann-Storch reaction, which consists in dissolving a small quantity of the fatty acids in acetic anhydride, and adding to a few drops of this solution 1 drop of 50 per cent, sulphuric acid. A violet coloration is produced with rosin acids. The amount of rosin may be estimated by the method devised by Twitchell Journ. Soc. Ghem. Ind., 1891, 804) which is carried out thus —... 

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