Potassium cyanide method, determining

Potassium Cyanide Method. Romijn also devised this method of formaldehyde determination which is considered by Mutschin to be as. accurate as the sodium sulfite, alkaline peroxide, and iodimetric methods for pure solutions of formaldehyde, and superior to them in the presence of acetoner acetaldehyde, benzaldehvde, higher aldehydes, and ketones. The procedure is based on the quantitative formation of cyanohi drin when formaldeh de is treated vith a solution containing a -known excess of potassium cyanide. 

For practice in the method, the cyanide content of potassium cyanide (laboratory reagent grade) may be determined. 

As esters the alkyl halides are hydrolysed by alkalis to alcohols and salts of halogen acids. They are converted by nascent hydrogen into hydrocarbons, by ammonia into amines, by alkoxides into ethers, by alkali hydrogen sulphides into mercaptans, by potassium cyanide into nitriles, and by sodium acetate into acetic esters. (Formulate these reactions.) The alkyl halides are practically insoluble in water but are, on the other hand, miscible with organic solvents. As a consequence of the great affinity of iodine for silver, the alkyl iodides are almost instantaneously decomposed by aqueous-alcoholic silver nitrate solution, and so yield silver iodide and alcohol. The important method of Ziesel for the quantitative determination of alkyl groups combined in the form of ethers, depends on this property (cf. p. 80). 

Estimation of Selenium in Sulphide Minerals.s—In various sulphite-cellulose manufactories difficulties have occurred which have been traced to the presence of selenium in the pyrites used for burning. Part of the selenium remains in the burnt pyrites and part volatilises with the sulphur dioxide. 20 to 30 grams of pyrites are dissolved in hydrochloric acid (dens.=1-19) and potassium chlorate. Zinc is added to reduce the iron to the ferrous condition more hydrochloric acid is then added, the solution boiled and stannous chloride added to precipitate selenium. Since the selenium may contain arsenic, it is collected on an asbestos filter, dissolved in potassium cyanide and reprecipitated using hydrogen chloride and sulphur dioxide. The element may then be estimated by the iodometric method described below. In order to determine the relative proportion of volatile to non-volatile selenium, the pyrites may be roasted in a current of oxygen. After this treatment the contents of the tube are dissolved in warm potassium cyanide and the selenium reprecipitated and estimated in the ordinary way. 

The above methods cannot be used if the spirit contains chlorides, as may happen if it has been broken down with water containing these salts. In this case the total hydrocyanic acid may be determined by distilling 100 c.c. of the spirit and collecting at least three-quarters (which will contain all the hydrocyanic acid present) in a dilute solution of silver nitrate of known titre. The liquid is then made up to a definite volume and filtered, the excess of silver in an aliquot part of the filtrate being titrated with thiocyanate as already described. The free hydrocyanic acid, in presence of chlorides, should be determined colorimetrically as follows a solution of about 0-05 gram of potassium cyanide per litre is prepared and its exact content of HCN determined by titration with silver nitrate and ammonium thiocyanate. In a series of test-tubes are placed such quantities of this... 

In order to prevent the reduction between iron(II) and formaldoxime occurring, another iron complexing agent (potassium cyanide) was used in the presence of a reductant (ascorbic acid) that reduces iron(III) to iron(II). Aluminium, titanium, uranium, molybdenum and chromium also form light-coloured complexes that normally do not interfere in the determination of manganese in water or plant material by this method. If the aluminium or titanium concentrations are higher than 40 ppm an additional masking flow of tartrate is recommended [31]. 

Funazo et al. [812] have described a method for the determination of cyanide in water in which the cyanide ion is converted into benzonitrile by reaction with aniline, sodium nitrite and cupric sulphate. The benzonitrile is extracted into chloroform and determined by gas chromatography with a flame ionisation detector. The detection limit for potassium cyanide is 3 mg L 1. Lead, zinc and sulphide ion interfere at lOOmg L 1 but not at lOmgL-1. 

The qualitative detection of thallium is easily achieved by emission spectroscopy, thallium giving a green flame color. Thallium(I) iodide is a yellow precipitate that is insoluble in water, nonoxidizing acids, ammonia, and potassium cyanide, but that can be dissolved in sodium thiosulfate. Traces of thallium can be detected by dyes such as Brilliant Blue or Rhodamine B. Tl (or Tl after reduction by SO2) can be determined by BrOs" or titrant. A gravimetric method uses Tl chromate. ... 

Kappelmeier [35] has suggested the use of aniline, benzylamine, and phenyl-ethyl-amine as reagents for the identification and analysis of urea in UF resins. He has provided evidence that the methylene-ether groups form a bridge between urea residues in UF resins. The use of benzylamine in particular (which yields dibenzylurea from urea derivatives), has been developed as a method of analysis. In determining the ratio of urea to formaldehyde in UF resins, the benzylamine method has been coupled with a process of formaldehyde estimation which involves depolymerization with phosphoric acid, followed by distillation into alkaline potassium cyanide solution [36]. 

Cyanide is determined by a modified Kjeldahl method. A suitable sample is distilled with 125 ml. of 3 A sulfuric acid 100 ml. of the distillate is caught in a solution of 0.1 N sodium hydroxide, which is then titrated with standard silver nitrate solution. Potassium and chromium are determined on the same sample. The sample is decomposed with aqua regia, evaporated to diyness, and taken up with water, and chromium(III) hydroxide is precipitated by addition of ammonia. The filtrate is evaporated with sul-... 

Toukairin-Oda reported an isocratic, reversed-phase HPLC method for determination of all six nutritionally active Bg vitamers in food (96). PLP fluorescence was enhanced by precolumn potassium cyanide treatment to convert PLP to the highly fluorescent 4-pyridoxic acid-5 -phosphate. However, potassium cyanide causes oxidation of PL to 4-pyridoxic acid lactone, which shows little fluorescence at the acid pH (pH = 3.5) of the mobile phase used (Table 2). This problem is circumvented by duplicate analysis (1) without prior potassium cyanide treatment to determine all the B vitamers except PLP, and (2) after potassium cyanide treatment to determine PLP as 4-pyridoxic acid-5-phosphate. This method has been applied to fruit juices, wheat flour, cream cheese, eggs, and baker s yeast. 

Potassium cyanide catalyzed oxidation of PLP with subsequent quantification of the highly fluorescent oxidation product, 4-pyridoxic acid-5 -phosphate, has been used to determine PLP levels in human plasma, brain tissue and cell cultures (74,126,127). The sensitivity of this method has been reported to be even better than methods based on PLP semicarbazone formation (127). PL is not determined by these methods this vitamer is oxidized to 4-pyridoxic acid lactone, which shows little fluorescence at pH 2.5 to 3.8 of the mobile phases used (Table 2). Hess and Vuilleumier (128) overcame this problem by alkaline delactonization of pyridoxic acid lactone to yield the highly fluorescent 4-PA. The determination of PL as 4-PA suffers from the disadvantage that each sample has to be analyzed twice. In the first analysis, cyanide oxidation is omitted and the basal 4-PA concentration is measured. In the second analysis, PL is converted to 4-PA as described. The concentration of PL is determined from the difference between the two assays for 4-PA. 

By whatever method the lead has been isolated, traces are generally determined for pharmaceutical purposes by matching the colour of the lead sulphide produced in alkaline solution by adding a few drops of a sodium sulphide solution. Iron and copper, even in traces, will interfere but the addition of potassium cyanide in ammoniacal solution inhibits the formation of the sulphides of these metals by converting them into complex cyanides. The iron present must be small in quantity and must be in the ferrous state (Wilkie ), obtained by boiling the acid solution with a crystal of potassium metabisulphite. It is essential that no precipitate or turbidity should develop in the solution being examined because lead salts... 

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