T.S. West

A study of the ceriumiii-alizarin complexan-fluoride reaction

Abstract The optimum pH range of the ceriumIII-alizarin complexanate method for fluoride has been established as pH 5.0–5.2 at which value the method may be applied over a wide concentration range from 5 μg of fluoride ion (0.1 ppm) to 1.6 mg (>160 ppm) using a conventional spectrophotometer. The nature of the changes produced in the colour system by variation of pH are briefly discussed and the interference of 23 selected cations and 3 common anions has been examined. Practically all of the serious cationic interference can be overcome by the simple addition of a masking agent but, in a few cases, a preliminary extraction with 8-hydroxyquinoline and chloroform is required.

A comparative study of some lanthanon chelates of alizarin complexan as reagents for fluoride

Abstract A study has been made of the comparative suitability of the ceriumIII, lanthanum and praseodymium chelates of alizarin complexan as reagents for the spectrophotometric determination of microgram amounts of fluoride. The ceriumIII reagent is most sensitive at pH v v , but the most sensitive means of determination is to use the lanthanum reagent in aqueous solution at pH 5.2 with measurement at 281 mμ. This procedure is 200% more sensitive than the standard method at 620 mμ.

A selective and sensitive colour reaction for silver

Abstract Bromopyrogallol red (BPR) and 1,10-phenanthroline(phen) may be used as a reagent system for the spectrophotometric determination of silver ions in aqueous solution in the range 0.02–0.20 ppm. Photometric and potentiometric methods have shown that the blue coloured ternary complex, which absorbs at 635 mμ, is most probably an ion-association system [(phen-Ag-phen) + ] 2 BPR 2− . The colour reaction, using EDTA, fluoride and hydrogen peroxide as masking agents, is free from interference of a 100-fold g ion excess over silver of some 24 cations and 11 anions investigated. Only gold(III), cyanide and thiosulphate were found to interfere. With a molar extinction coefficient of 51,000, the colour reaction is probably the most sensitive of all known colorimetric methods for silver.

Absorptiometric determination of niobiumv with 4-(2-pyridylazo)-resorcinol as reagent

4-(2-Pyridylazo)-resorcinol forms a 1; 1 purple-colored complex ( lambda /sub max/= 550 m mu ) with niobium(V) in an acetatetartrate medium as pH 5.8. This is suitable for the spectrophotometric determination of niobium down to 0.1 ppm. The color is formed within 45 min, and is stable thereafter for several days; the molecular extinction coefficient, epsilon /sub 550m mu / = 38,700, is as high as that reported for the wellknown thiocyanate procedure, and the stability is very much superior. The interference of over 40 ions was examined at the 1000- mu g level in the presence of excess of cyanide and EDTA; only uranium(VI), vanadium(V), and phosphate interfere. Vanadium may be masked by addition of zinc ions and uranium by ammonium oxalate. 1000 mu g of tartalum exhibit weak color formation with the reagent, but this can be eliminated by the addition of larger amounts of tartrate, with only a slight decrease in the sensitivity of the niobium reaction. The new procedure does not necessitate an extraction, and is easier to operate than the standard methods. (auth)

Spectrophotometric determination of niobium(V) with bromopyrogallol red

Abstract Bromopyrogallol Red reacts with niobium(V) in a tartrate medium at pH 6.0 to form an intense blue coloured 3:1 reagent: metal complex (ϵ 610 m μ = 60,000); the reaction is gelatin sensitised. In a medium made 10−2M with respect to EDTA a 2:1 complex is formed and though the sensitivity decreases slightly (ϵ 610 m μ = 53,000), the reaction becomes highly selective towards niobium. After the addition of masking agents to complex the few interfering ions, no interference is found from 1000-fold excesses of the 34 cations examined, including tantalum, tungsten, molybdenum, titanium, zirconium, beryllium and thorium, or from any of the common complexing anions, including phosphate and fluoride. The conditional stability constant for the 3:1 complex is 2.7 × 1018 and for the 2:1 complex, 1 × 1012. The colour system is stable and reproducible and the proposed method seems to be the most sensitive visible-range spectrophotometric method so far proposed for niobium(V).

The spectrophotometric determination of trace amounts of silver

Abstract Pyrogallol red may be used as a reagent for the spectrophotometric determination of silver ions in dilute solution. The reagent forms a yellow complex, [Ag 2 (C 19 H 8 O 8 S)] 2- , the colour of which is stable for at least 24 hr. Optical density measurements at 390 mμ show that at pH 7–7.5 Beers law is obeyed over the range up to 85 μg of Ag + . The colour system is unaffected by normal laboratory variations in temperature or lighting conditions and no special purification of reagents is necessary. None of the common anions interferes except the halides. Most cations interfere, but this is readily prevented by the addition of an amount of EDTA equivalent to the total molar concentration of the other metal ions. This total can readily be determined by a simple titration process on a separate aliquot of solution without separating the silver ions. The method appears to be more reproducible than the standard dithizone method. Bromopyrogallol red may be used similarly with measurements made at ca . 440 mμ.

The direct determination of oxygen in organic compounds: A study of various modifications

Abstract The Schutze method for the direct determination of oxygen in organic compounds has been modified by a number of investigators. It has not always been clear whether a particular modification offers any advantage. Several of these modifications have, therefore, been examined in turn and compared. In the course of this work the gases obtained by pyrolysis have been analysed in a mass spectrometer. As a result of this examination it is recommended that the organic oxygen-containing compound be pyrolysed over platinised carbon heated at 900°, that both reduced copper and soda asbestos be used to remove interfering gases, and that the determination be completed gravimetrically after conversion of carbon monoxide to carbon dioxide with Schutze reagent at room temperature. Alternative methods of determining carbon dioxide are discussed.

4-(2-Pyridylazo)resorcinol as a selective and sensitive spectrophotometric reagent for niobiumv

Abstract The reagent 4-(2-pyridylazo) resorcinol, PAR, in the presence of EDTA, gives a colour reaction with quinquevalent niobium which is not interfered with by any of the metals which normally accompany niobium. Of some 30 cations examined, only uraniumVI and vanadiumV interfere seriously. The reaction provides a sensitive method for the spectrophotometric determination of niobium, and is also applicable as a spot-test for amounts of niobiumV down to 0.1 μg. Even tantalum does not interfere when present in twenty-fold amounts, provided sufficient tartrate ion is added.

An investigation of the chelatometry of CuII with ethylenediamine-N,N',N',N- tetra-n-propionic acid

Abstract A selective new polyaminocarboxylic acid-metallochromic indicator system is proposed for the accurate and interference-free titration of copper in aqueous solution in the presence of other metals such as Pb, Zn, Cd, Al, Mg, Ca, Ba, Sr, etc. No separations or addition of masking agents are necessary in this procedure. Nickel interferes only slightly.