206 Kurze Mitteilungen

Kurze Mitteilungen

Determination of Ca, Mg, Fe and A1 in Rocks, Ores, Minerals, Cements and Waters by Complexometric Titrations in a Single Aliquot

Bestimmung yon Ca, Mg, Fe und Al in Gesteinen, Erzen, Mineralien, Zementen und W~ssern dutch knmplexo- metrische Titrationen aus einem einzigen Aliquot

P.P. Iqaidu and C. A. Sastry

Dept. of Chemistry and Dept. of Geology, Andhra University, Waltair, India

Received May 30, 1970; revised September 10, 1970

A new volumetric method has been worked out by which Ca, Mg, Fe and A1 can be determined in rocks, ores, minerals, cements and waters using only one single aliquot. I n this method iron and aluminium are separated by ammonia precipitation and are determined by EDTA titration at different pH. In the remaining solution the sum of Ca and Mg is titrated by EDTA using Eriochrome Black T as indicator and Mg is determined in the same solution by breaking down the Mg complex with sodium hydroxide and titrating the liberated EDTA with calcium chloride.

Experimental

Procedure Add a drop of Methyl Red indicator solution to the solution of the sample, add dilute ammonium hydroxide solution until the colour changes from red to yellow, filter the preci- pitate, dissolve it in dilute hydrochloric acid and reprecipi- tare. Filter again and add the filtrate to the original solution.

I~esidue. Dissolve the residue in 10--15 ml of N hydro- chloric acid, adjust the pH to 1.5--2.5 with sodium acetate or ammonium hydroxide and titrate with EDTA using Variamine Blue as indicator to obtain the iron content. Now increase the pH to 5--6 with sodium acetate, add a known excess of EDTA and titrate with zinc sulphate solution using xylenol orange as indicator. The titre gives the amount of EDTA equivalent to the aluminium present.

~iltrate. Add 1--1.5 ml of ammonium hydroxide/ammo- nium chloride buffer pH 10 and 2--3 drops of Eriochrome Black T indicator solution, dilute to 50 ml and titrate with EDTA solution until the colour changes from blue to red. The titre corresponds to the sum of calcium and magnesium. Now add 6--8 pellets of sodium hydroxide dissolved pre- viously in 10 ml of dist. water, whereby a precipitate of magnesium hydroxide is formed, and titrate the liberated EDTA with calcium chloride solution using Patton and Reader's indicator (0.5ml of 0.1~ solution). The titre corresponds to the magnesium content. Calcium is obtained from the difference.

Results

The method has been tested with a variety of samples of different rocks, minerals, ores, cements and waters and satisfactory results have been obtained, the error being about 0.30/0 on the average. 20 samples could be determined simultaneously by this proce- dure within 8--10 hours. Although EDTA forms complexes with several other ions the accuracy is generally not affected as the concentration of inter- feting foreign ions is negligibly small in many types of the above mentioned materials (basalt as example: 13--14~ Fe, 13--14~ A1, 6--70/0 Ca, 3--4~ Mg, 0,1--0,2~ Co + Ni + Cr + Ti + Mn + Cu ~- Ce + V + :M:o).

Acknowledgement. The authors wish to thank Prof. G. G. Rao, Retired Scientist, U. G. C. scheme, and Dr. J. S. R. Krishna Rao, Reader in Geology, Andhra University, Waltair, for their supervision and help throughout. Thanks are also due to Dr. Francis J. Flanagan, Liaison Officer, U.S. Geological Survey, Washington, F.C., for kindly supplying a set of six new standard silicate rocks. Dr. P. P. Naidu is thankful to University Grants Commission (India) for awarding a Senior Research fellowship, and C. Anjaneya Sastry likes to thai~k the authorities of Andhra University for awarding a scholarship.

Dr. P. P. Naidu Central Chemical Laboratories Airborne Mineral Surveys and Exploration N.M.D.C. Buildings Faridabad Haryana/India

l~ber die Verwendung yon Ammoniumfluorid bei der Bestimmung yon Aluminium mittels Atom-Absorptionsspektrometrie in der Luft/Acetylen-Flamme

Use of Ammonium Fluoride in the Determination of Alu- minium by Atomic Absorption Spectrometry in the Air- Acetylene Flame

ANDREAS HOFER Hauptlaboratorium der ~)sterreichische Stickstoffwerke A.G., Linz/Donau

Eingegangen am 29. Oktober 1970

Seit Einffihrung der Distickstoffoxid/Acetylen-Flam- me durch Willis [5] wird diese allgemein zur Bestim- mung yon Aluminium eingesetzt. Dessenungeachtet

Kurze Mitteilungen 207

ist die im folgenden beschriebene, die Absorption yon Aluminium in der Luft/Acetylen-Flamme erhShende Wirkung yon Ammoniumfluorid nach wie vor yon Interesse.

Die Versuche wurden mit dem Atom-Absorptionsspektro- photometer der Fa. Perkin-Elmer Modell 303 und der Ver- st~rkereinheit zur Ordinatendehnung (Empfindlichkeit • 10, Einstellzeit des Mel~instrumentes 4) in Verbindung mit dem Kompensationssehreiber Modell Servogor der Fa. Goerz (Empfindliehkeit 10 mY, Papiervorschub 20 ram/rain) durch- gefiihrt. Das Ger~t war mit dem Dreisehlitzbrennerkopf nach Boling [1] ausgeriistet. Ansonsten wurden die veto Hersteller [4] empfohlenen Arbeitsbedingungen (Wellenl~nge 3092,7 2~, Spaltbreite 0,3 ram, Perkin-Elmer Intensitron-A1- Hohlkathodenlampe, Lampenstrom 25 mA, Luft/Acetylen- Flamme mit EinsCellung 9 am Druckregelzusatz fiir beide Gase) eingehalten.

Bei Versuchen zur Bestimmung yon Alumininm in w~l~riger LSsung konnte im Bereich yon 50--500 ppm Aluminium bei Anregung in der Luft/Acetylen- Flamme in Gegenwart von Ammoniumfluorid eine etwa 10fache ErhShung der Absorption festgestellt werden (Ammoniumfiuorid kann yon der Fa. Merck, Darmstadt, bezogen oder nach Brauer [2] selbst hergestellt werden). Der Effekt ist bei Zugabe yon 1 g Ammoniumfluorid je 100 ml L6sung maximal. Ver- suche, durchZusatz yon 50 Vol-~ weitere Steigerung zu erzielen, blieben ohne Erfolg, hingegen bringt eine Zugabe yon n-Butanol (5 ml je 100 ml L6sung) noeh eine geringe ErhShung der Absorption, eine Erscheinung, die ~hnlich auch von Konopicky u. Schmidt [3] im Zuge einer Untersuchung fiber die EmissionserhShung des Aluminium-Flammenspek- trums durch Fluoridionen beobaehtet wurde. Ammo- niumfluorid ist in salpetersaurer L6sung (10 ml konz. Salpetersaure/100 ml), in salzsaurer LSsung (I0 ml konz. Salzs~ure/100 ml), in perchlorsaurer L6sung (5 ml 70~ Perchlors~ure/100 ml) und in essigsaurer LSsung (I0 ml Eisessig/t00 ml) gleich wirksam. In schwefelsaurer LSsung tr i t t der Effekt nieht auf. Bei Zugabe yon Natriumfluorid (1 g je 100 ml L6sung) anstelle yon Ammoniumfluorid ist die Absorptionserh6hung ffir Aluminium bedeutend geringer. In der Distickstoffoxid/Aeetylen-Flamme ist Ammoniumfluorid wirkungslos.

Der Direktion der 0sterreiehisehe Stiekstoffwerke A.G. danke ich fiir die Erlaubnis zur VerSffentlichung dieser Kurzmitteilung.

Literatur

1. Boling, E. A.: Spectrochim. Acta 22, 425 (1966). 2. Brauer, G.: Handbuch der pr~parativen anorganisehen

Chemie, Bd. 1, S. 150. Stuttgart: F. Enke 1954.

3. Konopicky, K., Schmidt, W. : diese Z. 174, 262 (1960). 4. The Perkin-Elmer Corp., Norwalk, Conn., USA: Analy-

tical Methods for Atomic Absorption Speetrophotometry. 5. Willis, J.B.: ~ature 207, 715 (1965).

Ing. Andreas Hofer Hauptlab. d. 0sterr. Stickstoffwerke A.G. A-4021 Linz, Postfach 296, 0sterreich

E x t r a c t i o n - P h o t o m e t r i c D e t e r m i n a t i o n

o f V a n a d i u m ( V ) w i t h N - m - N i t r o -

b e n z o y l - N - p h e n y l h y d r o x y l a m i n e

Extraktionsphotometrisehe Bestimmung yon Vanadium(V) mit N-m-Nitrobenzoyl-N-phenylhydroxylamin

N~n~])RA NAT~ G~osH and GAUTAIVl SIDDHANTA

Dept. of Inorg. Chemistry, Univ. College of Science, Calcutta-9 (India)

Received August 31, 1970

Vanadium forms two coloured products with N- Acyl-N-phenylhydroxylamines, a violet one with acid concentrations of 1 N or more and an orange one at pH-values ---- 2 or higher. In this report the extrac- tion behaviour of the orange complex with N-m- Nitrobenzoyl-N-phenylhydroxylamine has been in- vestigated. Isoamyl alcohol is used for the extraction which is quantitative within the pit-range 2.7 to 4.2. Measurements are taken at the absorption maximum of 435 nm. Absorption of the reagent is very small at this wave-length. For maximum intensity of the colour, which is stable for more than 48 h, a 35-fold excess of the reagent is required. Beer's law is obeyed from 0.2 to 11 ppm, optimum range is from 3.8 to 11 ppm. Large excesses of Na +, K+, Zn~+, Ca ~+, Cr207 ~-, ~Io042-, F- , CI-, Br-, I - , NO3-, Ae-, SOa*-, and P ea 3- do not interfere. 5 Moles of Fe 8+ per mole of V can be tolerated in presence of phos- phate. 2 Moles of U022+, A1 a+ and Ti 4+ per mole of V do not interfere. In presence of excess EDTA (20--30 times in molar units) V is completely masked. The molar extinction coefficient of the complex at 435 nm is 3230. Sensitivity (Sandell) is 0.016 ~g of V per cm 2. Though the extinction coeffi- cients of the violet complexes of the N-Acyl-N- phenylhydroxylamines are higher than those of the corresponding orange complexes the method describ- ed here is safer as the violet complexes are more susceptible to reducing agents.