Anil K. Mukherji

Titrations with a calcium activity electrode

The ca lc ium ac t i v i t y e lectrode r ecen t ly i n t roduced b y Orion Resea r ch Incorpora ted , Cambridge , Mass. , h a s been inves t i ga t ed for t he com pl exome t r i c d e t e r m i n a t i o n of ca lc ium. The electrode de tec t s ca lc ium ion j u s t as t h e conven t iona l glass e lectrode de tec t s t h e h y d r o g e n ion. T he electrode develops a po t en t i a l across t h e t h i n l aye r of wa te r immisc ib l e l iquid ion e x c h a n g e r he ld m e c h a n i c a l l y rigid b y a t h i n porous ine r t m e m b r a n e disc. The l iquid ion exchanger , a ca lc ium sa l t of a n o rganophosphor i c acid, exhib i t s a v e r y h i gh se lec t iv i ty for ca lc ium ions. T h e in t e rna l filling so lu t ion of ca lc ium chlor ide con t ac t s t h e ins ide sur face of t h e m e m b r a n e disc. T he ca lc ium ion in th is so lu t ion p rov ides a s table po ten t i a l be t ween inside of t he m e m b r a n e and t h e filling sohi t ion and changes in po t en t i a l a re en t i re ly due to changes in ca lc ium ac t i v i t y of t h e s ample solut ion. Solutions: A s tock so lu t ion of 0.0t M ca lc ium chlor ide was p repa red b y d isso lv ing appropr i a t e a m o u n t in dist i l led water . The so lu t ion was s t anda rd i zed b y E D T A t i t r a t i on u s ing a v i sua l end-po in t . A s tock so lu t ion of 0.0t M d i sod iume thy l e n e d i a m i n e t e t r a a c e t a t e was p repa red b y d i rec t we igh ing of t h e d i h y d r a t e sal t . Titration Procedure: B et ween 1 and 1 0 r a g of t h e ca lc ium sample in 10 ml so lu t ion is a d j u s t e d to a b o u t t0 p H b y add ing dropwise 7 M a m m o n i u m hydrox ide . T he E D T A solu t ion is added a n d t h e po ten t i a l m e a s u r e d a t in te rva l s . Po ten t i a l s are m e a s u r e d a t smal l i n c r e m e n t s of t h e t i t r a n t nea r t he endpoin t . Results and Discussion : There is a s h a r p drop in po t en t i a l nea r t he e n d p o i n t and t h e m i d p o i n t of inf lect ion in t he cu rve r ep resen t s t h e end-po in t . B e y o n d t h e end -po in t t h e po ten t i a l r ema ins fair ly cons t an t . For t to 10 m g ca lc ium samples , t h e error is be tween 0.8 to 2%. T h e precision, however , is imp roved r e m a r k a b l y in p resence of alkali m e t a l ions such as Na +, K + and Li +. I n p resence of B a ++, Mg ++ and Zn ++ a single inf lec t ion r ep re sen t s t h e combined t i t r a t i on of Ca ++ a n d t he above ions. I n p resence of Sr ++ t he cu rve is d r a w n ou t a n d t he e n d p o i n t c a n n o t be de t ec t ed accura te ly . A m m o n i u m ion causes no interference. A m o n g t h e an ions CI-, Br, I , CN-, NOn, NO2, SO4-, CrO4-, CIOa-, C104-, CNS, a n d Fe(CNg 4, do n o t interfere . P h o s p h a t e , F, COs -2, and oxa la te ions in ter fere w i th t h e t i t ra t ion . I n v e s t i g a t i o n s are in progress for eval ua t i ng t i t r a t i on p rocedures of ca lc ium wi t h d i f fe rent chelons and p rec ip i t an t s . T i t r a t i on of an ions w i t h ca lc ium is also be ing inves t iga ted . The e lect rode is also respons ive towards zinc ions and i t s t i t r a t i on w i t h E D T A wi t h o t he r r e su l t s will be pub l i shed shor t ly . Acknowledgement. Financ ia l s u p p o r t b y t he P e t r o l e u m Research F u n d a d m i n i s t e r e d b y t he A m e r i c a n Chemica l Socie ty is g ra te fu l ly acknowledged .

SIMULTANEOUS SPECTROPHOTOMETRIC DETERMINATION OF THORIUM AND THE RARE EARTHS WITH XYLENOL ORANGE

Abstract A spectrophotometric method is described for the determination of microgram amounts of thorium-rare earth mixtures with Xylenol Orange. Advantage is taken of the fact that only thorium forms a colored complex (λ max 576 mμ) with the reagent at 2 pH and the rare earths do not. At 6 pH, however, both thorium and the rare earths form complexes and the absorbances are additive. Concentration range for the determination effects of pH time and reagent and interferences are discussed. Reproducibility is excellent with an average error of ±1.2%.

Determination of halides with ion-selective electrodes

Abstract The solid-state halide electrodes and the sulfide electrode introduced by Orion Inc. were used in halide determinations, singly and in in mixtures. Potentiometric titrations with silver nitrate give good accuracy to concentration of 10−3 N with increasing errors at lower concentrations. The use of these electrodes with halide mixtures is limited by the formation of mixed crystals.

Amperometric determination of thorium and lanthanum in presence of nitrate

Abstract The reduction of nitrate ions in the presence of thorium, and lanthanum is utilized for the amperometric determination of these two metal ions. Thorium can be titrated with EDTA or benzenephosphonic acid at a voltage of −1.5 V vs S.C.E. Lanthanum titrations are carried out at the same voltage using EDTA as a titrant. It is possible that M-NO 3 (where M = Th 4+ or La 3+ -type complexes are reduced near the electrode. The effect of variation in experimental conditions and metal concentration, and the accuracy of determinations are discussed.

Some observations on the phosphonic acid cation-exchange resin

SummaryApparent dissociation constants for the phosphonic acid cation-exchange resin have been calculated (pK1=2.6±0.4 and pK2=7.4±0.4). The resin has been investigated in the hydrogen and sodium form for exchange behaviour with Ca2+, Cu2+, Co2+, Mg2+ and Ni2+. The order of preference in the hydrogen form of resin has been found to be Mg2+>Co2+ ≈ Ni2+> Ca2+>Cu2+. Fe3+ shows a great affinity for the resin and is retained by it even in presence of 4–6 N HCL Na+ has been found to show greater affinity than K+.ZusammenfassungEs wird über einige Untersuchungen an einem Phosphonsäurekationenaustauschharz berichtet. Die scheinbaren Dissoziationskonstanten wurden zu pK1=2,6±0,4 und pK2=7,4±0,4 errechnet. Das Harz wurde in der H- und Na-Form auf sein Austauschverhalten gegen Ca2+, Cu2+, Co2+, Mg2+ und Ni2+ geprüft. Folgende Reihenfolge der Bindungsstärke wurde gefunden (H-Form): Mg2+>Co2+ ⇌ Ni2+>Ca2+>Cu2+. Fe3+ weist eine starke Affinität zu dem Harz auf und wird selbst in Gegenwart von 4–6 n HCl daran zurückgehalten. Na+ besitzt eine größere Affinität als K+.