Applications involving the iodide ion—X determination of copper and analysis of cation mixtures and alloys

SHORT

COMMlJNlCATlONS

243

Interferences No mterferences due to the water matrix were present However. attention was grven to the effect of cyarude tons as thts IS often assocrated with Cd tn vartous waste waters. and has been found to be a posttrve mterference by Kuwata ef al ’ In the presence of a 600-fold excess of cyanide, the extraction of 20 ng/ml Cd was found to be enhanced, which 1s an effect attributed by Robmson et al 3 to the suppresston of Cd adsorptton on the walls of the glass vessels, but m the presence of a lOO,OOO-foldexcess of cyanide thts quantity of Cd remams completely unextracted The synergtstrc procedure however, permits the complete extractton of the Cd m the presence of a l~,~-~o~d excess oI’ CN- The extractton efficiency IS Improved and thts IS posstbly also due to the lack of adsorptton effects Department of Analyffcal Chemfsfr! Unwerstf~ of New South Wales Sydney. N S U’. Au\tralfa

K.J L E

DOOLAN SMYTHE

REFERENCES

1 2 3 4

K K J R

H Schaller, K Lmdner and G Lehnert, Arch Hyg Bakrerrot, 1968, 152, 298 Kuwata, K Htsatomt and T Hasegawa, At Abs Newsletter, 1971, 10, 111 Robmson, R Barnekow and P Lott. ibrd, 1969, 8, 60. Brooks R Presley and I Kaplan. Talanfa. 1967, 14, 809 Summmy-A very stmple and raprd procedure IS described m whtch the addttton of a large amount of Zn(Il) to a water sample before extraction by 2-mercaptobenzothtazole mto n-butyi acetate brmgs about almost total extraction of Cd and allows determmatton of concentrations down to at least 0.02 ng/ml Hugh prectston IS achieved, and the interference of cyanide IS also overcome Zusammenfassung-Em sehr emfaches und rasches Verfahren wtrd angegeben, be] dem dte Zugabe enter groBen Menge von Zn(I1) zu emer Wasserprobe vor der Extraktton mtt 2-Mercaptobenzthtazol m n-Butylacetat dte nahezu vollstandtge Extraktton von Cd bewtrkt Dtes erlaubt dre Besttmmung von Konzentrattonen bts herunter zu mmdestens 0.02 ng/ml Man errercht eme hohe Genautgkett. und dte Storung durch Cyamd wtrd ebenfalls ausgeschaltet. Rkume-On decrtt une techmque trts srmple et raptde dans laquelle I’addttton dune forte quanttti de Zn(II) a un ichanttllon d’eau avant extraction par le 2-mercaptobenzothtazle en acetate de n-butyle entraine une extraction presque totale du Cd et permet le dosage de concentrations descendant ~usqu’ii 0,02 ng/ml au moms Une haute precrston est attemte, et I’mterference du cyanure est aussr surmont&e

APPLICATIONS INVOLVING THE IODIDE DETERMINATION OF COPPER AND ANALYSIS MIXTURES AND ALLOYS (Recezred 5 Januarl

ION-X OF CATION

1972 Revised 9 June 1972 Accepted 17 August 1972)

The present worh 1s an extenston to the appltcatton of potentrometrtc back-tttratton of excess of todtde wtth mercury(H). whrch was recently apphed to the determmatton of oxtdtzmg agents.’ srlver.’ or Ions reduced with todtde 3 In the classrcal todometrtc determination of copper error may arose from loss of todme, smce CuI adsorbs some of It.&leadmg to earher end-pomts even m presence of thtocyanate Copper determmattons based on EDTA tttratron often lack selectivity The most Important separatton methods for copper m more than microgram amounts mvolve electrolysis or prectpttatton wtth sulphtde or orgamc reagents The present method mvolvmg selecttve separation of copper(I) as the todtde IS suitable for amounts In the range 1-35 mg of copper, either alone or mtxed with other catrons

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244

COMMUNICATIONS

EXPERIMENTAL

Reagents

Soluttons of copper(H) (0 1-001&f), iodide (O.l-0.02M). mercury(H) (0 05-OOlM), and all metal IONSmvolved. were prepared from htgh purity chemicals and twice dtstilled water. and standardized by recommended procedures None of the soluttons contamed chloride ions Procedure for copper WI pure solution or m cation nuxtures

To appropriate volumes of copper solutton (l-5 ml), m a lOO-ml beaker, add 15-20 mg of sodium sulphtte, 5M sulphunc acid (1 ml) and distilled water (5 ml), then add, with constant stirrmg, iodide solution (3-8 ml), coagulate the white precipitate of CuI by heating on a water-bath for 10-15 mm. whtch gives sufficient time for expulsion of any excess of sulphurous acid Filter off on a Whatman No 42 filter paper. wash thoroughly with water ttll the washmgs are free from todtde (usually five washes suffice) and titrate unreacted todtde m the filtrate and washmgs with Hg(I1) (delivered from a microburette wtth its tip immersed m the solution), usmg silver amalgam as the mdtcator electrode and saturated calomel as the reference electrode. Procedure for copper m alloys

From knowledge of the expected amount of copper m the alloy prepare a 0.03-007&f copper solutron by dtssolution m nitric acid, digestion on a water-bath, separation of hydrous stanmc oxide and lead sulphate and dilution to volume; determine copper in a fraction (2-4 ml) by the procedure above. RESULTS

AND

DISCUSSION

Tables 1 and 2 list results for copper alone, in presence of a variety of canons, and m alloys, mdicatmg the selectivtty and reliability of the method. With alloy No. 3 (copper taken, 7 47 mg) the results of copper determmation rn 9 parallel expertments were 7.49, 7 48, 7.48; 7.45, 7 45, 744, 744, 746, and 7 43 mg; wtth alloy No. 4 (copper taken, 7 36 mg) the results were 7 35, 7 35, 7.35, 7.32, 7.33, 7 34, 7.34, 7 37 and 7 37, showing respective standard deviations 0.021 and 0.017 mg, the relative standard devtattons bemg @28 and 0.23%. In determining copper by the present method, CuI was separated to avoid the metathesis 2 CuI + Hg2+ = HgI, + 2 Cu+ which IS due to the lower solubthty of HgI, (8 8 x lo-’ mole/l. at 18”)2 than that of CuI (105 x 10e6 mole/l. from K,, = 1 1 x 10-‘2)5, as verified experimentally The method has the advantages that, (a) any oxidizmg agent or higher oxidation state cation such as Fe(III) wdl not interfere, m the presence of added sulphite, (b) it IS posstble to titrate iodide selectively m presence of large amounts of a variety of cations, wtth accurate and precise potenttometrtc end-pomt determmation, wtth equihbrtum potentials obtained mstantaneously, (c) the titrated species IS todtde which, unlike iodme, IS non-volattle, and (d) tt can be successfully apphed to the analysts of copper-contammg alloys and related matertals. Table 1 Determmatton

of copper

Cu. mg Found

Error (* XJ

Potenttal break,

Taken 26.42 21 14 1409 12 72 636 2 54 38.13 28.18 9.54 6.36 3 18

26.33 2107 14.04 12.78 6 36 2.53 38.04 2805 9 52 6 34 3 17

0 34 0 33 0.35 0 50 0.00 0 39 0 19 046 020 0.31 031

363 382 367 410 390 285 434 335 328 395 388

No. 1 2 3 4 5 6 7 8 9 10 11

mV/O 1 ml

Nos. l-11 0099M I- + 005M Hg(I1) Also present No 7; 60 mg of Co; No. 8. 35 mg each of NI, Co and Mg; No 9 40 mg of Al + 35 mg of Fe(II1) + 40 mg of NI; No 10: 50 mg of Zn + 30 mg of Ni + 40 mg of Cd, No. 11 40 mg of Cd + 30 mg of Cr(II1) + 40 mg of NI

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245

COMMLJNICATIONS

Table 2 Determmatton

of copper m alloys

Cu. my

Alloy No

1

2

3

4 5

6

7 8

Taken

Found

9.18 1377 1836 464 6.96 9 28 7 47 1121 14.95 7.36 1104 14-72 7.18 1077 14 36 7.98 1196 15.95 892 13.38 1784 7.63 11.45 1526

9 12 13.86 1828 463 6.94 9 33 7.43 11.18 14.96 7.35 10.99 1466 721 1075 1430 7.95 11.92 15.89 8 88 13.38 1777 7.62 11.42 15.23

100.0 1000 100.0 47 2 47.2 47 2 58 8 58 8 58 8 85 5 85-5 85 5 74 3 74 3 74.3 95.0 95.0 950 82 8 82.8 82 8 88 0 88.0 88.0

994 1007 99.6 47 1 47 1 47 5 58 5 58 7 58.8 854 85 1 852 74.6 742 740 947 94 7 94.6 82.5 82.8 82.5 87 8 87.7 878

(a) Copper known by certified analysis (Chemtcal Department, Mimstry of Industry) (b) Copper found by the present method Nos. l-8 respecttvely. copper lOO%, cupromckel 51 l”/, Ni, 072% Fe and 0.050< Zn. 33.9% Zn, 1.62 Al, 1.03% Mn, lGl% NI, 0 71% Fe and 078% Pb, bronze 9.96% Sn, 1.869; Zn, 1 83y0 Pb, 0 24% Sb, Oil7% Fe, 004% NI, OG6% As, 0 43% P, 6 8% Sn, 4.2% Pb, 4.6% Zn, 0.05’$, Fe, 0.02% Al, 0 07% P, 4.26% Nt, 0-x Fe, OGO7% Pb; 7.08% Pb, 7.48% Sn, 0.021% Fe. 0.0457/, P. 0 35% Nl, rest Zn; 10 24% Sn, 1.37% Pb, 0.39% Ni, 0.02% P, OGO2%Fe.

Chemtstq Deparrment Carro Vniuerstt~ Cawo, V.A.R

H KHALIFA E A. EL-GAZZAR

REFERENCES

1 2 3 4. 5 6

H Khahfa and B Ateya. Mtcrochem J., 1968, 13. 147 tbrd. 1967, 12, 440 H Khahfa and B N Barsoum, ibtd., 1972, m the press E W Hammock and E H Swtft, Anal. Chem., 1949,21,975 H. Khalifa and M M. Khater, J. Chem V.A.R., 1967, 10, 123. A I. Vogel, Quuntrtatme lnorganrc Anafps, 3rd Ed., p. 1166. Longmans, New York, 1962 idem.

Summary-A

rapid, accurate and htghly selecttve method has been developed for estimatron of copper. based on separatmg tt as the shghtly soluble copper(I) rodtde, and potentiometric back-tttration of unreacted iodtde, m the filtrate. wtth mercury(H) By tts atd bmary, ternary and quaternary mtxtures as well as a varrety of copper alloys have beensuccessfully analysed

246

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COMMUNICATIONS

Zusammenfassung-Elne rasche. genaue und hochselekttve Metkode zur Bestlmmung von Kupfer wurde entwtckelt. Ste beruht auf semer Abtrennung als nur schwach loshches Kupfer (I)-Jodtd und potenttometrl~her Rucktrtratton des mcht verbrauchten Jodrds tm F&rat mtt Queckstlber (II) Mtt threr Htlfe wurden brnare und quaternare Gemtsche sowte verschtedene Kupferlegrerungen mit Erfolg analystert R&m&On a elabort une methode raptde. prectse et hautement selecttve pour le dosage du cutvre, bash sur sa stparatton sous forme d’todure de cutvre (I) faiblement soluble. et le tttrage ~tentlom~trlque en retour de l’todure non reagr, dans le filtrat. par le mercure (II). A l’atde de cette techmque, on a analyse avec succb des melanges bmarres, ternatres et quaternatres amst qu’une van&i d’alliages de cutvre

To/onto.

Vol

20, pp 246-248

Pergamon

Press, 1973 Prmted m Great Brtram

NOUVELLE MICROMETHODE COLORIMl?TRIQUE DE DOSAGE DE L’ION I- DANS LES EAUX ET LES SUBSTANCES ORGANIQUES (Requ le

9

mai

1972

Acceptb

fe

16 aoiit 1972)

Parmt les methodes proposees pour le dosage de fatbles quantrtb d’todures les colonmetrles offrent un mterdt certam.‘-to En parttculier, Lange et Ward’.2 ont d&rtt une determmatton de I,, I- et IO; en presence l’un de l’autre uttlisant comme r&actif une solutton alcoohque do-tohdme et la formatton dune coloratron vert-bleu. La mithode est toutefors laborieuse et la coloratron obtenue mstable. Cest pourquot Johannessor? a retenu comme reacttf une solutton chlorhydrtque d’@tolidme, la coloration etant alors Jaune Selon nos essats, effect& dans le but de doser de faibles quantttes d’ton I- dans les products naturels, une mtcrocoiortmttrie peut itre rQhsb sur le prtnctpe dune oxydatton de I- en I, par l’eau oxygente. a pH 3,5-4,5 et dtveloppement dune coloratton bleue stable avec l’o-tohdme. PARTIE

EXPERlMENTALE

Solutton do-tohdme obtenue en dtssolvant 0.1 g do-tohdme darts 4 ml d’alcool ethyhque a 96x, aJoutant 0,l g d’acrde sahcyhque, completant a 100 mf avec de l’eau ptns filtrant Le’rtactif dont le pH est comprts entre 3,s et 45 est stable pendant plusteurs mots. L’o-tohdme peut itre purrfih st n&essatre par dtssolutton en actde chlorhydrtque ou sulfurtque dtlue, decoloratton par un charbon acttf et prempitatton par l’hydroxyde de sodmm Solutton aqueuse a 20% de carbonate de potassmm Eau oxygbnee concentree (30%). Solutton &talon d’todure de potasstum a 0.6541 pour 1000 (500 ng I-/ml) dont la dilutton fourmt les soluttons B 0,1-l gg I-/ml. Solutton de sulfamate ~ammonium obtenue en dtssolvant 20 g de sulfamate ~ammonIum dans 50 ml d’eau, aJoutant 10 ml de solution aqueuse a 5% d’acide sulfamtque et completant a 100 ml avec de i’eau Solutron tampon pH = 4,5-4,6 contenant 10 g de phosphate dtsodtque, 2 ml d’actde phosphortque a 83’” (d = 1.70 g/ml) dam IO0 ml. Mode

opkatowe

Dans le cas des eaux potables, des elRuents (non chlores) ou des eaux mmirales (Cventuallement prtvees d’hydrogtne sulfuri par barbotage dun courant de CO2 aprb acldifi~tlon) SO-100 ml sont alcahmsis dans une capsule de nickel par la solution a 20% de carbonate de potassrum puts Cvaporb au bam-mane JUSqU’g stccttt SI le restdu n’est pas parfaitement blanc, 11 convtent de le calcmer au four tlectrique a 500-550” Pour les products orgamques. ahmentatres ou btologrques. la prose d’essai. l-5 g, (1 ml dans le cas du sang ou de l’urme) est dessechee, linement dtvts&e PUIS addttronnee de 2 ml de solutron a 20”; de carbonate de potassmm. Apris homog~n~~~tIon, pms desstccation au barn-mane on pro&de a la calcmatton a 500-550” Jusqu’a cendres prattquement blanches Dans tous les cas, le rbtdu de calcmatton est repros par trots fats avec 3 ml d’alcool a 96’; puts apres filtratton les solutrons sont Cvaporees en etuve a 80” Jusqu’a stcctte SI la teneur en NaCl est importante. 11 convtent de repeter I’extractton alcooltque