Spectrophotometric determination of iron with DTPA

SHORT COMMUNICATIONS

185

to make absorbance measurements within 5 min of the time that the reduction is carried out, since the silicon heteropoly blue colour is found to be stable for at least 24 h. Details of the modified procedure are being published in the form of a reportd.

sary

Analytical Division, Atomic Energy Estabmmrent Bombay-z8 (rftdia)

S. R. DESAI H. SAVITRI M. S. VARDE

Z’rombay,

1 0. MENIS AND Il.L. MANNING, Amf. Chim. Acfn, 16 (1957) G7. 3 S. I<. DESAI, N. SAVITH~ AND M. S. VARDE. Determirtafion o~Silicorr irr ,Thoriunr Nilralc, Energy Eetablishmcnt Trombay, Inrlio,‘XXcport No. A.E.E.T. (Anal.) 30, 1963.

(Received

January

Atomic

xst, xgo4) Atrul. Chim. Ada,

Spectrophotomktric

determination

31 (1964)

x84-185

of iron with DTPA

Almost simultaneously, scvcral workers 1-a described a reaction between the Fe(III)EDTA chelate and hydrogen peroxide in the PH region IO-II, which resulted in a complex with a maximum molar absorptivity of cu. 500 in the visible rqion at 520 mp. The reaction was applied for the quantitative determination of iron. Copper, cobalt, nickel and chromium interfcrcz at 520 rnp, but at 450 rnp the intcrfercncc of an zoo-fold amount of copper is negligible a. The intcrfcrcnce of not more than twice the amount of cobalt can be eliminated by the addition of cyanidedeb. Very recently, attention was given to this method by CHENG AN) GOYDISH~, CLULEY mined

AND by

NEWMAN~

measuring

‘the

and

from

this

differcncc

laboratory

7. In these

in .absorbancc

of two

procedures

tkolutiona

iron

is dcter-

containing

iron,

EDTA, to one of which hydrogen peroxide is added. The principle was earlier suggested by 1~xNcrjor.r3, but with few experimental details. Good results were obtained in the prescncc of Iooo-fold amounts,*,,of coppeP+ an4 nickel’, up to IO-fold amounts of cobalt7 (after prior oxiclation to-the trivalent state) and, under carefully controlled conditions, up to a xo-fold amount of chrommmf. In order to improve the analysis of iron by means of this procedure, we have investigated the same determination with various EDTA analogues, viz. HEDTA, DTPA, CyDTA and NTA. The iron(II.1) ‘chelates of these compoun’ds ‘all show 4 similar behaviour on the addition of hydrogen peroxide, but in all except one cast, the propcrtics of the resulting complex or of the ,interfcring ‘complexes make the ligand less suitable for analytical application than EDTA; oxygen evolution in the solution and instability of the resulting complexes arc the,main difficulties. The compourtcl that gives better results than EDTA ‘in’some cases is DTPA. the

interfering

* Tilt intcrfcrcncc not to occur.

elements

and

of large anlounts

of copper,

mcntioncd

in a previous

Anal.

paper’

C/rim. Acfn,

lutcr nppcarcd

31 (1964)

x85-186

SHORT COMMUNICATlONS

186

When DTPA is used in the presence of copper and nickel, the results obtained (Table I) are similar to the corresponding results with EDTA. When cobalt is present, the results are worse, particularly when other elements are also present (see Table I, experiments 6, 7 and 8). When chromium is present, the determination with DTPA is much easier to carry out, since the stability of Cr(III)-DTPA towards hydrogen peroxide in alkaline medium is much greater than the stability of the corresponding EDTA complex. There is a small increase in absorbance of the Cr(III)-DTPA chelate after the addition of hydrogen peroxide; this prevents the determination of iron in the presence of more than zs-fold amounts of chromium (see experiments 2,3 and 4). The maximum molar absorptivity of the Fe(III)-DTPA-Hz02 complex occurs at 520 rnp, which was chosen as the measuring wavelength. The molar absorptivity at 19 for Fe(III)-DTPA, 5.6 for this wavelength is 300 for Fe(III)-DTPA-H202, Cu-DTPA, 2.3 for Ni-DTPA, 75 for Cr(III)-DTPA, and 200 for Co(III)-DTPA. The procedure used was the same as that applied previously with EDTAT, except that I ml of 30% hydrogen peroxide and 5 ml of the buffer solution appeared to be sufficient in the case of DTPA.

TABLE

NutnDev

DETlSRMlNATION --Otirev elements prcsenf cv

co

-.

Ni

OF IHON WITH l>TI'A -~---_-_--_-.Ivan (HZ& (tng) Error __--_....-_~ ( ‘k) Pvesenf Fotwd CU ,--__.-_IO0 0.29G 0.298 0.6 20 0.29G 0.296 0.0 20 0.296 0.299 I .o I2 0.296 0.298 0.6

I 2 3

6 G

z -

4

8

-

2

*3

-4

I?-

12 -

4

4

4

4

z.

4

6 Solution was with nitrite.

4

100 20 20 12

I

4

4

allowed to stand ovcrnight

0.290 o.zgG 0.320 0.300 0.29G 0.420 0.296 0.317 -_.. sftcr tlic oxidation

HI ..I 40 7

_---of Co(lI)

c. DEN BOEF M. I;. RXEMERSMA

Laboratory for Analytical Chemistry, Uni~iqrsity of Amsterdam, Amsterdam (The Netlrevlands)

1 K. L. CHENG AND I'.1:.LOTT, Awl. Chetn., 28 (195G) 4G2. 0 l?. SCHNDIDRR AND J. JANKO, Collection Czech. Chm. Cornmtrn., 22 (1957) 242; Clrern.Lisly. so (1956) 899. 3 A. RINGBOM, S. SIITONEN AND 13.SAXEN, Anal. Chitn. Acta, 16 (1957) 541. 4 P. I;. LOTT AND I<. L. CHENG, Anal. Chern,, 29 (1957) x777. f~ H. J. CLULEY AND E. J. NEWMAN, A#taZysl,88 (1963) 45. 0 K. L. CHENG AND B. L. GOYDISH, Chemist-Analyst, 51 (rgbz) 45. 7 B. C. POIZDXR, G. DEN Bow AND C. E. M. FRANRWA, Amt. Citim Acta, 27 (rgG2) 339.

(Received

January

xgth, 19G4) Anal.

C/rim. Acta,

31 (rg6.1)

185-186