colorimetrìa intercambio iónico - 1976.pdf

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~~~ EXCHA~~ER CALORIMETRY I

MICRO DETERMINATION OF CHROMIUM IRON COPPER ANDCOBALT IN WATER

KAZUHISA YOSHIMUR~ HIROHIKO W KI and SHIGERU OH SHI

Department of Chemistry, Faculty of Science. Kyushu Umversitj. Hakozakt. Hlgashi-ku, Fukuoka. Japan

Received 8 July 1975. Reztwd 23 Sepremhcr 1975. Accepred 20 Norember 1975)

Summary-A new. senwtive. calorimetric method based on the direct measurement of light-absorptionby an ion-exchange resin phase. which has sorbed the sample complex species. has been developed.Detennmatlons of chromiumNIl with diphenylcarbazide. iron(H) with l,l~phenanthrolin~ copper withZincon and cobalt with thiocyanate have more than ten times the sensitivity obtainable wrth conven-

tional solution calorimetry. The present method can be applied to natural water samples contaimngvery low levels of these metals.

A spot-test with ion-exchange resin beads has beenproposed by Fujimoto, and by Kakihana and hisco-workers2 This technique has various advantagesfor qualitative microanalysis. In this method, concen-tration and selective sorption of the chemical speciesto be identified may occur simultaneously. In somecases, the sample species are converted into complexanions of higher ligand number within an anion-exchange resin phase, leading to remarkable enhance-ment of the sensitivity.

In spite of a number of publications on the resinspot-test3-a and on the interpretation of resin-phaseabsorption spectra of the inorganic complexes.g-3 nopapers on the quantitative analytical application ofthese resin-phase spectra could be found. A new spec-trophotometric microanalytical method. based on thedirect measurement of the resin-phase absorbanceafter the sorption of sample species, has been devel-oped for the determination of some transition metals.

In acid solution14 diphenylcarbazide forms a solu-ble. red-violet cationic complex with sexivalent chro-mium. having a metal-ligand molar ratio of 3:2. Thisreaction has been utilized for the micro determmationof chromium. l,lO-Phenanthroline is known as asensitive reagent for the calorimetric determinationof iron. The very stable red complex cationFe(phen):+ tS formed in weakly acidic, neutral andweakly alkaline media. A sensitive colorrmetricmethod for copper with Zincon (2-hydroxy-5-sulpho-phenylazobenzylidenehydrazinobenzoic aad) wasreported by Rush and Yoe.16 They succeeded indetermining zinc and copper in mixtures by appro-priate adjustment of the pH. The spot-test for cobalt-(III with anion~xchange resin beads and ammoniumthiocyanate was proposed by Fujimoto. This testwas very sensitive and specific.

The present paper describes the application of thesecolour reactions to quantitative studies on ion-exchange resins.

EXPERIMENTAL

~~.~orprjon rneusur~ellr~ on rhe r si n phase

The following ion-exchange resins were used. dependingupon the mechanism of the colour development: Dowex5OW-X2. H-form (SO-100 mesh and 100-200 mesh):Dowex l-X2. Cl--form IlOO-200 mesh). The mixture ofresin. sample solution and reagent was shaken mecham-tally. The coloured resin beads were separated from the

bulk solution and packed together with a small volumeof the solution into a I-mm quartz cell. by means of apipette. The absorbance was measured with a Hitachirecording spectrophotometer. Model EPS-3T. a perforatedmetal plate being used as a neutral density filter (of absor-bance 2.0) m the reJerence beam to balance the light m-tensities.

From the observed absorbance rl at a given wavelength,the net absorbance ART of the complex species sorbed onthe resin can be obtained from the equation

ARC = A -Awl. -AR -AM. 11

where ,4.,,,,, represents the absorbance of the interstitialsolution between the resm beads. AR that of the resm back-ground and ARL that of the reagent m the cell. Theabsorbance due to the sample complex m the interstitialliquid may be neglected. The values of ARC. AR and ARLare affected by the packmg of the resin beads because ofthe change in path-length or scatlermg behaviour in thecell. The packmg should therefore be reproducible. Thefollowing procedure was found to be adequate. Theab~rptjon spectrum of a resin layer containing no col-oured spenes was measured agamst pure water. The absor-bance at two different wavelengths. one corresponding tothe absorption maxImum of the coloured species and theother in a reB]on where the resm alone absorbs (700-800nml was read from the chart. The absorbance differencema) be assumed lo be constant under the sirnllar packingconditions. In practice. AR at 700 or 800 nm was constantto nithm &0.025. The value of AR at the absorption maxt-mum. m equation (I ). was calculated from the absorbancedifference and the measured value of AR at 700 or 800nm. Thus the net absorbance ARC an be obtamed b sub-tractmg AR from the overall absorbance. When 4Rl cannotbe neglected. ARC ARL. Instead of ARC. is obtained b)the same treatment.

449


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450 KXZUNISA YOSEIMJRA HIROHIKO WAKI and SHIGEXU OHASH~

Procedure jbr the determinatton o chromlum( VI) wt thdlphen urha;ide

To a ZOO-ml water sample contairimg 0.01-0.3 pmole of~hrorniu~~1~ enough 5N sufphursc acid was added tomake the concentration of this acid ap~roxImate1~ 0.05N.Then 5 ml of 0.25, acetone solution of diphenylcarb~~de

and 0.5Og of Dowex SOW-X2 (MO-200 mesh) in the hy-drogen form were added. The mixture was stirred for 15min and the supernatant solution discarded, the residualresin slurry transferred to the cell and the absorbancemeasured at SSOnm.

To a 200-ml water sample containing O.I-2 Mumole ofnon. 5 ml of O.OlM l.lO-phenanthroline. 5 ml of 105; hyd-roxylamine solutron, 5 ml of 0.5M acetic acid-sodium ace-tate buffer (PI-I 5) and OSOg of Dowex 5OW-X2 in thehydrogen form (100-200 mesh) were added and the mixturewas stirred for 30 min. The coloured resin was collected

and its absorbance measured at 514 nm.Procedure for the determinati on of copper w it h Zi ncon

To a 200-ml water sample containing 0.1-l mole ofcopper( 10 ml of 0.2M potassium hydrogen phthalate-sodium hydroxide buffer (pII 5.2) and OSOg of Zincon-treated resin were added and the mixture was stirred for30 min. The resin was collected arid* its absorbancemeasured at 63Onm. The Zincon-treated resin was pre-pared by shaking 30 g of Dowex 1-X2 in the chloride form(100-200 mesh) with 50 ml of 0.13% Zincon-0.02M sodiumhydroxide solution for 1 hr.

Procedure for the determinatw n of cobaft w it h tl ti o-cymate

To a 1000-ml water sample contaming 2-20mole ofcobalt(II), 20ml of 50?? ammomum thiooyanate solutionand 0.5Og of Dowex l-X2 in the chloride form (100-200mesh) were added and the mixture w+as tirred for 30 min.The blue resm was collected and its absorbance measuredat 630nm.

All ehemieals used were of analytical ,grade and all ex-periments were carried out at room temperature.

RESULTS AND DISCUSSION

dbsorpti on spectra in resin and solution

The complex of chr~rnj~rn~v~) with diphenyicarba-zide can be sorbed on cation-exchange resins and tosome extent on anion-exchange resins by molecularinteraction as well as by ion-exchange. The net absorb-ance curve of the sorbed complex was constructedfrom the difference between the resin phase curve andthe resin background curve. The net resin-phase ab-sorption spectrum of the complex is similar to thatobtained in solution but the maximum is shifted tolonger wavelengths (550nm), as shown in Fig. I. Forquantitative studies the cation-exchange resin Dowex

5OW-X2(100-200

mesh) was used in 0.05N sulphuricacid medium.Only ration-ex~h~ge resins sorb the ~ron~~~~~,~~

phenanthro~ine compiex and give the same absorp-tion spectrum as that of an aqueous solution.

The Zincon complex of copper(U) has a molar ratioof 1: 1 and has an absorption maximum at 6OOnmin solution, The maxunum for free Zincon is at470nm. When both species are sorbed on amon-

0

A, ml

Fig. 1. (a) Absorption spectra of Dowex 1-X2 resin contain-ing chromium complex of diphenyI~b~ide. A, assumedresin background of sample: IS. reference resin spectrum;(b) Net absorptton spectra of chromium complex ofdiphenylcarbazide. A, solution spectrum; B, Dowex 50

W-X2 resin spectrum; C, Dowex l-X2 resin spectrum

exchange resins, the maxima shift to 630 and 570 nmrespectively (Fig. 2). These maxima are so dose thatthe combined spectrum usually exhibits onfy ashoulder at 630nm. Consequently the absorbance at630 run may include a contribution from free Zincon.The copper-Zincon complex is not sorbed on anion-exchange resins from acidic solution. but the Zinconreagent is sorbed irreversibly from alkaline solution.The resin containing presorbed Zincon reagent wastherefore added to acidic water samples. The excess

x, i-mFig. 2. Absorption spectra of copper-Zincon complex andfree Zincon. --. solution spectrum: _ . Zincan pre-

sorbed on Dowex I-X? resin.


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lon-exchanger colorrmetry-I 451

A. in

Fig. 3. Absorptton spectra of cobalt-thiocyanate com-plexes. -. solution spectra A. 0.7M NH,SCN + Co(U):B. 0.7M NH&N + Co(H), I :I acetone-water; C, 8MNH,SCN + Co(D);. . . spectrum of Dowex l-X2 (100-200

mesh, Cl--form) equilibrated with solution A.

of uncomplexed Zincon was not desorbed during theequilibration.

Figure 3 shows the absorption spectrum of thecobalt(II)-thiocyanate complexes sorbed on theanion-exchange resin, together with spectra of thesolutions for comparison. It may be seen that theresin spectrum is similar to that obtained with solu-tions in which the thiocyanate concentration is as

high as 8M even when the thiocyanate concentrationin the equilibrating solution is as low as 0.7M. Thetendency of the complex to change to one with higherligand numbers in the anion-exchange resin phasemay be exploited.

Ti me-dependence of co/our development

Almost all of the chromium in 200ml of samplesolution is sorbed on the resin within 15 min equilib-ration (Fig. 4). The presence of other electrolytes. suchas sodium chloride (at the concentration level foundin sea-water) has no effect on the sorption rate ofthe complex. The chromium concentration can bedetermined with the aid of a calibration curve con-structed by use of a fixed equilibration time. eventhough the sorption of chromium is not complete.Figure 4 also shows that the use of resin particlesof larger size leads to a slower sorption rate. Equilib-rium with Dowex 5OW-Xl (SO-100 mesh) and 2OOmlof solution took more than 1 hr to reach.

The complete sorption of copper requires a longtime, probably because of the slow rate of internaldiffusion of the complex in the particles (Fig. 5). Forrapid analysis it is convenient to equilibrate until justafter the early sorption stage.

A study of the rate of development of the colourof the cobalt-thiocyanate complex indicates that withlarge sample volumes a longer equilibration time is

required for quantitative sorption, but the sensitivityis increased (Fig. 6). There is no limitation upon thesize of sample volume taken, but a large volumerequires a longer equilibration time. The calibrationcurve should be prepared under the conditions usedfor the sample to be analysed.

Calibrat ion

The calibration graph for chromium is reasonablylinear in the concentration range 5 x 10-s-1.5 x 10e6M, that for iron in the range

OBl

Time. mmFig. 4 Colour development of chrommm-diphenylcarbazide complex in the cation:exchange resinphase. Resin. 0 Dowex 5OW-X2 (50-100 mesh. H-form) 0.50 g. 0. 0 Dowex 5OW-X2 (100-200 mesh.H+-form) 0.50 g. Solution. 0. 0.15 pmole Cr(VI). 200ml + 5N H,SO,. 2ml. 0 0.15 pmole

Cr(V1) + 0.6M NaCl. 200 ml + 5N H2S04. 2 ml.


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452 KAZUHISA Y~~HIMLJRA, HIROHIKO WAKI and SHIGERU OHASHI

O6

___---________------

._ 04a __-- __--

__._-----

+x

I--

5.*

a I,

:,

I 02 ,f/I

2

0I I

60 I20

Time. mmFig. 5. Colour development of copper-Zincon complex in the anion-exchange resin phase. Resin, DowexI-X2 100-200 mesh Cl--form, Zincon presorbed) 0.50 g. Solution, 0.50 pmole Cu(II), 200 ml + 0.2M

phthalate buffer (pH 5.2). 10 ml.

5 x 10--l x 10e5M , that for copper in the range5 x lo--5 x lo-M and that for cobalt in therange 2 x 10e6-2 x 10e5M. Deviations are about*s-lo%.

Sensitivity

In Table 1 the sensitivity for each system is com-pared with that obtained with a conventional colori-metric method. The concentrations giving an absor-bance of 0.50 are listed. In each case the sensitivitywas about ten times that for conventional colori-metry.

6

t

za 0i

i

39 0

4bI2: 0:0,.e-

____-----I

v

d

__--__.__----___-- _---

_--_-- __--

/,/

.I

,

...I

.,

I30

_.I I I

60 90 120

Time, InI

Fig. 6. Colour development of cobalt-thiocyanate com-plexes in the amon-exchange resin phase. Resm, Dowex1-X2 (100-200 mesh, Cl--form) 0.50 g. Solution, 0 6 moleCo(III 1000 ml + 507; NH,SCN, 20 ml. 0 6 pmole Co(II).

100 ml + 506 NH&N. IO ml.

Effect s of oreign i ons

Most metals which interfere in the calorimetricdetermination of chromium, such as vanadium(V),iron(III) and molybdenum(V1) did not interfere whenpresent in up to one hundred times the concentration

of chromium(V1). Table 2 shows that. with the excep-tion of copper, errors in the range of 5-109, areobtained.

Iron(III), cobalt(H) and nickel(I1) ions were foundto interfere in the determination of copper when theirconcentrations exceeded ten times that of the copper(Table 3).

Table 4 shows the effects of several ions on thedetermination of cobalt(I1). Iron(II1) and high concen-trations of alkali caused considerable interference.

Appl i cat ions of ion-exchanger col ori metr p

The present method may be applied to the analysisof natural water samples such as sea. river and lakewater. The error of 5-10% is not excessive for the

Table I. Comparison of sensitivity of ion-exchanger colori-metry and conventional calorimetry (metal concentration

giving a final absorbance of 0.50)

Ion-exchangercalorimetry, M

Conventionalcalorimetry*. M

Cr(V1)

Fe ~cuco

6.2 x lo-t 1.8 x lo-56.7 x IO-3 1.8 x 1O-52.9 x 1o-6 3.9 x 10-S2.5 x 1o-6 2.2 x 10-s9.4 x 1o-6 3.0 x lo-

* l-cm cell.t 0.05N HISOL medium.J 0.05N H2SOJ and 0.6M NaCl medium.


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Ion-exchanger calorimetry--I 453

Table 2. Effect of foreign ions on the determination of chromium(W)

Added Cr taken Cr found. Relativemolar ratio to Cr I O- M 4 c I O- M error, y0

VW) 1001000

Cr(II1) 1001000

Fe(II1) 1001000

CU(I1) 110

Mo(V1) 1001000

1.0 0.092

5.1 0.3955.1 0.4355.1 0.260

5.1 0.4295.1 0.498

5.1 0.4345.1 0.4255.1 0.3755.1 0.299

5.1 0.3765.1 0.401

1.1

4.95.43.2

5.36.2

5.45.34.73.7

4.75.1

+ 10

-4+6-37

+4+22

+6+4

-8-27

-80

Table 3. Effect of oreign ions on the determination of copper(I1)

Added.molar ratio to

cuCo taken, Co found Relative

IO-M ARc+&L 10-6M error, y0

Fe(II1)

Co(I1)

Ni(I1)

Zn(I1)

880

8100

8100

100800

3.0 0.722 2.8

2.5 0.687 2.62.5 undeterminable

2.5 0.623 2.32.0 0.661 2.52.5 0.671 2.52.0 0.664 2.5

2.0 0.552 2.02.5 0.204 0.41

-7

+4

-8+25

0+25

0-84

Table 4. Effect of foreign ions on the determination of cobalt(H)

Added,molar ratio to

coCo taken,

I O- M ARC

Co found. Relativelo-M error, /b

Cr(II1)

Fe(II1)

Ni(I1)

CU(I1)

NaCl

NaOHHCI

10100

0.11

10100

110

lo410s

IO+104

0.100.501.5

1.01.0

1.01.0

1.01.0

1.01.0

1.01.0

1.01.0

0.0570.2650.769

0.5250.532

0.5081.142

0.4780.5500.4730.375

0.5120.451

0.000

0.523

0.11

0.501.4

1.01.1

0.962.2

0.911.2

0.900.71

0.970.86

+ 100

- 70

+ 10

- 4+ 120

- 9+ 20- 10- 29

- 3- 14

-100

- 1


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454 KAZUHISA YOSHIMURA. IROHIKO WAKI and SHIGER~ OHASHI

micro determination of metals in practical environ-mental analysis. The technique can be extended tothe determination of other metals which give com-plexes having characteristic absorption maxima.

REFERENCES

1. M. Fujimoto, Bull. Chem. Sot. Japan. 1954, 27, 48.2. H. Kakihana and T. Murase, Nippon Kagaku Zasshi,

1954, 75, 901.3. M. Fujimoto, Bull. Chem. Sot. Japan, 1954, 27, 341.4. Idem, ibid., 1957, 30, 875. M. Fujimoto and Y. Nakatsukasa, Anal. Chim. Acta,

1962, 26, 427.6. K. Kato and H. Kakthana. Nippon Kagaku Zasshi.

1963, 84, 405.

7. H. Kakihana and K. Kato. Bunsrki Kaqaku. 1966. 15,199.

8. T. Ichikawa K. Kato and H. Kakthana. N~ppor~Kagaku Zasshi. 1971. 92, 809.

9. E. Rutner. J. Ph~s. Chem.. 1961. 65. 1027.10. J. L. Ryan. tbul.. 1961, 65. 1856.

11. H. Waki. S. Takahasht and S. Ohashi. J I~org. .Vuc/.Chem., 1973. 35. 1259.12. C. Hettner-Wirgum and M. Gantz. tbrd.. 1973. 35, 3341.13. H. Wake, K. Yoshtmura and S. Ohashi. ibrtl.. 1974.

36, 1337.14. R. T. Pflaum and L. C. Howick. J. Am. Chem. Sot..

1956, 78, 4862.15 E. B. Sandeli. Colorimerrtc Determirtatron of Trtrcrs of

Metals. 3rd Ed. Interscience. New York. 195916. R. M. Rush and J. H. Yoe. Anal. Chrm.. 1954. 26. 1345.

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