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Talaata. 1967. Vol. 14. pp. 875 to 877. PersamoaRresa td. priatcd in Northan heland

PRELIMIN RY COMMUNIC TIONS

Sp~~ophotome~ic determination of chromium with

XylenoI Orange and ~e~yl~~ol I e

Received 3 Februar y 1967. Accepted 13 March 1967)

Cnno~~t.rr.$III) reacts with EDTA to form a purple complex.

the photometric determination of chromium .I-)

This reaction has been widely used for

It has been found that other polyamino carboxylic

acids also form purple complexes with chromium(111) upon heating, but these analogues do not

offer any advantages over EDTA as a chromogenic reagent for chromium because of lack of ~~~~ty.

It was ought that a phenolic dye containing an iminodiacetic acid group [-N(CHsCOOH)d or a

carboxylic group might form an intensely coloumd complex with cbromium(III) upon heating.

Xylenol Orange and Methylthymol Blue were chosen to test the speculation. The experimental

results have con8rmed the prediction. The chromium(II1) Xylenol Orange complex is red with a

maximum absorption at 53Om,n and the chromium(II1) Methylthymol Blue complex is straw-

yellow-red with a maximum absorption at 56Omp. It seems that the substituted immodiacetic

acids are chromogenic reagents for chromium(II1). This paper describes preliminary results for

dete~ation of chromium with Xylenol Orange and Me~ylth~ol Blue.

Reagents

EXPERIMENTAL

Xyienol Orange solution, 1 X 10-aM. Prepared from the sodium salt of S,sCbis{[bis(carboxy-

methyl)amino]methyl)+cresolsulphonphthalein.

MethyIthynwl BI ue solution, 1 x 10-aM. Prepared from the per&sodium salt of 3,3’-bis{[bis-

(~box~e~yl~o]methyl]~~o~ulphonphthale~. The solution was acidified with a small

amount of acetic acid.

Acetate bufl r soluti on, pH 3. Prepared by mixing 2M monochloroacetic acid and 1M sodium

acetate to give a reading of pH 3 on a pH meter.

Preparation of calibr ation curves

Transfer 0, 1.0, 2.0, 3-O and 4.0 ml of 2.5 X lO%f potassium chromium sulphate 8OhtiOU to a

series of 5Oml pyrex test-tubes, add 05 ml of the acetate buffer solution, and dilute to approximately

8 ml. Add 4 ml of 1 X 10-W Xylenol Orange solution or Methyl~~ol Bhte solution. Place the

tubes in boiling water for 20 min.

dilute to ~oi~me, and mix.

Cool to room temperature, transfer to a 25-ml vohrmetric flask,

Measure the absorbance at 530 rn@ for the Xylenol Orange complex, or

at 560 rnp for the Methylthymol Blue complex, against a reagent blank.

DISCUSSION AND RESULTS

Chromium(VI) does not react with Xylenol Orange or Methylthymol Blue. It is easily reduced to

chromium(II1). The red chromium(II1) Xylenol Orange. complex has a maximm absorption at

530 q. When Me~ylth~ol Blue is in large excess, rts c~omi~~I1) complex has a maximum

absorption at 560 nq~, but when chromium is in excess, a blue or violet chromium M~hyl~~ol

Blue complex is formed.

Similarly to NTA and

EDT

Xylenol Orange and Methylthymol Blue react with chromium(III)

extremely slowly at room temperature.

‘When miCrogram amounts of chromium were taken, no

reaction between chromium and Xylen01 Orange or Methylthymol Blue could be detected at room

temperature for several hours. The colOUr reactions were noticed when the temperature exceeded

70” and were complete at 100~ in 15-20 min. Rae and coworkers* reported the catalytic action of

bicarbonate ion on the formatton of the ~~o~~(III) EDTA complex and Irving and Tomlinson*

described the electron exchange e 1~8lS m the formation of c~o~um~II1) EDTA complex by

chrommm(II) generated by metalhc MC. The present author found a similar catalytic action of

carbon dioxide gas at pH 5 on the formatton of the coloured chromium(II1) EDTA complex.

a75

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876

Preliminary communications

However, no catalytic action of bicarbonate, carbon dioxide, or metallic zinc on the formation of

chromium(II1) Xylenol Orange complex or chromium(II1) Methylthymol Blue complex was observed

at pH 3 and room temperature.

The molar absorptivity of the chromium(II1) EDTA complex has been reported as varying from

155 to 201 by different authors.8 The molar absorptivity of the chromium(II1) Xylenol Orange

complex was found to be 19.0 x IO* which is comparable with those of other Xylenol Orange

complexes.4os Based on Sandell’s expression, the sensitivity of the Xylenol Orange method is 0.003 pg.

cn+ for 0.001 absorbance. Methylthymol Blue is a less sensitive reagent for chromium than

Xylenol Orange. The molar absorptivity of chromium(II1) Methylthymol Blue complex has a value

of 11.5 x l@ and its sensitivity is 0.005 ,ug. cm2 for 0.001 absorbance. The phenolic donor group

adjacent to the iminodiacetic acid donor groups is mainly responsible for the high molar absorptivity

of the Xylenol Orange complexes. Obviously, the chelation resulting in the formation of multiple

rings causes a bathochromic shift.

There are not many sensitive reagents for chromium.

Most existing photometric methods for

chromium are based on oxidation of a dye by chromate ion.

The Xylenol Orange method is a rare,

sensitive colour reaction occurring through complex formation with chromium(II1). Like other

Xylenol Orange complexes, the chromium(II1) complex is stable for at least a few days. Beer’s law

is obeyed for the range 4-40

x

10e6M chromium for both the Xylenol Orange and Methylthymol

Blue methods.

When we had finished the preliminary work, a brief note by MalBV was brought to our attention.

It noted that Xylenol Orange gave a red colour with chromium(111) in a weakly acidic medium upon

heating, and that the complex formed had a maximum absorption at 490 rnp and might be suitable

for the calorimetric determination of chromium. No procedure was given. It is surprising to note

the maximum absorption at 490 rnp reported by Mali% because Xylenol Orange shows a maximum

absorption at 440 rnp and most red Xylenol Orange complexes have their maximum absorptions

around 535 rnp or at longer wavelengths.

Xylenol Orange is not a selective reagent, but it is possible to correct for the absorbance obtained

at room temperature due to interfering metals if their amounts are smaller than the concentration of

chromium to be determined. It should be noted that niobium, aluminium, palladium and chromium

are the only four metals known to require a temperature of loo” to hasten their complex formation

with Xylenol Orange and Methylthymol Blue.

Further investigation is being undertaken to determine many factors affecting the colour develop-

ment, complex formation, and interferences when Xylenol Orange and Methylthymol Blue are used

as chromogenic reagents for chromium.

Acknowledgements-Financial support by the School of Graduate Studies, University of Missouri at

Kansas City and Office of Water Resources Research, U.S. Department of Interior is gratefully

their helpful

cknowledged. The author is indebted to P. F. Lott and R. 6. Barnekow, Jr. for

discussions.

L. CHENGepartment of Chemistry

Uni versity of Missouri at Kansas City

Kansas City, M issouri 64110

U.S.A.

K.

Summary_-A new simple and sensitive method for determining traces

of chromium is described. Xylenol Orange and chromium(II1) form a

red complex at pH 3 on heating in boiling water for 20 min.

The molar

absorptivity is 19.0 x lo*. No catalytic action of the bicarbonate ion,

carbon dioxide, or chromium(I1) generated by metallic zinc was

observed. Methylthymol Blue is a less sensitive reagent for chromium,

the molar absorptivity being 11.5 x 10s.

Zusarnmenfassung-Eine neue einfache und empfindliche Methode zur

Bestimmung von Chromspuren wird beschrieben. Xylenolorange und

Chrom(III) bilden bei pH 3 und 20-miniitigem Erhitzen in siedendem

Wasser einen roten Komplex. Der molare Extinktionskoeffizient ist

19,3 . lo*. Eine Katalyse von Bicarbonat, Kohlendioxid oder durch

metallisches Zink erzeugtem Chrom(II) wurde nicht beobachtet.

Methylthymolblau ist als Reagens filr Chrom weniger empfindlich,

der molare Extinktionskoeffizient bet@ 11,5 . lo*.

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Preliminary copulations

R&un&-On d&c& une aouvelle methode simple et sensible pour la

d&ermination de traces de chrome.

Le Xylenol OrangC: t le chrome(III)

former% un complexe rouge a pH 3 par chauffage dam l’eau bouillante

pendant 20 mn. Le coefficient d’absorption mol6culaire est 19,0 x 103

On n’a pas observe d’action catalytique de l’ion bicarbonate, du gax

carbonique ou du chrome(E) engendr6 par le zinc mt%allique. Lc

bleu de rn~~ylth~ol est un r&&if moms sensible du chrome, le

coefficient dabsorption molculaire &ant 11,5 X le.

877

REFERENCES

1. R. Pribii and I. Klubalov&, Collection Czech. Ckem. Commun., 1950, 15,42.

2. V. K. Rao, D. S, Sunder, and M. N. Sastri, Chemist-Analyst, 1965,54,86.

3. H. M. N. H. Irving and W. R. Tomlinson, ibiri, 1966,55,14.

4. K. L. Cheng, And. Ckim. Acta, 1963,28,41.

5. K. L. Cheng and B. L. Goydish, Tdanta, 1962,9,987.

6.

M. Malat,

Naturwissenckaften, 1961,48,569.

T ma, 1967, Vol. 14. pp. 877 to 878. Peraamor~ressLtd. Printed n Northernr ad

Solvent extraction of

mmine

complexes

Trrcr eparation of metals hasedon their ability to form halide and thiocyanate complexes

extr ct ble

by

many oxy~n~nt~~g organic solvents is widely used in analytical chemistry.1

Extractions based

on the decrease in hydration produced by the formation of simple ammine complexes [Me(NHs)i++l

have not been reported. It is obvious that the differences in the stabilities of ammine complexes of

metals could be used for useful extraction separations.

The ammine complexes should be extractable

as ion-association species* if a highly polar solvent and large hydrophobic organic anions are used.

The results obtained in our laboratory are in accord with these ideas.

If nitro~~ne is used as the

solvent, and dipi~yl~~te @PA-) or tetmphenylborate (TPB-) as the anion, the ammine complexes

of zinc and of cobalt can be extracted effectively.

Typical results are summarized in Table I, from

which it can be seen that both the formation of ammiu

e complexes and the presence of large anions

are necessary for the metal extraction. Consequently, it is believed that the species Zn(NH&* and

DPA- (or TPB-) exist in the organic phase and that partial association between them may occur.*

The driving force behind this type of extraction is the squeezing out of large, u~ydrat~, low-

charged ions by the hydrogen-bonded water structure.

4 The effect is to force these ions together so as

to maximize the water-water interactions and minimize the disturber caused in the water structure

by the presence of these ions, and the ion-pairs formed in this way are then easily extracted. The

cations accompanying the anions in the organic phase are those with the largest crystallographic

radius and the smallest degree of hydration. Con~quently, the sequence of increasing extractability

TABLLS

log lW&+I

fogNSI log

[DPA-IO,

log so

log?

S

-1.30 -2.17 -1.70

0.11 051 -1.49 1.93 @91

-1.30 -1.67 -1.70

2.16 2.56 O-56 3.83 2.58

-1.30 -1.17 -1.70 251 2.91 0.91 4.30 1.99

-1.30 -0.67 -1.70

2.49 2.88 0.88 -4*30 1.73

-1.30 -1.67 -3.0

-0.32 1.37 -0‘63 - -

-1*30 -1.67 -2.3

O-52 152 -0.48 - -

-0.67 - 1*70*

1.68 - - _ -

* [NaTFBk,,,.