Analytica Chimica Acla. 90 (1977) 307-309 alE!sevier Scientitic Publishing Company. Amsterdam - Printed in The Netherlands

Short Communication

THE DETERMINATION OF CADMIUM BY THE RING-OVEN TECHNIQUE

hIUHAMMAD HANIF, hIUHXhlhIAD SARWAR CHAUDHRY and TXUSEEF AHMAD QURESHI

Pakisfan Council of Scientific and Industrial Research Laboratories. Lahorc-lb (Pakistan)

(Received 15th September 1976)

Cadmium has been reported to be hazardous to human beings and animals in various ways [l, 21. Thus direct, quick, precise and sensitive determin-. ations of cadmium are valuable. The ring-oven technique, which has been used previously for the determination of cadmium [ 2, 31, offers good pos- sibilities for the purpose.

Cadmium reacts with p-nitrobenzenediazoaminoazobenzene (Cadion 2 B) to form a coloured lake [4], and the reaction is quite sensitive [3] . In the present work, this reaction was studied by the ring-oven technique; the stan- dard scale [ 31 and the segment technique [5-7] methods were evaluated.

Experimental

Cadmium stock solution. Prepare a solution containing 0.1 mg Cd” ml-’ by dissolving 0.057 g of 3CdS0, - SH,O (Riedel) in 250 ml of distilled water. Prepare a working solution containing 0.02 mg Cd” ml-’ by exact dilution for the standard scale method. Prepare other low concentrations similarly. For the segment technique, prepare standard solutions containing 0.02, 0.04, 0.08, 0.12, 0.16 and 0.2 mg Cd”’ ml-’ (called solutions I, II, IV, VI, VIII and X, respectively) from the stock solution by exact dilutions.

Cadion solution. Prepare an ethanolic 0.02% solution which is also 0.02 M in KOH.

Xl reagents used were of analytical grade. Apparatus. The ring-oven used was made in our precision workshop, from

standard measurements [3] _ The working temperature was 110°C. Procedure. Place, with a micropipette, 1 drop (1.5 pi) of unknown cad-

mium solution on the previously marked centre of a Whatman filter paper No. 41. Wash it into the ring zone with 0.5% acetic acid; S-10 washings suffice. Remove the paper immediately from the ring-oven and spray it first with cadion solution and after 1 min with 2 M KOH solution_ Within 1 min a pinkish-red ring is obtained against a yellowish background, which is removed by washing in running water. Dry the ring between filter papers and then with hot air. The dominant ring against the light yellow background is then ready for comparison with a standard cadmium scale prepared as above by taking 1, 2, 4, 6, 8 and 10 drops of the standard working solution containing 0.02 mg Cd*’ ml-l and getting rings numbered I, II, IV, VI, VIII and X, respectively.

SOS

For evaluation of the unknown cadmium solutions by the segment tech- nique [ 5-71, use standard solutions labelled I, II, lV, VI, VIII and X, as described uncler Cadmium stoch solufion.

Results and discussion Cadmium unknown solutions were analyzed by the above procedures;

some results are shown in Table 1. Cadmium can be determined in micro- gram amounts with a maximum error of lG.O%.

The standard scale for cadmium, prepared by the above method, was checked for stability by evaluating against it standard cadmium solutions after regular intervals of time, (Table 2). The scale is stable for 3 d after which its colour deteriorates significantly.

Interferences. Interferences were studied by the method of Dharmarajan and West [2] _ When the standard scale was used for evaluation of the un- known cadmium solutions, a ring (I) containing (say) 0.35 pg of the inter- fering ion and another ring (II) containing (say) 0.035 pg of cadmium and 0.35 pg of interfering ion were prepared. The substance was confirmed as non-interfering when ring (I) was identical to the blank ring (III) and ring (II) matched the ring of the standard scale containing 0.035 ,eg of cadmium.

When the segment technique was used, the interferences were checked as described earlier [S] _ The following ions do not interfere even in lOO-fold amounts: Na’, K’, Cu’+, Ba”, Sr’*, A13’, Ce’+, Zn”, Pb’*, Sn”, NH++, Cry, Fe-, Cl-, Br-, I-, F-, N03-, NOz-, AC-, COJ’-, HPOJz-, BOz-, SOJz-, SOJ’-, S203’-, SC. CrlOY’- and CrOl’. A 40-fold amount of Mn” or Ni” does not interfere, while Co” interferes at more than 20-fold and Ag’ and Hg’ inter- fere even at less than lo-fold.

The selectivity and sensitivity of the method is proved from the high levels cf diverse ions in whose presence cadmium can be determined.

TABLE 1

Determination of cadmillm by the standard scale and segment techniques (All results are given as ug PI-‘.)

Standard scale

Cd given Cd found

Segment technique

Cd given Cd found

0.010 0.011 0.010 0.009 0.016 O.Oli 0.056 0.058 0.031 0.037 0.080 0.083

0.061 0.065 0.095 0.094 0.075 0.080 0.120 0.118 0.097 0.095 0.150 0.153 O-i20 0.113 0.160 0.155 0.160 0.160 0.180 0.190 0.200 0.200 0.200 0.215

309

TABLE 2

The stability of the standard scale

(Results are given as gg P I-’ )

DaY Cd given Cd found Day Cd given Cd found

0 0.012 0.011 2 0.025 0.027

0.130 0.139 0.055 0.058

0.200 0.215 0.180 0.195

1 0.015 0.016 3 0.013 0.014 0.180 0.195 0.045 0.050

0.200 0.220 0.200 0.223

Part of this work was done by M.H. in the Federal Republic of Germany as a Postdoctoral Senior Research Fellow of the Alexander Von-Humboldt Stiftung. The authors are greatly indebted to Prof. Dr. Herbert Weisz, Department of Analytical Chemistry, Freiburg University, for guidance.

REFERENCES

1 H. E. Hesketh. Understanding md Controlling Air Pollution, Ann Arbor, Michigan. 2nd edn.. 1973. p. 117.

2 V. Dharmarajan and P. W. West, Anal. Chim. Acta. 57 (1971) 469. 3 H. W&z, Microanalysis by the Ring-Oven Technique, Pergamon Press, Oxford. 2nd edn.,

1970.

4 F. P. Dwyer. Aust. Chem. Inst. J. Proc.. 4 (1937) 26.

5 H. Weisz, S. Pantel and I. Vereno, hlikrochim. Acta (Wien), (1976) 289.

6 H. Weisz, Proc. Sot. Anal. Chem., 11 (1974) 319. 7 H. 1Veis.z. S. Pantel and I. Vereno. Mkrochim. Acta (Wien), (1975). 287.

8 H. Weisz and XI. Hanif. Anal. Chim. Acta. 81 (1976) 179.