Orig nN eNe teH

Ion-Chromatographic Determination of Divalent Metal Ions (Co, Ni, Cu, Zn, Cd) using EDTA as Complexing Agent Takashi Tanaka Government Industrial Research Institute, Osaka, Midorigaoka 1-8-31, Ikeda, Osaka, Japan

lonen-chromatographische Bestimmung von zweiwertigen Metallionen (Co, Ni, Cu, Zn, Cd) mit Hilfe yon EDTA als Komplexierungsmittel

Zusammenfassung. Die Metallionen wurden als anionische Metall-EDTA-Komplexe getrennt, wobei ein Ionenchroma- tograph mit Anionenseparatorsystem benutzt wurde. Die getrennten Anionenkomplex-Ionen wurden im Eluat (3 �9 10-3 M NaHCO3/2,4 �9 10-3 M Na2CO3) durch Leitf~i- higkeitsmessung erfaBt. In 100 ~tl Probel6sung mit l0 -4 M EDTA konnten 5,0 ppm Metall bestimmt werden. Das Ver- fahren wurde auf galvanische L6sungen und Abwasser ange- wendet. Bei Einffihrung der Probel6sung in das System er- h/ilt man ein Chromatogramm der vorhandenen Anionen. Wenn dann Probe + EDTA injiziert wird, ergibt sich ein Chromatogramm der Anionen und Metall-EDTA-Kom- plexe. Die Metallgehalte resultieren aus der Differenz.

Summary. Metal ions, such as cobalt, nickel, copper, zinc and cadmium, were separated as the anionic metal-EDTA complexes using an ion-chromatograph equipped with anion separator system. The separated complex anions in the eluent (3 x 1 0 - 3 M NaHCO3/2.4 x 10 -3 M NazCO3) were detected by conductivity measurement. When 100 gl of the sample solution containing 10 -4 M EDTA was introduced into the analytical system, up to 5.0 ppm of metal ions were determined. The method was applied to the determination of metal ions in plating solution and waste water samples. When the sample solution was introduced into the system, a chromatogram of anions in the sample was obtained. Then the sample solution with EDTA was introduced and a chromatogram of anions and metal-EDTA complexes was obtained. The metals were determined from the difference of the former and the latter chromatograms.

Introduction

Ion-chromatography is an effective analytical technique for simultaneous determination of many ions, especially for in- organic anions, in water. Monovalent cations were easily detectable by this method. To determine polyvalent metal ions, however, special eluents, such as m-phenylenediamine solution [6] and acid solutions of zinc [7], barium and lead [3, 4] were used. Complexing agents, such as c~-hydroxyiso- butyric acid [1], etbylenediammonium dinitrate [2], and

Table l. Analytical conditions

Eluent:

Flow rate: Separator:

Suppressor: Detector sensitivity: Attenuator of Sigma 10 chromatograph data station: Injection volume of sample solution:

3 x 10 -3 M NaHCO3/ 2.4x 10 -3 M Na2CO3 1.9 ml/min 3 x 150 mm anion precolumn and 3 x 500 mm anion separator column 6 x 250 mm column 30 gS/cm full scale

100 gl

tartrate [5] were used for a more selective chromatographic separation of metal ions using a cation separator column. Inorganic anions, calcium and magnesium, were recently simultaneously determined with EDTA as eluent [8].

This paper describes the determination of divalent transi- tion metal ions, such as cobalt, nickel, copper, zinc and cadmium, by an ion-chromatograph equipped with an anion separator system. The metal ions were separated as the anionic metal complexes by addition of EDTA to the sample solution, and the separated complexes were detected by con- ductivity measurement. By this method, anions and metal ions in the sample were successively determined. The method was applied to the determination of metal ions in plating solution and waste water.

Experimental

Apparatus. A Dionex model 10 ion-chromatograph equipped with an anion separator and a suppressor column was used. The chromatograms were recorded with a Perkin Elmer Sigma 10 chromatograph data station.

Reagents. All reagents were of analytical grade. Standard metal ion solutions were prepared by dissolving metal sulfate salts in deionized water. The complexing agent solution was prepared by dissolving disodium salt of EDTA with water.

Procedure. Sample solutions containing metal ions up to 5 ppm, 1 0 - 4 M EDTA and eluent were injected into the ion-chromatograph. The analytical conditions are shown in Table 1.

Fresenius Z Anal Chem (1985) 320:125-127 �9 Springer-Verlag 1985

@riliHal

30

E2 0

E

o

E

0 A

- Cu

_ Z n Co

Ni

, ,

B C D

Etuent

Fig. 1. Retention times of metal-EDTA complexes for various eluents. Eluent A: 5x10-3M NaHCOa/10-aM Na2COa; B: 3 x 10 -3 M NaHCO3/2.4 x 10 -s M NazCO3; C: 5.5 x 10 s M Na/CO3; D: 5 x 10 -3 M Na2CO3/10 -3 M NaOH

(a)

EDTA EDTA Cd Ni Co Zn Cu I II I I

i I I i I

(b) H2ro HPol-

I I I i I

0 10 20 Retention time, min

Fig. 3. Retention times of EDTA, metal-EDTA complexes and in- organic anions. (a) EDTA and metal-EDTA complexes; (b) In- organic anions

150

Ni

100

(a)

Cd

J, 0

SO~- Ni Co (b)

Zn

I I i i / l 10 20 30 0

Retent ion time, rain

E DTA

i 1 10

Fig. 2a, b. Chromatograms of metal-EDTA complexes and EDTA. (a) Metal-EDTA complexes. Each metal ion 1.5 ppm; EDTA 2 x 10 -4 M; (b) EDTA 10 -4 M

E E~

s

1 2 3 4 5 Meta l ion, ppm

Fig. 4. Peak heights of metal-EDTA complexes at various metal ion concentrations. EDTA, 10 -4 M

R e s u l t s a n d D i s c u s s i o n

Eluent. Various eluents were prepared by mixing sodium bicarbonate, sodium carbonate and sodium hydroxide, and the total concentration of the sodium salts in the eluents was kept at 5 x 1 0 - a ~ 6 x 10 -3 M. The relationships be- tween the eluents and retention times of metal-EDTA complexes are shown in Fig. 1. An optimum chromatogram of the metal-EDTA complexes (Fig. 2a) was obtained when a mixture of 3 x 1 0 aM NaHCO3 and 2 .4x i0 aM Na2CO3 was used as the eluent. Retention times of EDTA and the metal complexes are shown in Fig. 3 a. The differ- ence of the retention times of nickel-EDTA and cobalt- EDTA complexes was about 1 min, but the peaks of both complexes were not separated for the mixed solution of both metal ions. As two forms of EDTA dissociated hydrogen ions were present in the eluent solution, it was assumed that two peaks appeared in the chromatogram of EDTA (Fig. 2b).

126

Calibration Curve and Reproducibility. The sample solution containing up to 5 ppm of metal ion, 10 -4M EDTA and eluent was injected into the ion-chromatograph. The re- lationships between metal ion concentrations and peak heights of the metal-EDTA complexes are shown in Fig. 4. As the peaks of EDTA and zinc-EDTA complex were not separated, a large peak height and poor precision were obtained at low zinc concentration. The coefficients of varia- tion of peak heights of 10 measurements of 1.5 ppm of cobalt, nickel, copper, zinc and cadmium were 1.5, 2.4, 2.9, 5.1 and 2.7%, respectively.

Diverse Ions. Common metal ions, such as magnesium, calcium, barium, manganese (II) and lead, form complexes with EDTA in alkaline solution at room temperature, but they did not interfere in the determination.

Retention times of common inorganic anions, hypophosphite, phosphite are shown in Fig. 3 b.

Or

C

i: 0

c"

l

r"

r

/x.. r - - 0

c l - (a)

L NO 3

I I

�9 C[-~ EDTA

Ni

I I 10

SOl-

(b)

SC)~-

_,& I

20 30

Retention time, min

Fig . 5 a, b. Chromatograms of waste water from nickel plating bath and the same with EDTA added. (a) Waste water; (b) Waste water with 10 -4 M EDTA added

T a b l e 2. Analytical results of nickel plating solution and waste water

Sample Nickel found

Proposed method ICP method

Plating solution New 2.7% 2.8% Used 0.031% 0.025%

Waste water A 82 ppm 81 ppm B 155 ppm 172 ppm

1 pl of new plating solution, 0.1 ml of used plating solution and 0.2 ml of the waste waters (A and B) were diluted to 10 ml for analysis

Applications. For the determinat ion of nickel ion in nickel plat ing solution and waste water, the following two opera- tions were performed. (1) The sample was diluted to a suit- able concentrat ion and injected into the ion-chromatograph (Fig. 5a). (2) To the sample was added EDTA and it was diluted to the same concentrat ion as sample (1) (final EDTA concentrat ion 10 -4 M) and then injected (Fig. 5b). F r o m the chromatogram obta ined in operat ion (1), the amounts of anions were determined. F r o m the chromatogram obtained in the opera t ion (2), the amounts of anions and nickel-EDTA complex were determined. The nickel ion con- centrat ion was determined f rom the difference of peak heights of ch romatogram (1) and (2).

In Table 2 a compar ison is given of the nickel ion concen- trat ions in nickel plat ing solution and waste water as obtained by this method and inductively coupled argon plasma spectrometry (ICP).

Acknowledgements. The author is much indebted to Professor Yuroku Yamamoto of Hiroshima University and Dr. Kazuo Hiiro of this Institute for their guidance and encouragement throughout this work. He is also grateful to Mr. Akinori Kawahara and Mr. Shinichi Wakida for their advice.

R e f e r e n c e s

1. Elchuk S, Cassidy RM (1979) Anal Chem 51 : 1434 2. Fritz JS, Gjerde DT, Becker RM (1981) Anal Chem 52:1519 3. Lamb JD, Hansen LD, Patch GG, Nordmeyer FR (1981) Anal

Chem 53 : 749 4. Nordmeyer FR, Hansen LD, Eatough D J, Rollins DK, Lamb

JD (1980) Anal Chem 52:852 5. Sevenich GJ, Fritz JS (1983) Anal Chem 55:12 6. Wimberley JW (1981) Anal Chem 53:1709 7. Wimberley JW (1981) Anal Chem 53:2137 8. Yamamoto M, Yamamoto H, Yamamoto Y, Matsusha S, Baba

N, Ikushige T (1984) Anal Chem (in press)

Received April 6, 1984

127