Ga(III) and carminic acid (CA) was utilized for devel- oping a spectrophotometric method of gallium deter- ruination in the presence of the cationic surfactant.
Mikrochim. Acta 129, 57-63 (1998)
Mikrochimica Acta 9 Springer-Verlag 1998 Printed in Austria
Spectrophotometric Determination of Gallium(III) with Carminic Acid and Hexadecylpyridinium Chloride Hayati Filik, Esma Tiitem*, Re,at Apak, and Erol Er~ag Department of Chemistry,Facultyof Engineering, istanbul University,Avcllar, 34850 Istanbul,Turkey
Abstract. The coloured complex formed between Ga(III) and carminic acid (CA) was utilized for developing a spectrophotometric method of gallium deterruination in the presence of the cationic surfactant hexadecylpyridinium chloride (HDPC), which caused a bathochromic shift in the absorption spectrum and an increase in extinction. The Ga(III): CA molar ratio was 1:4 in the presence of HDPC. The complex exhibited a molar absorptivity of 3.0 x 104 dm 3 mo1-1 cm -1 at 570 nm in an aqeous solution of pH 4.0. Beer's law was obeyed between 2.0 x 10-6-2.0 x 10-SM Ga(III), and the relative standard deviation for gallium analysis was 1.4%. Most ions did not interfere, with a few exceptions which could be masked with either diethyldithiocarbamate, ascorbic acid, thioglycollic acid or fluoride. The developed method was successfully applied without any preliminary separation to gallium determination in gallium arsenide (GaAs) semiconductor materials, and with prior extraction in a geostandard tonalite sample containing very high proportions of Fe(III) and AI(III).
Key words: galliumdetermination, spectrophotometry,carminic acid, hexadecylpyridiniumchloride,galliumarsenide. Gallium compounds bear electroluminescence property and are used for the manufacture of light emitting diodes [1]. Gallium arsenide (GaAs), being an important gallium compound, has been used in semiconductor applications such as transistors, solar cells, lasers etc. [2]. The increasing use of this metal in electronics as well as in other metallurgical industries * To whomcorrespondenceshouldbe addressed
requires its selective separation and determination in different matrices [1]. Aside from the more sensitive and relatively interference-free atomic absorption and emission spectrometric methods of gallium quantification [3, 4], the cheaper and more common spectrophotometric methods require the use of colour-forming reagents such as rhodamine B [5], 4-(2-pyridylazo)resorcinol (PAR) [6], 1-(2-pyridylazo)-2-naphthol (PAN) [7], xylenol orange [8], eriochrome black T [9], 2,6,7-trihydroxy-9-phenyl-3H-xanthen-3-one (phenylfluorone) [10], salicylaldehyde-4-aminobenzoylhydrazone [11] and 2-[2-(3,5-dibromopyridyl)azo]-5-diethylaminobenzoic acid [12]. Unfortunately, most of these chromogenic reagents require preliminary operations in the form of Ga extraction into organic solvents [10]. Generally, colorimetric ligands having O- and Ndonor atoms, like PAR, PAN, 8-hydroxyquinoline and xylenol orange, are non-selective and subject to interference caused by hard Lewis acid cations, especially Fe(III) and AI(III), in the determination of Ga. Thus suitable masking agents can hardly be developed for differentiating the corresponding Gachelate from that of A1 and other hard acids which have similar stabilities [13]. The well-established rhodamine B extractivephotometric method [5] is effective only when it is applied in conjunction with preliminary separation, i.e., extraction of Ga with Et20 from 6M HC1 solution. The method utilizes benzene, a carcinogen, as a constituent of the organic solvent phase. Metals forming extractable chlorides in HC1 solution, e.g., Fe(III), Sb(V), TI(III) and Au(III), strongly interfere
58
[5]. Due to the non-specific character of the extraction of ion-associates, all large anions may be extracted by the rhodamine B cation into the organic phase [14] and the relative error of the claimed procedure may reach as high as 5-10% [15]. Among the few spectrophotometric methods that are claimed not to require preliminary separation, the phenylfluorone (PF) reagent bears the risk of turbidity development in ethanolic aqueous solutions of PF and its metal chelates [10], which can only be overcome by the use of the nasty reagent pyridine for Ga determination in solutions containing a cationic surfactant. The developers of this method state that A1, Fe, Sn, Ti, Cd, Mn and V cause error when present in 1:1 weight ratio to Ga [10], and that large quantities of Fe(III) and A1 require preliminary separation of Ga [10], but the limiting ratio of these interferents to Ga that cannot be compensated for by masking agents and require preliminary separation has not been indicated. This fact may give rise to problems in the application of the method in conventional laboratories as the hard acid cations (lithophile elements) of high abundance in the earth's crust usually accompany Ga in its ores [16] and cause interference. Carminic acid (7-/3-D-glucopyranosyl-9,10-dihydro3,5,6,8-tetrahydroxy- 1-methyl-9-10-dioxo-2-anthracene carboxylic acid), being a common dyestuff, has found use as a chromogenic reagent in the spectrophotometric determination of boron [17] and some other elements. Preliminary investigations revealed that this chelating reagent forms a coloured complex with Ga(III) [18], and that interference caused by hard acid cations may be partly overcome by suitable masking agents. In recent years, surfactants near micellar concentrations have found wide use in spectrophotometric metal analyses due to their favourable effects on the solubilization of metal chelates, and on the shift of maximum absorption wavelength and increase in molar absorptivity of these chelates as a result of ternary complex formation and changes in ionization equilibria of the ligand [19]. In particular, cationic surfactants have proved to be effective in Ga(III) determinations [10, 20] and in photometric analyses of other elements using carminic acid [21-23]. Moreover, spectrophotometric methods of gallium estimation in the presence of surfactants are normally expected to be less laborious than similar methods involving solvent extraction such as the rhodamine B [5] and 2-(2-pyridylazo)-5-monoethylamino-p-cresol
H. Filik et al.
(PAEAC) [24] procedures. These ideas led to a thorough investigation of the Ga(III)-carminic acid (CA)-hexadecylpyridinium chloride (HDPC) ternary system with the purpose of developing a sensitive and selective photometric method of gallium determination. Meanwhile, it has been aimed to avoid the use of nasty or carcinogenic organic solvents and reagents associated with the need for preliminary extraction of Ga.
Experimental Instruments A Hitachi 220 A UV-visible spectrophotometer with quartz cells of 1-cm path length was used for recording absorption spectra and absorbance measurements at selected wavelengths. The pH of solutions was measured by a Metrohm E-512 pH-meter using a glass electrode.
Chemicals and Reagents Ga(NO3)3. 8H20 and Pb(NO3)2 were supplied from Fluka. Gallium arsenide (GaAs) was supplied from MCT Ltd. (UK). The tonalite geostandard (containing 2 0 g g g -1 Ga) 071 T-1 originated from Msusule Pluton, Tanzania. Sodium diethyldithiocarbamate (NaDDC) was obtained from Sigma. 2,6,7-Trihydroxy-9-phenyl3H-xanthen-3-one (phenylfluorone) (PF), pyridine, 1-hexadecylpyridinium chloride monohydrate (HDPC), 1-hexadecyl-pyridinium bromide monohydrate (HDPB), ascorbic acid (AA), thioglycollic acid (TGA) and all the remaining chemicals were purchased from E.Merck, and were of analytical reagent grade. The reported results of the analysis of the geostandard tonalite 071 T-1 were as follows [25]: Major constituents (%): SiO2 62. 70, A1203 16.69, Fe203 2.71, FeO 2.88, MnO 0.10, MgO 1.89, CaO 5.08, Na20 4.39, K20 1.24, TiO2 0.58, P205 0.14, H 2 0 + 1.52, CO2 0.07, Trace constituents (in gg g-I ): Ba 660, Co 13, Cr 20, Cu 48, Ga 20, Ni 10, Pb 37, Rb 32, V 96, Zn 180, Zr 150. The Ga(III) stock solution ( 1 . 0 x l 0 - 3 M ) was prepared by dissolving the appropriate weight of gallium nitrate octahydrate in 10 .2 MHC1 solution and diluted to the desired concentration with distilled water. Ferric and aluminium solutions as interferents were prepared from the nitrate salts. Stock solutions of carminic acid (CA) at 1.0xl0-3M, hexadecylpyridinium chloride (HDPC) and hexadecylpyridinium bromide (HDPB) at 2.0x10 2M were prepared in hot distilled water, left to cool to room temperature, and diluted to final volume. 8.0• 5M phenylfluorone (PF) solution was prepared by dissolving the appropriate weight of PF in HCl:ethanol (1:1) mixture solution. Pyridine (Py) (2.48 34) was dissolved in water. Sodium diethyldithiocarbamate 2.0% (w/v), thioglycollic acid 2.0% (v/v), ascorbic acid 0.2% (w/v) and NaF 0.2% (w/v) solutions were prepared fresh in distilled water. The acetate buffer (0.2M) solutions in the pH range 3.5-6.0 were prepared by mixing suitable volumes of equimolar (0.2 M) sodium acetate and acetic acid aqueous solutions.
Procedures (a) Ga(IIl) determination in aqueous solution. To 1 mE of a gallium solution preferably at a concentration between 1.0x 10 -5 and 1.0• 10 -4 M, add 1 mE of 5.0x 10 4 M CA reagent, 1 mE of
Spectrophotometric Determination of Gallium(III)
59
2.5 x 10 -3 M HDPC and 2 mL of acetate (pH4.0) buffer, mix well, and measure the absorbance (A) against a reagent blank at 570 nm after 2 min (the colour is stable for at least 24 h). Find the Ga(III) concentration by means of a calibration curve.
0.6-
(b) Ga(III) determination in GaAs semiconductor. Dissolve the gallium arsenide sample (5-50 rag) in aqua regia and evaporate to
0.5-
dryness. Take up the residue with 100mL of 0.5MHC1. Dilute tenfold with water, and add a 0.5-mL aliquot to a test tube. Add 0.5mL of CA (1.0xl0-3M), 0.5mE of HDPC (5.0x10-3M), 05 mL of NaDDC (2% w/v), 1 mL of distilled water and 2 mL of acetate (pH4.0) buffer, and mix well. Proceed as described in Procedure (a). Alternatively, after HC1 dissolution of the residue, extract gallium from 6 M HC1 solution with diethyl ether in the form of H[GaC14], as described in literature [26], so as to separate it from arsenide. Evaporate the ether extract on a water bath, and carry out Procedure (a) for the purified gallium sample.
0.7-
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tl
t I # i ! I J I
ii I 0.4cs
/
t ~
I I
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0.3-
0.2-
0.1
(c) Ga(III) determination in the geostandard tonalite. Dissolve a 1.000g sample of the geostandard 071T-1 tonalite in I:IHFHC104 mixture in a Pt crucible, evaporate to dryness. Evaporate successively with HC1 (3-4 times) to dryness, take up the residue with 0.1M HC1 and dilute to 10mL with the same solution. This solution should contain 28.7 gMGa(III), according to the analysis certificate of the geostandard [25]. Take a suitable aliquot from this final solution (2 mL for the PF and 3 mL for the CA method), add sufficient HC1 so that the final acid molarity is 6 M [26], extract with diethyl ether (1:1 v/v) in two successive portions for 5 min, combine the organic phases and evaporate the ether on a water bath under a hood. Dissolve the residue in i mL of water and determine Ga as in Procedure (a). Alternatively apply the PF method as described by Sakuraba [10]. To 1 mL of the Ga(III) solution, add 2mL of 80raM PF, 2.5mL of 2.48M pyridine (in water), 2.5mL of 2.0x10-2M ItDPB and 2mL of pH 5.0buffer, in that order. Wait for 30min, and measure the absorbance at 570 nm (Average abs. = 0.267).
0.0
i
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52O
560
Wov~,~h
i I i
6OO
(rim)
Fig. 1. Absorption spectra of Ga(IlI) + CA mixture solution vs. CA blank ( ) and G a ( I I I ) + C A + H D P C mixture solution vs. C A + H D P C blank (. . . . ) [Ga(III)]=2.0xl0-SM, [CA]= 1.0xl0-4M, [HDPC] = 5.0x10 4M, pH4.0
the p r e s e n c e o f H D P C
with a 20-nm bathochromic
shift, i.e., Amax = 570 nm, a n d a m o r e t h a n t w o - f o l d i n c r e a s e in m o l a r a b s o r p t i v i t y w h e n the r e a g e n t b l a n k c o n t a i n s C A + H D P C (Fig. 1). T h e s e o b s e r v a t i o n s are
(d) Stu@ of interferences affecting gallium analysis. To 0.5 mL of
in a c c o r d w i t h m i c e l l a r s e n s i t i z e d s p e c t r o p h o t o m e t r i c
2.0x10-4M Ga(III) standard solution, add 0.5mL of the interferent solution under investigation, 0.5 mL of CA (1.0x 10-3 M), 0.5mL of HDPC (5.0x10-3 M), and 0.5mL of the appropriate masking solution (2.0% NaDDC, 0.2% NaF or 0.2% AA). Further add 0.5 mL of distilled water, and 2 mL of acetate buffer, mix well, and proceed as in Procedure (a). For studying the tolerance limits of major interferents, i.e., Fe(III) and AI(III), mix 0.5 mL of 2.0x 10 -4 MGa(III), 0.25 mL of 2.0xl0-ZMAI(III) and/or 0.25mL of 2.0• Fe 3+, add 0.1 mL of 2% (v/v) thioglycollic acid solution. Purge with nitrogen gas and add 0.1 mL of 1% (w/v) NH4F solution. Add 0.5 mL of CA reagent, 0.5 mL of HDPC solution and 2.0 mL of acetate buffer (pH 4.0). Let the colour reaction go to completion (5-10 rain), and measure the absorbance at 570nm against a reagent blank, the molar absorptivity for Ga being 3.0x 104 dm 3 mo1-1 cm ~.
m e t a l d e t e r m i n a t i o n s [ 19], and m a y b e a s s o c i a t e d w i t h
Results and Discussion
Colour Stability
ternary
complex
formation
as
well
as
with
the
changing ionization behaviour of the primary ligand ( C A ) in the p r e s e n c e o f the s u r f a c t a n t (Fig. 2).
Effect o f p H T h e p H o f G a : C A : H D P C m i x t u r e s at a m o l e ratio o f 1:5:25 w e r e v a r i e d b e t w e e n 3.5 and 6.0 b y the u s e o f a c e t a t e buffers (Fig. 3). S i n c e m a x i m a l a b s o r b a n c e was o b t a i n e d a r o u n d p H 4.0, this w a s s e l e c t e d as the w o r k i n g pH.
T h e c o l o u r o f G a : C A : H D P C m i x t u r e s at a m o l e ratio
Absorption Spectra
o f 1:5:25 w e r e stable after the first m i n u t e o f m i x i n g
W h i l e G a ( I I I ) f o r m s a c o l o u r e d c o m p l e x w i t h C A at
the r e a g e n t s ,
p H 4.0 s h o w i n g m a x i m u m
r e m a i n e d so for up to 2 4 h
absorption against a CA
b l a n k at 550 n m (Fig. 1), a v i o l e t c o m p l e x is f o r m e d in
mixture
was
as d e s c r i b e d maximal
after
in P r o c e d u r e
(a),
and
(the a b s o r b a n c e o f the 1 rain
and
remained
60
H. Filik et al.
1.4
0.8
1.2
/'f • \ 1.0
co
"~
k./i
/
t
0.8
o .s
