Mikrochim. Acta 129, 57-63 (1998) Mikrochimica Acta 9 Springer-Verlag1998 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,istanbulUniversity,Avcllar, 34850 Istanbul,Turkey Abstract. The coloured complex formed between 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 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 success- fully 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, hexadecylpyridinium chloride,galliumarsenide. Gallium compounds bear electroluminescence prop- erty and are used for the manufacture of light emitting diodes [1]. Gallium arsenide (GaAs), being an im- portant gallium compound, has been used in semi- conductor 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 spectrophoto- metric 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-aminoben- zoylhydrazone [11] and 2-[2-(3,5-dibromopyridyl)- azo]-5-diethylaminobenzoic acid [12]. Unfortunately, most of these chromogenic reagents require prelimin- ary operations in the form of Ga extraction into organic solvents [10]. Generally, colorimetric ligands having O- and N- donor 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 Ga- chelate from that of A1 and other hard acids which have similar stabilities [13]. The well-established rhodamine B extractive- photometric 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