Influence of Mixed Micelle on the Sensitized Coordination Compound of Gallium （Ⅲ） with o-Chlorophenylfluo-rone and Its Analytical Application

D0I:10.13374/i.issn1001-053x.1991.04.03M 北京科技大学学报 第13宿第4(【)期 Vol.13 No.4(I) 1991年7月 Journal of University of Science and Technology Beijing July 1991 Influence of Mixed Micelle on the Sensitized Coordination Compound of Gallium(IⅢ）with o-Chlorophenylfluo- rone and Its Analytical Application Chen Huaxu Shao Guangdi Xia Xinlong' (陈华序) (邵光约) (夏心龙) ABSTRACT:After comparing the sensitizing effect of various mixed surfactants on the chromophoric reaction of gallium (with orthochlorophenylfluorone, it has been found that the mixed micelle of cetyltrimethylammonium bromide and Tween-80 is most suitable.In the presence of this mixed micelle,not only both the sensitivity and stability improve markedly,but also a wider pH range is tolerable for the colour-development.From the study on the optimum conditions for the formation of the coloured coordination compound in the system of (Ga (I)-o-Chlorophenyl fluorone-catyltrimethylammo- nium bromide-Tween-80>and its main characters,a spectrophotometric method,by which.sensitivity and reproducibility are higher than those of ternary systems of gallium(I)has been developed.When it is combined with the dual-wavelength method,the molar absorptivity can be improved to 2.33x 1051.mol-1.cm-1,which is higher than that of most of other systems ever shown in the literatures;moreover the linear range is extended.From the determination of microamount of gallium in the copper minerals,the result is proved to be acceptable. KEY WORDS:gallium,orthochlorophenylfluorone,cetyltrimethylammonium bro- mide,mixed micelle,sensitization Although many reports concerning the chromophoric system of gallium(H) have been published in recent years,most of them are ternary systems of (Ga 1991一03一04收稿 ,化学系(Department of Chemistry) 385

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(M)-Chromophoric reagent-Sensitizer),and only few ones are quarternary systems of.《Ga(I)—Chromophoric reagent-一Sensitizer--Organic sol- vent),2.Since they always exhibit some shortcomings such as strict colour- ed conditions,less selectivity or narrow linear range ctc;so that their application are limited.In consideration of using the mixed micelle of a cationic surfactant and a nonionic surfactant has been proved to improve many chromophoric conditions of some metalss,but they have not yet been reported anywhere about the respect of gallium.In view of the fact that the sensitive chromophoric characters of phenylfluorone and its derivatives as well as their sensitive colouration with gallium()in the presence of cetyltrimethylammo- nium bromide alone had already reported+-),a study to develop a more satisfactory spectrophotometric method for the determination of microamount of gallium in the presence of mixed micelle seems to be necessary and possible to proceed. 1 Experimental 1.1 Reagents and Apparatus Stock solution of Ga(),300ug/ml,was prepared by dissolving 0.2016g of Ga2O3 (spectroscopically pure)in few ml of 1:1 hydrochloric acid by care- fully heating,then cooled the solution to room temperature and diluted it with 1:1 hydrochloric acid to 500.00ml.A working solution of Ga(),3.0ug/ml, was prepared from stock solution by diluting with 1:1 hydrochloric acid. Orthochlorophenylfluorone (o-CIPF)solution,1.0x 10-3mol/l,was pre- pared by dissolving 0.174g of solid o-CIPF in a mixture of 1:1 hydrochloric acid and 20ml of ethyl alcohol,and then diluting with ethyl alcohol to 500.00 ml in a brown volumetric flask. Cetyltrimethylammonium bromide (CTMAB)aq.solution,1.0x 10-3mol/l, was prepared by dissolving 1.82g of CTMAB with water to 500ml;if some insolubles appear,it could be dissolved by warming. Tween-80,10%(v/v)aq.solution. Phosphate buffer solution,0.2mol/l,was prepared by dissolving 27.3g potassium primary phosphate with 900ml of water,and adjusted its pH to 7.2 with an acidimeter by dropping sodium hydroxide solution,then diluted to 1000ml. 752-C UV spectrophotometer,calibrated with a Shimadzu UV-3000 spectro- photometer. Electrophoresis apparatus. 386

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1.2 Procedure 1 drop of p-nitrophenol solution is added to an aliquot of 1.00ml of Ga (working solution and then few drops of dilute sodium hydroxide solution are added until the solution to be just yellow.Subsequently 2.5ml of CTMAB solution,4.0ml of Tween-80 sofution,0.6ml of o-CIPF solution and 6.0ml of buffer solution are added according to proper order,then dilute it to 25.00ml. Measure the absorbance at 578nm against its reagent blank as reference after the mixture was placed aside for 10min. 2 Results and Discussions 2.1 Absorption Spectra After comparing the coloured sensitivities of Ga()with phenylfluorone, o-nitrophenylfluorone and o-chlorophenylfluorone,it has bcen found that the laiter is most sensitive,so that o-CIPF is chosen as the chromophoric reagent. Since o-CIPF may crystalize out in the absence of micelle under the experi- mental conditions,so that the formation of binary coordination compound in the system of (Ga()-0-CIPF)has difficulty.In the presence of micelle, especially the mixed micelle,the coloured coordination compound forms easily and stably.From the laboratory data,it has been found that the absorption 0.4 0.6 0.3 0.4 0.2 0.2 0 0.2 0.4 0.6 0.8 1.0 0-CiPF/ml 2 4 5 500 540580 620 Wave length/nm C1MA6 Or Tween 60/mL Fig.1 Absorption spectra Fig.2 Effects of the amounts of o-CIPF, curve 1.coordination compound against CTMAB and Twcen-80 reagents blank, curves:1.o-CIPF(10-3 mol/1), curze 2.reagents blank against water 2.CTMAB(10-2 mol/1), concentrations:Ga()=J.72x 10-6 mol/1, 3.Twcen-80(10%). CTMAB=10-3mol/1, all these conditions are same as Fig.1, 0-C1PF=2.4×10-5mol/1, except the variables Twcen-80=1.6% l=1c1,pH=7,2: 387

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peaks of o-CIPF and its coordination compound with Ga(I)is only 48nm apart in the presence of CTMAB micelle alone.Although the absorption peaks of both o-CIPF and its coordination compound with Ga(I)all shift batho- chromically in the presence of mixed micelle of CTMAB and Tween-80,but they situate at 530nm and 578nm respectively and their separation still remains at 48nm.The laboratory data are shown in Fig.1. 2.2 Optimum Chromophoric Conditions (1)Acidity:In the presence of CTMAB alone,a maximum and constant absorbance is obtained within the pH range of 7.2~7.6;but in the presence of mixed micelle of CTMAB and Tween-80,it is extended to pH 6.8~7.6; furthermore,its sensitivity is improved. (2)Amount of o-CIPF:To cause a maximum and constant absorbance, 0.3~0.5ml of o-CIPF solution is suitable for the ternary system of (Ga(I) -o-CIPF-CTMAB)but it is extended to 0.4~0.8m1 for the quarternary system of《Ga(I)—o-C1PF—Tween--80》. (3)Choice of surfactants:The sensitizing effect of 16 kinds of cationic and 8 kinds of nonionic surfactants have been tested.It has been found that the cationic surfactants shows obvious sensitization for the colouration of Ga (I)with o-CIPF,especially the CTMAB is most effective.After comparing various nonionic surfactants which belong to Triton X series,Tween series and emulsifier,it is found that the addition of Tween-80 to CTMAB can intro- duce a most sensitive colouration;moreover,it shows wider chromophoric conditions and better stability than with CTMAB alone. From the laboratory data shown in Fig.2,it has been found that the suitable amount of CTMAB solution and Tween-80 solution for 25.00ml of coloured solution should be 1.0~7.0ml and 3.0~6.0ml respectively.In the following experiments,2.5ml of CTMAB solution and 4.0ml of Tween-80 solu- tion are chosen;thus,a concentration of CTMAB is larger than the C.M.C. value of CTMAB alone. (4)Order of reagents adding:If the working solution of Ga(I)is mixed with o-CIPF before the presence of micelle,the absorbance is reduced.Besides, if the working solution of Ga()is mixed with buffer solution at first,the absorbance decreases markedly with the hydrolysis of Ga(),and reproduci- bility is also poor.Only after the micelle of one or two surfactants has already existed,will the colouration develop with a maximum and constant absorbance,.The order of“Ga(I)—CTMAB-Tween-80一o-ClPF buffer"has been proved to be most suitable for a rapid and complcte coloura- tion. 388

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2.3 Main Characters of Coordination Compound in the System of (Ga()- o-CIPF-CTMAB-Tween-80) (1)The colouration of this system develops at room temperature and a maximum and constant absorb:.nce can be reached after 10min.At higher temperature the absorbance will be reduced. (2)The absorbance of this system remains stably at room temperature at least within 12h,so that it is'proved to be more stable than various ternary systems. (3)By the method of molar ratio,method of equilibrium shift and method of straight linc,it has been shown that the composition ratio of Ga:o-CIPF is1:2. (4)By the test of electrophoretic property,it has been observed that the coloured coordination compoundm igrates toward the anode.Besides,the colour- ed coordination compound can be adsorbed by the anionice xchanger.Hence the coordination compound should be charged negatively. 3 Analytical Application 3.1 Influence of Foreign lons From Table 1,it is shown tuat the high valent ions and Al(),Cu(I), In(I)interfere seriously.By the solvent extraction with butyl acetate, most of the interfering metal ions can be removed and the residual small amo- unts will not interfere again.From the laboratory data,conclusion can be drawn that the co-existence of 700 fold Bi,Zn,Cu,Al or Fe;170 fold Mo, W or Zr;and equal amount of In do not interfere the spectrophotometric determ ination of microamount of gallium after their prior separation by the solvent extraction with butyl acetate. 3.2 Spectrophotometric Determination of Microamount of Gallium When the gallium is determined by mono-wavelength method,Beer's law is obeyed over a concentration range of 0~5.0ug/25ml of gallium,and the molar absorptivity is 1,66x1051.mol-1.cm-.Since the absorption peak of the coloured coordination compound is not situated away from that of its rea- gents blank (AA=48nm),so that a deep background is caused at them.of the coordination compound,which is not desirable.To overcome it,a dual- wavelength mcthod is applieds,.If an instrumenl of dual-wavelength is used,the absorbance of the coloured coordination compound,4:and 42,are measured at 578nm and 530nm respectively against its reagents blank as refer- 389

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