measured at 578nm against its reagents blank as reference;then the absorbance of reagents (A2)is measured at 530nm against the coordination compound (with excess reagents)as reference;and A4=4+42.The measured values of aA with these two types of instrument should be same.The calibration curve drawn by the dual-wavelength method shows a higher molar absorptivity (2.33x 1051.mol-i.cm-1)than that drawn by the mono-wavelength method. Besides,its linear range (0~7,0ug/25ml)is wider and its reproducibility is also better than that of mono-wavelength method (Fig.3). 3.3 Spectrophotometric Determination of Microamount of Gallium in the Copper Minerals Weigh accurately 0.5000~1.0000g sample,fuse it with 4~5g of sodium hydroxide in a silver crucible for 20min.Cool and then the fused mixture is leaching with almost 50ml of boiling water.Add 20ml of concentrate hydro- chloric acid and evaporate the mixture to dryness for the dehyhration of silicic acid;then dissolve the formed salts with few ml of 1:1 hydrochloric acid by carefully heating,subsequently dilute it to 50.00ml.An aliquot of 2~10ml (if it is less than 10ml,add 1:1 hydrochloric acid to 10ml)is treated with 15%titanium trichloride (dropped to the disappearence of purple colour),and place it aside for 30min;then it is extracted with 10ml of butyl acetate. Remove the raffinate and scrub the organic phase twice with 1:1 hydrochloric acid (at the first scrubbing,2 drops of titanium trichloride solution is added); then the gallium is stripped from the organic phase to the aqueous phase with 10ml of water for 1min.Remove the organic phase and dilute the aqueous phase to 25.00ml with water.An aliquot of this aqueous solution may be used to determine gallium according to the procedure described above. For the drawing of calibration curve,each aliquot of Ga(I)working solution should be diluted to 10ml with 1:1 hydrochloric acid,and then extra- ct,scrub and strip as the same treatment for the sample.The representative Table 2 Results for the determination of gallium in copper minerals(%) Determination by proposed method Sample Certified valuc mono-wavelength method dual-wavelength method detd,value variable coef. detd,value (#=6) (n=6) variable coef. Cu-1 0.00170 0,00174 3.1 0.00175 2.6 Cu-2 0.00135 0.00138 3.0 0.00138 2.4 .from north area of Hubei,China 391△ 一 △ ℃ 卜 一 。 一 一 一 。 ， 。 拼 一 。 。 。 ， · 。 ， 。 。 ， ， ， ， ， ， 一 ， ， ， ， ‘ ’ 一 一 。 ” 二 。 亡 。 ︸，立 一 。 一 。 。 。 。 。 。 ·