A sensitive spectrophotometric method for the determination of dopamine was carried out without any separation steps. Bromocresol green is adsorbed on Sephadex LH-20 gel but the sorption decreases in the presence of dopamine due to ion-pair formation between bromocresol green and dopamine in solution. This attenuation was used to the microdetermination of dopamine by measurement of absorbance of the solid phase (Sephadex LH-20 gel) in a 1.0？mm cell at 625？nm. Dopamine could be determined in the concentration range of 0.4–1.6？μg？mL？1 (10-mL Sample volume) with a relative standard deviation (RSD) of 0.03% ( ). The detection limit was obtained, 0.26？μg？mL？1 (1.7？μM). The method was used for determination of dopamine in pharmaceutical injection sample and satisfactory result was obtained. 1. Introduction Dopamine (DP) has been used for treating all kinds of shock syndromes. It is very important to find a simple and sensitive method to determine the content of DP in clinical medicine. Pharmaceutical quality standard of many countries describes a nonaqueous titration method for determination of DP in injection, for example, the 1990 edition of Chinese pharmacopoeia and USP XXI. HPLC method was described for the determination of DP in USP 24 and BP 2000 with expensive apparatus [1]. Chemiluminescence has also been applied to determine DP; however, chemiluminescence reactants have hardly found extensive applications due to the instability of the oxidation reagents [2, 3]. Electrochemical detection methods have also been introduced since these are the best ways to directly determine DP without any separation steps of samples. The existence of ascorbic acid (AA) is the main obstacle in electrochemical detection system since AA is oxidized at similar potentials to DP at conventional electrodes. Therefore, modified electrodes have been used to simultaneously detect both DP and AA at different potentials [4–12]. The spectrophotometry has also been used for determination of DP with the use of organic compounds that react with DP [13–20]. However, in this work, the determination of DP is carried out with inhibition of the sorption of bromocresol green (BCG) on a solid phase from an aqueous solution, and the subsequent measurement of absorption, directly in the solid phase. Solid phase spectrophotometry (SPS) in visible region has been less used for determination of organic compounds [21]. We present an innovative work to use SPS in visible region for determination of DP. A higher molar absorptivity was obtained by this proposed method than other spectrophotometric
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