A study on the distribution of plumbum, cadmium on soybeans and deprotonation of carboxyl functional groups of citric acid in the chelation process. This study was deprotonation phase of carboxyl functional groups of citric acid as chelating agent, that was review chemically activity (protons number) functional group of citric acid was caused of chelation environment pH changes. Research factors were 1) ratios of citric acid with water, consists of three levels i.e. 0,1:1; 0,2:1 and 0,3:1 second factors was chelation environment pH, consists of three levels i.e. 5; 7.5 and 10. The results showed that, the plumbum (Pb) accumulation in seed coat tissue average value 0,37 ± 0,03 ppm, whereas Pb on cotyledon tissue average value 0,39 ± 0,07 ppm. Cadmium (Cd) accumulation in seed coat tissue average value was 0,02 ± 0,004 ppm while the Cd on cotyledon tissue average value 0,02 ± 0,003 ppm. The highest deprotonation of functional groups citric acid as chelating agent 9,43cmol+kg was reached on chelation condition citric acid ratios with water 0,3:1 on chelation environment pH 10 (A3B3–1). The study result non significant difference with citric acid ratios with water 0,2:1 and 0,1:1 on chelation environment pH 10.ABSTRAKTelah dilakukan penelitian tentang distribusi plumbum, cadmium pada biji kedelai dan deprotonasi gugus fungsional karboksil asam sitrat dalam proses khelasi. Penelitian ini merupakan tahapan deprotonasi gugus fungsional karboksil asam sitrat, yaitu tinjauan secara kimiawi keaktifan (jumlah proton) gugus fungsional asam sitrat akibat perubahan pH lingkungan khelasi. Faktor penelitian meliputi ratio asam sitrat terhadap air yang terdiri dari tiga taraf 0,1:1, 0,2:1 dan 0,3:1 dengan pH lingkungan khelasi yang terdiri dari tiga taraf 5; 7,5 dan 10. Hasil penelitian menunjukkan bahwa, akumulasi plumbum (Pb) pada jaringan kulit biji kedelai rerata 0,37 ± 0,03 ppm, sedangkan Pb pada jaringan kotiledon rerata 0,39 ± 0,07 ppm. Akumulasi cadmium (Cd) pada jaringan kulit biji kedelai rerata 0,02 ± 0,004 ppm sedangkan Cd pada jaringan kotiledon rerata 0,02 ± 0,004 ppm. Deprotonasi gugus fungsional chelating agent asam sitrat tertinggi 9,43 cmol + kg –1 dicapai pada kondisi khelasi dengan ratio asam sitrat terhadap air 0,3:1 pada lingkungan khelasi pH 10 (A). Keadaan tersebut tidak berbeda nyata dengan perlakuan ratio asam sitrat 0,2:1 dan 0,1:1 pada lingkungan khelasi pH 10.