The detergency effect of trisodium phosphate (Na
3PO
4) on the removal of irreversibly adsorbed bovine serum albumin (BSA) from alumina (Al
2O
3) particles during cleaning with 0.05 M NaOH solution was kinetically studied. The desorption curve of BSA, obtained by plotting the logarithm of the amount of residual BSA against cleaning time, during cleaning with the NaOH solution with and without Na
3PO
4 could be apparently reduced to the sum of two straight lines with different slopes. This fact suggested that two species of BSA, i.e., a fasterdesorbing species (BSA
f) and a slower-desorbing species (BSA
s), were present on Al
2O
3 surfaces and desorbed according to a first-order process. The first-order desorption rate constant (
ks) of BSA
s obtained from cleaning with the NaOH solution alone was approximately 56-fold lower than that (
Kf) of BSA
f. The addition of Na
3PO
4 to the NaOH solution had no influence on the desorption of BSA
f, whereas it accelerated the desorption of BSA
s, with an approximately 7-fold increase in the
ks. Potentiometric titration showed that phosphate ions were adsorbed on Al
2O
3 surfaces after cleaning with the NaOH solution containing Na
3PO
4. The results indicated that hydroxide ion and phosphate ions could displace the slower-desorbing BSA
s species at Al
2O
3-water interfaces in a synergistic manner.
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