A kind of new functional polymeric microspheres with strong adsorption ability for creatinine was prepared

and the adsorption mechanism was studied in depth. First of all

the crosslinked copolymer microspheres of 2-hydroxyethyl methacrylate (HEMA) and N-vinylpyrrolidone (NVP) with an average diameter of 180 μm were prepared by suspension copolymerization and denoted as HEMA/NVP

which has biocompatibility. In the suspension copolymerization system

N

N′-methylene biscrylamide (MBA) was used as crosslinking agent

α

α′-azoisobisbutyronitrile (AIBN) was used as initiator

and Span-60 (Sorbitan monooleate) was used as suspension stabilizer. Subsequently

the microspheres HEMA/NVP were chemically modified with 3

5-dinitrobenzoyl chloride (DNBC)

and the functional microspheres DNBZ-HEMA/NVP

on which a number of 3

5-dinitrobenzoate (DNBZ) groups were bonded

were obtained. In the modification reaction

triethylamine was used as the agent to capture acid

and reaction could be carried out favourably. The chemical structure and composition of the functional microspheres were characterized with FTIR and chemical analytical method. The adsorption characteristics of DNBZ-HEMA/NVP for creatinine were studied

and the effects of various factors on the adsorption properties of the functional microspheres were investigated. Static adsorption experiments show that the functional microspheres DNBZ-HEMA/NVP have strong adsorption property for creatinine due to the chemical reaction analogous to Jaffe′ reaction between 3

5-dinitrobenzoate on the surface of the microspheres and creatinine. In the aqueous solution

creatinine has two kinds of tautomers

the keto form and the enol form. The tautomer with enol form is easy to loss a proton and produces a negative oxyanion. The negative oxyanions are attracted by the nitrogen atoms with positive electricity on the nitro groups of DNBZ. Finally

a complex reaction takes place and a complex of 1∶1σ is formed between DNBZ of the microspheres and the creatinine molecule. Obviously

the adsorption of the functional microsphere DNBZ-HEMA/NVP for creatinine is attributed to chemical adsorption

furthermore

it is a chemical adsorption driven by electrostatic interaction. The adsorption capacity of DNBZ-HEMA/NVP is enhanced 20 times as compared with that of the unmodified microsphere HEMA/NVP

and the saturated adsorption amount reaches 21 mg/g. Both pH value and salinity influence the adsorption capacity greatly. As pH value of the medium is lower

creatinine exists mainly as keto form

and there are few negative oxyanions

so there is weak electrostatic interaction between the microsphere DNBZ-HEMA/NVP and the creatinine molecule resulting in the poor adsorption ability of the microsphere DNBZ-HEMA/NVP for creatinine and lower adsorption capacity. With the increase of pH value

the equilibrium between the two tautomers of creatinine moves to enol form

and more negative oxyanions will be produced. So the electrostatic interaction is strengthened

resulting in the stronger adsorption ability of the microsphere DNBZ-HEMA/NVP for creatinine and higher adsorption capacity. However

the too high pH value is also disadvantageous to the electrostatic interaction. The experimental results show that as pH=8.5

there is the strongest electrostatic interaction between the microsphere DNBZ-HEMA/NVP and the creatinine molecule

resulting in a maximum adsorption capacity. The ionic strength weakens the lectrostatic interaction

so greater salinity leads to decreasing the adsorption ability of the microsphere DNBZ-HEMA/NVP for creatinine.