Synthesis and characterisation of starch phosphates

Monostarch monophosphates with different phosphorus contents were prepared via reacting starch with a mixture of primary and secondary sodium phosphates under weak acidic conditions in a semi-dry process. For a structural characterisation of starch phosphates 31P NMR and FT Raman spectra were recorded. The degrees of substitution (DSP) of modified starch were determined using a standard wet chemistry method. By recording the FT Raman spectra of starch phosphates a characteristic band at ∼975 cm−1 was found whose intensity depends on the degree of phosphorylation of starch. The integrated areas of this C–O–P stretching vibration were plotted versus the degree of substitution DSP of starch phosphates obtained from standard photometric method. A strong linear correlation was derived which is suitable to determine the level of phosphorylation of starch phosphates with unknown DSP value by Raman spectroscopy as a rapid and non-destructive method.