The reverse-phase ion-exchange HPLC was conducted to determine PHB content of the Nostoc cell biomass.
The dry cells were hydrolyzed by sulfuric acid to completion to obtain the PHB-hydrolyzed product.
The product samples were analyzed using HPLC at the 210-nm detection which specifically detects only acidic compounds. The hydrolyzed samples containing: (i) the sulfuric acid solvent; (ii) the PHB-hydrolyzed product (crotonic acid); and (iii) the internal standard (adipic acid) were separated into three distinct fractions at specific retention times according to their unique mass and polarity (Fig. 2A). The sulfuric solvent is the first eluted fraction since it is the most polar and the smallest. The adipic acid was the second fraction as it is a moderate polar. The PHB-hydrolyzed product, the crotonic acid is the third fraction since it is the most non-polar. The acid hydrolysis was proceeded followed by HPLC analysis of the cell samples along with the standard commercial PHB at different concentrations in order to set the standard PHB quantification curve as shown in Fig. 2C. The standard curve shown the correlation between the PHB concentrations and the ratios between peak areas of crotonic acid to adipic acid at R2 = 0.996.
The result showed that the analysis can determine the PHB content of the tested-strain, Nostoc sp. strain F which is 8.0% PHB weight to cell dry weight (w/cdw hereafter) (Fig. 2B). Thus, this HPLC analysis was used to determine the PHB content of all 28 strains of Nostoc in the next section.