Mid-infrared spectroscopy coupled to sequential injection analysis for the on-line monitoring of the acetone-butanol fermentation process

Fourier transform infrared (FTIR) spectroscopy, coupled to sequential injection analysis (SIA) was employed for the on-line monitoring of an acetone-butanol fermentation by simultaneously determining acetone, acetate, n-butanol, butyrate and glucose from the mid-IR spectra of the samples. The analysis system (SIA-FTIR) developed was completely computer controlled, requiring only minute amounts of NaOH and Na2CO3 as reagents and was capable of performing 30 analyte determinations per hour. From a batch fermentation run of 55h duration, samples were automatically drawn and analysed at 14 different points of time. The analysis by SIA-FTIR comprised of triplicate injections, from each of which two spectra one with 4cm-1 the other with 8cm-1 spectral resolution were obtained. In addition, triplicate reference analysis by gas chromatography and enzymatic test kits were also done at corresponding points of time. Based on the data of the reference analysis a partial least squares (PLS) model was established and validated by a leave-one-out cross validation. Best results were obtained using the second derivatised spectra collected at 8cm-1 resolution. The regression coefficients and standard errors of prediction (S.E.P.) were as follows: acetone, r= 0.999, S.E.P.=0.077g/l; acetate, r=0.998, S.E.P.=0.063g/l; butyrate, r=0.955 and S.E.P.= 0.058g/l; n-butanol, r=0.999, S.E.P.=0.301g/l and glucose, r=0.999, S.E.P.=0.493g/l. The high quality of the results obtained, and the observation that the precision of the SIA-FTIR analysis was as good and often better than those of the reference methods, showed that SIAFTIR is a powerful tool for rapid on-line bioprocess monitoring.