Concurrent Lactic and Volatile Fatty Acid Analysis of Microbial Fermentation Samples by Gas Chromatography with Heat Pre-treatment

Abstract

Organic acid analysis of fermentation samples can be readily achieved by gas chromatography (GC), which detects volatile organic acids. However, lactic acid, a key fermentation acid is non-volatile and can hence not be quantified by regular GC analysis. However the addition of periodic acid to organic acid samples has been shown to enable lactic acid analysis by GC, as periodic acid oxidizes lactic acid to the volatile acetaldehyde. Direct GC injection of lactic acid standards and periodic acid generated inconsistent and irreproducible peaks, possibly due to incomplete lactic acid oxidation to acetaldehyde. The described method is developed to improve lactic acid analysis by GC by using a heat treated derivatization pre-treatment, such that it becomes independent of the retention time and temperature selection of the GC injector. Samples containing lactic acid were amended by periodic acid and heated in a sealed test tube at 100°C for at least 45 min before injecting it to the GC. Reproducible and consistent peaks of acetaldehyde were obtained. Simultaneous determination of lactic acid, acetone, ethanol, butanol, volatile fatty acids could also be accomplished by applying this GC method, enabling precise and convenient organic acid analysis of biological samples such as anaerobic digestion and fermentation processes.

Ethanol and lactic acid production from sugar and starch wastes by anaerobic acidification

“…The lactic acid measurement was carried out by adding 480 μL of periodic acid (100 mM), and 300 μL formic acid (99%) to 720 μL of the standard as well as the sample [23]. The centrates were then filtrated through a Millex GP with filter unit 0.22 μm Millipore express PES membranes, 150 psi (10 bars) of housing limit.…”

“…To 1.2 mL of the standards/samples 300 μL formic acid (99%) was added. The lactic acid measurement was carried out by adding 480 μL of periodic acid (100 mM), and 300 μL formic acid (99%) to 720 μL of the standard as well as the sample [23].…”

Rapid determination of lactic acid in anaerobic biological treatment process using a portable sensitive lactate biosensor

“…To ensure the proper process of anaerobic digestion, the concentration of organic acids should be regularly monitored. Currently, the organic acid analysis of anaerobic digestion samples can be readily achieved using gas chromatography (GC), which easily measures vo-116 latile organic acids; however, since lactic acid is a nonvolatile acid, it could not be measured by GC (Darwin et al, 2018c). Thus, developing a simple and fast method for analyzing lactic acid obtained from anaerobic digestion samples would be very useful.…”

“…Thus, the stability of the column is required to rectify the chain structure (Kishore et al, 2013). Another method that could be used for determining lactate concentration in anaerobic digestion samples is gas chromatography (GC) (Darwin et al, 2018c). However, the determination of lactate by GC would also be impractical because the method requires 60 min of pre-heating and use of periodic acid (Darwin et al, 2018c).…”

“…Another method that could be used for determining lactate concentration in anaerobic digestion samples is gas chromatography (GC) (Darwin et al, 2018c). However, the determination of lactate by GC would also be impractical because the method requires 60 min of pre-heating and use of periodic acid (Darwin et al, 2018c). Furthermore, lactate is a non-volatile organic acid; thus, the determination of lactic acid in the samples of anaerobic digestion would not be directly accomplished.…”