Determination of Volatile Fatty Acids in Environmental Aqueous Samples

Volatile fatty acids (VFAs) are present in environmental waters in the range of 1 to 5,000 ppm and different methods have been reported for their determination. In this paper we have studied and compared analytical performance parameters for the distillation method followed by potentiometric titration, spec trophotometric and gas chromatographic methods. The main disadvantage of the distillation approach was quite poor absolute recovery (53-58%) from the given matrix and rather elevated limit of quantification (lOQ) at 110 mg/l. Direct potentiometric titration was characterized by acceptable accuracy (above 97%) and precision in the range 1.8%-15%. The lOQ value was 11 mg/l. The spectrophotometric method was sensitive for hydrogen carbonate alkalinity and phosphate ions; measured concentrations of acetic acid were lower than nominal. The precision and accuracy of the spectrophotometric method were in the ranges 1.3-14% and 82.1-104.2%, respectively. limit of quantification was 28 mg/l. however, if ion exchange bed is used prior to this method the lOQ can be reduced to 5 mg/l. The GC method is characterized by quite low lOQ (5 mg/l) and seems to be the best methodology to determine low VFA concentrations in environmental waters. The precision of the method ranged from 5.7 to 14.8% and accuracy was above 92%. Additionally, this method allows for determination of individual VFAs.