Effect of pH on the Analysis of 2-MIB and Geosmin in Water

Abstract

2-Methylisoborneol (2-MIB) and trans-1,10-dimethyl-trans-9-decalol (geosmin) are two commonly observed taste and odor compounds present in drinking water sources. The effects of pH on the analysis of the two chemicals are investigated using a gas chromatograph and mass spectrometric detector (GC/MSD) coupled with three preconcentration methods, namely solid-phase microextraction (SPME), purge-and-trap concentration (PTC), and liquid-liquid extraction (LLE). At neutral and alkaline pH conditions, the concentrations detected for both compounds remain constant. However, a substantial reduction of concentration for both chemicals is observed when the water solution pH is less than 5. Under acidic conditions (pH≅2.5), the 2-MIB concentrations detected by GC/MSD coupled with SPME, PTC, and LLE are 87%, 16%, and 37% lower than those measured at pH 6-7, respectively. For geosmin, a decrease in concentration is only observed when using GC/MSD-SPME, presumably due to the higher extraction temperature compared to the other two techniques. The pH-dependent behavior was attributed to dehydration of the tertiary alcohols of 2-MIB and geosmin under acidic conditions. The dehydration for 2-MIB and geosmin is reversible, and the analysis can be mitigated by adjusting the water solution pH back to a neutral condition.

Quantification of cork off-flavor compounds in natural cork stoppers and wine by multidimensional gas chromatography mass spectrometry

“…In white wine, the odor thresholds of GSM and MIB are 25 ng/l and 30 ng/l, respectively [2]. However, the role of GSM in wine was questioned as it was rapidly converted into the odorless argosmin under acidic conditions in model systems [11,13]. On the other hand, Darriet et al [14] found high concentrations of GSM in red and rosé wines and stated GSM to be relatively stable in acidic wines.…”

Trace analysis of off-flavor/odor compounds in water using liquid-liquid microextraction coupled with gas chromatography—positive chemical ionization-tandem mass spectrometry

“…Strong matrix effects on the peak intensity of the compounds were observed, requiring use of matrixmatched standards. Due to the use of matrix calibration techniques, recoveries were much higher than those reported in many studies [3,16,18,19]. Relative standard deviations (%) were similar ( < 10%) between both studies [16].…”

“…Extraction of a single sample was completed within five minutes; as opposed to requiring more than 20 min for SPME procedures [17,18]. Furthermore, sample throughput using SPME methods is limited by the number of SPME devices available.…”

“…Consumption of organic solvents is lower compared to other methods. Only 1 ml of organic solvent is needed to extract one water sample, which is much lower than the volume required for traditional liquid-liquid extraction (5 ml) [18] and SPE extraction methods ( > 10 mL) [16].…”

Development and optimization of analytical methods for the detection of 18 taste and odor compounds in drinking water utilities

“…2 ). Previous studies that reported loss of 2-MIB at low pH had attributed it to the dehydration of the tertiary alcohol in acidic environments ( Bu et al., 2017 ; Hsieh et al., 2012 ). Similarly, acid catalyzed hydrolysis mechanisms were discussed in the case of dioxolanes, which could be the cause of loss of EMD ( Fife and Natarajan, 1986 ).…”