Capillary HPLC/QTOF-MS for characterizing complex naphthenic acid mixtures and their microbial transformation

Area of Science:

• Environmental Chemistry
• Analytical Chemistry
• Environmental Science

Background:

• Canadian oil sands industry generates large volumes of toxic tailings containing naphthenic acids (NAs).
• Environmental risks of NAs are significant, but their fate is poorly understood due to analytical limitations.
• Developing advanced analytical methods is crucial for assessing NA environmental impact.

Purpose of the Study:

• To develop a sensitive and specific analytical method for characterizing NAs in oil sands tailings.
• To investigate the environmental fate and biodegradation of NAs.
• To provide new insights into NA isomer profiles and transformation products.

Main Methods:

• A novel dilute-and-shoot reversed-phase capillary High-Performance Liquid Chromatography/Quadrupole Time-of-Flight Mass Spectrometry (HPLC/QTOF-MS) method was developed.
• The method separated NAs based on carbon number, degree of cyclization, and alkyl branching.
• Interlaboratory studies and biodegradation experiments were conducted to validate the method and assess NA fate.

Main Results:

• The HPLC/QTOF-MS method offered a 350-fold increase in sensitivity and improved specificity compared to traditional methods.
• Significant differences in NA isomer profiles were observed between the new method and GC/MS, particularly in classifying oxidized NAs.
• Tailings water contained persistent, highly alkyl-substituted NA isomers, and biodegradation studies showed preferential depletion of less substituted fractions.

Conclusions:

• The developed HPLC/QTOF-MS method provides enhanced capabilities for analyzing complex NA mixtures in environmental samples.
• Understanding NA composition and transformation is key to mitigating environmental risks from oil sands operations.
• Microbial activity in tailings plays a significant role in shaping the persistent NA profile.