Understanding the Charge Issues in Mono and di-Quaternary Ammonium Compounds for Their Determination by LC/ESI-MS/MS

Quaternary ammonium compounds (QACs) are widely used biocides that possess antimicrobial effect against a broad range of microorganisms. These compounds are used for numerous industrial purposes, water treatment, antifungal treatment in horticulture, as well as in pharmaceutical and everyday consumer products as preserving agents, foam boosters, and detergents. Resistance toward QACs is widespread among a diverse range of microorganisms and is facilitated by several mechanisms such as modifications in the membrane composition, expression of stress response and repair systems, or expression of efflux pump genes. Development of resistance in both pathogenic and nonpathogenic bacteria has been related to application in human medicine and the food industry. QACs in cosmetic products will inevitably come into intimate contact with the skin or mucosal linings in the mouth and thus are likely to add to the selection pressure toward more QAC-resistant microorganisms among the skin or mouth flora. There is increasing evidence of coresistance and cross-resistance between QACs and a range of other clinically important antibiotics and disinfectants. Use of QACs may have driven the fixation and spread of certain resistance cassette collectors (class 1 integrons), currently responsible for a major part of antimicrobial resistance in gram-negative bacteria. More indiscriminate use of QACs such as in cosmetic products may drive the selection of further new genetic elements that will aid in the persistence and spread of antimicrobial resistance and thus in limiting our treatment options for microbial infections.

A sensitive and robust method of analysis for quaternary ammonium compounds (QACs) in marine sediments is presented. Methods for extraction, sample purification, and HPLC-time-of-flight MS analysis were optimized, providing solutions to problems associated with analysis of QACs, such as dialkyldimethylammonium (DADMAC) and benzalkonium (BAC) compounds experienced previously. Recognized in this study are the exceptionally high positive mass defects characteristic of alkylammonium or protonated alkylamine ions. No alternative and chemically viable elemental formulas exist within 25.2 mDa when the number of double bond equivalents is low, effectively allowing facile discrimination of this compound class in complex mixtures. Accurate mass measurements of diagnostic collision-induced dissociation fragment ions and heavy isotope peaks were obtained and also seen to be uniquely heavy compared to other elemental formulas. The ability to resolve masses of alkylamine fragment ions is much greater than for the molecular ions of BACs and many other chemicals, opening up a range of potential applications. The power of utilizing a combination of approaches is illustrated with the identification of nontargeted DADMAC C8:C8 and C8:C10, two widely used biocides previously unreported in environmental samples. Concentrations of QACs in sewage-impacted estuarine sediments (up to 74 microg/g) were higher than concentrations of other organic contaminants measured in the same or nearby samples, suggesting that further study is needed.

We have developed a highly selective and sensitive analytical method to quantify paraquat and diquat by use of high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS). The sample preparation includes solid phase extraction that uses weak cation exchange cartridges. These highly charged dual quaternary amines were not retained by standard reversed phase columns, but they could be adequately separated through HPLC with a HILIC column. The detection was carried out with a triple quadrupole mass spectrometer with an electrospray ionization probe in positive ion mode in multiple reaction monitoring. Repeated analysis in human urine samples spiked with low (5 ng/ml), medium (15 ng/ml), and high (30 ng/ml) concentrations of the analytes yielded relative standard deviations of less than 9%. The extraction efficiencies ranged from 77.7% to 94.2%. The limits of detection were in the range of 1 ng/ml.