Establishing Analytical Performance Criteria for the Global Reconnaissance of Antibiotics and Other Pharmaceutical Residues in the Aquatic Environment Using Liquid Chromatography-Tandem Mass Spectrometry

Abstract

The occurrence of antibiotics in the environment from discharges of wastewater treatment plants (WWTPs) and from the land application of antibiotic-laden manure from animal agriculture is a critical global issue because these residues have been associated with the increased emergence of antibiotic resistance in the environment. In addition, other classes of pharmaceuticals and personal care products (PPCPs) have been found in effluents of municipal WWTPs, many of which persist in the receiving environments. Analysis of antibiotics by liquid chromatography-tandem mass spectrometry (LC-MS/MS) in samples from different countries presents unique challenges that should be considered, from ion suppression due to matrix effects, to lack of available stable isotopically labeled standards for accurate quantification. Understanding the caveats of LC-MS/MS is important for assessing samples with varying matrix complexity. Ion ratios between quantifying and qualifying ions have been used for quality assurance purposes; however, there is limited information regarding the significance of setting criteria for acceptable variabilities in their values in the literature. Upon investigation of 30 pharmaceuticals in WWTP influent and effluent samples, and in receiving surface water samples downstream and upstream of the WWTP, it was found that ion ratios have higher variabilities at lower concentrations in highly complex matrices, and the extent of variability may be exacerbated by the physicochemical properties of the analytes. In setting the acceptable ion ratio criterion, the overall mean, which was obtained by taking the average of the ion ratios at all concentrations (1.56 to 100 ppb), was used. Then, for many of the target analytes included in this study, the tolerance range was set at 40% for WWTP influent samples and 30% for WWTP effluent, upstream, and downstream samples. A separate tolerance range of 80% was set for tetracyclines and quinolones, which showed higher variations in the ion ratios compared to the other analytes.

Figure 1

Deviation of ion ratios from the overall mean across different concentrations of 23 PPCPs without tetracyclines and quinolones.

Figure 2

Deviation of ion ratios of tetracyclines and quinolones from the overall mean across different concentrations.

Figure 3

Distribution of the deviation of the quantitative and qualitative ion areas from the mean.

Figure 4

Comparison of ion ratios in spiked matrices and in clean standards. (a) WWTP influent samples; (b) WWTP effluent samples; (c) upstream surface water samples; (d) downstream surface water samples.

Figure 5

False-positive detection of diclofenac in wastewater. The calculated ion ratio, 0.15, falls outside the ion ratio tolerance range of 1.57 to 3.67. The chromatograms show (a) the peak for the quantitative ion with a transition of 296 → 214 and (b) the peak for the qualitative ion with a transition of 296 → 250.