Enhancing concentration and mass sensitivities for liquid chromatography trace analysis of clopyralid in drinking water

Abstract

A theoretical treatment was developed and validated that relates analyte concentration and mass sensitivities to injection volume, retention factor, particle diameter, column length, column inner diameter and detection wavelength in liquid chromatography, and sample volume and extracted volume in solid-phase extraction (SPE). The principles were applied to improve sensitivity for trace analysis of clopyralid in drinking water. It was demonstrated that a concentration limit of detection of 0.02 ppb (μg/L) for clopyralid could be achieved with the use of simple UV detection and 100 mL of a spiked drinking water sample. This enabled reliable quantitation of clopyralid at the targeted 0.1 ppb level. Using a buffered solution as the elution solvent (potassium acetate buffer, pH 4.5, containing 10% of methanol) in the SPE procedures was found superior to using 100% methanol, as it provided better extraction recovery (70-90%) and precision (5% for a concentration at 0.1 ppb level). In addition, the eluted sample was in a weaker solvent than the mobile phase, permitting the direct injection of the extracted sample, which enabled a faster cycle time of the overall analysis. Excluding the preparation of calibration standards, the analysis of a single sample, including acidification, extraction, elution and LC run, could be completed in 1 h. The method was used successfully for the determination of clopyralid in over 200 clopyralid monoethanolamine-fortified drinking water samples, which were treated with various water treatment resins.

Droplets-based microextraction assisted SPME for GC-MS analysis of polar compounds such as clopyralid in water

“…The regulatory analytical methods for the determination of clopyralid from water samples, soil, and compost include gas chromatography (GC) [3][4][5][6][7][8][9][10] and liquid chromatography (LC). [11][12][13][14][15] Since clopyralid has a carboxylic group, the GC analysis required also the derivatization of the analyte as methyl ester, 4,6 1-butyl ester, 3,5,7 pentauorobenzyl ester 8 or silyl derivatives. 10 LC could be an attractive method because no derivatization is required, but the sensitivity of the UV detector is not enough to detect and quantify clopyralid at trace levels in a quality control lab without a mass spectrometer.…”

“…The classic liquid extraction requires high amounts of toxic solvents, is time consuming, and most of the analytes can be lost during the extraction procedures. The volume of solvent was reduced and the sensitivity for trace analysis was improved by solid phase extraction of clopyralid in drinking water 15 and solid phase microextraction (SPME) of clopyralid in atmospheric samples. 10 The above reported methods for clopyralid analysis in several matrices proved to be insufficient for analysis in soil and drinking water or require the use of critical chemicals and are too complicated for routine analysis.…”