Development of a Method to Better Quantify Levels of the Persistent Organic Pollutants Iodinated X-Ray Contrast Media and Artificial Sweeteners Found in Water
Abstract: Persistent organic pollutants (POPs) can cause long term damage to the environment. Two classes of organic molecules have come to the attention of regulators and water treatment authorities in recent years; iodinated X-Ray contrast media (XCM) and artificial sweeteners (AS). These molecules, by design, have a high degree of stability. Aware of the increased abundance of these molecules in waste water, the IWB Water Laboratory set out to develop a robust, simple method to analyse levels of these molecules in water from the river Rhine, ground water and drinking water.
Introduction
Solid-phase extraction (SPE) combined with liquid chromatography (LC)-electrospray ionization (ESI)-tandem mass spectrometry (MS/ MS) is the leading analytical methodology for the determination of XCM and AS. However, SPE methods can suffer from poor recovery, are time consuming, and expensive.
The aim of this study was to develop a simple, sensitive, and robust method for the quantification of seven XCM and three AS to regularly monitor the presence of these compounds at all stages of the drinking water production process.
Method Development
To achieve the required degree of separation High Performance Liquid Chromatography (HPLC) was used, coupled to an AB Sciex 5500 QTRAP MS.
In order to gain higher sensitivities, a 10-fold sample concentration step using a Genevac EZ-2 plus centrifugal vacuum evaporator was selected for sample preparation.
Using the EZ2 Plus Evaporator many samples can be loaded, and dried under vacuum automatically with a predefined method that required no operator attention.
- 10ml water samples, with added internal standard, were evaporated in a Genevac EZ2 Plus evaporator at a maximum temperature of 54 °C.
- The precipitate was reconstituted in 1 mL of eluent before submitting for LC-MS/MS analysis.
Results
A 10-point calibration curve was found to be linear over a working range of 10–500 ng/L for XCM and 10–1600 ng/L for AS. The coefficients of determination were higher than 0.999 for all compounds. LOQs below 10 ng/L could be achieved for all compounds.
The precision of 10 replicates was excellent with relative SD values ranging between 3 and 6 % for the lower working range limit and 1 and 3 % for the upper.
Sample preparation recovery was similar for all compounds with an excellent average recovery of 90±4 % and an average RSD of 2 % for triplicate injections.
Mean recoveries from five independent measurement series were between 78 and 113 %. In particular, for the three most important compounds, diatrizoic acid, iopamidol, and acesulfame, recoveries were found to be almost 100 % with relative standard deviations ≤5%
Conclusions
A sensitive LC-MS/MS method has been developed which allows the simultaneous quantification of seven XCM and three AS in water. The developed method supports increased sample throughput, is easier to perform and cheaper than comparable methods using SPE enrichment.
Validation confirmed the sample preparation and analytical method to be robust, repeatable and consistent with high linear working range, high sensitivity, and a standard deviation across all samples of <6%. The method has been accepted into routine use.
References
Development, validation, and application of a novel LC-MS/MS trace analysis method for the simultaneous quantification of seven iodinated X-ray contrast media and three artificial sweeteners in surface, ground, and drinking water. Waldemar Ens, Frank Senner, Benjamin Gygax & Götz Schlotterbeck. Analytical and Bioanalytical Chemistry. May 2014, Volume 406, Issue 12, pp 2789-2798.
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