Direct quantitative analysis of diquat and paraquat in drinking water samples using ultra-sensitive UPLC/MS/MS
Claude R Mallet
Waters Corporation (Milford, MA, USA)
About <br> world crop protection are usually associated with widespread use of pesticides, insecticides or herbicides. These agricultural products can be harmful to the environment and can affect the health of humans and animals. Despite the risks, but they are an important part of the global economy 1. For example, herbicides are important for controlling weed growth, and if we do not inhibit weeds, crop yields can be reduced by up to 80% 2 . In the herbicide family, bipyridine is widely used in agriculture to control the growth of broadleaf weeds and aquatic weeds. The most commonly used bipyridines are diquat and paraquat. They account for the largest share of the global market, until recently glyphosate exceed 3. Due to its high potency as a pre-harvesting desiccant and defoliant, diquat and paraquat are classified as highly toxic substances 4 . The World Health Organization (WHO) classification of these compounds are moderately toxic 5. Although their half-life in water is 48 h, intentional or unintentional intake may have a serious health impact. The US Environmental Protection Agency (USEPA) stipulates that the maximum concentration of diquat in drinking water is 20 ppb and the target limit for paraquat is 3 ppb 6 (not specified by EPA). European Union (EU) does not specify the level of concentration of these compounds in drinking water, but continue to use the limit value of 0.1 ppb 7.
Analysis of bipyridine herbicides may present certain difficulties, primarily because they are cationic molecules. Their inherently strong polarity and positive charge make it necessary to use ion-pairing additives when analyzing quaternary amines by reversed phase chromatography. US EPA Method 549.2 separates diquat and paraquat using reversed-phase chromatography and ion pairing and detects using a UV detector 8 . Since ion-pairing reagents inhibit ionization in the MS source, it is generally avoided to use ion-pairing reagents in ESI-MS applications. For MS applications, HILIC provides the right chromatographic analysis without the use of ion pair reagents 9 . However, recent advances in MS sensitivity have enabled direct analysis of trace contaminants in water and are highly appreciated. This eliminates the laborious and time consuming step of solid phase extraction and sample concentration, which is highly desirable. Direct injection of aqueous samples is well suited for reversed phase chromatography because the sample matrix is ​​similar to the initial mobile phase conditions. For HILIC, the water sample is first diluted with an organic solvent.
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