Benefits of MRM³ for the analysis of contaminants in food and water

With the SCIEX QTRAP 6500+ system

Carlos Bueno¹, Jack Steed², Jianru Stahl-Zeng^3
1SCIEX, Spain; ²SCIEX UK; ³SCIEX, Germany

Introduction

Pesticides, mycotoxins and other contaminates in food and water have long been a threat to human health and therefore, need to be detected and quantified to ensure that their levels are controlled to below maximum residue levels. Testing of these compounds has been widely and successfully adopted by utilizing analytical techniques such as LC-MS. Regulations on monitoring require both quantifier and qualifier ions be used for quantification in final methods. However, due to the complexity of these matrices, interferences or high background can be an issue when measuring the quantifier and/or qualifier ions. Therefore, a solution is needed to provide additional specificity to the analysis on selected compounds where needed, without impacting the currently used techniques and methods.

One acquisition type that can greatly improve specificity of analysis is the MRM³ analysis, unique to SCIEX QTRAP systems. This acquisition works similarly to an MRM acquisition but instead of performing a single fragmentation (precursor to fragment), two fragmentation steps are performed (precursor to initial fragment to secondary fragment). Specificity is increased due to a more unique and compound specific pathway, greatly reducing background interferences and increasing signal/noise (S/N) as seen in Figure 1. See Figure 2 for a diagram of how MRM³ acquisition operates.¹

Key features of MRM³ for food contaminate analysis

• Large reduction of background interferences is achieved by using a more specific acquisition mode
• Increased signal/noise (S/N) can provide an overall increase in sensitivity
• Easy integration into already existing methods so that MRM and MRM³ acquisition can be performed in a single injection
• Additional analysis tool for targeted quantification across different complex matrices

S/N and specificity increases

As described in Figure 2, a form of MS/MS/MS is used in order to analyze a very compound specific fragmentation pathway. By requiring this multiple level dissociation, both the background noise and specific interferences that are sometimes seen in the MRM data (a single level dissociation) are greatly reduced. In Figure 1, high noise is observed in the qualifier ion for cymoxanil in a tea matrix. But with MRM³ monitoring the same secondary ion has very reduced noise and therefore much higher S/N. Both come from the increased specificity afforded by using two fragmentations instead of one as is typically performed in an MRM acquisition. See Figures 1, 3 and 4 for examples of the S/N improvements observed.  

Confidence in detection

Regulations require that both quantifier and qualifiers are monitored to increase confidence that the right analyte is detected. Often the ion ratios between the peak areas of these two MRM transitions are also used to ensure correct detection.  This can make assay development challenging, requiring that low noise and minimal interferences are present in two MRMs.  Its usefulness is also clear when ensuring that two unique transitions are utilized (qualifier and quantifier), because in the case of background interferences or a lack of a suitable qualifier transition for some compounds, MRM³ can be utilized to guarantee accurate quantification and provide a secondary transition.

Conclusions

In tandem with existing MRM methods for analysis of contaminants, MRM³ acquisition can provide additional benefits for difficult to analyze components, by providing increased S/N values and lower amounts of background interferences. Here, improvements in S/N using MRM³ have been shown in tea, a complex food matrix. When using a QTRAP system, the MRM³ analysis can be included easily into existing methods, providing additional specificity and sensitivity.

References

1. MRM³ quantitation for highest selectivity in complex matrices. SCIEX technical note, RUO-MKT-02-2739-B.