Comprehensive Pesticide Residue Analysis by LC/MS/MS Using an Ultra Aqueous C18 column

• Easily resolve and quantify more than 280 pesticide species.
• Use LC/MS/MS to reliably monitor difficult polar and/or thermally unstable species.
• Aqueous C18 phase offers optimal selectivity and retention.

Food safety is a topic of great interest globally. With recent contamination issues in a wide range of commodities, ensuring the quality of our food supply is becoming increasingly important. Pesticide residue content is one area of concern. While pesticides have typically been monitored by gas chromatography, polar and/or thermally unstable pesticides are difficult or impossible to monitor using this approach. Thus, traditional HPLC techniques are used for select pesticide classes, such as the carbamate and phenylurea pesticides.

With recent advances in LC/MS/MS instrumentation, this technique is quickly gaining acceptance for pesticide residue testing. LC/MS/MS can be used to simultaneously monitor hundreds of potential contaminants—including those difficult to detect by GC. Using both LC/MS/MS and GC approaches allows for a faster, more complete picture of pesticide residues. MS/MS technology also permits identification of the target pesticides through the selection of specific MRM transitions for each compound. For example, aldicarb, a carbamate pesticide, uses two MRM transitions of 208.2->89.1amu and 208.2->116.1amu.

While the MS/MS detector allows for specific, sensitive detection of the pesticide species, the LC separation is still important to ensure the highest quality data. Conventional C18 stationary phases are typically used for pesticide monitoring, but the selectivity and retention is poor for more polar species. In contrast, Ultra Aqueous C18 columns are ideal for multi-pesticide residue monitoring methods. In Figure 1, the analysis of more than 280 pesticides using the 3µm Ultra Aqueous C18 is shown. Optimized stationary phase selectivity allows for an even distribution of the compounds throughout the retention time window (Tables I and II). As well, retention of more polar pesticides is greatly improved, as demonstrated in Figure 1C. The Ultra Aqueous C18 column, in a 100 x 2.1mm, 3µm configuration is the column of choice for LC/MS/MS pesticide monitoring methods.

Ultra-high pressure LC (UHPLC) can also be used with MS/MS detection for monitoring pesticide residues. UHPLC allows for higher sample throughput when used in conjunction with a highly efficient <2µm particle size column. The 1.9µm Pinnacle® DB Aqueous C18, in a 50 x 2.1mm configuration, is ideally suited for this application, as shown in Figure 2.

Using LC/MS/MS technology and Aqueous C18 columns, in combination with gas chromatography, results in the most comprehensive monitoring of pesticide residues. Labs interested in more complete multi-residue analysis of pesticides in food matrices, including difficult polar or thermally unstable compounds, should consider adding LC/MS/MS and Aqueous C18 columns to routine testing procedures. The Aqueous C18 phase is also available on 1.9µm Pinnacle® DB silica for UHPLC platforms.

Acknowledgements

The authors wish to thank the US FDA for their collaboration and recognize the participation of multiple FDA labs in this work.

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Figure 1: More than 280 pesticide residues—including difficult polar species—show excellent peak shape and retention on a 3µm Ultra Aqueous C18 column.

A. Pesticides in positive ion mode. See Table 1 for compound identification and MS details. B. Pesticides in negative ion mode. See Table 2 for compound identification and MS details. C. Improved retention of difficult pesticides. See Table 1 for compound identification and MS details. Column: Ultra Aqueous C18 Cat. #: 9178312 Dimensions: 100mm x 2.1mm Particle size: 3µm Pore size: 100Å Sample: multicomponent pesticide standard Inj.: 10µL Conc.: 1ppb each pesticide Sample diluent: acetronitrile Conditions: Instrument: Shimadzu Prominence® UFLCXR Mobile phase: A: 10mM NH4OAC in water B: 10mM NH4OAC in methanol Time (min.) %B 0.0 20 8.0 90 12.0 100 14.8 100 14.9 20 Flow: 500µL/min. Temp.: 35°C Det.: Applied Biosystems 4000 QTRAP® LC/MS/MS system Ion Source: TurboIonSpray® A&C: ESI+ B: ESI- IonSpray Voltage: 5kV (ESI+), -4.2kV (ESI-) Gas 1: 50psi Gas 2: 60psi Source Temp.: 600°C A. LC_FF0490 B. LC_FF0490A C. LC_FF0490B

Figure 2: Higher sample throughput can be achieved using UHPLC and MS/MS with a 1.9µm Pinnacle® DB Aqueous C18 column.

Compounds analyzed are a subset of those in Figure 1; data are shown for a qualitative overall run time comparison only. Column: Pinnacle® DB Aqueous C18 Cat. #: 9418252 Dimensions: 50mm x 2.1mm Particle size: 1.9µm Pore size: 140Å Sample: multicomponent pesticide standard Inj.: 5µL Conc.: 33.3ppb each pesticide Sample diluent: acetonitrile Conditions: Instrument: Shimadzu Prominence® UFLCXR Mobile phase: A: 10mM NH4OAc in water B: 10mM NH4OAc in methanol Time (min.) %B 0.0 10 1.0 10 8.0 90 10.0 90 11.0 10 Flow: 600µL/min. Temp.: 35ºC Det.: Applied Biosystems 4000 QTRAP® LC/MS/MS System Ion Source: TurboIonSpray®, ESI+ IonSpray Voltage, ESI voltage: 5kV (ESI+) Gas 1: 40psi Gas 2: 60psi Source Temp.: 500ºC; max pressure ~7,200psi LC_FF0479A

Data for 3µm Ultra Aqueous C18 column are shown.

Data for 3µm Ultra Aqueous C18 column are shown.