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Evaluating Inert Flow Path Components and Entire Flow Path for GC/MS/MS Pesticide Analysis

Evaluating Inert Flow Path Components and Entire Flow Path for GC/MS/MS Pesticide Analysis
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Evaluating Inert Flow Path Components and Entire Flow Path for GC/MS/MS Pesticide Analysis - 1

Evaluating Inert Flow Path Components and Entire Flow Path for GC/MS/MS Pesticide Analysis Application Note Food Testing & Agriculture Author Abstract Limian Zhao Flow path inertness plays a critical role in pesticide analysis accuracy and precision, especially for active analytes such as organophosphate pesticides. The Agilent Inert Flow Path, including Ultra Inert columns and liners, Ultra Inert gold seals, and inert split/splitless inlet, provides excellent surface inertness through the entire flow path, prevents loss of analyte response and peak shape distortion, and thus delivers reliable qualitative and quantitative analysis of pesticides. Other inert supplies, including UltiMetal Plus flexible metal ferrules and capillary flow technology devices, are also highly recommended for pesticide analysis in complicated matrices. Agilent Technologies, Inc. Introduction Flow path inertness plays a critical role in accurate, precise and reliable analysis of pesticides, especially for sensitive pesticides at trace levels. Active sites on the flow path surface can cause adsorption and degradation of active compounds, resulting in poor peak shape, loss of response, inaccurate integration, and poor quantitation. It is critical to minimize interaction of active analytes along the GC flow path, starting with the injector, to the column, and finally to the detector. The column and inlet liner contribute more than 90% of the contact surface after a sample is injected into the GC system. Other surfaces that the sample can contact include inlet seal, inlet weldments, ferrules, capillary flow technology (CFT) devices, and detectors. All of these surfaces can cause interaction with active analytes, resulting in poor or inaccurate results. To achieve the best inertness of the entire flow path, it is important to use an inert column and liner in combination with other inert supplies.

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Evaluating Inert Flow Path Components and Entire Flow Path for GC/MS/MS Pesticide Analysis - 2

Multiresidue analysis of pesticides is always a challenge in GC and GC/MS detection. The required quantitation limits for many pesticides are at low ppb levels, which demands more sophisticated analytical processes. Compared to widely used GC/MS analyses, GC/MS/MS techniques provide much better selectivity, thus significantly improving system detection limits. Pesticide compounds frequently contain functional groups such as hydroxyl (-0H) and amino (R-NH-) groups, imidazoles and benzimidazoles (-N=), carbamates organophosphate (-P=0) groups. These types of molecules are prone to interact...

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Evaluating Inert Flow Path Components and Entire Flow Path for GC/MS/MS Pesticide Analysis - 3

Table 2. Flow path supplies. Vials: Amber screw cap (p/n 5182-0716) Vial insert, 150 pL glass insert with polymer feet Vial caps: Blue screw cap (p/n 5182-0717) Vial inserts: 150 pL glass with polymer feet (p/n 5183-2088) Septum: Advanced green nonstick, 11 mm (p/n 5183-4759) UltiMetal Plus Flexible Metal ferrules (p/n G3188-27501) Inlet seal: Gold-plated inlet seal with washer (p/n 5188-5367) Ultra Inert gold seal with washer (p/n 5190-6144) Inlet liners: Agilent Ultra Inert deactivated single taper splitless liner with CFT: UltiMetal Plus Ultimate Union (p/n G3182-61580) Internal nut, CFT...

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Evaluating Inert Flow Path Components and Entire Flow Path for GC/MS/MS Pesticide Analysis - 4

The purpose of these tests was to use multiresidue pesticides as probes to assess inertness provided by Ultra Inert and UltiMetal Plus parts, then subsequently to compare an inert flow path to a standard flow path. Twenty-six representative and challenging pesticide compounds were selected for the evaluation and comparison (Table 3). These pesticides were from various pesticide groups such as organophosphates, organochlorine, carbamates, and so forth. Figure 1 shows a 500 ng/mL pesticide standard chromatogram using an inert flow path for peak identification of the analytes. Peak...

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Evaluating Inert Flow Path Components and Entire Flow Path for GC/MS/MS Pesticide Analysis - 5

Ultra Inert gold seal Ultra Inert gold seals were evaluated and compared to standard gold seals and Siltek treated stainless steel inlet seals. Two batches (three from each batch) of Ultra Inert gold seals were tested and compared to standard gold seals (n = 3) and Siltek treated stainless steel inlet seals (n = 3). These different types of inlet seals were tested alternatively to minimize the impact of instrument and column condition variations. The sequence for each inlet seal test included four injections of pesticide standards at each level. Calibration curves were generated for the...

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Evaluating Inert Flow Path Components and Entire Flow Path for GC/MS/MS Pesticide Analysis - 6

Agilent Ultra Inert gold seal Siltek treated stainless steel inlet seal ×10–1 Acephate 5 y = 0.501195 * x – 0.001887 R2 = 0.9998 4 ×10–1 Acephate y = 0.294158 * x + 0.003916 2 3 R = 0.9674 3 2 4 Relative reponses Relative reponses Relative reponses ×10–1 Standard gold seal 2 1 1 0 1 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 Relative concentration 3 2 0 Omethoate y = 0.372049 * x – 0.001070 4 R2 = 0.9270 2 1 3 2 1 0 0 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 Relative concentration 1 ×10–1 1 1 1 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 Relative concentration Relative reponses 4 2 1 ×10–1 Omethoate 4 y...

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Evaluating Inert Flow Path Components and Entire Flow Path for GC/MS/MS Pesticide Analysis - 7

Figure 4 shows the 10 ng/mL pesticide standard chromatogram overlay with UltiMetal Plus inlet and standard inlet. The UltiMetal Plus inlet provided higher responses for sensitive organophosphate pesticides, especially acephate and omethoate. Figure 5 shows the profile of average response factors of six injections on each inlet. To make the comparison, the average response factor values with the UltiMetal Plus inlet were normalized using the results with the standard inlet. More than a 20% increase in response was obtained for several active compounds. This specially designed experiment...

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Evaluating Inert Flow Path Components and Entire Flow Path for GC/MS/MS Pesticide Analysis - 8

UltiMetal Plus flexible metal ferrules SL/S Agilent UltiMetal flexible metal ferrules are novel metal ferrules designed and recommended for column connections with capillary flow technology (CFT) devices. These new metal ferrules are lighter and less stiff, thus providing flexibility to gently compress around the column, reducing both column breakage and damage to the fitting common with other metal ferrules. The flexible metal ferrules are treated with the UltiMetal Plus deactivation process to improve the inertness of ferrule surface. Agilent Triple Quadrupole GC/MS Control Agilent HP-5MS...

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