37
different commodity groups, including high water content (celery and kale), high acid content (lemon), and high starch/ protein with low water content (corn). Samples were immediately homogenised in a food processer and frozen until sample preparation was performed. QuEChERS extraction was performed according to the official AOAC method 2007.01 using Waters DisQuE™ Dispersive Solid Phase Extraction (d-SPE) product [6]. Figure 1 highlights the sample extraction.
Table 1: dSPE clean up conditions used for each sample matrix. Sample MgSO4 PSA GCB Volume
Celery 150 mg 25 mg 7.5 mg 1 mL Lemon 150 mg 25 mg - 1 mL Corn 150 mg 25 mg - 1 mL Kale 900 mg 150 mg 150 mg 6 mL
Experimental
LC-MS/MS Conditions LC system:
Column: Column temp.: ACQUITY UPLC H-Class
ACQUITY UPLC BEH C18 1.7 µm, 2.1 x 100 mm 45°C
Injection volume: 5 µl Flow rate:
0.45 mL/min
Mobile phase A: Water + 10 mM ammonium acetate
Mobile phase B: Methanol + 10 mM ammonium acetate
Gradient:
Time (min) % A % B 0.00 0.25
12.25 13.00 13.01 17.00
MS System:
98 98 1 1
98 98
2 2
99 99 2 2
Xevo TQ-S micro
Ionisation mode: ESI+ Capillary voltage: 1 kV Desolvation temp.: 500°C Desolvation gas flow:
Source temp.: Figure 1: DisQuE sample extraction method.
GC-MS/MS Conditions GC System:
Autosampler: Column:
Carrier gas: Flow rate:
Injection: Injector temp: Results and Discussion 7890A CTC PAL RTC
30 m x 0.25 mm x 0.25 µm Rxi-5MS Helium
2.0 mL/min Splitless
280°C
Injection volume: 1 µl Makeup gas:
Nitrogen at 250 mL/min
Transfer line temp.: 320°C Oven program:
Rate (°C/min) Temp. (°C) Hold (min) -
80
25 8
20 MS system:
150 270 320
Ionisation mode: APGC+ Ionisation mechanism:
Corona current:
1000 L/hr 150°C
Cone gas flow:
1.00 0.00 0.00 4.10
Xevo TQ-S micro
Proton transfer (3 vials of uncapped water in source)
20 µA for first 3.5 min 3.0 µA for rest of run 0 L/hr
Auxiliary gas flow: 250 L/hr Source temp.:
150°C
Method Management Using the Quanpedia Database
Working with methods involving large numbers of compounds can be time consuming when done manually and is prone to errors when setting up time segmented acquisition. Quanpedia is a compound centric database typically used for method generation, but it can also function as a method management tool. Initial methods for this analysis were generated using existing LC and APGC databases (Figure 2). Retention time changes resulting from further method development or method changes were updated in the database. This allowed for immediate and automatic updates to be made in the MS processing methods by re-generating the methods with three simple clicks.
Robust and Rapid Data Acquisition
For the successful analysis of large numbers of pesticides and their metabolites, it is important that the mass spectrometer can maintain sufficient sensitivity while acquiring MRM transitions with a fast scan speed in order to provide enough data points across each chromatographic peak (e.g. minimum of 12 points per peak).
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68
