7000A GC-QQQ ApplicationsPesticides in Foods (1)

Measuring Methamidophos in Garlic

• This application demonstrates the phenomenon called matrix-induced chromatographic response enhancement when analyzing trace components in complex matrices.

• The polar organophosphorus insecticide, methamidophos, a metabolite of acephate is a difficult compound to quantitate in foods due to its polar nature and very early elution in GC analyses.

GC-QQQ Full Scan Spectrum

Methamidophos Spectrum from Nist05

2x10

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

1.1

+ Scan (5.796 min) Cao_5ppmMix_Q1Scan_25Aug_Gason.D

94

141

644779 126111

Counts (%) vs. Mass-to-Charge (m/z)40 45 50 55 60 65 70 75 80 85 90 95 100 105 110 115 120 125 130 135 140 145 150 155 160

Methamidophos Spectrum by GC-QQQ

Methamidophos Calibration Curve (5, 10, 50,100ppb Solvent only)

Matrix Effect in Garlic

Spike (ppm) Calc. (ppm)

1 0.005 0.0187

2 0.01 0.0449

3 0.05 0.285

4 0.10 0.522

Methamidophos

All the calculated results are much higher than spiked even though linearity is very good. The is due to the “matrix effect”.

Matrix Effect and Protectants• A common problem in gas chromatography (GC) applications

is the analyte losses and/or peak tailing due to undesired interactions with active sites in the inlet and column. Analytes that give poor peak shapes or degrade have higher detection limits, are more difficult to identify and integrate, and are more prone to interferences than stable analytes that give narrow peaks. For susceptible analytes, significant peak quality improvements are obtained when matrix components are present because they fill active sites, thus reducing analyte interactions. This phenomenon is called matrix-induced chromatographic response enhancement.

• Analyte protectants are added to both sample extracts and calibration solutions. For this analysis the analyte protectant solution contained 3-ethoxy-1,2-propandiol and sorbitol.

Methamidophos 5 ppb in solvent without and with protectant

No protectant No methamidophos

With protectant, it’s there(Due to the protectant, R.T shifts)

Methamidophos 10 ppb in Garlic without and with protectant

Without protectant With protectant

Area:7084 Area:9442

Methamidophos Calibration Curve (5, 10, 50,100ppb with Protectant)

Outstanding Accuracy in Garlic

Spike (ppm) Calc. (ppm)

1 0.005 0.0054

2 0.01 0.0127

3 0.05 0.067

4 0.10 0.116

Methamidophos