ADV06-15_1-412

75 / 413

| 800-356-1688 | Feedback? E-mail 9
Column:Rxi®-5Sil MS 30 m, 0.25 mm ID, 0.25 µm (cat.# 13623), Rtx®-200 1.3 m, 0.25
mm ID, 0.25 µm (cat.# 15124);Sample: Diluent: Toluene; Injection: Inj. Vol.: 1 µL splitless
(hold 1 min.); Liner: Sky™ 4mm Single Taper w/Wool (cat.# 23303.1); Inj. Temp.: 250 °C;
Purge Flow: 40 mL/min.;Oven: Oven Temp: Rxi®-5Sil MS: 80 °C (hold 1 min.) to 310 °C at
5 °C/min., Rtx®-200: 85 °C (hold 1 min.) to 315 °C at 5 °C/min.;Carrier Gas: He, corrected
constant flow (2 mL/min.); Modulation: Modulator Temp. Offset: 20 °C; Second Dimen-
sion Separation Time: 3 sec.; Hot Pulse Time: 0.9 sec.; Cool Time between Stages: 0.6 sec.;
Instrument: LECO Pegasus 4D GCxGC-TOFMS; For complete conditions, visit
and enter GC_FF1204 in the search.
Orthogonal GC Columns Greatly Increase Separation
Power for More Accurate Pesticide Results
GCxGC is a powerful multidimensional approach that gives 2 indepen-
dent separations in 1 instrumental analysis. An Rxi®-5Sil MS and Rtx®-200
column combination distributes pesticides broadly in both dimensions,
providing a highly orthogonal GCxGC system. More important though
is separating pesticides from potential isobaric matrix interferences,
as seen in the surface plot for the insecticide cypermethrin (Figure 2).
Cypermethrin gas chromatographs as 4 isomers, and all would have
experienced qualitative interference and quantitative bias from peaks
in the foreground of the surface plot had only 1-dimensional GC been
used. With GCxGC-TOFMS, cypermethrin was unequivocally identified
in a marijuana sample at a low ppm level (Figure 3).
Summary
QuEChERS and cSPE produced usable extracts from highly complex
marijuana samples for high quality pesticide residue analysis. The
multidimensional separation power of GCxGC-TOFMS was then used
to correctly identify and quantify pesticides in these complex extracts.
Figure 2: GCxGC-TOFMS and orthogonal Rxi®-5Sil MS and
Rtx®-200 columns allow incurred cypermethrins in a mari-
juana extract to be separated from interferences (m/z 163
quantification ion).
Figure 3: Positive mass spectral identification of incurred cypermethrin in illicit marijuana.
GC_FF1204
Peaks RT 1 (sec.) RT 2 (sec.)
1. Cypermethrin 1 2292 1.50
2. Cypermethrin 2 2304 1.54
3. Cypermethrin 3 2310 1.53
4. Cypermethrin 4 2313 1.58
60 80 100 120 140 160 180 200 220 240 260 280 300 320 340 360 380 400
91 163
77
127 181
69 115 295
152 269
311 211
338 356
193 255 285
60 80 100 120 140 160 180 200 220 240 260 280 300 320 340 360 380 400
163
181 91 127
77
109 152 209
65 191 261
60 80 100 120 140 160 180 200 220 240 260 280 300 320 340 360 380 400
163
91
181
77 127
65
152 115
209
191
Caliper Spectrum
Deconvoluted Spectrum
(Match 840)
Reference Spectrum
GC_FF1206
Acknowledgment
Randy Hoffman, a Police Evidence Technician at The
Pennsylvania State University (PSU), supplied the
seized marijuana samples while overseeing their han-
dling. Frank Dorman at PSU assisted with QuEChERS
extractions.
ChromaBLOGraphy
For our technical blog, visit
See Figure 2 for
instrument conditions.
Table I: Pesticide recoveries for a QuEChERS extract of marijuana give
higher results when cSPE is used for cleanup. Dicofol and DDT are
degraded in the inlet for the dirtier extract, yielding high DDD results.
Pesticide Classification
With cSPE
Cleanup (%)
Without cSPE
Cleanup (%)
4,4´-DDD Organochlorine 83 230
4,4´-DDT Organochlorine 77 9
Bifenthrin Pyrethroid 86 89
Dicofol Organochlorine 84 ND
Azinphos methyl Organophosphorus 79 53
trans-Permethrin Organochlorine 68 17
Pyraclostrobin Strobilurin 73 19
Fluvalinate Pyrethroid 72 23
Difenoconazole Triazole 67 21
Deltamethrin Pyrethroid 68 20
Azoxystrobin Strobilurin 72 27
ND = no peak detected
Website : E-Mail : TelNo : 03 9762 2034 . . . in AUSTRALIA