Introduction

The analysis of pesticide residues in foods requires the separation and detection of trace amounts of target pesticides present in complex matrices, and therefore, analytical instruments used for such measurements must have high performance. The GC-MS/MS method is effective for simultaneous analysis of multiple components in complex matrices, and is currently used by many analytical institutions as a general analytical method. Naturally, detection sensitivity can differ depending on the analytical instrument used, but various methods exist to increase the sensitivity of conventional analytical methods. For the purpose of increasing sensitivity, it can be effective to apply a sample injection method that is different from the normal hot splitless injection method generally used in GC, and among them, a relatively large number of examples exist using large volume injection (LVI) technology. The Multi Mode Injector (MMI manufactured by Agilent) used in this study allows the selection of various modes, such as cold splitless mode and solvent vent mode, in addition to the general hot splitless mode, depending on the purpose of measurement. However, there are relatively few examples for the application of cold splitless injection methods for the analysis of pesticide residues in food products. In this study, we compare the results of various cold splitless injection methods using MMI to improve GC-MS/MS detection sensitivity by suppressing adsorption and thermal decomposition of the target pesticides in the GC inlet.

Experimental 1. Sample Conditions
Standard Reagents : Pesticide Mixture Standard Solution PL-1, 2, 3, 4, 5, 6, 9, 10, 11, 12, 13 made by FUJIFILM Wako Pure Chemical Co.
Sample Concentration : Pesticide mixed standard solutions were prepared at 0.1, 0.5, 1, 2, 5, 10, and 20 ppb
Sample Volume : 2 μL (+ 0.2 μL co-injection of analyte protectants : SFA10mix made by Hayashi Pure Chemical Industry Co.)
2. GC Conditions
Gas chromatograph : 8890GC (Agilent Technologies, Inc.)
Inlet mode : Hot/cold splitless mode
Inlet temperature (hot splitless) : 250°C
Inlet temperature (cold splitless) : 60°C (0.01 min) → 320°C (200°C / min, 10 min) → 60°C (200°C / min, 0 min)
Column : VF-5MS (length : 30 m, inner diameter : 0.25 mm, film thickness : 0.25 μm)
Oven temperature : 50°C (1 min) → 125°C (25°C / min, 0 min) → 300°C (10°C / min, 10 min)
Flow rate : 1.0 mL/min (constant flow)
3. MS Conditions
Mass spectrometer : JMS-TQ4000GC (JEOL Ltd.)
Measurement mode : SRM
SRM mode : High-sensitivity mode
Ion source temperature : 280°C
Interface temperature : 300°C
Ionization current : 50 μA
Ionization voltage : 70 eV

JMS-TQ4000GC

Results

Of the 292 components selected for measurement, a total of 283 components were detectable at 0.1 ppb by using hot splitless mode. The following page lists the compound names and retention times of the 283 components that were detectable. Nine components that were not detected at 0.1 ppb using the conventional hot inlet method included: procymidone, acetamiprid, halfenprox, imibenconazole, bifenox, flumiclorac pentyl, azoxystrobin, propaquizafop, and thiacloprid. On the other hand, all target components were detectable at 0.1 ppb using the MMI with cold splitless mode. Fig. 1 shows an EIC comparison of imibenconazole, bifenox, and azoxystrobin at 0.1 ppb as an example for the components that were not detected with a hot splitless injector. To confirm the effect of the application of the cold splitless mode on sensitivity, peak area ratios (cold/hot splitless) were calculated for the 283 components for which detection of 0.1 ppb was possible in both modes, and a scatter plot of the ratios sorted by compound number (retention time) is shown in Fig. 2.

Target Pesticides (No.1～150)
No. Compound name RT
1 Aldoxycarb (decomposed) 5.73
2 EPTC 7.98
3 Mevinphos 1+2 8.70
4 Acephate 8.81
5 Nitrapyrin 9.05
6 Etridiazole 9.06
7 Methacrifos 9.50
8 Chloroneb 9.66
9 Isoprocarb 9.98
10 XMC 10.26
11 Omethoate 10.63
12 Tecnazene 10.68
13 Fenobucarb 10.74
14 Propoxur 10.77
15 Propachlor 10.80
16 Chlorethoxyphos 10.86
17 Diphenylamine 11.05
18 Ethoprophos 11.07
19 Ethalfluralin 11.14
20 Trifluralin 11.30
21 Chlorpropham 11.31
22 Benfluralin 11.36
23 Dicrotophos 11.36
24 Bendiocarb 11.45
25 Monocrotophos 11.53
26 Cadusafos 11.60
27 Phorate 11.71
28 Hexachlorobenzene 11.98
29 Dimethoate 12.11
30 Dicloran 12.15
31 Carbofuran 12.19
32 Simazine 12.23
33 Atrazine 12.33
34 Propazine 12.41
35 Clomazone 12.41
36 Quintozene 12.48
37 Propetamphos 12.51
38 Terbufos 12.58
39 Cyanophos 12.61
40 Propyzamide 12.66
41 Diazinone 12.67
42 Phosphamidon 1 12.72
43 Pyroquilon 12.83
44 Pyrimethanil 12.85
45 Tefluthrine 12.90
46 Prohydrojasmon 1 12.90
47 Disulfoton 12.94
48 Isazophos 12.94
49 Terbacil 12.98
50 Triallate 13.10
No. Compound name RT
51 δ-BHC 13.16
52 Pirimicarb 13.20
53 Prohydrojasmon 2 13.22
54 Iprobenfos 13.23
55 Oxabetrinil 13.26
56 Benoxacor 13.38
57 Formothion 13.40
58 Phosphamidon 2 13.48
59 Benfuresate 13.54
60 Dichlofenthion 13.55
61 Dimethenamid 13.59
62 Propanil 13.62
63 Acetochlor 13.64
64 Bromobutide 13.68
65 Chloropyriphos-methyl 13.70
66 Metribuzin 13.71
67 Spiroxamine 1 13.76
68 Vinclozoline 13.77
69 Alachlor 13.84
70 Parathion methyl 13.84
71 Tolclofos-methyl 13.85
72 Simetryn 13.92
73 Mefenoxam 13.95
74 Ametryn 13.98
75 Carbaril 13.98
76 Prometryn 14.02
77 Fenchlorphos 14.04
78 Heptachlor 14.06
79 Pirimiphos methyl 14.21
80 Spiroxamine 2 14.28
81 Terbutryn 14.28
82 Fenitrothion 14.31
83 Ethofumesate 14.32
84 1-Naphthylacetamide 14.34
85 Bromacil 14.38
86 Malathion 14.43
87 Esprocarb 14.47
88 Metolachlor 14.59
89 Diethofencarb 14.59
90 Chlorpyrifos 14.61
91 Quinoclamine 14.62
92 (Z)-Dimethylvinphos 14.66
93 Benthiocarb 14.67
94 Cyanazine 14.69
95 Fenpropimorph 14.70
96 Fenthion 14.70
97 Flufenacet 14.71
98 Chlorthal dimethyl 14.72
99 Isofenphos oxon 14.75
100 Parathion 14.78
No. Compound name RT
101 Aldrin 14.79
102 Tetraconazole 14.80
103 Triadimefon 14.83
104 Nitrothal isopropyl 14.85
105 Dicofol (decomposed) 14.97
106 Fthalide 15.07
107 Bromophos 15.08
108 Diphenamid 15.08
109 Fosthiazate 1 15.11
110 Fosthiazate 2 15.15
111 trans-Chlorfenvinphos 15.23
112 Pendimethalin 15.26
113 Fipronil 15.28
114 Dimethametryn 15.36
115 Isophenphos 15.39
116 Penconazole 15.43
117 cis-Chlorfenvinphos 15.45
118 Allethrin 3+4 15.46
119 Mecarbam 15.47
120 Pyrifenox 2 15.53
121 Heptachlor Epoxide (isomer A) 15.53
122 Oxychlordane 15.55
123 Phenthoate 15.56
124 Diclocymet 1 15.57
125 Quinalphos 15.59
126 Heptachlor Epoxide (isomer B) 15.63
127 Methoprene 15.65
128 Triadimenol 1 15.67
129 Dimepiperate 15.70
130 Triflumizole 15.70
131 Thiabendazole 15.72
132 Zoxamide (decomposed) 15.76
133 Triadimenol 2 15.81
134 Bromophos ethyl 15.86
135 Propaphos 15.88
136 Diclocymet 2 15.89
137 Methidathion 15.90
138 Tetrachlorvinphos 15.97
139 Chlorbenside 15.97
140 trans-Chlordane 15.99
141 Butachlor 16.00
142 Pyrifenox 1 16.02
143 Paclobutrazol 16.05
144 Fenothiocarb 16.06
145 Butamifos 16.17
146 Fenamiphos 16.23
147 Imazamethabenz methyl 1 16.24
148 cis-Chlordane 16.24
149 Imazamethabenz methyl 2 16.26
150 Flutriafol 16.28
Target Pesticides (No.151～283)
No. Compound name RT
151 Flutolanil 16.29
152 Napropamide 16.31
153 Pretilachlor 16.42
154 Prothiofos 16.42
155 Hexaconazole 16.42
156 Chlorofenson 16.42
157 Isoprothiolane 16.44
158 Profenofos 16.50
159 Oxadiazon 16.52
160 Tribufos 16.59
161 Flamprop methyl 16.59
162 p,p'-DDE 16.60
163 Uniconazole P 16.61
164 Oxyfluorfen 16.62
165 Myclobutanil 16.65
166 Tricyclazole 16.65
167 Bupirimate 16.66
168 Kresoxim-methyl 16.67
169 Flusilazole 16.68
170 Buprofezin 16.70
171 Dieldrin 16.78
172 Imibenconazole debenzyl 16.80
173 Carboxin 16.80
174 Azaconazole 16.84
175 Chlorfenapyr 16.85
176 Isoxathion 16.92
177 Fenoxanil 17.01
178 Cyproconazole 1+2 17.05
179 1,1-Dichloro-2,2-bis (4-ethylphenyl) ethane 17.05
180 Flufenpyr ethyl 17.07
181 Pyriminobac methyl 1 17.12
182 Chlorobenzilate 17.20
183 Endrin 17.21
184 Fensulfothion 17.24
185 Ethion 17.33
186 Fluacrypyrim 17.37
187 Oxadixyl 17.37
188 p,p'-DDD 17.41
189 o,p'-DDT 17.46
190 Mepronil 17.61
191 Triazophos 17.64
192 Carfentrazone ethyl 17.73
193 Trifloxystrobin 17.79
194 Famphur 17.79
195 Azamethiphos 17.79
196 Benalaxyl 17.82
197 Norflurazon 17.91
198 Pyriminobac methyl 2 17.93
199 Pyraflufen-ethyl 17.95
200 Propiconazole 1 17.97
No. Compound name RT
201 Edifenphos 17.97
202 Quinoxyfen 18.01
203 Lenacil 18.06
204 Propiconazole 2 18.07
205 Endosulfan sulfate 18.11
206 p,p'-DDT 18.12
207 Hexazinone 18.21
208 Thenylchlor 18.29
209 Diflufenican 18.32
210 Diclofop methyl 18.33
211 Propargite 1+2 18.34
212 Resmethrin 1 18.34
213 Tebuconazole 18.36
214 Piperonyl butoxide 18.41
215 Resmethrin 2 18.45
216 Mefenpyr diethyl 18.58
217 Zoxamide 18.61
218 Epoxiconazole 18.62
219 Pyributicarb 18.65
220 Pyridafenthion 18.79
221 Iprodione 18.79
222 Bifenthrin 18.88
223 Phosmet 19.00
224 EPN 19.00
225 Picolinafen 19.00
226 Piperophos 19.01
227 Bromopropylate 19.02
228 Etoxazole 19.06
229 Fenpropathrin 19.10
230 Methoxychlor 19.12
231 Fenamidone 19.18
232 Tebufenpyrad 19.19
233 Anilofos 19.28
234 Furathiocarb 19.35
235 Phenothrin 1 19.36
236 Phenothrin 2 19.47
237 Tetradifon 19.56
238 Phosalone 19.63
239 Triticonazole 19.65
240 Cyhalothrin 1 19.67
241 Azinphos-methyl 19.75
242 Cyhalofop butyl 19.76
243 Pyriproxyfen 19.77
244 Cyhalothrin 2 19.84
245 Mefenacet 19.90
246 Acrinathrin 19.95
247 Pyrazophos 20.08
248 Fenarimol 20.22
249 Pyraclofos 20.41
250 Fenoxaprop ethyl 20.45
No. Compound name RT
251 Spirodiclofen 20.63
252 Bitertanol 1 20.69
253 trans-Permethrin 20.71
254 Bitertanol 2 20.80
255 cis-Permethrin 20.83
256 Fluquinconazole 20.91
257 Pyridaben 20.91
258 Prochloraz 20.97
259 Cafenstrole 21.20
260 Cyfluthrin 1 21.23
261 Fenbuconazole 21.30
262 Cyfluthrin 2 21.32
263 Cyfluthrin 3+4 21.42
264 Cypermethrin 1 21.56
265 Cypermethrin 2 21.66
266 Flucythrinate 1 21.70
267 Boscalid 21.73
268 Cypermethrin 3+4 21.76
269 Flucythrinate 2 21.90
270 Etofenprox 21.90
271 Fluridone 22.19
272 Fenvalerate 1 22.56
273 Flumioxazin 22.60
274 Fluvalinate 1 22.63
275 Fluvalinate 2 22.72
276 Fenvalerate 2 22.81
277 Difenoconazole 1 23.19
278 Difenoconazole 2 23.26
279 Deltamethrin 23.53
280 Famoxadone 24.11
281 Tolfenpyrad 24.18
282 Cinidon ethyl 25.14
283 Fluthiacet methyl 25.60

Fig.1 Comparison of EICs at 0.1 ppb (Hot / Cold Splitless)

Fig.2 Scatter diagram of area ratios of measured pesticides (Cold / Hot)

By using the cold splitless method, the peak area ratio for the components in the first half of the retention time range increased by 1.5 to 2 times. Additionally, several components near the middle of the retention time range had area ratios that increased by approximately 5 to 10 times. These compounds are presumed to be components that experience a large suppression effect caused by compound decomposition in the GC injection port. Similarly, the higher the boiling point component (higher retention time range), the larger the area ratio increases (up to 17 times). These results are likely due to the combination of suppressing decomposition and suppressing adsorption inside the inlet while using cold splitless mode. In this study, there were no components whose sensitivity decreased (area ratio < 1) due to the application of cold splitless mode when compared to the conventional hot splitless mode.

Conclusion

This study showed that cold splitless injections using MMI improved the sensitivity of pesticides analysis by GC-MS/MS when compared to the more traditional hot splitless injection method. Furthermore, a number of components showed very large improvements in sensitivity in the middle to late retention times that were likely due to both suppression of thermal decomposition and minimization of adsorption in the inlet when using cold splitless methods. These results show that cold splitless injection methods using MMI can be effective for improving overall GC-MS/MS pesticide sensitivity.

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Jeol Ltd. published this content on 12 March 2024 and is solely responsible for the information contained therein. Distributed by Public, unedited and unaltered, on 12 March 2024 06:03:04 UTC.