Gas chromatography-isotope dilution mass spectrometry method validation for target pesticides in soybeans

Figures & data

Table 1. GC-MS parameters for the determination of the selected pesticides.

		m/z (% relative abundance)
Pesticide	Retention time [min]	QT	QL1	QL2	Time window start time [min]
d10-Diazinon	9.58	183	314 (59)	232	8.0
Diazinon	9.69	179	304 (56)	227
d10-Malathion	12.75	183	132 (85)	184
Malathion	12.91	173	127 (86)	158	11.0
d10-Chlorpyrifos	12.95	324	200 (90)	326
Chlorpyrifos	13.12	314	197 (124)	316
d6-Captan	15.20	84	154 (28)	82
Captan	15.31	79	149 (17)	77	14.3
α-Endosulfan	16.56	339	341 (66)	337
^13C9-β-Endosulfan	19.53	348	350 (68)	346
β-Endosulfan	19.55	339	341 (66)	337	18.0
d6-Tebuconazole	22.74	256	87 (67)	258
Tebuconazole	22.85	250	70 (67)	252	21.3
d7-Iprodione	24.44	318	320 (66)	319
Iprodione	24.59	314	316 (65)	315
^13C6-Cypermethrin	28.78	187	215 (48)	214
Cypermethrin	28.68	181	209 (54)	208	27.0

QT: quantifying ion.

QL1 and QL2: qualifying ions.

Figure 1. Chromatogram obtained for a soybean sample spiked with pesticides corresponding to MRL levels.

Table 2. Working range and external calibration equation ^a. Results are shown for 1 day and are representative for all validation days (n = 5).

Pesticide	MRL soya beans [mg/kg]	Calibration range in Solvent [mg/kg]	Working range in Matrix [mg/kg]	Calibration Equation^a	S R,c	r	Lack of Fit P-value (α = 0.05)	LOD [mg/kg]	LOQ [mg/kg]
Diazinon	0.020	0.010–0.200	0.0046–0.040	Y = −0.068 + 1.120 X	0.096	0.9964	0.5287	0.0014	0.0046
Malathion	0.020	0.010–0.200	0.0026–0.040	Y = −0.016 + 1.529 X	0.069	0.9971	0.1691	0.0008	0.0026
Chlorpyrifos	0.050	0.025–0.500	0.0051–0.100	Y = −0.036 + 0.853 X	0.036	0.9969	0.5220	0.001	0.0033
Captan	0.070	0.010–0.200	0.0044–0.040	Y = −0.039 + 1.921 X	0.045	0.9992	0.2519	0.0013	0.0044
α-Endosulfan	0.500 ^b	0.250–5.000	0.0556–1.000	Y = 0.131 + 1.067 X	0.203	0.9995	0.6781	0.0069	0.0229
β-Endosulfan
Tebuconazole	0.150	0.005–1.000	0.022–0.200	Y = −0.277 + 1.498 X	0.343	0.9951	0.5606	0.0067	0.0223
Iprodione	0.010	0.010–0.200	0.0022 −0.040	Y = −0.009 + 0.930 X	0.010	0.9993	0.1196	0.0006	0.0022
Cypermethrin	0.050	0.025–0.500	0.005–0.100	Y = 0.013 + 0.901 X	0.009	0.9998	0.1937	0.0015	0.0051

^a Obtained from triplicate injection of the standard solutions. Y: area ratio analyte/I.S.; X: concentration ratio analyte/I.S.

^b Results for endosulfan expressed as the sum of α- and β- isomers (endosulfan sulfate not detected).S _R,c: Regression standard deviation

r: Correlation coefficient

Table 3. Precision of the method, precision of the trueness estimation and uncertainty budget.

Pesticide	RSDrep [%]	RSDip [%]	RSDtrue ^a [%]	U ^b [%]	U ^c[%]	Example of a soya sample measured (n = 3) with associated uncertainties [mg/kg]
Diazinon	2.6	1.0	1.9	2.7	4.3	0.038 ± 0.002
Malathion	2.3	1.4	1.1	1.8	3.0	0.025 ± 0.001
Chlorpyrifos	2.5	1.0	0.9	1.9	3.6	0.076 ± 0.003
Captan	4.8	3.4	3.0	4.2	6.5	0.028 ± 0.002
(α + β)-Endosulfan	2.2	1.3	0.3	1.2	2.6	0.714 ± 0.019
Tebuconazole	4.2	4.2	2.1	3.3	5.5	0.123 ± 0.006
Iprodione	2.7	0.6	0.6	1.6	3.2	0.027 ± 0.001
Cypermethrin	2.5	3.1	1.2	1.9	3.2	0.074 ± 0.002

^a Estimated as the RSD of the recovery at MRL level.

^b Estimated expanded uncertainty (k = 2) for the validation experimental set up (3 samples × 5 days, n; ₁ = 15, n₂ = 5, n₃ = 6).

^c Estimated expanded uncertainty (k = 2) for a result within the validated working range obtained from analysing one sample in triplicate (n₁ = 3, n₂ = 1).

Table 4. Mean recoveries (estimated as ratio of analytical concentration of target pesticides obtained by IDMS to the corresponding spiked concentration,%) and RSD (%, n = 5) obtained for the selected pesticides spiked at different levels in milled soyabeans.

	Spike	Recovery	RSD	Spike	Recovery	RSD	Spike	Recovery	RSD
Pesticide	level 1 [mg/kg]	[%]	[%]	level 2 [mg/kg]	[%]	[%]	level 3 [mg/kg]	[%]	[%]
Diazinon	0.010	115	1.0	0.020	109	1.9	0.030	108	2.2
Malathion	0.010	80	1.4	0.020	83	1.1	0.030	85	1.1
Chlorpyrifos	0.025	107	0.7	0.050	107	0.9	0.075	108	0.3
Captan	0.010	93	7.9	0.020	92	3.0	0.030	92	6.5
(α + β)-Endosulfan	0.250	96	0.9	0.500	94	0.3	0.750	94	0.4
Tebuconazole	0.050	85	4.5	0.100	86	2.1	0.075	88	2.1
Iprodione	0.010	101	1.3	0.020	103	0.6	0.030	104	1.2
Cypermethrin	0.025	110	2.3	0.050	108	1.2	0.075	107	0.8