AOAC Final Action Methods in 2018

Table 2014.09A. GC-MS retention times, quantifying ions, qualifying ions, ion abundances, LODs, and LOQs for the 20 pesticides

Retention time, min

Quantifying ion, m / z

Qualifying ion 1, m / z

Qualifying ion 2, m / z

LOQ, μg/kg

LOD, μg/kg

No.

Pesticide

ISTD a

Heptachlor-epoxide

22.15 15.43 17.35 17.43 18.94 19.00 19.77 19.83 19.90 20.37 22.75 23.12 23.95 24.57 24.79 27.40 27.15 27.68 28.62 28.73 29.46

353(100) b 306(100) 177(100) 198(100) 173(100) 166(100) 154(100) 265(100) 285(100) 290(100) 246(100) 359(100) 318(100) 283(100) 335(100) 247(100) 237(100) 148(100) 181(100) 266(100) 341(100)

355(79) 264(72) 197(26) 199(45) 255(23) 238(23) 230(43) 267(36) 287(69) 276(86) 318(34) 303(77) 316(80) 285(70) 303(43) 328(54) 272(37) 206(32) 166(32) 394(25) 183(54)

351(52) 335(7) 161(5) 200(5) 240(9) 138(8) 203(21) 250(10) 270(6) 305(74) 176(26) 357(74) 246(139) 255(15) 367(9) 408(51) 307(29) 325(8) 165(35) 267(14) 339(51)

1 2 3 4 5 6 7 8 9

Trifluralin Tefluthrin

20.0 10.0 10.0 10.0 20.0 10.0 10.0 40.0 20.0 25.0 10.0 10.0 10.0 20.0 10.0 10.0 10.0 10.0 20.0

10.0

5.0 5.0 5.0

Pyrimethanil Propyzamide

Pirimicarb

10.0

Dimethenamid Tolclofos-methyl Fenchlorphos Pirimiphos-methyl

5.0 5.0

20.0 10.0 12.5

10 11 12 13 14 15 16 17 18 19 20

2,4 ' -DDE

Bromophos-ethyl

5.0 5.0 5.0

4,4 ' -DDE

Procymidone Picoxystrobin Chlorfenapyr Quinoxyfen

10.0

200.0

100.0

5.0 5.0 5.0 5.0

Benalaxyl Bifenthrin

Diflufenican

Bromopropylate

10.0

a  ISTD = Internal standard. b  Numbers in parentheses are ion abundances.

(g)  Millipore filter membrane (nylon) .—13 mm × 0.2 μm. D. Preparation of Standard Solutions (a)  Prep aration of stock solutions.— Accurately weigh 5–10 mg individual pesticide and chemical pollutant standards (accurate to 0.1 mg) into a 10 mL volumetric flask. Dissolve and dilute to volume with methanol, toluene, acetone, acetonitrile, isooctane, etc., depending on each individual compound’s solubility. All standard stock solutions are stored in the dark at 0–4°C and can be used for 1 year. (b)  Preparation of mixed standard solution.— Depending on properties and retention times of compounds, all compounds are divided into a series of groups. The concentration of each compound is determined by its sensitivity on the instrument for analysis. Mixed standard solutions are stored in the dark below 4°C. (c)  Working standard mixed solution in matrix.— Prepare working standard mixture solution in matrix of pesticide and chemical pollutants by diluting an appropriate amount of mixed standard solution with blank extract, which has been taken through the method with the rest of the samples. Mix thoroughly. Used for plotting the standard curve. Working standard mixture solution in

( 2 )  Column .—DB-1701 capillary column (30 m × 0.25 mm × 0.25 μm; J&W Scientific, Folsom, CA, USA), or equivalent. ( 3 )  Column temperature .—40°C hold 1 min, 30°C/min to 130°C, 5°C/min to 250°C, 10°C/min to 300°C, hold 5 min. ( 4 )  Carrier gas .—Helium, purity ≥99.999%, flow rate 1.2 mL/min. ( 5 )  Injection port temperature .—290°C. ( 6 )  Injection volume .—1 μL. ( 7 )  Injection mode .—Splitless, purge on after 1.5 min. ( 8 )  Ionization mode .—EI. ( 9 )  Ion source polarity .—Positive ion. ( 10 )  Ionization voltage .—70 eV. ( 11 )  Ion source temperature .—230°C. ( 12 )  GC-MS interface temperature .—280°C. ( 13 )  Solvent delay .—14 min. ( 14 )  Ion monitoring mode .—Selected ion monitoring (SIM); one quantifying ion and two qualifying ions are selected for each compound. The retention times, quantifying ions, qualifying ions, and the expected ion abundances for each of the 20 pesticides included in the study and heptachlor epoxide are listed in Table 2014.09A . SIM acquisition parameters for ions monitored by GC-MS are shown in Table  2014.09B . (b) GC-MS/MS analysis.— ( 1 )  GC-MS/MS system .—Model 7890A gas chromatograph connected to a Model 7000B triple quadrupole mass spectrometer with EI source and equipped with a Model 7693 autosampler and Mass Hunter data processing software system (Agilent Technologies), or equivalent.

matrix must be freshly prepared. E. Apparatus and Conditions

(a) GC-MS analysis.— ( 1 )  System .—Model 7890A gas chromatograph connected to a Model 5975C mass selective detector with electron ionization (EI) source and equipped with a Model 7683 autosampler and Chemstation data processing software system (Agilent Technologies), or equivalent.

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