MA 472 / ANALYSIS OF N-METHYL CARBAMATE
PESTICIDES IN FOOD
BY HPLC WITH POST-COLUMN DERIVATIZATION AND FLUORESCENCE DETECTION
Carbamate pesticides are widely used around the world to protect agricultural produce. In addition, they are used in homes, gardens and industrial applications. The main route of exposure for people to N-Methyl Carbamates is through food pathways, so pesticide use in food crops is strictly regulated.
As part of FDA’s pesticide monitoring program, individual lots of domestic and imported foods and feeds are sampled and tested for pesticide residues in order to enforce the tolerances set by the EPA. Methyl carbamates are separated using a reversed-phase column and then react with o-Phthalaldehyde and a mercaptan after hydrolysis to form a highly fluorescent derivative. This post-column reaction is the basis for EPA Method 531.2 and AOAC official Method 985.23.
The “QuEChERS” (Quick, Easy, Cheap, Effective, Rugged, and Safe) method is a single step sample extraction and salting out technique that is combined with dispersive SPE clean-up for multi-residue pesticide analysis. AOAC official Method 2007.01 utilizes QuEChERS extraction and clean-up for wide range of pesticides in food matrices. This method abstract demonstrates that dispersive SPE can be successfully used in combination with post-column derivatization and fluorescence detection for analysis of carbamates in food.
Sample Preparation
Place 15 g (5 g for spices or other challenging matrices) of homogenized sample into 50 mL centrifuge tube and add 15 mL of 1% Acetic Acid in Acetonitrile (v/v). Mix well. Add one Q-sep packet (Cat. # 26238, Restek), containing 6.0 g Magnesium Sulfate and 1.5g of Sodium Acetate, to the mixture and immediately shake or vortex for 1 min. Centrifuge for 1 min to separate solid material.
Take 1 mL of supernatant and place into Q-sep d-SPE tube and shake vigorously for 2 min. Use to clean-up samples containing fats and waxes, 50 mg PSA, 150 mg MgSO4, and 50 mg C18 (Q-sep Cat # 26125, Restek). Use for intensely colored extracts, 50 mg PSA, 150 mg MgSO4, 50 mg C18 and 50 mg graphitized carbon (Q-sep Cat # 26219, Restek). Centrifuge the tube for 1 min to separate the solid material, filter through 0.45 um filter and place into injection vial for HPLC analysis.
Analytical Conditions
Column: Carbamate Column P/N 0846250 (250 x 4.6 mm), C8, 5 um
Flow Rate: 1 mL/min
Column Temperature: 42 ºC
Mobile Phase: see Table 1
Post-column Conditions
Post-column System: Pinnacle PCX or Vector PCX
Reactor 1: 100 ºC, 0.5 mL
Reactor 2: Ambient, 0.1 mL
Reagent 1: Hydrolysis Reagent CB130 or CB130.2
Reagent 2: 100 mg of OPA, 2 g of Thiofluor in 950 mL of CB910
Detection: FLD, Excitation 330 nm, Emission 465 nm
Injection Volume: 10-20 uL
TABLE 1 HPLC GRADIENT
|
TIME (Min) |
WATER, % |
METHANOL, % |
|---|---|---|
|
0 |
100 |
0 |
|
1 |
100 | 0 |
|
1.1 |
82 | 18 |
|
36 |
30 | 70 |
|
39 |
30 | 70 |
|
39.1 |
0 | 100 |
| 41 | 0 | 100 |
| 41.1 | 100 | 0 |
| 55 | 100 | 0 |
TABLE 2. RECOVERIES OF N-METHYL CARBAMATES IN FOOD MATRICES
| SAMPLE | APPLES | BANANA | GINGER POWDER | BROWN RICE | BLUE- BERRIES |
|---|---|---|---|---|---|
| Spike concentration | 10 ng/g | 10 ng/g | 25 ng/g, contaminated with 62 ng/g of Carbofuran | 25 ng/g | 10 ng/g |
| Aldicarb Sulfoxide | 99. 62% | 109.39% | 91.14% | 87.07% | 92.76% |
| Aldicarb sulfone | 107.02% | 98.35% | 79.83% | 81.82% | 92.52% |
| Oxamyl | 73.11% | 73.25% | 76.79% | 80.76% | 68.66% |
| Methomyl | 98.46% | 84.18% | 83.07% | 86.94% | 115.38% |
| 3-Hydroxycarbofuran | 39.1% | 0% | 39.1% | 100% | 39.1% |
| Carbofuran | 84.13% | 106.95% | 87.43% | 72.07% | 80.76% |
| Aldicarb | 89.69% | 99.81% | 77.83% | 87.15% | 87.50% |
| Propoxur | 101.51% | 91.04% | 72.39% | 88.36% | 86.54% |
| Carbofuran | 103.41% | 100.25% | 96.99% | 84.08% | 89.17% |
| Carbaryl | 76.20% | 111.84% | 81.83% | 83.40% | 82.19% |
| Naphthol | 61.56% | 82.30% | 74.99% | 75.81% | 37.15% |
| Methiocarb | 86.84% | 93.10% | 49.82% | 88.41% | 83.49% |
