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Method Abstract 108

MA 108 / POST-COLUMN LC ANALYSIS OF 23 N-METHYL CARBAMATES

AN EXPANDED METHOD USING WATER/ACETONITRILE OR WATER/METHANOL GRADIENTS

There are a number of carbamate pesticide compounds employed worldwide which are not included in the 10 compounds mandated by USEPA Method 531.1 and AOAC Protocol 29.A05.

This Application Note describes methods for separating as many as 23 compounds, using a Pickering C8, 5 μm silica, column with either Water/Acetonitrile or Water/Methanol gradients. Instruments, post-column derivatization and detection protocols, and reagents remain unchanged, as described Pickering’s brochure, Post-Column LC Systems for Environmental Pesticide Analysis (B-CA5) and User’s Manual 0101-0002.

Although there are only two co-elutions in each of the solvent gradient protocols, the compounds were assigned to two separate test mixtures, A and B, in order to demonstrate the full range of separation.

The differences in selectivity between the Acetonitrile and Methanol protocols enable the user to employ both solvent
systems as a means of confirming peak identification.

The following comparison of Acetonitrile to Methanol might be helpful in choosing which solvent system will be for used routinely, and which will be for confirmation:

  • Acetonitrile generally exhibits higher sensitivity and baseline noise.
  • It also costs more and its disposal is more restricted.

Eleven of the most widely occurring carbamate compounds and BDMC (internal standard) are supplied by Pickering Laboratories in its qualitative test mixtures, Cat. No. 1700-0063. These are designated by * in the test mixture tables below. Other compounds may be purchased from suppliers of environmental standards. A few may vary considerably in homogeneity and availability.

108

1 Aldicarb sulfoxide (Standak)
2 Aldicarb sulfone
3 Oxamyl (Vydate)
4 Methomyl (Lannate)
5 3-Hydroxy carbofuran
6 Aldicarb (Temik)
7 Propoxur (Baygon)
8 Carbofuran (Furadan)
9 Carbaryl (Sevin)
10 Methiocarb (Mesurol)
11 BDMC internal standard
12 Butocarboxim sulfoxide
13 Butocarboxim sulfone
14 Ethiofencarb sulfoxide
15 Ethiofencarb sulfone
16 Butocarboxim
17 Ethiofencarb
18 Thiofanox Sulfoxide
19 Thiofanox Sulfone
20 Methiocarb sulfoxide
21 Methiocarb sulfone
22 3-Ketocarbofuran
23 Thiofanox

METHOD

Analytical Conditions: Water/Acetonitrile Protocol
Column: 4.0 x 250 mm, Pickering Cat. No. 0840250
Sample Injection: 10 μl in MeOH (for all chromatograms shown)
Mobile Phase:
Solvent A: HPLC-grade Water
Solvent B: HPLC-grade Acetonitrile (ACN)

Program

TIME

H2O %

ACN %

GRADIENT

0

90

10

 

2

90

10

Isocratic

46

49

51

Linear

46.1

30

70

Step

49

30

70

Isocratic

Equilibration Time: 13 minutes
Eluant Flow Rate: 0.80 mL/minute
Column Temperature: 37 ˚C
Reagent 1: 0.3 mL/minute, CB130 Hydrolysis Reagent
Reagent 2: 0.3 mL/minute, OPA reagent1 for derivatization

Reactors:
Hydrolysis: 100 ˚C, 500 μL
Derivatization: Ambient, 100 μL

Flourescence Detection:
Excitation: 330 nm
Emission: 465 nm
Analytical Conditions: Water/Methanol Protocol

Mobile Phase:
Solvent A: HPLC-grade Water
Solvent B: HPLC-grade Methanol (MeOH)

Program:

TIME

H2O %

MeOH %

GRADIENT

0

100

0

 

10

1000

0

Isocratic

19

40

60

Linear

32

0

100

Isocratic

43

0

100

Step

43.1 0 0 Isocratic

 

1 o-Phthalaldehyde (O120) and Thioflour™ (3700-2000), Pickering’s
brand of Dimethylaminoethanethiol•HCI, in OPA Diluent (CB910)

REFERENCE:
R.T. Krause, J. Chromatography, 185, 615-624 (1979)
R.T. J. Chromatographic Science, 16, 281-288 (1978)
H.A. Moye, S.J. Scherer and P.A. St. John, Anal. Letters, 10, 1049-1073 (1977)
A. de Kok and M. Hiemstra, J. AOAC int’l, 75, 1063-1072 (1992)
Official Methods of Analysis, 15th Ed., AOAC Int’l, Arlington, VA, (291-293)
Method 531.1, U.S. Environmental Protection Agency