Measurement of n-Methylcarbamoyloxime and n-Methylcarbamates in Water by Direct Aqueous Injection HPLC with Postcolumn Derivatization

This Application brief demonstrates the measurement of n-Methylcarbamoyloxime and n-Methylcarbamates in water by direct aqueous injection HPLC with postcolumn derivatization.

Carbamates are used worldwide as commercial pesticides for food crops. The resulting agricultural runoff can carry them into surface water, groundwater, and other drinking water resources. The United States Environmental Protection Agency (US EPA) requires that drinking water and raw surface water to be monitored for the presence of carbamate pesticides and related compounds using an established EPA Method 531.2. The European Union (EU) regulation regarding drinking water, provides a general rule for pesticides and metabolites. This regulation limits the maximum admissible concentration (MAC) at 0.1 μg/L (ppb) for each individual component, with the total concentration not to exceed 0.5 ppb. Detection of regulated compounds at ever decreasing levels is a challenge faced by many water testing laboratories. Because the concentration of these substances in real samples may be in the low parts per billion (ppb) or μg/L, optimal sensitivity is the ultimate goal.

Sample Preparation

Oasis SPE Method for Carbamates

Method for Oasis HLB Cartridge, 6 cc, 200 mg 

Standard mix preparation

Pipette 25 μL of AccuStandard mix M-531M and M-531-IS each into 100 mL of preserved reagent water for a final concentration of 25 parts per billion (ppb) per analyte. Preserved reagent water is prepared by dissolving 9.35 g of potassium dihydrogen citrate and 0.2 g of sodium thiosulfate (anhydrous) in water and diluting to 1 L.

Eluent Preparation

Filter and degas all eluents through a 0.45 μm filter.

A: Water

B: Methanol

C: Acetonitrile

Post Column Reagent Preparation

Reagent 1: 0.05 N sodium hydroxide

Dissolve 2 g NaOH in water and dilute to 1 L, filter and degas.

Reagent 2: PA/2-mercaptoethanol

Dissolve 19.1 g of Borax (Na₂B₄O₇•10H₂O) Sodium borate in 1 L of water. To this, add a solution of 0.1 OPA (o-phthaldialdehyde) in 10 mL methanol. Swirl to dissolve, filter, and degas. To this, add 1.0 mL of 2-mercaptoethanol, ently swirl to dissolve. Protect from light. Post-column reaction temperature is 80 °C.

1. Waters Alliance Systems for Carbamate Analysis: 720000126EN
2. Carbamates in Drinking Water: 720000609EN
3. A Fully Automatic Multi-Analyte Quantification Protocol for Carbamates – A Comparison of LC-MS and LC-MS/MS: 720000672EN
4. LC-MS of 52 Carbamates: A Fully Automated Protocol: WA20274