Highly sensitive method for determination of carbamates in water as per ASTM D-7645 by LCMS-8045

Significance of the topic

Carbamate pesticides pose persistent risks to aquatic ecosystems and human health due to their mobility in water and potential bioaccumulation. Monitoring trace levels of these compounds in drinking and environmental water is crucial for regulatory compliance and safeguarding public health.

Objectives and study overview

This study aimed to develop and validate a highly sensitive LC-MS/MS method based on ASTM D-7645 for the direct determination of six carbamates (aldicarb, aldicarb sulfone, aldicarb sulfoxide, carbofuran, methomyl, oxamyl, thiofanox) in water samples. Emphasis was placed on improving detection limits, minimizing sample preparation steps, and ensuring method performance across tap, RO, and bottled water matrices.

Applied methodology

Sample preparation was streamlined by spiking 25 mL water aliquots with a 50 ppm carbofuran-D3 surrogate standard and calibration mix, followed by 0.45 µm syringe filtration. Calibration standards at nine levels (0.5–250 ppb) were prepared in water and plotted using an external standard approach with 1/C weighting to enhance low-concentration accuracy.

Used instrumentation

• UHPLC system: Shim-Pack Velox SP-C18 column (2.7 µm)
• Mobile phases: A (95% water/5% methanol, 5 mM ammonium formate), B (95% methanol/5% water, 5 mM ammonium formate)
• Flow rate: 0.4 mL/min; injection volume: 5 µL; column temperature: 40 °C
• Mass spectrometer: Shimadzu LCMS-8045 triple quadrupole with heated ESI probe
• MRM transitions optimized for each analyte; polarity switching at 5 ms; scan speed 30 000 u/sec

Main results and discussion

Calibration curves for all analytes exhibited excellent linearity (r² > 0.99) over 0.5–100 ppb. The detection verification level (0.25 ppb) was confirmed by clear MRM chromatograms. Method accuracy ranged from 83% to 101%, and signal-to-noise ratios at 0.5 ppb exceeded 90 for most compounds. Surrogate recoveries in all water types averaged around 50%, meeting ASTM criteria. The direct-injection approach achieved detection limits ≈20 times lower than conventional ASTM D-7645.

Benefits and practical applications

• Minimal sample preparation reduces analysis time and potential contamination.
• Ultra-fast polarity switching and heated ESI improve sensitivity and throughput.
• Direct compliance with ASTM D-7645 enables routine monitoring of trace carbamates in drinking and environmental waters.
• Lower detection limits support early warning and regulatory enforcement.

Future trends and applications

Further enhancements may include automation of sample loading, expansion to other polar pesticide classes, and integration with high-resolution mass spectrometry for non-target screening. Application to wastewater and surface water monitoring will support broader environmental surveillance programs.

Conclusion

A robust, highly sensitive LC-MS/MS method using the Shimadzu LCMS-8045 was established for direct quantitation of six carbamate pesticides in water. The validated approach meets and surpasses ASTM D-7645 performance requirements, offering low detection limits, high accuracy, and streamlined operation suitable for environmental and quality-control laboratories.

References

• ASTM D-7645: Determination of Aldicarb, Aldicarb Sulfone, Aldicarb Sulfoxide, Carbofuran, Methomyl, Oxamyl and Thiofanox in Water by Liquid Chromatography/Tandem Mass Spectrometry.