SPECIATION OF DICHLOROMETHANE AND CHLOROFORM USING NEGATIVE ION SIFT-MS

Importance of the Topic

Volatile chlorinated solvents such as dichloromethane and chloroform persist as environmental contaminants in water and air. Accurate separation and quantification are essential for monitoring compliance and risk assessment.

Goals and Study Overview

The aim of the study was to develop a negative ion SIFT MS method using OH- reagent ions to fully speciate dichloromethane and chloroform in aqueous samples. Preliminary data on linearity and repeatability were provided.

Methodology and Instrumentation

Headspace sampling and Selected Ion Flow Tube Mass Spectrometry were combined with robotic automation.

• Samples were incubated at 60°C for 15 minutes with agitation.
• Headspace vapour was injected into SIFT MS at 50 µL s-1.
• Analysis was carried out in full scan and Selected Ion Monitoring modes using both O2+ and OH- reagent ions.
• Calibration standards ranged from 2 to 2000 ppb prepared by serial dilution in water.
• An assumed reaction rate constant of 2 x 10 9 cm3 s-1 was used for OH reactions.

Instrumentation Used

• Syft Technologies Voice200ultra Dual Polarity SIFT MS
• GERSTEL MPS Robotic Pro autosampler
• Inlet temperature 150°C and flow 25 mL min-1
• Headspace syringe temperature 150°C and zero grade air makeup gas

Key Results and Discussion

• Positive O2+ reagent ions produced identical product ions for both solvents, preventing speciation.
• Negative OH- reagent ions yielded distinct ions at 119 and 117 Da for chloroform and 85 and 83 Da for dichloromethane, enabling clear separation.
• Linearity was excellent from 2 to 2000 ppb with R2 greater than 0.999 for all monitored ions.
• Repeatability showed RSDs below 7% for six replicates at 200 ppb, indicating good precision.

Benefits and Practical Applications

• Rapid direct analysis without purge and trap, enabling at least 15 samples per hour.
• Real time quantification supports high throughput environmental and QA QC workflows.
• Simplified calibration assures accurate speciation of chlorinated VOC mixtures.

Future Trends and Potential Applications

• Extension to other halogenated volatile organic compounds in water and air matrices.
• Integration of automated sample preparation to further improve precision.
• Field deployable SIFT MS systems for on site environmental monitoring.
• Coupling with data analytics for real time pollution mapping and exposure assessment.

Conclusion

Negative ion SIFT MS using OH- reagent ions provides a robust and rapid method to speciate and quantify dichloromethane and chloroform in aqueous samples with excellent linearity and reproducibility. The approach offers significant advantages in environmental monitoring and high throughput analysis.

References

• AS191 Automated Selected Ion Flow Tube Mass Spectrometry SIFT MS
• AS209 Rapid Analysis of BTEX in Water Using Automated SIFT MS
• AS211 Real time Speciation of Ethylbenzene for the Xylenes Using SIFT MS
• AS212 Rapid Analysis of Organochlorine Compounds in Water Using Automated SIFT MS