Fully automated liquid-liquid extraction method using a GERSTEL Dual Head Robotic with Robotic Pro of organochlorine pesticides and polychlorinated biphenyls in water

Significance of the Topic

The monitoring of organochlorine pesticides (OCPs) and polychlorinated biphenyls (PCBs) in water supplies is critical due to their persistence, bioaccumulation potential, and strict regulatory limits imposed to protect ecosystems and public health.

Objectives and Study Overview

This study aimed to develop and validate a fully automated on-line liquid-liquid extraction (LLE) method using a GERSTEL Dual Head Robotic with Robotic Pro system for trace analysis of OCPs and PCBs in water, focusing on improving throughput, reproducibility, and solvent efficiency.

Applied Instrumentation

• GERSTEL Dual Head Robotic/Robotic Pro with 2 m rail and interchangeable PSM (Preparation Syringe Module) and USM (Universal Syringe Module)
• GERSTEL QuickMix for automated sample agitation
• GERSTEL CIS4 cooled injector system
• Agilent 7890B GC coupled to a 5977B MS with High Efficiency Source (HES) and MassHunter software
• Agilent 7010 Triple Quadrupole MS (high-selectivity option)

Methodology

Water samples (18 mL) were dispensed into 20 mL vials and spiked with 600 µL extraction solvent via the PSM module. Calibration standards (5–200 ng/L) were prepared automatically by adding concentrated stock using the USM module. Samples were mixed at 1500 rpm for 5 minutes, a small volume of polar solvent was introduced to break emulsions, and 10 µL of the organic phase was injected into the CIS inlet. GC–MS analysis was conducted in selected ion monitoring (SIM) mode on a 30 m DB-5MS UI column.

Main Results and Discussion

The automated extraction delivered excellent linearity for triallate (R2 > 0.9996 single quadrupole, R2 > 0.9998 triple quadrupole) and PCB 28 (R2 > 0.9992 single quadrupole, R2 > 0.9964 triple quadrupole). Precision was confirmed with D6 gamma HCH as internal standard showing RSD of 4.28% (n=6). Automation eliminated manual pipetting errors, yielding highly reproducible and accurate quantitation.

Benefits and Practical Applications

The fully automated workflow doubled sample throughput—up to 55 samples per 24 h using the PrepAhead function—compared with three manual batches. It saved approximately 3900 analyst hours per year, reduced solvent consumption by over 120 L annually, minimized waste disposal costs and storage requirements, and lowered health and safety risks associated with manual LLE.

Future Trends and Potential Applications

Further miniaturization of extraction volumes, integration of automated centrifugation to address emulsion challenges, optimization of injection volumes and GC run times, and extension of the method to complex environmental and industrial matrices are promising directions to enhance applicability and throughput.

Conclusion

The GERSTEL Dual Head Robotic automated LLE method presents a robust, efficient, and reproducible solution for trace analysis of OCPs and PCBs in water, offering significant improvements in laboratory productivity, data quality, and sustainability over traditional manual extraction techniques.