Method Development
Method development encompasses sample preparation, Sensitivity Issues, Peak Tailing Issues, and Matrix Effect Issues.
Sample Preparation – Extraction Solvent
We must adopt the QuEChERS (Quick, Easy, Cheap, Effective, Rugged and Safe) technique.
We must also optimize the extraction solvent. Currently, the AOAC method solvent and USP method solvent do not do this. Only the Dyad method solvent has this capability.
Sample preparation – dSPE
Dispersive solid-phase extraction (dSPE) is a simple, low-cost, fast, and sorbent-based technique for sample cleanup. Different dSPEs were compared, and Agilent 5982-5122 dSPE was selected.
Sample Preparation – Low Recovery
Some pesticides have low recovery since they stick to the surface of containers during extraction. The analyte protectant (AP) can prevent this low recovery issue by occupying the container surface.
Sensitivity Issue – dMrm and RTL
Too many Multiple Reaction Monitoring (MRM) transitions can cause low sensitivity issue. A dynamic MRM(dMRM) mode can keep sensitivity by setting up different time segments for many analytes. dMRM requires consistent retention times. Retention Time Locking (RTL) ensures the consistency of retention time by adjusting as flow rate.
Peak Tailing Issue – AP with Sandwich Injection Mode
Some pesticides have peak tailing issue, which is caused by stickiness to the GC system. AP with hydroxyl groups can block active sites in GC system to prevent peak tailing issue.
Matrix Effect – Internal Standard (IS) Selection
USP 561 uses only one IS. AOAC 2007.01 uses two IS. Dyad Labs uses five IS.
Matrix Effect – MRM Transition Selection
Each pesticide has three MRM transitions. Choose the transition with the least interference and most sensitivity to minimize matrix effect.
Method Validation
Method validation consists of: specificity, linearity, sensitivity, accuracy, range, precision, stability, and batch size.
Specificity: Method specificity is evaluated by analyzing blank diluent, blank matrix extract, analyte only, and IS only. No significant contribution/interference peaks were observed in these samples.
Linearity and Sensitivity: Each pesticide has its own limit. Five different curve ranges were designed to cover all 112 pesticides using 9 standard curve points. The curve regression type is quadratic with weight of 1/x, and R2 must be ≥0.995.
Conclusion
This pesticide method is simple, fast, specific, sensitive, and comprehensive. This pesticide method has been successfully validated in both botanical and non-botanical dietary supplements. This pesticide method has been successfully applied for proficiency test samples.
