A Study of Filter Types Used in Sample Preparation of Cannabis/Hemp with HPLC Analysis

Importance of the topic

Cannabis potency analysis by HPLC requires effective removal of particulates to protect column performance and ensure accurate quantitation of phytocannabinoids. Filtration using syringe filters is standard to remove fine particulates after extraction, but filter material properties can cause analyte adsorption, compromising recovery.

Objectives and study overview

This study evaluated recovery rates of eleven phytocannabinoids using seven common 0.45 µm syringe filter materials (hydrophobic PVDF, hydrophilic PVDF, polypropylene, PTFE, nylon, cellulose acetate, and polyethersulfone) without pre-wetting. A Shimadzu Cannabis Analyzer for Potency™ HPLC-UV system with a high-sensitivity method was used to assess analyte adsorption and recovery variability across ten replicates per filter type.

Instrumental setup

• HPLC system: Shimadzu Cannabis Analyzer for Potency™ with built-in UV detector at 220 nm
• Column: NexLeaf CBX for Potency, 2.7 µm, 4.6 × 150 mm, with guard cartridge
• Mobile phases: 0.085% phosphoric acid in water (A) and 0.085% phosphoric acid in acetonitrile (B)
• Gradient: 70% B (0–3 min), 70–85% B (3–7 min), 85–95% B (7–7.01 min), 95% B (7.01–8 min), return to 70% B (8–8.01 min), re-equilibrate at 70% B (8.01–10 min)
• Flow rate: 1.6 mL/min; oven temperature: 35 °C; injection volume: 5 µL

Methodology

Samples of methanol spiked at 10 µg/mL with an 11-component phytocannabinoid standard were prepared. Initial calibration curves (0.5–100 µg/mL) and QC standards (20 µg/mL and 80 µg/mL) confirmed linearity (r2 ≥ 0.999) and accuracy within ±5%. Un-filtered spiked and blank samples were analyzed to establish baseline responses. Each filter type was challenged with ten replicates of spiked solvent; a fresh filter and solvent aliquot were used for each injection.

Main results and discussion

• Calibration performance: all compounds showed r2 ≥ 0.9992, RF RSD ≤ 8.6%, accuracy ~100%
• QC recoveries remained within ±2.7% across low and high standards, indicating system stability
• Un-filtered spiked samples yielded average recovery of 9.94 µg/mL (SD < 0.63%), confirming negligible system bias
• Filter comparison: nylon and PTFE filters exhibited the lowest average %RSD (0.82% and 0.87%) and minimal analyte hold-up, indicating superior recovery consistency
• PES and PVDF filters showed moderate variability (%RSD 1.7–2.2%), while CA and PP filters had higher variability (2.6–2.7%), suggesting greater adsorption or flow inconsistency
• No clear correlation was observed between filter hydrophilicity/hydrophobicity and cannabinoid recovery, indicating material chemistry alone is not predictive of performance

Practical benefits and applications

Effective filtration using nylon or PTFE syringe filters enhances reproducibility and accuracy in HPLC potency assays for cannabis and hemp, reducing sample preparation variability. Laboratories performing QA/QC, regulatory compliance, or research can adopt these filter types to minimize analyte loss, extend column lifetime, and streamline workflows.

Future trends and applications

Anticipated developments include tailored filter coatings to further reduce binding of lipophilic analytes, integration of microfiltration cartridges for higher throughput, and expansion of filter studies to include complex matrices and other bioactive compounds. Advanced filter materials may support direct injection of crude extracts, simplifying sample preparation.

Conclusion

The comparative evaluation demonstrates that nylon and PTFE syringe filters provide optimal recovery and precision for HPLC analysis of phytocannabinoids in methanolic extracts. Selection of appropriate filter material is essential for reliable potency measurements in cannabis quality control laboratories.