This article from issue 16 of the Analytix Reporter explores the effectiveness of syringe filters in removing particulates from samples before U/HPLC analysis. Through a two-part investigation, the authors evaluate the particle retention capabilities of different filters and correlate these findings with the operational longevity of U/HPLC columns under optimal system pressure. Also, the importance of the filtration of the mobile phase and the selection of the membrane filters is assessed.
The study concludes that syringe filters vary significantly in their ability to retain particles, directly affecting U/HPLC column operation. It underscores the necessity of careful filter selection for both sample and mobile phase preparation.
INTRODUCTION
Advancements in UHPLC technologies have significantly enhanced both throughput and sensitivity, making sample preparation ever more pivotal. Out of many strategies, filtration is valued for its straightforwardness and cost efficiency. The presence of undissolved particulates, even in minimal concentrations, can lead to the accumulation on column inlet frits, compromising data quality, instrument back pressure, and column life. Moreover, preparing the mobile phase frequently necessitates filtration, especially with the use of buffers and mixtures.
EXPERIMENTAL PROCEDURE
Part 1: Filter Retention Study
Studies on syringe filters from four manufacturers, featuring pore sizes of 0.2 µm and 0.45 µm, utilized hydrophilic polytetrafluoroethylene (PTFE) or regenerated cellulose (RC) materials. Tests involved 0.05% polystyrene bead solutions in water, with beads measuring 0.5 μm and 0.24 μm in diameter for the respective pore sizes. Each bead solution was processed through four syringe filters per lot, often across multiple lots. After filtering 3 mL of bead solution, the filtrate was analyzed using fluorescence or spectrophotometry against a six-point standard curve for characterization.
Part 2: Column Lifetime Study
Column lifespan was evaluated through repeated 10 μL injections of 0.05% bead solutions, both filtered and unfiltered. For filtered samples, bead solutions were filtered into 30 HPLC-certified vials using n=30 devices of each 0.45 μm pore size syringe filter device tested in Part 1. The change in back pressure was monitored after each injection for up to 500 injections or until reaching a pressure limit of 8000 psi/548 bar to prevent unsafe system pressure levels.
See the full article for details on:
- HPLC conditions
- Column cleaning, flushing, and equilibration conditions
RESULTS & DISCUSSION
Part 1. Filter Retention Study
Testing revealed significant variance in retention capabilities across different filters, with PTFE materials generally showing higher efficiency than RC in removing particulates. This variation directly affects analytical data accuracy and instrument protection.
Part 2. Column Lifetime Study
Pre-filtering samples before (U)HPLC analyses is beneficial for preventing column clogging and maintaining data quality. Studies show syringe filters' efficiency varies significantly, impacting column protection. Experiments with 0.45 µm filters and polystyrene beads demonstrate that PTFE filters, allowing over 500 injections without increased back pressure, outperform RC filters, which led to quicker clogging and reduced column lifespan.
Filtration of mobile phase using membrane filters: see the full article for results of this assessment.
CONCLUSION
This research demonstrated the significant impact of membrane filter type on the sample and mobile phase purity, with certain filters leading to heightened back pressure and potential instrument damage. The study also explores factors affecting membrane filter retention, such as pore size, shape, and material compatibility.
