Filtration and Solid Phase Extraction

What is Vacuum Filtration?

Vacuum filtration is a common laboratory technique used to separate solid particles from a liquid-gas mixture or a liquid suspension. It is significantly faster than gravity filtration because it utilizes a pressure differential across the filter medium. By reducing the pressure on one side of the filter, the atmospheric pressure on the other side forces the liquid through the filter more rapidly, leaving the solid residue (the filter cake) on the filter surface.

What is Solid Phase Extraction?

Solid Phase Extraction (SPE) is a widely used sample preparation technique designed to isolate, concentrate, and purify analytes from complex matrices before quantitative analysis (e.g., by chromatography). It involves passing a liquid sample through a cartridge or disk containing a solid sorbent. Analytes of interest are either retained on the sorbent while impurities pass through, or impurities are retained while the analytes pass through.

How Does SPE Work?

SPE typically involves four main steps, with vacuum often used to facilitate the movement of liquids through the sorbent bed at a controlled rate:  

1. Conditioning: The sorbent is treated with a solvent to activate it and ensure reproducible interaction with the sample.
2. Loading: The sample is passed through the sorbent. Analytes (or interferences) bind to the sorbent.
3. Washing: A specific solvent is passed through to remove weakly bound impurities while leaving the analytes of interest on the sorbent.
4. Elution: A different solvent is used to disrupt the analyte-sorbent interactions, releasing the purified and concentrated analytes for collection.  

Vacuum helps maintain a consistent and gentle flow rate, which is critical for effective separation and recovery.

• Pharmaceutical & Biotechnology: These sectors rely on vacuum filtration for critical sterile filtration of drug products and clarification of biological solutions. SPE is then essential for isolating and purifying active pharmaceutical ingredients (APIs) and metabolites during drug discovery, development, and quality control.
• Food & Beverage: The food and beverage industry uses vacuum filtration to clarify products like juices and wine, and for microbiological quality control. SPE plays a vital role in food safety by enabling the detection of contaminants such as pesticides or toxins, and for analyzing flavor and aroma compounds.

• Environmental Monitoring: Vacuum filtration is key for preparing water samples, for instance, by measuring suspended solids or for microbiological testing. Subsequently, SPE is crucial for extracting and concentrating pollutants like pesticides or industrial chemicals from water, soil, and air to ensure regulatory compliance.
• Chemical Manufacturing: In chemical production, vacuum filtration aids in separating solid products from reaction mixtures and in quality control of materials. SPE can be employed for purifying chemical intermediates or concentrating trace impurities for analytical verification of product purity.
• Clinical Diagnostics & Forensics: These fields utilize vacuum filtration for preparing biological specimens. SPE is indispensable thereafter for a wide range of applications, including toxicology screening, therapeutic drug monitoring, and the identification of drugs of abuse.

While both processes utilize vacuum, their specific needs can differ:

Based on the process needs, ideal lab vacuum pumps for these applications should have:

• Pump Type: Oil-free diaphragm pumps are strongly recommended. They are low maintenance, do not contaminate samples with oil, and can be designed for chemical resistance.
• Ultimate Vacuum:
  • Single-stage diaphragm pumps with an ultimate vacuum of around 70-100 mbar are often ideal for most filtration tasks.
  • Two-stage pumps, offering deeper vacuum (e.g., <10 mbar), can be used for SPE or to accelerate filtration with larger volumes or finer filters, but active vacuum control is highly advised.
• Chemical Resistance: For SPE and filtration involving organic solvents or acidic/basic solutions, pumps with fluoropolymer wetted parts (heads, diaphragms, valves) offer superior chemical resistance and vapor tolerance. These are often called chemistry diaphragm pumps.
• Vacuum Control: A manual vacuum regulator valve and gauge are highly beneficial, especially for SPE and when using two-stage pumps for filtration, to adjust and monitor the vacuum level.
• Accessories:
  • Inlet Catchpot (AK): Essential to protect the pump from accidentally ingested liquid droplets or particles.
  • Outlet Condenser/Separator (EK): Useful for capturing solvent vapors at the pump outlet, protecting lab air and the environment, and enabling solvent recovery.
• Automation: For high-throughput or repetitive tasks, chemistry pumping units equipped with electronic vacuum controllers can automate the process and ensure consistent conditions.

Tips to Choose the Best Laboratory Vacuum Pump for Filtration & SPE

• Assess Chemical Compatibility: Will you be working with aggressive solvents or corrosive chemicals? If yes, a chemistry diaphragm pump with fluoropolymer wetted parts is essential.
• Determine Vacuum Level Needs: For most filtration, ~100 mbar is sufficient. For SPE, precise control is more important than ultimate depth.
• Consider Pumping Speed: Larger filter setups, multiple SPE cartridges, or higher viscosity liquids may benefit from higher pumping speed.
• Evaluate Need for Control: SPE requires good vacuum control. For filtration with volatile solvents or when using deeper vacuum pumps, control is also important. Consider a pump with an integrated controller or add a manual regulator.
• Prioritize Oil-Free Operation: Diaphragm pumps avoid oil misting and sample contamination.
• Factor in Accessories: Always use an inlet catchpot. Consider an outlet condenser if working with significant solvent volumes.

BRANDTECH offers a wide range of oil-free vacuum pumps well-suited for filtration and SPE applications:

Please Note: All listed NT models represent an advanced generation with improved performance and durability. For precise control, especially with the two-stage pumps (ME 2C NT, ME 4C NT, ME 2 NT, ME 4 NT), consider pairing them with a manual vacuum regulator unit with a gauge or opting for a fully integrated chemistry pumping unit with electronic control for automated processes. Always protect your pump with an inlet catchpot (AK).