Cartridge Processing Options

The dense particle packing of the disks prevents liquids from freely flowing under gravity. Commonly used methods for processing samples through the cartridges include:

• Vacuum
• Positive Displacement
• Centrifugation
• Automated Liquid Handling Workstations

Vacuum Processing

A vacuum manifold is commonly used to draw liquids through the cartridge. Manifolds are available from several suppliers that can hold from 10 to 24 cartridges at once. Test tubes are placed below each cartridge position to collect liquids from each step.

Vacuum Manifold Assembly

Vacuum Recommendations

Empore™ standard density (SD) cartridges generally require about 10 -15 inches Hg (0.34-0.51 bar) vacuum in order to process biological fluids such as plasma and serum. Lower vacuum may be used for relatively clean samples of small volume. High density (HD) disk cartridges may require 17 – 20 inches HG (0.58 – 0.68 bar) to process samples.

Positive Displacement

Positive pressure displacement can be used for manual elution of the cartridges. One sample at a time is processed when the cartridge is attached to a syringe adapter that fits between the cartridge and the syringe. Air is forced through the cartridge and displaces the liquid. Good control of liquid flow can be achieved in this manner.

A single piece positive displacement device manufactured by Supelco eliminates the need for a separate adaptor.

Varian Sample Preparation Products and Krackeler Scientific, Inc. offer a positive pressure manifold for processing up to 24 cartridges at a time.

Centrifugation

Centrifugation is another option for processing samples through cartridges and is preferable to vacuum elution as it requires less manipulation and allows for more complete sample collection. With centrifugation, the cartridge conditioning is performed manually prior to suspending the cartridge in a suitable test tube and placement in the carrier tray of the centrifuge. Centrifugal forces of 75-120 G are suggested for loading and elution although higher forces can be employed. The effect on analyte recovery must be determined.

Centrifuge

Automated Liquid handling Workstations

Empore™ cartridges are suitable for use with most commercially available liquid handling workstations. These workstations use either positive pressure displacement or vacuum to move liquids through the cartridge and are ideal for improved throughput as the possibility of human error in pipetting and/or procedural error is eliminated.