Ultra-High Performance Liquid Chromatography a milestone in the evolution of LC in that columns packed with <2µm particles, used with instrumentation capable of handling the resulting high back pressures, make possible extremely fast and efficient separations. UHPLC is a very powerful tool for today’s practicing chromatographer, as it can significantly increase the efficiency of a chromatographic separation. In addition, the wider range of usable flow rates makes high speed separations possible.
Effect on efficience
The lower the particle size, the higher column efficience is (see graph below). With particle size decrease the column back pressure increases significantly. This leads to ultra high pressure of longer LC columns. It means that we cannot use 1,9µm UHPLC column the same lenth like 5µm column (eg. 250 mm long column). In the end we have lower or similar column efficieny as we have with standard HPLC columns. The main benefit of the UHPLC columns is the analysis run time, not the efficiency.
If you need to increase efficiency, look at phase chemistry first. In this case look at stationary phase list.
Many GC and LC problems can be avoided with routine preventive maintenance. If you are seeking the cause of the chromatography problem, go step by step. Never make more changes in your instrument at the same time, otherwise you will never find, what caused the problem.
Select your category of chromatography to read more about the troubleshooting: (GC troubleshooting is not available yet)
Resprep™ QuEChERS Products
QuEChERS Tubes For Extraction and Clean-Up of Pesticide Residues From Food Products
- Fast, simple sample extraction and cleanup using dSPE.
- Fourfold increases in sample throughput.
- Fourfold decreases in material cost.
- Convenient, ready to use centrifuge tubes with ultra pure, preweighed adsorbent mixes.
Quick, Easy, Cheap, Effective, Rugged, and Safe, the QuEChERS ("catchers") method is based on work done and published by the US Department of Agriculture Eastern Regional Research Center in Wyndmoor, PA.(1) Researchers there were looking for a simple, effective, and inexpensive way to extract and clean pesticide residues from the many varied sample matrices with which they routinely worked. They had been using the Modified Luke Extraction Method, which is highly effective and rugged, but is both labor and glassware intensive, leading to a relatively high cost per sample. Solid phase extraction also had been effective, but the complex matrices the investigators were dealing with required multiple individual cartridges and packings to remove the many classes of interferences, adding costs and complexity to the process. A new method would have to remove sugars, lipids, organic acids, sterols, proteins, pigments and excess water, any of which often are present, but still be easy to use and inexpensive.
The researchers developed a simple two-step procedure. First, the homogenized samples are extracted and partitioned, using an organic solvent and salt solution. Then, the supernatant is further extracted and cleaned, using a dispersive SPE technique. Multiple adsorbents are placed in a centrifuge tube, along with the 1mL of organic solvent and the extracted residues partitioned from step 1. The contents are thoroughly mixed, then centrifuged, producing a clean extract ready for a variety of GC or HPLC analytical techniques.(2) Validation and proficiency data for the QuEChERS method are available for a wide variety of pesticides in several common food matrices at www.quechers.com.
Using the dispersive SPE approach, the quantity and type of adsorbents, as well as the pH and polarity of the solvent, can be easily adjusted for differing matrix interferences and "difficult" analytes. Results from this approach have been verified and modified at several USDA and Food and Drug Administration labs, and the method now is widely accepted for many types of pesticide residue samples.
Restek products make this approach even simpler. The centrifuge tube format, available in 2mL and 15mL sizes, contains magnesium sulfate (to partition water from organic solvent) and PSA* adsorbent (to remove sugars and fatty acids), with or without graphitized carbon (to remove pigments and sterols) or C18 packing (to remove nonpolar interferences). Custom products are available by quote request. If you are frustrated by the time and cost involved with your current approach to pesticide sample cleanup, we suggest you try this simple and economical new method.
We have products compliant with AOAC, Multi-miniresidue and Draft European methods.
Inforamtion about products is available here.
- Anastassiades, M., S.J. Lehotay, D. Stajnbaher, F.J. Schenck, Fast and Easy Multiresidue Method Employing Acetonitrile Extraction/Partitioning and "Dispersive Solid-Phase Extraction" for the Determination of Pesticide Residues in Produce, J AOAC International, 2003, vol 86 no 22, pp 412-431.
- Schenck, F.J., SPE Cleanup and the Analysis of PPB Levels of Pesticides in Fruits and Vegetables. Florida Pesticide Residue Workshop, 2002