Should I use a 2.7 or 5 µm Raptor column?
13 Oct 2014“When you come to a fork in the road, take it.” Maybe that advice worked for Yogi Berra, but does not help much in decisions about your lab equipment.
If you are not certain whether you should use a Raptor column, please read my previous blog post "What is SPP and when should I use a Raptor column?" before proceeding.
Once you have made the decision to take advantage of the benefits of SPP, your next question might be which particle size to use, the 2.7 or 5 µm Raptor. The 2.7 µm column provides higher efficiencies, but the column must be matched with an instrument that is appropriate, in terms of system pressure and internal dwell volume. These considerations are described below:
Primary Consideration- System Pressure
As is the case with a 3 µm fully porous particle, the 2.7 µm Raptor column will operate at backpressures a little higher than the corresponding column with a 5 µm particle size. Pressure is a function of particle size, as well as column dimensions, flow rate and solvent properties, but is not a function of porosity. The following is a good example of how you can expect flow rate and particle size to affect the column back pressure. Please keep in mind that methanol and water both have higher surface tension, which results in higher backpressure. The data shown here was generating using acetonitrile/ water mobile phase.
Although the earlier blog post Building Up Pressure on HPLC? was written for fully porous particles, you can still get a pretty good idea of how pressures are affected by column dimensions, particle size, and solvent content by looking at the table shown in the post. The optimal flow rates will be a little different for SPP columns. Though the “optimal” flow rate for a SPP column is not much different versus a fully porous column, the SPP columns maintain their efficiency over a broader range of flow rates. Here is a good illustration, using a Van Deemter plot.
Secondary consideration-Dwell Volume
There is another factor to consider when transferring your method to a 2. 7 µm Raptor, and that is the system dwell volume. In other words, dead volume in your LC system may negate the advantages of choosing a 2.7 µm SPP column over a 5 µm particle (either fully porous or SPP). This is of highest concern when using columns of smaller dimensions also. A symptom of excess dwell volume is be band broadening, and can be confirmed by running the same column on a system with less dwell volume. Although there are some system updates that can be made to reduce dead volume, the options are limited and it is simpler to start with a well-matched system and column from the beginning. Fortunately, LC systems with maximum pressures of about 600 bar (8700 psi) are usually also designed with a lower internal dwell volume relative to the lower pressure systems. This actually makes our choices a little easier. As a result of both considerations, we recommend using systems with a 600 bar maximum operating pressure for the 2.7 µm Raptor columns, particularly those with 3.0 mm ID or smaller.
Here are examples of some LC Systems with a maximum pressure of at least 600 bar (8700 psi). Again, we recommend using a system with a max pressure of 600 bar, or higher, for use with a 2.7 µm Raptor columns with ID of 2.1 or 3.0 mm.
- Agilent 1200 Series- RRLC models only
- Agilent 1220 & 1260 Infinity
- Shimadzu Prominence UFLC-XR models only
- Thermo Ultimate 3000 -Basic Manual, Basic Automated, Binary Analytical, x2 Dual analytical, and Quaternary Analytical models
- Thermo Ultimate 3000 -RSLC nano, RSLC Binary, and RSLC X2 Dual (~700 Bar limit)
- Perkin Elmer Flexar -FX-10 models only
- ABSciex/Eksigent - microLC 200, nanoLC-Ultra and nanoLC 400 (~700 Bar limit)
You can also use a 2.7 µm Raptor column with a UHPLC system, which typically has a maximum operating pressure limit of 1200 bar/17,000psi.
When to use the 5 µm Raptor
Your next question might be when or why you should use a 5 µm Raptorcolumn. The 5 µm particle size for this SPP column allows you to obtain results that resemble that of a 3 µm particle fully porous particle column on an HPLC system that has a maximum pressure of 400 bar/ 5800 psi or less (which is often too low to use a column with a 2.7 or 3 µm particles). There are also other advantages described in our article "The Effects of LC Particle Choice on Column Performance 2.7 vs. 5 µm Diameter Superficially Porous particles (SPP)", which I highly recommend reading, by the way. Here are just a few examples of some LC systems that could be optimized by using them with a 5 µm Raptor column:
- Agilent 1100 & 1200 Series (except models listed above)
- Varian 920-LC & 940-LC
- Waters Alliance and Breeze models
- Jasco 2000 Series
- Perkin Elmer Series 200 & 275
The above list is definitely not all inclusive and there are many I have not shown. Generally, the older HPLC systems are more likely to have a lower pressure rating and many of them have 400 bar limits. The best way to find out is to consult your instrument manual or contact the manufacturer of the instrument.
I hope this has been helpful. Many thanks to our Innovations Chemists, Ty Kahler and Sharon Lupo for the data provided. Thank you for reading.