Laserchrom HPLC - Shodex Silica Based Reverse Phase Columns

Shodex Silica Based Reversed Phase HPLC Columns

Silica based reverse phase (RP) columns are used for most HPLC methods. They have the advantage of being robust, able to withstand very high back-pressures (allowing higher flow rates and fast analysis), and ther are many published methods available. Columns differ from each other on several respects. Firstly the support silica. Original silica columns used what are known as "Type A" silicas. In the manufacturing process, traces of metal ions were trapped in the silica matrix. These contributed to band broadening, especially with polar compounds, but also sometimes helped with the separation. Newer silicas, known as Ultrapure silicas or "Type B" silicas, have these metal ions removed, and hence tend to give significantly sharper peaks, although sometimes they give less peaks! Endcapping is a secondary process used to react all residual silanol sites on the surface of the silica, giving a truly non-polar surface. Columns which are not end capped will give a very different selectivity, usually broader peaks, and very different retention times.

In order for comparison to be made with the polymer-based columns available, some of the other features of the silica-based reversed phase columns are listed below. Note a few general points for silica columns. The bonded phase is stripped off (the bonding is hydrolysed) below pH2 The silica will dissolve at an unacceptable rate over pH7. It also tends to dissolve more rapidly at high temperatures, in high buffer concentrations, and in highly aqueous eluents

Other features to note are:
Pore Size	The bigger the pore size the wider the range of molecular weight species that can be analysed, but the lower the maximum back pressure the column can withstand.
Particle Size	Typically 3-10 μm.
Efficiency	Some columns give sharper peaks than others
Solvent Range	Some columns are damaged by 100% water. Most are damaged by >0.5M buffer.
pH Range	Always pH2-7 for silica based columns.
Temp Range	Much less critical than with a polymer, but silica will dissolve quite rapidly at higher temperatures (esp 80C upwards!)
Max Pressure	Silica columns are packed at 8000psi upwards, so can withstand any normal HPLC system backpressure.
More information is available below or at the Shodex website www.shodex.com

Column Details

Packing	Particle Size (μm)	Pore Size (A)	Efficiency (N/m)	Functional Group	pH Range	Temp Range (oC)
ODSpak	5 3	100	56,000 100,000	C18	2-7	5-80
This is a conventional TypeA silica material, with a 14% carbon loading and fully end-capped. It is available in 3 and 5u particle size. For pricing and ordering information click here, or for more info see www.shodex.com
Silica C18M	5	100	70,000	C18	2-7	5-80
This is an ultrapure Type B silica, with a monomeric C18 bonded phase. (Each C18 chain is bonded on in one place only. This gives a very even coverage of the silica.) It has a 16% carbon load and is fully end-capped. This material would be expected to give sharper peaks than ODSpak, but sometimes, ODSpak resolves more peaks. The advanced total end-capping system used makes this material excellent for analysing basic substances and some metal complexes, where any trace of residual silanol sites would have cause peak tailing. For pricing and ordering information click here, or for more info see www.shodex.com
Silica C18P	5	100	70,000	C18	2-7	5-80
Also an ultrapure Type B silica, but with the c18 chain polymerically bonded to the silica. This means that the C18 chains are bonded to each other, and to the silica in more than one place. It causes a slighly denser coverage, and hence the carbon loading is slightly higher at 17%. But these columns are more resistant to having the bonded phase stripped off under acid conditions, and are recommended for separations of acidic species where low pH is required for ion suppression. For pricing and ordering information click here, or for more info see www.shodex.com
Silica 5C8	5	100	60,000	C8	2-7	5-80
An ultrapure Type B silica with a C8 chain and total end-capping. Recommended for use when C18 gives too long retention times. For pricing and ordering information click here, or for more info see www.shodex.com
Silica 5C4	5	100	60,000	C4	2-7	5-80
An ultrapure TypeB silica with a C4 chain and total end-capping. This column gives even shorter retention times than C8, so can be used for separating materials which bind strongly to C18, or which have a wide polarity difference. This column is less selective than C8 or c18, and hence the peaks may elute closer together. For pricing and ordering information click here, or for more info see www.shodex.com
Silica 5TMS	5	100	50,000	C1	2-7	5-80
An ultrapure type B silica with just trimethylsilane (TMS) bonded on. This is effectively a C1 column. This is much less non-polar than C8 or C18, and much less selective. It equilibrates really fast, and may be suitable for very non-polar samples which would otherwise bind very strongly to C18 and possibly require non-aqueous reversed phase. It may also be applicable where the polarity range is so wide that a gradient may otherwise have been required. we would be happy to try out applications for you. For pricing and ordering information click here, or for more info see www.shodex.com
Silica 5NPE	5	100	55,000	Nitrophenylethyl	2-7	5-80
This is an unusual material with a nitrophenylethyl bonded phase. It gives a very different selectivity, and has been found to be effective in separating stereoisomers. We would be pleased to try samples for you if required. For pricing and ordering information click here, or for more info see www.shodex.com
Silica 5PYE	5	100	55,000	Pyrenylethyl	2-7	5-80
Another unusaul material, this time with a pyrenylethyl bonded phase. It too gives a very different selectivity, and has been found to be effective in separating stereoisomers. We would be pleased to try samples for you if required. For pricing and ordering information click here, or for more info see www.shodex.com