Today the demands of separation devices are higher than ever before. Increasing productivity in high performance liquid chromatography (HPLC), through higher sample throughput and reduced analytical time, is one of the major challenges with which analysts are faced.
Dr W. Kraas reports.
The most commonly used HPLC standard column of 125 or 250mm in length, approximately 4mm inner diameter and filled with 5µm modified silica particles, requires a considerable amount of analysis time and solvent consumption for successful chromatographic separation.
The introduction of high sample throughput devices, the automation of separation procedures and the use of modern technologies, such as LC-MS technology, forced a lot of analysts to look for alternative stationary phases and instruments to keep pace with these demands.
The first generation of conventional manufactured silica gels was mainly prepared from water glass (alkaline silicate).
Avoiding contamination
One of the major problems was the impossibility of avoiding metal contamination when using water glass as the silica source.
The metal impurities remain on the surface and, even more seriously, inside the network of the silica structure. This can cause peak tailing or even irreversible adsorption especially of chelating and basic compounds (Fig. 1).
To overcome this problem researchers started to find alternatives in preparing silica gel particles. The introduction of high-purity silica as base material for the development of new stationary phases has been one of the most important improvements during the past 10 years.
Reduced separation time
Short (30mm and 55mm in length) columns significantly reduce separation time. Prior to the development of these new sorbents, short columns gave very poor separations.
However this new type of column, with 3µm particle size, provides the HPLC user both with excellent separations performance and advantages regarding time, solvent consumption, reproducibility and stability.
In comparison with the conventional columns of 250mm length, the separation time can be reduced by the factor of 4,5 when using 55mm cartridges and even by a factor of 8 with 30mm.
But not only time can be saved by using short columns, there is additionally the lower solvent consumption which has to be taken in consideration. This not only reduces the initial costs of solvents but also reduces significantly the costs associated with waste disposal.
The use of modern chromatographic material, such as Purospher Star RP-18e, 3µm, combine the properties of one of the best highly pure silica materials with a complete cross linked reversed phase modification.
Conclusions
In summary, we can conclude that new highly pure silica gel Purospher chromatography columns are for the separation of numerous complex compounds (eg basic, acidic or metal chelating). These columns therefore provide the HPLC user with a standard column of incredible versatility, therefore reducing significantly the number of different columns needed.
Combined with the significant advantages of reduced separation time per analysis, greater sample throughput as well as the financial savings in solvent and waste disposal costs, new high speed HPLC columns can make a very important contribution to increasing laboratory productivity and efficiency.
Enquiry No 43
Dr W. Kraas is with Merck, Daemstadt, Germany.
