The Column - December 2008 - (Page 18)

Knöfel and Marten The Column www.thecolumn.eu.com December 2008 Lauren Nicole/Getty Images UHPLC for the Analysis of Paracetamol Anke Knöfel and Silvia Marten, Applications and Columns Department, Knauer, Berlin, Germany. Increased efficiency is always required in the laboratory. This can be achieved in liquid chromatography (LC) using short separation columns in combination with small particles. Compared with classical HPLC, ultra high performance liquid chromatography (UHPLC) systems require specially optimized equipment and low system volumes, high data acquisition rates and the ability to work at high back pressures up to 1000 bar. The performance of this new technology in practice is illustrated with the analysis of paracetamol and its accompanying by-products and degradation products. The UHPLC method developed using a fast gradient means the analysis time for a complex mix of substances can be reduced to less than 2 minutes. Whether a particular analytical method is used to determine the content and purity of active pharmaceutical substances depends on a variety of criteria. Sensitivity (low detection and quantification limits), selectivity, robustness, analysis time and costs play a deciding role. Changing over from established high performance liquid chromatography (HPLC) methods and taking particular factors into account goes a long way towards meeting the required demands. Why should short columns and small particles ( 2 µm) be used? The effect of smaller particle sizes when it comes to significantly higher chromatographic performance is demonstrated in the empirical van Deemter equation.1 It describes the relationship between height equivalent to a theoretical plate (HETP) and linear rate. Particle size is one of the critical factors in achieving an increase in efficiency. If Authors: Anke Knöfel and Silvia Marten Contact: knoefel@knauer.net / marten@knauer.net columns with a low (HETP) are used at high linear flow-rates, there is no loss of separation efficiency. Clearly, analysis times can be reduced in this way many times over. The HPLC system must satisfy certain requirements to take advantage of the benefits of higher resolution, increased sensitivity and the higher throughput associated with this column technique. First, it must be taken into account that sub-2 µm particles allow less to pass through the column bed. According to Darcy’s Law, the back pressure of a full column increases by the square of the reciprocal of the particle diameter, while the pressure drop decreases linearly with the length of the column. Thus, there is a significantly higher back pressure when small particles are used, despite the shorter columns. As for the HPLC pump, it is required to handle pressures up to 1000 bar. 18 http://www.thecolumn.eu.com

Table of Contents for the Digital Edition of The Column - December 2008

The Column - December 2008
Contents
Do Wrinkle Creams Really Work?
News
Incognito
Market Trends and Analysis
Tips and Tricks: GPC/SEC
UHPLC for the Analysis of Paracetamol
Q&A

The Column - December 2008