The Column - March 2008 - (Page 9)

March 2008 www.thecolumn.eu.com The Column Zosimus Never Mind The Selectivity — Look at the Plate Count! I have recently been more heavily involved in the practice of so called “Fast HPLC” and the experience has caused me to question the actual benefits of this technology in the “real world”. It is true that there has been an almighty clamour to jump on the “Fast” HPLC band wagon from the majority of instrument and column manufacturers — but we need to question the science and actual benefits derived from recent “advances”. The premise, with the exception of solid core type particle technologies, is that by reducing particle size (usually to under 2 µm in diameter), the resistance to mass transfer (van Deemter’s “C” term) is reduced — thus reducing plate height and in most instances flattening the plate height versus linear velocity (van Deemter) curve. This effectively allows higher flow-rates to be used without appreciable loss in efficiency, resulting in the possibility of equivalent separations within shorter timescales. So the equipment and the column technology exist and are pretty well established — but do we really know how to best implement this technology into our workflow and are we using the technology to best effect? A senior industrial scientist I spoke to recently, who had just had a demonstration of this technology had some serious doubts. The plate count on the column she was shown was approaching 50000. However, as she pointed out the selectivity of the C18 material for her analytes was not great. For sure the separation had been achieved, but perhaps a phase with a different selectivity could have achieved something similar without having to resort to a high pressure “Fast LC” solution. I believe we are setting a dangerous precedent here in that surely we can have all the efficiency possible, however, without the basic ability to “chemically” distinguish between analytes, with HPLC we are nowhere. Even high resolution capillary GC needs to have 5–10 broad categories of chemically different phases to achieve the range of separations we demand of it! So, is “Fast LC” a dumbing down of the noble art of HPLC? Maybe soon all our analysts will not bother looking at different stationary phases and solvent combinations and simply take a C18 column and turn the plate count to “max”. I think that would be a sad day. Author: Zosimus E-mail: zosimus@thecolumn.eu.com One certainty is that manufacturers should be prepared to offer their full range of chemistries in sub-2 µm or “Fast” column formats, then the process of screening phases for a particular separation will become very much quicker and running screening gradients for submission to in-silico prediction software will be much shorter, hence making the process of phase selection very much faster — hurray a tangible benefit!! Further, the length of the actual HPLC analysis itself is not the bottle neck in every laboratory nor even most laboratories. Instrument preparation time, sample preparation, mobile phase preparation and preparation of standards can all be significant brakes on increasing productivity. Lengthy post analysis processing of the results can also make any savings in analysis time rather irrelevant. Take for instance the practice of taking peak areas from chromatography data systems and using spreadsheets to calculate the results from overly complex formulae — a practice I see used a lot, when the power of most chromatography data systems surely renders this old fashioned and time consuming process redundant. And so finally… on this subject, just exactly how fast do we need to be and does the increase in speed of analysis have a direct link to the complexity and robustness of equipment required to drive high speed and subsequently pressure separations? Well — let’s take an analogy from the motor industry — the Guinness Book of Records states that the fastest production road car in the world is the SSC Aero (Shelby Super Cars) achieving 0–60 mph in 2.78 seconds with a top speed of 257 mph. It costs $239000 and, apparently, will need a partial engine rebuild every 1000 miles. My concern as I place my order for the Aero is — will I be able to realize it’s true potential on UK roads and will Mrs Zosimus really fully appreciate the return on our investment? Anyone out there with the SSC Aero of Fast HPLC systems who is realizing full potential and can demonstrate extended service intervals should feel free to present their case to me — I’ll publish their results as the fastest production HPLC system in the world! 9 http://www.thecolumn.eu.com

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

The Column - March 2008
Contents
News
Zosimus - Never Mind the Selectivity - Look at the Plate Count!
HPLC Analysis of Lysozyme in Different Types of Wine
Market Trends & Analysis
A Holistic Approach to Increasing Analytical Throughput on a Modern Gas Chromatograph
If It's Broke, Fix It - Q&A
The Applications Book
LC World Talk - Shimadzu's Newsletter for the HPLC Global Community
LC World Talk Contents
Applications of Ultra Fast HPLC
The World's Most Advanced Liquid Chromatograph
2D-HPLC for Bioanalysis "Co-Sense for BA" System
Metabolite Identification Software

The Column - March 2008