The Column - August 2008 - (Page 16)

Incognito The Column www.thecolumn.eu.com August 2008 Epoxy/Getty Images The Generic Generation I was recently asked by a client to develop a “generic” solidphase extraction and LC–MS method for a category of low molecular weight basic drug molecules from various physiological matrices. This wasn’t a particularly unusual or surprising request, however it did remind me of my deep seated unease at anything “generic” within analytical science and the rapid increase in the frequency with which I come across this term. The Oxford English Dictionary of “generic” is — “belonging to a genus or class; applied to a large group or class of objects; general (opposed to SPECIFIC or SPECIAL).” While I really don’t want to enter into a semantic discussion here — I was being asked to develop a “non-specific” SPE method. I, therefore, began to consider the use of a polymeric resin-based sorbent as these are often used to develop widely applicable SPE protocols (a quick Google search revealed over 140 relevant hits with the terms “SPE”, “generic” and “polymeric” or “resin” in the body text). These polymeric sorbent materials are designed to incorporate several functional group types that can efficiently retain structurally related compound classes. I have used them in previous development work and my strong feeling is that they produce significantly dirtier extracts than other materials, such as mixed mode silica-based sorbents. The premise of these polymeric materials is to retain a wide(r) range of analyte types using a variety of interactions — and so will, therefore, by definition also retain more interferents without (as far as I have been able to tell) any novel way of discriminating between analyte and interferent during the wash or elution protocol steps. So why, then, are these materials so popular? Recent data I received from a prominent vendor showed polymeric sorbent sales growing three times faster than silica sorbents. I suggest that the use of “generic” sorbent materials arises from one of a number of imperatives: the need for high throughput analytical methodology; a lack of skilled method developers with enough subject knowledge to develop more specific protocols; lack of time to develop such protocols; cost savings in rationalizing the number of solvents and sorbents required — I could go on. Are we now prepared to accept a Author: Incognito E-mail: incognito@thecolumn.eu.com larger amount of lower quality data, or a reduction in our fundamental understanding, so long as we can generate a number in a table of results? My worry is that we are heading towards this situation and are “dumbing down” our analytical methods (even poor methods may validate!). The question I am posing here is: “Do we fully understand the implications of the “generic” approach and its effects on data quality?” Further examples of this approach that I have recently encountered serve only to reinforce my concerns and I have highlighted two typical examples below: “Generic” LC–MS conditions: This term is nonsense, especially in electrospray (ESI) mode, yet I know of many laboratories who rarely optimize their interface parameters. Different nebulizing voltages, pneumatic assistance gas flows and drying gas flows are required to optimize ionization efficiency when changing flow-rate, organic modifier type or the buffer strength of the eluent. Further, the effects of changing (optimizing!) eluent pH can be staggering when dealing with ionizable analytes and often small changes in pH can lead to very large differences in MS sensitivity. The use of eluent systems containing 0.1% TFA or equivalents of acetate or formate buffers, is another excellent example of the “generic” approach. A 0.1% solution of TFA has a pH of around 2.1 — ensuring most basic analytes will be fully protonated in solution and will, therefore, give a strong electrospray response and rugged HPLC separations. I’ve seen these eluent systems being used to analyse samples containing both acidic and basic analytes — however, this is the “generic” screening method and must be used. Problems arise when the end user doesn’t understand that the poorly retained small peaks at the start of the chromatogram are actually important acidic analytes. Unless the analytes are chemically very similar and the eluent systems identical, then a generic LC–(ESI) MS method, which gives a satisfactory separation with good general MS sensitivity, will be very elusive. “Generic” HPLC method development strategies: Usually involving a set of four to six analytical columns under which the test samples are analysed using “scouting” gradient conditions and the data subsequently (or dynamically) processed using optimization software. I must say here that 16 http://www.thecolumn.eu.com

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

The Column - August 2008
Contents
Pesticide Residues in Fruit and Vegetables - From Avocados to Zucchinis
News
Incognito
Market Trends and Analysis
Tips and Tricks: GPC/SEC What are The Applications for Polymer Reference Standards?
Transferring Existing HPLC Methods to MicroLC
Q&A

The Column - August 2008