Quantitative HPLC Analysis for Chemists – Open Access

During early phases of chemical development it can be difficult to get a good handle on the performance of reactions and processes in the absence of developed analytical methods.  Most often we have to rely on the initial analytical methods and comparison of area% values, so true quantitation is not being discussed, with of course the risk that relative response factors could result in chemists being mis-directed.

Phil Borman et al of GSK published an article in the October 2010 edition of Pharmaceutical Technology (Supplement to October 2010 edition, page s6) in which they describe the approach taken at GSK which has resulted in efficient open access system that enables chemists to acquire quantitative data with good accuracy and precision.  This strategy has a number of advantages to the development team, including of course allowing chemists to promptly gain an understanding of the mass balance of their process whilst taking some of the pressure of their analytical colleagues as they strive to identify and develop the finalised analytical method(s) for the processes.

The authors comment that during 2009, there were about 2000 quantitations for yield in solution carried out by chemists at GSK’s UK site in Stevenage.  There were far fewer analyses done by chemists to get assay data for isolated solids or concentrates (ca 50 quantitations).  This is of course in addition to data provided by analytical colleagues.  Moreover, they comment that the methods developed at GSK result in chemists getting data that was typically (more than 90% of the time) within ±3%w/w of the true value where a trained analyst would get to within about ±0.5%w/w of the true result.  Notwithstanding this, the level of accuracy for chemists on an open access system is generally adequate to help guide the development effort and of course screen out samples that need not then be submitted for more formal assessment.

The approach is simple:

• Typically they use benzophenone as an external standard added to the analyte solution
• Prepare a good quality sample of your analyte
• Obtain the relative response factor between benzophenone and the analyte
• Use this data for subsequent analyses, taking known amounts of analyte solution and using known amounts of benzophenone to derive the amount of target product in the analyte matrix

The paper discusses a number of issues they overcame and checks they have incorporated into the system to allow chemists to readily apply the general approach and guard against errors due to things such as equipment malfunction – for instance the system runs a series of test mixtures first thing in the morning and if any fall outside the acceptable ranges a message is automatically sent to a ‘duty analyst’ to come and resolve the issue before chemists risk generating erroneous data.  They developed the protocols to allow analyses of reaction solutions, crystallising mixtures to determine end-points as well as more dilute solutions (as one might get in mother liquors or extractions) so a wide range of options are covered for determining mass balance and supporting effective and efficient process development.