HPLC systems trends

Several HPLC system trends highlighted below have become evident in recent years. 

Summary Sheet for HPLC Since all 10 calibration results are very close to 100% and no trend is apparent, the HPLC system is regarded as being in control. ... 

Davankov, V. A., Separation of enantiomeric compounds using chiral HPLC systems. A brief review of general principles, advances, and development trends, Chromatographia, 27, 475, 1989. 

Experiments have been performed on a preparative SFC system using pure CO2 as the mobile phase under significant pressure drop. The retention times, pressure drop characteristics and the mass transfer behaviour were studied. The trends observed differ from the behaviour of HPLC systems. These trends also emphasize the complexity involved in analyzing the data for SFC measurements, which imply in turn greater complexity of the SFC model as compared to standard liquid chromatography model. 

There are two major disadvantages to attaching a mass spectrometer to a preparative HPLC system. The first disadvantage is cost. An autoprep system may be purchased for approximately 30,000 but the corresponding MS-prep system costs approximately 150,000. However, because the mass spectrometer is a very sensitive detector and the sample concentration will be very high, an older, possibly redundant mass spectrometer may be redeployed for this task. It should also be noted that the price of mass spectrometers is falling rapidly and this trend appears to be continuing. 

Sensitivity, which is defined as a measure of the minimum amount of sample that can be detected, is often a major concern. Sometimes these problems can be resolved by employing a fluorescence or electrochemical detector and/or preparing a derivative of the analyte. True microbore (i.e. coliunn i.d. < 1.0 mm) HPLC systems can provide gains in sensitivity but these are not used extensively in forensic laboratories mainly because of practical problems associated with reproducibility and short column lifetimes. However, there is a trend towards using narrow-bore columns of 2-3 mm i.d. 

High-performance liquid chromatography (HPLC) is a versatile analytical technique using sophisticated equipment refined over several decades. An in-depth understanding of the working principles and trends is useful for more effective application of the technique. This chapter provides the reader with a concise overview of HPLC instrumentation, operating principles, recent advances, and modern trends. The focus is on the analytical scale HPLC systems and modules (pump, injector, and detectors). System dwell volume... 

Low-dispersion HPLC systems are necessitated by the increasing trend of using shorter and narrower HPLC columns, which are more susceptible to the deleterious effects of extra-column band-broadening. HPLC manufacturers are designing newer analytical HPLC systems with improved instrumental bandwidths compatible with 2-mm i.d. columns by using micro injectors, smaller i.d. connection tubing, and detector flow cells. A new generation of ultra-low dispersion systems dedicated for micro and nano LC is also available. 

Accurate data acquisition is essential for successful metabolic studies. The current trend from HPLC-based to LC/MS/MS-based analytical tools in ADME research, particularly in the pharmaceutical industry, demonstrates this requirement for accurate data acquisition. General aspects of the operation of LC/MS/MS are described below, together with a brief overview of traditional HPLC systems. 

An overview of HPLC instrumentation, operating principles, and recent advances or trends that are pertinent to pharmaceutical analysis is provided in Chapter 3 for the novice and the more experienced analyst. Modern liquid chromatographs have excellent performance and reliability because of the decades of refinements driven by technical advances and competition between manufacturers in a two billion-dollar-plus equipment market. References to HPLC textbooks, reference books, review articles, and training software have been provided in this chapter. Rather than summarizing the current literature, the goal is to provide the reader with a concise overview of HPLC instrumentation, operating principles, and recent advances or trends that lead to better analytical performance. Two often-neglected system parameters—dwell volume and instrumental bandwidth—are discussed in more detail because of their impact on fast LC and small-bore LC applications. 

The trend is toward multiple hyphenation techniques like HPLC-UV-MS and HPLC-UV-NMR. These have an enormous potential for the rapid investigation of plant extracts. Multiple hyphenation in a single system provides a better means of identification of compounds in a complex matrix. 

The trend toward automatic injection will become predominant with increasing routine application. Currently, satisfactory injection devices are only available for GC septum injection from Hewlett-Packard, Varian, etc. These have been adapted to HPLC with good results [6] within the general limitations of septum injection. Automatic injection usually results in better reproducibility with relative standard deviations of less than 1% and external standardization can be used [6]. Automatic systems based on loop injection have been announced by several manufacturers, e.g. DuPont, Varian, Altex. 

In summary, the requirements of selectivity show that the relative velocity difference V/V must remain substantial, but Eq. 9.17 tells us that the velocity increments must occur over a short distance d. As the distance d between velocity extremes decreases, the shear rate and the pressure gradient needed to generate high shear increases. Thus a trend to increasing pressure drops in F(+) systems is a natural outgrowth of these basic considerations. Again the most direct confirmation of theory is HPLC, where pressures of several hundred atmospheres are common. 

Rekker, R.F. and de Vries, G. (1993). A Basic Confrontation of Rekker s Revised 2f-System with HPLC Retention Data Obtained on a Mixed Series of Aliphatic and Aromatic Hydrocarbons. In Trends in QSAR and Molecular Modelling 92 (Wermuth, C.G., ed.), ESCOM, Leiden (The Netherlands), pp. 132-136. 

The antioxidant activity of a compound depends upon which free radical or oxidant is used in the assay (Halliwell and Gutteridge, 1995), and a different order of antioxidant activity is therefore to be expected when analyses are performed using different methods. This has been demonstrated by Tsuda et al. (1994) in their study of antioxidative activity of an anthocyanin (cyanidin-3-O-p-D-glucosidc) and an anthocyanidin (cyanidin) in four different lipophilic assay systems. Both compounds had antioxidative activity in all four systems, but the relative activity between them and their activity, compared with Trolox, varied with the method used. Fukumoto and Mazza (2000) reported that antioxidant activity of compounds with similar structures gave the same trends, although not always the same results, when measured by P-carotene bleaching, DPPH and HPLC detection of malonaldehyde formation in linoleic acid emulsion. 

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