HPLC instruments, major manufactures

The majority of HPLC instruments use pumps based on alternating pistons. In order to avoid variations in the flow rate that are caused by single piston pumps (solvent in/solvent out), manufacturers have developed pumps that use two pistons. These pumps can be classified into two categories series and parallel. 

Major manufacturers of HPLC instruments include Waters, Agilent (formerly Hewlett Packard), and Shimadzu, PerkinElmer, Thermo, Beckman, Varian, Hitachi, Jasco, Dionex, Gilson, Scientific Systems (SSI), and Isco. The Internet addresses of these companies can be found in the reference section. HPLC is a mature technology and most manufacturers have highly reliable products with sufficient performance and feature sets to be competitive in the market place. However, there can still be significant differences between the vendors on these performance characteristics on systems (dwell volume, dispersion), pumps (low flow, seal life), autosamplers (carryover, speed, sample capacity, minimum sample volume), and detectors (sensitivity, gradient baseline shift). 

The selectivity of a chromatographic method is determined by the column stationary phase chemistry and the mobile phase composition consequently, it is advisable to keep the mobile phase and column chemistry the same when the method is transferred between HPLC and UHPLC. This means that in labs where exchange of methods between instrument types is anticipated, chromatographers are advised to choose column brands where both UHPLC and HPLC columns with the same stationary phase chemistry are available. Table 3.7 lists the column brands currently provided by the major manufactures. It can be seen that not all brands carry both columns packed with the conventional 3-5 xm and the sub-2 xm particle sizes. Within each brand, not all stationary phases are available in both platforms. In such situations, column equivalence assessment needs to be performed to find the best alternative column by using tools such as the reversed-phase colunm selectivity charts available from column vendors. 

In the late 1970s, Hewlett-Packard introduced the HP-3300 series data-acquisition system, which was able to connect to 60 chromatographic instruments through an A/D converter. This was the beginning of what would become a revolution in CDS development within the analytical instrument industry. By the mid-1980s, all of the major analytical instrument manufacturers offered network-based data-acquisition systems Beckman, HP, PE, VG, and Waters. These were multi-user, time-sharing systems that used A/D converters to acquire data from the instruments. Instrument control, both HPLC and GC, was a capability that would soon follow. Several CDS manufacturers offered serial control of the HP 5890 GC while Waters also offered instrument control for their own HPLCs. 

The second drawback of NMR is that it cannot be easily interfaced with modern chromatographic separation techniques. Thus GC (gas chromatography), HPLC (high performance liquid chromatography), SFC (supercritical fluid chromatography), and CZE (capillary zone electrophoresis) are all routinely interfaced with MS but not with NMR, although the major instrument manufacturers JEOL (Japan), Varian (USA), and Bruker (Germany) have now developed NMR probes compatible with HPLC columns. If NMR spectra of individual components of a mixture are required then the mixture usually has to be... 

Most modern instrumentation will meet these requirements. During the last 20 years or so the hardware of most manufacturers has become comparable in reliability, performance and durability. The ease with which chromatograms (and spectra in PDA detection) can be evaluated, therefore, should be the major criterion for selecting a new HPLC system. The ease of software handling and its capabilities appear to be the most important issues of concern. 

As we have seen in this book, three developments appear to have provided the necessary momentum, and all three are still works in progress . The first was the development of TOF instruments, which could accomodate electrospray ionization by using orthogonal extraction or combining ion trapping with the TOF analyzer, which led to the possibility of carrying out on-line HPLC analysis. Considerable improvements are required to enable ESI-TOF instruments to be commercially competitive with existing quadrupole (and triple quadrupole) ESI mass spectrometers, but this is sure to be a major focus of development by both University laboratories and instrument manufacturers. 

In terms of instrumentation, the only other part of the HPLC column system that requires consideration here is the temperature control module of the column. Most of the early workers obtained high-performance separations at room temperatures with the columns exposed to the laboratory as shown in Figure I. However, by 1969, Maggs (10) had concluded from his studies that it was necessaiy to control the column temperature to within 0.2°C if repeatability of retention volumes was to be maintained within 1 %. The fact that many workers have not thermostatted their HPLC columns and yet have obtained reproducible separations is probably due to the fact that many air-conditioned laboratories maintain ambient temperature to within 1 °C. Since the majority of HPLC separations are performed at room temperature, column temperature control modules are therefore still regarded by many HPLC manufacturers as an c jtional extra (7) and one such is shown in Figure 9. 

There are a variety of HPLC columns used in the pharmaceutical industry. To convert HPLC methods to UHPLC, one should always contact the HPLC column vendors to see if they provide UHPLC columns with the same chemistry. The major UHPLC instrument manufacturers such as Waters Cor. (Milford, MA) and Agilent Technologies, Inc. (Santa Clara, CA) also provide some UHPLC columns with the same chemistry of their HPLC columns. Table 1.5 lists some examples. 

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