Column technology

Scotts technology (17) uses fluid-bed (Wurster column) technology to apply polymeric coatings to a number of fertilizer substrates including urea, potassium nitrate, potassium sulfate, and monoammonium phosphate (MAP). The coating material is appHed as a water-borne latex onto the fluidized substrate. As the substrate is fluidized with warm air (40—50°C), water is driven off and the latex coalesces into a continuous film around the fertilizer particle. The particular latex compositions used have selected glass-transition and blocking temperatures, which enable quick removal of the water before the soluble fertilizer core dissolves. This obviates the need to use precoats prior to the latex appHcation. 

PSS columns for organic eluents PSS SDV columns are based on proven styrene-divinylbenzene type sorbents with improved sorbent characteristics and column technology. 

This chapter illustrates the improvements in SEC column technology and modern applications of SEC separations. The better understanding of SEC column design and separation parameters described in the theoretical sections of this chapter will help the reader fine-tune his or her own work. The same is true for column performance tests, which should be applied regularly, especially after a column purchase. In order to obtain reproducible results, it is recommended to choose column manufacturers who can assure constant quality and performance and to invest in knowledgeable, well-trained support personnel and experienced application chemists. 

More and more interesting and specialized SEC columns will appear on the market in the near feature, enabling us to do our work more reliably and efficiently. However, the author does not expect quantum jumps in SEC column technology in the next decade, which have been seen since the late 1970s. 

Whereas for organic SEC column technology a particular type of bead (PS/ DVB) is used almost universally, in the field of aqueous SEC there have been a variety of approaches to derive polymeric beads suitable for the application. For this reason there is more secrecy about the chemical composition of the packing materials and columns produced by different manufacturers. 

The instrumentation of HdC, including a pump, an injector, a column (set), a detector, and a recorder or computer, is very similar to size exclusion chromatography SEC). The essence of this technique is the column. There are two types of HdC columns open microcapillary tubes and a nonporous gel-packed column. This chapter emphasizes column technology and selection and the applications of this technique on the molecular weight analysis of macromolecules. 

SFC has been performed with either open capillary columns similar to those used in GC or packed columns transferred from LC, and the instrumentation requirements differ for these two approaches [12]. This chapter will focus on the use of packed column technology because of its dominance in the area of pharmaceutical compound separations. Current commercial instrumentation for packed column SFC utilizes many of the same components as traditional LC instruments, including pumps, injection valves, and detectors. In fact, most modem packed column SFC instm-ments can also be used to perform LC separations, and many of the same stationary phases can be used in both LC and SFC [9]. 

Little has been said concerning the column diameter which, unfortunately, is an aspect of column technology that involves extensive theoretical discussion which is probably not appropriate here. Each column that is optimized to analyze a particular sample in the minimum time and with the minimum solvent consumption will also have an optimum diameter. The optimum column diameter... 

Fast chromatography involves the use of narrow-bore columns (typically 0.1-mm i.d.) that will require higher inlet pressures compared with the conventional wide-bore capillary columns. These columns require detectors and computing systems capable of fast data acquisition. The main disadvantage is a much-reduced sample loading capacity. Advances in GC column technology, along with many of the GC-related techniques discussed below, were recently reviewed by Eiceman et... 

Continuous Improvements in column technology have made many of the early studies on column preparation obsolete. We will present only a brief account of these older methods in the following sections. For a more extensive view of the evolution of column technology standard texts [136-142] and review articles [35,143-146] should be consulted. 

The most common types of preparative-scale gas chromatographic instruments are based on pacXed column technology [489-491]. The primary objective in preparative-scale gas chromatography is to obtain a high sample throughput. An inevitable result of this goal is that either resolution or separation time, or both, must be compromised. The primary method... 

Spherical microparticles have been preferred in modem column technology since they form more hMiogeneous, stable and permeable column beds. Irregular microparticles are less expensive and still widely used, largely because in practice, it has not been shorn that their properties are significantly inferior. Particle shape may become more important as the particle size is reduced, and spherical microparticles are considered superior for particle dieuaeters less than 5 micrometers [33]. 

Upon substitution of the reduced parameters given above the separation time for a packed column and an open tubular column would be Identical if d 1.73 dp given the current limitations of open tubular column technology the column diameter cannot be reduced to the point %diere these columns can compete with packed columns for fast separations. This is illustrated by the practical txanple in Figure 6.3 (57). Ihe separation speed cannot be Increased for an open tubular column by increasing the reduced velocity since the reduced plate height is increased... 

Implementation of SFC has initially been hampered by instrumental problems, such as back-pressure regulation, need for syringe pumps, consistent flow-rates, pressure and density gradient control, modifier gradient elution, small volume injection (nL), poor reproducibility of injection, and miniaturised detection. These difficulties, which limited sensitivity, precision or reproducibility in industrial applications, were eventually overcome. Because instrumentation for SFC is quite complex and expensive, the technique is still not widely accepted. At the present time few SFC instrument manufacturers are active. Berger and Wilson [239] have described packed SFC instrumentation equipped with FID, UV/VIS and NPD, which can also be employed for open-tubular SFC in a pressure-control mode. Column technology has been largely borrowed from GC (for the open-tubular format) or from HPLC (for the packed format). Open-tubular coated capillaries (50-100 irn i.d.), packed capillaries (100-500 p,m i.d.), and packed columns (1 -4.6 mm i.d.) have been used for SFC (Table 4.27). 

Scheme 4.5 illustrates HPLCphase selection. Column manufacturers may have an applications database from which they can recommend a column and a method. Specific methods have been established for quite a large number of analytes, such as additives (e.g. antioxidants). Column selection and column technology have been reviewed [549]. Contrary to GC, and with the exception of SEC, selectivity in HPLC is determined not by the column alone but also by the mobile phase. There is therefore no one-for-one assignment between an analytical problem and the best column for this problem. 

Microbore and packed capillary HPLC column technology has not yet met the requirements for breakthrough of new technologies [554]. On commercial instruments in general efficiency and detectability with microbore columns are lower than with normal-bore columns. Microbore and capillary HPLC suffer from... 

Several reviews [767,768] and books [51,757,767, 769] deal with SEC in relation to the molecular weight characterisation of synthetic polymers (see also Bibliography). Trends in the development of column technology, detectors and data handling for SEC have recently been discussed [770,771]. The field produces some 1200 papers per year. 

Special Issue on Recent Developments in LC Column Technology, LC.GC Europe 16 (6a) (2003). 

For a reference experiment the mixture was separated by LCCC using conventional column technology resulting in a baseline separation of all components, see Fig. 17.8. The time requirement for this separation, however, was about 140 min. 

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