Size exclusion chromatography operations

The programs are described at length in the NBS publication NBS-IR 87-3669, System of Hardware and Software Developed for Size Exclusion Chromatography by B. Dickens and F.L. McCrackln, National Bureau of Standards, 1987, and available from NTIS under order number 88153697. Host of that report is concerned with interactive operation of the programs. 

Many of the possible column combinations that are useful in 2DLC are listed in Chapter 5. Besides the actual types of column stationary phases, for example, anion-exchange chromatography (AEC), size exclusion chromatography (SEC), and RPLC, many other column variables must be determined for the successful operation of a 2DLC instrument. The attributes that comprise the basic 2DLC experiment are listed in Table 6.1. 

A viscosity online detector in a size exclusion chromatography (SEC) instrument allows for a universal calibration for polymers with known K- and a-values. For polymers that are only soluble at high temperature, e.g., polyolefines, high-temperature detectors are available, which can be operated up to 200°C. In addition to molar mass measurements, viscosity detectors have also been employed successfully to obtain structural information of branched polymers [28]. 

To sum up, the choice of operating conditions for a specific FFF application is made in a way that recalls the general criteria used in chromatography. An accurate search of literature addressed to similar samples that have been already analyzed by FFF techniques is very useful. A number of specific reviews have been published concerning, for example, enviromnental, pharmaceutical, and biological samples (see Section 12.5). As previously mentioned above, one of the most important factors is the stability of the considered colloidal system, for which a great deal of information can be obtained from specialized literature, such as colloid, polymer, and latex handbooks [33], For example, the use of the proper surfactant (e.g., Fl-70) is common for SdFFF applications. Polymer analysis with ThFFF requires solvent types similar to those employed in size exclusion chromatography. 

Inductively coupled plasma-mass spectrometry (ICP-MS) is a powerful technique that uses an inductively coupled plasma as an ion source and a mass spectrometer as an ion analyzer. It can measure the presence of more than 75 elements in a single scan, and can achieve detection limits down to parts per trillion (ppt) levels for many elements—levels that are two or three orders of magnitude lower than those obtained by ICP-AES (Keeler 1991). It is more expensive than ICP-AES and requires more highly skilled technical operation. Aluminum levels in urine and saliva were detected down to 0.02 g/mL and in blood serum to 0.001 g/mL using ICP-MS (Ward 1989). Speciation studies have employed ICP-MS as a detector for aluminum in tissue fractions separated by size-exclusion chromatography (SEC) with detection limits of 0.04 g/g in femur, kidney and brain (Owen et al. 1994). 

In what concerns ultrafiltration, it has replaced size-exclusion chromatography in almost all final formulation processes. Charged ultrafiltrafion membranes, in conjunction with optimum operating parameters, as previously discussed, can also be used to enable protein purification with HPTFF. In fact, recent developments in membrane chromatography and FIPTFF enable, for the first time, complete purification of proteins using membrane systems [1],... 

Procedure (See Chromatography, Appendix IIA.) Use a liquid chromatograph suitable for size-exclusion chromatography and equipped with a refractive index detector and a 60-cm x 7.5-mm (id) column packed with 5-p.m, 500A porosity PL-Gel, or equivalent, both operated at 40°. Operate the chromatograph at 500 to 1500 psi at a flow rate of 1.0 mL/min. 

Profile The company was founded in 1976 to develop techniques and instrumentation for the characterization of polymer systems, and to develop high-technology polymer products for chromatography, and for diagnostic and pharmaceutical applications. The company operates from offices in the USA, UK, and Europe. Primary products are in the specialized areas for gel permeation/size exclusion chromatography (GPC/SEC) including columns, standards, advanced high temperature systems and detectors, and GPC/SEC software. 

However, fractional separation has been the basis for most asphalt composition analysis (Fig. 15.5). The separation methods that have been used divide asphalt into operationally defined fractions. Three types of asphalt separation procedures are now in use (a) chemical precipitation in which n-pentane separation of asphaltenes is followed by chemical precipitation of other fractions with sulfuric acid of increasing concentration (ASTM D-2006) (b) adsorption chromatography with a clay-gel procedure in which, after removal of the asphaltenes, the remaining constituents are separated by selective adsorption/desorption on an adsorbent (ASTM D-2007 and ASTM D-4124) and (c) size exclusion chromatography in which gel permeation chromatographic (GPC) separation of asphalt constituents occurs based on their associated sizes in dilute solutions (ASTM D-3593). 

The size exclusion chromatography, which is generally used as an analysis technique, can also serve to prepare samples by fractionation. However, this method, which will be studied in detail in Section 6, calls for rather heavy equipment which is not to be found in most laboratories, and the operation in itself is rather costly... 

The first step in the characterization of polymers is to fractionate the unknown sample, and then to determine the stmctures of the separated fractions. Separation is best performed by modem liquid chromatographic methods. Depending on the kind of heterogeneity it is necessary to select the most suitable chromatographic method, i.e. either Size-Exclusion Chromatography (SEC) or Liquid Adsorption Chromatography (LAC). Furthermore, the meanwhile well-established Liquid Adsorption Chromatography at Critical Conditions (LACCC) is also used. A separation system that operates near critical conditions sometimes has to be applied. 

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