Column micro-particulate

Different approaches utilizing multidimensional EC or SEC systems have been reported for the analysis of middle distillates in diesel fuel. A method, based on the EC separation of paraffins and naphthenes by means of a micro-particulate, organic gel column has been described (23, 24). The complete system contained up to four different EC columns, a number of column-switching valves and a dielectric constant detector. However, the EC column for the separation of paraffins and naphthenes, which is an essential part of the system, is no longer commercially available. 

The rapid development of HPLC columns for example was due to three major technical achievements the ability to manufacture micro-particulate silicas, the invention of air elutriation technique as sizing technology and progress in the slurry technique for packing HPLC columns. However, it took more than ten years to build up sufficient know-how to produce stable, robust and reproducible HPLC columns that satisfied the continuously increasing demands of the chemical and pharmaceutical industry (Fig. 1.2). 

The choice of the column is therefore mainly determined by the sample properties and by the application. In HPSEC, columns with micro-particulate packings are normally used because short analysis times and high efficiencies are required. On the other hand, columns with coarse particles are selected for preparative applications. 

It is prudent to use columns of a length that just satisfies the requirements of the separation and no more in process scale SFC because the micro-particulate packings are so expensive. 

These factors make it necessary to reduce the amount of solvent vapor entering the flame to as low a level as possible and to make any droplets or particulates entering the flame as small and of as uniform a droplet size as possible. Desolvation chambers are designed to optimize these factors so as to maintain a near-constant efficiency of ionization and to flatten out fluctuations in droplet size from the nebulizer. Droplets of less than 10 pm in diameter are preferred. For flow rates of less than about 10 pl/min issuing from micro- or nanobore liquid chromatography columns, a desolvation chamber is unlikely to be needed. 

Sample preparation embraces all processes that convert the analyte into a form suitable for analysis. This includes a possible comminution, homogenization, digestion, dissolution, and filtration of the sample. Ideally, the sample should be dissolved in the eluent being used since the negative peaks that are observed during the dead time in conductivity detection mode do not occur. Before injecting the sample solution, it should be micro-filtrated (0.22 or 0.45 pm) to prevent particulate matter from entering the column. 

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