Liquid purification or separation – With means to add treating material – Chromatography
Reexamination Certificate
1999-07-30
2001-03-27
Drodge, Joseph W. (Department: 1723)
Liquid purification or separation
With means to add treating material
Chromatography
C096S101000, C065S086000, C138S111000, C422S070000
Reexamination Certificate
active
06207049
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an analytical instrument, and more particularly to a column for performing capillary chromatographic separations useful in, for example, high performance gas and liquid chromatography, or capillary electro-chromatography, or supercritical chromatography.
BACKGROUND OF THE INVENTION
Analytical instruments which detect one or more characteristics of a fluid are commonly employed in a wide variety of applications, such as sample purification, chemical analysis, clinical assay, and industrial processing. Gas and liquid chromatographs are particular examples of analytical instruments wherein certain characteristics related to a particular fluid are detected, e.g., the presence or absence of a fluid component, such as an analyte or contaminant.
Capillary chromatographic separation methods are preferably performed in synthetic fused silica tubing with internal diameters ranging from 5 to 530 micrometers. Such tubing consists of a silica (SiO
2
) glass drawn at high temperature from a quartz preform provided with a protective outside layer such as polyamide or aluminum. See, for example, U.S. Pat. No. 4,293,415, issued to Dandeneau et al., which disclosed the use of a fused silica capillary having wall coatings on the inside surface to stimulate specific interactions when employed in open tubular capillary gas or liquid chromatography, for open tubular supercritical fluid chromatography. Fused silica capillary columns are also known for use in capillary electrophoresis and capillary electro-chromatography.
The resolution of a capillary column, and the time required for carrying out a separation, are functions of several interrelated column and operational parameters. The major factors that influence a separation are: column internal diameter, column length, the type of stationary phase and its film thickness, the type of carrier gas, the carrier gas velocity, and the column temperature. Among these factors, a reduction in the column length is understood to decrease the analysis time, but at the expense of resolution. For fast capillary gas chromatography without a significant loss in resolution, the column internal diameter is typically reduced to 0.1 mm or less. Hence, there are advantages and limitations in the use of narrow-bore well coated open tubular column (WCOT) for high-speed capillary gas chromatography. In a typical example for use in current instrumentation, a 100 micrometer internal diameter column of 5 to 10 meters in length may be used.
However, the most serious limitation of the reduced diameter column is its associated decrease in sample capacity. Capacity is known as the ability of a column to tolerate high concentrations of solutes. Degradation of chromatographic performance is observed when the column capacity is exceeded. This condition is commonly referred to as “overload” and is indicated by peak broadening and asymmetry. Sample capacity is also related to the film thickness and phase ratio. Thus, a chromatographer will expect a limit in the sample capacity that is set according to the internal diameter for a given phase ratio or film thickness. Small diameter (<0.2 mm internal diameter) columns will offer the advantages of high-efficiency and high-resolution, but at the expense of sample capacity. Low resolution, wide-bore fused silica columns have a much higher sample capacity and are typically employed for performing simple, packed-column separations. Accordingly, the elements of efficiency, speed, capacity, and resolution are factors which must be balanced when optimizing a chromatographic separation.
Accordingly, it would be desirable to employ a capillary column suited for use in the aforementioned modes of chromatography that has the practical advantages of a relatively large internal diameter column (and in particular, its capacity) but also exhibits the high resolution and the rapid analysis obtained by a relatively small internal diameter column.
One approach has been to assemble a plurality of parallel, narrow-bore capillary columns, in which each of the columns presumably have identical properties, in an attempt to eliminate the disadvantage residing in the limited capacity of the narrow-bore capillary column. By using a larger number of such capillary columns coupled in parallel, one would expect to separate large quantities of samples while maintaining the aggregate abilities of each of the capillary columns. However, this proposed “multi-capillary” column device has not been found to be practically useful, due largely in part to the difficulty in providing a column composed of several capillaries coupled in parallel, wherein the individual capillaries exhibit identical behavior. Some examples of the causes of differences that may arise in the performance of individual capillaries are: deformation of the capillaries in different amounts depending on their position in the composite column assembly; temperature gradients over the cross-section of the column (wherein it is difficult to change the temperature of the column without causing radial temperature gradients which subsequently result in different separation rates of the different capillaries); differing stationary phase thicknesses; disparity in column aging, etc. See, for example, U.S. Pat. Nos. 4,424,127 and 4,818,264.
SUMMARY OF THE INVENTION
The advantages of the invention are achieved in a multichannel capillary column suitable for use in an analytical instrument.
A preferred embodiment of the multichannel capillary column includes an interior wall defining a single internal bore, wherein the interior wall comprises a plurality ofn channels and n ridges and the adjacent channels are partially separated by a respectively interposed ridge, and wherein a central, coaxial portion of the internal bore communicates with each of the channels to allow cross-channel fluid communication between all of the n channels.
In a first aspect of the present invention, the multichannel capillary column includes a single internal bore optionally having an internal coating of stationary phase on the interior wall, thus enabling its use as a well-coated open tubular separation column for performing an analysis of a large volume of sample at high speed without diminished resolution.
In another aspect of the present invention, the interior wall offers an increase in the total surface area of the stationary phase and an effective reduction, along at least one transverse section of the multichannel capillary column, in the average distance traveled by sample molecules during diffusion to reach a proximate portion of the stationary phase.
In another aspect of the present invention, the interior wall of the multichannel capillary column is constructed to provide the capacity of a large bore capillary column and the speed and resolution of a small bore capillary column. The interior wall of the multichannel capillary column, however, includes a single internal bore having a plurality of channels, wherein adjacent channels are partially separated by a respectively interposed ridge, and the surfaces of the channels and ridges include a stationary phase coating.
In another aspect of the present invention, n channels are evenly distributed about the central longitudinal axis of the column. When n refers to an even number, first and second imaginary axes of symmetry may be understood to distinguish the internal geometry of the n channels and n ridges, such that each of then channels exhibit identical, or nearly identical, cross-sectional dimensions. When n refers to an odd number, there are corresponding first, second, . . . n imaginary axes of symmetry that may be seen to distinguish the internal geometry of the n channels and n ridges.
In another aspect of the present invention, the internal geometry of the interior wall is accordingly symmetrical about such axes of symmetry such that each of the n internal channels preferably exhibit identical or nearly identical, and at least functionally equivalent, cross-sectional dimensions so as to achieve uniform separat
Agilent Technologie,s Inc.
Drodge Joseph W.
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