Chemical apparatus and process disinfecting – deodorizing – preser – Analyzer – structured indicator – or manipulative laboratory... – Means for analyzing liquid or solid sample
Reexamination Certificate
2001-06-08
2003-01-21
Ludlow, Jan (Department: 1743)
Chemical apparatus and process disinfecting, deodorizing, preser
Analyzer, structured indicator, or manipulative laboratory...
Means for analyzing liquid or solid sample
C204S536000, C204S542000, C210S198200, C436S161000
Reexamination Certificate
active
06508985
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to method and apparatus using continuous suppression of electrolyte in eluents particularly for the analysis of anions or cations in ion chromatography.
Ion chromatography is a known technique for the analysis of ions which typically includes a chromatographic separation stage using an eluent containing an electrolyte, and an eluent suppression stage, followed by detection, typically by an electrical conductivity detector. In the chromatographic separation stage, ions of an injected sample are eluted through a separation column using an electrolyte as the eluent. In the suppression stage, electrical conductivity of the electrolyte is suppressed but not that of the separated ions so that the latter may be determined by a conductivity cell. This technique is described in detail in U.S. Pat. Nos. 3,897,213, 3,920,397, 3,925,019 and 3,926,559.
Suppression or stripping of the electrolyte is described in the above prior art references by a bed of ion exchange resin particles commonly referred to as a packed bed suppressor (PBS). The PBS requires periodic regeneration by flushing with an acid or base solution.
While packed bed suppressors have proven useful in ion chromatography, there are a number of disadvantages of a PBS. These disadvantages include a) periodic regeneration of the PBS which interrupts sample analysis, b) a loss of resolution due to band broadening in the PBS and c) changes in retention of certain analytes as a function of the degree of exhaustion of the PBS.
The volume and capacity of the PBS is generally large relative the separation column to contain sufficient ion exchange resin so that the suppression reaction can be performed for a large number of analysis (e.g. 15 to 50) prior to regeneration. By making the volume and capacity of the suppressor sufficiently large, the need to regenerate is less frequent which permits a larger number of samples to be analyzed before the system must be disrupted to regenerate the suppressor. Regeneration typically requires placing the suppressor out of line of the analytical system and pumping a concentrated acid or base solution (regenerant) through the suppressor.
If the suppressor's void volume is too large, the separation of the analytes achieved in the separator column is compromised due to re-mixing of the analytes in the void volume, resulting in lower resolution. Thus, the suppressor volume is a compromise between regeneration frequency and chromatographic resolution.
The regeneration process typically requires 20-60 minutes, depending on the volume of the suppressor. A strong acid or base solution is first pumped through the PBS in order to convert the resin to the acid (H
3
O
+
) or base (OH
−
) form. After this conversion, deionized water is pumped through the suppressor until any traces of the highly conductive acid or base regenerant have been removed. The PBS is then placed back in line with the analytical system and is allowed to equilibrate before sample analysis is performed.
In U.S. Pat. Nos. 5,597,734 and 5,567,307, a method is described of regenerating a packed bed suppressor after each analysis. In this apparatus, the packed bed suppressor has limited capacity for just one or several sample analysis before the suppressor requires regeneration. The liquid flow through the low volume packed bed suppressor is used with suitable valving to pass liquid stream through the system. During analysis, eluent from the separator passes through the suppressor and to the conductivity cell. Immediately after the analysis, valving diverts a flow of chemical regenerant through the suppressor for regeneration. The valving then diverts eluent to the suppressor for equilibration prior to sample analysis. The regeneration and equilibration of this type of PBS can be performed in a short time with a small volume PBS.
Another form of packed bed suppression uses intermittent electrolytic regeneration as described and published in U.S. Pat No. 5,633,171. A commercial product using this form of suppression is described in “Electrochemically regenerated solid-phase suppressor for ion chromatography” Saari-Nordhaus, R. and Anderson, J. M., American Laboratory, February 1996. In this product, an electrical potential is applied through the resin in the packed bed suppressor while flowing an aqueous liquid stream to electrolyze water in the stream. For the analysis of anions, a PBS containing fully sulfonated cation exchange is fitted with a cathode embedded in the resin at the suppressor inlet and an anode embedded in the resin at the suppressor outlet. Hydronium ions generated at the anode displace the sodium ions which associate with the hydroxide ions for passage to waste, in this instance through the conductivity cell. This process electrochemically regenerates the suppressor, and after the electrical potential is turned off, the device can be used as a conventional PBS. In a further embodiment, a second ion exchange resin bed is used with suitable valving to pass liquid streams through the system. In one alternative of this system, a second sample in an eluent stream is chromatographically separated, typically on a chromatographic column using an eluent. The eluent and separated second sample flow through a second packed bed suppressor including ion exchange resin to convert the electrolyte to weakly ionized form. Then, the separated sample ionic species in the suppressor effluent are detected in the detector. The effluent then flows through the first packed bed suppressor, forming the aqueous liquid stream required for regeneration and an electrical potential is applied and regeneration of the first packed bed suppressor is accomplished. The second suppressor may be similarly regenerated by positioning it after the detection cell and flowing through the detector effluent of the first sample and applying an electrical potential. This form of suppression does not require an external regenerant source and allows for uninterrupted operation although it is not considered continuous. This system uses two PBS's, additional valving and electronics to control the valve switching and timing.
A different form of a suppressor is described and published in U.S. Pat No. 4,474,664, in which a charged ion exchange membrane in the form of a fiber or sheet is used in place of the resin bed. The sample and eluent are passed on one side of the membrane with a flowing regenerant on the other side, the membrane partitioning the regenerant from the effluent of the chromatographic separation. The membrane passes ions of the same charge as the exchangeable ions of the membrane to convert the electrolyte of the eluent to weakly ionized form, followed by detection of the ions.
Another suppression system is disclosed in U.S. Pat. No. 4,459,357. There, the effluent from a chromatographic column is passed through an open flow channel defined by flat membranes on both sides of the channel. On the opposite sides of both membranes are open channels through which regenerant solution is passed. As with the fiber suppressor, the flat membranes pass ions of the same charge as the exchangeable ions of the membrane. An electric field is passed between electrodes on opposite sides of the effluent channel to increase the mobility of the ion exchange. One problem with this electrodialytic membrane suppressor system is that high voltages (50-500 volts DC) are used. As the liquid stream becomes deionized, electrical resistance increases, resulting in substantial heat production. Such heat can be detrimental to effective detection because it increases noise and decreases sensitivity.
In U.S. Pat. No. 4,403,039, another form of eletrodialytic suppressor is disclosed in which the ion exchange membranes are in the form of concentric tubes. One of the electrodes is at the center of the innermost tube. One problem with this form of suppressor is limited exchange capacity. Although the electrical field enhances ion mobility, the device is still dependent on diffusion of ions in the bulk solution to the
Avdalovic Nebojsa
Liu Yan
Riviello John M.
Small Hamish
Srinivasan Kannan
Brezner David J.
Dionex Corporation
Dorsey & Whitney LLP
Ludlow Jan
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