Membrane based volatile component-removal devices for liquid chromatography

a liquid chromatography and volatile component technology, applied in liquid degasification, separation processes, instruments, etc., can solve the problems of high background current and noise, limitation that the cosub>2 /sub>had to traverse through the tubing wall material, and the fragility of silicone rubber tubing used in the above work

Inactive Publication Date: 2008-09-18
DIONEX CORP
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Problems solved by technology

In HPLC applications with electrochemical detection the presence of oxygen leads to higher background current and noise.
The other tubings used in the above investigation had lower permeability to CO2 along with the limitation that the CO2 had to traverse through the tubing wall material.
The silicone rubber tubings used in the above work however were fragile.
However, the tubings used in the above work were fragile and in some cases had pinholes allowing liquid transport across the tubing walls.
In some samples this carbonate peak appears as a relatively broad tailing peak and depending on the concentration can interfere with the identification and quantitation of anions that elute in the general vicinity during elution with hydroxide or borate eluents.
The problem is particularly acute when a large sample volume is injected.
In alkaline (basic) samples, however the dissolved CO2 is largely present in the ionized form (as bicarbonate and carbonate) anion and cannot be easily removed by degassing approaches.
However in some samples the presence of high concentrations of dissolved CO2 / carbonate may still cause problems with the analysis.
In general, the above tubings tended to be fragile and did not offer the pressure stability offered by tubings of the present invention.
Although the tubing is described to be pressure resilient, it is extremely expensive.
When using a preconcentration technique in anion analysis the presence of excessive amounts of carbon dioxide / carbonate in the sample stream will affect the performance of the concentrator column, as the concentrator column will concentrate the carbonate ion along with other sample anions of interest.
In addition to reducing the effective capacity of the concentrator the presence of carbon dioxide / carbonate in the sample can also impact the capture efficiency of the concentrator column as the carbonate ions tend to elute the other sample ions of interest.
The peak shapes can also suffer because the sample plug is diffused in the concentrator due to partial elution and the sample is injected as a broad plug into the separator.
Similarly in cation analysis, presence of high levels of ammonia during the preconcentration step has a deleterious effect as discussed above.

Method used

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  • Membrane based volatile component-removal devices for liquid chromatography
  • Membrane based volatile component-removal devices for liquid chromatography
  • Membrane based volatile component-removal devices for liquid chromatography

Examples

Experimental program
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Effect test

example 1

[0082]Construction of CO2 Removal Device (GRD)

[0083]This example will be described with respect to FIGS. 2(a) and (b). Microporous tubular polypropylene membranes (400 μm i.d., 25 μm wall, nominal pore size 0.02 μm, surface porosity 40%, Celgard X-20, Celanese Corp., Charlotte, N.C.) were coated with silicone rubber by immersing the membrane tube in a solution of silicone rubber adhesive (Macklanburg-Duncan or General Electric, translucent type for household use) in hexane. Unless otherwise stated, the concentration was 1.5-2% (w / v). A length of the membrane tube was pulled through the solution in one direction and then pulled back in the opposite direction. The membrane was then suspended vertically and allowed to dry in a dust free enclosure for ≧4 h. The desired length of the coated membrane tube 20 was cut and a 200 μm diameter nylon monofilament (4 lb strength, STREN, duPont) was inserted, in the hollow fiber, with ends of the filament protruding out of the fiber. One end of th...

example 2

[0115]A DX600 system from Dionex Corp. was used in this work. A gas permeable tubing (400 um id.×150 cm length) as described in U.S. Pat. No. 5,439,736 was obtained from Neomecs (Eden Prairie, Minn.) and installed in a device as illustrated in FIG. 1. The device is designated as a GRD and is used for removal of carbon dioxide. The device was then installed as a post suppressor device as shown in FIG. 1. A large loop injection (1 mL sample loop) was done using a tap water sample. A control run was done without the GRD using AS18 chemistry and 23 mM NaOH at 1 ml / min (shown in FIG. 11A) and compared to a run done with the GRD (shown in FIG. 11B). The suppressor waste (a base) was diverted into the GRD as a fluidic flow to aid removal of the carbon dioxide and then diverted to waste. The results indicate a substantial portion of the carbonate peak is removed as per the present invention.

example 3

[0116]The experimental conditions were similar to Example 2 except a standard mixture comprising of 7 anion standards was analyzed with a proprietary column from Dionex Corp. with 38 mM NaOH at 1.2 mL / min flow rate and a 25 μL injection loop. The run done without the GRD (FIG. 12A) shows that the carbonate peak elutes close to Nitrite which makes it difficult to quantitate the Nitrite peak. The run done with the GRD (FIG. 12B) on the other hand showed removal of the peak corresponding to carbonate, thus leading to improved integration for Nitrite.

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Abstract

In a liquid chromatographic system, removing at least part of a volatile component from the liquid sample stream after separation by flowing it through a volatile component-removal device including a porous wall having a surface coating of a permeable polymer less than 10 μm thick. A liquid chromatographic system suitable for performing the method. Also, a liquid chromatographic system in which volatile component is removed prior to separation across the same type of membrane or across a membrane made of a copolymer of perfluoro-2,2-dimethyl-1,3-dioxole.

Description

CROSS-REFERENCE TO RELATED APPLICATION[0001]This application is a divisional application of pending U.S. application Ser. No. 10 / 924,236 filed on Aug. 23, 2004.BACKGROUND OF THE INVENTION[0002]The present invention relates to the removal of gases such as C02 from analyte streams in liquid chromatography.[0003]The process of suppression as currently practiced minimizes the conductivity of the eluent or mobile phase while maximizing the conductivity of most analytes. This technique is described in several patents (U.S. Pat. Nos. 3,897,213; 3,920,397; 3,925,019; 3,926,559; 4,474,664; 4,999,098).[0004]In HPLC applications with electrochemical detection the presence of oxygen leads to higher background current and noise. Reim in Anal. Chem, 55, 1983, 1188-1191, showed that the oxygen background can be minimized with the use of gas permeable tubing. The tubings tested for oxygen gas permeability were silicone rubber, Teflon® 4-methyl-1-pentene, Tygon® and Nafion®. Silicone rubber tubing w...

Claims

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Application Information

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Patent Type & AuthorityApplications(United States)
IPC IPC(8): B01D15/20
CPCB01D19/0031G01N2030/8423G01N30/96G01N30/34B01D19/00
InventorDASGUPTA, PURNENDU K.ULLAH, S.M. RAHMATSRINIVASAN, KANNAN
OwnerDIONEX CORP