Ion chromatography systems with flow-delay eluent recycle

#Since it was introduced in 1975, ion chromatography has become a widely used analytical technique for the determination of anionic and cationic analytes in various sample matrices. In ion chromatography, dilute solutions of acids, bases, or salts are commonly used as the electrolytes in chromatographic eluents.

#Traditionally, these eluents are prepared off-line by dilution with reagent-grade chemicals. Off-line preparation of chromatographic eluents can be tedious and prone to operator errors, and often introduces contaminants. For example, dilute NaOH solutions, widely used as the electrolytes in eluents in the ion chromatographic separation of anions, are easily contaminated by carbonate. The preparation of carbonate-free NaOH eluents is difficult because carbonate can be introduced as an impurity from the reagents or by adsorption of carbon dioxide from air. The presence of carbonate in NaOH eluents often compromises the performance of an ion chromatographic method, and can cause an undesirable chromatographic baseline drift during the hydroxide gradient and even irreproducible retention times of target analytes. Therefore, there is a general need for convenient sources of high purity acid, base, or salt for use as eluents in the ion chromatographic separations.

#The continuous operation of an ion chromatography system can consume a significant amount of eluents. The consistent preparation of such large amount of the eluent as well as the disposal of the used eluent can pose serious logistical challenges to the system operators in terms of costs and labor, especially in cases where unattended or less frequently attended operations are required. Even though it overcomes a number of issues associated conventional approaches of eluent preparation in ion chromatography, the use of on-line electrolytic eluent generation devices still requires a constant supply of high purity water from an external source for continuous operation and waste disposal issue remains.

#FIGS. 1-8 are schematic representations of apparatus according to different embodiments of the present invention.

#FIGS. 9-16 are graphs illustrating experimental results using the present invention.

#The system of the present invention is useful for determining ionic species which are solely anions or cations. Suitable liquid samples include surface waters, other liquids such as industrial chemical waste, body fluids, beverages or drinking water. The term “ionic species” includes molecular species in ionic form and molecules which are ionizable under the conditions of the present invention. The term “eluent” refers to the solution flowing in a liquid chromatography system which carries a sample to be detected. At times herein, the term eluent also refers to the electrolyte in that solution. The eluent normally is water-based but can include an organic solvent so long as it is electrochemically stable.

#In certain embodiments, the invention includes a suppressor. The purpose of a suppressor is to reduce the conductivity and noise of the analysis stream background while enhancing the conductivity of the analytes (i.e., increasing the signals/noise ratio), while maintaining chromatographic efficiency.

#In other embodiments, the invention relates to improved catalytic gas removal devices and methods and to improved systems for using catalytic gas removal devices and systems disclosed in U.S. Pat. No. 7,329,346, incorporated in its entirety by reference. The invention will first be described for the embodiment of FIG. 1.