The Column - August 2006 - (Page 12)

Jones The Column August 2006 Sample Preparation Techniques for Ion Exchange Chromatography Peter Jones, Metrohm UK Ltd, Buckingham, UK. An overview of the different approaches to sample prep in ion exchange chromatography. ionic species in the sample are at odds with each other, Separation of ionic species can be achieved by HPLC using ion resulting in overloading of either the column or detector. The exchange columns that employ charged functional groups pH of the sample or organic loading can also affect the supported on a polymer or gel stationary phase and a resultant chromatography, especially if the sample is of a conductivity detector. concentrated nature 50% sodium hydroxide, glacial acetic As in any industry, the consumer places ever more stringent acid or honey for example. Alternatively, if the sample is not in demands and requirements upon the manufacturer, and the a form capable of being injected into the ion chromatograph world of ion chromatography is no different. The ease-of-use a powder or viscous liquid for example then it must be with which ion chromatography as a method can be dissolved or diluted to allow analysis. manipulated means the end user wants to analyse ions in Samples such as these would normally require pretreatment. increasingly complicated sample matrices. This would not have In some instances, dilution is not an option as this could reduce been possible until recently because of lower capacity the concentration of the analyte below the limit of exchange resins. High capacity resins result not only in being quantification of the system. Strong acids or alkalis can able to inject more concentrated samples improving limits of damage ion exchange columns. Proteins, dust and insoluble detection but also in the separation between components grit can precipitate on the column resin, increasing back within the sample reducing interferences and false positives. pressure and reducing the working lifetime of a column. Recent technological advances means automation of the major sample preparation techniques can be employed resulting in a Dilution large scale reduction in the cost of analysis and improved repeatability. The most common form of sample preparation is dilution. This presents an intrinsic problem of altering the concentration of Automated Sample Preparation the analytes to be measured. For accurate analysis several repeat solutions have to be prepared and the results averaged Sample preparation for ion chromatography can be to account for discrepancies and inconsistencies in the problematic given the wide range of factors that affect the ion- glassware used and the habits and judgement of the person exchange separation process and the conductivity detected. performing the dilution. However, automated burette systems Manual preparation is often time-consuming, requiring skilled can perform the dilution reproducibly, without error, using analysts to perform volumetric adjustments to the sample in smaller volumes than a human could readily achieve. duplicate or triplicate. The Holy Grail of analytical This has the advantage that several solvents can be attached instrumentation design is complete automation of sample to the same device dilution and neutralization or matrix handling, eliminating the intrinsic errors associated with human matching for standards could be performed in a short time by input and ensuring skilled workers are gainfully employed. a completely automated process. Powders in a large-volume Often the capacity of the column and the concentration of Author: Peter Jones E-mail: 12

Table of Contents for the Digital Edition of The Column - August 2006

Market Trends & Analysis
Sample Preparation Techniques for Ion Exchange Chromatography
Characterizing Aerosols using Comprehensive Two-dimensional Chromatography
Non-Classical Methods in Comprehensive Two-Dimensional Gas Chromatography
Supplies & Services
Recent Developments in Column Technology Supplement

The Column - August 2006