Optimizing sample matrices for Ion Chromatography

Thermo Scientific™ Dionex™ Ion Chromatography (IC) is a rugged technique with a high level of sensitivity, meaning that sample dilution is often the only sample preparation that is needed. However, because some sample matrices such as waste or surface waters, food, and petroleum products can be extremely challenging, some form of sample preparation is necessary. The large diversity of matrices has led to many sample preparation options, and it can be difficult to identify the most appropriate technique. Sample preparation methods for ion chromatography include simple filtration, automated inline sample preparation using Thermo Scientific™ Dionex™ Guardcap™ vial caps to remove interferences, inline sample preparation using Thermo Scientific™ Dionex™ InGuard™ columns, and offline benchtop pretreatment cartridges using Thermo Scientific™ Dionex™ OnGuard™ II cartridges. AutoDilution is another technique used to work with samples which have high analyte concentration.

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Proper sample preparation prior to injection helps improve data quality, extends column and suppressor lifetimes as well as reduces hardware maintenance costs

Evaluating filtration options for ion chromatography 
The United States Environmental Protection Agency recommends point of collection filtration. However, if filtration at the point of sample collection is not possible, then some form of particulate removal prior to introduction of the sample into the eluent stream is recommended to protect the components of the ion chromatograph. The use of Thermo Scientific™ Dionex™ filter caps or Dionex Guardcap vial caps incorporates sample filtration directly into the autosampler. This approach is amenable for a wide range of samples, including those which are heavily loaded with particulates. Each vial cap has its own individual filter which eliminates sample carry over related to the filter.

 

High Pressure inline filtration is another technology which saves on time and labor costs. A filter backflush approach can be implemented where particulate loading of samples is heavier or concerns about sample carry over remain. Utilizing two filters, a 2-position 10-port high pressure valve, and an auxiliary high-pressure pump (Figure 4), this approach allows for filters to be backflushed with ultrapure water to eliminate carryover and increase filter lifetimes by up to a factor of 100X.

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Solve your matrix interference problems with Dionex Guardcap vial caps, InGuard cartridges, and OnGuard II cartridges
Automatically remove matrix interferences for better performance in many IC applications.
Dionex Guardcap vial caps are embedded with ion exchange resin and designed for use with Dionex AS-DV autosamplers for automatic inline removal of cations (including alkaline earth and transition metals) or surfactants from samples and particle filtration. These ready-to-use vial caps require no pre-conditioning and are easy to use, greatly reducing the time, effort, and expense associated with traditional offline sample preparation.

 

Installed inline between the IC autosampler and injection valve, Thermo Scientific™ Dionex™ InGuard™ cartridges remove cations (including transition metals and iron), anions, or hydrophobic substances. Each cartridge can be used for multiple sample injections, depending on the matrix concentration and injection volume.

 

Offline sample preparation is also an option with Dionex OnGuard II cartridges. Choose from 10 Dionex OnGuard chemistries in two cartridge sizes developed for 17 common applications including removal of phenols, metals, cations, anions, or hydrophobic substances. These cartridges can be used individually or in series for optimal performance. Need help choosing the best Dionex OnGuard cartridge for your application? Let the Dionex OnGuard Selection Tool guide you through proper cartridge selection. If desired, samples can be processed in parallel using the Dionex OnGuard Workstation.

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Achieve trace level ion analysis using anion or cation concentrator columns
Dionex IonPac Concentrator Columns are designed primarily for high-purity water analysis. The Thermo Scientific™ Dionex™ IonPac™ UTAC-2 Series Ultratrace Anion Concentrators represent the latest in anion concentration technology and can be used with carbonate/bicarbonate, borate, and hydroxide eluents. Thermo Scientific™ Dionex™ IonPac™ TCC Trace Cation Concentrators are optimized for use with carboxylated cation-exchange columns using methanesulfonic acid, sulfuric acid, or hydrochloric acid eluents.

 

The columns retain ions from a measured volume of aqueous sample matrix, thereby concentrating the analyte species and lowering detection limits. The advantage of using concentrator columns is the ability to perform routine analysis for ions at µg/L (ppb) to ng/L (ppt) levels.

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Streamline lab workflows by utilizing AutoDilution
Challenging samples, such as wastewater, often contain compound concentrations that exceed the range defined by a calibration curve. Operators need to identify these outliers, dilute the samples, and rerun the standards along with the diluted samples. These time-consuming steps have now been eliminated with the AutoDilution option, an integral part of the Intelligent Run Control (IRC) feature of Thermo Scientific™ Chromeleon™ 7 CDS software IRC can be used with the Thermo Scientific™ Dionex™ AS-AP Autosampler to automatically determine when compound concentrations exceed a set concentration, then reanalyze those the samples by injecting a smaller sample volume. AutoDilution can be accomplished by making partial loop injections as seen in this Thermo Scientific Technical Note. Alternatively, AutoDilution can be done by drawing sample from one vial into a second, then automatically diluting in the second vial, using vial to vial dilution. A third method called Large/Small loop Autodilution is also an option.

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