Factors Affecting Accuracy and Reproducibility of Ion Chromatographs - An Introduction

When it comes to Ion Chromatography (IC), accuracy and reproducibility are crucial factors that determine the reliability of the results obtained. The ability to achieve a high percentage of accuracy and reproducibility in IC analysis depends on several key factors. In this article, we will explore these factors and discuss the percentage that is possible to achieve with a properly maintained and professionally operated IC system.

Calibration and Standardization

One of the primary factors that influence the accuracy and reproducibility of an ion chromatograph is the calibration and standardization process. Calibration involves the use of known standards to establish a relationship between the detector response and the concentration of the analyte. Standardization, on the other hand, ensures that the calibration standards used are accurate and traceable to recognized reference materials.

To achieve high accuracy and reproducibility, regular calibration and standardization of the IC system are essential. This ensures that the instrument is properly calibrated and that the measurements obtained are reliable and consistent over time.

Sample Preparation

Another critical factor that affects the accuracy and reproducibility of IC analysis is the sample preparation process. Proper sample preparation ensures that the analyte of interest is in a suitable form for analysis and that any interfering substances are removed or minimized.

Factors such as sample filtration, dilution, extraction, and derivatization can significantly impact the accuracy and reproducibility of the results. It is important to follow standardized sample preparation procedures to minimize errors and obtain reliable data.

Column Selection

The choice of column in ion chromatography plays a crucial role in achieving accurate and reproducible results. Different columns have varying selectivity, capacity, and efficiency, which can affect the separation and detection of analytes.

It is important to select a column that is appropriate for the analytes of interest and the matrix being analyzed. The column should provide good resolution, minimal peak tailing, and high column efficiency to ensure accurate and reproducible results.

Eluent Composition

The composition of the eluent used in ion chromatography is another factor that can impact the accuracy and reproducibility of the analysis. The eluent should be carefully selected to optimize the separation of analytes and minimize interference from other components based on the chemistry of the column.

Factors such as pH, ionic strength, and buffer concentration can influence the retention time, peak shape, and resolution of analytes. It is important to optimize the eluent composition to achieve the best separation and obtain accurate and reproducible results based on column type and chemistry, use of suppressor, injection volume, and optimized flow path of the system.

Detector Selection

The performance of the detector used in ion chromatography is crucial for obtaining accurate and reproducible results. Different types of detectors, such as conductivity, UV-Vis, and amperometric detectors, have different sensitivities and selectivities.

Regular maintenance and calibration of the detector as well as the overall system are essential to ensure its optimal performance. This includes cleaning the detector cell, checking the baseline noise, and verifying the linearity of the detector response. A well-maintained detector will provide reliable and consistent results.

Operator Skill and Training

The skill and training of the operator also play a significant role in the accuracy and reproducibility of IC analysis. A properly trained operator understands the principles of IC, is familiar with the instrument's operation, and knows how to troubleshoot common issues that may arise.

Operator errors, such as improper injection technique, incorrect sample handling, or inadequate maintenance, can introduce errors and affect the reliability of the results. Regular training and refresher courses for operators are essential to ensure accurate and reproducible IC analysis.

Percentage Achievable with Properly Maintained and Operated IC

With a properly maintained and operated ion chromatograph, it is possible to achieve a high percentage of accuracy and reproducibility in the analysis. While the exact percentage may vary depending on the specific factors mentioned above, it is not uncommon to achieve accuracy and reproducibility levels above 95%.

But with that said, in the early days of IC, let's say back before the turn of the century (but I won't say what century...), a wise colleague told me this, and I quote, "An IC operating at its optimal settings, performing a Chloride standard analysis at 10 ppm, by an experienced operator, is reproducible to 3% RSD over 10 injections." Applying this definition to the average lab, operating an average IC, maintained at an average performance, which is less than optimal, by an average operator, a chloride analysis at 10 ppm would actually only be able to achieve an RSD of greater than 5%, which I have proven time again.

I am happy to report that an IC in my laboratory performing chloride at 100 ppb (not 10 ppm), which would be more difficult to achieve in many labs, performs at better than 1% RSD. This is only achievable by carefully controlling sample and standard preparation, system performance, temperature performance, detector optimization, and the right column/eluent for the job.

However, it is important to note that achieving high levels of accuracy and reproducibility requires careful attention to all the factors discussed in this article. Regular calibration, standardized sample preparation, appropriate column selection, optimized eluent composition, a well-maintained system, and skilled operators are all essential components for obtaining reliable and consistent results in ion chromatography.

In conclusion, the accuracy and reproducibility of an ion chromatograph depend on various factors. By understanding and addressing these factors, it is possible to achieve a higher percentage of accuracy and reproducibility than other average laboratories, with a properly maintained and operated IC system. This ensures that the results obtained are reliable and can be trusted for critical analytical purposes. If you aren't currently measuring % RSD of your standards, it is unlikely to know how an unknown sample will perform or that the data would even be acceptable for your needs. Maybe an onsite consultation would be beneficial.