A Step-By-Step Guide to Developing a Sample Preparation Method

Preparing samples for analysis is an essential stage in the field of analytical chemistry, as some testing cannot be conducted without it. In sample preparation, a piece of material or substance is extracted from a larger material for further investigation. Various methods can be used to prepare a sample, but the quality of the sample preparation method is critical for the accuracy, reliability, and sensitivity of analysis results. 

Developing a suitable sample preparation method for your study can be complex for several reasons, ranging from complex samples to contamination and other factors. It is also possible that many stages need to be introduced to adequately prepare a sample, whereas other methods may only require one to four steps.1 In this blog post, we provide a step-by-step guide to developing a sample preparation method that yields accurate and reliable results.

Sample Preparation

Samples can be taken from many materials, including biological matter, cells, gas, liquid, solids, or a combination of the above. If a sample is obtained or prepared incorrectly, all subsequent stages in the analytical process can be negatively affected. Before we look at how to develop an optimal sample preparation method, it is crucial to note that when developing a sample preparation method, researchers must take note of every decision they make throughout the process. If the method is suitable, others must be able to accurately and easily follow the steps involved. On the other hand, if the method isn’t suitable or an error occurs, the research can evaluate and analyze any mistakes.

Define the Analytical Goal

The analytical goal must be clearly defined before beginning any sample preparation. Consideration must be made about what type of sample is being analyzed and what outcome is required, such as chemical composition, contamination, or something else. The target analyte, sample matrix, and instruments available will all have an important role in how the analysis can be effectively conducted.

Sampling

Sampling is the first main step in developing a sample method. The sample collected should be representative of the bulk material, and depending on the target analyte, several methods are available for collection. In some cases, the sample must be taken from a specific area of the bulk material, such as the side or the center, to ensure the representative sample can be suitably analyzed; therefore, this must also be considered.

Extraction and Pre-Treatment of the Sample

Sample extraction typically involves three stages: removing the sample from its target population, preserving it, and preparing it for analysis.2  There are several extraction and sample preparation techniques. A sample can be pre-treated by distillation, enzymatic treatment, and precipitation by chemical reaction, liquid-to-liquid (LLE), or solid-phase extraction. The most suitable depends on the target analyte.

The pre-treatment of a sample is a stage during which the selected analyte is treated to remove any interfering substances. Still, it can also be usd to concentrate the analyte. This stage is crucial for ensuring the accuracy, precision, and sensitivity of the analysis and involves optimizing the sample preparation conditions to best suit the analyte.

Validate the Method 

Validating the chosen sample preparation method is critical because it will prove it is suitable for analytical testing by meeting specific acceptance criteria. Throughout the validation process, the accuracy, linearity, precision, selectivity, and sensitivity of the method will be evaluated.4 Once validated, the method can be used for routine analysis, but it must be monitored over time to ensure it continuously meets the specific criteria.

Document the Method

Documentation in sample method development is necessary to ensure the reproducibility and traceability of the analysis conducted. This involves recording every step taken during the analysis, as well as any relative details such as the extraction conditions, pre-treatment methods, validation methods, and more.

To ensure the method is conducted correctly, all documentation should be clear and concise and contain all the information for another scientist to follow the same procedure. It must also meet regulatory guidelines for documentation, as set out by authorities such as the FDA. 

XRF Scientific

XRF Scientific offers a wide range of support for sample method development, including on-site validation procedures, sample preparation beads and pressed pellets, and calibration support for analytical instruments. 

Contact a member of XRF Scientific today to learn more about developing a suitable sample preparation method.

References

1. https://www.sciencedirect.com/science/article/abs/pii/S0166526X06470021

2. https://chem.libretexts.org/Bookshelves/Analytical_Chemistry/Analytical_Chemistry_2.1_(Harvey)/07%3A_Obtaining_and_Preparing_Samples_for_Analysis

3. https://www.azolifesciences.com/article/How-Critical-is-Sample-Preparation-to-Analytical-Chemistry.aspx

4. https://link.springer.com/chapter/10.1007/978-1-4419-9631-2_10