样品制备不准确对分析结果的影响：蛋白质测定和氧化稳定性测试案例

29/08/2023

Sample preparation is the most important step in any chemical analysis. Regardless of the type of analysis, any sort of sample has to be properly prepared to guarantee a high level of accuracy, prevent contamination and minimize the risk of bad results.

Sample preparation is a crucial step in chemical analysis. It involves a series of techniques and procedures, such as homogenization, mixing, grinding, drying, extracting, isolating, concentrating, and purifying, that transform a raw sample into a form suitable for analysis.

The quality of the sample preparation directly impacts the accuracy, precision and sensitivity of the analytical method used. By selecting appropriate sample preparation techniques, scientists can optimize the detection limits and overall quality of the analysis, thereby enabling successful identification and quantification of analytes in a wide range of samples.

The real impact of sample preparation on results

Whether your sample is liquid, solid, or semi-solid; coming from the food, chemical, pharmaceutical, or environmental sector, the quality and appropriateness of sample preparation directly impact the reliability and accuracy of analytical results.

1. NITROGEN/PROTEIN DETERMINATION

When performing the Nitrogen/Protein determination according to the Dumas method using the NDA 702 Elemental Analyser as well as according to the Kjeldahl method using digestion units and distillers, the homogeneity of the sample has a great impact on the results.

For example, in the following table, it is evident how an accurate grinding of the feed samples before starting the analysis is crucial:

Sample	Method	Assigned value Protein%	Min-Max Value	Not grinding Result Protein%	Grinding Result Protein%
Feed	Dumas	16.3	15.8-16.8	17.3	16.5
Feed	Kjeldahl	16.1	15.6-16.6	16.9	15.66

A clear improvement of the %Protein values in the last column of the table proves the importance of better homogeneity when determining the Nitrogen/Protein following both the Dumas and the Kjeldahl methods.

2. OXIDATION STABILITY STUDIES

Images 1A and 1B show how the sample preparation in biscuits is important when performing analyses with the OXITEST to determine the oxidation stability.

Clear differences are visible in the 2 graphs when identifying the Induction Period (IP) - the time required to reach the starting point of oxidation, corresponding to either a level of detectable rancidity or a sudden change in the rate of oxidation.

In particular, the use of ground samples makes the identification of the IP more precise (Image 1A) than the unground one (image 1B): it is possible to note that in Image A there is a sharp point in which the absolute pressure changes, while in Image B there is not a well-defined mark.

Optimize your analytical procedures

A chemical analysis must be considered a multi-stage process, where the measurement is just one of the last steps of the entire process. In this regard, as we have seen in the previous sections, how inaccurate sample preparation can significantly influence the accuracy and the reproducibility of the final results.

VELP offers analytical and application support to ensure that our customers are proficient in using the equipment by following the best practices for sample preparation and analysis.

By analyzing your processes, our experts work with you to find out how your application can be optimized: we can advise you on method and procedure development as well as, task formulation even when it comes to new applications.

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