Contaminant analysis in complex matrices
Sampling
Taking a sample is a crucial step. If the sampling is not performed properly, the analysis will be falsified.
In order to take a sample correctly, you have to raise a number of questions, as indicated below.
Where? When?
It is very unusual for the object of analysis (which is sampled) to be homogeneous. There can be two types of heterogeneity, possibly simultaneous: spatial and temporal heterogeneity.
To take into account heterogeneity, it is advisable to take several samples (in space and/or in time, depending on the type of heterogeneity) - to avoid multiplying the analyses. These samples can then be combined to obtain what is called a composite sample.
If this is not possible, a minimum sample size is required when the object of study is heterogeneous.
Where? When?
It is very unusual for the object of analysis (which is sampled) to be homogeneous. There can be two types of heterogeneity, possibly simultaneous: spatial and temporal heterogeneity.
To take into account heterogeneity, it is advisable to take several samples (in space and/or in time, depending on the type of heterogeneity) - to avoid multiplying the analyses. These samples can then be combined to obtain what is called a composite sample.
If this is not possible, a minimum sample size is required when the object of study is heterogeneous.
How?
The tools used to take the sample, as well as the container used to collect it, must be adapted so as not to cause over-contamination or, conversely, lead to the adsorption of the contaminant that you are looking for on the walls of the container, for example.
YOUR INVESTIGATION
What strategy do you suggest to analyze the cargo of green coffee?
CLUE
Take several samples (setting up a statistical sampling plan is an option) to obtain a composite sample that will provide an estimate of the average contamination of the coffee cargo. Moreover, if the cargo is not stored under proper conditions, the ochratoxin A content may increase with the storage duration.