Over the past year we have noticed an increase in requests from participants for blank samples to accompany the purchase of the Progetto Trieste Proficiency Tests.
In order to identify the ways in which blank samples are commonly used by testing laboratories during routine analysis and when participating in interlaboratory circuits, and to understand whether these differ, laboratories that were happy to participate in the initiative were asked to take part in a survey on the use of blank samples, the results of which are set out below.
Results
In our survey, first of all, participants were asked to indicate whether or not blank samples are used in their routine analyses and if the answer is yes, also how they are used.
The results showed that most laboratories (87.1%) make use of blank samples in routine analyses and that these are mainly used as matrices for the creation of the calibration curve or to create an additive control sample.
But are blank materials also used in the same way during the laboratory participation in a Proficiency Test?
As can be seen, the percentage of laboratories using a blank sample during the course of a PT (87.1%) is in agreement with the percentage of laboratories using the blank routinely (87.1%). However, compared to what one might think, not all the laboratories who answered that they do not use the blank sample are the same as those who answered “No” to this last question.
Next, the participants were asked about their preferences regarding the use of blanks during PT. The aim of the question was to find out whether the participants prefer to use their own routine blanks for the analyses they perform during PT, or whether they prefer to purchase blank material directly from the PT provider (regardless of whether or not they have their own blank material at home).
More than half of the respondents (64.3%) stated that they preferred to use their own routine blank even when participating in ring tests, in order to fully evaluate the analytical method. In the event that the laboratory did not have a blank sample in house, of this 64.3%, 42.9% stated that they would adopt other correction factors during PT that did not involve the use of blank samples, while 21.4% preferred to request this from the PT provider.
On the other hand, 28.6% opt to purchase blank material directly from the PT provider, even if they already have blank material at home. Finally, about 7% say they use both their own blank and the one provided by the PTp.
What are the main reasons for a laboratory to purchase blank material from the provider even though it is already used for routine analysis? The most frequent answers given by the participants are summarised below:
- Avoid possible differences in matrix effect between the blank material used in routine and the PT sample matrix
- Having information on recovery %
- Perform analysis with matrices as similar as possible
But what if the PT provider does not provide the blank sample of the relevant Proficiency Test? Would the laboratory still participate or is the blank provided by the provider a fundamental tool for PT enrolment?
100% of respondents stated that they would still participate in PT, either by using other correction factors or by purchasing only blank material elsewhere.
All those who stated that they preferred to purchase the blank provided by the PTp were asked to reflect on their quality system and were asked the following question: “have you verified that your quality system allows your participation in the PT to follow a different analytical process than the routine one?”
Although the percentage of laboratories that had not verified that their quality system allows the use of blank samples other than those used in routine is a low percentage, it shows that the choice of PT is not always aligned with their quality system. Participation in this type of survey can help laboratories become more aware of their choices.
The whole survey was set up as a description of the laboratory’s mode of operation, while in the concluding part we wanted to collect the operator’s opinion as to the appropriateness of participating in a PT using the blank not used during the routine.
A somewhat provocative question but one that gave interesting food for thought. First of all, most laboratories prefer to participate in the PT following the same routine and therefore do not use the blank provided by the PT provider, but if necessary they accept its use.
Usually Test Veritas provides blank materials only for the Pesticide Residues line, because we believe that if a laboratory uses a blank material in routine analysis, the choice of the blank material itself is part of the analytical method and consequently should be evaluated during proficiency testing (PT). In other words, considering that during PT you need to test the performance of your method, you should use the same blank sample that you use during routine analysis, as it forms part of the method.
However, based also on the responses received during this survey, we realise that laboratories may have difficulties in obtaining blank samples for both routine and PT. Consequently, we have decided to start providing blanks for some specific PTs of Veterinary Drugs, starting with the PT for Metabolites in Nitrofurans in Honey (cod. H4505) to be held in the Round of November 2024. The H4505blank sample will be a ‘pre-spiking’ blank sample, i.e. the same matrix as the PT before the addition of contaminants (as with the blank samples from the pesticide line).
For 2025, on the other hand, we want to go one step further, so don’t miss out on all the new things we will be offering next year!