Production of calibration standards
The production of calibration standards in analytical laboratories is a time-consuming process. It is not only important to ensure that the standard is prepared correctly, but also to meet the high requirements for documentation. These are regulated for pesticide analysis in SANTE Document 12682/2019. These requirements can also be applied to other groups of substances.
Requirements of SANTE 12682/2019
The SANTE document essentially sets out four requirements for the production of calibration standards:
- Reference substances and stock solutions should be stored in a cool place, preferably in a freezer, excluding light and humidity.
- The documentation created during production should ensure full traceability of all steps.
- The standards should be permanently marked and should be remixed after heating to room temperature.
- If septa are punctured during standard production, they should be replaced as soon as possible.
Implementation with the CHRONECT Workstation MultiMix
- Peltier-cooled drawer system
The aliquot of the stock solutions is stored in a Peltier-cooled drawer system, which is flushed with nitrogen to exclude moisture. By regularly closing the drawers, the standards are stored in the dark.
- Documentation by barcodes
Traceability is ensured through the use of 2D barcodes and a software package. The barcode reader was developed by Axel Semrau and is fully integrated into the system. The software creates suitable labels for the stock solutions, which are printed on solvent-resistant foil by means of a barcode printer. Before each dosage, the barcode is used to check the correctness of the stock solution.
- Mixing by Vortex-Mixer
Re-mixing after heating to room temperature is achieved by using a vortex mixer.
- Protection of the septa
To prevent the septa from being punctured, the vial is opened with a DeCapper before dosing and closed again after collection.
Advantages of automated production of working mixes
- Compliance with SANTE guidelines
- Production independent of working hours through automation
- Less production time than with manual production
- Accuracy of the concentrations can be checked at any time through volumetric dosing and gravimetric precision
- High accuracy
- High reproducibility
- Reliability through integrated controls
- Transferable from pesticide analysis to other substance groups
The supplied software uses a SQL database and supports the user by managing and maintaining all important data such as analyte name, CAS number, best before date, weight, date of manufacture, etc. The weighing results generated during the standard creation are entered online into the database. This prevents transmission errors.
Existing data from the laboratory database can be imported from Excel. A database with more than 600 pesticides is included in the scope of delivery, thus eliminating tedious input routines. The system can be expanded to include additional analytes at any time. This does not only refer to pesticides, but to all fields of application in which mixtures have to be created.
Avoidance of carryover
A further requirement is the prevention of carry-over. To eliminate any carry-over, the CHRONECT Workstation MultiMix uses disposable pipette tips for dosing the stock solutions. These pipette tips are calibrated for the particular solvent used to achieve the target concentration of the analyte as accurately as possible. This calibration is carried out during installation and can be automated at any time by a supplied workflow in the control software.
To complete the traceability and to ensure the highest possible precision of the created working mixes, each liquid dosage is gravimetrically controlled in the CHRONECT Workstation MultiMix. For this purpose, the system includes a scale with five-digit display from Mettler-Toledo. The obtained weighing results are written directly into the database, thus ensuring complete documentation and the accuracy of the concentration of the analyte in the working mix. The obtained actual concentrations can be exported to calibration files for GC-MS or LC-MS data systems.
For example, the creation of a mix can consist of 500 individual substances and requires 5 minutes preparation time for the input of the data into the software. Afterwards the mix is created fully automatically overnight. The time required is about 20 hours. A corresponding manual process takes about 32 working hours on average. For an 8 hour day this corresponds to 4 working days.
Commissioning of the system
All CHRONECT Workstations are pre-installed and tested in Axel Semrau's application laboratory. Only after passing the Factory Acceptance Test is the system delivered, installed in the customer's laboratory and checked again in a Site Acceptance Test. This ensures that the system is immediately ready for routine operation.