Analysis of polycyclic aromatic hydrocarbons
Polycyclic aromatic hydrocarbons, PAHs, are among the most studied contaminants in different matrices, since many of them are considered potentially carcinogenic.
The determination of PAHs is a great challenge for analytics. One reason for this is the large number of possible food matrices. In addition, laboratories have to meet requirements such as reducing turnaround time without compromising analytical parameters such as sensitivity, precision and accuracy. As a result, highly automated analytical procedures are required for the analysis.
Advantages of the automated determination of PAHs
- LOD 1/100 of the limit value for baby food (example substance: benzo[a]pyrene)
- No consumables like SPE cartridges due to LC-LC-Clean-Up
- Longer maintenance intervals due to Clean-Up-Technology
- Fast results
- Protection of the GC
- High degree of automation
- Excellent reproducibility
- Expandable to further applications
Pitfall sample preparation
All samples must be prepared before the actual measurement. Depending on the sample matrix, this is easier or more complex. Due to the necessary sensitivity, a high quantity of food sample must be used from which the PAHs must be extracted. However, care must be taken not to extract other substances in addition to PAHs, which could falsify the analysis or, in the worst case, damage the expensive analytical equipment.
The ideal basis for the determination of PAHs is the CHRONECT LC-GC technology by Axel Semrau, which has been established in the routine analysis of food for several years. For this application an LC-LC-GC-MS(/MS) solution and the imPAHct method were developed: innovative multidimensional PAH cleanup technology.
Manual sample preparation and associated pitfalls can be reduced to a minimum by this application. The figure shows the sample preparation procedure with this application depending on the food group. Edible oils can usually be injected directly after dilution, while other food groups are prepared in only 10-15 minutes.
To determine PAHs, a simple and fast extraction of the sample is performed. The extract is purified after a short manual processing in Axel Semrau's LC-GC system by a two-stage LC separation (LC-LC-Cleanup).
After injection of the sample by the xyz robot CHRONECT Robotic, the sample is freed from all substances that are more polar than PAHs. A bare silica gel column in normal phase HPLC mode is used for this purpose.
However, the purified PAH fraction still contains numerous interfering substances that have to be separated by means of a second LC dimension. A so-called π donor-acceptor chromatography is used for this purpose, which can selectively enrich π electron-rich substances. The resulting PAH-rich sample extract is then transferred to the gas chromatograph as described above and separated, detected and quantified using classical GC-MS(/MS) analysis.
Fast results and low detection limits
This intelligent matrix management makes it possible to determine the PAHs prescribed by the EFSA for analysis fully automatically. Depending on the detector, detection limits are achieved that are lower by a factor of 100 than the prescribed European limits for infant food.
The final sample result is available after 45 minutes after the sample has been placed in the system.
- LOD for all EFSA PAH between 0.01 - 0.02 µg/kg
- LOQ for all EFSA PAH < 0.06 µg/kg
- The sensitivities apply when using a current GC-MS system
- Repeatability < 10 % for total procedures
- Analysis duration: 45 min
The system already successfully uses classic assemblies from Agilent and Shimadzu. It is also possible to use other GC-MS systems, such as those from Bruker or others. The control software CHRONOS is the core of the control and combination of the individual modules. In combination with the LC-GC interface, CHRONOS coordinates all subsystems so that they perform the right action at the right time - independent of the data system of the individual equipment manufacturers.
Axel Semrau's LC-GC solutions are pre-installed and tested in a Factory Acceptance Test in the application laboratory. They are delivered to the user ready for use and are checked again there within the scope of a Site Acceptance Test. This ensures the fastest possible start of routine measurement operations.
Marco Nestola was awarded the Ernst Bayer Prize in 2016 for his publication on this separation technology. In the same year, this application also made it onto the Application Award shortlist. With this prize, the German specialist magazine Laborpraxis at analytica honors practical and innovative applications.