Page 7 - Shimadzu Journal vol.7 Issue2

Food Development

Sample preparation Mineral oil in rice – analytical result
Depending on the expected mineral oil concentration, 1 - 10 g of Figure 3 shows two chromatograms of a MOSH fraction of a rice
homogenized and finely ground samples were used. The samples sample spiked with 5 mg/kg of a mineral oil. Before flash chromatography
were extracted in hexane, after the addition of an internal standard with alox n-alkanes in the range of C25 - C35 are present. “False
mixture (Restek MOSH / MOAH standard Cat.#:31070 containing 9 positive” integration would give a MOSH value of 10.8 mg/kg.
internal standards) at room temperature for 2 hours or overnight After flash chromatography the n-alkanes were completely removed
under occasionally shaking the flask. The glass columns with inserted and data evaluation is possible without any interferences. The
filters were filled with 10 g of aluminium oxide (90, basic, 0.063 mm result for the MOSH value is 4.31 mg/kg this time. The MOAH
- 0.2 mm, activated for 16h at 500 ºC) and 3 g of silica gel (60, 60 value that was measured prior to flash chromatography gives a
µm - 200 µm or 70 mesh-230 mesh respectively, activated for 16h at concentration of 0.64 mg/kg and results in a total MOAH recovery
40 ºC). The columns were washed with 20 mL of n-hexane prior to of 4.95 mg/kg of the spiked 5 mg/kg.
loading the sample. The extracts were centrifuged, if necessary,
concentrated to a volume of about 1 mL under a stream of nitrogen.
About 100 µL were taken and filled into an autosampler vial with
micro insert for analysis of MOAH, the remaining samples was loaded
onto the column. The MOSH fraction was eluted with 20 mL of
n-hexane, concentrated in an automated solvent concentrator and
transferred into a 2 mL autosampler vial. This was placed in the
autosampler rack of the LC-GC system. Aliquots of 50 µL were
injected into the LC and 450 µL were transferred directly on the
pre-columns for the MOSH fraction only.

Fig. 3 Chromatograms of rice sample before and after flash chromatography with alox
Conclusion
Flash chromatography with aluminium oxide and silica gel gives an
important tool for the removal of naturally occurring odd-numbered
n-alkanes and allows an interference free analysis of complex food
material such as rice or chocolate.

References
[1] EFSA Panel on Contaminants in the Food Chain (CONTAM) [4] Biedermann, M.; Grob, K. On-line coupled high performance liquid
Scientific Opinion on Mineral Oil Hydrocarbons in Food DOI: chromatography–gas chromatography for the analysis of contamination
10.2903/j.efsa.2012.2704 by mineral oil. Part 2: Migration from paperboard into dry foods:
Interpretation of chromatograms. Journal of Chromatography A 2011,
[2] K. Fiselier, D. Fiorini, K. Grob, Activated aluminum oxide
selectively retaining long chain n-alkanes. Part I, description of the 1255, 76-99, doi:10.1016/j.chroma.2012.05.096.
retention properties, Analytica Chimica Acta. 634 (2008) 96-101. [5] Biedermann, M.; Grob, K. On-line coupled high performance liquid
doi:10.1016/j.aca.2008.12.007. chromatography–gas chromatography for the analysis of contamination
by mineral oil. Part 1: Method of analysis. Journal of Chromatography
[3] K. Fiselier, D. Fiorini, K. Grob, Activated aluminum oxide
selectively retaining long chain n-alkanes: Part II. Integration into A 2011, 1255, 56-75, doi:10.1016/j.chroma.2012.05.095.
an on-line high performance liquid chromatography–liquid
chromatography–gas chromatography–flame ionization detection
method to remove plant paraffins for the determination of mineral
paraffins in foods and environmental samples, Analytica Chimica
Acta. 634 (2008) 102-109. doi:10.1016/j.aca.2008.12.011.

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