title: Supercritical fluid extraction of amino acids from birch (Betula pendula Roth) leaves and their liquid chromatographic determination with fluorimetric detection.
abstract: A method for supercritical fluid extraction (SFE) of amino acids was adapted and optimal experimental conditions were selected for a matrix consisting of dry leaves. The matrix-dependent SFE method uses a mixture of MeOH-H(2)O-acetonitrile (10:10:1 v/v/v) as a modifier (0.5 mL in situ, 300 muL on-line) at 70 degrees C and 40 MPa and no HCl is needed as an entrainer. The amino acids were quantified using high-performance liquid chromatography with fluorimetric detection (HPLC/FLD) after gradient elution on Zorbax Eclipse AAA columns (4.6x150 mm, 3.5 mum) with aqueous Na(2)HPO(4 )buffer of pH 7.8 and ACN-MeOH-water as a mobile phase. In comparison with Soxhlet extraction, SFE gave higher recovery and selectivity, but it required longer extraction time (90 min) and it was more labor-intensive (clean-up step after the pre-concentration). Both methods should be used separately or in combination according to the matrix, number of samples, and levels of ballast compounds.
authors.affiliation: Department of Chemistry and Biochemistry, Mendel University of Agriculture and Forestry Brno, Brno, Czech Republic.
authors.forename: Borivoj
authors.initials: B
authors.lastname: Klejdus
authors.forename: Lea
authors.initials: L
authors.lastname: Lojková
authors.forename: Emanuel
authors.initials: E
authors.lastname: Kula
authors.forename: Ivan
authors.initials: I
authors.lastname: Buchta
authors.forename: Petr
authors.initials: P
authors.lastname: Hrdlicka
authors.forename: Vlastimil
authors.initials: V
authors.lastname: Kubán
mesh_terms: D000097:Acetonitriles / Q000032:analysis*; D000596:Amino Acids / Q000032:analysis* / Q000302:isolation & purification; D029662:Betula / Q000378:metabolism*; D002853:Chromatography, Liquid / Q000379:methods*; D025924:Chromatography, Supercritical Fluid / Q000379:methods*; D018153:Czech Republic; D006863:Hydrogen-Ion Concentration; D000432:Methanol / Q000737:chemistry; D018515:Plant Leaves / Q000378:metabolism; D011312:Pressure; D015203:Reproducibility of Results; D012997:Solvents / Q000737:chemistry; D013696:Temperature; D013997:Time Factors; D014867:Water / Q000737:chemistry
chemical_list: D000097:Acetonitriles; D000596:Amino Acids; D012997:Solvents; D014867:Water; D000432:Methanol; C032159:acetonitrile