title: Size fractionation of non-volatile dissolved organic compounds and metal species in German white wines by combining on-line tangential-flow multistage ultrafiltration, a home-built carbon analyser, and inductively coupled plasma mass spectrometry.
abstract: Organic metal species and their size fractions in three German white wines were characterized by combining multistage ultrafiltration (MST-UF), determination of non-volatile dissolved organic carbon (NV-DOC) by a home-built carbon analyser, and metal quantification by inductively coupled plasma mass spectrometry (ICP-MS). First, NV-DOC and metal species in selected "dry" German white wines were fractionated on-line using MST-UF in the size range of >100 kDa to <1 kDa. For this purpose a 20 mL sample of the wine under study diluted 1:10 with high-purity water was processed through a cascade system of hydrophilized polyethersulfone-based flat membranes of decreasing cut-off (100, 50, 10, 5, and 3 kDa). An aliquot of the fraction <3 kDa was additionally processed through a commercial UF tube (MidGee system, cut-off: 1 kDa) to obtain low-molecular size fractions also. A home-built carbon analyser was applied to determine NV-DOC in the wines and their size fractions. The NV-DOC found in a German reference wine and its size fractions was as follows: total NV-DOC: 8.97 mg mL(-1); F(1) (>100 kDa), 0.15%; F(2) (50-100 kDa), 0.44%; F(3) (10-50 kDa), 0.74%; F(4) (5-10 kDa), 0.76%; F(5) (5-3 kDa), 0.7%; F*(6) (3-1 kDa), 0.9%; F(7) (<1 kDa), 81.6% (related to total NV-DOC). The NV-DOC recovery was 85.2%. Accordingly, most of the NV-DOC in this wine consists of low-molecular mass organic compounds of <1 kDa, presumably carboxylic acids as typical in wine. Parallel metal determinations in these wines and their fractions were performed by ICP-MS. The measurements showed that the major part of the metals investigated, up to 25 elements, were dissolved in the size fraction of <1 kDa except Ba, Sr and Pb which appeared also in other fractions. In addition, conventional UV-VIS spectroscopy was applied to characterise the studied wines and their size fractions. According to this, the UV absorbance between 254 and 280 nm of these white wines shows a parallel trend to their NV-DOC.
authors.affiliation: Institut für Spektrochemie und Angewandte Spektroskopie, Bunsen-Kirchhoff-Strasse 11, 44139 Dortmund, Germany. castineira@isas-dortmund.de
authors.forename: Maria del Mar
authors.initials: Mdel M
authors.lastname: Castiñeira
authors.forename: P
authors.initials: P
authors.lastname: Burba
authors.forename: N
authors.initials: N
authors.lastname: Jakubowski
authors.forename: J
authors.initials: J
authors.lastname: Andersson
mesh_terms: D001464:Barium / Q000032:analysis; D002244:Carbon / Q000032:analysis*; D005591:Chemical Fractionation / Q000295:instrumentation / Q000379:methods*; D002850:Chromatography, Gel / Q000379:methods; D005504:Food Analysis / Q000379:methods; D005858:Germany; D007854:Lead / Q000032:analysis; D013058:Mass Spectrometry / Q000379:methods; D008670:Metals / Q000032:analysis*; D009930:Organic Chemicals / Q000032:analysis*; D010316:Particle Size; D013324:Strontium / Q000032:analysis; D014462:Ultrafiltration / Q000379:methods*; D014920:Wine / Q000032:analysis*
chemical_list: D008670:Metals; D009930:Organic Chemicals; D001464:Barium; D007854:Lead; D002244:Carbon; D013324:Strontium