Sample preparation grape extracts

Revilla E and Ryan JM. 2000. Analysis of several phenolic compounds with potential antioxidant properties in grape extracts and wines by high-performance liquid chromatography—photodiode array detection without sample preparation. J Chromatogr 881(1-2) 461 169. 

Reversed-phase HPLC is used for the analysis of the different groups of phenols, phenolic acids, hydroxycinnamic acids, flavonoids, and procyanidins in grapes and wines (22,46,47,77-80). However, due to the presence of a large quantities of various compounds, wine analysis is difficult. Thus, different sample preparation procedures, including fractionation and extraction, are often applied when various groups of phenolic compounds are studied together. 

Sample Preparation for Analysis of HCTA and Flavonols in Grape Extracts and Juice... 

Sample preparation and derivatization methods for GC analysis of BAs have been also proposed. In a method developed by Daudt and Ough (1980), amines are distilled from the alkalized grape juice or wine sample and trapped in an acidified solution. After concentration under vacuum, methylamine, dimethylamine, ethylamine, diethylamine, n-propylamine, isobutylamine, a-amylamine, isoamylamine, pyrrolidine, and 2-phenethylamine in their salt form are derivatized with triflu-oroacetic (TFA) anhydride. TFA derivatives are extracted with ethyl ether and analyzed by GC-MS with a capillary fused silica poly( ethylene) glycol (PEG) column and the following oven temperature program 8 min at 70 °C, l°C/min to 160 °C, isotherm for 90 min. 

To perform sample preparation, 75 g of grape are extracted with 200 mL of ethyl acetate. After filtration an aliquot of 10 mL of the organic layer is evaporated to dryness, the residue is re-dissolved with 1.5 mL of methanol and the solution is injected for LC-MS/MS analysis without any further purification. Recoveries of pesticides range between 70-100%. 

Extraction of Grape and Wine Proteins and Peptides 7.2.1. Sample Preparation... 

A satisfying method of sample preparation for GC/MS analysis of grape extract and used in several studies (Mateo et al., 1997 Chassagne et al., 2000 Flamini et al., 2001 2006), was proposed by Williams et al. (1982) and Di Stefano (1991). Skins of 100 berries are separated from the pulp and are extracted with 35 mL of methanol for 4h in the dark. Pulp and juice are reunited in a glass containing lOOmg of sodium metabisulfite. 

The usual methods for the assessment of ochratoxin A are immunochemical detection or RPLC coupled with fluorescence detection (ilex=247 nm, 2eni = 480nm). For ochratoxin sample preparation, the sample is mixed with HCl and MgCli, followed by extraction into toluene. The toluene supernatant is passed through a silica gel column and the column is washed with hexane, toluene-acetone, and toluene. Ochrotoxin A is eluted with toluene-acetic acid and dried down to 40°C. The residue is dissolved in a mobile phase, filtered, and analyzed by HPLC. The limit of ochratoxin A in grape juice is proposed to be fixed at 3 pg per kg. 

Grape seed extracts used were commercially available. Polyphenols in grape seed extracts selected were chalcone, pelargonidin, cyanidin, delphinidin and resveratrol. All samples were dissolved in DMSO or DMF to prepare 0.5-2.0 mg/mL for O2 and... 

The dry grape seed extract is dissolved in acetone or methanol at 2mg/mL, a 2,5-dihydroxybenzoic (DHB) acid matrix is prepared in tetrahydrofuran (THF) at 20mg/mL, and the sample and matrix solutions are mixed at a 1 1 (v/v) ratio. Sodium apparently arises from the seeds themselves and only a minute amount of sodium is needed. The use of DHB and water-free solvents, such as anhydrous THF, acetone, or methanol for the sample and matrix preparation was reported to lead to the best analytical conditions in reflectron mode, providing the broadest mass range with the least background noise (Yang and Chien, 2000). 

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