Liquid chromatography method to determine polyamines in thermosetting polymers.

A simple, robust and sensitive analytical method to determine three polyamines commonly used as hardeners in epoxy resin systems and in the manufacture of polyurethane is reported. The studied polyamines are: one tetramine, TETA (triethylenetetramine), and two diamines, IPDA (Isophorone diamine) and TCD-diamine (4,7-methano-1H-indene-5,?-dimethanamine, octahydro-). The latter has an incompletely defined structure, and, as far as we know, has not been previously determined by other methods. All three polyamines contain primary amines; TETA also contains secondary amines. The analytical method involves derivatization with 6-aminoquinolyl-N-hydroxysuccinimidyl carbamate, used for the first time for these compounds, followed by high performance liquid chromatography (HPLC) analysis with a fluorescence (FL) detector (lambda excitation 248nm, lambda emision 395nm). The HPLC-DAD-LTQ Orbitrap MS was used in order to provide structural information about the obtained derivatized compounds. The hybrid linear ion trap LTQ Orbitrap mass spectrometer has been introduced in recent years and provides a high mass accuracy. The structures of the derivatized analytes were identified from the protonated molecular ions [M+H](+) and corresponded to the fully labelled analytes. The following analytical parameters were determined for the method using the HPLC-FL: linearity, precision (2.5-10%), instrumental precision intraday (0.8-1.5%) and interday (2.9-6.3%), and detection limits (0.02-0.14mgL(-1)). The stability of stock solutions and derivatized compounds was also investigated. The method was applied to determine the amine free content in epoxy resin dust collected in workplaces.

Principal components of phenolics to characterize red Vinho Verde grapes: anthocyanins or non-coloured compounds?

Phenolic profile of 10 different varieties of red "Vinho Verde" grapes (Azal Tinto, Borraçal, Brancelho, Doçal, Espadeiro, Padeiro de Basto, Pedral, Rabo de ovelha, Verdelho and Vinhão), from Minho (Portugal) were studied. Nine Flavonols, four phenolic acids, three flavan-3-ols, one stilben and eight anthocyanins were determined. Malvidin-3-O-glucoside was the most abundant anthocyanin while the main non-coloured compound was much more heterogeneous: catechin, epicatechin, myricetin-3-O-glucoside, quercetin-3-O-glucoside or syringetin-3-O-glucoside. Anthocyanin contents ranged from 42 to 97%. Principal component analysis (PCA) was applied to analyse the date and study the relations between the samples and their phenolic profiles. Anthocyanin profile proved to be a good marker to characterize the varieties even considering different origin and harvest. "Vinhão" grapes showed anthocyanins levels until twenty four times higher than the rest of the samples, with 97% of these compounds.

Experimental design for extraction and quantification of phenolic compounds and organic acids in white "Vinho Verde" grapes.

An experimental design was applied for the optimization of extraction and clean-up processes of phenolic compounds and organic acids from white "Vinho Verde" grapes. The developed analytical method consisted in two steps: first a solid-liquid extraction of both phenolic compounds and organic acids and then a clean-up step using solid-phase extraction (SPE). Afterwards, phenolic compounds and organic acids were determined by high-performance liquid chromatography (HPLC) coupled to a diode array detector (DAD) and HPLC-UV, respectively. Plackett-Burman design was carried out to select the significant experimental parameters affecting both the extraction and the clean-up steps. The identified and quantified phenolic compounds were: quercetin-3-O-glucoside, quercetin-3-O-rutinoside, kaempferol-3-O-rutinoside, isorhamnetin-3-O-glucoside, quercetin, kaempferol and epicatechin. The determined organic acids were oxalic, citric, tartaric, malic, shikimic and fumaric acids. The obtained results showed that the most important variables were the temperature (40 degrees C) and the solvent (acid water at pH 2 with 5% methanol) for the extraction step and the type of sorbent (C18 non end-capped) for the clean-up step.

Antioxidant content of and migration from commercial polyethylene, polypropylene, and polyvinyl chloride packages.

Antioxidants commonly used in polyolefins were studied in commercial food packages made of low- and high-density polyethylene (LDPE and HDPE), polypropylene (PP), polyvinylchloride (PVC), and polyethylene terephtalate (PET) and in a LDPE film extruded at the laboratory. The phenolic antioxidants BHA, BHT, AO 2246, AO 425, Ethanox 330, Irganox 1010, and Irganox 1076 were studied together with the phosphite Irgafos 168 and their two degradation products, phosphate and DBP. Antioxidants were extracted from polyolefins using microwave energy and analyzed using high-performance liquid chromatography (HPLC) to determine the antioxidant content in the diverse commercial films. Irganox 1010 and Irganox 1076 were found in the majority of the samples generally together with the phosphite Irgafos 168 and its oxidized product (phosphate). Specific migration levels of each antioxidant were determined by HPLC after pretreatment with solid-phase extraction (SPE) in aqueous food simulants and after their dilution with tetrahydrofuran (THF) in fatty food simulant. These levels were much lower than limits allowed by legislation.

Solid-phase extraction versus matrix solid-phase dispersion: Application to white grapes.

The use of matrix solid-phase dispersion (MSPD) was tested to, separately, extract phenolic compounds and organic acids from white grapes. This method was compared with a more conventional analytical method previously developed that combines solid liquid extraction (SL) to simultaneously extract phenolic compounds and organic acids followed by a solid-phase extraction (SPE) to separate the two types of compounds. Although the results were qualitatively similar for both techniques, the levels of extracted compounds were in general quite lower on using MSPD, especially for organic acids. Therefore, SL-SPE method was preferred to analyse white "Vinho Verde" grapes. Twenty samples of 10 different varieties (Alvarinho, Avesso, Asal-Branco, Batoca, Douradinha, Esganoso de Castelo Paiva, Loureiro, Pedernã, Rabigato and Trajadura) from four different locations in Minho (Portugal) were analysed in order to study the effects of variety and origin on the profile of the above mentioned compounds. Principal component analysis (PCA) was applied separately to establish the main sources of variability present in the data sets for phenolic compounds, organic acids and for the global data. PCA of phenolic compounds accounted for the highest variability (77.9%) with two PCs, enabling characterization of the varieties of samples according to their higher content in flavonol derivatives or epicatechin. Additionally, a strong effect of sample origin was observed. Stepwise linear discriminant analysis (SLDA) was used for differentiation of grapes according to the origin and variety, resulting in a correct classification of 100 and 70%, respectively.

Determination of antioxidants by solid-phase extraction method in aqueous food simulants.

An analytical method for the determination of specific migration levels of phenolic antioxidants and one phosphite antioxidant in the aqueous food simulants established by European legislation has been developed. This method involves solid-phase extraction (SPE) of the antioxidants with silica C(18) cartridge and their determination by liquid chromatography (LC) with diode-array detection. The achieved results in the studies of elution volume determination, breakthrough volume and accuracy are showed. Recoveries in the range of 78-104% and a relative standard deviation between 2.0 and 7.7% have been achieved.

Determination of antioxidant migration levels from low-density polyethylene films into food simulants.

An analytical method for the determination of specific migration levels of phenolic antioxidants from low-density polyethylene (LDPE) into food simulant has been developed. The screening and response surface experimental designs to optimize the liquid-liquid extraction (LLE) of these antioxidants have been tested and the analyses have been carried out by reversed-phase high-performance liquid chromatography (HPLC) coupled with ultraviolet diode-array detector. The procedure developed has been applied to specific migration tests in different commercial LDPE films. The considered antioxidants have not been found upper the legislation limits although Ethanox 330 and Irgafos 168 have been found at trace level.