The bioactivities and bioavailability of plant polyphenols including proanthocyanidins and other catechin derivatives may be affected by covalent reaction between polyphenol and proteins. Both processing conditions and gastrointestinal conditions may promote formation of covalent complexes for polyphenol-rich foods and beverages such as wine. Little is known about covalent reactions between proteins and tannin, because suitable methods for quantitating covalent complexes have not been developed. We established capillary electrophoresis methods that can be used to distinguish free protein from covalently bound protein-polyphenol complexes and to monitor polyphenol oxidation products. The methods are developed using the model protein bovine serum albumin and the representative polyphenol (-)epigallocatechin gallate. By pairing capillaries with different diameters with appropriate alkaline borate buffers, we are able to optimize resolution of either the protein-polyphenol complexes or the polyphenol oxidation products. This analytical method, coupled with purification of the covalent complexes by diethylaminoethyl cellulose chromatography, should facilitate characterization of covalent complexes in polyphenol-rich foods and beverages such as wine.

The use of a 4.6 × 250 mm, 5 μm cyanopropyl column is effective for the liquid chromatography (LC) separation of asphaltenes with sequential ultraviolet (UV) and florescence detection. The mobile-phase composition is an optimized gradient from acetonitrile (MeCN) and water to N-methyl-2-pyrrolidone (NMP) and tetrahydrofuran (THF). A low flow rate of 0.5 mL min–1 is used to maintain lower operating pressure to minimize aggregate formation. Using a 0.02 g L–1 asphaltene sample for preliminary optimization, three peaks, with two partially resolved, are evident in the fluorescence chromatogram. The UV chromatogram revealed an extra weakly retained peak, suggesting aggregates that quench fluorescence. Aggregation of asphaltenes increases with time up to about 10 h and is dependent upon the choice of sample solvent. On the basis of the reversed-phase mobile-phase gradient, the relative polarity of the peaks from least to most retained can be estimated over the polarity index (P′) range from about 6.3–4.3 on a scale of 0.1 for hexane (least polar) to 10.6 for water (most polar). The sample concentration is increased to 1 g L–1 for separation and collection of 12 fractions. Selected fractions are subjected to characterization using atmospheric pressure chemical ionization mass spectrometry (APCI–MS) using a linear quadrupole ion trap (LQIT). The variation of the molecular-weight distribution of the asphaltenes for the 12 fractions is fairly constant, indicating that the retention mechanism is not controlled by size exclusion but likely a partitioning/adsorption mechanism.

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This study was undertaken to address the need for an improved analytical method to detect and quantify hindered phenolic antioxidant additives in Navy mobility fuels that overcomes the limitations of currently available methods. It was demonstrated that hindered phenols in fuels can be accurately quantified using capillary gas chromatography−mass spectrometry with selected ion monitoring (GC−MS/SIM) of mass fragments unique to each analyte. Using this approach, three methods were developed for the analysis of antioxidants in fuels: (1) a single-column GC−MS/SIM method that, because of co-elution of fuel constituents, is only suitable for quantifying tri-tert-butylphenol, (2) a two-column heart-cutting method that overcomes the problem of co-eluting fuel components but requires modification of the instrument, and (3) a GC−MS/MS method that does not require modification of the instrument. The heart-cutting method was developed as a practical method for the routine determination of each of the five hindered phenolic antioxidants in any type of fuel, with a method quantitation limit (MQL) of 0.5 mg/L, with minimal interference from fuel. The GC−MS/MS method provides a lower MQL of 0.05 mg/L. Both methods offer a significant advantage over traditional high-performance liquid chromatography with electrochemical detection (HPLC− ECD) methods, which are more labor-intensive and not capable of separating each of the individual phenolic antioxidants.

The high cost and limited availability of emerging alternative fuels and/or fuel blending stocks with unknown compositions are often major impediments to the certification of these materials as Fit-For-Purpose (FFP) for the U.S. Navy. A method was desired whereby a candidate fuel could be rapidly prescreened to determine if it would be suitable for further, moreextensive FFP testing. The goal of this research was to employ statistical analysis strategies to establish linkages between the chemical constituency of any given fuel or fuel stock, regardless of type or source, and the resultant performance, and/or fuel properties. A chemical profiler developed during the course of this work has previously been used to quantify the constituencies of fuels using gas chromatography−mass spectrometry (GC-MS) data. These constituencies were then correlated to specification properties using partial least-squares regression modeling reconfigured into a multistep, iterative strategy. While this modeling strategy was shown to be successful at predicting the performance properties not only of the training data but also of uncalibrated alternative fuels, the underlying data abstraction strategy was determined to be inherently unsuitable for use with the disparate data from multiple GC-MS instruments due to instrument-based overfitting. The following report details a novel modeling strategy that makes use of normalized total ion chromatography (TIC) peak areas to both streamline the procedural complexity of the previous modeling strategy and more ably quantify chemical constituencies for the purposes of multi-instrument FFP fuel modeling.