High-performance liquid chromatography with infrared spectrometry

Initially, simple methods such as ultraviolet-visible (UV-Vis), fluorescence or infrared (IR) spectroscopy were proposed in order to estimate the total amount of antioxidants in various food samples. However, coupled methods such as gas chromatography-mass spectrometry (GC-MS), high performance liquid chromatography with ultraviolet-visible (HPLC-UV-Vis) or nuclear magnetic resonance detector (HPLC-NMR) and liquid chromatography-mass spectrometry (LC-MS) are employed more to quantify individual tocols or carotens from various corn-based food samples. In this chapter all these methods of analysis will be briefly described. 

We will first describe briefly the main experimental techniques coupled with electrochemical methods Infrared Reflectance Spectroscopy (IRS), Electrochemical Quartz Crystal Microbalance (EQCM), Differential Electrochemical Mass Spectrometry (DEMS), Chemical Radiotracers and High Performance Liquid Chromatography (HPLC). 

Chemical analysis of hazardous substances in air, water, soil, sediment, or solid waste can best be performed by instrumental techniques involving gas chromatography (GC), high-performance liquid chromatography (HPLC), GC/mass spectrometry (MS), Fourier transform infrared spectroscopy (FTIR), and atomic absorption spectrophotometry (AA) (for the metals). GC techniques using a flame ionization detector (FID) or electron-capture detector (BCD) are widely used. Other detectors can be used for specific analyses. However, for unknown substances, identification by GC is extremely difficult. The number of pollutants listed by the U.S. Environmental Protection Agency (EPA) are only in the hundreds — in comparison with the thousands of harmful... 

Creatinine can be analyzed in automatic colorimetric analyzers using the Jaffe method, by gas chromatography-mass spectrometry (GC-MS) after derivatization, or simultaneously with creatine by high-performance liquid chromatography (HPLC) or capillary electrophoresis (CE). Enzyme-based methods for both creatine and creatinine are used for colorimetric analyses as well as in biosensors. Creatine can be converted to creatinine to be analyzed by the Jaffe reaction. Eluorescence analyses and methods involving partial least squares (PLS) with ultraviolet (UV), infrared (IR), or near-infrared (NIR) spectra can also used. 

A variation on the GC-MS technique includes coupling a Fourier transform infrared spectrometer (FT-IR) to a gas chromatograph. The substances that elute from the gas chromatograph are detected by determining their infrared spectra rather than their mass spectra. A new technique that also resembles GC-MS is high-performance liquid chromatography-mass spectrometry (HPLC-MS). An HPLC instrument is coupled through a special interface to a mass spectrometer. The substances that elute from the HPLC column are detected by the mass spectrometer, and their mass spectra can be displayed, analyzed, and compared with standard spectra found in the computer library built into the instrument. 

In most respects, the standard approach taken to analyze the fatty acids of functional foods is similar to that for conventional foods. The steps are to extract the total lipids or fatty acids, convert the fatty acids to a suitable derivative (often to fatty acid methyl esters (FAME)), and analyze the derivatized fatty acids by a suitable chromatographic technique, usually GC with flame ionization detection (FID), Other chromatographic techniques, including gas chromatography-mass spectrometry (GC-MS) and high-performance liquid chromatography (HPLC), may be required. Nonchromatographic techniques such as infrared (IR) spectroscopy may be used in some simations, perhaps because of the speed of analysis. 

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