Phenolic compounds HPLC systems

Papadopouluo-Mourkidou E. et al., 2001. Use of an automated online SPE-HPLC method to monitor caffeine and selected aniline and phenol compounds in aquatic systems of Macedonia-Thrace, Greece. Frese-nius J Anal Chem 371 491. 

Phenolic compounds in Sicilian wines were directly detected by La Torre et al. [373] using an HPLC with a DAD coupled on-line with a MS system equipped with ESI source operating in the negative-ion mode and a quadruple mass analyzer. The structure was elucidated by recording MS spectra at different voltages, in addition to the molecular mass information. The method allowed both the identification and determination of 24 phenolic compounds in 22 different commercial Sicilian red wines by direct injection without any prior purification of the sample. Figure 19.10 reproduced an HPLC trace obtained in this work. 

The technique of CPC was also employed as a key step in the purification of 26 phenolic compounds from the needles of Norway spruce (Picea abies, Pinaceae). An aqueous extract of needles (5.45 g) was separated with the solvent system CHCl3-Me0H-i-Pr0H-H20 (5 6 1 4), initially with the lower phase as mobile phase and then subsequently switching to the upper phase as mobile phase. Final purification of the constituent flavonol glycosides, stilbenes, and catechins was by gel filtration and semipreparative HPLC. °... 

III. HPLC SYSTEMS FOR PHENOLIC COMPOUNDS A. Chromatographic Conditions... 

For phenolics in fruit purees and jams (54), an HPLC condition similar to that used for apple juice, but with acidified water (5% formic acid) and methanol, was utilized as a solvent system. In most cases, detection was achieved with diode array detection, at UV 280 nm and 320 nm. The different phenolic compounds were identified by their UV spectra and by chromatographic comparisons with authentic standards. Several classes of phenolic compounds (cinnamic acids, catechins, dihydrochalcones, and flavonol glycosides) could be detected along with arbutin in... 

However, due to the artifacts resulting from oxidation, hydrolysis of esters or ethers, or isomerization of phenolics during pretreatment of wines, as well as due to the low recovery rates of some phenolics, analysis of wine phenolics via direct injection of the filtered wine into the chromatographic column is often selected (80,82-84). For the red wine and musts (80), which were injected directly into the HPLC without sample preparation, a ternary-gradient system was often employed for phenolic compounds. Twenty-two phenolic compounds, including 10 anthocyanins, were analyzed from red wine. The separation of cinnamic acid derivatives (313 nm),... 

A dual-electrode liquid chromatography-electrochemistry (LCEC) system used in the detection and identification of flavanols and procyanidins in wines and grape seeds is a valuable tool (30). Voltammetric behavior of phenolic compounds by LCEC could provide information that cannot be obtained using HPLC with UV detection, for which the identification is usually based on a comparison of the retention time with that of standard compounds, especially for the identification of catechins and procyanidins with a small amount of sample available (30). Figure 10 shows the procyanidins commonly found in wines. 

Normal aqueous micellar media can also be employed to extract and purify components from solid matrices. Proteins have been extracted from wheat kernals using aqueous NaLS (399). This same surfactant system has been employed in an improved method for the extraction of filth from cheese (417). In another application, aqueous solutions of Brij-35 micelles have been employed to extract components (i.e. vanillin and ethylvanillin) from smoking tobacco (106). In a similar manner, various phenolic compounds have been extracted from herbal/plant leaves using nonionic Triton X-100, Brij-35, or octyl glucoside (0G) (393). In both of these latter examples, the indicated compounds could be identified and quantitated by reversed phase HPLC using as mobile phase the same micellar solutions (refer... 

Analysis of Phenolic Compounds. A Hewlett-Packard (Palo Alto, CA) Model 1090 HPLC System, was used to determine the levels of specific phenolic components. The HPLC system was equipped with a ternary solvent delivery system, a diode array UV-VIS detector, and HP ChemStation software for data collection and analysis. Full chromatographic traces were collected at 280, 520, 316, and 365 nm, and spectra were collected on peaks. The stationary phase was a Hewlett-Packard LiChrosphere C-18 coliram, 4mm X 250 mm, with 5 pM particle size packing. Operating conditions include an oven temperature of 40 C, injection volume of 25 pL, and flow rate of 0.5 mL/minute. The mefriod was based on a previously published method for phenolic components in wine (30) and used the modified solvent gradient shown in Table II. Solvent A was 50 mM dihydrogen ammonium phosphate, adjusted to pH 2.6 with orthophosphoric acid. Solvent... 

As previously mentioned, the RP-HPLC of phenolic compounds is carried out with polar eluents. Simple HPLC systems use one pump that pumps a single solvent or, more frequently, a solvent mixture through the column. This is known as isocratic HPLC. More complex gradient systems use more than one pump governed by a computer and pump changing mobile phases that can involve several solvents. Water is usually one of the components in the mixmre the other components most frequently include methanol, acetonitrile, and, more rarely, tetrahydrofuran, etc. The pH of the eluent is always acidic, and this acidity can be attained by the addition of acids such as acetic, formic, phosphoric, trifluoroacetic, and others. The selection of the acid used is dependent on the specific separation problems that need to be solved. 

Use of the reverse-phase HPLC system is highly flexible since it can also be applied to ionizable compounds such as carboxylic acids, phenols, and amines. The partition coefficients relate to the unionized compounds that are generally assumed to be the principal forms in which these compounds are transported into biota, even though their concentration may be low in comparison with the dissociated states at physiological pH values acidic compounds such as highly chlorinated phenols or many carboxylic acids have... 

Phenolic compounds Waters, soils Monolithic minicolumn with polys tyrene-divinylbenzene UV-Vis <1 ng mL 1 Multi-syringe flow system coupled to HPLC minicolumn before the sampling loop [507]... 

RP HPLC has proved to be the method of choice for the separation of a variety of flavonoids in different samples. The phenolic nature of these compounds requires the use of acidic mobile phases for satisfactory separation and peak shapes, whereas the detection is usually carried out with photodiode array detectors which are also very helpful for their identification of the characteristic absorption spectra of the flavonoids. In the last decade, mass spectrometers connected to HPLC systems introduced a greater selectivity and sensitivity in flavonoid analysis. Improving the characteristics of the stationary phases and developing more sophisticated instruments as well as devices for more efficient and faster sample preparation are the challenges for all modem analysts. Discovering... 

An example that could be classified as a hybrid of traditional HPLC and UHPLC applications is the work carried out by Garcia-Villalba et al. [10], in which the characterization and quantification of extra-VOO phenolic compounds by an RRLC (rapid resolution liquid chromatography) method coupled to diode-array and TOE MS detection systems was developed. The RRLC method, transferred from... 

HPLC-MS is a fast and reliable method for structural analyses of nonvolatile phenolic compounds, since better techniques (interfacing systems) have been developed for the removal of the liquid mobile phase before ionization. 

Fan et al. [150] studied the selective analysis of 4-nitrophenol (4-NP) from water samples using online SPE coupled to HPLC system. They have utilized the (3-cyclodextrin-bonded silica (CDS) as the selective sorbent for 4-nitrophenol compound. Using 100 mL of sample solution spiked with 4-NP and six other phenols (Ph) in double-distilled water, they have shown that the sorbent has a strong capacity in adsorbing 4-NP and the recovery was 104% with the detection limit of 0.017 xg/L. Figure 16.2 and Figure 16.3 show chromatograms obtained from online SPE-HPLC systems [150]. 

---