Analytical Detection of Phenols

Phenols are soluble in NaOH but not in NaHCOj. With Fe + they produce complexes whose characteristic colors are green, red, blue, and purple. 

Infrared stretching bands of phenols are 3200-3600 cmfor the O—H (like alcohols), but 1230cm for the C—O (alcohols 1050-1150cm ). Nmr absorption of OH depends on H-bonding and the range is 5 = 4-12 ppm. 

---

In this assay, the product, phenol, was separated by chromatography on a Develosil ODS-7 analytical column (4.6 mm x 150 mm). The mobile phase was a 70 30 mixture of 10 mM acetate buffer (pH 4.0) and methanol at a flow rate of 1.5 mL/min. For detection of phenol, the electrode potential was set at 1.2 V against an Ag/AgCl reference electrode. 

Direct UVA IS analysis of plastics may be performed on transparent films or compression moulded plaques, with sample thicknesses usually between 50 and 500 /xm depending on the absorbances of the analytes and the polymer. For purposes of reproducibility it is advised to press several thin films of various polymer granules. In-polymer UV analysis of a UV transparent polyolefin matrix allows detection of phenolic AOs (at 280 nm) or UVAs (at 330-340 nm) down to 25 ppm level. 

Increased selectivity and prevention of passivation of the BDD surface may be also achieved by its modification. An enzyme-based amperometric sensor was proposed for detection of phenolic compounds by Notsu et al. BDD was anod-ically polarized for the introduction of hydroxyl groups onto its surface, then treated with (3-aminopropyl)triethoxysilane (APTES), and finally coated with a tyrosinase film cross-linked with glutaraldehyde. Tyrosinase catalyzes oxidadmi of phenol and various phenol derivatives to o-benzoquinone derivatives via catechol derivatives and thus the quinones generated are ready to be reduced electrochemically at an appropriate potential and obtained reduction currents serve as good analytical signals for the determination of the phenol derivatives. Bisphenol A and 17-/ -estradiol were detected at —0.3 V vs. Ag/AgCl with the detection limit of 1 pmol in FIA. However, the biosensor retained its activity only for a few days due to weak bonding of APTES to BDD surface. 

The comparison of analytical characteristics HPLC methods of determination of phenols with application amperometric and photometric detectors was caiiy out in this work. Experiment was executed with use liquid chromatograph Zvet-Yauza and 100 mm-3mm 150mm-3mm column with Silasorb C18 (5 10 p.m). With amperometric detector phenols were detected in oxidizing regime on glass-cai bon electrodes. With photometric detector phenols were detected at 254 nm. 

Chau and Terry [146] reported the formation of penta-fluorobenzyl derivatives of ten herbicidal acids including 4-chloro-2-methyl-phenoxy acetic acid [145]. They found that 5h was an optimum reaction time at room temperature with pentafluorobenzyl bromide in the presence of potassium carbonate solution. Agemian and Chau [147] studied the residue analysis of 4-chloro-2-methyl phenoxy acetic acid and 4-chloro-2-methyl phenoxy butyric acid from water samples by making the pentafluorobenzyl derivatives. Bromination [148], nitrification [149] and esterification with halogenated alcohol [145] have also been used to study the residue analysis of 4-chloro-2-methyl phenoxy acetic acid and 4-chloro-2-methyl phenoxybutyric acid. Recently pentafluorobenzyl derivatives of phenols and carboxylic acids were prepared for detection by electron capture at very low levels [150, 151]. Pentafluorobenzyl bromide has also been used for the analytical determination of organophosphorus pesticides [152],... 

The retention times, limit of detection and repeatabilities of the analytes are compiled in Table 2.59. It has been concluded from the results that this easy-to-carry-out method can be used even in routine laboratories for the quantitative analysis (UV detection) and for the identification (ESI-MS) of this class of phenolic compounds in various complicated matrices [164]. 

RP-HPLC has been employed for the determination of flavonoids and other phenolic compounds in cranberry juice. The neutral and acidic analytes were preconcentrated octadecyl silica SPE cartridges conditioned with distilled water (neutral analytes) or with 0.01 M HC1 (acidic compounds). Hydrolysis of samples was carried out in aqueous methanol solution acidified with 6 M HC1 at 35°C for 16h. Chromatographic separation was performed in an ODS column (150 X 4.6mm i.d. particle size 5/.an). Solvents A and B were water-acetic acid (97 3, v/v) and methanol, respectively. The gradient started with 0 per cent B (flow rate, 0.9 ml/min), reached 10 per cent B in lQmin (flowrate, 1.0 ml/min) and increased to 70 per cent B in 40min (flowrate, 1.0 ml/min). Analytes were detected at 280 and 360 nm. Some typical chromatograms are presented in Fig. 2.71. The concentrations of flavonoids and phenolic acids are compiled in Table 2.69. It was stated that the SPE-HPLC procedure makes possible the simultaneous determination of phenolic compounds and flavonoids, therefore, it can be employed for the measurement of these classes of analytes in other fruit juices [188],... 

Analytical methods for detecting phenol in environmental samples are summarized in Table 6-2. The accuracy and sensitivity of phenol determination in environmental samples depends on sample preconcentration and pretreatment and the analytical method employed. The recovery of phenol from air and water by the various preconcentration methods is usually low for samples containing low levels of phenol. The two preconcentration methods commonly used for phenols in water are adsorption on XAD resin and adsorption on carbon. Both can give low recoveries, as shown by Van Rossum and Webb (1978). Solvent extraction at acidic pH with subsequent solvent concentration also gives unsatisfactory recovery for phenol. Even during carefully controlled conditions, phenol losses of up to 60% may occur during solvent evaporation (Handson and Hanrahan 1983). The in situ acetylation with subsequent solvent extraction as developed by Sithole et al. (1986) is probably one of the most promising methods. 

It is used in IC systems when the amperometric process confers selectivity to the determination of the analytes. The operative modes employed in the amperometric techniques for detection in flow systems include those at (1) constant potential, where the current is measured in continuous mode, (2) at pulsed potential with sampling of the current at dehned periods of time (pulsed amperometry, PAD), or (3) at pulsed potential with integration of the current at defined periods of time (integrated pulsed amperometry, IPAD). Amperometric techniques are successfully employed for the determination of carbohydrates, catecholamines, phenols, cyanide, iodide, amines, etc., even if, for optimal detection, it is often required to change the mobile-phase conditions. This is the case of the detection of biogenic amines separated by cation-exchange in acidic eluent and detected by IPAD at the Au electrode after the post-column addition of a pH modiher (NaOH) [262]. 

Hoyt and Sepaniak have used capillary zone electrophoresis to determine procaine in pharmaceuticals as a cation of benzylpenicillin [148]. A benzylpenicillin potassium tablet (250 mg) was treated with 20 mL of a 0.2% phenol solution (the internal standard), and dispersed in water. The solution was diluted to 500 mL, and samples were introduced into the fused silica capillary tube (70 cm x 50 gm) by siphoning. With 10 mM Na2HP04-6mM Na2B407 buffer as the mobile phase, the samples were subjected to electrophoresis at 30 kV (25 to 30 pA), and the emerging analytes detected at 228 nm within 10 minutes. 

---