Nitrophenols analysis

The procedure of simultaneous extracting-spectrophotometric determination of nitrophenols in wastewater is proposed on the example of the analysis of mixtures of mono-, di-, and trinitrophenols. The procedure consists of extraction concentrating in an acid medium, and sequential back-extractions under various pH. Such procedures give possibility for isolation o-, m-, p-nitrophenols, a-, P-, y-dinitrophenols and trinitrophenol in separate groups. Simultaneous determination is carried out by summary light-absorption of nitrophenol-ions. The error of determination concentrations on maximum contaminant level in natural waters doesn t exceed 10%. The peculiarities of application of the sequential extractions under fixed pH were studied on the example of mixture of simplest phenols (phenol, o-, m-, />-cresols). The procedure of their determination is based on the extraction to carbon tetrachloride, subsequent back-extraction and spectrophotometric measurement of interaction products with diazo-p-nitroaniline. 

Eor the selective pre-concentration of deactivated phenols a new silica-based material with the grafted 2,3,5-triphenyltetrazole was proposed. This method is based on the formation of molecular chai ge-transfer comlexes of 2,3,5-triphenyltetrazole (7t-acceptor) with picric acid (7t-donor) in the phase of the sorbent. Proposed SPE is suitable for HPEC analysis of nitrophenols after their desorption by acetonitrile. Test-system for visual monitoring of polynitrophenols under their maximum concentration limits was developed using the proposed adsorbent. 

The perspective of using consecutive reactions is grounded on the example of the analysis of isomeric mono-nitrophenols and anion surface-active substances. The variants of systematic analysis of mixtures of tri-, di- and mono-nitrophenols, anion surface-active substances, based on the combination of measurements of consecutively received extracts at different pH values are discussed. 

The effects of pH on electrokinetic velocities in micellar electrokinetic chromatography was studied by using sodium dodecyl sulfate solutions [179]. Micellar electrokinetic capillary chromatography with a sodium dodecyl sulfate pseudostationary phase has been used to determine the partition constants for nitrophenols, thiazolylazo dyes, and metal chelate compounds [180]. A similar technique was used to separate hydroquinone and some of its ether derivatives. This analysis is suitable for the determination of hydroquinone in skin-toning creams [181]. The ingredients of antipyretic analgesic preparations have also been determined by this technique [182], The addition of sodium dodecyl sulfate improves the peak shapes and resolution in chiral separations by micellar electrokinetic chromatography [183]. 

Nitrophenol and 4-nitrophenol glucuronide are excreted in urine. The studies of urinary excretion of methyl parathion metabolites, including those reported in this section, generally hydrolyze the glucuronide prior to analysis and report the resulting total 4-nitrophenol values. 

A recent method, still in development, for determining total 4-nitrophenol in the urine of persons exposed to methyl parathion is based on solid phase microextraction (SPME) and GC/MS previously, the method has been used in the analysis of food and environmental samples (Guidotti et al. 1999). The method uses a solid phase microextraction fiber, is inserted into the urine sample that has been hydrolyzed with HCl at 50° C prior to mixing with distilled water and NaCl and then stirred (1,000 rpm). The fiber is left in the liquid for 30 minutes until a partitioning equilibrium is achieved, and then placed into the GC injector port to desorb. The method shows promise for use in determining exposures at low doses, as it is very sensitive. There is a need for additional development of this method, as the measurement of acetylcholinesterase, the enzyme inhibited by exposure to organophosphates such as methyl parathion, is not an effective indicator of low-dose exposures. 

Although the inhibition-based biosensors are sensitive, they are poor in selectivity and are rather slow and tedious since the analysis involves multiple steps of reaction such as measuring initial enzyme activity, incubation with inhibitor, measurement of residual activity, and regeneration and washing. Biosensors based on direct pesticide hydrolysis are more straightforward. The OPH hydrolyzes ester in a number of organophospho-rus pesticides (OPPs) and insecticides (e.g. paraoxon, parathion, coumaphos, diazinon) and chemical warfare agents (e.g. sarin) [53], For example, OP parathion hydrolyzes by the OPH to form p-nitrophenol, which can be measured by anodic oxidation. Rainina... 

When environmental water was analyzed with respect to a possible contamination with 4-nitrophenol, it could be shown that by using an MI-SPE polymer selective for 4-nitrophenol the following LC-analysis was much facilitated due to the cleaner matrix and the reduction of interference caused by humic acids [91 ]. 

Nitrophenolic compounds were analyzed by GC-MS-SIM, after trimethylsilylation by the flash heater derivatization procedure, which is suitable for nitrophenols not easily derivatized by the conventional methods. The method is suitable for identification of complex mixtures and for quantitative analysis in the nanogram range510. 

The buried Cys-212 of human carbonic anhydrase B (3 pM) is virtually unreactive towards 2-chloromercuric-4-nitrophenol (60 pM) at pH 9.2, but upon the addition of only 40 pM CN , the half-life drops to 10 minutes which is an, at least, 75-fold rate enhancement. On first analysis, this would suggest that inhibitor binding to the enzyme has produced a conformational change or altered the — SH environment of the Cys—212. This is unexpected. How would you prove by kinetic experiments that the CN is binding to the mercury compound and not the enzyme and that this is changing the reactivity. The rate reaches a constant value at high [CN ]. 

Toxic nitrophenols (4-nitrophenol, 2-nitrophenol, and 2,4-dinitrophenol) present in air samples are sampled on silica gel or XAD-2 polymeric resin, extracted, and analyzed by the HPLC/DAD technique [240], Nitrophenols are also determined in rain and snow precipitations through HPLC/ UV analysis after SPE [241]. 

One unit of a-D-mannosidase liberates 1 fig of p-nitrophenol from 6 mM p-nitrophenyl a-D-mannoside in 1 hr at 37° and pH 5. Protein was determined by the method of Lowry and coworkers,5 with bovine albumin as the standard. Metal analysis was performed by atomic absorption spectrophotometry. The enzyme preparation was purified to stage 5 of the original procedure (see Table V) and dialyzed at pH 8 to remove the excess of Zn2+ finally, gel chromatography was conducted at the same pH. 

The use of indicators for the detection of carboxylic acids has been examined. Stahl et al. [58] used the sodium salt of o-nitrophenol for the UV analyses of nanoequivalents of acids. This technique could be applied to fluorescence analysis with indicators such as umbelliferone which exhibits strong fluorescence in the protonated form. 

In the case of pesticides which are not ChE inhibitors, exposure is measured by the analysis of blood and/or urine for the active ingredient or its metabolites. Baseline levels of pesticides and/or metabolites are not usually determined, with the exception of methyl bromide. In this case, a blood sample is taken to check for bromide ion before fumigators use the pesticide. Blood and urine tests are run only in the case of spills or other accidents to assist in identifying the cause of poisoning or to monitor workers in a workplace. Paraquat, chlorinated hydrocarbons, mercury, p-nitrophenol, and dinitrophenol are examples of pesticides or metabolites of pesticides that have been found in the urine of exposed workers. 

Selected data published by Patsias and Papadopoulou-Mourkidou [114] illustrate sorption s dependence on sample volume (Figure 2.36). Their research pursues development of an automated online SPE-HPLC methodology for analysis of substituted anilines and phenols. Recovery (%) was measured for numerous compounds on various polymeric sorbents, but the only data presented here are those in which a styrene-divinylbenzene polymeric sorbent was used for analysis of aniline, phenol, 4-nitroaniline, and 4-nitrophenol. Aqueous sample volumes of 5, 10, 25, 50, 75, 100, 125, and 150 mL were acidified to pH 3 before SPE. 

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