Selective detection of carboxylic acids, ureas and phenols and semiquantitative determination of citric acid by capillary solid-state spot-tests

Solid-state spot-tests for the selective detection of carboxylic acids, ureas and phenols have been developed. Mixtures of p-dimethylaminobenzaldehyde with N-methylurea and of p-dimethylaminobenzaldehyde with phthalic acid are used as reagents. Based on these tests a semiquantitative determination of citric acid is also developed. These tests utilize three properties of the coloured boundary: colour, length and direction of movement. Our work on capillary solid-state spot-tests,(1) has now been extended to some further organic compounds.     

Sensitive tests for nitrite through azo-dye formation

The diazonium cation resulting from the interaction of nitrite with sulphanilic acid is coupled with pyridinols to give red azo-dyes. Compared to many other colour reactions employed for detection of nitrite, the present systems afford greater sensitivity. Many ions do not affect the colour; thus detection and determination are selective. The method is applied in determination of nitrite in water samples.     

A new spray reagent for selective detection of dichlorvos by thin-layer chromatography

The misuse of dichlorvos (DDVP), an organophosphorus insecticide, results in many instances of poisoning. This paper describes a new spray reagent for selective detection of dichlorvos in biological materials by thin-layer chromatography. Dichlorvos in presence of moisture breaks down to dichloroacetaldehyde which in turn reacts with phenylhydrazine hydrochloride to give a yellowish red colour. In acidic media the colour is intensified and consequently the sensitivity of detection increases. The reagent is selective for dichlorvos, other organophosphorus insecticides failed to give a coloured spot. Moreover organochlorine, carbamate and synthetic pyrethroid insecticides or even constituents of visceral extracts (amino acids, peptides, proteins etc.) do not interfere. The limit of detection is ca 10 mug.     

Thin-layer chromatographic detection of monocrotophos in biological materials

An organophosphorus insecticide monocrotophos is increasingly being used in agriculture to control insects on a wide range of crops. Its ready access has resulted in misuse in many instances of homicidal and suicidal poisoning cases. This paper describes a chromogenic spray reagent for the detection of monocrotophos in biological materials by thin-layer chromatography. Monocrotophos on alkaline hydrolysis yields N-methylacetoacetamide which in turn reacts with diazotized sulphanilamide or sulphanilic acid to give a red colour. Other organophosphorus insecticides do not give a coloured spot. Moreover, organochlorine and synthetic pyrethroid insecticides and constituents of viscera (amino acids, peptides, proteins etc.) which are generally co-extracted with the insecticides, do not interfere. However, phenolic compounds and hydrolysed product of carbamate insecticides, may interfere and are differentiated from monocrotophos by R_F values. The limit of detection is ca 1 μg.     

Derivatisation for liquid chromatography/electrospray mass spectrometry: synthesis of pyridinium compounds and their amine and carboxylic acid derivatives

A simple method has been developed for the pre-column derivatisation of low molecular weight primary and secondary amines and carboxylic acids using quaternary nitrogen compounds to enhance their detection by liquid chromatography/electrospray ionisation mass spectrometry (LC/ESI-MS). The synthesis of seven novel quaternary nitrogen reagents is described. The derivatives are designed to be relatively small molecules to avoid some of the steric hindrance problems that may be associated with larger derivatisation reagents. The compounds have amine and carboxylic acid functional groups with which to derivatise carboxylic acids and amines, respectively. Two of the compounds contain a bromine atom in order to assess the advantages of a bromine isotope pattern in the mass spectra. This acts as a simple marker for derivatisation and enables data processing by cluster analysis.Activation of the carboxylic acid group was achieved by the use of either 1-chloro-4-methylpyridinium iodide (CMPI) or the more reactive 1-fluoro-4-methylpyridinium p-toluenesulphonate (FMP).1 Using both of these active reagents, the degree of nucleophilic substitution was investigated for the derivatisation of a variety of small molecules. Whilst giving some increase in the ESI-MS response for the derivatised compounds, the FMP itself acted as a derivatising reagent in a competing reaction. In the light of this finding, FMP was reacted with the test compounds separately and gave positive results as a derivatising reagent. Detection of the 'pre-charged' derivatives of amines and carboxylic acids by LC/ESI-MS was investigated with respect to their ESI response and chromatography.     

利用Fe^3＋与SCN^—的显色反应检测内燃机车冷却液中的亚硝酸钠

1　引言内燃机车冷却液中NaNO2(18～22gL)的测定是采用KMnO4容量滴定法[1]。该方法重现性差、误差大[2]。作者改用稀乙酸调节冷却液酸度,以硫脲作还原剂,在波长476nm下[3]测其吸光度可求出NaNO2的含量。2　试验21　主要仪器和试剂752C型紫外可见分光光度计。标样(NaNO2标?..     

Flow injection spectrophotometric determination of nitrite

4-Nitroaniline, which gives intensely yellow solution on dissolution in dilute hydrochloric acid, has been found to react with nitrite almost instantaneously in acidic medium yielding a colourless product that has been identified as 4-nitrophenyl diazo cation. The measurement of decrease in colour intensity suggested a new, simple and one-step reaction procedure that has been used for the reversed flow injection determination of 5microg-5 mg/l. NO(2)-N. The limit of detection has been found to be 2 microg/l. NO(2)-N. A number of species such as copper(II) and lead(II), which interfere in other spectrophotometric procedures, do not affect the results. The method has been applied to determine nitrite in natural waters when the %RSD was in the range 1.8-3.5%.     

Tüpfelnachweis von Säureanhydriden

Zusammenfassung Für den Nachweis von Säureanhydriden wird eine Tüpfelmethode vorgeschlagen, die darauf beruht, daß o-Nitrophenylhydrazin mit Anhydriden einen Säure-Base-Indikator bildet, der sich in alkalischem Milieu violett bis blau färbt. Das Reagens ist kein Säure-Base-Indikator, daher stört es den Nachweis nicht. Säurechloride und einige Oxoverbindungen geben den Nachweis auch, nicht aber Säureamide, Imide, Ester, Sulfamide und Peroxide. Mit dieser Reaktion können Säureanhydride neben Säuren, z. B. 0,01% Essigsäureanhydrid in Essigsäure, tüpfelanalytisch nachgewiesen werden.

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Spot test detection of acid anhydrides

Summary For the detection of acid anhydrides it is suggested that a spot test method be employed that is based on the fact thato-nitrophenylhydrazine yields an acid-base indicator with anhydrides. This product gives a violet to blue colour in an alkaline milieu. The reagent is not an acid-base indicator and consequently does not interfere with the test. Acid chlorides and some oxo compounds likewise respond to the test but acid amides, imides, esters, sulfamides and peroxides do not. By means of this reaction it is possible to detect acid anhydrides in the presence of acids by spot test methods, for instance, 0.01% actetic anhydride in acetic acid.

     

Optimisation of post-column reaction detector for HPLC of explosives

Summary Improvements in selectivity and sensitivity in the analysis of common explosives, like nitrate esters, nitramines and nitroaromatic compounds can be achieved by post-column derivatisation in a two step reaction detector. The first step in derivatisation is the photolysis of the analytes with UV at 254 nm. The photo reactor consists of a crocheted 20 m Tefzel capillary, which is coiled around a low pressure mercury lamp. In second step the nitrite ion generated is subsequently detected by a colourimetric reaction. The azo dye formed can be selectively detected at 540 nm.Addition of alkali after chromatographic separation to prevent oxidation of initially formed nitrite to nitrate during photolysis leads to a complex multistage arrangement. However, the contribution to peak broadening by the reactor is negligible and it is possible to detect 25–50 ppb of nitramines and 30–100 ppb of nitrate esters. Another advantage of the method is the selective detection of nitro compounds, even in complex matrices.The trace analysis of explosives is of growing interest in forensic science as well as in environmental analysis. It has been shown [1] that explosives can easily be extracted from soil and debris by the use of supercritical carbon dioxide. The separation and determination of explosives by gas chromatography is hindered by their thermal instability. In HPLC only the nitro aromatic explosives can be detected with sufficient sensitivity. Other types of explosives like the esters of nitric acid or nitramines do not absorb sufficiently in the UV region for sensitive detection. It has been shown [2] that explosives are liable to photochemical decomposition in the UV region, resulting in nitrate and nitrite, which have been detected after separation by ion-pair chromatography with electrochemical detection. A more sensitive and selective detection of nitrite has been possible in flow injection analysis [3]. Here a modified Griess reaction has been used. In a first step nitrite ions are used to form the diazonium salt with sulfanilamide which is coupled in a second step with N-[naphthyl-(1)]-ethylene diamine (NED) to form a redviolet azo dye with an absorption maximum at 540 nm. The advantage of this method is selective detection in the visible region, where hardly any other organic components are detected, which might be present in a crude environmental sample.In this paper the transfer of the Griess reaction to post-column derivatisation in RP chromatography of explosives will be described, and the optimisation of trace analysis of these solutes will be discussed.     

A novel method for bromodecarboxylation of α,β-unsaturated carboxylic acids using catalytic sodium nitrite

A first novel synthetic utility of catalytic sodium nitrite in combination with aqueous HBr, for bromo decarboxylation of α,β-unsaturated carboxylic acid is described. α,β-Unsaturated carboxylic acid compounds successfully converted into corresponding bromo compounds. The advantages of this protocol are shorter reaction time and moderate to good yields.     

Detection and spectrophotometric determination of EDTA with cobalt(II) and phosphomolybdic acid in urine and detergents

A simple, rapid, sensitive and selective method for the microgram detection and spectrophotometric determination of EDTA in water, human urine and detergents, based on its reaction with Co(II) and phosphomolybdic acid at pH 0.5–2.0 is reported. Absorbance is measured against Co(II)–phosphomolybdic acid reference solution at 750 nm. The effect of time, temperature, pH and Co(II) or phosphomolybdic acid concentration is studied, and optimum operating conditions are established. Beer's law is applicable in the concentration range 0.3–1.9 μg ml⁻¹ of 10⁻⁵M EDTA. Its detection limit is 0.14 μg in the solution phase and 0.03 μg in the resin phase. The relative standard deviation is ±0.13 μg. Ag(I), Zn(II), Cu(II), Ni(II), Pb(II), Cd(II), Ca(II), Mg(II), Fe(III), Cr(III), U(VI), chloride, nitrite, phosphate, oxalate, borate and amino acids do not interfere.     

Uranium carbide dissolution in nitric acid: speciation of organic compounds

The direct dissolution of UC, a potential fuel for generation-IV nuclear reactors, in nitric acid can produce organic complexants that may interfere with the consumed fuel reprocessing based on liquid–liquid extraction. This study shows the presence of 17 % of carboxylic and polycarboxylic acids (e.g. benzenepentacarboxylic acid). 25 % of the carbon mass balance seemed to correspond to unfunctionalized polyaromatic compounds with more than 3–4 aromatic rings. Under an active oxidation process, these compounds become smaller and very functionalized polyaromatic compounds. Structures have been proposed for 8 % of the carbon mass balance.     

Selective Kinetic Spectrophotometric Determination of Nitrite in Food and Water

Abstract

A highly selective and sensitive method for the kinetic spectrophothometric determination of sub-microgram amounts of nitrite has been development based on its reaction with Nile blue 2B in acidic medium. The reaction is monitored spectrophotometrically at 595 nm at a fixed time of 4.5 min. The change in absorbance at 595 nm is related to the concentration of nitrite in the range 0.005 - 1.100 μg.ml^?1 The detection limit is 0.001 μg.ml^?1. The relation standard deviation is 1% for 0.020 μg.ml^?1 of nitrite for ten replicate measurements. Most common anions and cations do not interfere. The procedure was applied to the determination of trace amounts of nitrite in sausage and water.     

Laser-induced fluorescence detection in liquid chromatography after preliminary derivatization of carboxylic acid and primary amino groups

The development of selective derivatization for the determination of carboxylic acids, amino acids and peptides in aqueous solutions is described as a preliminary study for the determination of these compounds in biological materials. The derivatization reactions are completed before the liquid chromatographic separation and laser-induced fluorescence detection for which a continuous-wave argon-ion gas laser is used in the ultraviolet or visble mode. Carboxylic acid groups arre derivatized with 9-hydroxymethylathracene and primary amino groups are derivatized with fluorescein isothiocyanate. Detection limits, in aqueous solutions, for the carboxylic acid derivatives are ca. 190 fg (ultraviolet mode). In the visible mode, the detection limits are ca. 1 fg for the primary amino derivatives of amino acids and peptides. In al the chromatographic analyses, the derivatization mixtures are injected onto a standard reversed-phase or reversed- phase ion-pair system and conventional flow cells are used without expensive photon counting or optical systems.     

羧酸的还原方法

羧酸的还原是有机化学中的一类重要反应，有着广泛的用途。氯化铝锂是还原羧酸的常用试剂，但是，该试剂能还原多种官能团，因此选择性较差，近年来，化学工作者研究亲报道了许多新的还原方法，如用NaBH4/I2、NaBH4/H2SO4、NaBH4/BOP体系等还原羧酸成醇以及还原羧酸成醛的特殊方法。本文拟对这些新的研究进展作一介绍。     

Hydroxyl group deprotection reactions with Pd(OH)2/C: a convenient alternative to hydrogenolysis of benzyl ethers and acid hydrolysis of ketals

Benzyl ethers, ketals and orthoformates were cleaved with Pd(OH)₂/C in methanol, to generate the corresponding alcohol; carboxylic acid esters were stable under these reaction conditions. Pd(OH)₂/C in methanol was used for the deprotection of hydroxyl groups during the preparation of sequoyitol via myo-inositol orthobenzoate. This method of deprotection has the potential to be useful in the synthesis of different classes of organic compounds since the reaction conditions do not involve strong acids, bases or hydrogen.     

A fluorescence test for vanadium(V) with resorcinol

Summary In continuation of our previous work in which salicylic acid was reported to give a very sensitive and an almost specific colour reaction with vanadium(V), we have now found that vanadium(V) reacts with resorcinol in 20 N sulphuric or phosphoric acid solution to give a blue coloured product, which gives a vivid red fluorescence under filtered ultraviolet light. A sensitive test for vanadium(V) has now been developed making use of this red fluorescence or of the bright blue colour. Dichromate gives a somewhat less sensitive violet colour with the resorcinol reagent under the same conditions, but the product does not fluoresce. Manganese(VII), cerium(IV), iron(III), titanium(IV), uranium(VI), molybdenum(VI) and tungsten(VI) do not interfere with the colour reaction or the fluorescence test for vanadium(V).     

Activation of Carboxylic Acids in Asymmetric Organocatalysis

Organocatalysis, catalysis using small organic molecules, has recently evolved into a general approach for asymmetric synthesis, complementing both metal catalysis and biocatalysis. 1 Its success relies to a large extent upon the introduction of novel and generic activation modes. 2 Remarkably though, while carboxylic acids have been used as catalyst directing groups in supramolecular transition‐metal catalysis, 3 a general and well‐defined activation mode for this useful and abundant substance class is still lacking. Herein we propose the heterodimeric association of carboxylic acids with chiral phosphoric acid catalysts as a new activation principle for organocatalysis. This self‐assembly increases both the acidity of the phosphoric acid catalyst and the reactivity of the carboxylic acid. To illustrate this principle, we apply our concept in a general and highly enantioselective catalytic aziridine‐opening reaction with carboxylic acids as nucleophiles.     

Dendrimer Modified Thiolated Gold Surfaces as Sensor Devices for Halogenated Alkyl‐Carboxylic Acids in Aqueous Medium. A Promising New Type of Surfaces for Electroanalytical Applications

Thiolated gold electrodes bearing either carboxylic or amino terminal groups were exposed to dilute PAMAM dendrimer aqueous solutions in which the ramified polymers have the complementary opposite charge. The novel interfaces that result from dendrimer electrostatic aggregation, were then probed as electrochemical sensors for three halogenated carboxylic acid compounds in aqueous solution. The results show an increased sensitivity for the electrochemical detection of the three acids using the modified surfaces as compared to bare gold electrodes. The use of this type of novel interfacial architecture, is presented as a potentially new and important approach for the development of electroanalytical sensors for the detection of organic contaminants in water.     

Fluorimetric determination of α-keto acids with 4,5-dimethoxy-1,2-diaminobenzene and its application to high-performance liquid chromatography

A highly sensitive fluorimetric method for the determination of α-keto acids of biological importance is described. The α-keto acids react in dilute hydrochloric acid with 4,5-dimethoxy-1,2-diaminobenzene to give a compound which fluoresces in neutral solution. The method is selective for α-keto acids and the limits of detection are 30–750 pmol ml^?1 of test solution. The fluorescent compounds in a reaction mixture of ten α-keto acids are separated within 18 min by high-performance liquid chromatography on a reversed-phase column with isocratic elution. The limits of detection for the acids are in the range 9–780 fmol in a 10-μl injection volume.