Micro solid‐phase derivatization analysis of low‐molecular mass aldehydes in treated water by micellar electrokinetic chromatography

A MEKC method was developed for the determination of aliphatic and aromatic low‐molecular mass aldehydes (LMMAs) in treated water samples. The method involves the precapillary derivatization and extraction of the aldehydes on a Telos?ENV μ‐SPE column impregnated with 2,4‐dinitrophenylhydrazine . After elution of the hydrazones with ACN, the derivatives were analyzed using MEKC–DAD. Resolution of the MEKC procedure was studied by changing the pH and the concentration of the buffer, the type, and the concentration of surfactant, and the organic modifier content in the BGE. A running buffer consisting of a phosphate buffer (pH 7.2, 75 mM) with CTAB (50 mM) and ACN (30%) gave the best results. Linearity was established over the concentration range 0.5–500 μg/L and LODs from 65 to 775 ng/L; the interday precision was expressed as the RSD of the aldehydes ranging from 6.6 to 8.4%. Matrix effects were shown to be negligible by comparing the response factors obtained in ultrapure and treated waters. Aldehydes were readily determined at 1.1–8.4 μg/L levels in ozonated and chlorinated water samples, the method proposed being the first CE contribution developed for the systematic analysis of both aliphatic and aromatic LMMAs in water samples.     

Aldehyde detection by chromogenic/fluorogenic oxime bond fragmentation

Amination of 4-nitrophenol, umbelliferone and 4-methylumbelliferone gave the corresponding oxyamines 1-3. These oxyamines react with aldehydes and ketones to form oximes. In the case of aliphatic aldehydes and electron-poor aromatic aldehydes, the oximes undergo base-catalyzed fragmentation in aqueous buffer in the presence of bovine serum albumin to give the parent phenols, which is the acyclic analog of Kemp's elimination reaction of 5-nitrobenzisoxazole 28. The process can be used as a spectrophotometric assay for formaldehyde under aqueous neutral conditions.     

Novel applications of chloroperoxidase: enantioselective oxidation of racemic epoxyalcohols

The CPO-catalysed enantioselective oxidations of racemic glycidol and cis-2,3-epoxyhexanol to the corresponding aldehydes were studied using tert-butyl hydroperoxide in the 9:9:1 and 18:1 mixtures of hexane:ethyl acetate:buffer and hexane:buffer, respectively. Temperature and pH (100 mM citrate buffer, pH 4.0–7.0) effects on enantioselectivity in the terms of ee for the less reactive alcohol enantiomers with conversion were studied.     

Analysis of low‐molecular mass aldehydes in drinking waters through capillary electrophoresis with laser‐induced fluorescence detection

The potential of CZE with LIF detection in the separation and determination of low‐molecular mass aldehydes involving precolumn derivatization with fluorescein 5‐thiosemicarbazide was investigated. Different variables that affect derivatization (pH, fluorescein 5‐thiosemicarbazide concentration, time and temperature) and separation (pH and concentration of the BGE, kind and concentration of surfactants at levels higher and lower than CMC, and applied voltage) were studied. The separation was conducted within 16 min by using borate buffer (60 mM; pH 10) with 10 μM polyethylene glycol tert‐octylphenyl ether as modifier. Good linearity relationships (correlation coefficients ranged from 0.9978 to 0.9994 for aldehydes) were obtained between the peak areas and concentration of the analytes (0.5–100 μg/L). The LODs for aldehydes were achieved at submicrogram‐per‐liter level (0.15–0.35 μg/L), which indicated that the proposed method surpassed other electrophoretric alternatives in terms of LOD, in many cases even at ca. 1000‐fold. The inter‐day precision (RSD, %) of the aldehydes ranged from 5.2 to 8.3%. Finally, the method was successfully applied to bottled drinking‐water samples, and the aldehydes were readily detected at 0.6–4.4 μg/L levels with average recoveries ranging from 99.1 to 103.5%.     

Highly efficient aldol additions of DHA and DHAP to N-Cbz-amino aldehydes catalyzed by L-rhamnulose-1-phosphate and L-fuculose-1-phosphate aldolases in aqueous borate buffer

Aldol addition reactions of dihydroxyacetone (DHA) to N-Cbz-amino aldehydes catalyzed by L-rhamnulose-1-phosphate aldolase (RhuA) in the presence of borate buffer are reported. High yields of aldol adduct (e.g. 70-90%) were achieved with excellent (>98?:?2 syn/anti) stereoselectivity for most S or R configured acceptors, which compares favorably to the reactions performed with DHAP. The stereochemical outcome was different and depended on the N-Cbz-amino aldehyde enantiomer: the S acceptors gave the syn (3R,4S) aldol adduct whereas the R ones gave the anti (3R,4R) diastereomer. Moreover, the tactical use of Cbz protecting group allows simple and efficient elimination of borate and excess of DHA by reverse phase column chromatography or even by simple extraction. This, in addition to the use of unphosphorylated donor nucleophile, makes a useful and expedient methodology for the synthesis of structurally diverse iminocyclitols. The performance of aldol additions of dihydroxyacetone phosphate (DHAP) to N-Cbz-amino aldehydes using RhuA and L-fuculose-1-phosphate aldolase (FucA) catalyst in borate buffer was also evaluated. For FucA catalysts, including FucA F131A, the initial velocity of the aldol addition reactions using DHAP were between 2 and 10 times faster and the yields between 1.5 and 4 times higher than those in triethanolamine buffer. In this case, the retroaldol velocities measured for some aldol adducts were lower than those without borate buffer indicating some trapping effect that could explain the improvement of yields.     

Efficient and Highly Selective Oxidation of Primary Alcohols to Aldehydes by N-Chlorosuccinimide Mediated by Oxoammonium Salts

2,2,6,6-Tetramethyl-1-piperidinyloxy catalyzes efficient oxidation of primary alcohols to aldehydes by N-chlorosuccinimide, in a biphasic dichloromethane-aqueous pH 8.6 buffer system in the presence of tetrabutylammonium chloride. Aliphatic, benzylic, and allylic alcohols are readily oxidized with no overoxidation to carboxylic acids. Secondary alcohols are oxidized to ketones with a much lower efficiency. Very high chemoselectivities are observed when primary alcohols are oxidized in the presence of secondary ones. Primary-secondary diols are selectively transformed into hydroxy aldehydes, with, in some cases, no detectable formation of the isomeric keto alcohols.     

Derivatizing assay for the determination of aldehydes using micellar electrokinetic chromatography

In this work, the use of a novel derivatization agent for the determination of aldehydes (in this particular case: formaldehyde, acetaldehyde, propionaldehyde, and valeraldehyde) using micellar electrokinetic chromatography is reported. The derivatization reaction is based on the reaction of aldehydes with benzhydrazide to form the corresponding derivates with maximum absorbance at 250 nm. The experimental conditions of the derivatization reaction as well of the separation were optimized. The adducts were separated with a +22 kV voltage at a temperature of 29°C. The adducts’ separation was performed in less than 14 min using as the running buffer a mixture containing 110 mmol/L of sodium dodecyl sulfate and 27 mmol/L of sodium tetraborate at pH 9.45. Samples were injected using hydrodynamic mode (50 mbar × 5 s). The calibration curves were linear up to 15.0 mg/L with r ² above 0.99. Intra and inter‐day precisions were in average 3 and 4%, respectively, and recoveries were in average of 95%. Limits of detection and quantification were around 0.5 and 1.5 mg/L, respectively. The developed method was successfully applied in the analysis of low molar weight aldehydes in yogurt and vinegar samples.     

1,2-Diamino-4,5-ethylenedioxybenzene as a highly sensitive fluorogenic reagent for aromatic aldehydes

1,2-Diamino-4,5-ethylenedioxybenzene is shown to be a highly sensitive reagent for aromatic aldehydes, especially for benzaldehydes having a hydroxy group. The reagent reacts selectively with aromatic aldehydes at pH 3.0 (phosphate buffer) within 30 min at 60°C; the products fluoresce most intensely at pH 11. In the manual method, the lower limits of detection vary from 6 pmol ml^?1 to 7 nmol ml^?2. The fluorescent derivatives of aromatic aldehydes can be separated by reversed-phase high-performance liquid chromatography. The fluorescent product from 4-hydroxybenzaldehyde is shown to be 2-(4-hydroxyphenyl)-5,6-ethylenedioxybenzimidazole.     

Study on the (R)-oxynitrilase activity of Pouteria sapota

Mamey (Pouteria sapota) defatted meal was used to catalyze the enantioselective addition of HCN to α,β-unsaturated aldehydes. Using a biphasic system of diisopropyl ether and citrate buffer (0.1 M, pH 5.0, 10% v/v), the (R)-cyanohydrins obtained showed good conversion (from 54 to 98%) and enantiomeric excess (from 74 to 99%).     

Analysis of low molecular weight aldehydes in air samples by capillary electrophoresis after derivatization with 4-hydrazinobenzoic acid

This work reports the analysis of selected aldehydes in air samples using capillary electrophoresis (CE). The method is based on the reaction of aldehydes with 4-hydrazinobenzoic acid (HBA) to give the corresponding hydrazones with maximum absorbance at 290 nm. Under optimized CE conditions, the HBA derivatives of four carbonyls (formaldehyde, acetaldehyde, propionaldehyde, and acrolein) were completely separated from one another, in less than 6 min, using a pH 9.3 tetraborate buffer at 0.040 mol L(-1) concentration as background electrolyte. A few method validation parameters were determined revealing good migration time repeatability (< 1.5% CV) and area repeatability (< 2% CV), excellent linearity (50-300 microg/L, r > 0.996) and adequate sensitivity for environmental applications. The limits of detection with respect to each single aldehyde were in the range of 2.7-8.8 ng L(-1). The methodology was applied to the determination of aldehydes indoors. Samples were collected in HBA impregnated octadecylsilica cartridges, at different times during the day. The most abundant carbonyls in the samples were acetaldehyde followed by formaldehyde, with estimated peak concentrations of 4.3 and 2.9 ppbv, respectively.     

Laser-induced fluorescence and UV detection of derivatized aldehydes in air samples using capillary electrophoresis

In this work, two capillary zone electrophoresis methodologies using UV absorption detection (214 nm) and laser-induced fluorescence detection (He/Cd laser, 325 nm excitation, 520 nm emission) of selected aldehydes (formaldehyde, acetaldehyde, propionaldehyde and acrolein) derivatized with dansylhydrazine (DNSH, 5-dimethylaminonaphthalene-1-sulfohydrazide) were proposed and validated. The aldehydes react with DNSH to form negatively charged molecules in methanolic medium. In both methodologies, nine DNSH-derivatives, including isomers of acetaldehyde, propionaldehyde and acrolein and two impurities were baseline separated in 20 mmol l(-1) phosphate buffer at pH 7.02, in less than 9 min. The limits of detection for the UV and LIF methodologies ranged from 1.1-9.5 microg l(-1) and 0.29-5.3 microg l(-1), respectively. The applicability of both methodologies to contemplate real samples was confirmed in the analysis of aldehyde-DNSH derivatives in indoor and outdoor air samples.     

Optimization of the separation of phenolic compounds by micellar electrokinetic capillary chromatography

A group of phenolic compounds including phenolic aldehydes, acids and flavonoids are separated by micellar electrokinetic chromatography (MECC). The influence of buffer (concentration and pH), concentration of sodium dodecylsulphate (SDS) and applied voltage were studied. To increase the selectivity of the separation and the resolution of the solutes organic solvents are added to the separation buffer, the best results were obtained when methanol was used at lower percentages. An optimized buffer (150 mM boric acid (pH 8.5)-50 mM SDS-5% methanol) provides the optimum separation with regard to resolution and migration time. This method was applied to the determination of these compounds in wine samples with good results.     

Nucleotide and aldehyde analysis by HPLC for determination of radical induced damage

Summary The analysis of two metabolite groups, nucleotides and aldehydes, is necessary for assessment of oxygen radical metabolism during hypoxia and reoxygenation.Nucleotides and their derivatives were determined by HPLC using gradient elution with 10 mM NH₄H₂PO₄ buffer containing 2 mM t-butylammoniumphosphate and acetonitrile.Aldehydes occuring after lipid peroxidation were analyzed by derivatisation to dinitrophenylhydrazones followed by TLC and HPLC separation with methanol/water on an ODS column.     

Some aspects of the crosslinking of gelatin by dextran dialdehydes

The present paper describes the formation of hydrogels by reaction of gelatins with periodate oxidized dextrans. The effect of a number of reaction parameters on the rate of gelation is investigated. It is demonstrated that the time to onset of gelation depends on the nature of the gelatin, the nature of the dextran dialdehyde, the type of buffer, the ionic strength and the presence of added salts. The gelation time decreases with increasing concentration of aldehydes, increasing pH and increasing molecular weight of the dextran dialdehyde. In general, the gelation occurs more rapidly with decreasing concentration of indifferent electrolytes, except for the reaction in phosphate buffer where an increase in gelation is observed with increasing buffer strength. Ammonium and calcium salts are found to retard significantly the crosslinking reaction.     

Aspects of Electrochemical Behavior of Aldehydes and Ketones in Protic Media

Reduction of carbonyl group in aldehydes and ketones, as well as oxidation of numerous aldehydes is discussed, as well as those reductions of organic compounds where the C?O group activates cleavage of an adjacent C? X bond where X is a good leaving group like halogen, OH, NH₂ or SR or activates hydrogenation of an adjacent C?C group. Survey involves aliphatic and aromatic aldehydes, aryl alkyl and diaryl ketones, as well as α‐ketoacids, 1,2‐diketones and compounds where the carbonyl group is a part of a ring. The role of acid–base, hydration–dehydration and in some cases keto–enol equilibria on electrochemical behavior is pointed out, as well as the role of buffer kind and concentration and the nature of the cation of supporting electrolyte. Better understanding of these factors promises finding of best conditions for electroanalytical procedures.     

Baker’s yeast (Saccharomyces cerevisiae) mediated transformations of C-aryl-N-phenylnitrones

C-Aryl-N-phenylnitrones are transformed to a mixture of azoxybenzene and aryl aldehydes when treated with a mixture of Baker’s yeast and sucrose in pH = 6.0 phosphate buffer medium at 32 °C.     

Spectral and acidity constants of some heterocyclic nitrogen Schiff bases

The spectral behaviour of some arylidene-2-aminopurines in pure and mixed organic solvents as well as in buffer solutions of varying pH have been studied. It is recognized that the hydroxy derivatives form an intermolecular hydrogen bond solvated molecular complex with DMF solution. The pK values of the purine compound and the aminopurine Schiff bases of some aromatic aldehydes have been determined and discussed.     

Amperometric determination of alcohols, aldehydes and carboxylic acids with an immobilized alcohol oxidase enzyme electrode.

A new enzyme electrode has been developed for the rapid and simple measurements of blood ethanol. A platinum electrode was coupled with immobilized alcohol oxidase, sensing the dissolved oxygen consumption amperometrically. Blood ethanol can be measured within several minutes without any pretreatments. The only reagent required is phosphate buffer. The enzyme electrode was found to respond not only to alcohols but also to aldehydes and carboxylic acids.     

Anti-selective direct asymmetric Mannich reaction catalyzed by protease

The anti-selective direct asymmetric Mannich reaction of (hetero) aromatic aldehydes, 4-anisidine and O-protected hydroxyacetones for the synthesis of stereodefined anti-β-amino-α-hydroxycarbonyl compounds was developed. Protease type XIV from Streptomyces griseus (SGP) was used as a biocatalyst in 1,4-dioxane/phosphate buffer under mild reaction conditions. The excellent diastereoselectivities of up to >99:1 (anti/syn) and good enantioselectivities of up to 90% ee were achieved. This method provides a more sustainable complement to chemically catalyzed anti-selective direct asymmetric Mannich reactions.     

柱前衍生高效液相色谱法同时测定水性涂料中6种醛类化合物

建立了柱前衍生高效液相色谱同时测定水性涂料中甲醛、乙醛、丙醛、苯甲醛、正戊醛和对甲基苯甲醛等6种醛类化合物的方法。样品经水超声提取后,与2,4-二硝基苯肼乙腈溶液在酸性条件下衍生,再经0.45 μm针式过滤器过滤后进样分析。系统考察了酸度调节剂、pH值、反应温度、时间等因素对衍生反应的影响,优化的反应条件为：以稀释后的盐酸溶液作为酸度调节剂,缓冲溶液pH=3,反应温度为60 ℃,反应时间为30 min。在此条件下,于0.08~2.0 mg/L浓度范围内,6种醛类化合物呈良好的线性关系;检出限为0.05~2.50 mg/kg;在2.0、4.0、6.0 mg/kg 3个水平下的加标回收率为87.0%~112.8%;RSD为1.12%~9.54%。结果表明,本方法具有较宽的线性范围,良好的精密度和准确度,适用于水性涂料中6种醛类化合物的同时测定。