Numerical Method for Determination of Composition of Weak Acid Mixtures by Potentiometric Titration

An equation describing the state of weak acid mixtures was derived from the relationships between mole balance and charge balance. The equation was solved with numerical method and the compositions of the acid mixtures were determined. The advantages of this treatment were demonstrated by analyzing binary mixtures of chloroacetic, formic and acetic acids.     

Determination of Surface pKa of Pure Mercaptoacetic Acid and 2-Mercaptobenzothiazole Mixed Monolayers by Impedance Titration

Interfacial proton transfer reactions of pure mercaptoacetic acid (MA) and 2-mercaptobenzothiazole (Mbz) mixed self-assembled monolayers (SAMs) have been studied using a.c. impedance titration method. The charge-transfer resistance (Rct) is measured with the monolayer composition and the ionic strength ofpH solution. The surface pKa can be obtained by the plots of Rct and pH, the reasons of shifts of surface pKa are also explained.     

Determination of ß-Diketones by Oscillometric Titration

Abstract

An oscillometric titration technique has been applied to the determination of ß-diketones. Typical accuracies of about ± 1.5% were obtained for the compounds studied. The technique is rapid and simple, and should be suitable to the serial analyses of many compounds of pharmaceutical interest.     

Determination of Lead in Dinnerware by an Ion Exchange Filter Paper ‐ X-Ray Fluorescence Method

Abstract

Lead leached from a variety of pottery dinnerware was determined by x-ray fluorescence after collecting and concentrating the lead on an ion exchange resin loaded filter paper disc. A 0.01 M HCl solution, to simulate acidic foodstuffs, used for the leaching was shown to have a leaching rate almost identical to that of white vinegar. The leaching rate increased with increasing temperature. The relative standard deviation for successive determinations of the same lead content was 1.8%, and the detection limit was 1.08 μg of total lead which corresponded to 0.0072 ppm when 150 ml of leaching solution was used.     

An Efficient Procedure for Esterification of Aryloxyacetic Acid and Arylthioacetic Acid Catalyzed by Silica Sulfuric Acid

Aryloxyacetate and arylthioacetate are wildly used in herbicides, plant regulator and insecticides. Recently, Wille et al. have reported that methyl aryloxyacetate is an efficient agent to prevent and treat allergic contact dermatitis.[1] The most popular synthesis is by heating sodium phenoxide (mercaptide) with ethyl chloroacetate in DMF,[2] or by the esterification of acid with alcohol using concentrated H2SO4 as catalyst.[3] In this paper, synthesis of aryloxyacetate and aryl thioacetate from aryloxyacetic acid and arylthioacetic acid respectively in ether catalyzed by silica sulfuric acid in 83%～94% yields is described. The catalyst is reused for 3 times without significant loss of activity (Entry 4). Compared with common procedures, the present procedure possesses the advantages of the operational simplicity, short reaction time,less-corrosion, high yield and reusable catalyst.     

Improved Method for the Determination of Cyanuric Acid in Animal Feed by GC–MS

A specific and sensitive analytical method for the quantitative determination of cyanuric acid in animal feed was developed. Sample preparation involved the diethylamine/acetonitrile/water extraction of feed using sonication and shaking. The extract was subjected to clean-up by dual solid phase extraction using mixed mode anionic and cationic extraction cartridges. After removal of clean-up solvent, cyanuric acid was converted to a tert-butyldimethylsilyl derivative and was determined by gas chromatography–mass spectrometry in the selected ion monitoring mode. ¹³C ₃ ¹⁵ N₃-cyanuric acid was employed as the internal standard. The calibration curve was found to be linear up to 4 mg kg^?1. LOD and LOQ were determined to be 0.06 to 0.4 mg kg^?1 for fish and chicken feed. The mean recovery of cyanuric acid was 96 to 98% with relative pooled standard deviation of 1.8–7.4% in the range of 0.5 to 100 mg kg^?1 for fish and chicken feed. The validated method was applicable for analysing cyanuric acid in animal feed.     

The Determination of Perphenazine by a New Simple Flow‐Injection Chemiluminescence Method

Abstract

A rapid and simple flow‐injection chemiluminescence (CL) method is described for the determination of perphenazine, which is based on the CL intensity that generated from the redox reaction of Ce (IV)-perphenazine in HNO₃ medium is proportional to the perphenazine concentration without any sensitizers. The proposed method allows the determination range within 1.0×10^?7–7.0 ×10^?5 g mL^?1 with a detection limit of 8.0×10^?8 g mL^?1, and it has been successfully applied to the determination of the perphenazine in pharmaceutical tablet compared well with the official method.     

Synthesis of New β-Acetamido Carbonyl Derivatives Using Cellulose Sulfuric Acid as an Efficient Catalyst

New β-acetamido ketone derivatives are synthesized through a one-pot, four-component reaction of benzaldehyde, dimedone, acetyl chloride, and acetonitrile in the presence of cellulose sulfuric acid as an efficient reusable catalyst. The procedure offers advantages in terms of good yields, short reaction times, mild reaction conditions, and reusability of the catalyst.     

Determination of Lipoic Acid in Biological Samples with Acetonitrile–Salt Stacking Method in CE

An acetonitrile–salt stacking method was established for the assay of lipoic acid (LA) in biological samples. Samples were deproteinized with acetonitrile at a final concentration of 60 % (v/v) and then injected hydrodynamically at 3.45 × 10³ Pa for 180.0 s. The optimum background electrolyte was found to be 90.0 mmol L^?1 pH 9.1 borate buffer. LA could be detected within 35 min at +7.0 kV with satisfactory repeatability (relative standard deviations, RSDs, of migration times and peak areas were both below 10 % for intraday and interday; n = 6/9) and a relatively low limit of detection of ca. 0.5 μmol L^?1.     

Enantioselective Hydrolysis of α-Amino Acid Ester by Chiral Metallomicelles

Metall0ndcellesmadeup0ffunctionalizedsurfactants(orliP0philicligands)caPable0feffectivechelationofmetalionsarecurrentlyreceivingc0nsiderableinterestbecauseoftheircatalyticabilitytomindcmetall0enzymes.OfpatticularinterestarethendcellarmodelsofhydrolghcmetalloenZyInes,whichareabletoprom0tethecleavageofphosphoricandcarboxylicesters0raAndes.'-'M0stofthemaref0cused0ntheligandscontainingidridazole',pyridine'orl,lO-phenanthroline'asthebasicchelatingsubunitandasthem0lecularjunctionfortheparaffmiccha…     

Rapid and Simple Method of Monoacylation of Polyols by β‐Ketoesters Using Microwave Irradiation

Abstract

Polyols undergo rapid selective transesterification with β‐ketoesters upon microwave irradiation in solvent‐free and catalyst‐free conditions to form monoesters.     

Determination of Six Resorcylic Acid Lactones in Feed by GC–MS

A method was developed to simultaneously detect six resorcylic acid lactones in feed by GC–MS. Samples were extracted with methanol followed by a two step liquid–liquid extraction and an HLB SPE clean-up. The samples were derivatized with BSTFA + TMCS (99/1; v/v) and determined by GC–MS. For all analytes, the ranges of recoveries were 81.2–98.2%, with RSDs of 3.2–15.2%, and the LODs were 0.2–0.6 μg kg⁻¹.

     

Simultaneous Determination of the Endogenous Free ��-Lipoic Acid and Dihydrolipoic Acid in Human Plasma and Erythrocytes by RP-HPLC with Electrochemical Detection

A highly sensitive, precise, and accurate reversed-phase high-performance liquid-chromatography/electrochemical detection method for simultaneous determination of the endogenous free ??-lipoic acid and dihydrolipoic acid in biological matrices was developed and validated. The two analytes were extracted from the samples with acetonitrile/10% metaphosphoric acid solution_(aqueous) (50/50 v/v). To determine the total lipoic acid, samples were treated with tris(2-carboxyethyl)phosphine solution in phosphate buffer, pH 2.5 with 85% orthophosphoric acid prior to deproteination. The two analytes were separated on a C₁₈ (150 × 4.6 mm, 5 ??m) analytical column using acetonitrile-50 mM phosphate buffer, pH 2.5 with 85% orthophosphoric acid (35/65 v/v) as the isocratic mobile phase pumped at a flow rate of 2.0 mL min^?1 at the column oven temperature of 35 °C. The column eluents were monitored at a potential of 0.9 V. These analytes were efficiently resolved in <7 min. The present method was sufficiently robust and specific for simultaneous determination of the two analytes and demonstrated acceptable values for linearity (r ² = 0.999 in the range of 0.1?C500 and 0.25?C1,000 ng mL^?1 for ??-lipoic acid and dihydrolipoic acid, respectively), recovery (>97%), precision (RSD% <2), and sensitivity (on column limit of detection, 150 and 375 fg for ??-lipoic acid and dihydrolipoic acid, respectively and limit of quantification: 0.5 and 1.25 pg for ??-lipoic acid and dihydrolipoic acid, respectively), indicating that the proposed method was more sensitive, precise, economical, and versatile, and has higher throughput than the previously reported methods for simultaneous determination of the two analytes.     

Formation and Oxidation of Hydrogen Molybdenum Bronze on Platinum Electrode in Sulfuric Acid Solution

Hydrogen molybdenum bronze (HxMoO3) can be electrodeposited on platinum and oxidized in two steps to the hydrogen molybdenum bronze with less amount of hydrogen HyMoO3 (y相似文献   

Simple LC–MS Determination of Citric and Malic Acids in Fruits and Vegetables

A rapid, reliable and sensitive method has been developed to determine malic and citric acid in fruits and vegetables. The methodology is based on simple extraction with an aqueous solution of ethanol (80% v/v) and subsequent chromatographic analysis by liquid chromatography coupled to mass spectrometry. Electrospray ionization in negative mode was used. The best response for citric and malic acid was provided by molecular ions [M?H]^? at m/z 191 and 133 respectively. These ions were used for quantification, whereas other fragments were used as confirmation ions. Different variables involved in the separation and detection process, such as mobile phase, gradient profile and flow rate have been optimised. Linearity, repeatability, recovery and limits of quantification were evaluated. Good linearity was obtained up to 5,000 mg kg^?1. Recovery ranged from 90.0 to 104.6%, repeatability (expressed as RSD) was <8% for tested matrices, and limits of quantification were equal or lower than 65 mg kg^?1. Finally, the method was applied to the analysis of samples of orange, tomato and pepper.     

A Novel Sensitive Method for the Determination of Cadmium and Lead Based on Magneto‐Voltammetry

Abstract

A novel method for the ultratrace determination of Cd²⁺ and Pb²⁺ based on magneto‐voltammetry was developed. In the presence of a low strength magnetic field of 0.6 T, square wave stripping voltammetry (SWSV) of Cd²⁺ and Pb²⁺ was performed in this determination. A high concentration of redox species Fe³⁺ was added to the analytes to generate a large cathodic current during the preconcentration step. A large Lorentz force arising from the flux of net current through the magnetic field resulted in convective solution flow due to magnetohydrodynamics. Then more metal ions deposited on the electrode surface at a faster rate and an enhancement as large as 160% for the stripping peak current was observed. Under the optimal conditions, this method exhibits high sensitivities of 5.67 µA µM^?1 for Cd²⁺ and 6.98 µA µM^?1 for Pb²⁺, over the 1×10^?8 – 1×10^?6 mol l^?1 range. Detection limits as low as 9.0×10^?10 and 8.6×10^?10 mol l^?1 for Cd²⁺ and Pb²⁺ were obtained with a 2 min preconcentration time, respectively. The method was successfully applied to detect Cd²⁺ and Pb²⁺ in real water samples and the results were in agreement with atomic absorption spectrometry.     

Use of HPLC in the Determination of the Molar Absorptivity of 4��-Geranyloxyferulic Acid and Boropinic Acid

Natural prenyloxycinnamic acids were shown to exert in vitro and in vivo remarkable and valuable anti-cancer and anti-inflammatory effects. Among these, 4??-geranyloxyferulic acid [3-(4??-geranyloxy-3??-methoxyphenyl)-2-trans-propenoic acid] was discovered as an efficient orally active chemopreventive agent of several types of cancer, and its structural analogue boropinic acid was shown to exert a valuable inhibitory effect both in vitro and in vivo against the growth of Helicobacter pylori. As a continuation of our chemical, chemico-physical, and pharmacological studies on these secondary metabolites, we report herein the comparison between traditional UV/Vis assays and HPLC?CDAD methods for the determination of the molar absorptivity coefficient of 4??-geranyloxyferulic acid (?? ₃₁₀ = 12,950 and ?? ₂₈₈ = 11,910 L mol^?1 cm^?1) and boropinic acid (?? ₃₁₀ = 13,510 and ?? ₂₈₈ = 12,350 L mol^?1 cm^?1). Ferulic acid was merely used as a reference standard to test the possibility of the application of these two assays to the oxyprenylated compounds. The data reported in the present study will represent an essential aid for future studies aimed to better define the pharmacological profile and the mechanism of action of these compounds and are an important starting point to evaluate other natural products where standard powders are not available.     

Optimized Synthesis and Simple Purification of 2,5‐Diamino‐thiophene‐3,4‐dicarboxylic Acid Diethyl Ester

A stable diamino thiophene was synthesized in high purity with a three‐fold increase in yield over previous reports via simple crystallization using inexpensive reagents.     

Determination of the Glass Electrode Parameters by Means of Potentiometric Titration of Acetic Acid in Aqueous Sodium or Potassium Chloride Solutions at 25°C

Single-ion activity coefficient equations are presented for the calculation of stoichiometric (molality scale) dissociation constants K _m for acetic acid in aqueous NaCl or KCl solutions at 25°C. These equations are of the Pitzer or Hückel type and apply to the case where the inert electrolyte alone determines the ionic strength of the acetic acid solution considered. K _m for a certain ionic strength can be calculated from the thermodynamic dissociation constant K _a by means of the equations for ionic activity coefficients. The data used in the estimation of the parameters for the activity coefficient equations were taken from the literature. In these data were included results of measurements on galvanic cells without a liquid junction (i.e., on cells of the Harned type). Despite the theoretical difficulties associated with the single-ion activity coefficients, K _m can be calculated for acetic acid in NaCl or KCl solutions by the Pitzer or Hückel method (the two methods give practically identical K _m values) almost within experimental error at least up to ionic strengths of about 1 mol-kg^–1. Potentiometric acetic acid titrations with base solutions (NaOH or KOH) were performed in a glass electrode cell at constant ionic strengths adjusted by NaCl or KCl. These titrations were analyzed by equation E = E _o + k(RT/F) ln[m(H⁺)], where m(H⁺) is the molality of protons, and E is the electromotive force measured. m(H⁺) was calculated for each titration point from the volume of the base solution added by using the stoichiometric dissociation constant K _m obtained by the Pitzer or Hückel method. During each base titration at a constant ionic strength, E _o and k in this equation were observed to be constants and were determined by linear regression analysis. The use of this equation in the analysis of potentiometric glass electrode data represents an improvement when compared to the common methods in use for two reasons. No activity coefficients are needed and problems associated with liquid junction potentials have been eliminated.     

Synthesis of Macrocycles Containing Amino Acid Ester and Aryl-heterocyclic Units

AmongmanynatUraImacrocycleswithbiologicalactivity,therearealInostsomekeystrUctUreunitS.ForinStance,thereareesterresidueinmacrocycliclactonesI'],andaminoacidresidueincycIopeptidesI'].Thesyntheticmacrocycles,ontheotherhand,havebeenfocusedoncrownether,whichhavebeenwelldevelopedfrOmsingleoxygen-containingcrownethertoaza-,thiaandaZahiacrownether.BecauseoftheirspecialtyasenZyInemodels,theyhavebeingcloselycormectedwithBiomirneticChemisnyl'].lnordertoboitatethecomplexnatUrlmacrocycles,weusednat…