Indirect atomic absorption spectrometric determination of citric acid by continuous precipitation

A continuous precipitation and filtration flow system for the separation of citric acid by precipitation with lead and indirect flame atomic absorption spectrometry is proposed. The precipitate is formed by injecting the lead solution into a carrier containing the sample and is subsequently retained on a filter. By using this reversed precipitation flow-injection configuration, citric acid was determined in the range 2–40 μg mL^–1, with a relative standard deviation of 2.9% at a sampling frequency of 60 samples h^–1. This method has been applied to the determination of citric acid in fruit juices, carbonated soft drinks and sweets. Received: 19 March 1999 / Revised: 27 May 1999 / Accepted: 31 May 1999     

Solvent‐free polymerization of citric acid and D‐sorbitol

Copolymers of citric acid and D ‐sorbitol were synthesized with a solvent‐free vacuum‐oven synthesis with molar ratios of citric acid to D ‐sorbitol ranging from 1/1 to 6/1. The extent of the reaction was followed by the monitoring of the residual acid content of the system. As expected, the reaction occurred much more rapidly at 150 than at 110 °C. The Fourier transform infrared (FTIR) spectra of the products showed the expected FTIR bands at approximately 1735 and 1188 cm^?1, which were indicative of ester formation. Gel permeation chromatography showed a major product with a molecular weight of approximately 3500 Da. An insoluble material with a water‐absorption index of up to 17 was also synthesized and could lead to possible applications as absorbers, thickeners, and biobased seed coatings. Additionally, the mono‐ and disodium salts of citric acid were also polymerized with D ‐sorbitol in a manner similar to that of the citric acid system. Soluble polymers were synthesized with a residual acid content of 5 mequiv/g of polymer. These materials showed Ca⁺²‐sequestering ability (up to 0.56 mmol of Ca⁺²/g of the product). © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4259–4267, 2006     

A rapid automated method for wine analysis based upon sequential injection (SI)-FTIR spectrometry

A new process control methodology for the simultaneous determination of sugars, alcohols and organic acids in wine based on multivariate evaluation of mid-IR transmission spectra of wine samples is presented. In addition to ethanol several lower level wine components (glucose, fructose, glycerol, citric-, tartaric-, malic-, lactic- and acetic acid) were determined. To establish a multivariate calibration model a set of 72 calibration solutions was prepared and measured, using a novel, fully automated sequential injection (SI) system with Fourier transform infrared (FTIR) detection. The resulting spectra were evaluated using a partial least square (PLS) model. The developed PLS model was then applied to the analysis of real wine samples containing 79–91 g L^–1 ethanol, 5.9–8.1 g L^–1 glycerol, 0.4–6.9 g L^–1 glucose, 1.5–7.5 g L^–1 fructose, 0.3–1.6 g L^–1 citric acid, 1.0–1.7 g L^–1 tartaric acid, 0.02–3.2 g L^–1 malic acid, 0.4–2.8 g L^–1 lactic acid and 0.15–0.60 g L^–1 acetic acid, yielding results which were in good agreement with those obtained by an external reference method (HPLC-IR). The short analysis time (less than 3 min) together with high reproducibility makes the newly developed method applicable to process control and screening purposes (average of the standard deviations calculated from four repetitive measurements of six different real samples: ethanol: 0.55 g L^–1, glycerol: 0.037 g L^–1, glucose: 0.056 g L^–1, fructose: 0.036 g L^–1, citric acid: 0.020 g L^–1, tartaric acid: 0.010 g L^–1, malic acid: 0.052 g L^–1, lactic acid: 0.012 g L^–1 and acetic acid: 0.026 g L^–1).     

Determination of citric acid in soft drinks using flow injection with potentiometric detection

A flow injection analysis (FIA) system with potentiometric detection has been developed for the determination of citric acid in commercial fruit juices using a copper-selective tubular electrode. It consists of the complexation of citrate ion with copper (II) ion, monitoring the free copper (II) concentration. Linear relationships between the potential and log concentrations of citric acid in the range of 1 × 10^–3 mol/L – 1 × 10^–2 mol/L were attained with samples injected in the system without prior treatment. Repeatability was determined by assessing the relative standard deviation for ten replicate injections of different juice samples which varied from 1.2% to 3.0%. The results provided by the automated system were compared with those of an enzymatic conventional method used for the analysis of citric acid in food and a relative deviation of less than 4.0% was found. Recovery trials resulted in values from 97.0% to 101.0%. The system allows a sampling frequency of 60 samples/h.     

Spectrophotometric determination of tantalum with 4,5-dibromo-o-nitrophenylfluorone

Micro amounts of tantalum can be determined directly by spectrophotometry with 4,5-dibromo-o-nitrophenylfluorone, citric acid, hydrogen peroxide and Triton X-100 in 0.5–5 mol l^?1 sulphuric acid. The apparent molar absorptivity of tantalum at 530 nm is 1.84 × 10⁵ l mol^?1 cm^?1. Beer's law is obeyed for 0–10 μg of tantalum in 25 ml of solution at 530 nm and a large amount of niobium and most foreign ions can be tolerated. Results obtained by applying the proposed method to niobium oxide, ferroniobium, nickel-base alloy and a mineral are satisfactory. The synthesis of the complexing agent is described.     

Polar-Functionalized,Crosslinkable, Self-Healing,and Photoresponsive Polyolefins

The nonpolar nature of polyolefins is one of their biggest limitations. Now, an efficient route to generate polar-functionalized, crosslinkable, self-healing, photoresponsive polyolefins with thermoplastic, elastomeric, and thermosetting properties is reported. Tunable amounts of carboxylic acid and a cyclic comonomer are installed onto polyolefins by palladium-catalyzed terpolymerization reactions. The incorporated carboxylic acid unit can alter the surface properties of polyolefins. The subsequently introduced Fe³⁺/citric acid combination induces dynamic crosslinking and enables self-healing. Under UV light irradiation, citric acid reduces Fe³⁺ to Fe²⁺ and decreases the crosslinking density. The Fe²⁺ moiety can be easily oxidized back to Fe³⁺, making the process reversible at the expense of citric acid. The incorporated cyclic comonomer modulates the crystallinity of polyolefins, provides elastic properties, and installs carbon–carbon double bonds for sulfur-induced vulcanization.     

Citrate complexes of tin(IV) studied by liquid-liquid extraction with 5,7-dichloro-8-quinolinol

The tin(IV)/5,7-dichloro-8-quinolinol/chloroform extraction system is used to determine the composition and the stability constants of the aqueous complexes of tin(IV) with citric acid, in the pH range 2.0–3.5. The tin(IV):citric acid ratios found are 1:1 and 1:2, depending on the concentration of the acid. The conditional stability constants are (5.5 ± 0.4) × 10³ and (1.3 ± 0.3) × 10³ for the 1:1 and 1:2 complexes, respectively. This extraction system is convenient in studies of aqueous tin(IV) complexes that cannot be extracted into chloroform.     

Study on the selective leaching of low-grade phosphate ore for beneficiation of phosphorus and rare earths using citric acid as leaching agent

In the study the organic/inorganic chemical leaching and enrichment technology were used for selective extraction of the dolomite which co-existed in the Zhijin low-grade phosphate ore for beneficiation phosphorous and rare earths (RE) by using citric acid as leaching agent. The effects of acid concentration, reaction time, reaction temperature, liquid/solid ratio, and particle size on P₂O₅ and rare earths grade and the recovery ratio of them were investigated. The results show that under the optimized experimental conditions (acid concentration 9%, reaction time 240 min, reaction temperature 40°C, liquid/solid ratio 50: 1, and ore particle size 0.18–0.125 mm) the P₂O₅ grade can be increased from 15.47 to 34.82%, and P₂O₅ recovery rate comes up to 88.02%. The rare earths are mainly enriched in the leaching residues. Meanwhile, the recovery rate of rare earths is 72.08%. ΣREO grade can be increased from 978.06 × 10^–4 to 1998 × 10^–4%. In addition, the reaction kinetics of the chemical reaction between citric acid and dolomite are also discussed, the results show that the leaching process is controlled by chemical reaction. The activation energy for leaching was found to be 36.6337 KJ mol^–1 and k₀ was 3.67×104 s^–1, and the rate of the leaching based on the chemical reaction-controlled process could be expressed as 1–(1–a)^1/3 = 3.67 × 10⁴e^–36.63/RTt. Compare to the conventional process, the method provided in this study not only has advantages including higher phosphate concentration and rare earth grade, and higher recovery rate, but also using less amount of chemicals. Meanwhile, the citric acid can be recycled, avoiding discharge wastewater.     

Synthesis and characterization of nanocrystalline tin oxide by sol–gel method

Nanocrystalline SnO₂ particles have been synthesized by a sol–gel method from the very simple starting material granulated tin. The synthesis leads a sol–gel process when citric acid is introduced in the solution obtained by dissolving granulated tin in HNO₃. Citric acid has a great effect on stabilizing the precursor solution, and slows down the hydrolysis and condensation processes. The obtained SnO₂ particles range from 2.8 to 5.1 nm in size and 289–143 m² g⁻¹ in specific surface area when the gel is heat treated at different temperatures. The particles show a lattice expansion with the reduction in particle size. With the absence of citric acid, the precursor hydrolyzes and condenses in an uncontrollable manner and the obtained SnO₂ nanocrystallites are comparatively larger in size and broader in size distribution. The nanocrystallites have been characterized by means of TG-DSC, FT-IR, XRD, BET and TEM.     

Atomic-absorption determination of vanadium and molybdenum in tap water and mineral waters after anion-exchange separation.

A method is described for the determination of vanadium and molybdenum in samples of tap and bottled mineral water. After acidification with citric acid the water sample is heated to about 80°C to remove CO₂; sodium citrate and ascorbic acid are added and the resulting solution of pH 3 is passed through a column of the strongly basic anion-exchange resin Dowex 1-X8 (citrate form) on which both vanadium and molybdenum are adsorbed as anionic citrate complexes. Vanadium is eluted with 6 M hydrochloric acid; molybdenum is recovered with 2 M perchloric acid-1 M hydrochloric acid. Vanadium and molybdenum are determined in the eluates by atomic-absorption spectrometry. The samples analysed contained 0.1–0.9 μg l^?1 vanadium and 0.2–13 μg l^?1 molybdenum.     

Aqueous polymerization of acrylonitrile initiated by the Mn3+/citric acid redox system

Kinetics of polymerization of acrylonitrile initiated by the redox system Mn³⁺/citric acid were investigated in aqueous sulphuric acid in the range of 20–25°; initial rates of polymerization and Mn³⁺ disappearance etc. were measured. The effects of certain water miscible organic solvents and certain cationic and anionic detergents on the rate of polymerization have been examined. A mechanism has been suggested involving formation of a complex between Mn³⁺ and citric acid, decomposition of which yields the initiating free radical and with polymerization being terminated by mutual interaction of growing radicals.     

Polar‐Functionalized,Crosslinkable, Self‐Healing,and Photoresponsive Polyolefins

The nonpolar nature of polyolefins is one of their biggest limitations. Now, an efficient route to generate polar‐functionalized, crosslinkable, self‐healing, photoresponsive polyolefins with thermoplastic, elastomeric, and thermosetting properties is reported. Tunable amounts of carboxylic acid and a cyclic comonomer are installed onto polyolefins by palladium‐catalyzed terpolymerization reactions. The incorporated carboxylic acid unit can alter the surface properties of polyolefins. The subsequently introduced Fe³⁺/citric acid combination induces dynamic crosslinking and enables self‐healing. Under UV light irradiation, citric acid reduces Fe³⁺ to Fe²⁺ and decreases the crosslinking density. The Fe²⁺ moiety can be easily oxidized back to Fe³⁺, making the process reversible at the expense of citric acid. The incorporated cyclic comonomer modulates the crystallinity of polyolefins, provides elastic properties, and installs carbon–carbon double bonds for sulfur‐induced vulcanization.     

Purification and properties of carnitine acetyltransferase from citric acid producingAspergillus niger

Carnitine acetyltransferase was purified from the citric acid producingA. niger mycelium with a protein band showing a relative molecular weight of 77,000 and a pH optimum of 7.3. TheK _m values for the purified enzyme for acetyl-CoA and for carnitine were 0.1 mM and 1 mM, respectively. Carnitine acetyltransferase was located both in the mitochondria and in the cytosol. Both mitochondrial and cytosolic enzyme were purified using ammonium sulfate precipitation, Mono Q and Superose 12 separation. Regarding the localization, except for maximum velocity, there were no differences observed in substrate specificity and inhibition. Inhibition of the enzyme with micromolar concentrations of Cu²⁺ could contribute to a greater citric acid biosynthesis. Carnitine acetyltransferase can be considered as an enzyme necessary for the transport of acetyl groups through mitochondrial membrane in both directions.     

Structural Analysis of Ti And Pb Citrate Using NMR and FT-Raman Signals and Quantum Mechanics Simulations

Titanium citrate and lead and titanium citrate were prepared by polymeric precursor method in aqueous solution. This citrate was analyzed by ¹H, ¹³C NMR and gHMBC–NMR (Hetero-nuclear multiple-bond correlation) to investigate the formation of the citrate complexs and influence of the Pb²⁺ ion in this complex. These complexs were characterized by interaction between Ti⁴⁺ ion and citric acid carboxyls. Quantum mechanic simulations in level ab initio were used to study the electronic structure and natural charges (NBO) to both the complexs. Such techniques indicated the formation of an octahedral complex with an arrangement similar to Ti atom in the crystalline structure of the PbTiO₃. A study using the technique FT-Raman made possible the confirmation of the interaction among the Ti⁴⁺ and Pb²⁺ ions with the citric acid carboxyls.     

Spectrophotometric Determination of Trace Amounts of Ascorbic Acid

Abstract

Colourless silver-gelatin complex is quantitatively reduced by ascorbic acid to yellow silver sol in water within the pH range 7.5–10.0 at room temperature. The determination of 1–10μg/ml of ascorbic acid is possible at 415 nm in the presence of glycine, alanine, fructose, sucrose, citric, tartaric, oxalic, malic, succinic acids and also in the presence of various reducing agents. The molar absorptivity of ascorbic acid at the δ_max is found to be 21500 lit mol^?1 cm^?1 and the Sandell sensitivity of the sol is 8.18x10^?3 μg ascorbic acid cm^?2 for 0.001 absorbance. The relative standard deviation is ±0.22% and the confidence limit (20 determinations, 95%) being 8.806±0.0093%.     

Influence of combustion reagent and microwave drying method on the characteristics of nano-sized Nd<Superscript>3+</Superscript>:YAG powders synthesized by the gel combustion method

Nanosized Nd³⁺ doped Y₃Al₅O₁₂ (Nd³⁺:YAG) powders have been synthesized by the gel combustion method using different combustion reagent such as citric acid, ethylene diamine tetraacetic acid (EDTA), glycine, glycol and the combination of citric acid and EDTA with different ratio. The pure YAG phase was obtained at relatively low temperature around 950 °C for citric acid or EDTA and 1,050 °C for glycine or glycol as combustion reagent, respectively by the gel combustion method. It was found that citric acid and EDTA are the better combustion reagents and yield rather homogeneous and well dispersed club-shape Nd³⁺:YAG samples, and the particle size synthesized by EDTA is larger than that by citric acid. Moreover, the particle size of Nd:YAG was enlarged when the ratio of EDTA was increased in the combination reagent, and the better dispersion of YAG was obtained when the ratio of citric acid to EDTA was 1:1 compared to that of other ratios and pure one as combustion reagent. On the other hand, the results showed that the microwave assisted in drying process of gel to xerogel produced more smaller Nd³⁺:YAG particles in size, and more homogeneous dispersion of the Nd³⁺:YAG particles than that of the traditional dry method.     

A Simple Method for Determination of Homologue Imidazolium Cations in Ionic Liquids Using IC with Direct Conductivity Detection

An investigation was carried out into the fast determination of five homologue imidazolium cations in ionic liquids by ion chromatography using a cation-exchange column and direct conductivity detection. Ethylenediamine, complex organic acid (citric acid, oxalic acid and tartaric acid) and organic modifiers (acetonitrile) were used as mobile phase. The influences of the eluent types, eluent concentration, eluent pH and column temperature on separation of the cations were discussed. Simultaneous separation and determination of the five homologue imidazolium cations in ionic liquids were achieved under an optimum condition. The optimized mobile phase was consisted of 0.25 mmol L^?1 ethylenediamine + 0.5 mmol L^?1 citric acid + 3% acetonitrile (v/v) (pH 4.1), set at a flow rate of 1.0 mL min^?1. The column temperature was 40 °C and detection limits were obtained in the range of 1.1–45.6 mg L^?1. The relative standard deviations of the chromatographic peak areas for the cations were <3.0% (n = 5). This method was successfully applied to separate imidazolium cations in ionic liquids produced by organic synthesis. The recoveries of spiked components were 92.5–101.9%.     

Voltammetric Determination of Lead Labelled Albumin and of Albumin Antiserum by Immunoassay

Abstract

Differential pulse polarography was utilized in voltammetric immunoassay to determine human albumin and albumin antiserum. Albumin was labelled with lead, which exhibited a reduction peak with E_1/2 at ?680 mV vs SCE. The current is proportional to the concentration of lead labelled albumin, and hence the albumin at a fixed lead concentration, and it decreases in proportion to the amount of albumin antiserum added. Albumin concentrations of 2.0 × 10^?6–10 × 10^?6 M and 10–50 μl of goat albumin antiserum (titer 1:16 = maximum dilution causing precipitation with equal volume of 1 mg/ml human albumin) were measured in the presence of 2 × 10^?6 M lead.     

Liquid/liquid extraction separation of hafnium with amberlite La-1 from zirconium and other elements in citric acid solutions

Hafnium (10–110 μg ml^?1) is quantitatively extracted at pH 4.5 from 0.01 M citric acid with 0.1 M Amberlite LA-1 in xylene; it can be stripped with 0.1 M perchloric acid and determined spectrophotometrically with xylenol orange at 540 nm. Hafnium can be separated from binary and multicomponent mixtures by selective extraction and back-extraction. The method is suitable for determining hafnium in zircon.     

The determination of low lead levels in the bone of lead-depleted mice by graphite furnace atomic absorption spectrometry

Low lead levels in the femurs of mice fed with a lead-depleted diet have been determined by use of electrothermal atomic absorption spectrometry with Zeeman-effect background correction. The method is based on the use of Mg(NO₃)₂/Pd as matrix modifier which enables significant reduction of the spectral interferences prevalent if chemical modifiers based on NH₄H₂PO₄ with either Ca or Mg are used for samples rich in Ca₃(PO₄)₂ matrix. The method was developed and validated by use of the NIST standard reference material 1486 bone. Bones were decomposed in a pressurized microwave-heated system using 70% nitric acid. Forty-three mice femurs, with a mass of 74.62 ± 12.54 mg, were dissolved in concentrated nitric acid. The lead results found in SRM 1486 (1.25 ± 0.15 μg g^–1, n = 9) were in good agreement with the certificate (1.335 ± 0.014 μg g^–1). Recoveries of 200 ng lead added to the SRM before or after digestion were 99.0 ± 1.4% and 98.5 ± 1.6%, respectively. The lead detection limit in bone samples is 0.06 μg g^–1 dry mass. This method is, therefore, suitable for the determination of very low lead levels (0.06–0.20 μg Pb kg^–1 bone) in the femurs of mice fed a diet with lead level of < 20μg kg^–1.