Biosensor based on laccase and an ionic liquid for determination of rosmarinic acid in plant extracts

Novel biosensors based on laccase from Aspergillus oryzae and the ionic liquids (ILs) 1-n-butyl-3-methylimidazolium hexafluorophosphate (BMIPF₆) and 1-n-butyl-3-methylimidazolium tetrafluoroborate (BMIBF₄) were constructed for determination of rosmarinic acid by square-wave voltammetry. The laccase catalyzes the oxidation of rosmarinic acid to the corresponding o-quinone, which is electrochemically reduced back to rosmarinic acid at +0.2 V vs. Ag/AgCl. The biosensor based on BMIPF₆ showed a better performance than that based on BMIBF₄. The best performance was obtained with 50:20:15:15% (w/w/w/w) of the graphite powder:laccase:Nujol:BMIPF₆ composition in 0.1 mol L⁻¹ acetate buffer solution (pH 5.0). The rosmarinic acid concentration was linear in the range of 9.99 × 10⁻⁷ to 6.54 × 10⁻⁵ mol L⁻¹ (r = 0.9996) with a detection limit of 1.88 × 10⁻⁷ mol L⁻¹. The recovery study for rosmarinic acid in plant extract samples gave values from 96.1 to 105.0% and the concentrations determined were in agreement with those obtained using capillary electrophoresis at the 95% confidence level. The BMIPF₆-biosensor demonstrated long-term stability (300 days; 920 determinations) and reproducibility, with a relative standard deviation of 0.56%.     

Biomimetic sensor based on MnMn complex as manganese peroxidase mimetic for determination of rutin

A novel biomimetic sensor for rutin determination based on a dinuclear complex [Mn^IIIMn^II(Ldtb)(μ-OAc)₂]BPh₄ containing an unsymmetrical dinucleating ligand, 2-[N,N-bis(2-pyridylmethyl)-aminomethyl]-6-[N-(3,5-di-tert-butyl-2-oxidoben-zyl)-N-(2-pyridylamino)aminomethyl]-4-methylphenol (H₂Ldtb), as a manganese peroxidase mimetic was developed. Several parameters were investigated to evaluate the performance of the biomimetic sensor obtained after the incorporation of the dinuclear complex in a carbon paste. The best performance was obtained in 75:15:10% (w/w/w) of the graphite powder:Nujol:Mn^IIIMn^II complex, 0.1 mol L⁻¹ phosphate buffer solution (pH 6.0) and 4.0 × 10⁻⁵ mol L⁻¹ hydrogen peroxide. The response of the sensor towards rutin concentration was linear using square wave voltammetry in the range of 9.99 × 10⁻⁷ to 6.54 × 10⁻⁵ mol L⁻¹ (r = 0.9998) with a detection limit of 1.75 × 10⁻⁷ mol L⁻¹. The recovery study performed with pharmaceuticals ranged from 96.6% to 103.2% and the relative standard deviation was 1.85% for a solution containing 1.0 × 10⁻³ mol L⁻¹ rutin (n = 6). The lifetime of this biomimetic sensor was 200 days (at least 750 determinations). The results obtained for rutin in pharmaceuticals using the biomimetic sensor and those obtained with the official method are in agreement at the 95% confidence level.     

Determination of oleic acid in sunflower seeds by infrared spectroscopy and multivariate calibration method

A method for the determination of oleic acid in sunflower seeds is proposed. One hundred samples of sunflower seeds were analyzed by near-infrared diffuse reflectance spectroscopy (NIRDRS). The direct measures were realized in ground and sifted seeds. The PLS multivariate calibration model was obtained using first derivate absorbance values as response matrix, while the oleic acid concentration matrix was obtained analyzing the seed samples by gas chromatography with a flame ionization detector (GC-FID). The NIRDRS-PLS model was validated externally using unknown samples of sunflower seeds. The accuracy and precision of the method was evaluated using GC as reference method. The following figures of merit (FOM) were obtained: LOD = 3.4% (w/w); LOQ = 11.3% (w/w); SEN = 8 × 10⁻⁵; SEL = 0.15; analytical sensibility (γ) = 1.5 and linear range (LR) = 18.1-89.2% (w/w). This method is useful for the fast determination of oleic acid in sunflower seeds and for quality control of raw materials.     

Sunflower leaves tissue-based bioelectrode with amperometric flow-injection system for glycolic acid determination in urine

A novel plant tissue-based bioelectrode obtained by incorporating sunflower (Helianthus annuus L.) leaves tissue as a source of glycolate oxidase and peroxidase into a ferrocene-mediated carbon paste electrode for the determination of glycolic acid was developed. It was coupled with the flow-injection (FI) system and used as the basis to develop a novel FI amperometric procedure for glycolic acid determination. The flow-injection amperometric measurements were performed by injecting aliquot of glycolic acid solution into the flowing stream of 0.05 mol L⁻¹ of phosphate buffer solution having pH 8.0 with a flow rate of 0.3 mL min⁻¹. The bioelectrode consisted of 20% (w/w) of sunflower leaves tissue and 5% (w/w) of ferrocene at 0.00 V (vs Ag/AgCl). The bioelectrode exhibited a linear response from 1.0 × 10⁻⁶ up to 2.0 × 10⁻³ mol L⁻¹ glycolic acid with a detection limit (S/N = 3) and a quantitation limit (S/N = 10) of 1 × 10⁻⁶ and 3.3 × 10⁻⁶ mol L⁻¹, respectively. The sampling rate of 12 h⁻¹ and a relative standard deviation of 1.67% (n = 15) were achieved. The bioelectrode response decreased to 70% of the original value within 90 continuous injections. The proposed bioelectrode was satisfactorily applied to glycolic acid determination in human urine samples after appropriate sample pretreatment. Results obtained by the FI method were compared favorably with those obtained by HPLC. It offers advantages, which included rapidity, high activity, limited stability, ease of preparation and low cost.     

Schiff bases as cadmium(II) selective ionophores in polymeric membrane electrodes

The construction and performance characteristics of polymeric membrane electrodes based on two neutral ionophores, N,N′-[bis(pyridin-2-yl)formylidene]butane-1,4-diamine (S₁) and N-(2-pyridinylmethylene)-1,2-benzenediamine (S₂) for quantification of cadmium ions, are described. The influences of membrane compositions on the potentiometric response of the electrodes have been found to substantially improve the performance characteristics. The best performance was obtained with the electrode having a membrane composition (w/w) of (S₁) (2.15%):PVC (32.2%):o-NPOE (64.5%):KTpClPB (1.07%). The proposed electrode exhibits Nernstian response in the concentration range of 7.9 × 10⁻⁸ to 1.0 × 10⁻¹ M Cd²⁺ with limit of detection 5.0 × 10⁻⁸ M, performs satisfactorily over wide pH range (2.0-8.0) with a fast response time (10 s). The sensor has been found to work satisfactorily in partially non-aqueous media up to 30% (v/v) content of methanol, ethanol and acetonitrile and could be used for a period of 2 months. The analytical usefulness of the proposed electrode has been evaluated by its application in the determination of cadmium in real samples. The practical utility of the membrane electrode has also been observed in the presence of surfactants.     

A practical method for the determination of sulphur in coal samples by high-resolution continuum source flame atomic absorption spectrometry

Sulphur in coal was determined using a high-resolution continuum source flame atomic absorption spectrophotometer (HR-CS-FAAS) with actylene/air flame. The C-S absorption band at 258.056 nm was found the most suitable analytical line with respect to sensitivity and spectral interferences. The instrumental parameters were optimized. The coal samples were dried and dissolved using microwave-assisted digestion technique. The validity of the method was tested using standard reference material and certified values were found in the limits of 95% confidence level. Since the concentrations of matrix elements of coal other than carbon are low enough not to cause any spectral interferences, the linear calibration method was applied in all quantifications without any problem. The calibration standards were prepared in sulphuric acid. The method was accurate, fast, simple and sensitive. The limit of detection (LOD, 3δ, N = 10) and the limit of quantification (LOQ, 10δ, N = 10) were found to be 0.01 and 0.03% (w/w), respectively. The sulphur concentrations of various kinds of the coal samples received around Turkey were determined. The sulphur contents of the coal samples were ranged from ≤LOQ to 1.2%.     

Determination of chlorogenic acid in coffee using a biomimetic sensor based on a new tetranuclear copper(II) complex

A new tetranuclear copper(II) complex which mimics the active site of catechol oxidase was synthesized and characterized by IR, CHN, electronic spectroscopic and ¹H NMR methods. The title complex [Cu₂(μ-OH)(bpbpmp-NO₂)]₂[ClO₄]₂ was employed in the construction of a novel biomimetic sensor and used in the determination of chlorogenic acid by square wave voltammetry. The performance and optimization of the resulting biomimetic sensor were studied in detail. The best response of this sensor was obtained for 75:15:10% (w/w/w) ratio of the graphite powder:nujol:Cu(II) complex, 0.1 mol L⁻¹ phosphate buffer solution (pH 7.0), with frequency, pulse amplitude, and scan increment at 30 Hz, 100 mV, and 3.0 mV, respectively. The chlorogenic acid concentration was linear in the range of 5.0 × 10⁻⁶ to 1.45 × 10⁻⁴ mol L⁻¹ (r = 0.9985) with a detection limit of 8.0 × 10⁻⁷ mol L⁻¹. This biomimetic sensor demonstrated long-term stability (250 days; 640 determinations) and reproducibility, with a relative standard deviation of 10.0%. The recovery study of chlorogenic acid in coffee samples gave values from 93.2% to 106.1% and the concentrations determined showed good agreement when compared with those obtained using capillary electrophoresis at the 95% confidence level.     

Comparative study on 2-amino-1,4-naphthoquinone derived ligands as indium (III) selective PVC-based sensors

The three different ligands (Q₂ to Q₄) based on 2-amino-1,4-naphthoquinone (Q₁), have been synthesized and explored as neutral ionophores for preparing polyvinyl chloride-based membrane sensors selective to indium (III). The addition of potassium tetrakis(4-chlorophenyl) borate and various plasticizers, viz., o-NPOE, DBP, DBBP, DOP and CN has been found to substantially improve the performance of the sensors. The best performance was obtained with the sensor no. 16 having membrane of ligand (Q₂) with composition (%, w/w) ionophore Q₂ (3.0%):PVC (30.0%):o-NPOE (63.0%):KTpClPB (4.0%). This sensor exhibits Nernstian response with slope 19.8 mV/decade of activity in the concentration range 2.5 × 10⁻⁷ to 1.0 × 10⁻² M indium (III), performs satisfactorily over wide pH range of (2.5-7.5) with a fast response time (10 s). The sensor was also found to work satisfactorily in partially non-aqueous media up to 20% (v/v) content of acetonitrile, ethanol and methanol. The proposed sensor can be used over a period of 3.5 months without significant drift in potentials. The quantitative application of sensor was also evaluated by comparative analysis of artificially made sea water with AAS.     

Comparative evaluation of Dy(III) selective poly(vinyl) chloride based membrane electrodes of macrocyclic tetraimine Schiff's bases

Three different derivatives of macrocyclic tetraimine Schiff's base have been synthesized and explored as a neutral ionophores for preparing poly(vinyl chloride) based membrane sensors selective to Dy³⁺. The addition of sodium tetraphenyl borate and various plasticizers, viz., o-NPOE, DBP, DBBP, DOP and CN has been found to substantially improve the performance of the sensors. The best performance was obtained with the sensor no. 1 having membrane of Schiff's base (SL-1) with composition (w/w) SL-1 (4.5%): PVC (30.5%): o-NPOE (59.5%): NaTPB (5.5%). This sensor exhibits Nernstian response with slope 19.4 mV/decade of activity in the concentration range of  10⁻⁸ to 1.0 × 10⁻² M Dy³⁺, performs satisfactorily over wide pH range of (2.8-7.2) with a fast response time (10 s). The sensor was also found to work satisfactorily in partially non-aqueous media up to 20% (v/v) content of acetonitrile, methanol or ethanol. The proposed sensor can be used over a period of 1.5 months without significant drift in potentials. The sensor has been also utilized for the determination of Dy³⁺ level in different soil samples.     

Electrothermal atomic absorption spectrometric determination of germanium in soils using ultrasound-assisted leaching

A procedure for determining germanium in soil samples using electrothermal atomic absorption spectrometry is discussed. The analyte is leached from the solid sample by the addition of 1 ml of concentrated hydrofluoric acid to 10-300 mg of sample, and the mixture is then submitted to a 10 min ultrasonic treatment. After adding 0.4 g boric acid and 3 ml concentrated hydrochloric acid, germanium is extracted into 1 ml chloroform and back-extracted into an aqueous phase containing (0.05%, w/v) nickel nitrate. Ten micro liter of aqueous phase are introduced into the atomizer and the analytical signal from germanium is obtained using a fast-heating cycle. The detection limit, calculated using three times the standard error of estimate (s_y/x) of the calibration graph, is 0.015 μg g⁻¹. The reliability of the procedure is verified by analyzing several certified reference materials.     

Comparative study of Ag(I) selective poly(vinyl chloride) membrane sensors based on newly developed Schiff-base lariat ethers derived from 4,13-diaza-18-crown-6

The six Schiff-base lariat ether chelates based on 4,13-diaza-18-crown ether, have been synthesized and explored as a neutral ionophores for preparing poly(vinyl chloride) based membrane sensors selective to silver(I). The addition of potassium tetrakis(4-chlorophenyl) borate and various plasticizers, viz., o-NPOE, DBP, DBBP, DOP and CN has been found to substantially improve the performance of the sensors. The best performance was obtained with the sensor no. 5 having membrane of chelate (A₆) with composition (w/w) chelate (2.8%):PVC (45.7%):o-NPOE (48.6%):KTpClPB (2.8%). This sensor exhibits Nernstian response with slope 59.3 mV/decade of activity in the concentration range 5.6 × 10⁻⁸-1.0 × 10⁻¹ M Ag(I), performs satisfactorily over wide pH range of (3.0-8.0) with a fast response time (12 s). The sensor was also found to work satisfactorily in partially non-aqueous media up to 25% (v/v) content of acetonitrile, methanol or ethanol and can tolerate the concentration 1.0 × 10⁻² M of ionic (SDS, TBC) and nonionic (Triton X-100) surfactants. The proposed sensor can be used over a period of 4 months without significant drift in potentials. The response of the sensor was highly selective to Ag⁺ over a large number of cations and it could therefore be used for Ag⁺ estimation in blood of occupationally exposed persons.     

Near-infrared diffuse reflectance spectroscopy and neural networks for measuring nutritional parameters in chocolate samples

A rapid and non-destructive method has been developed for the characterization of chocolate samples based on diffuse reflectance near-infrared Fourier transform spectroscopy (DRIFTS) and artificial neural networks (ANNs). This methodology provides a potentially useful alternative to time-consuming chemical methods of analysis. To assess its utility, 36 chocolate samples purchased from the Spanish market were analyzed for the determination of the main nutritional parameters like carbohydrates, fat, proteins, energetic value and cocoa content.Direct triplicate measurements of each sample were carried out by DRIFTS. Cluster hierarchical analysis was used for selecting calibration and validation data sets, resulting in a calibration set comprised of 19 samples and a validation data set of 17 samples. As it is common the presence of non-linear effect in reflectance spectroscopy, ANNs was chosen for data pretreatment. The root-mean-square error of prediction (RMSEP) values obtained for carbohydrates, fat, energetic value and cocoa were 1.0% (w/w), 1.0% (w/w), 50 kJ (100 g)⁻¹ and 1.4%, respectively. The mean difference (d_x-y) and standard deviation of mean differences (s_x-y) of the carbohydrates, fat, proteins content, energetic value and cocoa content were 0.9 and 2.4% (w/w), 0.2 and 1.0% (w/w), 9.1 and 50 kJ (100 g)⁻¹, and −0.5 and 1.4%, respectively. The maximum relative error for the prediction (QC) of any of these parameters for a new sample did not exceed 5.2%.     

A novel cobalt(II)-selective potentiometric sensor based on p-(4-n-butylphenylazo)calix[4]arene

A new poly(vinyl chloride)-based membranes containing p-(4-n-butylphenylazo)calix[4]arene (I) as an electroactive material along with sodiumtetraphenylborate (NaTPB), and dibutyl(butyl)phosphonate in the ratio 10:100:1:200 (I:DBBP:NaTPB:PVC) (w/w) was used to fabricate a new cobalt(II)-selective sensor. It exhibited a working concentration range of 9.2 × 10⁻⁶ to 1.0 × 10⁻¹ M, with a Nernstian slope of 29.0 ± 1.0 mV/decade of activity and the response time of 25 s. This sensor shows the detection limit of 4.0 × 10⁻⁶ M. Its potential response remains unaffected of pH in the range, 4.0-7.2, and the cell assembly can be used successfully in partially non-aqueous medium (up to 10%, v/v) without significant change in the slope of working concentration range. The sensor has a lifetime of about 3 months and exhibits excellent selectivity over a number of mono-, bi-, and tri-valent cations including alkali, alkaline earth metal, heavy and transition metal ions. It can be used as an indicator electrode for the end point determination in the potentiometric titration of cobalt ions against ethylenediaminetetraacetic acid (EDTA) as well as for the determination of cobalt ion concentration in real samples.     

Protein separation using toroidal columns by type-J synchronous counter-current chromatography towards preparative separation

Separation of large bioactive molecules such as proteins, DNAs and RNAs using aqueous two-phase systems (ATPSs) and liquid–liquid partition-based counter-current chromatography (CCC) can avoid risks of sample loss and denaturation, and greatly reduce processing time. We have constructed toroidal columns (length 26–140 m, column volume 51–280 ml, bore size 1.6 mm) suitable for mounting onto a commercially available preparative CCC apparatus. With the use of an ATPS containing 12.5% (w/w) PEG1000 and 12.5% (w/w) K₂HPO₄ and at a rotational speed of 800 rpm for the rotor of the CCC device, the lower phase (i.e. the phosphate-enriched phase) has been used as the mobile phase and a pair of proteins, myoglobin and lysozyme, as model proteins for demonstrating the separation capability of the CCC system. For a toroidal column with a length of 53.5m and a column volume of 107.5 ml, and operated for the Coriolis force parallel flow mode at 0.62 ml/min, protein sample loading (containing 2.2 mg/ml myoglobin and lysozyme, respectively) at 1.7% and 7.4% to the column volume led to peak resolution (with theoretical plate number TP and stationary phase retention S_f shown in the parenthesis) of R_s = 1.5 (N = 211 and N = 113 TP for myoglobin and lysozyme, respectively, and S_f = 45.0%), and R_s = 1.4 (218 and 152 TP, and S_f = 34.0%). However, further increase of the loading to 13% failed to separate the two proteins. Although proteins eluted at positions predictable from the distribution coefficients, they showed broader peaks when compared with small dipeptides under identical CCC operating conditions. This confirms that the molecular weight of the partitioned species is an important factor causing peak broadening on CCC chromatograms. These results paved the way for further scaling-up toroidal CCC columns for processing larger quantities of samples containing large biomolecules.     

A simplified approach to the determination of N-nitroso glyphosate in technical glyphosate using HPLC with post-derivatization and colorimetric detection

A simple and sensitive HPLC post-derivatization method with colorimetric detection has been developed for the determination of N-nitroso glyphosate in samples of technical glyphosate. Separation of the analyte was accomplished using an anionic exchange resin (2.50 mm × 4.00 mm i.d., 15 μm particle size, functional group: quaternary ammonium salt) with Na₂SO₄ 0.0075 M (pH 11.5) (flow rate: 1.0 mL min⁻¹) as mobile phase. After separation, the eluate was derivatized with a colorimetric reagent containing sulfanilamide 0.3% (w/v), [N-(1-naphtil)ethilendiamine] 0.03% (w/v) and HCl 4.5 M in a thermostatized bath at 95 °C. Detection was performed at 546 nm. All stages of the analytical procedure were optimized taking into account the concept of analytical minimalism: less operation times and costs; lower sample, reagents and energy consumption and minimal waste. The limit of detection (k = 3) calculated for 10 blank replicates was 0.04 mg L⁻¹ (0.8 mg kg⁻¹) in the solid sample which is lower than the maximum tolerable accepted by the Food and Agriculture Organization of the United Nations.     

Synthesis and application of doxorubicin-loaded silica gels as solid materials for spectral analysis

A new approach to synthesis and the possibility of application of solid gel matrices containing the target analyte, a cancer drug—doxorubicin for the calibration of UV-vis spectrometers is presented. The doxorubicin-loaded gels were prepared by the acid-catalyzed sol-gel pre-doping method. The efficiency of doxorubicin encapsulation in gels by the sol-gel process was 100 ± 1.2% (w/w). The amount of doxorubicin encapsulated per unit mass of the gel (1 g) was found to be independent of the mass of the gel taken for analysis, which demonstrates the homogeneity of encapsulation of the drug in the gel matrix. The gelation process of doxorubicin in the sol was found to be both repeatable (R.S.D. = 11.2% for n = 80, confidence level P = 95%) and reproducible (largest value of R.S.D. = 4.8% for n = 27, P = 95%).The prepared doxorubicin-loaded gel matrices are characterized primarily by their lack of toxicity as compared to the toxic free form of doxorubicin as well as by high stability over a long-time span.     

Rosmarinic acid determination using biomimetic sensor based on purple acid phosphatase mimetic

A new heterodinuclear Fe(III)Zn(II) complex which mimics the active site of the hydrolytic enzyme red kidney bean purple acid phosphatase was synthesized and characterized by IR, CHN and X-ray crystallographic analyses. This complex, [Fe^IIIZn^II(μ-OH)bpbpmp-CH₃](ClO₄)₂, containing the ligand (H₂bpbpmp-CH₃ = {2-[bis(2-pyridylmethyl)aminomethyl]-6-[(2-hydroxy-5-methylbenzyl) (2-pyridyl-methyl) aminomethyl]-4-methyl-phenol}) was employed in the construction of a biomimetic sensor and used in the determination of rosmarinic acid in plant extract samples. The response parameters and optimization of the biomimetic sensor design were evaluated. The best performance of this sensor was obtained for 75:15:10% (w/w/w) of the graphite powder:nujol:Fe(III)Zn(II) complex, 0.1 mol L⁻¹ phosphate buffer solution (pH 7.5), 1.19 × 10⁻⁴ mol L⁻¹ hydrogen peroxide with frequency, pulse amplitude, and scan increment at 30 Hz, 100 mV, and 0.6 mV, respectively. The rosmarinic acid concentration was linear in the range of 2.98 × 10⁻⁵ to 3.83 × 10⁻⁴ mol L⁻¹ (r = 0.9991) with a detection limit of 2.30 × 10⁻⁶ mol L⁻¹. This biomimetic sensor demonstrated long-term stability (300 days; 900 determinations) and reproducibility, with a relative standard deviation of 12.0%. The recovery study of rosmarinic acid in plant extract samples gave values from 90.3 to 98.3% and the concentrations determined showed agreement when compared with those obtained using capillary electrophoresis at the 95% confidence level.     

Comparative studies of ONNO-based ligands as ionophores for palladium ion-selective membrane sensors

Palladium sensors based on two neutral ionophores, N,N′-bis(acetylacetone) cyclohexanediamine (L₁) and N,N′-bis(o-hydroxyacetophenone)-1,2-cyclohexanediamine (L₂) for quantification of palladium ions are described. Effect of various plasticizers (o-NPOE, DBP, DEP, DOP, TBP, and CN) and anion excluder, sodium tetra phenyl borate (NaTPB) has been studied. The best performance is obtained with a membrane composition of PVC:o-NPOE:ionophore (L₁):NaTPB of 150:300:5:5 (%, w/w). The sensor exhibits significantly enhanced selectivity towards palladium ion over the concentration range 1.0 × 10⁻⁸ to 1.0 × 10⁻¹ M with a lower detection limit of 4.0 × 10⁻⁹ M and a Nernstian compliance (29.1 ± 0.3 mV decade⁻¹ of activity) within pH range 2.0-6.0 and fast response time of 10 s. Influence of the membrane composition and possible interfering ions has also been investigated on the response properties of the electrode. Fast and stable response, good reproducibility and long-term stability of the sensor are demonstrated. The sensor has been found to work satisfactorily in partially non-aqueous media up to 20% (v/v) content of methanol, ethanol and acetonitrile and could be used for a period of 4 months. Selectivity coefficients determined with fixed interference method (FIM) indicate high selectivity for palladium. The proposed electrode shows fairly good discrimination of palladium from other cations. The application of prepared sensor has been demonstrated in determination of palladium ions in spiked water sample.     

Inductively coupled plasma atomic emission spectrometric determination of 27 trace elements in table salts after coprecipitation with indium phosphate

The coprecipitation method using indium phosphate as a new coprecipitant has been developed for the separation of trace elements in table salts prior to their determination using inductively coupled plasma atomic emission spectrometry (ICP-AES). Indium phosphate could quantitatively coprecipitate 27 trace elements, namely, Be, Ti, Cr, Mn, Fe, Co, Ni, Cu, Zn, Cd, Pb, Sc, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu, in a table salt solution at pH 10. The rapid coprecipitation technique, in which complete recovery of the precipitate was not required in the precipitate-separation process, was completely applicable, and, therefore, the operation for the coprecipitation was quite simple. The coprecipitated elements could be determined accurately and precisely by ICP-AES using indium as an internal standard element after dissolution of the precipitate with 5 mL of 1 mol L⁻¹ nitric acid. The detection limits (three times the standard deviation of the blank values, n = 10) ranged from 0.001 μg (Lu) to 0.11 μg (Zn) in 300 mL of a 10% (w/v) table salt solution. The method proposed here could be applied to the analyses of commercially available table salts.     

Influence of interfacial properties on Ostwald ripening in crosslinked multilayered oil-in-water emulsions

The influence of interfacial crosslinking, layer thickness and layer density on the kinetics of Ostwald ripening in multilayered emulsions at different temperatures was investigated. Growth rates of droplets were measured by monitoring changes in the droplet size distributions of 0.5% (w/w) n-octane, n-decane, and n-dodecane oil-in-water emulsions using static light scattering. Lifshitz-Slyozov-Wagner theory was used to calculate Ostwald ripening rates. A sequential two step process, based on electrostatic deposition of sugar beet pectin onto fish gelatin or whey protein isolate (WPI) interfacial membranes, was used to manipulate the interfacial properties of the oil droplets. Laccase was added to the fish gelatin-beet pectin emulsions to promote crosslinking of adsorbed pectin molecules via ferulic acid groups, whereas heat was induced to promote crosslinking of WPI and helix coil transitions of fish gelatin. Ripening rates of single-layered, double-layered and crosslinked emulsions increased as the chain length of the n-alkanes decreased. Emulsions containing crosslinked fish gelatin-beet pectin coated droplets had lower droplet growth rates (3.1 ± 0.3 × 10⁻²⁶ m³/s) than fish gelatin-stabilized droplets (7.3 ± 0.2 × 10⁻²⁶ m³/s), which was attributed to the formation of a protective network. Results suggest that physical or enzymatic biopolymer-crosslinking of interfaces may reduce the molecular transport of alkanes between the droplets in the continuous phase.