Use of expanded bed adsorption to purify flavonoids from Ginkgo biloba L.

Three techniques (liquid–liquid extraction, packed bed adsorption and expanded bed adsorption) have been compared for the purification of flavonoids from the leaves of Ginkgo biloba L. A crude Ginkgo extract was obtained by refluxing with ethanol for 3 h. The yield of flavonoids achieved by this crude extraction was about 19% (w/w) and the purity of flavonoids in the concentrated extract was between 1.9 and 2.3% (w/w). The crude extract was then dissolved in deionized water and centrifuged where necessary to prepare clarified feedstock for further purification. For the method using liquid–liquid extraction with ethyl acetate, the purity, concentration ratio and yield of flavonoids were 25.4–31.0%, 16–18 and >98%, respectively. For the method using packed bed adsorption, Amberlite XAD7HP was selected as the adsorbent and clarified extract was used as the feedstock. The dynamic adsorption breakthrough curves and elution profiles were measured. For a feedstock containing flavonoids at a concentration of 0.25 mg/mL, the appropriate loading volume to reach a 5% breakthrough point during the adsorption stage was estimated to be 550–600 mL for a packed bed of volume 53 mL and a flow rate of 183 cm/h. The results from the elution stage indicated that the majority of impurities were eluted by ethanol concentrations of 40% (v/v) or below and efficient separation of flavonoids from the impurities could be achieved by elution of the flavonoids with 50–80% ethanol reaching an average purity of ∼25%. The recovery yield of flavonoids using the packed bed purification method was about 60% of the flavonoids present in the clarified feedstock (corresponding to around 30% for the total flavonoids in the unclarified crude extract). For the method using expanded bed adsorption also conducted with Amberlite XAD7HP as the adsorbent, the optimal operation conditions scouted during the packed bed experiments were used but unclarified crude extract could be loaded directly into the column. For an expanded bed with a settled bed height of 30 cm, the loss of flavonoids in the column flow-through was about 30%. The two-step elution protocol again proved to be effective in separating the adsorbed impurities and flavonoids. More than 96% of the bound impurities were completely removed by 40% ethanol in the first elution stage and less than 4% remained in the final product eluted by 90% ethanol in the second elution stage. Also, ∼74% of the adsorbed flavonoids on column (corresponding to 51% of the total flavonoids in the unclarified feedstock) were recovered in the product. In addition to higher recovery yield, the average process time to obtain the same amount of product was decreased in the expanded bed adsorption (EBA) process. The results suggest that the adoption of EBA procedures can greatly simplify the process flow sheet and in addition reduce the cost and time to purify flavonoids from Ginkgo biloba. These results clearly demonstrate the potential for the use of EBA to purify pharmaceuticals from plant sources.     

Direct recovery of recombinant nucleocapsid protein of Nipah virus from unclarified Escherichia coli homogenate using hydrophobic interaction expanded bed adsorption chromatography

A direct recovery of recombinant nucleocapsid protein of Nipah virus (NCp-NiV) from crude Escherichia coli (E. coli) homogenate was developed successfully using a hydrophobic interaction expanded bed adsorption chromatography (HI-EBAC). The nucleic acids co-released with the recombinant protein have increased the viscosity of the E. coli homogenate, thus affected the axial mixing in the EBAC column. Hence, DNase was added to reduce the viscosity of feedstock prior to its loading into the EBAC column packed with the hydrophobic interaction chromatography (HIC) adsorbent. The addition of glycerol to the washing buffer has reduced the volume of washing buffer applied, and thus reduced the loss of the NCp-NiV during the washing stage. The influences of flow velocity, degree of bed expansion and viscosity of mobile phase on the adsorption efficiency of HI-EBAC were studied. The dynamic binding capacity at 10% breakthrough of 3.2 mg/g adsorbent was achieved at a linear flow velocity of 178 cm/h, bed expansion of two and feedstock viscosity of 3.4 mPa s. The adsorbed NCp-NiV was eluted with the buffer containing a step gradient of salt concentration. The purification of hydrophobic NCp-NiV using the HI-EBAC column has recovered 80% of NCp-NiV from unclarified E. coli homogenate with a purification factor of 12.5.     

Fractionation analysis of manganese and zinc in beers by means of two sorbent column system and flame atomic absorption spectrometry

In the present article, a method of operational fractionation of Mn and Zn in beer using flame atomic absorption spectrometry was developed. The proposed fractionation scheme was based on use of a hydrophobic adsorbing resin Amberlite XAD7 (first column, 2 g resin bed) connected in a series with a strong cation exchanger Dowex 50Wx4 (second column, 1 g resin bed). After passing the samples of beers through the columns, distinct groupings of Mn and Zn species retained on the sorbents, i.e., hydrophobic fraction of polyphenols bound metal species and cationic metal species fraction, respectively, were determined in respective eluates obtained after complete recovery of Mn and Zn species with 10 ml of 2.0 mol l⁻¹ HNO₃ (first column) and 10 ml of 4.0 mol l⁻¹ HCl (second column). In addition, the effluents collected were analyzed prior to the evaluation of the third, residual fraction, presumably attributed to any hydrophilic anionic and inert metal species. The established fractionation patterns for Mn and Zn were discussed in reference to likely associations of metals with endogenous food bioligands and possible availability of the distinguished metal species classes. The quality of the results was proved by the recovery experiments.     

Simultaneous determination of tetracyclines in poultry muscle by capillary zone electrophoresis

A capillary zone electrophoresis method with UV detection was developed for the simultaneous detection and quantification of three tetracyclines in chicken meat samples: tetracycline (TC), oxytetracycline (OTC) and doxycycline (DOC). The separation conditions were: a running buffer containing 30 mM sodium phosphate, 2 mM EDTA disodium salt and 2.5% 2-propanol, pH 12.0, a 5 s hydrodynamic injection and a 14 kV separation voltage. Two different clean-up methodologies were employed: solid-phase extraction with C₁₈ cartridges and ion exchange with Amberlite XAD7 resin. Analytes were detected at 360 nm in less than 12 min. LODs ranged from 61 μg kg⁻¹ for OTC to 68 μg kg⁻¹ for DOC with C₁₈ cartridges, and 81 μg kg⁻¹ for DOC to 89 μg kg⁻¹ for TC with Amberlite XAD7 resin. The recoveries for TC, OTC and DOC obtained by both methods were between 85 and 95%, and the peak area repeatability for all of the samples was below 5% in all cases. Twenty-four samples of commercial chicken drumsticks were examined with both clean-up methodologies. In nine cases (37.5%) TC was detected, in a range from 197.8 to 2564.3 μg kg⁻¹, and in seven cases (29.2%) OTC was detected in a range from 83.0 to 2049.3 μg kg⁻¹. DOC was not detected in any of the tested samples. This method would be useful for the routine monitoring of TCs residues in poultry muscle.     

Mathematical modeling and simulation of inulinase adsorption in expanded bed column

A mathematical model for an expanded bed column was developed to predict breakthrough curves for inulinase adsorption on Streamline SP ion-exchange adsorbent, using a crude fermentative broth with cells as the feedstock. The kinetics and mass transfer parameters were estimated using the PSO (particle swarm optimization) heuristic algorithm. The parameters were estimated for each expansion degree (ED) using three breakthrough curves at initial inulinase concentrations of 65.6 U mL⁻¹. In sequence, the model parameters for an ED of 2.5 were validated using the breakthrough curve at an initial concentration of 114.4 U mL⁻¹. The applicability of the validated model in process optimization was investigated, using the model as a process simulator and experimental design methodology to optimize the column and process efficiencies. The results demonstrated the usefulness of this methodology for expanded bed adsorption processes.     

Expansion and hydrodynamic properties of β-cyclodextrin polymer/tungsten carbide composite matrix in an expanded bed

The expansion and hydrodynamic properties of matrix are significant for expanded bed adsorption (EBA) processes. A series of new composite matrices CroCD-TuC are studied and estimated in an expanded bed. It is found that the heavier matrix is better suited for high operation fluid velocity than the lighters. Although the Richardson–Zaki equation can well correlate the bed voidage with fluid velocity for all CroCD-TuC matrices tested, the modifications are proposed to improve the accuracy of theoretical predictions of correlation parameters, including terminal settling velocity (U_t) and expansion index (n). Residence time distributions (RTDs) are determined, and the Bodenstein number (Bo) and axial dispersion coefficient (D_ax) are employed to analyze the liquid mixing in the expanded bed. It is found for CroCD-TuC matrices, both parameters notably changed with the variation of fluid velocity and viscosity. Furthermore, D_ax is an intuitive parameter estimating the bed stability on various operating conditions, and also a restriction on developing the matrix for high operation fluid velocity. The comparison of the hydrodynamic properties on different matrices reveals that CroCD-TuC 3 and CroCD-TuC 4 seem superior to other matrices in hydrodynamic properties, making them promising matrices for further use. The correlations as the functions of fluid velocity and viscosity have been established which may provide beneficial information for practical applications of CroCD-TuC matrices in EBA processes.     

Determination of flavonoids in Houttuynia cordata Thunb. and Saururus chinensis (Lour.) Bail. by capillary electrophoresis with electrochemical detection

Four flavonoids (rutin, hyperoside, quercitrin and quercetin) in Houttuynia cordata Thunb. and Saururus chinensis (Lour.) Bail. were determined by capillary electrophoresis with wall-jet amperometric detection. The working electrode was a 500 μm diameter carbon disc electrode and the detection potential was +0.95 V (versus Ag/AgCl). Effects of several important factors, such as the running buffer and its corresponding pH and concentration, separation voltage, injection time were investigated to acquire the optimum conditions for separation of these four flavonoids. Baseline separation for the four flavonoids was obtained within 21 min in a 60 cm length capillary at a separation voltage of 15 kV with a 60 mmoL/L Na₂B₄O₇-120 mmoL/L NaH₂PO₄ buffer (pH 8.8) as running buffer. The relationship between peak currents and analyte concentrations was linear over about two orders of magnitude with detection limits (defined as S/N = 3) ranging from 0.02 to 0.05 μg/mL for all analytes. This method was applied for the determination of the above four flavonoids in H. cordata Thunb. and S. chinensis (Lour.) Bail. with simple extraction procedures, and the assay results were satisfactory.     

Sensitive voltammetric determination of rutin at an ionic liquid modified carbon paste electrode

An ionic liquid modified carbon paste electrode (IL/CPE) had been fabricated by using hydrophilic ionic liquid 1-amyl-3-methylimidazolium bromide ([AMIM]Br) as a modifier. The IL/CPE was characterized by scanning electron microscope and voltammetry. Electrochemical behavior of rutin at the IL/CPE had been investigated in pH 3.29 Britton-Robinson (B-R) buffer solution by cyclic voltammetry (CV) and square wave voltammetry (SWV). The experimental results suggested that the modified electrode exhibited an electrocatalytic activity toward the redox of rutin. The electron transfer coefficient (α) and the standard rate constant (k_s) of rutin at the modified electrode were calculated. Under the selected conditions, the reduction peak current was linearly dependent on the concentration of rutin in the range of 4.0 × 10⁻⁸ to 1.0 × 10⁻⁵ mol L⁻¹ (r = 0.9998), with a detection limit of 1.0 × 10⁻⁸ mol L⁻¹ (S/N = 3). The relative standard deviation (R.S.D.) for six times successful determination of 8.0 × 10⁻⁷ mol L⁻¹ rutin was 1.2%. The proposed method was applied to determine rutin in tablet and urine sample. In addition, the IL/CPE exhibited a distinct advantage of simple preparation, surface renewal, good reproducibility and good stability.     

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.     

Thermochemistry of n-alkylamines interaction with ETS-10 titaniunsilicate

According to the data from calorimetric adsorption of methylamine, under the best experimental conditions, 10 mg ETS-10 was saturated with 20 μl portions of an aqueous solution of methylamine at 0.05 mol dm⁻³ concentration corresponding to 0.490 mmol of methylamine per gram of solid. From calorimetric titration data, the thermodynamic values of ΔH, ΔG and ΔS were calculated, showing favourable n-alkylamine-ETS-10 interactions, from which the most favourable occurs for n-butylamine. The adsorption of these bases did not affect the structure of the titaniunsilicate as the XRD profile of ETS-10 is not altered. The FTIR spectra showed that with the increase in the amine mass the bands corresponding to the symmetric and asymmetric deformations at 1390 and 1467 cm⁻¹ increase in intensity along with the NH₂ deformation at 1530 cm⁻¹ as expected. The thermogravimetry shows two mass losses for ETS-10 that correspond to physisorbed water and water in smaller channels and cavities. After methylamine adsorption, the same behaviour was observed, however for butyl- and pentylamine three other mass losses were observed corresponding to decomposition and/or release of n-alkylamines.     

Highly sensitive and selective fluorescence optosensor to detect and quantify benzo[a]pyrene in water samples

We describe here a method for detecting and quantifying the highly carcinogenic polycyclic aromatic hydrocarbon (PAH) benzo[a]pyrene (BaP) in water, based on a flow-trough optical sensor. The technique is fast (response time of 40 s) and simple and at the same time meets the standards of sensitivity and selectivity required by the European Guidelines on Water for Human Consumption. The optosensor is based on the on-line immobilization of BaP on a non-ionic resin (Amberlite XAD-4) solid support in a continuous-flow system. BaP was analyzed in a 15 mM H₂PO₄⁻/HPO₄²⁻ buffer solution with 25% (v/v) 1,4-dioxane at pH 7. Fluorescence intensity was measured at λ_ex/em=392/406 nm. The experimental conditions (reagent phase, pH, type and concentration of buffer solution and organic solvent) and flow-injection values (flow rate and injection volume) were carefully controlled. Under these conditions the optosensor was sensitive to a linear concentration range of between 3.0 and 250.0 ng l⁻¹ with a detection limit of 3.0 ng l⁻¹ and a standard deviation of 1.5% at 150 ng l⁻¹. The optosensor was applied to the quantification of BaP in drinking and waste water samples (95-105% recovery) in presence of the other 15 EPA PAHs at 1000 ng l⁻¹ concentration level. The influence of other fluorescent polycyclic aromatic hydrocarbons and potential interference from ions usually present in water was also evaluated.     

High-temperature crystal structure and transport properties of the layered cuprates Ln2CuO4, Ln=Pr, Nd and Sm

High-temperature crystal structure of the layered cuprates Ln₂CuO₄, Ln=Pr, Nd and Sm with tetragonal T′-structure was refined using X-ray powder diffraction data. Substantial anisotropy of the thermal expansion behavior was observed in their crystal structures with thermal expansion coefficients (TEC) along a- and c-axis changing from TEC(a)/TEC(c)≈1.37 (Pr) to 0.89 (Nd) and 0.72 (Sm). Temperature dependence of the interatomic distances in Ln₂CuO₄ shows significantly lower expansion rate of the chemical bond between Pr and oxygen atoms (O1) belonging to CuO₂-planes (TEC(Pr-O1)=11.7 ppm K⁻¹) in comparison with other cuprates: TEC (Nd-O1)=15.2 ppm K⁻¹ and TEC (Sm-O1)=15.1 ppm K⁻¹. High-temperature electrical conductivity of Pr₂CuO₄ is the highest one in the whole studied temperature range (298-1173 K): 0.1-108 S/cm for Pr₂CuO₄, 0.07-23 S/cm for Nd₂CuO₄ and 2×10⁻⁴-9 S/cm for Sm₂CuO₄. The trace diffusion coefficient (D_T) of oxygen for Pr₂CuO₄ determined by isotopic exchange depth profile (IEDP) technique using secondary ion mass spectrometry (SIMS) varies in the range 7.2×10⁻¹³ cm²/s (973 K) and 3.8×10⁻¹⁰ cm²/s (1173 K) which are in between those observed for the manganese and cobalt-based perovskites.     

Solid phase extraction and preconcentration of uranium(VI) and thorium(IV) on Duolite XAD761 prior to their inductively coupled plasma mass spectrometric determination

A simple and effective method is presented for the separation and preconcentration of thorium(IV) and uranium(VI) by solid phase extraction on Duolite XAD761 adsorption resin. Thorium(IV) and uranium(VI) 9-phenyl-3-fluorone chelates are formed and adsorbed onto the Duolite XAD761. Thorium(IV) and uranium(VI) are quantitatively eluted with 2 mol L⁻¹ HCl and determined by inductively coupled plasma-mass spectrometry (ICP-MS). The influences of analytical parameters including pH, amount of reagents, amount of Duolite XAD761 and sample volume, etc. were investigated on the recovery of analyte ions. The interference of a large number of anions and cations has been studied and the optimized conditions developed have been utilized for the trace determination of uranium and thorium. A preconcentration factor of 30 for uranium and thorium was achieved. The relative standard deviation (N = 10) was 2.3% for uranium and 4.5% for thorium ions for 10 replicate determinations in the solution containing 0.5 μg of uranium and thorium. The three sigma detection limits (N = 15) for thorium(IV) and uranium(VI) ions were found to be 4.5 and 6.3 ng L⁻¹, respectively. The developed solid phase extraction method was successively utilized for the determination of traces thorium(IV) and uranium(VI) in environmental samples by ICP-MS.     

A facile flow-through phosphorimetric sensing device for simultaneous determination of naptalam and its metabolite 1-naphthylamine

This paper presents the development of a single flow-through phosphorescence optosensor for simultaneous determination of pesticide N-1-naphthylphthlamic acid (NAP) and its metabolite 1-naphthylamine (NNA). The system works as a simple and rapid phosphorimetry-biparameter sensor. It is based in the on-line immobilization of the analytes onto a non-ionic resin solid support (Amberlite XAD 7) in a continuous flow system, followed by the measurement of their native phosphorescence. The determination was performed using 0.2 M TlNO₃ and 15 mM Na₂SO₃ in a carrier flow. The developed sensor was satisfactorily applied to the determination of these pesticides in drinking and mineral waters (recovery percentages between 82.8 and 114.1% with inferior relative standard deviations to 3.1%).     

Direct electrochemistry of cytochrome c on a phosphonic acid terminated self-assembled monolayers

The direct electrochemistry of cytochrome c (cyt c) on a gold electrode modified with 3-mercaptopropylphosphonic acid [HS-(CH₂)₃-PO₃H₂, MPPA] self-assembled monolayers (SAMs) was for the first time investigated. Electrochemical measurements and surface-enhanced infrared absorption spectroscopic reveal that the adsorption kinetics of cyt c on the MPPA-SAMs is very fast (saturation adsorption is completed within 5 s) and the immobilized cyt c molecules retain their native secondary protein structure. The nature of interaction between cyt c and -PO₃H₂ groups is mainly the electrostatic interaction. The direct electrochemistry of the immobilized cyt c on the -PO₃H₂ terminated SAMs with short chain is nearly reversible. Its formal potential (E⁰′ = 18 ± 3 mV vs. SCE) is very close to that of cyt c in an aqueous solution (E⁰′ = 18-22 mV vs. SCE). In addition, the electron transfer rate of cyt c immobilized on -PO₃H₂ terminated SAMs is relatively slow as compared to -SO₃H and -COOH terminated SAMs, indicating excess negative charge density on the SAMs surface will decrease the electron transfer rate of cyt c.     

Room-temperature luminescence optosensings based on immobilized active principles actives: Application to nafronyl and naproxen determination in pharmaceutical preparations and biological fluids

This paper presents two easy and selective methods for determining the active principles nafronyl (NFL) and naproxen (NAP), using a flow-through fluorescence optosensor based on the on-line immobilization on a nonionic-exchanger (Silica Gel, Davisil™ and Amberlite XAD 7, respectively) solid support. The determination was performed in 5×10⁻³ M HAc/NaAc buffer solution at pH 5 for NFL and 15×10⁻³ M glycine/HCl buffer solution at pH 2.5 for NAP at a working temperature of 20 °C. The fluorescence intensities were measured at λ_ex/em=294/336 nm and λ_ex/em=332/354 nm for NFL and NAP, respectively. The response time for these optosensors were practically instant, obtaining a linear concentration range between 0 and 700.0 ng ml⁻¹ with a detection limit of 20.8 ng ml⁻¹, an analytical sensitivity of 10.1 ng ml⁻¹ and a standard deviation of 1.27% at a 500 ng ml⁻¹ concentration level for NFL and a linear concentration range between 0 and 200.0 ng ml⁻¹ with the detection limit of 13.3 ng ml⁻¹, an analytical sensitivity of 6.0 ng ml⁻¹ and a standard deviation of 3.52% at a 100 ng ml⁻¹ concentration level for NAP. The proposed methods were satisfactorily applied to real samples (three commercial formulations and urine samples). The effects of the possible interferences were evaluated in all cases.     

Influence of hydrophobe content on the solution rheology of hydrophobically modified terpolymer of SO2, N,N-diallyl-N-carboethoxymethylammonium chloride

Rheological properties of hydrophobically modified copolymer of SO₂, N,N-diallyl-N-carboethoxymethylammonium chloride and the hydrophobic monomer N,N-diallyl-N-octadecylammonium chloride were studied. The influence of hydrophobe content (HP) and polymer concentration was investigated. Polymers with HP content in the range 1.5-5% were examined and the concentration was varied in the range 2-5 wt%. Both dynamic and steady-shear experiments were performed in ARES rheometer. Copolymers were observed to exhibit typical viscoelastic behavior even with low HP content. Both the dynamic viscosity, η′ and storage modulus, G′, increase with the increase of both the polymer concentration and the HP content of the system. The viscosity of the high HP content polymer showed a strong shear dependency, while G′ was a weak function of frequency and gel-like behavior was observed. The zero-shear viscosity, η₀, showed a strong concentration dependency (η₀ ∼ ?^α; 1.1 < α < 5.9). The concentration dependency of η₀ suggests that intermolecular association is dominant in the high HP content polymer. Control of the HP content and polymer concentration of this class of polymers can lead to a wide range of interesting rheological properties.     

Application of the diffusive gradients in thin films technique for available potassium measurement in agricultural soils: Effects of competing cations on potassium uptake by the resin gel

The utilization of Amberlite (IRP-69 ion-exchange resin, 100–500 wet mesh) as the binding phase in the diffusive gradients in thin films (DGT) technique has shown potential to improve the assessment of plant-available K in soils. The binding phase has recently been optimized by using a mixed Amberlite and ferrihydrite (MAF) gel which results in linear K uptake over extended deployment periods and in solutions with higher K concentrations. As restriction of K uptake by Ca on the Amberlite based resin gel has been previously proposed, potential competing effects of Ca²⁺, Mg²⁺ and NH₄⁺ on K uptake by the MAF gel were investigated. These cations had no effect on K elution efficiency which was 85%. However, K uptake by the MAF gel was restricted in the presence of competing cations in solution. Consequently, the diffusion coefficient of K decreased in the presence of cations compared to previous studies but was stable at 1.12 × 10⁻⁵ cm² s⁻¹ at 25 °C regardless of cation concentrations. Uptake of K by the DGT device was affected by the presence of excessive Ca in more than 30% of twenty typical Australian agricultural soils. However, this problem could be circumvented by using a shorter deployment time than the normal 24 h. Moderate correlation of concentrations of K extracted by DGT with Colwell K (extracted by NaHCO₃, R² = 0.69) and NH₄OAc K (R² = 0.61) indicates that DGT measures a different pool of K in soils than that measured by the standard extractants used. In addition, the MAF gel has the ability to measure Ca and Mg simultaneously.     

Speciation of dissolved Fe(II) and Fe(III) in environmental water samples by micro-column packed with N-benzoyl-N-phenylhydroxylamine loaded on microcrystalline naphthalene and determination by electrothermal vaporization inductively coupled plasma-optical emission spectrometry

A novel solid phase extraction technique for the speciation of trace dissolved Fe(II) and Fe(III) in environmental water samples was developed by coupling micro-column packed with N-benzoyl-N-phenylhydroxylamine (BPHA) loaded on microcrystalline naphthalene to electrothermal vaporization inductively coupled plasma-optical emission spectrometry (ETV-ICP-OES). Various influencing factors on the separation and preconcentration of Fe(II) and Fe(III), such as the acidity of the aqueous solution, sample flow rate and volume, have been investigated systematically, and the optimized operation conditions were established. At pH 3.0 Fe(III) could be selectively retained by micro-column (20 mm × 1.4 mm, i.d.) packed with BPHA immobilized on microcrystalline naphthalene, and Fe(II) passed through the micro-column. Both Fe(II) and Fe(III) could be adsorbed by the micro-column at pH 6.5. Thus, the total Fe could be determined without the need for preoxidation of Fe(II) to Fe(III). The retained Fe(III) or the Fe(II) and Fe(III) was subsequently eluted by 0.1 ml of 1 mol l⁻¹ HCl. The adsorption capacity of the solid phase adsorption material was found to be 45.0 mg g⁻¹ for Fe(III) at pH 3.0 and 65.3 mg g⁻¹ for Fe(II) at pH 6.5, respectively. The detection limit (3σ) of 0.053 μg l⁻¹ was obtained with a practical enrichment factor of 156 at a sample volume of 17 ml. The relative standard deviations of 4.2% and 4.6% (C_Fe(III) = C_Fe(II) = 10 μg l⁻¹, n = 7) for Fe(III) and total iron were found, respectively. The method was successfully applied to the determination of trace Fe(II) and Fe(III) in environmental water samples (East Lake water, local tap water and mineral water). In order to validate the method, the developed method was applied to the determination of total iron in certified materials of NIES NO.10-b rice flour and GBW07605 tea leaves, and the results obtained were in good agreement with the certified values.     

Rapid determination of acetaminophen and p-aminophenol in pharmaceutical formulations using miniaturized capillary electrophoresis with amperometric detection

Capability of fast analysis of a novel miniaturized capillary electrophoresis with carbon disk electrode amperometric detection (mini-CE-AD) system was demonstrated by determining acetaminophen and p-aminophenol in dosage forms. Factors influencing the separation and detection processes were examined and optimized. Under the optimum conditions, the end-capillary 300 μm carbon disc electrode amperometric detector offered favorable signal-to-noise characteristics at a relatively low potential (+600 mV versus Ag/AgCl) for detecting acetaminophen and p-aminophenol. Two analytes can been separated within 150 s in a 8.5 cm length capillary at a separation voltage of 2000 V using a Na₂B₄O₇-KH₂PO₄ running buffer (pH 7.2). Acetaminophen and p-aminophenol could be detected down to the 1.4 × 10⁻⁶-5.9 × 10⁻⁷ mol L⁻¹ level with linearity up to the 1.0 × 10⁻³ mol L⁻¹ level examined. The inter-day repeatability for analytes in peak current (R.S.D. ≤ 2.3%) and migration times (R.S.D. ≤ 1.3%) were excellent. The proposed mini-CE-AD system should find a wide range of analytical applications in pharmaceutical formulations as an alternative to conventional CE and μ-CE.