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Analytical Methods (v.2, #1)

Analytical Methods

Front cover (pp. 1-1).

Degradable hollow nanospheres are prepared by self-assembly of rod-coil Alg-g-PEG/α-CD (Alginate-g-Poly(ethylene glycol)/α-Cyclodextrin) complexes in water, in which the rod-like segments were formed by inclusion between α-CDs and grafted PEG chains and the coil-like segments were protonated alginate backbones.

Inside front cover (pp. 2-2).

Three interpenetrated metal–organic supramolecular isomers were synthesised using a flexible tetrahedral organic linker and Zn2 clusters that sorb CO2 preferably over N2, H2 and methane at room temperature.

Contents (pp. 3-10).

We herein report the investigation of N@C60 exposed to laser flash excitation to exhibit the acceleration of the decay of (N@C60)* by the encased N atom.

Analytical Methods scope (pp. 11-11).

Diethyl sulfide was chemically immobilized on the surface of silica gel (0.2–0.5 and 0.06 mm) for the formation of two newly synthesized silica gel phases (S1 and S2). A new chelating resin containing meso-tetramethyl-tetrakis-(thiophene)calix[4]pyrrole, CP(I), was also synthesized via the condensation of CP(I) with formaldehyde. The selection of this receptor is based on fundamental studies. Among the cations and anions considered, CP(I) interacts only with mercury(ii). The functionalized silicas and the calixpyrrole resin were characterized by elemental analysis and mass spectrometry. The batch removal of metal cations (Hg²⁺, Pb²⁺ and Cd²⁺) by these materials from aqueous solutions was investigated. The uptake capacities of the silica based materials (S1 and S2) and calixpyrrole polymers (R1) for the Hg²⁺ cation were determined. The Hg(ii) cation uptake data have been found to fit both, the Langmuir and Freundlich isotherms, and the coefficients indicated favorable uptake of this cation by these materials. Parameters such as the kinetics of the uptake process, pH, temperature, silica particle size and metal-ion concentration effects were evaluated. The data obtained clearly indicate that S1 has the higher uptake capability and faster retention rate for Hg(ii) ions relative to S2 and R1. In a column operation, it was observed that the Hg²⁺ cation was effectively removed from aqueous solution by the calixpyrrole resin, R1. The percentage of recovery of this resin for the Hg²⁺ cation was found to be higher than 95%. The results obtained are compared with previously reported materials for mercury removal from aqueous solutions.

Editorial Board profiles (pp. 14-16).

The intended purpose of this work is to develop and validate a dissolution test for misoprostol tablets containing 200 μg misoprostol [1% in hydroxypropyl methylcellulose {HPMC}] using a reverse-phase liquid chromatographic method. After testing sink conditions, dissolution medium and stability of the drug, the best conditions were: paddle at 50 rotations per minute (rpm) stirring speed, deaerated water dissolution medium with volume of 500 ml, as per very low label content of the drug substance & drug product. The method was validated to meet requirements for a global regulatory filing and this validation included specificity, precision, linearity and accuracy. Release of more than 85% of the label amount was achieved over 30 min in the medium through out the study. The dissolution test developed was adequate for its purpose and could be applied for quality control of misoprostol formulation dosage form.

Glycoprotein microarray for the fluorescence detection of antibodies produced as a result of erythropoietin (EPO) abuse by Sinéad M. Hardy; C. Jane Roberts; Pamela R. Brown; David A. Russell (pp. 17-23).

With the commercial availability of recombinant human erythropoietin (rHuEPO), there is significant scope for athletes, especially those competing in endurance sports, to illicitly enhance their performance by increasing their aerobic capacity through enhanced erythrocyte production and hence oxygen transport. While such abuse has been confirmed in a number of human sports, there is also the possibility that rHuEPO can be abused in animal based sports such as thoroughbred horseracing. The direct detection of rHuEPO abuse, using either urine or blood samples, is challenging as the recombinant glycoprotein is similar to that produced endogenously and typically can only be measured above background levels within 4 days of administration. However, it is known that an immune response occurs when horses are doped with rHuEPO. The production of a specific antibody in response to doping with rHuEPO provides a target analyte that is not only different to endogenous species but one which resides in the body for considerably longer than the glycoprotein itself, significantly extending the measurement window. Here we have developed a glycoprotein microarray which exploits the antibody–antigen interaction to provide a means of detecting rHuEPO abuse in animals through the measurement of erythropoietin (EPO) antibodies (anti-HuEPO antibodies). Three commercially available isoforms of rHuEPO (Eprex^®, Aranesp^® and NeoRecormon^®) were arrayed onto the planar surface of a nitrocellulose-coated microarray slide to act as the capture molecule in the assay. The assay was achieved by incubation of the microarray with solutions containing the anti-HuEPO antibody, followed by incubation with a fluorescently tagged secondary antibody. This ‘sandwich’ based assay enabled the fluorescent based detection of anti-HuEPO antibodies using an array-scanner. The EPO glycoprotein microarray was shown to be specific for anti-HuEPO antibodies. To detect anti-HuEPO antibodies in spiked serum samples an optimal dilution of the serum with buffer of 1 : 4 was established. Using Eprex^®-10,000 IU as the capture molecule, the lowest concentration of anti-HuEPO antibody which was detected using the microarray was 148 pM, suggesting that the developed microarray platform could be used as a screen of EPO abuse.

Sol-Gel-Au nano-particle modified carbon paste electrode for potentiometric determination of sub ppb level of Al(iii) by Mohammad Hossein Mashhadizadeh; Hadi Khani (pp. 24-31).

This work describes a new carbon paste electrode modified by Sol-Gel-Au nano-particle (SGAN) in the presence of 2,2′-dihydroxy-1-naphthylidine-1′-naphthyl methyl amine (DNMA) as ionophore for determination of Al(iii) by potentiometric method. Gold nano-particles (GNPs) were self-assembled onto silica Sol-Gel network and incorporated within carbon paste. The nano-structured matrix with DNMA shows well-defined potentiometric behavior for the determination of Al³⁺ in aqueous solutions. The sensor exhibits significantly enhanced selectivity toward Al³⁺ ions over a wide concentration range of 5.0 × 10⁻¹⁰ to 5.0 × 10⁻² M with a lower detection limit of 2.0 × 10⁻¹⁰ M (0.054 ppb) and a Nernstian slope of 20.0 ± (0.1) mV decade⁻¹ of Al³⁺ activity. It has a fast response time of 5 s and can be used for at least 70 days without any considerable divergence in potentials. The potentiometric response of the electrode is independent of pH of test solution in the pH range 3–7. The interaction between DNMA and Al³⁺ was studied spectrophotometrically and it exhibits that stoichiometry of complex is 1 : 1 in methanol solution. Finally, this electrode was successfully used as an indicator electrode for potentiometric determination of Al³⁺ in some real samples.

Laser induced breakdown spectroscopy for rapid identification of different types of paper for forensic application by Arnab Sarkar; Suresh K. Aggarwal; D. Alamelu (pp. 32-36).

The goal of this work was to examine the probability of instant identification of confidential documents for forensic application by comparison with a spectral library generated using laser induced breakdown spectroscopy (LIBS). The library consisted of representative spectra from different types of papers used for official (governmental) work. Statistical methods using linear and rank correlations were applied to identify the unknown paper. Both correlation methods yielded probabilities of correct identification close to unity for all the studied samples. The approach would have applications in forensic science.

Enantioanalysis of S-Ibuprofen using [5–6] fullerene-C70 and diethyl (1,2-methanofullerene C70)-71-71-dicarboxylate by Raluca-Ioana Stefan-van Staden (pp. 37-40).

[5–6] Fullerene-C70 and diethyl (1,2-methanofullerene C70)-71-71-dicarboxylate are used as chiral selectors for the construction of enantioselective, potentiometric membrane electrodes used in the enantioanalysis of S-Ibuprofen. The sensitivities (slopes) of the electrodes were 55.70 mV/pS-ibuprofen for [5–6] fullerene-C70 based electrode and 56.10 mV/pS-ibuprofen for diethyl (1,2-methanofullerene C70)-71-71-dicarboxylate based electrodes and the linear concentration ranges were between 10⁻¹⁰ and 10⁻³ mol L⁻¹ (limit of detection 1 × 10⁻¹¹ mol L⁻¹), and between 10⁻¹⁰ and 10⁻⁴ mol L⁻¹ (limit of detection 5.4 × 10⁻¹¹ mol L⁻¹), respectively. The recovery tests proved that these electrodes can be reliable used for the enantioanalysis of S-ibuprofen raw material (recovery higher than 99.00%) and from its pharmaceutical formulations (recovery higher than 98.40%).

Optimization of Tribenuron-methyl determination by differential pulse polarography using experimental design by Soha Ahmadi; Alireza Ghassempour; Ali Reza Fakhari; Mehdi Jalali-Heravi; Hassan Y. Aboul-Enein (pp. 41-48).

Differential pulse polarography (DPP) was applied for the determination of the herbicide Tribenuron-methyl (TBM). This is a first study for various parameters affecting the reduction peak current were simultaneously optimized using experimental design and these results are different from other reports. The effect of factors such as voltage step, voltage step time, pulse amplitude, pulse time, sample pH, concentration of the supporting electrolyte and the mercury drop size were assessed by means of a (2^7-2) fractional factorial design. It was found that the effects and interactions of four out of seven factors were significant. Consequently, a central composite design (CCD) with four factors, i.e., voltage step time, pulse amplitude, pulse time and sample pH was performed and an optimum response surface equation was derived. The statistical parameters of the derived model were R² = 0.95 and F = 20.38. The limit of detection (LOD), limit of quantification (LOQ), linear range and relative standard deviation (RSD) were 36 μg L⁻¹, 119 μg L⁻¹, 0.07–20 mg L⁻¹ and 0.03, respectively. The promising results for the determination of TBM in a trace level show the efficiency of factorial design and response surface methodologies in optimizing the parameters of a DPP method.

Method for cadmium and lead longitudinal profiles determination in hair by solid sampling graphite furnace atomic absorption spectrometry by Cassiana Seimi Nomura; Pedro Vitoriano Oliveira (pp. 49-53).

This paper describes methods for the direct determination of Cd and Pb in hair segments (c.a. 5 mm, ∼80 μg) by solid sampling graphite furnace atomic absorption spectrometry, becoming possible longitudinal profiles in a single strand of hair. To distinguish endogenous and exogenous content, strands of hair were washed by using two different procedures: IAEA protocol (acetone + water + acetone) and the combination of IAEA protocol with HCl washing (acetone + water + acetone + 0.1 mol l⁻¹ HCl). The concentration of Cd and Pb increased from the root until the tip of hair washed according to IAEA protocol. However, when the strand of hair was washed using the combination of IAEA protocol and 0.1 mol l⁻¹ HCl, Cd concentrations decreased in all segments, and Pb concentrations decreased drastically near to the root (5 to 12 mm) and was systematically higher in the end. The proposed method showed to be useful to assess the temporal variation to Cd and Pb exposure and can be used for toxicological and environmental investigations. The limits of detection were 2.8 ng g⁻¹ for Cd and 40 ng g⁻¹ for Pb. The characteristic masses based on integrated absorbance were 2.4 pg for Cd and 22 pg for Pb.

Application of dispersive liquid–liquid microextraction combined with sweeping micellar electrokinetic chromatography for trace analysis of six carbamate pesticides in apples by Shuaihua Zhang; Chao Li; Shuangju Song; Tao Feng; Chun Wang; Zhi Wang (pp. 54-62).

A rapid and sensitive method for the multiresidue analysis of six commonly used carbamate pesticides in apples was developed by using dispersive liquid–liquid microextraction (DLLME) coupled with sweeping micellar electrokinetic chromatography (MEKC). Parameters that affect the extraction and sweeping efficiency, such as the kind and volume of the extraction and disperser solvent, extraction time, salt addition, sample matrix and concentration of organic modifiers in the separation buffer were investigated and optimized. Under optimized conditions, the enrichment factors were achieved in the range from 491 to 1834. The linearity of the method for methiocarb, diethofencarb, carbaryl and isoprocarb was in the range of 6–500 ng g⁻¹, and for fenobcarb and tsumacide in the range of 9–500 ng g⁻¹, with the correlation coefficients (r) ranging from 0.9952 to 0.9990. The limits of detection (LODs) at a signal-to-noise ratio of 3 ranged from 2.0 to 3.0 ng g⁻¹. The recoveries of the six carbamates for apple samples at spiking levels of 20.0 and 100.0 ng g⁻¹ were 85.5–108.1% and 85.4–113.3%, respectively. The proposed method has been successfully applied to the analysis of the target carbamate residues in apple samples with satisfactory results.

Diethyl sulfide modified silica and calix[4]pyrrole chelating resin: Synthesis and mercury(ii) cation retention properties by Angela Danil de Namor; Ismail Abbas (pp. 63-71).

Development & validation of an in vitro dissolution method with HPLC analysis for misoprostol in formulated dosage form by Jigar Mehta; Kanhaiyalal Patidar; Vipul Patel; Nayan Kshatri; Niranjan Vyas (pp. 72-75).

Determination of piroxicam in pharmaceutical preparations by continuous-flow chemiluminescence by J. A. Murillo Pulgarín; A. Alañón Molina; N. Boras (pp. 76-81).

A simple and rapid chemiluminescent method for the assay of piroxicam in pure and in pharmaceutical formulations by flow analysis is proposed. The method is based on the reaction of this drug with N-bromosuccinimide (NBS) in alkaline medium in the presence of fluorescein as sensitizer. The emission intensity is greatly enhanced by the presence of cetyltrimethylammonium bromide (CTAB). The optimum chemical conditions for the chemiluminescence emission were investigated. The calibration graph was linear for the concentration range from 2.0 to 12.0 μg mL⁻¹. The detection limit, according to Clayton et al.(C. A. Clayton, J. W. Hines and P. D. Elkins, Anal. Chem., 1987, 59, 2506), was 0.72 μg mL⁻¹. For analysis of 10 solutions of 8.0 μg mL⁻¹ of this anti-inflammatory, if error propagation theory is assumed, the relative error was less than 1.5%. The present chemiluminescence procedure was applied to the determination of piroxicam in Spanish pharmaceutical formulations, with excellent recoveries, as the determination is free from interference from common excipients.

Determination of free acid in rare earth solution by a fixed pH method by Zhaowu Zhu; Zhenyu Bian; Zhiqi Long (pp. 82-85).

A fixed pH method was developed for free acid determination in solutions containing large amounts of rare earths, especially Ce(IV). With Ca–EDTA as the masking regent at a fixed pH of 4.5, free acid was determined in a solution containing about 100 g/L of rare earths including about 50 g/L Ce(IV) with a relative standard deviation (RSD) of less than 1%. The deviation error for 50 measurements in 5 groups for a known amount of H2SO4 solution was −1.44%. Compared with other reported methods, the newly developed method has the advantages of higher precision, higher accuracy, simpler procedure and no need for an indicator.

Quantitative determination of additives in a commercial electroplating nickel bath by spectrophotometry and multivariate analysis by Maider Vidal; José Manuel Amigo; Rasmus Bro; Miren Ostra; Carlos Ubide. (pp. 86-92).

An electroplating nickel bath is usually composed of a number of organic additives to improve the plating process as well as to preserve its durability. Supreme Plus Brightener (SPB) and A-5(2X), used in a commercial electroplating nickel bath show highly overlapped UV-Vis spectra. These two additives are the only ones that present absorbance in the UV-Vis wavelength range. Therefore, a mixture of them can be resolved using multivariate calibration methods of UV-Vis measurements. In this work, Partial Least Squares (PLS) regression and Classical Least Squares (CLS) have been used to quantify both additives during the whole duration of an electroplating nickel bath. It was found that PLS regression provided the best results. To avoid negative influence of baseline drifts, first derivative spectra were used. Between 0.14 and 1.40 mL of the commercial product SPB per L of nickel bath can be determined with mean errors of about 6%. Between 4 and 24 mL of the commercial product A-5(2X) per L of nickel bath can be determined with mean errors of about 8%. The limits of detection (LOD) found for SPB and A-5(2X) were 0.11 mL L⁻¹ and 3 mL L⁻¹ respectively. The calibration models proved to be valid for at least eight months, including a change of spectrophotometer. The SPB concentration decays along the bath life according to a first order rate law, but A-5(2X) remains unchanged. Independent brightness measurements showed that it was intimately related to the SPB concentration, in such a way that any of them can be deduced from the other one. This is of prime importance to keep the bath conditions under control.

An illustration of the physical robustness of silica monolithic rod columns by Paul Geoffrey Stevenson; Ross Andrew Shalliker (pp. 93-95).

A commercial silica monolithic rod column (100 × 4.6 mm) was cut into smaller sections using a saw. Each time a section was cut from the column, the performance of the remaining intact monolith was retested. No significant change in the performance of the bed was recorded following the removal of 40 mm of the column in three separate cut sections. The work illustrates that monoliths are extremely robust and that they can be remodelled to different lengths if required, or a blocked section of the column (i.e. inlet) could be removed in much the same manner as for GC columns.

Back matter (pp. 96-98).

We demonstrate a simple water washing process for large-scale fabrication of highly ordered and aligned rectangular silver nanowire monolayers from polyol systems. These monolayers exhibit unique structure-dependent chemical reactivities for the galvanic replacement reaction with HAuCl4, and novel gold nanoneedle arrays with sharp tips and a uniform structure have been produced.

Back cover (pp. 99-100).

Uniform multicolor upconversion luminescent RE³⁺ doped NaYF4 nanocubes are fabricated through a facile ethylene glycol (EG)/ionic liquid interfacial synthesis route at 80 °C, with the ionic liquids acting as both reagents and templates.

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Analytical Methods (v.2, #1)