Vol 73, No 9 (2018)

The work considers a possibility of creating standard reference samples of aqueous dispersions of unmodified fullerenes and endohedral fullerenes. Procedures for preparing highly concentrated dispersions and methods for determining the concentration of the main component, elemental impurity composition, organic composition, and dimensional characteristics are discussed. Commercially available fullerenes C₆₀ and C₇₀ and endohedral fullerene Y@C₈₂ (C_2v isomer) synthesized by the electric arc method were used as the starting materials. Aqueous fullerene dispersions (AFDs) were prepared by replacing the organic solvent (toluene) under additional ultrasonic treatment. The maximum concentrations of fullerenes C₆₀, C₇₀, and Y@C₈₂ were 150 ± 3, 55 ± 2, and 2.8 ± 0.1 mg/L, respectively. The long-term stability of solutions (more than 5 years) on storage was found. A set of methods and procedures that enable the determination of the main components of AFDs (fullerenes) and accompanying components (impurities of organic solvents and metals at the level of trace concentrations) is discussed. The sizes of fullerene clusters in solutions (from 100 to 120 nm for all solutions) are characterized; the stability of dispersions is estimated based on the electrokinetic potential (ca. –40 mV). The combined use of spectrophotometry, determination of total organic carbon, inductively coupled plasma atomic emission spectrometry, headspace gas chromatographic analysis, and HPLC offers a complete description of the physicochemical properties of AFDs, which further ensures the validation of AFDs as standard reference samples.

A molecularly imprinted polymer (MIP) was synthetized through precipitation polymerization method for the detection of tartaric acid. Acrylamide or methacrylic acid as functional monomers as well as amount of cross-linker were regarded as polymerization variables. The reactants were dissolved in acetonitrile-ethanol (8 : 2) solution. The synthetized polymers were characterized by HPLC, fourier transform infrared spectrometry (FTIR), thermogravimetric and dynamic light scattering techniques. Batch adsorption experiments with control by HPLC revealed better binding capacity of acrylamide-based polymers compared to methacrylic acid polymers in phosphate buffer saline solution as binding medium. Highest binding capacity was obtained at 30 : 1 cross-linker to template ratio. Tartaric acid complexation with acrylamide was affirmed by FTIR. Tartaric acid is the dominant acid in red grape and can be utilized as red grape juice “fingerprint” in other juices like pomegranate juice which is known to be adulterated in beverage industry. Based on the obtained results, this easily synthesized polymer for tartaric acid can be used in the detection of the presence of red grape juice in pomegranate juice. The synthesized MIP can potentially be applied in sensors for tartaric acid.

A method of acid digestion is optimized for the simultaneous determination of five alkali elements in geological samples of different compositions and genesis by flame atomic emission spectrometry with multichannel spectrum registration. It provides an increase in the analytical signals and the expansion of the analytical range for each determined element. The accuracy and precision of the results are validated by the analysis of natural standard samples and by the method of standard additions. The application of the proposed method of the acid digestion of powder samples reduced the cost of analysis.

Three simple, low-cost, sensitive and diversely applicable UV-Vis spectrophotometric methods have been developed for the estimation of drug Mirabegron. Method A is based on the reaction of Mirabegron with ninhydrin in the presence of sodium molybdate at pH 5.5. Method B is based on the reaction of the drug with 1,2-napthaquinone-4-sulphonate and cetyltrimethyl ammonium bromide in an alkaline medium. Method C is based on a redox reaction of the drug with Folin–Ciocalteu reagent in sodium carbonate medium. Beer’s law was obeyed in the concentration ranges of 2.5–22.5, 5–35, and 5–70 μg/mL for methods A, B, and C. The proposed methods can be applied to drug formulation and recommended for the routine analysis in quality control laboratories.

We propose a simple biochemical detector of cholinesterase inhibitors in water that is based on an enzymatic reaction. The detector was designed as a detection tube containing (i) an indication layer with an immobilized butyrylcholinesterase, (ii) a layer with substrate and chromogenic reagent and (iii) an ampoule with buffer. The chromogenic reagent contained a mixture of two triphenylmethane dyes: Guinea Green B and Fuschsin Basic. The absence of inhibitors was indicated by changing the blue color of the indication layer to violet-red. In the presence of inhibitors, the indication layer remained blue-colored. Color change was evaluated visually (by naked eye). The functionality of the detector was verified on aqueous solutions of alkaloid physostigmine and two chemical warfare agents: sarin and VX. The achieved detection limits were 0.01 μg/mL for physostigmine and sarin and 0.005 μg/mL for VX.

The United States Pharmacopeia 39 uses an HPLC–UV method for the assay of acarbose and its impurities in bulk form. However, there is no information about the stability-indicating nature of the proposed method for the assay of acarbose in tablets. Therefore, in this study, stress tests were firstly applied on the bulk and drug product based on International Conference on Harmonization. Then, verification and revalidation of the proposed method were performed using stressed and untreated samples. Separation was achieved on a Lichrospher^®‒100–NH₂, 5 µm, 250 × 4.6 mm i.d. column using a mobile phase consisting of acetonitrile–0.007 M phosphate buffer (pH 6.7) (750 : 250, v/v) at a flow rate of 2 mL/min and UV detection at 210 nm. The column was maintained at 35°C and an injection volume of 10 µL was used. The linearity of the developed method was investigated in the range of 2.5–20 mg/mL (R² = 0.9995). Peak purity results using a diode array detector have shown that degradation products did not interfere with the detection of acarbose and the assay can thus be considered stability-indicating.

A procedure is developed for the rapid screening and sensitive determination of penicillins G and V in vegetables and fruits using ultra-high-performance liquid chromatography‒quadrupole time-of-flight high resolution mass spectrometry for exact masses of ions of protonated penicillin adducts with methanol. A simple and quick method of sample preparation (simplified QuEChERS method) is proposed for the analysis of fruits and vegetables (oranges, lemons, plums, pears, peaches, cabbage, potatoes, onions, carrots, beets, avocados, cucumbers, tomatoes, eggplants). Identification is carried out by the exact ion masses of analytes, retention time, and the pattern of the isotope distribution of ions (mSigma). Because of the significant matrix effect, analysis should be performed by the method of standard additions, by internal standard method (oxacillin), or using matrix grading. The limits of detection were 0.05‒0.3 ng/g, the analytical ranges were 0.2 (0.9)‒10 ng/g (R² ≥ 0.99), the duration of analysis was 15‒20 min, RSD ≤ 10%.