Molecularly imprinted coated graphene oxide solid-phase extraction monolithic capillary column for selective extraction and sensitive determination of phloxine B in coffee bean

A method was developed to sensitively determine phloxine B in coffee bean by molecularly imprinted polymers (MIPs) coated graphene oxide (GO) solid-phase extraction (GO-MISPE) coupled with high-performance liquid chromatography and laser-induced fluorescence detection (HPLC–LIF). The GO-MISPE capillary monolithic column was prepared by water-bath in situ polymerization, using GO as supporting material, phloxine B, methacrylic acid (MAA), and ethylene dimethacrylate (EDMA) as template, functional monomer, and cross-linker, respectively. The properties of the homemade GO-MISPE capillary monolithic column, including capacity and specificity, were investigated under optimized conditions. The GO-MIPs were characterized by scanning electron microscopy (SEM) and Fourier transform-infrared spectroscopy (FT-IR). The mean recoveries of phloxine B in coffee bean ranged from 89.5% to 91.4% and the intra-day and inter-day relative standard deviation (RSD) values all ranged from 3.6% to 4.7%. Good linearity was obtained over 0.001–2.0 μg mL⁻¹ (r = 0.9995) with the detection limit (S/N = 3) of 0.075 ng mL⁻¹. Under the selected conditions, enrichment factors of over 90-fold were obtained and extraction on the monolithic column effectively cleaned up the coffee bean matrix. The results demonstrated that the proposed GO-MISPE HPLC–LIF method can be applied to sensitively determine phloxine B in coffee bean.     

Benefits of near-infrared spectroscopy for characterization of selected organo-montmorillonites

The potential of near infrared (NIR) spectroscopy in characterization of organically modified clay minerals is introduced. Selected organo-clays, possibly perspective fillers in clay polymer nanocomposites, were prepared from Na-montmorillonite and different surfactants containing octylammonium chain(s), hexadecylammonium chain(s) or a benzene ring with or without a reactive double bond. Based on the stretching (ν) and bending (δ) vibrations observed in the middle IR (MIR) region, the first overtone (2νXH) and combination (ν + δ)XH modes of XH groups (X = O, C, N) are identified. The effect of larger alkylammonium cations on the vibrations of Si-O and OH bonds in montmorillonite layers is observed. The changes in the intensity of the (ν + δ)H₂O band near 5250 cm⁻¹ allows for comparison of the amount of water adsorbed on the montmorillonite surface. The water content decreases with the size of the organic cation reflecting increasing hydrophobicity of the montmorillonite surface. The NIR region shows the 2νCH₃ and 2νCH₂ bands in the 5900-5500 cm⁻¹ region, an upward shift is observed for the complex band due to 2νCH(Ar) of aromatic benzene ring. The NIR spectra are extremely useful in identification of NH₂⁺, NH⁺ and vinyl groups, which are difficult to recognize in the MIR spectra of organo-clays due to overlapping with other absorption bands. The intense bands corresponding to overtones and combination vibrations of NH₃⁺ and NH₂⁺ groups are found in the 6600-6050 cm⁻¹ and 5000-4600 cm⁻¹ regions, the (ν + δ)NH⁺ is unambiguously identified near 4750 cm⁻¹. The characteristic band assigned to 2νCH₂ in H₂CC is detected near 6130 cm⁻¹.     

Infrared spectroscopy and outer product analysis for quantification of fat, nitrogen, and moisture of cocoa powder

The combination of the near infrared (NIR) and Fourier-transform infrared (FTIR) absorbance spectra (1100-2500 nm and 4000-600 cm⁻¹) of 100 cocoa powder samples was used to build calibration models for the determination of the content of fat, nitrogen, and moisture. The samples that comprised the dataset had an average composition of 13.51% of fat, 3.77% nitrogen, and 3.98% moisture. The fat content ranged from 2.42 to 22.00%, the nitrogen from 0.88 to 4.48%, and moisture from 1.60 to 7.80%. For NIR, the relative root mean square error of cross-validation (RMSECV) was 7.0% (R² = 0.96) for fat, 1.7% (R² = 0.98) for nitrogen, and 5.2% (R² = 0.94) for moisture. For FTIR, the relative RMSECV was 10.4% (R² = 0.94) for fat and 3.9% (R² = 0.95) for nitrogen. However, for moisture, it was not possible to build a calibration model with suitable predictability. The combination of the NIR and FTIR domains (data fusion) by outer product analysis PLS1 allowed to predict these parameters and to characterise frequencies in one domain based on the information of the other domain. This work allows to conclude that the second derivative of NIR is the recommended procedure to quantify fat, nitrogen, and moisture content in cocoa powders by infrared spectroscopy.     

Chemical and thermal analysis of the biopolymers in thyme (Thymus vulgaris)

Thyme (Thymus vulgaris) has been known, long time ago, for its aromatic properties. It contains essential oils and polymers such as cellulose (mixture of hemicellulose and cellulose) and lignin. The thyme, studied in this work, was gathered from the same place, in the period from November 1999 to October 2000. The chemical analysis (water, total ash, essential oils, extractive substances, cellulose, holocellulose and lignin) can be used roughly in the characterisation of the four periods that correspond to the four seasons of the year. The cellulose level was found to be more than lignin level in the wet periods (growth of the plant). The opposite was found in the dry periods. The total ash and essential oil levels were found to be high during the period of high pluviometry. The thermal decomposition of cellulose and holocellulose was found to fit well with the first-order kinetics. The activation energy, under air flow, was 185 and 196 kJ mol⁻¹ for cellulose and holocellulose, respectively. The maximum decomposition rate and thermal analysis heating rate of lignin were found to have a direct linear relationship.     

Application of affinity capillary electrophoresis and density functional theory to the investigation of benzo-18-crown-6-ether complex with ammonium cation

Affinity capillary electrophoresis (ACE) and quantum mechanical density functional theory (DFT) calculations have been employed for investigation of non-covalent interactions between macrocyclic ligand, benzo-18-crown-6-ether (B18C6) and ammonium cation, NH₄⁺. Firstly, by means of ACE, the strength of the B18C6-NH₄⁺ complex in mixed binary hydro-organic solvent system, methanol–water (50/50, v/v), was determined from the dependence of effective electrophoretic mobility of B18C6 (corrected to reference temperature 25 °C and constant ionic strength, 10 mM) on the concentration of ammonium ion in the background electrolyte (BGE) using non-linear regression analysis. The logarithmic form of the apparent binding (stability) constant (log K_b) of B18C6-NH₄⁺ complex in the above binary solvent system was found to be equal to log K_b = 1.63 ± 0.10. Secondly, the structural characteristics of B18C6-NH₄⁺ complex were described by quantum mechanical density functional theory (DFT) calculations. According to these calculations, in the energetically most favoured form of the B18C6-NH₄⁺ complex, three strong hydrogen bonds are formed between central ammonium ion and B18C6 ligand, one of them is directed to aryl-O-alkyl (Ar–O–CH₂) ethereal oxygen and the other two hydrogen bonds are oriented to alkyl-O-alkyl (CH₂–O–CH₂) ethereal oxygen atoms of the macrocyclic crown ligand.     

High glass transitions of novel organosoluble polyamide-imides based on noncoplanar and rigid diimide-dicarboxylic acid

A series of novel polyamide-imides (PAIs) with high glass transition temperature were prepared from diimide-dicarboxylic acid, 2,2′-bis(trifluoromethyl)-4,4′-bis(trimellitimidophenyl)biphenyl (BTFTB), by direct polycondensation with various diamines in N-methyl-2-pyrrolidinone using triphenyl phosphite and pyridine as condensing agents in the presence of dehydrating agent (CaCl₂). The yield of the polymers was obtained was high with moderate to high inherent viscosities (0.80-1.03 dL g⁻¹). Gel permeation chromatography (GPC) of the polymers showed number-average and weight-average molecular weights up to 8.6 × 10⁴ and 22 × 10⁴, respectively. The PAIs were amorphous in nature. Most of the polymers exhibited good solubility in various solvents such as N-methyl-2-pyrrolidinone (NMP), N,N-dimethylacetamide (DMAc), N,N-dimethylformamide (DMF), pyridine, cyclohexanone and tetrahydrofuran. The polymer films had tensile strength in the range of 79-103 MPa, an elongation at break in the range of 6-16%, and a tensile modulus in the range between 2.1 and 2.8 GPa. The glass transition temperatures of the polymers were determined by DMA method and they were in the range of 264-291 °C. The coefficients of thermal expansion (CTE) of PAIs were determined by TMA instrument and they were between 29 and 67 ppm °C⁻¹. These polymers were fairly thermally stable up to or above 438 °C, and lose 10% weight in the range of 446-505 °C and 438-496 °C, respectively, in nitrogen and air. These polymers had exhibited 80% transmission wavelengths which were in the range of 484-516 nm and their cutoff wavelengths were in between 418 and 434 nm. The PAIs with trifluoromethyl group have higher bulk density resulting in higher free volume and then lowering the dielectric constant.     

Fourier transform near- and mid-infrared spectroscopy can distinguish between the commercially important Pelargonium sidoides and its close taxonomic ally P. reniforme

Pelargonium sidoides is indigenous to South Africa and abundant in the Eastern Cape Province. Several herbal products have been formulated using P. sidoides of which Umckaloabo^® is probably the most popular and successfully marketed in Germany. The objective of this study was to discriminate between P. sidoides and Pelargonium reniforme by FT-IR spectroscopy. Absorbance spectra were collected for P. sidoides (n = 96) and its close taxonomic ally P. reniforme (n = 57) in the near infrared (NIR) and mid infrared (MIR) regions. The spectroscopic data were analysed using chemometric computations including principal component analysis and orthogonal projections to latent structures discriminant analysis. Phytochemical variation of 5.79% in the NIR dataset (R²X(cum) = 0.962; Q²(cum) = 0.918) and 9.22% variation in the MIR dataset (R²X(cum) = 0.497; Q²(cum) = 0.658) was responsible for the separation of the two species. Seven absorption areas were identified as putative biomarkers responsible for the differences between the two species. These results indicate that FT-NIR and FT-MIR spectroscopy can be used to discriminate between these two closely related species which occupy a sympatric distribution in South Africa.     

Speciation of chromium in Australian fly ash

The concentrations of chromium (III) and (VI) in fly ash from nine Australian coal fired power stations were determined. Cr(VI) was completely leached by extraction with 0.01 M NaOH solution and the concentration was determined by inductively coupled plasma atomic emission spectrometry (ICP-AES). This was confirmed by determining Cr(III) and Cr(VI) in the extracts of fly ash that had been spiked with chromium salts. These analytical measurements were done using a combination of ion-exchange chromatography and ICP-AES. The elutant was 0.05 M HNO₃ containing 0.5%-CH₃OH. When the column was operated at a flow rate of 1.2 ml min⁻¹ and samples were injected by use of a sample loop with a volume of 100 μl, Cr(III) and Cr(VI) in sample solution was exclusively separated within approximately 10 min. The detection limits (3σ) were 5 ng for Cr(III) (0.050 mg l⁻¹) and 9 ng for Cr(VI) (0.090 mg l⁻¹), respectively. A relative standard deviation of 1.9% (n = 6) was obtained for the determination by IC-ICP-AES of 0.25 mg l⁻¹ Cr(III) and Cr(VI).     

Sulfonylcalix[4]arenetetrasulfonate as pre-column chelating reagent for selective determination of aluminum(III), iron(III), and titanium(IV) by ion-pair reversed-phase high-performance liquid chromatography with spectrophotometric detection

Sulfonylcalix[4]arenetetrasulfonate (SO₂CAS) has been examined as a pre-column chelating reagent for ultratrace determination of metal ions by ion-pair reversed-phase high-performance liquid chromatography with spectrophotometric detection. Metal ions were converted into the SO₂CAS chelates in an acetic buffer solution (pH 4.7). The chelates were injected onto a n-octadecylsilanized silica-type Chromolith™ Performance RP-18e column and were eluted using a methanol (50 wt.%)-water eluent (pH 5.6) containing tetra-n-butylammonium bromide (7.0 mmol kg⁻¹), acetate buffer (5.0 mmol kg⁻¹), and disodium ethylendiamine-N,N,N′,N′-tetraacetate (0.10 mmol kg⁻¹). Under the conditions used, Al(III), Fe(III), and Ti(IV) were selectively detected among 21 kinds of metal ions [Al(III), Ba(II), Be(II), Ca(II), Cd(II), Co(II), Cr(III), Cu(II), Fe(III), Ga(III), Hf(IV), In(III), Mg(II), Mn(II), Mo(VI), Ni(II), Pb(II), Ti(IV), V(V), Zn(II), and Zr(IV)]. The detection limits on a 3σ blank basis were 8.8 nmol dm⁻³ (0.24 ng cm⁻³) for Al(III), 7.6 nmol dm⁻³ (0.42 ng cm⁻³) for Fe(III), and 17 nmol dm⁻³ (0.80 ng cm⁻³) for Ti(IV). The practical applicability of the proposed method was checked using river and tap water samples.     

Synthesis and structure of the monometallic cationic complex [Cp(CO)2Fe{η-(CH2CHCH2CH3)}]PF6 (Cp = η-C5H5)

The bimetallic carbocation complex [{Cp(CO)₂Fe}₂(μ-C₄H₇)]PF₆ reacted with trifluoroacetic acid to give the mononuclear cationic complex [Cp(CO)₂Fe{η²-(CH₂CHCH₂CH₃)}]PF₆, which formed yellow orthorhombic crystals in the space group P2₁2₁2₁ with a = 7.652(4), b = 13.422(7), c = 14.037(7); α = β = γ = 90.00 and Z = 4. The carbocation is coordinated to the metal in a η²-fashion forming a chiral metallacyclopropane type structure. The β-CH carbon (C9) is disordered over two positions (C9A and C9B), each having about 50% occupancy. This is attributed to there being both the R and S enantioface isomers in equal amounts in the crystal sample. NMR data indicate that the metallacyclopropane structure observed in the solid state is preserved in solution.     

Thermodynamic properties on quaternary aqueous solutions of chlorides charge-type 1-1*2-1*2-1: XCl + MgCl2 + CaCl2 + H2O with (X ≡ Na; NH4)

In this investigation, the quaternary aqueous solutions of chlorides charge-type 1-1*2-1*2-1 with a cation (Na⁺; NH₄⁺; Mg²⁺; Ca²⁺) have been studied using the hygrometric method at 298.15 K. The water activities of the systems NH₄Cl + MgCl₂ + CaCl₂ + H₂O and NaCl + MgCl₂ + CaCl₂ + H₂O are measured at total molalities from 0.60 mol kg⁻¹ to saturation for different ionic-strength fractions NH₄Cl or NaCl, y = 0.20, 0.50, 0.80, and z ratio ionic-strength for other solutes, with z = 0.20, 0.50 and 0.80 for each y. The obtained data allow the deduction of osmotic coefficients.     

Micelle-mediated cloud point extraction and spectrophotometric determination of rhodamine B using Triton X-100

A new micelle-mediated cloud point extraction method is described for sensitive and selective determination of trace amounts of rhodamine B by spectrophotometry. The method is based on the cloud point extraction of rhodamine B from aqueous solution using Triton X-100 in acidic media. The extracted surfactant rich phase is diluted with water and its absorbance is measured at 563 nm by a spectophotometer. The effects of different operating parameters such as concentration of surfactant and salt, temperature and pH on the cloud point extraction of rhodamine B were studied in details and a set of optimum conditions were obtained. Under optimum conditions a linear calibration graph in the range of 5-550 ng mL⁻¹ of rhodamine B in the initial solution with r = 0.9991 (n = 15) was obtained. Detection limit based on three times the standard deviation of the blank (3S_b) was 1.3 ng mL⁻¹ (n = 10) and the relative standard deviation (R.S.D.) for 50 and 350 ng mL⁻¹ of rhodamine B was 2.40 and 0.87% (n = 10), respectively. The method was applied for the determination of rhodamine B in soft pastel, hand washing liquid soap, matches tip and textile dyes mixture samples.     

Determination of 36 elements in plant reference materials with different Si contents by inductively coupled plasma mass spectrometry: comparison of microwave digestions assisted by three types of digestion mixtures

Closed-vessel microwave digestion of nine standard reference plant materials (NIST, BCR, IAEA) and a laboratory standard of plant material with different Si contents assisted by HNO₃ + H₂O₂ (procedure A), HNO₃ + H₂O₂ + HF + H₃BO₃ (procedure B) and HNO₃ + H₂O₂ + HBF₄ (procedure C) were used to determine the recovery of 36 elements by ICP-MS: Ag, Al, As, Ba, Be, Bi, Cd, Ce, Co, Cr, Cs, Cu, Fe, Ga, Ge, In, La, Li, Mn, Mo, Nd, Ni, Pb, Pr, Rb, Sb, Se, Sn, Sr, Th, Tl, U, V, W, Y, Zn. Additions of HF + H₃BO₃ and HBF₄ in procedures B and C exceeded by 10% (B1, C1) and 100% (B2, C2) the equivalent concentrations of Si in the samples determined by ICP-OES. Most recoveries of certified elements (e.g., Al^*, Cu, Mo^*, Rb^*, Sb^*, Th) decreased significantly (^*p ≤ 0.05) with increasing Si content in plant reference materials digested by procedure A, while the recoveries from procedures B and C decreased insignificantly only for Mo and Sb. Digestions B and C gave significantly higher recoveries of Al, Sb, W and REEs, which were tighter to the reference values of these elements. A similar effect was found for Cu, Fe, Li, Ni, Sn, Th, Tl, V, Zn, Ba, Rb and Sr recoveries in samples with Si contents exceeding 2000 μg g⁻¹. If the Si content in plant samples is less than 10 mg g⁻¹, digestion of 0.5 g of plant samples through 0.05 mL of HF and 0.5 mL of 4% H₃BO₃ or 0.1 mL of HBF₄ is recommended to get satisfactory results for most of the elements. For materials with Si content exceeding 10 mg g⁻¹ the weight of the sample for digestion should be reduced to 0.25 g. However, the operation of potential interferences should be taken into account and eliminated through correction equations and adequate dilution of the samples.     

Synthesis of phenol-formaldehyde resol resins using organosolv pine lignins

Lignin was extracted from white pine sawdust by organosolv-extraction using hot-compressed ethanol-water co-solvent. The optimum conditions for extracting lignin from the pine sawdust were found to be at 180 °C with ethanol-water solvent (1:1 wt/wt), where the lignin yield attained ca. 26% with a purity of ca. 83%. The lignin under such conditions was oligomers with a broad molecular weights distribution: M_n of 537, M_w of 1150 and polydispersity of 2.14. Bio-based phenol-formaldehyde resol resins were synthesized using the resultant lignin as the replacement of petroleum-based phenol at varying ratios from 25 to 75 wt.% by condensation polymerization catalyzed by sodium hydroxide. Upon heating the lignin-phenol-formaldehyde resols could solidify with a main exothermic peak at around 150-175 °C, typical of the conventional phenolic resol resins, and a secondary peak at 135-145 °C, likely due to the exothermic reactions between the free formaldehyde with phenol or lignin to form methylophenols. The replacement of phenol with lignin at a large ratio deferred the curing process, and the introduction of lignin in the resin formula decreased the thermal stability of the resin, leading to a lowered decomposition temperature and a reduced amount of carbon residue at elevated temperatures. For practical applications, it is suggested that the replacement ratio of phenol with lignin be less than 50 wt.%. The thermal stability can however be improved by purifying the lignin feedstock before the resin synthesis.     

Synthesis,characterization and spectroscopic studies of a new ligand [N′-(2-methoxybenzoyl)hydrazinecarbodithioate] ethyl ester and its Mn(II) and Cd(II) complexes: X-ray structural study of Mn(II) complex

A new dithioligand [N′-(2-methoxybenzoyl)hydrazinecarbodithioate] ethyl ester (H₂mbhce, 1) formed complexes [M(Hmbhce)₂]_n {M = Mn(II), Cd(II)} which have been characterized with the help of elemental analyses, magnetic susceptibility measurements, IR, UV–Vis, ¹H and ¹³C NMR and mass spectrometry. [Mn(Hmbhce)₂]_n (2) crystallized in monoclinic system with space group P₂₁/n. In the polymeric structure of 2, the ligand acts as an uninegative tridentate N(1), O(1), S(3) donor and forms a five membered chelate ring with N(1), C(2) and O(1). The intermediate bond lengths (between single and double bond distances) O(1)–C(2) = 1.241(3), N(2)–C(2) = 1.325(3), N(1)–N(2) = 1.393(2), N(1)–C(8) = 1.311(3) ? and C(8)–S(3) = 1.704(2) Å suggest considerable delocalization of charge which develops slightly aromatic character in the chelate ring.     

Biosensor for chlorogenic acid based on an ionic liquid containing iridium nanoparticles and polyphenol oxidase

A biosensor based on the ionic liquid, 1-n-butyl-3-methylimidazolium hexafluorophosphate containing dispersed iridium nanoparticles (Ir-BMI.PF₆) and polyphenol oxidase was constructed. This enzyme was obtained from the sugar apple (Annona squamosa), immobilized in chitosan ionically crosslinked with oxalate. The biosensor was used for determination of chlorogenic acid by square wave voltammetry. The polyphenol oxidase catalyzes the oxidation of chlorogenic acid to the corresponding o-quinone, which is electrochemically reduced back to this substance at +0.25 V vs. Ag/AgCl. Under optimized operational conditions the chlorogenic acid concentration was linear in the range of 3.48 × 10⁻⁶ to 4.95 × 10⁻⁵ mol L⁻¹ with a detection limit of 9.15 × 10⁻⁷ mol L⁻¹. The biosensor was applied in the determination of chlorogenic acid in organic and decaffeinated coffee and the results compared with those obtained using the capillary electrophoresis method. The recovery study for chlorogenic acid in these samples gave values of 93.2-105.7%.     

Prediction of phenolic compounds in red wine fermentations by visible and near infrared spectroscopy

Near infrared (NIR) spectroscopy was used to simultaneously predict the concentrations of malvidin-3-glucoside (M3G), pigmented polymers (PP) and tannins (T) in red wine. A total of 495 samples from 32 commercial scale red wine fermentations over two vintages using two grape varieties (Cabernet Sauvignon and Shiraz), and also including as additional variables two types of fermenters, two different yeasts, and three fermentation temperatures were used. Samples were scanned in transmission mode (400-2500 nm) using a monochromator instrument (NIRSystems6500). Calibration equations were developed from high performance liquid chromatography (HPLC) and NIR data using partial least squares (PLS) regression with internal cross validation. Using PLS regression, very good calibration statistics (R_cal²>0.80) were obtained for the prediction of M3G, PP and T with standard deviation (S.D.)/standard error in cross validation (SECV) ratio (residual predictive deviation, RPD)) ranging from 1.8 to 5.8. It was concluded that near infrared spectroscopy could be used as rapid alternative method for the prediction of the concentration of phenolic compounds in red wine fermentations.     

Spectrophotometric determination of cyclotrimethylenetrinitramine (RDX) in explosive mixtures and residues with the Berthelot reaction

On-site colorimetric methods are a valuable, cost-effective tool to assess the nature and extent of contamination in remediated sites and to enable on-site screening for police criminology laboratories. The existing colorimetric method for cyclotrimethylenetrinitramine (RDX) based on a Griess reaction suffers from the non-quantitative reduction to nitrite and from the unstable character of HNO₂ in acidic medium. Thus we propose a novel spectrophotometric RDX assay in explosive mixtures and residues, based on (Zn + HCl) reduction of RDX in a microwave oven, followed by neutralization of the reduction products to ammonia and low molecular-weight amines, and Berthelot reaction of these amine-compounds with phenol and hypochlorite in alkaline medium to give an intensely blue indophenol dye absorbing at 631 nm. The molar absorptivity and limit of detection (LOD) for RDX were (1.08 ± 0.04) × 10⁴ L mol⁻¹ cm⁻¹ and 0.18 mg L⁻¹, respectively. Application of the method to synthetic mixture solutions of RDX and trinitrotoluene (TNT) at varying proportions showed that there was minimal interference from TNT (which could be compensated for by dicyclohexylamine colorimetry), since the Berthelot reaction was essentially non-responsive to m-substituted anilines derived from TNT upon (Zn + HCl) reduction. The proposed method was successfully applied to military-purpose explosive mixtures of (RDX + inert matter) such as Comp A5, Comp C4, and Hexal P30, and to (RDX + TNT) mixtures such as Comp B. The molar absorptivity of RDX was much higher than that of either ammonium or nitrate; RDX could be effectively separated from ammonium and nitrate in soil mixtures, based on solubility differences. The Berthelot method for RDX was statistically validated using Comp B mixtures against standard HPLC equipped with a Hypersil C-18 column with (40% MeOH-60% H₂O) mobile phase, and against gas chromatography-thermal energy analysis (GC-TEA) system.     

Direct determination of kanamycin in raw materials, veterinary formulation and culture media using a novel liquid chromatography-evaporative light scattering method

A novel method for the direct determination of kanamycin A and its minor component kanamycin B was developed and validated based on reversed phase liquid chromatography with evaporative light scattering detector (ELSD). ELSD response to kanamycins was found to be enhanced by: (a) decrease of peak width and asymmetry (obtained by controlling the mobile phase acidity or ratio of organic solvent to water), (b) use of ion-pairing acidic reagents of increased molecular mass, and (c) increase of mobile phase volatility. Utilizing an Spherisorb ODS-2 C₁₈ column, the selected optimized mobile phase was water-acetonitrile (60:40, v/v), containing 11.6 mM heptafluorobutyric acid (isocratic elution with flow rate of 1.0 ml min⁻¹). Kanamycin A was eluted at 3.9 min and kanamycin B at 5.0 min with a resolution of 2.7. Logarithmic calibration curves were obtained from 0.6 to 28 μg ml⁻¹ (r > 0.9998) for kanamycin A and 4-36 μg ml⁻¹ (r > 0.9994) for kanamycin B, with a LOD equal to 0.20 and 1.4 μg ml⁻¹, respectively.In kanamycin acid sulfate pharmaceutical raw materials, the simultaneous determination of sulfate (t_R = 2.1 min, LOD = 2.3 μg ml⁻¹, %R.S.D. = 1.7, r > 0.9998) and kanamycins was feasible. No significant difference (t-test) was found between the results of the developed LC-ELSD method and those of reference methods, while recovery from kanamycin B spiked samples ranged from 95 to 105%. The developed method was also applied with very good accuracy for the determination of kanamycin A in veterinary formulation (%recovery 95-103, %R.S.D. < 1.4, n = 3) and for the determination of kanamycins A and B in bacteria culture media (%recovery 102 and 99, respectively).     

Comparability of composition of carbon functional groups in humic acids between inverse-gated decoupling and cross polarization/magic angle spinning 13C nuclear magnetic resonance techniques

To find a certain relation between the composition of carbon functional groups of humic acids derived from liquid state ¹³C nuclear magnetic resonance (NMR) spectra acquired with inverse-gated decoupling (IGD), known as a quantitative pulse sequence, and that by solid-state ¹³C NMR with cross polarization/magic angle spinning (CPMAS) techniques, fifteen soil humic acid samples with a wide range of aromaticity were analyzed. Relationships between the proportions of humic acid carbon as alkyl, O-alkyl, and aromatic carbon assessed by the two methods could be regressed to y = ax (r = 0.932-0.956; P < 0.005), respectively. The contents of alkyl, O-alkyl, and aromatic carbon assessed by CPMAS method were larger than those found by IGD method. However, the differences between the two methods were small and exclusive regression to y = x was also significant (r = 0.775-0.941; P < 0.005). Aromaticity calculated from ¹³C CPMAS NMR data also did not differ significantly from those computed from ¹³C NMR spectra with IGD. These observations indicated the comparability of the relative content of carbon functional groups in humic acids except for carboxyl and carbonyl carbon.