Fluorescence polarization studies of the conformation of soil fulvic acid

The conformation of soil fulvic acid was studied by fluorescence polarization as a function of pH, concentration, and ionic strength. Rotational relaxation times were measured from the slopes of plots of polarization vs. the ratio of temperature to viscosity. The rotational relaxation time did not change over the pH range 5–8 or over the concentration range 3.3 X 10^-5–3.3 × 10^-4 M fulvic acid. This suggests that fulvic acid does not aggregate or change conformation. Changes in ionic strength also do not cause a measurable change in rotational relaxation time. A net rotational relaxation of 2.0 ns was calculated for fulvic acid. This value is based on a fluorescence lifetime of 2.1 ns which is the best single exponential fit to the observed fluorescence decay. A molecular weight of 2400 was calculated for fulvic acid assuming that fulvic acid is spherical. The discrepancy between this value and the true number-average molecular weight of 990 suggests that fulvic acid exists in a flat extended conformation.     

Graft polymerization of acrylic monomers onto starch fractions. III. Effect of carbohydrate structure

Grafted PMMA was isolated by the acid hydrolysis method. Weight-average and number-average molecular weights were determined by gel permeation chromatography. The number-average molecular weight of the grafted chains was about 475,000 for amylopectin and 403,000 for amylose. The number of grafted chains (mmol) ranged from 2.4 × 10^?3 to 4.6 × 10^?3 for amylopectin graft copolymers and from 2.9 × 10^?3 to 6.8 × 10^?3 for those of amylose. These results were related to others obtained from ceric ion consumption studies. The values suggest that amylopectin, because of its complex structure, favors a higher consumption of ceric ion in homopolymerization reactions and inhibits the initiation reactions of the copolymerization.     

Molecular structure of polyethylene. XIII. An improved cryoscopic method for determining number-average molecular weight of polyethylene

The determinations of the number-average molecular weight of polyethylene by cryoscopy has been improved, permitting precise measurements with both linear and branched polyethylenes in the molecular weight range 4,000–30,000. Improvements include a cryometer of new design, a lower-melting cryoscopic solvent containing a nucleating agent to control supercooling and rate of crystallization of the solvent, and more precise measurement of freezing point depression. Polyethylene samples are dissolved in hexamethylbenzene admixed with 0.1% of cadmium iodide, and steady-state freezingpoint depressions are measured with a thermistor to a maximum sensitivity of 5 × 10^?5°C. Molecular weight measurements are reproducible to within ±10%. The cryoscopic apparatus and procedure are described in detail, and results obtained with samples of linear and branched polyethylene are presented and discussed.     

Apparatur zur Molekulargewichtsbestimmung an hochverdünnten (10−4M). Lösungen mittels Dampfdruckosmometrie

A vapour pressure osmometer for the determination of number-average molecular weights is described. With this improved design 10^?4M solutions can be measured with a standard deviation of 1.3% (carbon tetrachloride, 30°C). Molecular weight determinations up to 160000 (± 7.5%; polystyrene in carbon tetrachloride) are presented.     

Determination of urinary chromium levels for healthy men and diabetic patients by electrothermal atomic absorption spectrometry

Urinary chromium levels for healthy and diabetic men were determined by direct graphite-furnance atomic absorption spectrometry. The average values were 0.72 ± 0.31 ng ml^?1 for 23 healthy men aged 23 to 35, 0.39 ± 0.19 ng ml^?1 for 19 healthy men aged 47 to 69, and 1.0 ± 0.9 ng ml^?1 for 23 diabetic patients aged 13 to 79. Some urines of diabetic patients exhibit values > 1.3 ng ml^?1, which are never found in healthy men. The proposed method involves direct injection of 20 μl of urine inot a pyrolytically-coated graphite tube, and a standard addition calibration procedure involving a pooled urine sample. The results are compared with those obtained by a liquid-liquid extraction method.     

Copper speciation in aqueous solutions of fulvic acid and related molecular weight distributions

Potentiometric and fluorescence measurements of aqueous solutions of fulvic acid containing Cu(NO₃)₂ or Cu(ClO₄)₂, respectively, were carried out at 25?°C and pH 5.5 to determine naturally occurring Cu species. The fulvic acid used was isolated by XAD-8 from filtrated (0.3 μm) water of a peat bog in the Dachauer Moos near Munich. From the results an operational molecular weight of fulvic acid of about 750 g/ mol was estimated, which was confirmed by molecular weight distributions determined by high-performance size-exclusion chromatography (HPSEC), gel permeation chromatography (GPC) and time-of-flight secondary ion mass spectrometry (ToF-SIMS). Using this molecular weight and assuming that mainly 1:1 Cu-fulvic acid complexes are formed, a conditional stability constant of the Cu-fulvic acid complex of 10^5.9 could be calculated. These data are essential for the assessment of organic carrier-mediated migration of Cu as well as of the toxicological risk potential of Cu in aqueous environment and can be used as input parameters for geochemical modeling of the Cu species distribution in aqueous solutions.     

Study of the complex formation of copper(II) by humic and fulvic substances

A study of the complexation of copper(II) by fulvic substances, based on ion-selective electrode measurements, is reported. The influences of the copper concentration (10^-6 –1O^-4 M), fulvic acid concentration (2–100 mg 1^-1), pH (3–8) and calcium concentration (10^-4–5 × 1O^-3 M) are given particular attention. The effects of statistical errors on the measurement of the values of the complex-formation parameters are considered. These parameters are measured for various surface-water samples, aqueous soil extracts, peat water and solutions of organic matter formed by in vitro decomposition of leaves. In general, these parameters vary little with actual source for a particular type of water.     

Measurements of rubidium in standard reference samples by wavelength-modulation diode laser absorption spectrometry in a graphite furnace

An investigation of the capabilities of the WM-LDAS-GF (wavelength-modulation laser diode absorption spectrometry in graphite furnaces) technique for detection of Rb at low pg ml⁻¹ concentrations in samples with complex matrices has been performed. Five reference materials were investigated with respect to their Rb content by the WM-LDAS-GF technique: corn bran (NIST 8433); NIST water; (1643d) riverine water (SLRS-2); estuarine water (SLEW-1); and sea water (NASS-3). Freeze-dried corn bran was found to have a Rb concentration of 440 ± 70 ng g⁻¹. This compares well with the certified concentration of 500 ± 300 ng g⁻¹. The Rb content of the NIST water was assessed to 12.7 ± 1.7 ng ml⁻¹. This compares excellently with the specified (although not certified) level of 13 ng ml⁻¹. None of the three other reference materials has any certified Rb level. The Rb content of riverine water was found to be 3.4 ± 0.8 ng ml⁻¹. Chemical interferences were encountered when estuarine water and sea water were analyzed (loss of Rb as RbCl). Addition of NH₄NO₃ as the matrix modifier increased the Rb recovery values considerably (although not fully to unity). Estuarine water and sea water were found to have Rb contents of 30 ± 10 ng ml⁻¹ and 140 ± 50 ng ml⁻¹, respectively. A detection limit for Rb in deionized water of 10 fg (corresponding to a concentration of 1 pg ml⁻¹ using a 10 μL aliquot) was obtained. This is identical to (and thus verifies) the previously published result by the group of K. Niemax. These results show that the WM-LDAS-GF technique is capable of detecting traces of Rb in samples also with complex matrices.     

Purification and Properties of a Thermostable Xylanase GH 11 from Penicillium occitanis Pol6

An extracellular, endo-??-1,4-xylanase was purified to homogeneity from the culture filtrate of the filamentous fungus Penicillium occitanis Pol6, grown on oat spelt xylan. The purified enzyme (PoXyn2) showed a single band on SDS?CPAGE with an apparent molecular weight of 30?kDa. The xylanase activity was optimal at pH?3.0 and 65?°C. The specific activity measured for oat spelt xylan was 2,368?U?mg^?1. The apparent K _m and V _max values were 8.33?mg?ml^?1 and 58.82???mol?min^?1?ml^?1, respectively, as measured on oat spelt xylan. Thin-layer chromatography experiments revealed that purified PoXyn2 degrades xylan in an endo-fashion releasing xylobiose as main end product. The genomic DNA and cDNA encoding this protein were cloned and sequenced. This PoXyn2 presents an open reading frame of 962?bp, not interrupted by any introns and encoding for a mature protein of 320 amino acids and 29.88?kDa.     

Flow-injection spectrophotometric determination of ascorbic acid by reduction of vanadotungstophosphoric acid

Ascorbic acid may be determined spectrophotometrically at 360 nm based on reduction of vanadotungstophosphoric acid using flow-injection analysis. The carrier stream was distilled water and the reagent streams were buffer solution (pH 3.0), 1.735 × 10^?3 M dodecatungstophosphoric acid and 1.735 × 10^?3 M sodium vanadate. The injection rate was 80 h^?1. The calibration graph was linear up to 80 μg ml^?1 ascorbic acid and the relative standard deviation for the determination of 20 μg ml^?1 ascorbic acid was 1.5% (n=10). The detection limit was 1.0 μg ml^?1 ascorbic acid, based on an injection volume of 250 μl. The system was applied to the determination of ascorbic acid in vitamin C tablets.     

Comparison of Ion-Pairing and Reversed Phase Liquid Chromatography in Determination of Sulfamethoxazole and Trimethoprim

Abstract

Two simple, rapid, and sensitive HPLC methods have been developed for the simultaneous determination of sulfamethoxazole and trimethoprim in their pure and dosage forms, one utilizing reversed phase HPLC and the other ion-pair HPLC. In the reversed phase HPLC method (A) the mobile phase consists of 0.05% aqueous solution of formic acid with pH adjusted to 4.5±0.2 with triethylamine : acetonitrile:tetrahydrofuran 50 : 49 : 1 (v/v), and the mobile phase pumped at flow rate of 1.0 ml min^?1. An Appolo LC18 column (5.0 µm), 250 mm length × 4.6 mm diameter, was utilized as the stationary phase. Detection was affected spectrophotometrically at 254 nm. In the ion-pair HPLC method (B) the mobile phase consisted of methanol : buffer 35 : 65 (v/v) with the buffer composed of potassium dihydrogen phosphate 0.3 M and sodium heptan sulfonic acid 5.0 mM. To 500 ml of buffer was added 2.0 ml triethylamine, and then the pH was adjusted to 5.0 with phosphoric acid, and the mobile phase was pumped at a flow rate of 1.2 ml min^?1. A Hypersil C₁₈ column (5.0 µm), 150 mm length × 4.6 mm diameter, was utilized as the stationary phase. Detection was affected spectrophotometrically at 254 nm. Linearity ranges for sulfamethoxazole and trimethoprim were 1.0–110 and 1.5–98 µg ml^?1, respectively, with method A and 0.5–100 and 1.0–125 µg ml^?1, respectively, with method (B). Minimum detection limits obtained were 0.1969 and 0.3451 µg ml^?1 for sulfamethoxazole and trimethoprim, respectively, with method A, and 0.1377 and 0.2454 µg ml^?1 with method (B). The proposed methods were further applied to the analysis of tablets containing the two drugs, and the results were satisfied.     

Rate Coefficients for the Gas‐Phase Reactions of Chlorine Atoms with Cyclic Ethers at 298 K

Rate coefficients of reactions of Cl atoms with cyclic ethers, tetrahydropyran (THP), tetrahydrofuran (THF), and dihydrofurans (2,5‐DHF and 2,3‐DHF) have been measured at 298 K using a relative rate method. The relative rate ratios for THP and THF are 0.80 ± 0.05 and 0.80 ± 0.08, respectively, with n‐hexane as the reference molecule. The relative rate ratios for THF and 2,5‐DHF with n‐pentane as the reference molecule are 0.95 ± 0.07 and 1.73 ± 0.06, respectively, and for 2,5‐DHF with 1‐butene as reference is 1.38 ± 0.05. The average values of the rate coefficients are (2.52 ± 0.36), (2.50 ± 0.39), and (4.48 ± 0.59) × 10^?10 cm³ molecule^?1 s^?1 for THP, THF, and 2,5‐DHF, respectively. The errors quoted here for relative rate ratios are 2σ of the statistical variation in different sets of experiments. These errors, combined with the reported errors of the reference rate coefficients using the statistical error propagation equation, are the quoted errors for the rate coefficients. In the case of 2,3‐DHF, after correcting for the dark reaction with CH₃COCl and assuming no interference from other radical reactions, a relative rate ratio of 0.85 ± 0.16 is obtained with respect to cycloheptene, corresponding to a rate coefficient of (4.52 ± 0.99) × 10^?10 cm³ molecule^?1 s^?1. Unlike cyclic hydrocarbons, there is no increase with increasing number of CH₂ groups in these cyclic ethers whereas there is an increase in the rate coefficient with unsaturation in the ring. An attempt is also made to correlate the rate coefficients of cyclic hydrocarbons and ethers with the molecular size as well as HOMO energy.     

Spectrophotometric Determination of Acebutolol Hydrochloride and Nicoumalone with Metol and Potassium Permanganate

Abstract

A spectrophotometric method is described for the determination of Nicoumalone and Acebutolol hydrochloride based on the formation of molecular complex with the reduction product of Nicoumalone or hydrolysis product of Acebutolol hydrochloride and p-N-methyl benzoguinone monoimine [formed in situ from met01 (p-N-methylaminophenol sulfate) and potassium permanganate, PMBQMI] at pH 3.3. Quantitative measurements were made at the maximum absorption of 525 nm. Beer's law is obeyed in the range of 5–50 μg ml^?1 and 5–60 μg ml^?1 for Nicoumalone and Acebutolol hydrochloride respectively. The proposed method is comparable with the reference method when applied to pharmaceutical preparations, and tablets, An average percentage recovery of 99.5 ± 0.8 was obtained.     

Photochemically induced fluorimetric determination of the antimalarial mefloquine

Mefloquine (MQ) was determined quantitatively in pharmaceutical tablets by irradiating the MQ solution for 2–7 min with a high-pressure UV lamp, measuring simultaneously the increase in fluorescence signal at room temperature (298 K) and comparing the signal with that of a standard. The effects of several solvents (acetone, dioxane, ethanol, methanol, propan-2-ol, tetrahydrofuran, water) and “pH” on the fluorescence properties of MQ and its photochemical decomposition product were studied. The limit of detection of MQ was 50 ng ml^?1. The mean overall recovery from pharmaceutical tablets was 102.3 ± 4%.     

Utility of p-chloranilic Acid and 2,3 Dichloro-5,6-dicyano p-Benzoquinone (DDQ) for the Spectrophotometric Determination of Triamterene

Abstract

Two simple and sensitive spectrophotometric procedures are suggested for analysis of triamterene. The first procedure is based on the reaction of triamterene with p-chloranilic acid (p-CA) in methylene chloride to form a highly stable coloured product, exhibiting maximum absorbance at λ 530 nm. Beer's law is obeyed in the range of 40–220 μg.ml^?1 with a mean percentage accuracy of 99.98 ± 0.446. Limit of determination is 20 μg.ml^?1. In the second procedure, the drug is determined via charge transfer complex formation with 2,3 dichloro-5,6-dicyano p-benzoquinone (DDQ) using methylene chloride as a solvent. Here the reaction product has two well defined maxima at 460 nm and 530 nm where each has been utilized for quantitative determination. Beer's law is obeyed in concentration ranges of 25–125 μg.ml^?1 and 25–150 μg.ml^?1 with mean percentage accuracies of 99.92 ± 0.449 and 100.00 ± 0.511 for both maxima. 460 and 530 nm. respectively. Limit of determination is 12.5 μg.ml^?1 at both maxima. Optimum conditions for each procedure have been studied and the stoichiometry of both reactions was ascertained using Job's method of continuous variation. The validity of the suggested procedures was assessed by applying the standard addition technique using the drug capsules. Both procedures are statistically analyzed as compared with BP method for analysis of triamterene (non aqueous titration) revealing good accuracy and precision as indicated by t and F tests.     

Precipitation polymerization of acrylamide using vazo-33 as an initiator and acetonitrile/water mixtures as the solvent

Precipitation polymerization of acrylamide initiated by a thermal initiator, Vazo-33 (DuPont Vazo Initiator), was achieved at a solvent composition of acetonitrile/water = 4/6 (vol/vol). The polymerization kinetics were investigated in the acrylamide [M] concentration range 0.86–2.27M, Vazo-33 [I] concentration range 1.4–11.0 × 10^?4M, and temperature range 30–40°C. Polymerization was carried out in reaction ampules and the rate was determined gravimetrically. Number-average molecular weight was obtained from intrinsic viscosity. The precipitation polymerization rate varied as [M]^2.16 and [I]^0.44. Number-average molecular weight was proportional to [M]^1.22 and inversely proportional to [I]^0.31. The overall reaction activation energy was calculated as 17.3 kcal/mol in the temperature range studied. The optimal reaction conditions studied were: acetonitrile/water = 4/6, temperature = 40°C, [M] = 1.95M and [I] = 2.8 × 10^?4M. One hundred percent conversion was achieved in 90 min and a polymer with a number-average molecular weight of 1,200,000 was obtained.     

Polarography of disodium pentacyanonitrosylferrate(II): Part 2. Determination at Therapeutic Levels in Serum,Plasma, and Whole Blood

Disodium pentacyanonitrosylferrat(II) (sodium nitroprusside) is determined at therapeutic (ng ml^?1) levels in plasma, serum and blood with conventional and high-performance differential pulse polarography (d.p.p. and h.p.d.p.p.) at a dropping mercury electrode or a static mercury drop electrode. Serum or plasma (3 ml) is treated with perchloric acid containing 1 mg ml^?1 potassium hexacyanoferrate(II), centrifuged for 10 min and subjected to polarography. For spiked serum, calibration graphs are linear over the range 30–1000 ng ml^?1 sodium nitroprusside, regardless of the polarographic technique; the estimated detection limit is 15 ng ml^?1 (5 × 10^?8 M). Calculated therapeutic levels range from 100 to 1000 ng ml^?1. Similar results were obtained for spiked plasma. A similar procedure is suitable for whole blood and was used to study the in-vitro degradation of sodium nitroprusside (200 ng ml^?1) on incubation at 37°C. The in-vitro loss is rapid (t_{$\text{1}\text{2}$} ≈ 6 min) but meaningful in-vivo levels can be obtained when the blood is collected in a 0.9% sodium chloride solution at 0°C. Thiocyanate, the main metabolite of nitroprusside, and thiosulphate, which is a potential antidote for cyanide, do not interfere.     

Spectrophotometric and Spectrofluorimetric Determination of Cyclophosphamide and Its Isomer Ifosphamide

Abstract

Based on the condensation reaction between amino groups of either cyclophosphamide or ifosphamide with the carbonyl group of ninhydrin, giving coloured and fluorescent products, a spectrophotometric procedure for both drugs is suggested in the range from 30 to 90μg ml^?1 at 564 nm, with accuracies of 100.6 ± 1.06% and 100.8 ± 1.02% for cyclophosphamide and ifosphamide, respectively. Also, a spectrophotometric procedure for both drugs is proposed in the range from 1.2 to 3.6 μg ml^?1 at 465 nm and 485 nm for cyclophosphamide and ifosphamide, respectively, using 380 nm as an excitation wavelength for both drugs with accuracies of 100.4 ± 1.83% and 99.5 ± 1.64%, respectively. This condensation reaction, however, does not differentiate between the two isomeric drugs.

Another new method is, therefore, suggested. It depends on the fact that the secondary amino group of ifosphamide is hindered electronically and sterically, while the nucleophilic amino group of cyclophosphamide reacts with the nitrosyl group of sodium nitroprusside molecule, giving a bluish green colour measurable at 708 nm. This colour is used for the determination of cyclophospahmide in the presence of its isomer ifophamide in the range from 0.2 to 1 mg ml^?1 with repeatability of 99.2 ± 1.49%.

The suggested procedures are applied successfully to pharmaceutical formulations of cyclophosphamide and ifosphamide, and their validities are assessed by applying the standard addition technique. The results obtained by applying the proposed procedures are statistically analyzed and compared with those obtained by adopting the United States Pharmacopoeial method.     

An improved spectrophotometric determination of manganese(II) with 1-(2-quinolylazo)-2,4,5-trihydroxybenzene with applications to medicinal plants and chemical reagents

The effects of organic solvent, time and temperature on the colour-forming reaction are described. For nine solvents tested, the molar absorptivities were in the range 2.0×10⁴?6.7×10⁴ mol^?1 cm^?1; best sensitivity was obtained with a 1:1 water/2-propanol solution after a standing time of 35 min; temperature should be controlled to ±2°C. Beer's law was obeyed for 0–1.45 μg ml^?1 Mn(II). The improved method was applied to determinations of manganese(II) in various herbs and chemical reagents; the values found were in the range 5.4–48.4 μg g^?1 in herbs, and 0.001-0.012% (w/w) in reagents.     

Spectrophotometric Determination of Diphenadione Via its Metal Complexes

Abstract

Spectrophotometric procedure is described for the quantitative determination of diphenadione [2-(diphenylacetyl)-1,3-indandione], based on direct spectrophotometric measurements of the absorbances of its iron (III), iron (II) and cobalt (II), metal complexes at 488 nm, 505 nm and (334 nm, 372 nm), respectively. The drug reacts with metals in the ratio of 3:1 and 2:1 for iron (III) and for both iron (II) and cobalt (II) respectively. The obtained complexes have apparent molar absorptivities of 1.48 × 10³ 1 mol^?1 cm^?1, 0.714 × 10³ 1 mol^?1cm^?1 and (1.70 × 10³ 1 mol^?1cm^?1, 1.93 × 10³ 1 mol^?1cm^?1) for iron (III), iron (II) and cobalt (II) complexes, respectively. The procedure is suggested for the determination of 51–400 μg.ml^?1 diphenadione via the iron (II) complex and 35–170 μg.ml^?1 diphenadione via both cobalt (II) and iron (III) complexes. The suggested procedure has accuracies of 99.79 ± 0.67%, 99.64 ± 0.37% and (100.09 ± 0.53%, 99.99 ± 0.42%) for the metal complexes of iron (III), iron (II) and cobalt (II), respectively.