Hemijske karakteristike visoko-krečnjačkih zemljišta koje određuju raspodelu fosfora

Phosphorus fractions from three highly calcareous soils (average, 24.9 +/- 4.8 %CO32-) from sampling sites with a Mediterranean climate were isolated by sequential extraction. In order to provide a more reliable basis for the definition of the obtained P-fractions, principal component analysis was applied and from the chemical characteristics of the 14 investigated soils, those characteristics which define at he content and association features of the P-fractions were assessed. The soils are characterized by a relatively high pH (8.0-8.2) and by significantly differing contents of organic mater, acid-soluble Mg and total P. These differences affected the various association features of the P-fraction with the soil constituents. The NH4F-P fraction (isolated with 0.5 M NH4F, pH 8.2) is defined by the contents of the main metals of the oxide-hydroxide-clay associations (Al, Fe, Mn) or by the the redox potential (Eh) of Mn. The accumulation of NaOH-phosphorus (extractable with 0.1 M NaOH) depended on the constituents of the oxide hydroxide-clay association, the humic substances and Eh-related factors. In those soils in which NaOH-P is defined by the oxide-hydroxide-clay association, the participation of Fe as a bridge-forming metal is proposed. The main part of total P, i.e., Delta P = TP - (NH4F-P + NaOH-P) is defined by the status of Mn- and Fe-humic complexes or by the concentration of hydroxyl-ions.Iz tri visoko-krečnjačka zemljišta (prosečni sadržaj CO 3 2- 24.9 ± 4.8%, pH 8.0 - 8.2), sa lokacija sa sredozemnom klimom, izolovane su frakcije fosfora sekvencijalnom ekstrakcijom. U cilju obezbeđivanja pouzdanije osnove za definisanje dobijenih frakcijafosfora (P-frakcija), primenjena je analiza principalne komponente (PC-analiza). Među 14 hemijskih karakteristika zemljišta, izdvojene su one koje definišu sadržaj pojedinih P-frakcija i prirodu njihove asocijacije sa sastojcima zemljišta. Frakcija NH 4-P (izolovana sa 0,5M NH 4F, pH = 8,2) definisana je sadržajem glavnih metala oksidne-hidroksidne-glinene asocijacije (Al, Fe, Mn) ili Eh-statusom izraženim sadržajem Mn. Akumulacija NaOH-P (ekstrahovanog sa 0,1 M NaOH) zavisila je od sastojaka oksidne-hidroksidne-glinene asocijacije, od huminskih supstanci i od faktora koji stoje u vezi sa Eh. U onim zemljištima u kojima je NaOH-P definisana sastojcima oksidne-hidroksidne-glinene asocijacije, pretpostavljeno je vezivanje fosfora preko Fe-mostova. Glavna količina fosfora ∆P = TP - (NH 4F-P + NaOH-P), u pojedinim zemljištima definisana je ili statusom Mn- i Fe-huminskih kompleksa, ili pH-vrednošću

Analitička primena derivativne spektrofotometrije

1. Introduction 2. Basic characteristics of derivative spectrophotometry 2.1. Increase of spectra resolution 2.2. Elimination of the influence of baseline shift and matrix interferences 2.3. Enhancement of the detectability of minor spectral features 2.4. Precise determination of the positions of absorption maxima 2.5. Signal-to-noise ratio (SNR) 2.6. Quantitative analysis 3. Analytical applications 3.1. Inorganic analysis 3.2. Organic and pharmaceutical analysis 3.3. Analysis of food and water 3.4. Application of derivative spectrophotometry for the determination of equilibrium constants.Razmatrani su osnovni principi derivativne spektrofotometrije (DS) i njene prednosti i ograničenja u odnosu na normalnu spektrofotometriju. Dat je pregled analitičke primene DS u različitim oblastima: neorganskoj i organskoj analizi, analizi farmaceutskih preparata, kliničkoj analizi, analizi hrane, hemije životne sredine, hemijskoj ravnoteži

Protolitičke ravnoteže bromazepama

The protolytic equilibria of bromazepam, an ampholyte sparingly soluble in water, in homogeneous and heterogeneous systems were studied in the pH range 0–14 at 25ºC and at ionic strength of 0.1 mol/dm3 (NaCl). On the basis of 13C-NMR spectra, the protonation site was predicted – in acidic media the pyridine nitrogen of bormazepam is protonated. The acidity constants of bromazepam were determined spectrophotometrically (pKa1 2.83 and pKa2 11.60) and potentiometrically (pKa1 2.99). In the heterogeneous system the following equilibrium constants were determined: Ks0 =[HA](pKs0 3.44), Ks1 =[H2A+]/[H3O+](pKs1 0.61), and Ks2 =[A-][H3O+](pKs2 15.04).Proučavane su protolitičke ravnoteže bromazepama, amfolita iz klase 1,4-benzodiazepina, slabo rastvornog u vodi. Ispitivanja su vršena u homogenom i heterogenom sistemu u pH intervalu 0–14, na temperaturi 25ºC i pri jonskoj sili 0,1 mol/dm3 (NaCl). Na osnovu 13C-NMR spektara pretpostavljeno je da do protonovanja u molekulu bromazepama dolazi na piridinskom atomu azota. Kiselinske konstante određene su spektrofotometrijski (pKa1 2.83 and pKa2 11.60) i potenciometrijski (pKa1 2,99). U heterogenom sistemu određene su sledeće ravnotežne konstante Ks0 =[HA](pKs0 3.44), Ks1=[H2A+]/[H3O+](pKs1 0.61), and Ks2 =[A-][H3O+](pKs2 15.04)

Protolitičke ravnoteže u homogenom i heterogenom sistemu ketokonazola i njegovo direktno spektrofotometrijsko određivanje u tabletama

The acid-base equilibria of a diprotic, slightly hydrosoluble base ketoconazole were studied in homogeneous and heterogeneous water systems. The determinations were performed at 25ºC at a constant ionic strength of M(NaCl). The acidity constant Ka1 was determined by potentiometric (pKa1 3.20) and spectrophotometric (pKa1 3.26) methods. A pKa2 constant of 6.10 was obtained based on the equilibrium constants pKs0 4.84 and pKs1 -1.26, determined in a heterogeneous ketoconazole system. The obtained values of the constants served to calculate the solubility and the distribution of the equilibrium forms of ketoconazole as a function of pH. On the basis of the distribution of the equilibrium forms of ketoconazole, a spectrophotometric method for the determination of its content in commercial tablets was developed. The determinations were performed at 225 nm in 0.1 M HCl. The method is simple and rapid and enables the direct spectrophotometric determination of the content of ketoconazole without previous isolation.Proučene su kiselinsko-bazne ravnoteže u homogenom i heterogenom vodenom sistemu ketokonazola, diprotične teško rastvorne baze. Određivanja su vršena na temperaturi 25ºC i pri konstantnoj jonskoj sili 0,1M(NaCl). Kiselinska konstantaKa1 određena je potenciometrijski (pKa1 3,20) i spektrofotometrijski (pKa1 3,26). Konstanta pKa2 6,10 izračunata je iz ravnotežnih konstanti određenih u heterogenom sistemu: pKs0 4,84 i pKs1 -1,26. Na osnovu dobijenih vrednosti za konstante izračunata je rastvorljivost i raspodela ravnotežnih oblika ketokonazola u funkciji pH. Na bazi raspodele ravnotežnih oblika ketokonazola predložena je spektrofotometrijska metoda za njegovo određivanje u komercijalnim tabletama. Određivanja su vršena na talasnoj dužini 225 nm u 0,1M HCl.Metoda je jednostavna i brza, i omogućava direktno spektrofotometrijsko određivanje ketokonazola, bez prethodnog izolovanja

Određivanje pKa vrednosti i korelacija sa strukturom p-supstituisanih trans-2,3-epoksi-4-okso-4-fenilbutanskih kiselina

The pKa values for a series of eight p-substituted trans-2,3-epoxy-4-phenyl butanoic acids (p-substituted trans-β-aroylepoxyacrylic acids) have been determined potentiometrically in aqueous media at 25 °C at an ionic strength of 0.1 mol/dm3 (NaCl). The transmission of polar effects from the substituents on the phenyl nucleus to the carboxylic group through the side chain involving a carbonyl group and an epoxide ring was investigated. The pKa values were correlated with structure using the Hammett, Taft and Yukawa-Tsuno approaches. The Hammett ρ constant (0.34) was compared with analogue values for structurally similar acids.Određene su pKa vrednosti za seriju od osam p-supstituisanih trans-2,3-epoksi-4-okso-4-fenilbutanskih kiselina (p-supstituisanih trans-β-aroilepoksiakrilnih kiselina). Vrednosti su određene potenciometrijski u vodenoj sredini na 25 °C i jonskoj sili 0.1 mol/dm3 (NaCl). Proučavan je prenos polarnih efekata sa supstituenata na fenil jezgru ka karboksilnoj grupi kroz bočni niz koji sadrži karbonilnu grupu i epoksidni prsten. pKa vrednosti su korelisane sa strukturom primenom Hammett-ovog, Taft-ovog i Yukawa-Tsuno-ovog pristupa. Hammett-ova ρ konstanta (0,34) je upoređena sa analognim vrednostima za strukturno slične kiseline

Spectrophotometric determination of flurazepam in pharmaceutical formulations

Two spectrophotometric methods are proposed for the determination of flurazepam in pharmaceutical formulations. The first one, a very sensitive and fast direct spectrophotometric method is based on the measurement of the absorbance of aqueous flurazepam monohydrochloride solution (pH 6) at the wavelength of maximum absorption at 230 nm. The second one, a difference spectrophotometric method, is based on the measurement of the absorbance difference between equimolar solutions of flurazepam monoprotonated (pH 6) and diprotonated (pH 0) forms at 225 nm. Both methods were applied to the determination of flurazepam in capsules which contain flurazepam monohydrochloride. To extend the application range of both methods, we examined optimum conditions which enable the determination of flurazepam in formulations in form of flurazepam dihydrochloride

A spectrophotometric method for the determination of equilibrium constants of the reversible 1,4-benzodiazepine ring-opening reaction

A general spectrophotometric method is proposed for the quantitative investigation of the hydrolysis of 1,4-benzodiazepines which, under the effect of nucleophilic hydration, undergo reversible cleavage of the 4,5-azomethine bond, followed by simultaneous simple acid-base reactions. The method is based on establishing the pH region of the solution in which, at the state of complete equilibration, three species dominate, as well as on using suitable isosbestic points and the differences in rates of simple protolysis and hydrolysis. The method is presented using flurazepam as an example, but it also can be applied to other compounds which hydrolyse by a similar mechanism

Study of protolytic equilibria of flurazepam

Protolytic equilibria of flurazepam, a diprotic base which is sparingly soluble in water, were investigated. The investigations were carried out in the pH range 0-12, at constant ionic strength (0.1 M NaCl) and 25 ± 0.1 °C, by the application of spectrophotometric, pH-metric and solubility methods. The acidity, hydrolysis and equilibrium constants in the heterogeneous system were determined. In addition, a method, based on the application of a formation function to the hydrolytic process, is proposed. Finally, buffer characteristics of flurazepam in the homogeneous and heterogeneous systems were studied

Derivative spectrophotometric method for determination of acidity constants of single step acid-base equilibria

A general derivative spectrophotometric method for determination of acidity constants is developed. The method appears suitable in cases when classical spectrophotometry cannot be employed due to little differences in the absorption spectra of conjugated acid-base pairs. Based on theoretical considerations, seven variants of the method have been established and their validity was checked, determining acidity constants of lorazepam and flurazepam as model compounds