Robert Skibiński

Revisiting thin-layer chromatography as a lipophilicity determination tool—A comparative study on several techniques with a model solute set

The lipophilicity of a compound is a fundamental property related to pharmaceutical and biomedical activity. As many approaches are mixed together in every-day published studies, the subject needs some standardization. The paper presents a comparative study on several approaches of TLC lipophilicity determination: a single TLC run, extrapolation of a retention, principal component analysis of a retention matrix, PARAFAC on a three-way array and a PLS regression. All techniques were applied to 35 model solutes with simple molecules, using nine concentrations of six modifiers: acetonitrile, acetone, dioxane, propan-2-ol, methanol and tetrahydrofurane. The elaborated comparative analysis formed several general recommendations. Methanol and dioxane were the best modifiers, while acetonitrile gave the worst and inacceptable correlation of retention with lipophilicity. Surprisingly, good correlations were obtained for the single TLC runs and this method is underestimated in the literature. The advanced chemometric processing proposed recently, such as PCA, PARAFAC and PLS did not show a visible advantage comparing to classical methods. A need to use a robust regression and robust correlation measures, due to presence of significant outliers, was also noticed and studied.

Chromatographic analysis of new antidepressant drugs by normal- and reversed-phase TLC

The selectivity of the TLC separation of six new antidepressant substances has been investigated on silanized silica gel C18 and on silica gel GF254. Optimization of the retention and selectivity of these compounds on reversed-phase plates (RP C18) was performed by changing the pH and the concentration of organic solvent (methanol, acetonitrile, tetrahydrofuran) in the aqueous mobile phases. The substances were separated in horizontal chambers and the drugs were detected by use of a videoscanning system and illumination of the plates at λ = 254 nm. The drugs were also separated on silica gel GF254 after solid phase extraction (SPE) from plasma. The best separation was achieved with benzene-acetone-ethanol-ammonia, 9 + 7 + 2 + 1 (v/v) as mobile phase.

Studies on photodegradation process of psychotropic drugs: a review

Consumption of psychotropic drugs is still increasing, especially in high-income countries. One of the most crucial consequences of this fact is significant release of them to the environment. Considerable amounts of atypical antipsychotics, benzodiazepines, antidepressants, and their metabolites were detected in river, lake, and sea water, as well as in tissues of aquatic organisms. Their ecotoxicity was proved by numerous studies. It should be noticed that interaction between psychotropic pharmaceuticals and radiation may lead to formation of potentially more toxic intermediates. On the other hand, photo-assisted wastewater treatment methods can be used as an efficient way to eliminate them from the environment. Many methods based on photolysis and photocatalysis were proposed and developed recently; nevertheless, the problem is still unsolved. However, according to recent studies, photocatalysis could be considered as the most promising and far more effective than regular photolysis. An overview on photolytic as well as homogenous and heterogeneous photocatalytic degradation methods with the use of various catalysts is presented. The photostability and phototoxicity of pharmaceuticals were also discussed. Various analytical methods were used for the photodegradation research, and this issue was also compared and summarized. Use of high-resolution multistage mass spectrometry (Q-TOF, ion trap, Orbitrap) was suggested. The combined techniques such as LC–MS, GC–MS, and LC–NMR, which enable qualitative and quantitative analyses in one run, proved to be the most valuable in this case. Assembling of MS/MS spectra libraries of drug molecules and their phototransformation products was identified as the future challenge.

Identification of photodegradation product of amisulpride by ultra-high-pressure liquid chromatography–DAD/ESI-quadrupole time-of-flight-mass spectrometry

Photostability of amisulpride under UVA irradiation in methanol solution was investigated and structural elucidation of its photodegradation products was performed. For the purpose of the quantitative and qualitative analysis of amisulpride and the stress degradation products elucidation, the reversed phase UHPLC-DAD system coupled with accurate mass hybrid ESI-Q-TOF mass spectrometer was used. During one run (10 min) with the use of auto MS/MS mode all essential data for the determination of photodegradation kinetics and for the structural formulas elucidation of the products was collected. Four degradation products were found and their masses with high accuracy (0.53-3.05 ppm) and formulas were obtained--258.0666 (C(10)H(14)N(2)O(4)S), 367.1564 (C(17)H(25)N(3)O(4)S), 341.1412 (C(15)H(23)N(3)O(4)S) and 385.1665 (C(17)H(27)N(3)O(5)S). For all the analyzed compounds MS/MS fragmentation spectra were obtained (collision energy 19.8-26.1 V) allowing structural elucidation of unknown degradation products and indicating photodegradation pathways of amisulpride. UHPLC-DAD/ESI-Q-TOF system was found to be a powerful analytical tool for the fast and accurate stability analysis of pharmaceutical substances.

Synthesis, biological evaluation and molecular modeling of new tetrahydroacridine derivatives as potential multifunctional agents for the treatment of Alzheimer's disease.

A novel series of 9-amino-1,2,3,4-tetrahydroacridine derivatives with 4-dimethylaminobenzoic acid moiety was synthesized and tested towards inhibition of cholinesterases and amyloid β aggregation. Target compounds were designed as dual binding site cholinesterase inhibitors able to bind to both the catalytic and the peripheral site of the enzyme and therefore potentially endowed with other properties. The obtained derivatives were very potent inhibitors of both cholinesterases (EeAChE, EqBChE) with IC50 values ranging from sub-nanomolar to nanomolar range, and the inhibitory potency of the most promising agents was higher than that of the reference drugs (rivastigmine and tacrine). The kinetic studies of the most active compound 3a revealed competitive type of AChE inhibition. Moreover, all target compounds were more potent inhibitors of human AChE than tacrine with the most active compound 3b (IC50 = 19 nM). Compound 3a was also tested and displayed inhibitory potency against AChE-induced Aβ 1-42 aggregation (80.6% and 91.3% at 50 μM and 100 μM screening concentration, respectively). Moreover, cytotoxicity assay performed on A549 cells did not indicate toxicity of this agent. Compound 3a is a promising candidate for further development of novel multi-functional agents in the therapy of AD.

Comparative validation of quetiapine Determination in tablets by NP-HPTLC and RP-HPTLC with densitometric and videodensitometric detection

Two new simple and accurate methods for determination of quetiapine in tablets-normal phase (NP) and reversed-phase (RP) high performance thin layer chromatography (HPTLC), each with densitometric and videodensitometric detection, were developed and validated. NP-HPTLC was developed with HPTLC silica F254 plates and hexane-dioxane-propylamine 1:9:0.4 (v/v) as mobile phase. RPHPTLC was carried out using HPTLC RP8 F254 plates with tetrahydrofuran-phosphate buffer, pH 9.0, 5:5 (v/v) as mobile phase. The silica gel plates were developed to a distance of 9 cm and RP8 plates to a distance of 4.5 cm. Both analyses were performed in horizontal chambers and scanned with a densitometer at 243 nm and a video-densitometer at 254 nm. Calibration plots were linear in the range 0.2-1.2 μg quetiapine per spot for NP-HPTLC and in the range 0.1-1.1 μg for RP-HPTLC. The precision and accuracy of the four methods were fully compared and no significant differences were observed. The methods can be used in routine pharmaceutical analysis.

Stability studies of cefpirome sulfate in the solid state: Identification of degradation products.

The process of degradation was studied by using an HPLC-DAD method. Four degradation products were identified with a hybrid ESI-Q-TOF mass spectrometer. The influence of temperature and relative air humidity (RH) on the stability of cefpirome sulfate was investigated. In the solid state the degradation of cefpirome sulfate was a first-order reaction depending on the substrate concentration. The kinetic and thermodynamic parameters of degradation were calculated.

Determination of Citalopram in Tablets by HPLC, Densitometric HPTLC, and Videodensitometric HPTLC Methods

Abstract Three simple, rapid, and accurate analytical methods for the determination of citalopram in tablets were developed. The high performance liquid chromatography method was carried out using Waters Nova‐Pak C18 column with a mobile phase composed of methanol–0.067 M phosphate buffer pH 2.00 (55:45, v/v), UV‐VIS detector at 239 nm, and moclobemide as the internal standard. High performance thin layer chromatography was performed on silica gel 60F254 HPTLC plates with a mixture of benzene–acetone–ethanol–25% aqueous ammonia (45:40:10:5, v/v/v/v) as a mobile phase. The detection and quantification were carried out at 226 nm (densitometry) and 254 nm (videodensitometry). The linearity range for the HPLC method was 5–50 µg/mL and for both HPTLC methods was 0.2–3.2 µg per spot. The RSD values obtained for the standard solutions were <2.0% for HPLC, <2.4% for densitometry, and <2.9% for videodensitometry. The recovery values obtained for the model mixtures were between 99.47% and 102.70%, between 102.17% and 104.44%, and between 100.74% and 104.01%, respectively.

Determination of fluoxetine and paroxetine in pharmaceutical formulations by densitometric and videodensitometric TLC

Two new, simple, rapid, and accurate thin-layer chromatographic methods have been developed for determination of fluoxetine in capsules and paroxetine in tablets. The drugs were chromatographed on silica gel 60 F254 plates in horizontal chambers with benzene-acetone-ethanol-25% aqueous ammonia, 9 + 7 + 2 +1 (v/v) as mobile phase. Densitometric detection was performed at λ = 218 nm and 293 nm for fluoxetine and paroxetine, respectively; videodensitometric detection was performed at λ = 254 nm for both drugs. The range of linearity was 2–10 μg per spot for fluoxetine and 0.5–8 μg per spot for paroxetine. The relative standard deviation for determination of these antidepressants in pharmaceuticals was less than 4.3% for densitometry and less than 4.9% for videodensitometry. Recovery of fluoxetine from capsules was 105.1% by use of densitometry and 104.3% by use of videodensitometry; recovery of paroxetine from tablets was 99.15% and 98.2%, respectively.

LC determination of moclobemide and three metabolites in plasma.

Moclobemide and three metabolites were quantified using 1 ml of plasma and solid-phase extraction with Bakerbond CN column after the addition of nadolol as the internal standard (I.S.). Separation and detection the analysed substances were achieved isocratically with acetonitrile-methanol-0.067 M phosphate buffer pH 2.65-0.4% triethylamine (12.7:1.9:85:0.4, v/v/v/v), a Nova-pak C(8) column and UV detection at 230 nm. The lower limits of quantitation for moclobemide was 10 ng ml(-1), for M1 (Ro 16-3177)-8 ng ml(-1), for M2 (Ro 12-5637)-10 ng ml(-1) and for M3 (Ro 12-8095)-15 ng ml(-1) (as the metabolites). Accuracies calculated of three concentrations in each of three separate runs were between 84.55 and 93.68 for moclobemide, 83.28 and 92.30 for M1, 86.31 and 92.66 for M2 and 88.42 and 93.40 for M3. Precision data within day were between 5.71 and 7.50 for moclobemide, 2.91 and 6.58 for M1, 4.98 and 6.40 for M2 and 0.94 and 4.73 for M3.