Systematic and statistical errors in quantitative evaluation in TLC and HPTLC. 4. Linear calibration

Analytical results are often obtained from reflectance or fluorescence measurements in TLC or HPTLC with the aid of calibration lines. Curve fitting may not be done by conventional least squares methods for both the independent and the dependent variables are erroneous; errors occur in the volumes spotted on to the plate and in the reflectance/fluorescence measurements. Therefore the sum of the squares of the distances to the calibration line has to be minimized instead of the squared sum of the errors of the dependent variable. The algorithms used are derived and explained. Implications of error propagation for the analytical result are also given.     

Studies of correlation between chemical structure and Rf-value in high performance TLC

Correlation between chemical structure and Rf-values was studied in the case of aniline and its derivatives using high performance TLC and a U-chamber. The characteristic group constants referring to each substituent were determined by chromatographing derivatives with one substituent and aniline in toluene and dibutyl ether respectively. On the basis of these constants the R_M and Rf values of derivatives with more substituents were calculated. Comparing the calculated and measured values good agreement was found.     

Systematic and statistical errors in quantitative evaluation in TLC and HPTLC. 3. The determination of the primary statistical errors

The paper describes the measurement and calculation of the primary statistical errors in the evaluation of TLC or HPTLC using in situ reflectance measurements. The primary errors are the errors of the sample volume spotted onto the plate, errors caused by the chromatographic process itself, the positioning error of the plate with respect to the centre of the light beam and the error in the light measurement. By scanning the same spot, the same track or the same plate under different conditions, the various errors can be determined.     

TLC Separations of Some Closely Related 3-Hydroxy-6H-Benzofuro [2, 3-C] [1] Benzopyran-6 -Ones and Their Basic Ethers

Abstract

During the present study, the TLC separation of some closely related 3-hydroxy-6H-benzofuro [2, 3-C] [1] benzopyran-6-ones and their basic ethers have been carried out.     

TLC Densitometric Method for the Quantification of Eugenol and Gallic Acid in Clove

Eugenol and gallic acid are reported from the flower buds of Syzygium aromaticum (L.) Merr. & Perry (clove). Both the compounds have been shown to give interesting biological activities and hence serve as biomarkers. We report a simple TLC densitometric method for the quantification of eugenol and gallic acid in clove. The method was validated for precision, repeatability and accuracy. The method was found to be precise with RSD of 0.61 and 1.3 (intraday) and 0.96 and 0.24 (interday) for different concentrations of eugenol and gallic acid respectively. Instrumental precision was 0.24 and 0.21 (% CV) for eugenol and gallic acid respectively. Accuracy of the method was checked by conducting recovery study at two different levels for eugenol and gallic acid and the average percentage recoveries were found to be 99.79% and 97.90% respectively. The contents of eugenol and gallic acid in different samples of clove, as estimated by the proposed method, were found to be in the range of 12.9–14.6% and 0.31–0.61% respectively. The proposed HPTLC method for the estimation gallic acid and eugenol was found to be simple, precise, specific, sensitive and accurate and can be used for routine quality control of clove.     

Liquid chromatography/tandem mass spectrometric method for the simultaneous determination of tobacco-specific nitrosamine NNK and its five metabolites

A sensitive and robust high-performance liquid chromatography-electrospray ionization tandem mass spectrometry method to analyze 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) and its five metabolites in one passage was developed and validated. The method achieved excellent reproducibility and accuracy. Linearity was observed for all six compounds (R² = 0.999) with detection limits (S/N ≥ 3) ranging from 0.2 to 2.4 pg on column and 0.01-0.12 ng ml⁻¹ in samples injected. Average intra-day and inter-day variations (% R.S.D.) were 1.2 and 3.5%, respectively. A sample preparation method involving C8 and C18 solid phase extraction provided satisfactory recovery of the analytes in mouse urine. Each NNK metabolite was identified by its chromatographic retention time and specific fragmentation pattern. Since the carcinogenicity of NNK is related to its metabolism, the method described in this report should facilitate toxicological investigations into the carcinogenesis due to NNK exposure in the environment.     

Analysis of polar compounds on PEG-40M/KF glass capillary columns

The chromatographic properties of potassium fluoride as an additive to the polyethylene glycol stationary phase were investigated. This unique base in organic chemistry was shown to succeed in yielding good results for the analysis of polar compounds, including the primary amines. Glass capillary columns of high selectivity for primary and secondary aliphatic amines were obtained by the “hexane plug” procedure by which a thin layer of KF is deposited on the inner surface of glass capillary columns. Some possible types of donor-acceptor interactions occuring within the system PEG/KF/solute were considered.     

Sample preparation methods for subsequent determination of metals and non-metals in crude oil—A review

In this review sample preparation strategies used for crude oil digestion in last ten years are discussed focusing on further metals and non-metals determination. One of the main challenges of proposed methods has been to overcome the difficulty to bring crude oil samples into solution, which should be compatible with analytical techniques used for element determination. On this aspect, this review summarizes the sample preparation methods for metals and non metals determination in crude oil including those based on wet digestion, combustion, emulsification, extraction, sample dilution with organic solvents, among others. Conventional methods related to wet digestion with concentrated acids or combustion are also covered, with special emphasis to closed systems. Trends in sample digestion, such as microwave-assisted digestion using diluted acids combined with high-efficiency decomposition systems are discussed. On the other hand, strategies based on sample dilution in organic solvents and procedures recommended for speciation analysis are reported as well as the use of direct analysis in view of the recent importance for crude oil field. A compilation concerning sample preparation for crude oil provided by official methods as well as certified reference materials available for accuracy evaluation is also presented and discussed.     

Review of the applications of different analytical techniques for coxibs research

An extensive survey of the literature published in analytical and pharmaceutical chemistry journals has been conducted and analytical methods which were developed and used for the determination of some of the COX-2 inhibitors, a subclass of non-steroidal anti-inflammatory drugs (NSAIDs) in bulk drugs, formulations, and biological fluids have been reviewed. This review covers the time period from 1999 to present, during which over 140 analytical procedures including chromatographic, spectrometric, electrophoretic and voltammetric techniques were reported. Presented applications concern analysis of coxibs from pharmaceutical formulations and biological samples.