Dependence Of Peak Area Research Articles

Effects of the Discrimination of Sample Composition with the Use of Split Injection into Gas Chromatographic Capillary Columns

The manifestation of noticeable effects of the discrimination of sample composition upon split injection into short capillary columns with large diameters at small splitting ratios is discussed. They consist in the anomalously strong dependences of the peak areas of even volatile components on the injector temperature, the solvents used and, to a lesser extent, on the amounts of injected samples. It is proposed to consider the following criteria for assessing the degree of manifestation of these factors: (1) the dependence of the absolute peak areas of different analytes on the injector temperature and (2) the analogous dependence of the relative peak areas of the same components in different solvents. In this case, the relative peak areas of various components in the same solvents remained almost constant regardless of the injector temperature. The above effects complicate quantitative determinations based on the measurement of absolute peak areas (the method of internal normalization and the determination of distribution coefficients in partition chromatography). For these purposes, it is preferable to use standard capillary columns with split sample injection at a sufficiently high splitting ratio.

Features of injection and chromatographic separation of samples in high boiling viscous organic solvents using the capillary columns at a low split ratio

The features of injection and gas chromatographic separation of stock analytes in their solutions in high boiling viscous polar organic solvents (on the example of 1,3-butanediol) using a short capillary column of large internal diameter (Megabore type) at low split ratios are considered. The manifestation of so-called discrimination effects is confirmed, with the main of them being the dependence of absolute peak areas vs . injection temperature as well as similar dependence of relative peak areas in different solvents. However, these effects are manifested in a lesser degree than the same effects for the samples dissolved in low boiling solvents. It is demonstrated that the dependencies of peak areas vs . injector temperature ( S = aT + b ) are principally different for solvents with various boiling points. Thus, for the solutions of butyl acetate, cyclohexanone, anisol, butyl butyrate, and acetophenone in low boiling 2-propanol the linear dependencies S ( T ) are revealed for the injector temperature range of 120-180°С only (with correlation coefficients r = 0.986 – 0.999), while at the higher injector temperatures (210-240°С) the significant deviations from linearity are typical. At the same time, the solutions of the same components in higher boiling 1,3-butanediol demonstrate the linear S ( T ) dependencies within the whole temperature range (120-240°С). It is confirmed that the discrimination effects have no significant influence on the results of gas chromatographic analyses of the samples in high boiling solvents if the method of internal normalization is used. The main uncertainties of the results are caused by the column’s overloading with the solvent, which leads to the broadening and asymmetry of its peaks and their overlapping with the peaks of some analytes. DOI: http://dx.doi.org/10.15826/analitika.2018.22.3.005 Keywords : High boiling viscous organic solvents, gas chromatographic analysis, capillary columns, discrimination effects (Russian) Igor G. Zenkevich, Eugene Leleev St. Petersburg State University, Russian Federation, 198504, St. Petersburg, Universitetskii prosp., 26

Validation of HPTLC method for the analysis of luteolin in Cardiospermum halicacabum Linn.

Background: Luteolin is one of the constituent of Cardiospermum halicacabum, which is traditionally used as an important component of plant‑based medicine. Aim and Objective: This study presents the first report of thin layer chromatography (TLC) densitometric method, which has been developed and validated for quantification of luteolin from aerial parts of C. halicacabum. Materials and Methods: Chromatographic separation was achieved on silica gel 60 F254 plates with using the solvent system of Toluene:Ethyl acetate: Formic acid (10:9:1). Detection of luteolin was carried out in the absorption‑reflection mode at 254 nm. TLC plates were dried under stream of hot air and then subjected to densitometric scanning using a Camag TLC scanner III (Camag, Switzerland) with win CATS software in the absorbance‑reflectance scan mode. The accuracy of the method was checked by conducting various validation parameters according to ICH (International Conference on Harmonizaation) guidelines. Results: The system was found to give compact spots for luteolin (retention factor, Rf = 0.55). The calibration plot was linear in the range of 500-3000 ng of luteolin. The correlation coefficient of 0.997 was indicative of good linear dependence of peak area on concentration. The concentration of luteolin was found to be 0.50% w/w in aerial parts of C. halicacabum. The limit of detection (LOD) and limit of quantification value for luteolin were found to be 22.45 ng and 68.03 ng, respectively. Recovery values from 99.37 and 99.80 to 100.58 showed excellent reliability and reproducibility of the method. Conclusion: The proposed HPTLC method for quantitative monitoring of luteolin in C. halicacabum can be used for routine quality testing of C. halicacabum extract used in formulations. Key words: Cardiospermum halicacabum, high performance thin layer chromatography, luteolin

Thin-layer chromatographic selective and stability-indicating method for assay of cefixime in pharmaceuticals

A thin-layer chromatographic (TLC) method is developed for the analysis of cefixime using precoated silica gel 60F254 TLC aluminum sheets as stationary phase. The mobile phase was optimized to ensure that no other drug from cephalosporin class and degradation products (formed under stress condition) of the drug interfered with the estimation. By using toluene-ethyl acetate-formic acid-water (10:58:22:10, ν/ν) as mobile phase, a sharp, well-defined, and symmetrical peak was obtained in the chromatogram with an RF value 0.54 ± 0.02. Densitometric measurement was made in the reflectance/absorbance mode at 293 nm. The calibration curve was established as dependence of peak area on amount 500–1500 ng. The second-order polynomial fit was deduced to be suitable for the quantitative analysis. The method was validated as per International Conference on Harmonization guidelines. The method is simple, sensitive, selective, and precise. It can be applied for the quantitative analysis of cefixime in raw materials, mar...

Integrated Membrane Filters for Minimizing Hydrodynamic Flow and Filtering in Microfluidic Devices

Microfluidic devices have gained significant scientific interest due to the potential to develop portable, inexpensive analytical tools capable of quick analyses with low sample consumption. These qualities make microfluidic devices attractive for point-of-use measurements where traditional techniques have limited functionality. Many samples of interest in biological and environmental analysis, however, contain insoluble particles that can block microchannels, and manual filtration prior to analysis is not desirable for point-of-use applications. Similarly, some situations involve limited control of the sample volume, potentially causing unwanted hydrodynamic flow due to differential fluid heads. Here, we present the successful inclusion of track-etched polycarbonate membrane filters into the reservoirs of poly(dimethylsiloxane) capillary electrophoresis microchips. The membranes were shown to filter insoluble particles with selectivity based on the membrane pore diameter. Electrophoretic separations with membrane-containing microchips were performed on cations, anions, and amino acids and monitored using conductivity and fluorescence detection. The dependence of peak areas on head pressure in gated injection was shown to be reduced by up to 92%. Results indicate that separation performance is not hindered by the addition of membranes. Incorporating membranes into the reservoirs of microfluidic devices will allow for improved analysis of complex solutions and samples with poorly controlled volume.

Verification of gamma-spectroscopy programs: Accuracy and detectability

The newly revised ANSI N42.141.2 has provided analysis software developers with a set of well defined, consistent and unbiased procedures designed to evaluate the accuracy and limitations of peak search and peak area analysis programs. This work uses two of the procedures outlined in this standard to evaluate five peak analysis algorithms currently in use in Canberra and Nuclear Data software packages. The first procedure examines a program's behavior as the centroid separation and peak height ratio of a doublet are varied. A previous review of these data3 demonstrated significant peak area inaccuracies at peak separations at or below 1.5 FWHM. We will discuss improvements made to some of these programs and the impact on the doublet results. The second procedure examines a program's behavior as the Compton continuum beneath a fixed peak area is increased. For the same five algorithms we will discuss the dependence of peak area on Compton continuum and also explore the limits of peak detectability.

Methods of investigation concentration effects and the determination of additional parameters in gel-chromatographic analysis of polyisoprene

A study was made of the effect of sample concentration on gel-chromatographic analysis of polyisoprene samples directly taken from a polymerization reactor, i.e. highly concentration solutions of previously unknown concentration. The range of operating concentrations of the sample in GPC analysis of polyisoprene was determined. The dependence of peak area on the concentration of the sample introduced was established and it was shown that using this dependence in addition to the molecular weight distribution of the polymer, several further parameters, e.g. the concentration of the initial highly concentrated polymer sample and the gel fraction content may be determined from one analysis.