Gas chromatographic retention indices of fentanyl and analogues

Narcotic analgesics of the fentanyl class are characterized by high potency and relatively short duration of action. These compounds nowadays have become a substitute for heroine and are highly addictive for abusers. Herein, we report retention indices of fentanyl and its eighteen analogues relative to the homologous n-alkane series. These values are determined on a moderately polar BP-5 capillary column under programmed temperature and isothermal chromatographic conditions. The analogues differ in the substituent attached to the piperidine ring nitrogen, and retention indices are found to vary according to the nature of the substituent. The effects of chromatographic conditions like temperature programming rate, carrier gas flow rate, and oven temperature are studied. Retention indices are also determined on a non-polar BP-1 column to study the influence of stationary phase polarity. Standard deviation of all the RI values is less than one index unit.     

Extrapolation and interpolation of gas chromatographic retention times

Summary An empirical method of extrapolating and interpolating gas chromatographic retention times obtained at three equally spaced isothermal temperatures is described. The accuracy of the method was evaluated from retention time data obtained using packed glass columns. A procedure for constructing retention time tables for homologous series and the derivation of an equation for calculating retention times as a function of temperature is also presented.     

Pyrolysis and gas chromatographic examination of phytol and isoprenoid hydrocarbons: Pre-calculation of retention indices by computer

For the identification of isoprenoid-type compounds and other degradation products derived from the pyrolysis of phytol and plant pigments, a calculation method was developed to the evaluate the chromatograms, determining the retention indices or net retention volumes of different compounds. Calculations were made by means of computer for different stationary phases and temperatures. Gas chromatographic and derivatographic measurements were made with natural plant pigments and phytol, including the thermal degradation of the compounds mentioned above. Close agreement was found between the measured and calculated data and with literature data.     

Calculation of gas chromatographic retention indices of organic compounds from the boiling points of their structural analogs

The possibility of calculating gas chromatographic retention indices (1) is discussed. The indices are important parameters for chromatospectral identification of organic compounds from the boiling points of their structural analogs (T _b ^* ) using the linear logarithmic equation log I = a log T _b ^* + bA + c, where A are the structural parameters reflecting the one- to- one position of the compounds being compared in the corresponding taxonomic groups, including homologous series.     

Binary chromatographic retention times from perturbations in flowrate and composition

This work is a theoretical and experimental investigation of the binary retention time (t _step) when the disturbance is made to a chromatographic system by adding a small flow of one of the pure components. The established theory is for addition of a pulse: in this case, the retention time (t _pulse) depends on the two binary isotherm gradients, and should be independent of the choice of pulse gas. From the column material balance, the value of t _step also depends on the column pressure drop and perturbation gas—the value of t _step should always be greater for the more-adsorbed component. The theory has been validated from results on the nitrogen–argon–5A zeolite system at 25, 54 and 81 °C. For a 50% mixture at 25 °C with a column pressure drop of 0.1 bar, the values of t _step are 257 and 254 seconds for the nitrogen and argon perturbations. The values of t _step are different because addition of the perturbation flow causes a very small increase in average column pressure (about 0.5 mbar), which causes the binary isotherm gradients to be measured in (slightly) different directions along the isotherm surface. The intention is to determine the value of t _step for the case of a zero change in the average column pressure: experimentally, this would require a column with a zero pressure drop. The material balance shows that t _step for a column with a zero pressure drop is obtained from a simple weighted function of the values of t _step for the two pure-component perturbations. Accurate determination is essential because the “zero pressure drop” values are used to determine binary adsorption isotherms which are, of course, at a fixed pressure.     

Calculation of retention indices in temperature-programmed gas chromatography

Summary A new method is presented for the calculation of the retention indices under linear temperature programming with or without an initial isothermal period. The data calculated by the method are in good agreement with the isothermal retention indices.     

Gas chromatographic retention indices of sulfur vesicants and related compounds

Temperature-programmed retention indices, relative to a n-alkane homologous series, were determined for 37 sulfur vesicant or vesicant-related compounds using DB-1, DB-5 and DB-1701 fused-silica capillary columns. Many of the compounds, including long chain dichloro, vinylchloro, vinylalcohol and macrocyclic compounds have either not been previously identified or have not been associated with sulfur vesicant analysis. Reproducibility of the retention indices, based on Van den Dool's equation, was excellent over the course of the study. In addition, changes in retention index (delta RI), which may enable the prediction of uncharacterized homologue chromatographic behaviour, were calculated for several homologous series.     

Gas chromatographic retention indices of trimethylsilyl derivatives of terpene alcohols

This paper presents the experimentally determined retention indices (RI(TMS)) for a set of 75 silylated terpenols (33 monoterpenols and 42 sesquiterpenols). The attempt was made to assess the dependence of RI(TMS) on RI (for non-silylated terpenols) and on RI(Ac) (for acetylated terpenols). Satisfactory linear regression parameters (RI(TMS)=b(0)+b(1)RI) were observed for tertiary substituted monoterpenols and primary or secondary substituted sesquiterpenols. The mass spectra of silylated terpenols that were not found in the available literature are in Supplementary information.     

Prediction of protein retention times in gradient hydrophobic interaction chromatographic systems

A two-step methodology has been developed for the prediction of protein retention time in linear-gradient HIC systems. Isocratic retention parameters were determined from ln(k')-salt concentration plots for a number of commercially available proteins with a range of properties. Quantitative structure property relationship (QSPR) models based on a support vector machine (SVM) approach were generated for predicting isocratic retention parameters for proteins not included in the model generation. The predicted parameters were then used to calculate protein gradient retention times and the results indicate that this approach is well suited for predicting experimental gradient retention data. The approach presented in this paper may have implications for HIC methods development at both the bench and process scales.     

Calculation of retention indices of isoparaffins on different phases

Summry The changes in the retention indices of isoparaffins on phases with different polarities (according to the Rohrschneider-McReynolds system) are examined. It is established that the values of the retention index do not depend on the polarity of the following phases: squalane, normal C₂₄, C₂₈, C₃₀, C₃₂, C₃₄ and C₃₆ paraffins, C₈₇H₁₇₆, the silicones SE-30, OV-1, OV-101, as well as dinonyl phthalate and acetyl tributyl citrate. An empirical equation established peremits the prediction of retention indices of C₆–C₁₀ isoparaffins at different temperatures on all these phases.     

Calculation of retention factors in capillary electrochromatography from chromatographic and electrophoretic data

Retention factors in capillary electrochromatography (CEC) were calculated by means of theoretically derived equations and experimentally determined parameters in microcolumn liquid chromatography and capillary zone electrophoresis. It was found that the retention factor of uncharged components in CEC was about 20% higher than was calculated. The derived equations do not take into account alteration of the nature of the stationary phase or distribution constant by the applied electric field. However, the influence of the electric field on the retention in CEC can be estimated. Individual field contributions could not be determined.     

Calculation of retention indices and peak widths in temperature programmed gas-liquid chromatography

Summary Isothermal chromatographic measurements lead directly to H _v ^o and A (entropy term) of solutes, and three constants of an empirical relationship between peak width and column temperature. From the thermodynamic parameters H _v ^o and A retention temperatures have been computed by means of a theoretical model including temperature dependence of carrier gas viscosity, and subsequently retention times; programmed retention indices have been determined by linear and polynomial interpolations. By substituting the value of the calculated retention temperature in the above-mentioned relationship, peak width at half-height for a linear temperature may be estimated. Predicted retentions correlate with observed data, with a P-value 0.01; simulation accuracy is generally 6–10% for peak widths.Retention indices of some organochlorine species, separated on an OV-101 capillary column, may differ by as much as 26 units depending on the method of calculation. Polynomial-calculated indices are more consistent with the retention index scheme, and have smaller standard deviations and better constancy at different heating rates.