Extracting Vapor Pressure Data from Gas–Liquid Chromatography Retention Times. Part 2: Analysis of Double Reference Approach

Abstract

The vapor pressures of 46 compounds including n-alkanes and their monofunctionalized derivatives, some monoterpenes, as well as chloro-and alkylbenzenes were determined by GLC exploring the Kovats retention indices (KI) technique, primarily in its basic form using two alkane references (GLC-RTKI). The fundamental advantage of the GLC-RTKI method is that it guarantees appropriate selection of alkane reference compounds. Typical relative errors in vapor pressures accompanying this method were below 30% for compounds of low polarity, while for polar compounds (nitriles, alcohols) the errors can reach percentages in the hundreds. In contrast, vapor pressures obtained from the modified Kovats method, relying on reference standards whose functional group matches that of the test compound (GLC-RTmKI), were found mostly within 5% of directly measured values. However, the success of this method is dependent on the availability of reliable vapor pressure data for compounds to serve as reference standards. As our methodology eliminates possible secondary error sources (e.g., data extrapolation, or recalculation from supercooled liquid-to-solid phase or vice versa), we propose that the results obtained are as accurate as is feasibly possible with GLC-RTKI and GLC-RTmKI methods. This study also yielded a novel set of directly measured (static method) data on the vapor pressures of C7−C9 alkyl nitriles.

Estimating Vapor Pressure Data from Gas–Liquid Chromatography Retention Times: Analysis of Multiple Reference Approaches, Review of Prior Applications, and Outlook

“…Note that the use of I i as the retention descriptor has some advantage over relative retention times, retention volumes, or retention factors in that they are independent of the film thickness, column dimensions, carrier flow, and phase ratio. At this point, we would like to point out that our recent article contains a few typographic errors, namely, the left-hand side of eq 9 to eq 12 is erroneously written as “log I x ( T )” instead of the correct expression “ I x ( T )” and the same holds for these equations listed in the legend of Figure 15. The changes do not alter the results of ref .…”

“…At this point, we would like to point out that our recent article contains a few typographic errors, namely, the left-hand side of eq 9 to eq 12 is erroneously written as “log I x ( T )” instead of the correct expression “ I x ( T )” and the same holds for these equations listed in the legend of Figure 15. The changes do not alter the results of ref .…”

“…The present study is a continuation of the series of papers − in which we have focused our efforts on a better understanding of indirect gas–liquid chromatography (GLC) based strategies for estimating the vapor pressure of liquid compounds using chromatographic retention times (RT) and on identifying an efficient way of optimizing the operating conditions. In Part 1, we analyzed a method for determining the supercooled vapor pressures based on relative retention times with single reference standards (denoted the GLC-RT1S method).…”

Regression against Temperature of Gas–Liquid Chromatography Retention Factors. Van’t Hoff Analysis

“…Gas–liquid chromatography (GLC) is a valuable analytical technique of proven power for physicochemical measurements and generating thermodynamic data of analytes, with the advantage of its simplicity as compared with direct techniques such as the calorimetric and equilibrium methods. , Basic physicochemical quantities, namely the vapor pressure, − heat of vaporization, − equilibrium distribution constant K , − enthalpy of solvation, and entropy of solvation, , and even the octanol–air partition coefficient − can be determined from the retention data, such as specific or net retention volumes, , Kovats retention indices ( I ), , or retention factors ( k ) − and their temperature dependence. In this study, we use the isothermal retention factor k as the most relevant and reproducible chromatographic measure of the retention.…”

“…This paper is not a part of our series of investigations that were focused on the use of GLC retention data of model organic compounds in calculating vapor pressures of these compounds, − but it represents the prerequisite for continuing this series. The central theme of this work is geared toward potential pitfalls in using magnitudes of isothermal GLC retentions as inputs for physicochemical calculations.…”