However, warmer columns ↑ do not have longer but shorter, following temperature programming experience. Pure liquid vapor pressure rises exponentially with so that we do get shorter warming the column ↑. Solubility of compounds in the stationary phase may rise or fall with , but not exponentially. is referred to as selectivity or polarity by gas chromatographers today. Isothermal Kovats index in terms of the physical properties becomes: Isothermal Kovats index is independent of , any GC dimension or ß or carrier gas velocity , which compares favorable to retention time . Isothermal Kovats index is based on solubility and vapor pressure of compound i and n-Alkanes (). dependence depends on the compound compared to the n-alkanes. Kovats index of n-alkanes is independent of . Isothermal Kovats indices of hydrocarbon were measured by Axel Lubeck and Donald Sutton. Temperature-programmed Kovats index IUPAC defines the temperature programmed chromatography Kovats index equation: & retention times of trailing and heading n-alkanes, respectively. NOTE: TPGC index does depend on temperature program, gas velocity and the column used ! ASTM method D6730 defines the temperature programmed chromatography Kovats index equation: Measured Kovats retention index values can be found in ASTM method D 6730 databases. An extensive Kovats index database is compiled by NIST . The equations produce significant different Kovats indices. Method translation Faster GC methods have shorter times but Kovats indexes of the compounds may be conserved if proper method translation is applied. Temperatures of the temperature program stay the same, but ramps and times change when using a smaller column or faster carrier gas. If column dimensions Length×diameter×film are divided by 2 and gas velocity is doubled by using H2 in place of He, the hold times must be divided by 4 and the ramps must be multiplied by 4 to keep the same index and the same retention temperature for the same compound analyzed. Method translation rules are incorporated in some chromatography data systems. References Chromatography Analytical chemistry Hungarian inventions Hungarian inventors Hungarian scientists