Introduction

Gas chromatography (GC), the longest established instrumental chromatographic technique, dominated

L Length of the column, usually expressed in metres for column length, in cm for the determination of U, and in mm for the determination of H. N Theoretical plate number; N = [tR/a]2, where a is the standard deviation of the peak. Nreq Number of theoretical plates required to separate two solutes of a given alpha and given retention factors to a given degree of resolution: Nreq = 16R2[(k+1)/k]2[a/(a-1)]2. o.d. Outer diameter of the column. rc Inside radius of the column. Rs Peak resolution. A measure of separation as evidenced by both the distance between the peak maxima and by the peak widths. ASTM and IUPAC definitions are based on wb (peak width at base) measurements, which require extrapolation. If peaks are assumed to be Gaussian, then Rs =

a Standard deviation of a Gaussian peak. tM Gas hold-up time. The time (or distance) required for a nonretained substance (e.g. mobile phase) to transit the column. tR Retention time. The time (or distance) from the point of injection to the peak maximum. tR Adjusted retention time. Equivalent to the residence time in stationary phase; difference of the solute retention time and the gas hold-up time:

u Average linear velocity of the mobile (gas) phase:

u (cm s_1) = L (cm)/t (s). V Volume. VM and VS represent volumes of the mobile and stationary phases, respectively. W Peak width at base. Determined by measuring the length of baseline defined by intercepts extrapolated from the points of inflection of the peak, and equivalent to four standard deviations in a Gaussian peak.

wh Peak width at half-height. Measured across the peak halfway between baseline and peak maximum, this can be measured directly without extrapolation, and is equal to 2.35 standard deviations in a Gaussian peak.

the separation field from the early 1950s until the mid-1970s when high performance liquid chromatography (HPLC) became a competitive technique. During this 20-year period, considerable effort was expended in developing procedures to make compounds sufficiently volatile, more thermally stable and less polar so that they would be more amenable to GC analysis. Such efforts were aimed almost

Solar Panel Basics

Solar Panel Basics

Global warming is a huge problem which will significantly affect every country in the world. Many people all over the world are trying to do whatever they can to help combat the effects of global warming. One of the ways that people can fight global warming is to reduce their dependence on non-renewable energy sources like oil and petroleum based products.

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