Similarity and dissimilarities:

Similarly, there are many points of similarity and dissimilarities as summarized below:

i) GC can be used to separate gaseous or low boiling. pt. liquid solutes can be analyzed whereas in HPLC can be used to separate volatile and nonvolatile, including solids soluble in organic solvents.

ii) The amount of sample required in GC is of the order of a few nanograms per mL whereas in HPLC even a fraction of microlitre may be sufficient. However, in both the cases, the sample is introduced using a microsyringe.

iii) The column tubing in GC can be circular, in a loop or bent so as to have long column but in HPLC it should always be a straight column or else mobile phase will not flow smoothly.  No bending is allowed or else pressure will not be uniform.

iv) The instrumental set up in two cases is widely different. In case of GC, it is essential to have the sample injection chamber, column and detector, all housed in a thermo stated oven and an inert gas carrier is used. On the other hand, in HPLC, quite often a mixture of high purity solvents with low pressure gradient is used and then it is allowed to pass through stationary phase column under high pressure.

v) Though some detectors are common for GC and HPLC but not all the detectors used in GC or HPLC can be used by another. Flame ionization (FID) or electron capture (ECD) detectors commonly used in GC cannot be used in HPLC. Similarly, a fluorescence or refractive index detector used in HPLC cannot be used in GC. In principle, GC can be coupled to an UV detector but it is rarely done. On the other hand, GC is often coupled to infrared detector though a fast scanning and sensitive detector is required. However, HPLC frequently uses fixed wavelength UV detector though variable wavelength detectors can also be used. Infrared detection of eluting compounds can also be carried out.

vi) The optimization of experimental procedure in GC is easier whereas in case of HPLC, it is difficult.

vii) The basic mechanism of separation in GC is adsorption or partition whereas in HPLC different mechanisms of adsorption, partition, ion-exchange, etc. are operative.

viii) GC has limited applicability for gaseous solutes only though it is useful for the identification of hydrocarbons of a homologous series. On the other hand, HPLC has much wider applicability to a variety of organic and inorganic compounds.

ix) GC cannot be used for the separation of ionic species whereas such species can be easily separated by HPLC.