The advantages of GC over TLC were discussed in an earlier article. The characteristics that make HPLC popular were also discussed in the article Why is HPLC the most popular technique in analytical laboratories today.
HPLC is the successor of TLC and has made significant contributions to the growth of analytical science and its diverse applications in pharmaceuticals, foods, polymers and plastics, environmental monitoring and clinical fields.
A comparison on characteristic features of HPLC that make it score over TLC are discussed in the present article
In TLC separations it becomes difficult to differentiate between overlapping bands and spots. In contrast the peaks in HPLC can be easily resolved and evaluated by controlling operational parameters such as flow rate of mobile phase, buffer control of the mobile phase, column oven temperature, etc.
Speed of analysis
In TLC separations the carrier liquid progression on the plate is dependent on gravitational force or capillary action. However, in HPLC the flow of mobile phase through the column is fast as it is pushed through with the help of a pump.Different pump pressure ranges can be achieved using normal as well as ultra high pressure systems
Quantification of results
HPLC software is capable of reporting precise and accurate results based on area counts of peaks. TLC quantifications are based on visual comparisons or spot intensity matching techniques which can be less quantitative in practice.
HPLC offers a large number of detector options to choose from such as UV, refractive index, electrochemical, fluorescence, conductivity, mass selectivity detector. Simultaneous detection is also possible using the photodiode array detection system. Such large and sensitive detection options are not available in TLC separations.
HPLC software is capable of reporting precise and accurate results based on area counts of peaks. In addition software also helps set and monitor operational parameters such as flow rate, detector wavelength, column temperature,etc.
Choice of stationary phase and columns
A large number of stationary phases are available to suit different range of applications .Similarly columns of different bores and lengths are available for micro level determinations to preparative scale preparations. This unique facility is not available on TLC plate separations.
Storage of results
Like GC it is possible to keep a permanent record of generated chromatograms as hard or soft copies. TLC plates cannot be stored due to fading of spots over time and requirement of proper storage conditions. However, pictures of TLC plates can be taken and stored as permanent records.
HPLC has been successfully coupled with mass spectrometers and FT-IR systems and this has resulted in significant improvement in both resolution and sensitivity. This option is not possible in TLC separations.
Reuse of Columns
The columns if maintained properly and operated under carefully controlled conditions without overloading can be used repeatedly for significant time periods. In contrast new TLC plates are required for each analysis.
HPLC is undoubtedly a rapidly growing chromatography technique but like any other analytical technique it has certain limitations which will be discussed subsequently in another article.