Curcuma longa L. (Zingiberaceae) is a rhizomatous perennial herb. It is a medicinally important plant commercially known as Haldi, Turmeric, or Indian saffron. It has a long history of traditional uses ranging from folk medicine to various culinary preparations. The paste of C. longa rhizome is commonly used traditionally in the treatment of asthma, leucoderma, tumor, piles . In the Indian system of medicine, it is well reported as an anti-inflammatory and skin protective agent . C. longa is the potential source of many secondary metabolites namely curcuminoids, curcumin, demethoxycurcumin, bisdemethoxycurcumin, turmerone, atlantone, and zingiberone, sesquiterpenoids, sugars, resins, proteins, vitamins, and minerals.
Curcumin is the major active constituent of C. longa. Structurally, Curcumin is 1,7-bis(4-hydroxy-3-methoxyphenyl)-1,6-heptadiene-3,5-dione (Fig. 1). It is a natural polyphenol procured from the rhizomes of C. longa . It is a bright yellow-orange colored powder. Curcumin exhibits various pharmacological activities including antioxidant, anti-inflammatory, anticarcinogenic, hypocholesterolemic, wound healing, antispasmodic, anticoagulant, antitumor, and hepatoprotective activities . Curcumin is included in various herbal remedies to treat skin inflammation and its infection. It is therapeutically used for the treatment of amenorrhea, dislocation of joints, diarrhea, diabetes, liver disorder, bronchitis, ringworm infection, toothache, anemia, and weakness of eyesight [1, 4, 5].
The variation in the content of phytoconstituents in herbal extract presents a major challenge to control the quality of herbal products. To assess the safety and efficacy of plant material, qualitative and quantitative analyses are useful techniques which mostly related to the content of marker compounds present in the plant [6, 7]. Curcumin, the principal active constituent largely responsible for the therapeutic efficacy of C. longa, is recognized as the marker compound .
In recent years, the advancement of chromatographic and spectral fingerprints plays an important role in the quality control of herbal medicines . Chromatographic fingerprint investigation has been demonstrated to be a realistic and practical method for quality assessment and authentication of various herbal medicines. This method can be used to identify the presence or absence of markers as well as the ratio of all detectable compounds . Although several methods for the quantification of curcumin were reported by various researchers including supramolecular solvent-based liquid–liquid microextraction (SMS-LLME) , isocratic high-performance liquid chromatography (HPLC) [8, 9], ultra-performance liquid chromatography–mass spectrometry (UPLC-MS) , and reversed-phase liquid chromatography (RPLC) . However, HPTLC has become a routine analytical technique due to its advantages [5, 12, 13]. The TLC chromatogram pattern comparison seems to be promising for fingerprinting the active compounds in plant extracts. HPTLC has been known as the fast tool for the detection of compounds . Analytical quantification of chemical markers through HPTLC has the advantage of combining chromatographic separation on a silica layer, along with in situ densitometric quantification of the separated compounds . This results in an efficient, quick, accurate, and relatively inexpensive method for the quantification of separated phytoconstituents , thus eliminating the possible interference given by other structurally related compounds. HPTLC method provides many other benefits such as rapid analysis time, i.e., many samples can be analyzed simultaneously, low solvent usage on a per-sample basis, low operating cost, high sample throughput, and the need for minimum sample clean-up. It can detect more compounds than HPLC, although the resolution is poorer [5, 6, 13]. Additionally, the compounds having no UV absorption can be detected by reagent spraying. Utilizing a data analysis system and optimized experimental conditions, HPTLC is also feasible for the development of chromatographic fingerprint methods to determine and identify complex herbal extracts just like HPLC and GC. The compounds which cannot be eluted still can be detected. Furthermore, the colorful picture, like the HPTLC image, provides extra-intuitive parameters of visible color and/or fluorescence. Moreover, the colorful pattern and quantification at the micron and nanogram levels help to differentiate various samples on the same plate [12,13,14].
Comparing to the GC and HPLC, the HPTLC method has few restrictions, such as a low plate efficiency and narrow developing distance. Despite that, it remains a valuable tool for quality assessment of natural products due to its ease, low cost, and few requirements, and it has been profitably utilized to develop a chromatographic fingerprint for various natural products, herbal drugs, and commercial herbal formulations [5, 6]. However, with the advancement in analytical techniques, a smartphone-enabled alternative of TLC densitometric scanning was developed which is economic, precise, and accurate to serve the purpose. Such techniques are especially effective in low-income countries and the methods developed with traditional HPTLC can easily be reciprocated to Smartphone-based image analysis [15, 16]. But this method requires technical experience.
Looking into the benefits, in the present work, a densitometric HPTLC method has been developed and validated according to International Conference on Harmonization (ICH) guidelines for the quantitation of curcumin from methanolic extract C. longa.