Determination of Quinine in Tonic Water and Caffeine in Coffee and Cola Drinks Using TLC-MS

Abstract

High Performance Thin Layer Chromatography coupled with Mass spectrometry (HPTLC–MS) is an analytical technique that requires low-level of sample preparation. Here it is illustrated with the determination of quinine in tonic water and caffeine in coffee and cola drinks. Tonic water and the analyzed cola drinks were decarbonized through ultrasonication, and boiled coffee was extracted through an appropriate 0.45 µm PTFE syringe filter. After the initial chromatographic separation, specific bands were eluted with an TLC-MS interface and detected with mass spectrometry.

Results

Caffeine (hRf = 56, m/z = 195.2, 236.2, Figure. 2) and quinine (hRf = 37, m/z = 325.4, Figure. 4) were detected under UV light (254 nm, Figure. 1; 366nm, Figure. 3) and measured by TLC-MS.

Figure 1. (left) Developed plate at 254 nm. Figure 2. (right) Mass spectrum of caffeine in coffee

Figure 3. (left) Developed plate at 366 nm; Figure 4. (right) mass spectrum of quinine in tonic water

Conclusion

These results demonstrate that caffeine and quinine can easily be analyzed by HPTLC-MS with a minimum of sample preparation in coffee, cola drinks or tonic water.

Table 1. Chromatographic data

Track	Compound	Conc. [mg/mL]	Application volume [µL]	hRf	Detected mass m/z
1	Caffeine standard	1	1	56	195.2, 236.2
2	Coffee		1	56	195.2, 236.2
3	Cola drinks		1	56	195.2, 236.2
4	Tonic water		1	37	325.4
5	Quinine standard	1	1	37	325.4
6	Caffeine standard	1	2	56	195.2, 236.2
7	Coffee		2	56	195.2, 236.2
8	Cola drinks		2	56	195.2, 236.2
9	Tonic water		2	37	325.4
10	Quinine standard	1	2	37	325.4

Table 2. Application data

Chromatography
Plate	HPTLC Silica gel 60 F254 MS-grade, 20x10cm
Sample preparation	Caffeine and quinine standard diluted in Methanol; Cola drinks and tonic water were decarbonated; Coffee boiled and filtered with a 0.45 µm syringe filter.
Sample application	ATS 4 sample applicator (Camag), 6 mm bandwise
Application volume	1.0 and 2.0 µL
Mobile phase	Isopropanol / n-Heptane / Water 7/3/1 + 1% Triethylamine
Migration distance	5 cm
Migration time	49 min
Extraction
Extraction equipment	TLC-MS Interface “Plate Express” (Advion)
Extraction solvent	Acetonitrile / Water 95/5 (v/v) + 0.1% Formic acid
Extraction flow	0.2 mL/min
Detection
Wavelength	UV light at 254 nm and 366 nm
Staining	None
MS equipment	expression CMS (Advion)
MS detection	ESI (+) mode (m/z 150 - 400)