Thin Layer Chromatography Identification Test for Dextromethorphan following European Pharmacopeia Monograph on Silica Gel G 254 Plates

Introduction

Dextromethorphan is a drug of the morphinan class. It is a cough suppressant with sedative, dissociative, and stimulant properties (at higher doses) and it is the active ingredient in many over-the-counter cold and cough medicines.

This application note illustrate how Silica Gel G plates are suitable for the analysis of Dextromethorphan following the European pharmacopeia identification TLC test experimental conditions (version 9.0).

Figure 1. Dextromethorphan Hydrobromide

Table 1. Experimental Conditions

TLC Plate	Silica Gel 60G F254 20 x 20 cm	Injection volume	5 µL
Detection	Spray with potassium iodobismuthate solution R2 (Potassium iodobismuthate solution: Suspend 1.7 g of bismuth subnitrate R and 20 g of tartaric acid R in 40 mL of water R. To the suspension add 40 mL of a 400 g/L solution of potassium iodide R and stir for 1 h. Filter. The solution may be kept for several days in brown bottles. Mix immediately before use 5 mL of the stock solution with 15 mL of water.
Mobile Phase	Concentrated ammonia: methanol : methylene chloride : ethyl acetate : toluene 2:13:10:20:55 (v/v/v/v/v )
Development	Over 2/3rd of the plate
Diluent	Methanol
Drying	In air
Standard	Dissolve 25 mg of standard timolol maleate in methanol and dilute to 10 ml with the same solvent
Sample	Dissolve 25 mg substance to be examined in methanol and dilute to 10 ml with the same solvent.

Figure 2. TLC plate development

Figure 3. Chromatograms

Figure 4. Spectrum

Figure 5. Chromatographic Data (Standard Solution)

Figure 6. Chromatographic Data (Sample Solution)

	Compound	Rf
1	Dextromethorphan	0.29

	Compound	Rf
1	Dextromethorphan	0.29

Table 2. Standard Repeatability

STD 1	2363
STD 2	2347
STD 3	2494
STD 4	2453
STD 5	2461
Mean	2423.6
Standard Deviation	64.7
RSD (%)	2.7

1. The principal spot in the chromatogram obtained with the test solution is similar in position, colour and size to the principal spot in the chromatogram obtained with reference solution.
2. All the spots for the reference solution have a repeatability better than 3% RSD.
3. Merck silica gel G plates provides repeatable and reproducible results for Dextromethorphan identification test and comply to all requirements as per European Pharmacopoeia.