SPE/TLC/Densitometric Quantification of Selected Synthetic Food Dyes in Liquid Foodstuffs and Pharmaceutical Preparations

Received Apr 28, 2017; Accepted Jun 18, 2017

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1. Introduction

Synthetic food dyes are still common food additives despite the growing awareness of their negative influence on the human organism. The particularly harmful food colorants are azo dyes that exhibit carcinogenic and potentially genotoxic activity [1]. The list of dyes permitted in the European Union contains over 30 substances of which 12 are synthetic colorants [2].

Legal requirements and limitations regarding the application of food dyes have led to the development of several analytical techniques that enable the detection and quantification of these food additives. Liquid chromatography, including thin layer chromatography (TLC) in normal (NP) and reversed (RP) phase mode, has been successfully used to quantify food dyes in different matrices. Selected references on TLC methods proposed to separate and quantify permitted and illegal synthetic food dyes are listed in Table 1.

Table 1

Selected references on TLC separation and/or quantification of synthetic food dyes (including some illegal or delisted examples).

Dyes	Sorbent	Eluent	Detection method	Ref.
Amaranth, indigotine, tartrazine, Ponceau 4R, orange yellow, Allura Red, Brilliant Blue, food green 3	Silica gel RP18	Methanol-acetonitrile-5% aq.Na2SO4 (3 : 3 : 10, v/v/v)Methanol-butanone-5% aq.Na2SO4 (1 : 1 : 1, v/v/v)	Densitometry	[14]
Detection of illegal dyes	RP-18	Methanol-acetonitrile-5% aq.Na2SO4 (3 : 3 : 10, v/v/v)Methanol-butanone-5% aq.Na2SO4 (1 : 1 : 1, v/v/v)Methanol-butanone-5% aq.Na2SO4 (1 : 1 : 1, v/v/v)	Mass spectroscopy	[13]
Tartrazine, azorubine, orange yellow	NH2	i-PrOH-Et2O-NH3 (2 : 1 : 1 v/v/v)	Video-scanning	[15]
Ponceau 4R, tartrazine, orange yellow	Silica gel 60	i-PrOH-NH3-H2O(10 : 1 : 1 v/v/v)	Sorbent scraping, extraction, and spectrophotometry	[11]
Indigotine, Ponceau 4R, orange yellow, tartrazine, amaranth	MgO	Sodium citrate 15% aq.-methanol(4 : 1 v/v)	Visual	[20]
Amaranth, tartrazine, orange yellow	Silica gel	n-butanol-ethanol-H2O-NH3(10 : 5 : 5 : 2 v/v/v/v)	Visual	[3]
Tartrazine, Allura Red	RP-18W	Methanol-citric buffer pH 3.5 (45 : 55 v/v)	Densitometry