Dispersive liquid–liquid microextraction coupled to liquid chromatography for thiamine determination in foods

Abstract

A miniaturized dispersive liquid-liquid microextraction (DLLME) procedure coupled to liquid chromatography (LC) with fluorimetric detection was evaluated for the preconcentration and determination of thiamine (vitamin B(1)). Derivatization was carried out by chemical oxidation of thiamine with 5 × 10(-5) M ferricyanide at pH 13 to form fluorescent thiochrome. For DLLME, 0.5 mL of acetonitrile (dispersing solvent) containing 90 μL of tetrachloroethane (extraction solvent) was rapidly injected into 10 mL of sample solution containing the derivatized thiochrome and 24% (w/v) sodium chloride, thereby forming a cloudy solution. Phase separation was carried out by centrifugation, and a volume of 20 μL of the sedimented phase was submitted to LC. The mobile phase was a mixture of a 90% (v/v) 10 mM KH(2)PO(4) (pH 7) solution and 10% (v/v) acetonitrile at 1 mL min(-1). An amide-based stationary phase involving a ligand with amide groups and the endcapping of trimethylsilyl was used. Specificity, linearity, precision, recovery, and sensitivity were satisfactory. Calibration graph was carried out by the standard additions method and was linear between 1 and 10 ng mL(-1). The detection limit was 0.09 ng mL(-1). The selectivity of the method was judged from the absence of interfering peaks at the thiamine elution time for blank chromatograms of unspiked samples. A relative standard deviation of 3.2% was obtained for a standard solution containing thiamine at 5 ng mL(-1). The esters thiamine monophosphate and thiamine pyrophosphate can also be determined by submitting the sample to successive acid and enzymatic treatments. The method was applied to the determination of thiamine in different foods such as beer, brewer's yeast, honey, and baby foods including infant formulas, fermented milk, cereals, and purees. For the analysis of solid samples, a previous extraction step was applied based on an acid hydrolysis with trichloroacetic acid. The reliability of the procedure was checked by analyzing a certified reference material, pig's liver (CRM 487). The value obtained was 8.76 ± 0.2 μg g(-1) thiamine, which is in excellent agreement with the certified value, 8.6 ± 1.1 μg g(-1).

Enhanced spectrofluorimetric determination of hypochlorite based on the catalytic oxidation of thiamine to thiochrome in the presence of trace ferrocyanide

“…In basic medium, thiamine could selectively reacted with ferricyanide to give thiochrome and this specic reaction has been employed for the detection of thiamine with agreeable results. 18 Similar to the catalytic oxidation by potassium ferricyanide (Fig. 6, curve 4), the interaction of thiamine with potassium ferrocyanide and sodium hypochlorite generated the same results (Fig.…”

“…19 It is also noted that the concentration of ferricyanide was quite high in previously published methods, ranging from 5 Â 10 À4 $0.01 mol L À1 . 18,20 However, in our experiment, it need minimum amount of ferrocyanide (2 Â 10 À6 mol L À1 ) owing to the inimitable catalytic circle, just as illustrated in Scheme 1. To the best of our knowledge, it was the lowest one if ferrocyanide was converted to ferricyanide.…”

Dispersive Liquid-Liquid Microextraction in the Analysis of Milk and Dairy Products: A Review

“…Viñas et al determined the concentration of thiamine in infant formula and fermented milk using traditional DLLME with HPLC fluorometric detection [13]. All samples underwent a derivatisation reaction to differentiate between thiamine and its esters.…”

Spectrofluorometrical Determination of Vitamin B1 in Different Matrices Using Box‐Behnken Designed Pipette Tip Solid Phase Extraction by a Carbon Nanotube Sorbent

“…Almost all of these techniques require a separation or extraction step, since severe matrix interferes in real sample can increase the risk of detection error especially in trace analysis . For preconcentration of thiamine, various techniques such as solid phase extraction, dispersive liquid–liquid microextraction, ion exchange and cloud point extraction were used. Miniaturized SPE has attracted attention of analytical chemists because of its ability to isolate concentrate analytes from extremely dilute sample solutions and its versatility and flexibility in the pre‐ concentration step of most instrumental analysis ,.…”