Determinação indireta de fosfolipídios em lecitina de soja por espectrometria de absorção molecular em forno de grafite com fonte contínua de alta resolução

Abstract

Soy lecithin is a compound extracted from the crude soybean oil by the degumming process. It is a brown viscous liquid rich in phospholipids. It has an amphiphilic nature, which makes it the natural emulsifier most widely used in pharmaceutical, cosmetic and food industries. Various studies have suggested the therapeutic use of lecithin, improvement of memory, liver protection and cholesterol reduction. Due to its wide application becomes necessary methods for the monitoring of marketed lecithin quality. This paper presents a method for indirect determination of the phospholipids in soy lecithin samples through phosphorus determination by high-resolution continuum source graphite furnace molecular absorption spectrometry (HR-CS GF MAS) via absorption of phosphorus monoxide (PO). For injection of samples in equipment, they were diluted in methyl isobutyl ketone (MIBK). Thermal conditions were studied to phosphorus measured via PO at different transition lines: 213.561; 246.400 and 324.620 nm. The best conditions were established in 213.561 nm: pyrolysis temperature of 1300 °C, volatilization temperature of 2300 °C and Mg as chemical modifier. To increase the analytical sensitivity, the measurement of the absorbance signal was obtained by the sum of four lines of molecular transition PO surrounding the of 213 nm: 213.5610; 213.5259; 213.6172 and 213.6374 nm. Comparison of calibration curves of the aqueous solutions of NH4H2PO4 and solutions of the samples prepared in MIBK no showed matrix effect, and it was possible external calibration with aqueous standards. The limits of detection and quantification were found to be 2.35 and 7.83 mg g-1, respectively. The correlation coefficient (R) was 0.9976 for a linear response range between of 0 and 200 mg L-1.The precision evaluated as relative standard deviation (RSD) was 2.47% (n = 10) for a sample of soy lecithin containig 2.2% (w/v) of phosphorus. The developed method was applied to analysis of the samples of soy lecithin commercial. To validation the method, samples were also analyzed after wet digestion in digester block, followed by of phosphorus determination by inductively coupled plasma optical emission spectrometry (ICP OES). The concentration of phospholipids in the samples varied between 38.1 and 45% (w/v) to the proposed method and between 37 and 49.5% (w/v) for comparative method. The paired t-test proved that there is no significant difference between the results obtained by the two methods (95% confidence level).