An Experimental design approach in optimization of an extraction procedure for AAS determination of Ca, Mg, Zn, Cu and Fe in multimineral dietary supplements

Sample preparation, as the most sensitive and time-consuming step in AAS, can be usually performed by digestion or extraction methods. Compared to digestion methods, extraction is simpler, safer, cheaper and represents a valuable alternative to laboratories that lack the possibility of having expensive equipment and instrumentation (Longas et al., 2009; Paula et al., 2013). The application of experimental design approach for optimization of the extraction procedure, compared to univariate approach, offers the advantages of simultaneous evaluation of several experimental conditions, performing smaller number of experiments (Soriano et al., 2007a; Kenduzler et al., 2008). The aim of our study was application of experimental design approach in optimization of ultrasonic stirring acid extraction of Ca, Mg, Zn, Cu and Fe in multimineral dietary supplements followed by determination using FAAS. The influence of ultrasonic extraction time (10 - 30 min), temperature (20 – 60 ˚C) and              HCl concentration (1.0 -5.0 mol L -1 , extraction solution) was investigated using full factorial 2 3 design (MODDE 10.0). The selection of experimental variables was performed considering the study of Soriano et al., (Sorriano et al., 2007b). Experimental response (extraction efficiency) was evaluated by calculation of element’s recovery after extraction. Ultrasonic stirring extraction was performed using 150 mg sample and 10 ml of extraction solution. The determination of the mineral content was performed on Shimadzu AA-7000 atomic absorption spectrometer. The analysis of Contour plots of experimental responses using Response Surface Methodology (RSM) has shown that optimal recovery for the studied elements is obtained when HCl concentration is 3.0 mol L -1 , the extraction temperature is 25 ˚C and the ultrasonic extraction time is 30 min. Also, this investigation showed that the ultrasonic extraction time and the temperature had higher influence on the extraction process, compared to the influence of acid concentration. The optimized method was validated in terms of linearity, accuracy and precision, limit of detection and limit of quantification. The application of experimental design approach enabled a simple and a reliable method for determination of Ca, Mg, Zn, Cu and Fe in multimineral dietary supplements. References: Kenduzler, E., Yalcinkaya, O., Baytak, S., Turker, A. Application of full factorial design for the preconcentration of chromium by solid phase extraction with Amberlyst 36 resin Microchim. Acta 2008, 160, 389 – 395 DOI: 10.1007/s00604-007-0773-4 Longas, N., Arrona, G.R., Ostra, M., Millan, E. Application of experimental design in acid digestion optimization for Cd, Cr and Pb determination in plastic materials by atomic absorbtion spectrometry, At. Spectros . 2009, 30, 47-53 Paula, C., Caldas, F.L., Brum, D., Cassella R. Development of a focused ultrasound-assisted extraction method for the determination of trace concentrations of Cr and Mn in pharmaceutical formulations by ETAAS, J. Pharm. Biomed. Anal. 2013, 74, 284 – 290, DOI: 10.1016/j.jpba.2012.11.013 Soriano, S., Netto, P.A., Cassella, R. Multivariate optimization of a microwave-assisted leaching procedure using dilute acid solutions, for FAAS determination of Cu, Fe, Mn and Zn in multivitamin/multimineral supplements, Anal. Bioanal Chem , 2007a, 387, 1113 -1120, DOI: 10.1007/s00216-006-0973-5 Soriano, S., Netto, P.A., Cassella, R. Determination of Cu, Fe, Mn and Zn in multivitamin/multimineral dosage forms or tablets after an acidic extraction, J. Pharm. Biomed. Anal. 2007b, 43, 304 – 310, DOI: 10.1016/j.jpba.2006.06.009