title: Calibration strategies for the direct determination of Ca, K, and Mg in commercial samples of powdered milk and solid dietary supplements using laser-induced breakdown spectroscopy (LIBS).
abstract: This study describes the application of laser-induced breakdown spectroscopy (LIBS) for the direct determination of Ca, K and Mg in powdered milk and solid dietary supplements. The following two calibration strategies were applied: (i) use of the samples to calculate calibration models (milk) and (ii) use of sample mixtures (supplements) to obtain a calibration curve. In both cases, reference values obtained from inductively coupled plasma optical emission spectroscopy (ICP OES) after acid digestion were used. The emission line selection from LIBS spectra was accomplished by analysing the regression coefficients of partial least squares (PLS) regression models, and wavelengths of 534.947, 766.490 and 285.213nm were chosen for Ca, K and Mg, respectively. In the case of the determination of Ca in supplements, it was necessary to perform a dilution (10-fold) of the standards and samples to minimize matrix interference. The average accuracy for powdered milk ranged from 60% to 168% for Ca, 77% to 152% for K and 76% to 131% for Mg. In the case of dietary supplements, standard error of prediction (SEP) varied from 295 (Mg) to 3782mgkg-1(Ca). The proposed method presented an analytical frequency of around 60 samples per hour and the step of sample manipulation was drastically reduced, with no generation of toxic chemical residues.
authors.affiliation: Group for Applied Instrumental Analysis, Department of Chemistry, Federal University of São Carlos, Rod. Washington Luís, km 235, 13565-905 São Carlos, São Paulo State, Brazil.
authors.forename: Amanda
authors.initials: A
authors.lastname: Dos Santos Augusto
authors.affiliation: Department of Analytical Chemistry, Institute of Chemistry, São Paulo State University (Unesp), Rua Professor Francisco Degni, 55, 14800-060 Araraquara, São Paulo State, Brazil.
authors.forename: Paulo Lopes
authors.initials: PL
authors.lastname: Barsanelli
authors.affiliation: Department of Analytical Chemistry, Institute of Chemistry, São Paulo State University (Unesp), Rua Professor Francisco Degni, 55, 14800-060 Araraquara, São Paulo State, Brazil.
authors.forename: Fabiola Manhas Verbi
authors.initials: FM
authors.lastname: Pereira
authors.affiliation: Group for Applied Instrumental Analysis, Department of Chemistry, Federal University of São Carlos, Rod. Washington Luís, km 235, 13565-905 São Carlos, São Paulo State, Brazil. Electronic address: erpf@ufscar.br.
authors.forename: Edenir Rodrigues
authors.initials: ER
authors.lastname: Pereira-Filho
mesh_terms: D000818:Animals; D002118:Calcium / Q000032:analysis*; D002138:Calibration; D003132:Commerce; D019587:Dietary Supplements / Q000032:analysis*; D005504:Food Analysis / Q000379:methods*; D006801:Humans; D007834:Lasers; D016018:Least-Squares Analysis; D008274:Magnesium / Q000032:analysis*; D008892:Milk / Q000737:chemistry*; D011188:Potassium / Q000032:analysis*; D011208:Powders; D015203:Reproducibility of Results; D013057:Spectrum Analysis
chemical_list: D011208:Powders; D008274:Magnesium; D011188:Potassium; D002118:Calcium
keywords: Calibration; Chemometrics; Dietary supplements; Direct solid analysis; Laser-induced breakdown spectroscopy; Powdered milk