Potentially Toxic Elements in Commercial Soap and Powder Detergent Samples

Dry decomposition, wet digestion, and dissolution in aqueous medium for direct analysis were evaluated for the preparation of eight samples of liquid and bar soap and one powder detergent for later determination of Cd, Mg, Pb, and Zn by inductively coupled plasma optical emission spectroscopy (ICP OES). The evaluation of the best conditions for digestion of the samples were chosen from a set of tests where conventional heating using 1 mol L^-1 HNO₃ with addition of 30% H₂O₂ proved to be the most effcient method. The average hydrodynamic diameter of 525 nm was determined using dynamic light scattering measurements. The concentrations found were: Cd and Pb (< limit of detection (LOD)), Mg (50.89 to 1119 μg g 1), and Zn (280.25 to 537.54 μg g 1). After evaluating the sample preparation methods, the accuracy of the methodology was verifed through recovery tests of analytes, obtaining values between 83 and 119% and a relative standard deviation (RSD) ≤ 4.30% (n = 6; 4 mg L 1). The LOD ranged from 0.015 to 0.5 µg g 1 and the limits of quantifcation (LOQ) from 0.045 to 2 µg g 1. The soaps and powder detergent samples studied here may be used without any harm to health as the contents were within the limits established by the legislation.

Keywords:
sample preparation; ICP OES; dynamic light scattering; dissolved organic carbon; elements determination