Vinegar; factorial design; ICP OES.

Vinegar is a condiment food composed mainly of acetic acid and water, whose therapeutic properties have been demonstrated in various scientific studies. With the aim of understanding the elemental composition of this food, the present work developed a method for decomposing vinegar samples assisted by microwave radiation using diluted nitric acid and hydrogen peroxide for the determination of Ca, Cd, Co, Cr, Cu, Fe, Mg, Mn, Ni, Pb, and Zn by Inductively Coupled Plasma Optical Emission Spectrometry (ICP OES) and K and Na by flame photometry. Sixteen samples of vinegar, including alcohol vinegar, balsamic vinegar, apple vinegar, and red wine vinegar, were analyzed. A 2³ factorial design, with three repetitions at the central point, was employed to evaluate the sample decomposition procedure, and the responses of the factorial design were the residual carbon content (RCC) and residual acidity (RA). The best decomposition condition was achieved considering 1.0 g of sample and a digestion mixture composed of 7 mL of 0.3 mol L⁻¹ nitric acid and 1 mL of H₂O₂, for 45 minutes at a temperature of 200 °C. This condition allowed obtaining final digests with an average residual carbon content and residual acidity of 13.6% and 0.73%, respectively. Considering the measurements in ICP OES, the detection limits (DL) ranged from 0.001 mg L⁻¹ for Cd, Co, Cu, and Mn, up to 0.076 mg L⁻¹ for Ca. For K and Na measured in the flame photometer, the detection limits were 0.333 mg L⁻¹ and 0.455 mg L⁻¹, respectively. The mineral elements present in the vinegar samples showed the following concentration ranges, in µg g⁻¹: Ca (7.4 - 148.7), Cu (<0.046 - 0.129), Fe (<0.388 - 7.03), K (<15.16 - 2097.0), Mg (6.4 - 97.1), Mn (<0.023 - 3.23), Na (<20.6 - 514.1), Zn (<0.398 - 0.75). There is no Brazilian legislation establishing maximum levels of elements in vinegar; however, referring to Spanish legislation, it is observed that the levels of Cu, Pb, and Zn were lower than 10 mg L⁻¹, 0.5 mg L⁻¹, and 10 mg L⁻¹, respectively, which are the maximum limits established by the Spanish government for these samples. Principal Component Analysis (PCA) was employed to assist in the analysis of the data, which allowed us to observe a trend of separation of balsamic vinegars from the others.