## 2 Material and Methods
### Analytical Method and Quality Control  
Essential elements (K, Na, Ca, Mg, Fe, Zn, Cu, Co, Mo, Mn) and toxic elements (Al, Cd, Pb, B, Ba, V, Sr, Li, Ni) were determined by inductively coupled plasma optical emission spectrometer (ICP-OES) model ICAP 6300 Duo Thermo Scientific (Waltham, MA, USA) with an auto sampler (CETAX model ASX-520). It is a technique frequently used in the determination of elements in different food and biological matrices [7; 58; 59; 60], and it is one of the most sensitive and precise techniques of instrumental analysis, just behind ICP-MS [60]. The instrumental ICP-OES conditions were: sample injection to the 50 rpm flow pump; stabilization time of 0 s, approximate RF power of 1150 W and gas flow (nebulizer gas flow, auxiliary gas flow) of 0.5 L/min [31; 61]. Instrumental wavelengths (nm) of the analyzed elements. Instrumental quantification limits (LOQ) of the analyzed elements were calculated as 10 times the standard deviation (SD), resulting from the analysis of 15 targets under reproducibility conditions [62] (Table 3). Calibrations were performed using certified standard solutions. Specifically, for the metals Na, Ca, K and Mg, the certified standard IV-STOCK-2 of Inorganic Ventures was used, with a certified concentration for each of the metals of 10,000 ug/mL and for the rest of the metals (V, Mn, Fe, Cu, Zn, Cr, Mo, Co, B, Ba, Li, Sr, Ni, Si, Al, Pb and Cd), the certified standard Multi-Element Std, SCP28 AES from SCP Science, with a certified concentration for each of the metals of 100 mg/L, has been used. From these, and for each of the metals analyzed in this study, the different concentrations of the calibration standards for the preparation of the calibration lines were prepared, all of them in sufficient quantity for 100 mL in 1.5% nitric acid. Table 4 shows the recovery study performed with Certified Reference Materials (CRM) in order to check the accuracy and precision of the analytical method. The CRM used, from the National Institute of Standards and Technology (NIST), were: SRM 1515 Apple Leaves, SRM 1548a Typical Diet, SRM 1577b Bovine Liver and SRM 1567a Wheat Flour. The standard additions method was used in the case of Li, by adding known quantities of Li to dehydrated samples of baby food from jars. The recovery percentages obtained were good (over 92%). Figure 1: Experimental procedure of mineralization by incineration. The criteria, from an analytical point of view, that guarantee the correct evaluation of the results presented in the work have been validated, with the parameters of Accuracy (established as recovery), Precision (established as reproducibility) and Specificity (it has been carried out by checking that the method is free of spectral interferences for each of the metals studied) applied to the reference materials used in the study. In addition to these, the following parameters were also monitored and evaluated:  
* The sensitivity of the calibration line: this was carried out with the response of the lowest standard of the calibration lines for each of the metals, setting as an acceptance criterion a response 3 times higher than the response of the blank (1.5% HNO\({}_{3}\) solution). * The linearity of the calibration line: this was established by applying the relative calibration errors, setting as acceptance criteria a maximum of 15% of this error for all metals in the lowest standards of each line and 10% in the rest of the points of the calibration lines. * The repeatability precision of the method: it was established with samples analyzed in duplicate, setting as acceptance criterion the following formula: r = 2\(\surd\)2\(\cdot\)Sr, where Sr is the repeatability standard deviation.