Multivariate Optimization Of Ultrasonic And Infrared Assisted Extraction For Multielement Determination In Animal Feed

CORA JOFRE, FLORENCIA; SAVIO, MARIANELA

Conferencia; 2nd European Sample Preparation e-Conference and 1st Green and Sustainable Analytical Chemistry e-conference; 2022

For elemental determination in complex samples, the analytical techniques commonly used are flame atomic absorption spectrometry (FAAS), microwave-induced plasma optical emission spectrometry (MIP OES) or inductively coupled plasma (ICP OES), and mass spectrometry (ICP MS). However, prior to analysis, animal feed sample preparation involves a critical step due to the high content of organic matter that implies its total destruction. Thus, digestion methods involving the use of concentrated oxidizing acids, high temperatures and high pressures are frequently used. The use of ultrasonic (US) and infrared (IR) energy in sample preparation has advantages related to simplicity, low cost, and safety. On the other hand, the use of dilute acids has been shown to have significant advantages such as cost reduction, production of smaller amounts of waste, reduction of blanks, minimization of equipment damage, and lower acidity of digested samples. Thus, the combination of both represents advances in the development of cleaner and more efficient methods, in accordance with the principles of green chemistry. The application of multivariate optimization techniques makes it possible to investigate factors that may influence the experimental procedure, in order to obtain the best conditions for the sample preparation procedure.The objective of this work was to develop and optimize an alternative analytical strategy for the preparation of complex samples extracted with dilute acids and assisted by ultrasound (USAE) and infrared (IRAE) for multielement determination by MIP OES. Likewise, a comparative analysis was carried out between the two procedures under their optimal conditions.For experimental conditions optimization of each sample preparation system, a central composite design centered on the faces was carried out, considering 4 and 5 factors for IRAE and USAE, respectively, that significantly influence the responses to be evaluated: dissolved organic carbon (DOC) and residual acidity (RA). The response surface methodology was implemented to find the best combination of mass, diluted reagents (HNO3 and H2O2), time and temperature in order to minimize both responses for elemental extraction in animal feed samples. The selected factors were evaluated in a range of 100-500 mg (sample mass), 15-45 min (heating time), 2-7 M (HNO3 concentration) and 10-30 % (H2O2 concentration) for both designs and the temperature between 30-60°C was considered in the USAE design while for the IRAE it was kept constant at 190°C. The analysis of both designs yielded the optimal combinations of each system, which after their experimental validation, were implemented for the multielement determination.The procedure´s trueness (IRAE and USAE) was confirmed using the optimized conditions in the analysis of certified reference materials (CRM). Recoveries ranged from 80 to 120%, with good precision (relative standard deviation (RSD)