A Comparison of Pretreatment Methods for Determination of Macroelements in Milk by ICP-OES

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Mineral elements have important role in human body. They are involved in bone formation or membrane transport of essential substances, regulate different metabolic pathways and enzyme activities and support proper functioning of organ system. Insufficient or increased intake of mineral elements above critical levels can cause various metabolic disorders that can result in damage to internal organs. Therefore it is necessary to ensure steady and regulated intake of mineral elements. Milk and milk products are a suitable source of mineral elements and other important nutrients in daily diet. Especially infants and adolescents require a higher intake of mineral elements for proper development of the skeletal and other organ systems. However, in the technological processing of raw milk the mineral content may decrease due to partial processes such a standardization of fat content or ultrafiltration, so it is necessary to monitor content of macroelements to maintain the desired nutritional value of final products. Milk is a relatively complicated matrix because it is a polydisperse system of many components, including lactose, milk fat, proteins, enzymes, mineral salts and vitamins. It means that the sample pretreatment is a critical step to obtain precise results in elemental analysis. This study was focused on comparison of several commonly used methods, such as slurry dispersion, alkaline solubilization, wet ashing, dry ashing and microwave assisted ashing, for sample preparation before ICP-OES analysis. A reference material ERM® – BD150 with certified values of monitored macroelements was used as a model milk matrix for individual experiments. The slurry dispersion analysis is simple, fast and easy method for elemental analysis of milk matrix, but significant difference between measurements results and certified values of monitored macroelements except Mg was found. More corresponding results for K was obtained after acidification of slurry dispersion with nitric acid to final concentration of 1M HNO3 and subsequent sonication, but in this case filtration was necessary before ICP-OES analysis due to precipitation of milk proteins. Moreover, lower concentration of P was measured after acid pretreatment of slurry dispersion. Another simple and reproducible pretreatment method is using TMAH reagent, which promotes the complete solubilization of the samples. On the other hand, TMAH presents problems of determination for some analytes, especially K. The most relevant results to certified valuesof macroelements were achieved using wet ashing, dry ashing and microwave assisted ashing pretreatment methods. Then other factors should be considered, such as time, number of partial processes and cost, to choose the appropriate pretreatment method. However, the optimization of pretreatments for element analysis in comlex matrix may still be a challenge.

pretreatment methods, macroelements, ashing, milk, ICP-OES

KŘIKALA, J.; DIVIŠ, P.

21. 11. 2019

Vysoké učení technické v Brně, Fakulta chemická

978-80-214-5807-9

Studentská odborná konference Chemie je život 2019

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