Influence of rice sample preparation on elemental composition - application of total reflection X-ray fluorescence spectroscopy

Abstract

Riža je namirnica koja se u velikim količinama konzumira svakodnevno diljem svijeta. Zbog zagađenosti okoliša, može biti kontaminirana teškim metalima te je stoga određivanje elementarnog sastava riže od iznimne važnosti za očuvanje ljudskog zdravlja. Glavni cilj ovoga rada jest odrediti utjecaj različite predobrade uzoraka riže na elementarni sadržaj te usporediti učinkovitost korištenih tehnika u određivanju sadržaja metala (TXRF-Mo, ICP-MS). Prikupljeni uzorak riže prije postupka mikrovalne digestije korišten je i) bez prethodne obrade, ii) nakon što se tri puta isprao s ultra čistom vodom, iii) nakon što je usitnjen u mlinu. Svi uzorci su nakon predobrade podvrgnuti postupku mikrovalne digestije te analizirani primjenom TXRF-Mo i ICP-MS. U svim ispitanim uzorcima određeni su slijedeći elementi: željezo, bakar, mangan, cink, stroncij i nikal. Dobiveni rezultati za sadržaj elemenata u uzorcima samljevene riže i riže tri puta isprane s ultračistom vodom uspoređeni su sa sadržajem elemenata u uzorcima riže bez prethodne obrade. Sadržaj analiziranih elemenata određenih s TXRF tehnikom usporediv je s rezultatima ICP-MS tehnike. U usporedbi s netretiranim uzorkom, rezultati analize su utvrdili da ispiranje zrna riže, za razliku od mljevenja, uzrokuje značajnije promjene sadržaja za sve određene elemente. Prethodna obrada uzorka je pokazala najveći utjecaj na sadržaj željeza, a najmanji na mangan. Unatoč tome, nije utvrđena statistički značajna razlika kod dodatne obrade uzorka te je stoga donesen zaključak kako predpriprema uzorka nije potrebna. Analiza TXRF tehnikom iziskuje vrlo male količine uzoraka i reagensa, proizvodi malo kemijskog otpada, ne iziskuje rashladne sustave i plinove te uključuje jednostavnu kvantifikaciju dodatkom unutarnjeg standarada što ju čini bržom, jednostavnijom te ekološki i ekonomski prihvatljivijom tehnikom od ICP-MS-a.Rice is consumed daily in large quantities all over the world. Due to environmental pollution, rice can be contaminated with heavy metals, which is why controlling the elemental composition of rice grains is extremely important for the preservation of human health. The main objective of this work is to determine the influence of different pretreatments of rice samples on elemental analysis and to compare the effectiveness of the techniques used to determine the metal content (TXRF-Mo, ICP-MS). The rice sample collected before microwave digestion was used i) without pretreatment, ii) after washing three times with ultrapure water and iii) after milling in a mill. After processing, all samples were subjected to microwave digestion and analyzed by TXRF-Mo and ICP-MS. The following elements were determined in all analyzed samples: iron, copper, manganese, zinc, strontium and nickel. The results for the content of elements in samples of milled rice and rice washed three times with ultrapure water were compared with the content of elements in samples of rice without prior treatment. The content of the elements analyzed with the TXRF technique corresponds to the ICP-MS element content. Compared to the untreated samples, the results showed that washing the rice grains, as opposed to milling, caused more significant changes in the content of all analyzed elements. The pre-treatment of the sample had the greatest influence on the iron content and the least on the manganese content. Regardless of this, no statistically significant difference was found with additional sample preparation, so it was concluded that pretreatment of the samples is not necessary. Analysis using the TXRF technique requires very small amounts of samples and reagents, generates little chemical waste, does not require cooling systems or gasses and involves simple quantification with internal standards, making it a faster, simpler and more environmentally and economically acceptable technique than ICP-MS