Application of atmospheric pressure microwave digestion to total Kjeldahl nitrogen determination in pharmaceutical, agricultural and food products

Abstract

Abstract. The kinetics of Kjeldahl's digestion for nitrogen determination was compared between microwave and classical heating conditions. Various parameters (micr owave power, concentrations, time) of micr owave digestion were studied in order to define the optimal digestion conditions. Finally, the Kjeldahl's analysis of nitrogen using microwave digestion was applied to various pharmaceutical, agricultural and food products. Key words.Microwave -Kjeldahl -nitrogen -digestion. Analusis, 1998, 26, 205-209 © EDP Sciences, Wiley-VCH Article available at http://analusis.edpsciences.org or http://dx.doi.org/10.1051/analusis:1998133 digest because of the high nitrogen concentration 32.18 g per 100 g. Classical procedureAccording to the french standard method AFNOR [12][13][14][15], 0.2 g of the sample was added to 20 mL of sulphuric acid and 2 g of a catalyst (composed of 1 g of selenium, 10 g of CuSO 4 and 100 g of K 2 SO 4 ). The digestion is the principal phase in the protocol and takes several hours. The success of the analysis depends on the efficiency of this digestion process. It must be conducted with the highest rigour and it is necessary that all the nitrogeneous forms are transformed into ammoniacal nitrogen. The digestion was carried out using an electrical heating block "Büchi 430". The distillation stage allows to shift the ammoniac from the digestion solution to a boric acid solution using a distillation block "Büchi 315". Finally, titration gave the nitrogen concentration of the analysed samples. Microwave procedureMicrowave digestion was reached at atmospheric pressure in a Prolabo Maxidigest 350 monomode microwave oven cavity operating at 2.45 GHz with a power range from 0 to 300 watts. The borosilicate reactor has a capacity of 20 to 150 mL. The incident microwave power is controlled with a programmer which allows to work with one or several steps of microwave incident power according to the durat i o n expressed in minutes [1].A microwave digestion protocol was adopted from several scientific works in this field [8][9][10]. First, the sample was mixed with 20 mL of sulphuric acid without heating. Then, microwave carbonisation of the organic matrix was carried out. The carbonisation duration represents 80 to 90% of the digestion time. After that , hy d rogen peroxide wa s added without heating. Finally, microwave oxidation permits the destruction of the most resistant molecules. This step represents only 20% of the total duration.Microwave digestion was conducted without a catalyst or antifoaming agent, to avoid pollution problems and to reduce chemical reagents. The hydrogen peroxide was selected as an oxidant agent to complete the digestion [3,10]. At the end, the solution was distilled then proportioned according to the standard method AFNOR. The degree of nitroge n rep o rted in this study is given from the ave rage of thre e identical tests. Results and discussion Kinetic study of the arginine digestionThis kinetic study has been realised following the degree of nitrogen during the arginine ...

Focused microwave-assisted digestion of vegetal materials for the determination of essential mineral nutrients

“…However, P1, P3, T3, and H 2 O 2 volume are the most significant factors for N, P, K, and Mg recoveries. A 2 4 factorial ( Table 2, runs [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19] was then performed to evaluate the factors as well as the interactions. Results from an ANOVA test showed no significant effects (p>0.05) on Mg, K, and P recoveries, whereas P1 T3, P3, and P1*T3 have a significant influence (p<0.05) on N recovery.…”

“…Many microwave-assisted digestions have been reported depending on the kind of sample and the element to be determined [5,6,7,8]. The microwave digestion most frequently described for mineral elements in plants uses nitric acid as oxidant [9,10,11], but if nitrogen is determined, samples have to be digested with sulfuric acid [12,13]. In recent years, the laboratory of the Estación Experimental del Zaidín has been engaged in various nutritional and environmental studies where the determinations of N, P, Ca, Mg, K, Fe, Cu, Mn, and Zn in numerous vegetal samples were requested.…”

An Intelligent Detector for Sensing Pork Freshness In Situ Based on a Multispectral Technique

“…Therefore, judging the freshness of fresh pork based on TVC and TVB-N content is increasingly valued by producers and consumers. Traditional detection methods based on physicochemical and biological analyses, such as the Kjeldahl method [ 5 ] and colony counting method [ 6 ], can achieve accurate measurements, but they are time-consuming and destructive. It is thus difficult to meet the needs of producers and consumers for rapid on-site non-destructive detection.…”