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Magnetic nanoparticles (NPs) have attracted great attention owing to their applications in the biomedical field. In the present work, maghemite (γFeO) NPs of 6.5 nm were prepared using a sonochemical method and used to prepare magnetic beads through silanization with 3-aminopropyltrimethoxysilane (APTS). Subsequently, amino groups in the resulting APTS-γFeO beads were converted to carboxylic acid (CARB-γFeO) through the succinic anhydride reaction, as confirmed by transmission electron microscopy (TEM), Fourier transform infrared spectroscopy and dynamic light scattering (DLS) measurements. The size of these beads was measured as 12 nm and their hydrodynamic diameter as 490 nm, using TEM analysis and DLS, respectively. The CARB-γFeO beads were further functionalized by immobilizing rabbit antibodies on their surfaces; the immobilization was confirmed by flow cytometry and ionic strength. The samples were further characterized by Mössbauer spectroscopy and DC magnetization measurements. Studies on magnetic relaxivities showed that magnetic beads present great potential for application in MR imaging.

In this contribution we propose, for the first time, the use of Methylene Violet 3 RAX dye for the detection and determination of nitrite in cured meats and vegetables. Quantification is based on the decrease in absorbance of the dye, which is proportional to the nitrite concentration. The proposed method presents linear response (r > 0.99) in the range from 1.8 to 9 μmol L -1 of nitrite, with a limit of detection of 0.14 μmol L -1 . Satisfactory accuracy with the official Association of Official Agricultural Chemists (AOAC) method was achieved, and the method was successfully applied to a wide range of cured meats and vegetables. The proposed method offers similar or superior performance to other optical methods used for the determination of nitrite in different matrices, with advantage in terms of reduction of chemical waste for each analysis, by minimizing amounts of reagents and products.Keywords: nitrite, food analysis, cured meat, spectrophotometry, Methylene Violet 3RAX IntroductionNitrite was first recognized as an active component in the meat curing process at the end of the 19 th century. 1The presence of nitrite as an impurity in salt resulted in an attractive red color in cured meats such as bacon, ham, and sausages, and also enhanced the flavor. 2 Moreover, nitrite is widely recognized to protect against Clostridium botulinum spores, assisting in the prevention of botulism.3 In addition to cured meats, nitrogen species occur naturally in vegetables consumed by humans. The nitrate ion is the main species present, because plants take up nitrogen from the soil in this form. Nitrates can be reduced to nitrites due to the action of bacteria. 4It is well known that once in the stomach, nitrite can react with secondary and tertiary amines to form N-nitroso compounds.5 Exposure to N-nitrosamines shows a strong association with increased risk of gastric and esophageal cancer. 6 In addition, nitrite ions oxidize iron atoms in the hemoglobin of red blood cells, forming methemoglobin, resulting in decreased oxygen carrying capacity of the blood and leading to the disease known as methemoglobinemia. 7High concentrations of nitrite in drinking water can be hazardous to health, especially in the case of infants and pregnant women. Due to these toxic effects, agencies worldwide regulate the nitrite content of foods. An acceptable daily intake (ADI) for nitrite of 0-0.07 mg kg -1 body weight per day was established by the Joint FAO/WHO Expert Committee on Food Additives (JECFA). 9 The Brazilian National Health Surveillance Agency (ANVISA), the federal regulatory agency responsible for the monitoring of food additives in Brazil, has established a concentration limit for nitrite in cured meats of 150 mg kg -1 . 1529 Vol. 28, No. 8, 2017 electrochemistry. 6 Separation techniques (i.e., high performance liquid chromatography and capillary electrophoresis) provide suitable sensitivity, however they are usually time-consuming, laborious and require bulkiness and expensive instruments. Electrochemical methods generally s...