A study was made from the basic viewpoints of determination of cadmium in rice (especially in unpolished and polished rice) by atomic absorption spectrophotometry after ashing samples at low temperature by means of exited oxygen plasma. Unlike the conventional ashing methods, low-temperature ashing method made it possible to retain Cadmium (Cd) almost completely without its volatilization, thus we have obtained 97.2% in average recovery from the experiments by the addition of Cd to the polished rice, and in the following atomic absorption analysis we have found an excellent linear relation in the calibration range from 0.05 to 1.5ppm in concentration.
In the previous paper dealing with the thin layer chromatography of EDTA, it was shown that EDTA was identified in the presence of α-amino acids, but this method could not be applied to the determination. In the present paper, gas-liquid chromatographic detection and determination of EDTA in foods after methyl esterification is described. Methanolic hydrochloride was a suitable reagent for methyl esterification of EDTA but diazomethane and trifluoroborone unsuitable. The sample was dehydrated under vacuum, added methanolic hydrochloride and heated for two hours under reflux. After cooling same volume of water was added to the reaction mixture and then washed with ethyl acetate, neutralized by a saturated solution of sodium bicarbonate and extracted with chloroform. The chloroform solution was condensed to suitable volume on water bath and the concentrate was injected for the gas chromatography. Diphenyl phtalate was used as an internal standard. gas chromatography: Shimazu GC-3AF (FID) column: 5% QF-1 (Gas-chrom Q, 60/80 mesh) 4mm×108cm glass tube 5% OV-1 (Gas-chrom Q, 60/80 mesh) 3mm×150cm stainless steel tube
Cyclamate in liquid foods were extracted with ethyl acetate, after the samples were saturated with magnesium sulfate subsequently to acidification with 10% sulfuric acid. Ethyl asetate was removed from the extracts under reduced pressure, and the residue was dissolved in a small portion of ethanol. Solid foods were homogenated with water, and cyclamate was dialyzed using a cellulose tube or a collodion tube, and the outer solution obtained by dialysis was treated in the same manner as liquid foods. The ethanol solution was spotted on a silica gel plate, and developed with a mixture of benzene, ethyl acetate and formic acid (10: 7: 3). The developed plate was sprayed with a solution of 2% o-tolidine in ethanol and 1% hydrogen peroxide solution, and then placed in an oven at 40°C. After 10 minutes, cyclamate appeared as a blue spot. Saccharin was also detected as a blue spot, however, both could be identified from each other by their Rf values (cyclamate: 0.54; saccharin: 0.80). Other substances, preservatives, antioxidants, coal-tar colors and amino acids, could be separated from cyclamate.
The method presented in the previous paper (J. Food Hyg. Soc. Japan, 8, 345, 1967) was applied to detection and determination of sodium cyclamate in various foods. The cyclamate in food was reacted with nitrous acid, and cyclohexyl nitrite produced was extracted with n-hexane, and then injected to a gas-liq. chromatograph. The recoveries of the cyclamate added in various foods were shown in Table 1. The recoveries from some kinds of foods in the reaction at room temperature (22°C) were better than that of in ice water (Table 2) and decreased as lower contents of the cyclamate in them (Fig. 4). Therefore, the detection limits in these kinds of foods were higher than that obtained in a water solution of cyclamate (Table 3). We could find that this method was applicable to detect cyclamate in various foods with good results more than in the range of 10-50ppm, and this method will be applied to the determination of cyclamate in the many kinds of foods.