RAPID PHOTOMETRIC DETERMINATION OF NITRITES IN FOODSTUFFS BY ITS COLOR-FADING REACTION WITH METHYL ORANGE

It was found that in a dilute acetic acid solution,fading of the color of methyl orange was observed due to its reaction with nitrite ion under room temperature.The optimum condition of this color-fading reaction was tested and a new photometric method for the determination of nitrites in foodstuffs was proposed.The photometric measurements made either at 416 nm or at 506 nm gave consistent analytical results.Linear relationships between the decrease of color intensity of methyl orange(ΔA) and the concentration of nitrite ion were found in the range of 5.0-600.0 mg·L~(-1) with its molar absorptivity of(e_(416)) 1.1×10~4L·mol~(-1)·cm~(-1) and in the range of 1.0-(300.0 mg·L~(-1)) with its molar absorptivity of(e_(506)) 5.2×10~4L·mol~(-1)·cm~(-1).The linear regression equations and correlation coefficients were found as follws: ΔA_(416)=0.000 344 6 c+0.002 23,r=0.999 6,ΔA_(506)=0.000 147 c+0.021 02,r=0.985 3.Detection limits were found to be 5.0 mg·L~(-1) and 1.0 mg·L~(-1) at 416 nm and 506 nm respectively.In its application to the analysis of 5 foodstuff samples,results obtained were in consistency with the results obtained by the standard method given in GB/T 5009.33-1996,and the RSD′s and recoveries found were in the ranges of 0.2%-4.2% and 98%-103% respectively.