and F. T. JohnsonZ Oak Ridge Associated Universities Oak Ridge, T e n n k e e 37830
I
Determination of Nitrite in Meat Samples
Recent controversy concerning food additives has involved the use of sodium nitrite and nitrate a s color fixatives and preservatives in meat products.3.4 Although nitrate is not considered to be hazardous per se, its conversion t o nitrite b y many organisms is well known.5 Among the meat products often treated with sodium nitrite are frankfurters, bologna, spiced ham, Vienna sausage, and smoked salmon. Present regulations allow a s much a s 200 mg (as N a N 0 2 ) per kg of meat (200 ppm). Alarm regarding t h e use of these food additives stems from t h e possible reaction of nitrite with naturally occurring amines in the meat t o produce carcinogenic nitrosamines a n d from the interaction of nitrite a n d hemoglobin t o produce methemoglobin with loss of ability t o transport oxygen in the blood. T h e present naDer describes a colorimetric method for determining niirice in meat products. T h e procedure may he modified t o determine nitroeen dioxide for air nollution studies.6 T h e experiment should find application i n chem'To whom correspondenceshould he addressed. ORAU Research Trainee, Summer 1912, Morehouse College, Atlanta, Georgia. 3Archer, M. C., Clark, S. D., Thilly, J . E., and Tannenbaum, S. R., Science, 174,1341(1971). Sanders, H. J., Chem, and Eng News, 19 (July 12,1971). Wolff,I.A., and Wasserman, A. E., Science, 177,15 (1972). Stern, A. C. (Editor), "Air Pollution," Academic Press, New Y O I ~VOI. , n, 1968, p. 80. ABauseh and Lomb Spectronic 20 was used. 8This mixture is difficult to filter and the task is quite time consuming (up to 2 hr). For students to complete the analysis in one lab period, the lab instructor prepared the meat extract on the day previous to the students' analysis. Nitrite-free meat extract was "spiked" with known amounts of NaNOa at this point so that percent recovery and student accuracy could be determined.
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426 / Journal of Chemical Education
istry courses for nonscience majors a n d environmental chemistry programs. Experimental The colorimetric reagent is prepared by adding 5 g of sulfanilic acid to 140 ml of glacial acetic acid and diluting with 800 ml of distilled water. Add 20 mg of N-(l-naphthy1)-ethylenediamineto the solution and dilute to a final volume of I 1 with distilled water. A stock solution is orenared h dissolvine 25 me NaNO, in distilled water in a I M - m l ;,olum&ic flask n& dilu;ng to the mark wnh distilled water The stork solution is further drluted to give etandards w t h a cunrpnrration range of 2-15 ug ml. One rnillili. ter of standard solution is added to 10 ml of e&rimetric reagent, 15 min allowed for the color to stabilize, and the absorbance at 505 mp is measured7 against a blank containing 1 ml of distilled water and 10 ml of the colorimetric reagent. The absorbance readings are plotted against the concentrations of the resulting solutions. Beer's law is followed for the range of 0.1 to 1.5pg/ml. The NH&l buffer solution is prepared by adding 20 ml of concentrated HCI to 500 ml distilled water. Add 50 ml of aqueous ammonia (sp.gr. 0.880) and dilute to 1 I with distilled water. A 20-g sample of meat is macerated with 70 ml of hat distilled water (70°C) and 5 ml of NHICI buffer in a blender. The mixture is poured into a beaker, the blender rinsed with hot distilled water, and the rinsings added to the extract. The mixture is filtered through cheesecloth to remove coarse material and then filtered with suction through filter paper tapped with a layer of Celite.8 The extract9 is transferred to s 500-ml beaker, heated to 8TC and the pH adjusted to 6 + 0.5 (hydrion paper) with a saturated solution of potassium aluminum sulfate. The mixture is cooled to room temperature allowing coagulation of suspended matter and filtered with suction. The filtrate is transferred to a 250-ml volumetric flask and diluted to the mark with distilled water. One milliliter of the solution is added to 10 ml of the colorimetric reagent, and 15 min are allowed for the color to stabilize. The ahsarhance is read at 505 mp against a blank, and the coneentration of diluted extract is determined from the Beer's law plot of
Table 1. Recovery of Nitrlte from Mean Extracta
NaNOz added
NaN02 found
Percent
Table 2. Student Data Corrected for 82.5% Recovery
NaN02 concentration (pdml) 14.0
4.0 3.0
3.20 1.91
Mean
80.0 63.7* 82.5
NaNO* found (pglml) 11.8 11.8 11.6 12.0 11.8 12.1 s.d. 0.2
NaNOa corrected (pgfml) 14.3 14.3 14.1 15.5 14.3 14.7
Percent error 2 2 1 11 2 5 mean 4 5 3 4 5 4 1 10 10
See footnote 9. Lar e losses were encountered below initial concentrations of 4pgfmf. This value was not used in calculationof the mean. a
0
ppm in meat sample 179 179 176 194 179 184
mean 5
the standard solutions. The concentration of nitrite (as NaN02) of the original meat sample is calculated inpglg (ppm). Results and Discussion
Table 1 gives the data for 9 independent determinations by the laboratory instructor. For a concentration range from 4 to 20 irg/ml in the diluted extract the mean recovery was 82.5%. This figure was used by the students to correct their values for losses during the procedure. When concentrations were below 4 #g/ml, recoveries were well below 82.5%. Table 2 gives students' data obtained on repeated analyses of two "unknowns." Both the precision and accuracy of the determination indicate that students can perform the analysis quite satisfactorily. Single determinations by students are given in Table 3. It should be noted that a t concentrations below 4 &g/ml in
Table 3. Student Data for Single Determinations (Corrected)
NaN02 concentration (palml)
NaN02 found (ualml)
NaNOs corrected (ualml)
Percent error
ppm in meat sam~le
the extract, the recovery falls drastically below 82.5% and the error in analvsis is corres~ondinelvlaree. The authors k i s h t o express their appreciation to the participants in the ORAU Trace Analysis Institute during the summer of 1972 for obtaining the data presented in Tables 2 and 3.
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Volume 50, Number 6, June 1973
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