Magnesium Acetate as an Ashing Agent in Fluorine Analysis WILLIAM E. CRUTCHFIELD, J R . Kettering Laboratory of Applied Physiology, College of Medicine, University- of Cincinnati, Cincinnati, Ohio
I
oxide was determined to be 20 * 2 per cent. C:siny the amounts of magnesium oxide derived from magnesium peroxide and magnesium acetate tetrahydrate as a basis, the amount of magnesium acetate necessary to fix all the fluorine present was established. Comparative studies were then undertaken on identical samples. I n order to establish the eficacy of recovery of known amounts of fluorine with magnesium acetate, six urine samples were selected, the fluorine present was determined, and varying amounts of fluorine were added to each sample. Although the added amounts of fluorine varied from 20 to 100 micrograms, 100 per cent recovery was secured in every case (Table I). Since these results were promising, 20 food samples were selected and duplicate analyses performed on each; the technique used was the same as for the urine samples except that 7.5 ml. of 60 per cent magnesium acetate tetrahydrate were substituted for 1.5 grams of magnesium peroxide per 150 grams of macerated mixed food samples (Table 11). To check the reproducibility of duplicate analyses, 44 food samples were selected and divided into two sets of 22 samples each; one ..et mas analyzed in duplicate with magnesium per-
N SEARCHISG for a suitable reagent to use in ashing
organic materials for the determination of small amounts of fluorine it became apparent that any compound to be acceptable must have certain properties: It should have a greater alkalinity than pH 11.00, to prevent the loss of fluorine compounds that are volatile in acid solution; it must form a basic matrix to forestall “fluffing” and loss of ash through handling; and it must be capable of forming completely homogeneous mixtures to ensure even suspension in such semisolid substances as may be encountered-e. g., macerated food samples. OF ADDEDFLUORISE TABLEI. RECOVERY
Urine Sample
F Present in
F Added a s
Sample
KaFa
i
0.260 0.197 0.143 0.188 0.241 0.138
M Q
2 3
! 6
.
MQ. 0.020 0.020 0.060 0.060 0.100 0.100
T o t a l F Recovered MQ.
0.281 0.21s 0.201 0.244 0.343 0.238
The literature suggests several compounds which are un,questionably satisfactory for use when the minimum amount of fluorine encountered is in excess of 0.005 gram ( 1 ) . Unfortunately, however, all such compounds were found t o contain fluorine in concentrations ranging from 12 to 60 micrograms per gram of material. Since the total quantity of fluorine in samples such as tlioae represent’ing a 24-hour fluid intake, 24hour food intake, or 24-hour urine output is often less than 100 micrograms, in niaiiy instances the blank values for these ashing agents would contribute a larger amount of fluorine than that present in the sample, and in 25 per cent of the cases there would be a possible source of error in excess of 40 per cent (Tables 111and IT). This is particularly true in s ~ 0.1 the case of aliquot samples of food that contain 1 ~ than mg. of fluorine. Magnesium peroxide (AIallinckrodt’s snulytical reagent grade, Control Series JHTI) was used as reagent 11-it11 fair success for some 2000 analyses. Samples representing a 24hour fluid intake, 24-hour urine output, and 24-hour fecal excretion gave analytical results which checked excellently. Difficulty was encountered, however, in the aixtlysis of food samples by the aliquanting method reported by Largent, (2). It was found on occasion that identical quantities of material showed variations amounting t o as much as 40 per cent (Table 111), and in many inst’ances from two to five rechecks were needed to establish the aniount of fluorine actually pres.ent. Because it confornied to the requirements for an ashing agent of this type, magnesium acetate was suggested as a substitute for magnesium peroxide (3, 6). I’reliminary analyses proved that c. P. magnesium acetate, prepared from electrolytic magnesium and obtained from one source (Coleman and Bell, Cincinnati, Ohio) was practically free from fluorine. Other sources of this chemical have not been inrest’igated. For the purpose of simulating experimental conditions as nearly as possible, solutions of magnesium acetate were prepared over a range of concentrations sufficient to cover anticipated reqiiireinente and the calcined yield of magnesium
TABLE 11. RESULTS OF DUPLICATE ANALYSES Food Sample 1 2 3 4
5
6 6
9 10
11 12 13 14 15 16 17 18 19 20
MQ.
F Found with MgAc .\f Q .
0.147 0.104 0.081 0.058 0.093 0.129 0.084 0.156 0.139 0.136 0.154 0.068 0.211 0.119 0.147 0.099 0.121 0.091 0.198 0.183
0.125 0.108 0.094 0.073 0.082 0.112 0.068 0.142 0.132 0.147 0.174 0.067 0.193 0.124 0,129 0.083 0.135 0,101 0.176 0.203
F Found with AIgO2
TABLE111. DUPLIC-lTE FLUORIXE DETERMISATIO~YS (MgOz a s ashing agent) Food Sample Fluorine Found No. hliquant I hliquant I1 -4verage 1
2 3 4 5
s
9 10 11 12 13 14 15 16 17 18 19 20 21 22
57
0.180 0.144 0.180 0.166 0.096 0.19i 0.152 0.102 0.178 0.320 0.170 0.157 0.189 0.189 0.119 0.071 0.060 0.079 0.146 0.090 0.264 0.250
0.14s 0.166 0.147 0,260 0.066 0.167 0.176 0.107 0.159 0.227 0.202 0.116 0.169 0.168 0.158 0.056 0.161 0.116 0.116 0.078 0.184 0.182
0.164 0.155 0.163 0.213
0.081
0.182 0.164 0.104 0.168 0.273 0.186 0.177 0.179 0.179 0.138 0.063 0.110 0.096 0.131 0.084 0.219 0.216
variation
0.032 0,022 0.033 0.094 0.030 0,030 0.024 0,005 0.019 0.093 0.032 0.041 0.020 0.021 0.039 0.015 0.101 0.037 0.030 0.012 0.070 0.068 Av. 0.040
19.5 14.4 20.1 44.2 27.0 16.6 14.2 4.8 11.3 34.2 17.2 23.1 11.2 11.7 28.3 23.9 Y1.5 38.4 22.9 14.3 31.9 31.4 26.0
INDUSTRIAL AND ENGINEERING CHEMISTRY
58
TABLEIV. DUPLICATE FLUORINE DETERMINATIONS [Mg(CzHaOz)z,4HzO as ashing agent] Food Sample Fluorine Found So. -4liauant I Aliauant I1 Average Variation 1 2 3
4 5 6 7 S
9 IO 11 12 13 14 15 16 17
IS 15
20 21 22
0.129 0.084 0.156 0.139 0.136 0.164 0.068 0.107 0.050 0.139 0.075 0,056 0.087 0.075 0.092 0.066 0.048
0.082 0.117 0.116 0.092
0.083 Av 0 . 0 9 7
0.112 0.064 0.142 0.132 0.140 0.174 0,067 0.107 0.04i 0.139
o.09n 0.053 0.084 0.073 0.106 0.070 0,047 0,076 0.094
0.120 0.100 0.082 0 097
0,120 0.074 0.149 0.133 0.138
0.017 0.020 0.014 0 .O O i 0.004
0.169 0 . ntji 0.10i
0.010 0.001 0,000
0,048
0.003 0.000 0.015 0.003
0.138 0 . 082 0.054 0.08n 0 . Oil 0 . OO!) 0 ,068
0.04T OGY 0.10ci
n
0.122 0 096 0.082 0 097
0,003
0 . on2 0.014 0.004
0.001 0.014 0.023
n.oix
0.OOh 0.001 0 008
14.1 36.9 5.4 5.1 2.5 5.9 1.4 0.0 6.3 0.0 18.3 5.6 3 . ;r 2.7 14.1 5.9 2.1 20.0
21.3 10.6 8.3 1.2
Method A duplicate of the food consumed in each 24-hour period is collected in glass-topped, quart-size, fruit jars. The composite sample is ground in a household electric mixer with grinding attachment, the met weight is determined, and the ashing agent is added. If magnesium peroxide is employed, 1.0 gram per 100 grams of wet food is added; if magnesium acetate (60 per cent aqueous solution), 5 ml. per 100 grams. Mixing is continued for 0.5 to 1.5 hours, depending upon the size and character of the sample. Two 150-gram aliquants are weighed into 200-ml. nickel evaporating dishes, dried on an electric burner, and then placed in the automatically controlled electric muffle furnace, set at 570’ C. After complete combustion, the ash is weighed and prepared for distillation. The fluoride is separated from the ash by distillation with perchloric acid according to MacIntire and Hammond’s ( 4 ) modification of the method of Willard and Winter (6). Silver sulfate, as recommended by McClure (3),is added to the ash to prevent volatilization of the fluorides. The back-titration method of Dahle, Bonnar, and Wichman (1) is employed from this point on; the unconcentrated distillate is used.
3.2
oxide as the ashing agent (Table 111),and the other likewise with magnesium acetate (Table 117). The results might give the unwarranted inference that determinations made with magnesium peroxide gave higher fluorine values in comparable samples. Actually the two sets of samples differed in their fluorine content, their variability in this respect being in no wise unusual. (Experience has shown that considerable variability occurs from week to week as a n expression both of dietary selection and of differences in tile fluorine content of the same articles obtained at different seasons and from different localities.) It is obvious from Tables 111and IV that the use of magnesium acetate has increased the reproducibility of the results not only on samples of low fluorine content but also over the entire range of quantities dealt with.
Vol. 14, No. 1
Conclusions Comparative results indicate that magnesium acetate can be used advantageously in ashing organic materials in preparation for fluorine analysis. Since the blank is negligible, good results can be obtained when fluorine is present in either high or low concrntrations. The reagent can be handled in solution, thus saving the time required to weigh solid agents.
Literature Cited (1) D a h h D., Bonnar, R. U.,and Wichman, H. J., J . Assoc. Oficial Agr. Chem., 21, 459 (1938). (2) L ~E. J., ~ ~ cHEM., ~ ~ En., 3,~93 (1931). . , , (3) McClure, F.J., I b i d . , 11, 171 (1939). (4) MacIntire, W.H., and Hammond, J. W., J . Assoc. Oficial Chem., 22, 231 (1939). ( 5 ) Willard, H. H., and Tvinter, B., IND. ENQ. CHEM., ANaL. ED,, 5, 7 (1933). (6) Winter, 0. B., J . Assoc. OficinE Agi. Chem., 19, 359 (1936).
Determination of Hydrazine J
A Rapid Ferricyanide-Ceriometric Method C. J. DERNRACH’ WITH J. P. MEHLIG, Oregon State College, Corvallis, Ore.
C
ERIC sulfate as a standard oxidant in titrimetry has
been used more and more in the last few years, partly because of the availability of a n increasing number of good reversible redox indicators (9). The many advantages of this reagent-its extreme stability, simplicity of chemical change, and use in hydrochloric acid solution-make it far superior to potassium permanganate, and in many respects to potassium dichromate. There are many different methods in the literature for the determination of hydrazine. Ray and Sen (IO)were the first to determine the quantitative relationship between hydrazine and alkaline ferricyanide solutions. The reaction proceeds as follows:
They made this reaction the basis for a gasometric method for the determination of hydrazine. The reaction was found to take place without the formation of ammonia, as is the case when many oxidizing agents react with hydrazine. Cuy and Bray (6) Present address, Electro Metallurgical Sales Corporation, Xiagara Falla, x. Y. 1
showed that the oxygen error is negligible it the alkali is added after the ferricyanide. They determined conclusively that in alkaline solution it is the atmospheric oxidation of the hydrazine that produces a weakening of the solution and not the decomposition of the hydrazine. They also su gested a titrimetric method for hydrazine, in which excess of standard potassium ferricyanide solution is added to the alkaline hydrazine solution and the excess ferricyanide determined iodometricnlly. However, since several more rapid methods were available, they did not recommend this procedure for the determination of hydrazine. Benrath and Ruland (2) state that hydrazine is oxidized by ceric sulfate to nitrogen and ammonia according to the following equation: 2Ce (SO& 2N2H4 +NZ (SH4)2SOc Cez(S04)a
+
+
+
However, Lang (8) determined hydrazine and hydrazoic acid together by adding an excess of standard ceric sulfate solution, treating the excess with an excess of standard arsenious acid, and completing the titration with standard ceric sulfate. The hydrazine was then determined in a separate sample by the iodine cyanide procedure. The purpose of the present work was to develop a simple method for the determination of hydrazine by making use of potassium ferricyanide and ceric sulfate. The method con-
