B
= coefficient of axial or longitudinal diffusion in gas phase of resistance t o mass transfer in liquid phase coefficient of resistance to mass transfer in moving gas phase diffusion coefficient of sample into carrier gas a t column outlet pressure, sq. em. see.-' diffusion coefficient of sample into column liquid phase, sq. cm. see.-' effective liquid film thickness, em. effective moving-gas diffusional path length, cm. effective stagnantcgas diffusional path length, cm. coefficient of relatively stagnant gas within column packing
D
=
Do0 =
DC dl
=
=
dm = d.
=
E
=
fi=
1°F (a)2
average HETP = em. = effective length of column packing, cm. pi = column inlrt absolute pressure, atm. P o = column outlet absolute pressure, atm. sa,= relative separation of sample peak from air peak =
L
t.
I.
Table
c = coefficient
A , Cm. 0.008
Results of Evaluation of Coefficients
c
B
1.16
di 2 Sec. Dl, 0.00566
Sq. Cm.
D dm',
E ds2, Sq. Cm.
0.000182
0.000576
Contribution of Individual Terms to
Sample Air Butane Cyclohexane
A 0.008
0.008 0.008
B 0.026 0.021 0.016
elution time of air, see. width of peak, measured between base fine intercepts of tangents to inflection points of peak, sec. u. = carrier gas velocity a t outlet of column packing, em. see.-'
t, t,
= =
LITERATURE CITED
(1) Deemter, J. J. van, Zuiderweg, F. J., Klinkenberg, A., Chem. Eng.Sci. 5, 271
(1956).
C 0
0.014 0.003
R Optimum, Cm. D E 0 0.005 0.013
0.026 0.003 0.000
(2) Jones, W. L., Gas Chromatography Symposium, U. S. Public Health Service, Cincinnati, Ohio, Feb. 21, 1957. (3) Jones, W. L., Southwide Chemical Conference, ACS-Instrument Society of America, Memphis, Tenn., Dec. 6, 1956. RICHARD KIESELBACH Engineering Research Laboratory Engineering Department E. I. du Pont de Semours & Co., Inc. Wilmington, Del. RECEIVEDfor review April 4, 1960. Accepted April 18,1960.
Determination of Primary Nitroparaffins by the Nitrous Acid Reaction SIR: The determination of nitroparaffins and particularly of primary nitroparaffins was reviewed recently (3). -4 spectrophotometric method for determining microgram quantities of primary nitroparaffins by coupling with diazotized sulfanilic acid was described ( 3 ) . I n the course of investigating the gas-phase products of olefins and nitrogen oxides ( I ) , the reactions of some representative members of various classes of nitroparaffins with nitrous acid also were measured. This type of reaction goes back to the classical red, white, and blue reaction of Meper and Locher (4). The blue reaction of nitrous acid with secondary nitroparaffins was investigated as a colorimetric procedure (8). I n the present work the nitrous acid reaction with primary nitroparaffins is of immediate interest, but the reactions of secondary nitroparaffins, dinitroparaffins, and a variety of nitroalcohols also are measured. EXPERIMENTAL
Nitro Compounds. T h e sources and purities of t h e nitroalkanes used were discussed previously (3). The 2nitro-1-butanol and 2,2-dinitropropane
were obtained from K & K Laboratories, Jamaica, N. Y. The 2-nitro-2-methyl1-propanol, 2-nitro-2-methyl-1,3-propanediol, 2-nitro-2-ethyl-l,3-propant diol, and tris(hydroxymethy1)nitromethane were provided by Commercial Solvents Corp. Procedure. To 2 ml. of a n aqueous solution of t h e sample containing t h e nitroalkane, a d d a b o u t 0.1 gram (one pellet) of potassium hydroxide t o ensure solution; then a d d 0.25 gram of potassium nitrite and 0.6 ml. of 1 8 N sulfuric acid. Shake this solution with 10 ml. of diethyl ether and separate t h e layers, saving t h e ether layer. Add 3 ml. of water and 4 or 5 drops of saturated sodium hydroxide solution to the ether layer, shake, and transfer the aqueous layer to the absorption cell. Read the absorbance a t 330 mp 5 minutes after mixing. RESULTS AND DISCUSSION
The final alkaline aqueous extract of 1-nitropropane has a n absorption band a t 330 mp. This absorption results from the formation of sodium propylnitrolate. Sodium ethylnitrolate has been reported to have a n absorption a t 325 m l with a molar absorptivity of about 7500 mole-' liter em.-' (6).
I n the present work, the absorbance of the propylnitrolate anion was found to be linear with concentration of l-nitropropane from 2 to a t least 50 y per rnl. The absorptivity was 0.054 =t0.006 y-' ml. em.-', corresponding to a molar absorptivity of about 6300 mole-' liter em.-'. Sodium propylnitrolate decomposes slowly with time as do the other alkylnitrolates (6). Because the decrease in absorbance amounts to 10% in the first
Table 1. Absorptivities of a Number of Aliphatic Nitro Compounds
Absorptivity, a, Y-'
Compounds 1-Kitropropane 2-Kitropropane 2,2-Dinitropropane 2-Nitro-1-butanol 2-Nitro-2-methyl-1-propanol 2-Xitro-2-methyl- 1,3propanediol
bll. Cm.-'
diol Tris(hydroxymethy1)nitromethane
0.04
2-Nitro-2-ethyl-1,3-propane-
VOL. 32, NO. 7, JUNE 1960
0.054
0.008 0.00
0.035 0.002 0.05
0.025
881
half hour, it is desirable to read the absorbance within 10 minutes. However, as the rate of decrease is slow, with appropriate calibration, readings after 30 minutes or even after a longer period may be possible without a prohibitive loss of sensitivity. The reaction of nitrous acid with primary nitroparaffins gives solutions with red-orange or red-brown colors of low intensity. These colors result from far weaker absorption in the visible spectrum than that found a t 330 mp. The blue color resulting from the reaction of nitrous acid Kith secondary nitroparaffins also is of low intensity, as shown previously (8). Consequently, the visible absorption observed is not usable in making determinations in the microgram range. The present method for 1-nitroparaffins is somewhat more sensitive than the previous method involving coupling ivith p-diazobenzenesulfonic acid ( 3 ) .
It is better than a n order of magnitude more sensitive than the method of Scott and Treon ('7). Interferences were determined for a number of other aliphatic nitrocompounds. These compounds and their approximate absorptivities in y-l ml. em.-' a t 330 mp are listed in Table I. Although interference from 2-nitroalkanes and 2,2-dinitroalkane is small, most of the nitroalcohols do have appreciable absorbance a t 330 mp. 2Kitro-1-butanol has an absorption maximum a t about 330 m p and another maximum a t 285 mp. 2-Kitropropane also has a weak maximum a t 285 n ~ p . Kitrolic acids have been re1,oited as the products of the nitrosation of primary amines ( 2 , 6). Consequently, the same reaction possibly could be used for the analysis of primary amines. Conversely, primary amines as well as large amounts of secondary amines, if present, also will interfere with the
analysis of the primary nitroparaffins (2, 6). LITERATURE CITED
(1) Altshuller, A. P., Cohen, I. R., Ind. Eng. Chem. 51, 776 (1959). (2'1 . . Clark, S. J., Norgan. D. J., Jfikrochem. .&tu 1956, 96g (\ 3- ), Cohen. I. R.. Altshuller. A. P..ASAL. CHEY.31, 1638 (1959). ' ( 4 ) Meyer, V., Locher, J., Ber. deut. chem. Ges. 8, 219 (1875). (5'1 ~, 3Iorgan. D. J.. Mikrochim. Acta 1958, 104. (6) Mornan. D. J.. J . Baal. Chem. I
,
A . P. ALTSHULLER
I. R. COHEN
Air Pollution Engineering Research Robert A. Taft Sanitary Engineering Center Cincinnati 26, Ohio
Removal of Molybdenum in Analysis of Uranyl and Other Phosphates SIR: K i t h modification of the universally used hydrogen sulfide method for removal of molybdenum (6) some complex phosphate minerals can be completely analyzed faster and with smaller samples than before. The author has performed several complete phosphate analyses using this method with satisfactory results (2-5). This paper redescribes the method, introduces some changes, and shows that it is adaptable for complete uranyl phosphate analysis (autunite). PROCEDURE
Five hundred milligrams of the phosphate is dissolved by digesting on a water bath with nitric and hydrofluoric acids (Teflon crucible) or aqua regia, or if insoluble in these, by treating with 1 to 3 ml. of concentrated sulfuric acid on a sand bath in a covered platinum dish.
A 5- to 15-minute treatment in hot fuming sulfuric acid usually makes the phosphate more easily soluble in hot nitric acid. Longer treatment should be avoided, but if the platinum dish is covered so that no large amounts of sulfur trioxide fumes escape, phosphorus pentoxide losses are negligible. Short fuming with sulfuric acid also expels hydrofluoric and hydrochloric acids, which impair the precipitation of ammonium phosphomolybdate. If sulfuric acid is used, calcium or strontium present in many phosphates \\-ill cause serious difficulties during the later part of the analysis, making it necessary 882
ANALYTICAL CHEMISTRY
to precipitate calcium in oxalic acid solution before precipitation of aluminum as aluminum hydroxide and before removal of molybdenum. If sulfuric acid is added, all precipitations must be repeated at least twice. Molybdenum cannot be removed in this case in nitric acid solution without partly precipitating calcium sulfate. Phosphorus is precipitated as ammonium phosphomolybdate from s;iproximately 130 ml. of solution {approximately 100 ml. of slightly acid (nitric acid) solution of the dissolved mineral 20 ml. of concentrated nitric 10 ml. of concentrated ammoacid nium hydroxide]. The precipitate is allowed t o settle for 4 to 5 hours (better overnight) and is washed by decantation five to six times with 5y0 ammonium nitrate solution made slightly acid with nitric acid. The combined filtrates and wash solutions are evaporated on a water bath, preferably using a n infrared lamp, until a hard crust of molybdic acids, HzMo04.Hz0 (canary yellow) and H2Mo04(white needles) ,is formed on the bottom of the beaker and the ammonium nitrate starts to crystallize out. The ammonium nitrate-saturated liquid is slightly diluted with hot distilled water and immediately filtered through a medium-porosity filter. The yellow crust is crushed with a glass rod and washed three to four times with small amounts of solution containing approximately 1% nitric acid and 5y0 ammonium nitrate. The filtrate contains all the cations free from phosphorus and some molybdenum. The molybdic acid crust is dissolved in ammonium hydrox-
+
+
ide and boiled until very slightly ammoniacal. If any precipitate forms, it is washed with 2% ammonium chloride solution, dissolved, and added to the filtrate. The rest of the molybdenum is precipitated in the customary way as molybdenum trisulfide after the nitrates have been destroyed. After removal of molybdenum, the usual procedure is followed (6), taking into account that a complete analysis is to be done. Because it is difficult to decompose acetic, citric, and tartaric acids with nitric acid, their addition must be avoided if the alkali metals are to be determined. Cations other than ammonium ion and sulfuric and phosphoric acids must also be avoided. Oxalic acid can be easily decomposed by nitric acid and slight ignition in a borosilicate glass beaker. I n case of minerals containing manganese, aluminum, iron, and beryllium i t is advantageous to make a double precipitation of iron, aluminum, and beryllium as the hydroxides, while manganese is prevented from precipitating by adding 1 to 3 ml. of ethyl alcohol to each 100 ml. of solution. T h e n magnesium, lithium, sodium, and potassium are present, lithium chloride can be separated from magnesium, sodium, and potassium chlorides by one of the amyl alcohol methods, and magnesium as carbonate from sodium and potassium. RESULTS
-4 mixture of separately analyzed uranyl nitrate and sodium phosphate
