Carefully add 100 ml of water and 5Z potassium permanganate solution until a permanent pink color is obtained. Cool the solution to 20 “C and continue as in the above procedure adding the hydroxylamine sulfate-sodium chloride solution and the stannous sulfate solution. RESULTS AND DISCUSSION
The values obtained in establishing the calibration curve and the results obtained from the analysis of nickel and cobalt samples are given in Table 11. Table I11 lists the values obtained on U. S. Geological Survey rocks G-1 and W-1 using the modified procedure. Results obtained in this laboratory using the dithizone procedure of Kimura and Miller ( I ) and other available data are also shown.
Also shown in Table I11 are the results of seven determinations performed on a finely-ground rock sample used as a secondary standard. From these data the precision of the method was calculated. There are few interferences under the conditions described. The procedure cannot be applied to metal samples such as copper, which is easily reduced, thus preventing the complete aeration of mercury. Large amounts of elements such as tellurium, which are easily reduced to their elemental state, cause low results by coprecipitating some of the mercury. Usually this interference can be detected by visual inspection of the solution after the addition of stannous sulfate. Normally these elements are not present in sufficient quantity to cause interference. RECEIVED for review May 27, 1968. Accepted July 18, 1968.
Enhancement of Zirconium Atomic Absorption by Nitrogen-Containing Compounds and its Use in the Determination of Ammonia A. M. Bond Department of Inorganic Chemistry, Unicersity of Melbourne, Parkville, Victoria 3052, Australia J. B. Willis Diaision of Chemical Physics, CSIRO Chemical Research Laboratories, P. 0. Box 160, Clayton, Victoria 3168, Australia The absorption by zirconium atoms in the nitrous oxide-acetylene flame is enhanced in the presence of many nitrogen-containing compounds which can act as Lewis bases. For ammonia the magnitude of this enhancement is proportional to the concentration of base over the range 1 X l F 4to 5 X 10-aMand can be used to determine ammonia in the absence of phosphate and of certain nitrogen-containing compounds. When interfering species are present the method can be used, after prior distillation of the ammonia, to replace spectrophotometric methods which require considerable time for color development. The analytical usefulness of the enhancement technique is demonstrated by the determination of ammonia in biological systems.
AMOSAND WILLIS(1) observed that fluoride ion enhanced the absorption by zirconium atoms in the nitrous oxide-acetylene flame, and Bond and O’Donnell (2), while investigating this effect as a method for determining fluoride, found that ammonium ion interfered by causing an enhancement similar to that produced by fluoride. This suggested that the atomic ab sorption technique might be applied to the determination of ammonia and be a useful supplement to existing methods, most of which require prior distillation of the ammonia and time-consuming color development before making spectrophotometric measurements (3). In order to investigate further the principles behind the enhancement of zirconium absorption by ammonia, a range of other nitrogen-containing compounds was also investigated. (1) M. D. Amos and J. B. Willis, Spectrochim. Acta, 22, 1325, 2128 (1966). (2) A. M. Bond and T. A. O’Donnell, ANAL. CHEM.,40, 560 (1968). (3) I. M. Kolthoff and P. J. Elving, “Treatise on Analytical Chemistry,” Part 11, Vol5, Interscience, New York, 1961, pp 279-85.
EXPERIMENTAL
Ammonium chloride (B.D.H. “AnalaR” quality) and zirconium oxychloride octahydrate (B.D.H. “L.R.” quality, 98.5z ex. C1 analysis) were assumed to be stoichiometric. Other nitrogen-containing compounds were of analytical reagent grade wherever available, and if any doubts existed about purity the materials were purified by distillation or recrystallization, as appropriate. Atomic absorption measurements at the 3601.2A line of zirconium were made with an AA-4 or AA-100 atomic absorption spectrophotometer (Varian Techtron Pty. Ltd., North Springvale, Victoria 3170, Australia) fitted with a 50- X 0.5-mm slot burner for use with nitrous oxide-acetylene mixtures. Absorption was measured in a fuel-rich, slightly luminous flame having an interconal zone about 30 mm high. ESH.%\CE\IENT OF ZIRCONIU\I ABSORPTION BY SITROGEN-COSTz\ISISG COMPOUSDS
Figure 1 shows the effect of a number of nitrogenous compounds on zirconium absorption. The absorbance at first increases linearlj, with the concentration of compound, and then flattens out to a plateau when the molar ratio of nitrogenous compound to zirconium exceeds a value of about four. The solutions measured contained 0.8M hydrochloric acid to keep the nitrogenous compounds in solution and 0.006M potassium chloride to suppress the ionization of zirconium, which is appreciable in the nitrous oxide-acetylene flame (4). Table I shows the results of semi-quantitative survey of a wider range of compounds; in general, the most basic compounds show the strongest enhancement of zirconium absorption, which seems to depend principally on the availability of an unshared electron-pair at the nitrogen atom. (4) D. C. Manning, Atomic Absorption Newsletter, 5, 127 (1966). VOL. 40, NO. 14, DECEMBER 1968
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Table I. Enhancement of Zirconium Absorption by Nitrogen-Containing Compounds Magnitude of Compound pKb" enhancement* Compound pKC Inorganically substituted Heterocyclics ammonias 8.77 C~HBN 4.75 3 3" Quinoline 9.20 5.77 3 NHz.NH2 2-Hydroxyquinoline 8.79 3 C&IS*NH.NWZ 8-Hydroxyquinoline 9.21 3.97 2 HO*NH% N-methylnicotinamide iodide Aliphatic amines Aminoacids 3.36 3 CHa. NHz 11.85 3.28 3 (CHs)z*NH 11.64 4.26 3 (CHd3.N 4.63 3 CBHSGHz .NHz 0 (CzHs)4NfBrAromatic amines C6H6NHZ
CsH5 . NH .CHa CaH5.N(CHsh p-NHz. C8H4.NHI 2 :4 :6-Triaminotoluene a-Naphthylamine
9.42 9.30
8.94 7.96 10.08
2 2 2 2 2 2c
H2N*CHz*CH29GH2"2Hz* C#2*CH(NH2) * COOH (HOOC * CH&*N *CHz* CH2 * N .(CHzCOOH)z Miscellaneous (NHdzCO (NH2)2C:NH CHs.CQ.NHz p-NH2. CeH4. SO%* NH2 CH3.CN NaSCN CHa C(N0H). C(NOH).CHs
5.05
Magnitude of enhancementb 3 3
3 3 0 0 0 0 0
1 0
13.82
3d
12.60
3 0 3 0
12.6
0 0
Values in aqueous solution at 20 or 25 OC, mostly from reference (5). Measured as far as possible with solutions containing 0.020M Zr and 0.8M HCl. The figures 0, 1, 2, and 3 correspond to enhancement of the zirconium absorption plateau by 0.00, 0.004.05, 0.05-0.1, and >0.1 absorbance units, respectively. c Low solubility makes magnitude of enhancement somewhat uncertain. This compound is readily and rapidly hydrolyzed to ammonia. Q
b
It is unlikely that the enhancement is due to improved atomization brought about by deflagration in the flame of particles of organic materials, both because the concentration of organic compound is so low (
