gen which later desorbs. Titanium evaporation is minimized by extracting t h e hydrogen a t t h e lowest temperat u r e (800 "C) t h a t permits quantitative extraction in a relatively short time. It is estimated t h a t t h e hydrogen content when extraction is complete to be less t h a n 0.5 ppm. T h i s estimate is based on t h e work of Albrecht a n d Mallett (3). Their expression for t h e hydrogen solubility in Ti is: log10 -= 2020 - 0.723 pl/* T where S is the solubility in ppm, p is t h e partial pressure in microns, T i s t h e absolute temperature. Other factors involve t h e high reactivity of T i at elevated temperatures. At 800 "C, titanium reacts with a number of substances to produce extraneous hydrogen. High blanks are obtained (Ref. I ) when hydrogen-free titanium ( Flame
\120-C2H2 Flame
Cationb Observedc,% Correctedd. % Observed', % Corrected", Oh NH4+ Na+ K+ Mg2+ Can+ Co2+ Fen+
Mn2+ Cu2+ Zn2+
101 109 111 112
109 150 245 118 105 102
100 100 99 72 39 127
105 97 102 105 113 165 267
87
121
101
105 108
...
95
105 9;
102 92 97
... 246 106 105 10;
a Concentration of Phosphorus is 0.05 M. Concentrations of cations are 0.06 M. Values observed at 246.0 nm without correction. Background absorptions at 241.0 nm were corrected.
"
Table 111. Analysis of Phosphorus in Nucleotides Using the PO Band in a Nitrous Oxide-Acetylene Flamea Nucleotide UMP GMP CMP CMP-FA~ CDP
Calculated, mg P/ml
Found. mg P/ml
3.89 4.41 4.40 5.93 3.40
3.48 3.58 3.65 5.74 3.39
Aqueous solutions of phosphoric acid were used as the standard. Dissolved in 2 N HC1 acidic solution.
environment of the nitrous oxide-acetylene flame. According to emission and absorption flame spectrometry, in fact, molecule PO, t h e dissociation energy of which is 6.4 eV ( 5 ) , is a stable species in a high temperature, b u t other phosphorus oxides give the backgrounds even in the air-hydrogen flame ( 1 3 ) , a n d atomic phosphorus can be observed in t h e nitrous oxide-acetylene flame (10, 11).T h e d and continuous band systems of PO near 324 a n d 540 n m could n o t be observed in this experiment (19). T h e analytical curves for phosphorus in t h e air-acetylene and in the nitrous oxide-acetylene flames were examANALYTICAL CHEMISTRY, VOL. 48,
NO. 4 ,
APRIL 1976
* 785
ined in the concentration range from 0.01 to 0.1 M , where the phosphorus compounds of H3P04, (NH4)H2P04, NaH2P04, and KH2P04 were used as the standard materials. In the analytical curves, the wavelength of 246.0 nm was used for the PO absorption and t h a t of 241.0 nm for the background absorption. In the air-acetylene flame, the net absorbances of P O become smaller because of the background absorptions for all the salts. In the nitrous oxideacetylene flame, no appreciable background absorptions are observed, and the analytical curves for all the salts are almost linear and consistent within the experimental error less than 5%. T h e detection limit (defined by SIN = 2) was estimated about 100 pglml, when the deuterium lamp of hollow cathode type was used. T h e detection limits of absorption techniques are dependent on source intensities as a general rule. So the 200-W deuterium lamp was used to improve the detection limit, where the detection limit of phosphorus was about 20 pg/ml. T h e interfering effects of cations on the P O absorption were investigated, and the results are summarized in Table 11. T h e results are expressed by the ratios, Robsd and R,,,,, defined by the following equations;
Robsd = (Az46/A:46)X 100 (%)
R,,,,
=
- A,241)/(A,246- A:41)] X
(1)
100 (%)
b
LITERATURE CITED
(2)
where Robsd and R,,,, are the observed and corrected ratios, respectively; and the absorbances of reference solution, 0.05 M H 3 P 0 4 , a t 246.0 and 241.0 nm, respectively; and and Ai4' the absorbances of the sample solutions, 0.05 M H 3 P 0 4 and 0.06 M cations, a t 246.0 and 241.0 nm, respectively. In the nitrous oxide-acetylene flame, was almost 0. In the case of Co2+,the correction could not be made because the atomic lines of Co 240.7 and 241.2 nm interfere optically with the P O absorption a t 241.0 nm. T h e large values of both Robsd and R,,,, for Fez+ and Co2+ can be ascribed t o the optical interferences due to the atomic lines of Fe 245.8 and 246.3 nm and Co 246.1 and 246.5 nm, respectively. Therefore, when Co and Fe coexist in the samples, those elements should be excluded by an ion-exchange or another methods as suggested by Davis e t al. (13),or an alternate band head of P O except for 246.0 nm should be used to eliminate the optical interferences. As can be seen from Table 11, almost all the observed ratios are more than 100%. This suggests t h a t most cations produce phosphates besides phosphorous oxides in the flames, and t h a t phosphates may contribute to the absorptions because of the background absorption or light-scattering. In fact, it has been known that atomic spectrometry of Mg and Ca in the lower temperature flame is interfered by phosphate ion because of the formations of the refractory compounds such as M P 0 4 and MzP207 (20). T h e fact is also supported by the results for Mg2+ and Ca2+ in the airacetylene flame in Table 11, where the corrected ratios for t h e m are significantly smaller than 100%. T h e values for Mn2+ and Zn2+ also suggest the formation of phosphates in the air-acetylene flame. I t has been known t h a t in flame spectrometry, Mn2+ and Znz+ are interfered by phosphate ion (21). I t should be noted here that the formations of the refractory phosphates are overcome in the nitrous oxideacetylene flame for almost all the elements, while such formations are still slightly observed in the cases of Mg2+,
786
Ca2+,and Mn2+. This is consistent with the previous study t h a t no significant interferences by the foreign cations were observed in phosphorus atomic absorption spectrometry in the nitrous oxide-acetylene flame (11). T h e molecular absorption of P O a t 246.0 nm was applied t o the analysis of phosphorus in some nucleotides. T h e results are shown in Table 111, where the nitrous oxide-acetylene flame was used, and the observed values are compared with those calculated from the molecular formula. In this analysis, the precision was within 5% for all the samples. Emission spectrometry using the H P O band is most sensitive, as is summarized in Table I, but H P O molecule can be produced only in the cool or cooled flames, and then the interfering effects of the concomitants, even sodium, on H P O emission are very serious. T h e emission of P O has similar situations. In atomic absorption spectrometry of phosphorus, it is inconvenient to use a nitrogen-replaced spectrometer. So, a t the present stage, all the methods listed in Table I have the advantages and disadvantages, and more studies for the convenient and practical method are desirable. Further study of P O molecular absorption is in progress.
ANALYTICAL CHEMISTRY, VOL. 48, NG. 4, APRIL 1976
(1) H. Haraguchi and K. Fuwa, Spectrochim. Acta, Part B, 30, 535 (1975). (2) H. G. C. Human and P. J. Th. Zeegers, Spectrochim. Acta, Part B, 30, 203 (1975). (3) J . A. Fiorino, R. N. Kniseley, and V. A. Fassel, Spectrochim. Acta, Part 8,23, 413 (1968). (4) K. Fuwa and E. L. Vallee. Anal. Chem., 41, 188 (1969). (5) A . G. Gaydon, "Dissociation Energies and Spectra of Diatomic Moiecules", 3rd ed., Chapman and Hall, London, 1968. (6) S.R. Koirtyohann and E. E. Pickett, Anal. Chem., 38, 585 (1966). (7) H. Haraguchi and K. Fuwa, Chem. Lett., 1972, 913. (8) K. Fujiwara, H. Haraguchi, and K. Fuwa, Anal. Chem., 47, 743 (1975). (9) H. Haraguchi and K. Fuwa, Bull. Chem. SOC.Jpn, 48, 3056 (1975). (10) D. C. Manning and S. Slavin. At. Absorp. Newsl., 8, 132 (1969). (1 1) G. F. Kirkbright and M. Marshall, Anal. Chem., 45, 1610 (1973). (12) R. K. Skogarboe, A. S. Gravatt, and G. H. Morrison, Anal. Chem., 39, 1602 (1967). (13) A. Davis, F. J. Dinan, E. J. Labbett, J. D. Chazin, and L. E. Tufts, Anal. Chem., 36, 1066 (1964). (14) R. M. Dagnall, K. C. Thompson, and T. S. West, Analyst (London), 93, 72 (1968). (15) K. M. Aidous, R. M. Dagnall, and T. S. West, Analyst (London), 95, 417 (1970). (16) A. Syty, Anal. Lett., 4, 531 (1971). (17) K. Fuwa, H. Haraguchi, K. Okamoto, and T. Nagata, Bunseki Kagaku, 21, 945 (1972). (18) W. E. Pearse and A. G. Gaydon, "The Identification of Molecular Spectra", Chapman and Hall, London, 1950. (19) N. Furuta, private communication. According to his recent work, the weak system of the PO bands could be observed in absorption. (20) G. L. Baker and L. H. Johnson, Anal. Chem., 26, 465 (1954). (21) W. Slavin, "Atomic Absorption Spectroscopy", Interscience, New York. 1968.
0
Hiroki Haraguchi* Department of Chemistry and Physics National Institute for the Environment Yatabe, Tsukaba, Ibaraki 300-21, Japan
Keiichiro Fuwa Department of Chemistry Faculty of Science T h e University of Tokyo Hongo, Bunkyo-ku, Tokyo 113, Japan
RECEIVEDfor review November 11, 1975. Accepted J a n u ary 8,1976.
