Anal. Chem. 1980, 52, 1762-1764
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CORRESPONDENCE Determination of Germanium, Vanadium, and Titanium by Carbon Furnace Atomic Absorption Spectrometry Sir: Germanium is a rare element, being widely disseminated rather than being concentrated in natural waters. Vanadium appears in natural waters in very small concentrations. In drinking water in the USA, the medium concentration of vanadium was 0.006 ppm. In small concentrations, vanadium influenced the mineral distribution in man's osseous disposition ( I ) . For determination of titanium in polypropylene and wear metal analysis in engine oil the sample must be transferred into aqueous solution. In the determination of germanium, vanadium, and titanium by flame AAS, i t is difficult to obtain high sensitivity owing to the formation of highly stable oxide species in the flame. Germanium was determined in natural waters by spectrographic methods after extraction into CHCl, as a complex with oxine ( 2 ) or N-benzoyl-N-phenylhydroxylamine(3-6). Germanium was determined by flame AAS after extraction from 8 M hydrochloric acid into n-butyl ether (7). Germanium was indirectly determined as molybdogermanic acid by flame AAS (8). Atomic absorption spectrometry of germanium with a tungsten electrothermal atomizer was described (9). Vanadium was determined in waters and plants by spectrographic methods after extraction into CHC13 as a complex with diethyl dithiocarbamate ( I O , I I ) , cupferron (12,13),or N-benzoyl-N-phenylhydroxylamine( 1 4 ) . Vanadium was determined by flame AAS after extraction into methyl isobutyl ketone as a complex with cupferron (15). Vanadium was indirectly determined as vanadium molybdophosphoric acid by flame AAS (16). T h e nature of the interference of nitric acid in the determination of vanadium by flameless AAS was described (17). Titanium was determined in waters and plants by spectrographic methods after extraction into CHC13 as a complex with diethyl dithiocarbamate (10,11),cupferron (12, 13),and N-benzoyl-N-phenylhydroxylamine( 1 4 ) . Titanium was indirectly determined as titanium molybdophosphoric acid by flame AAS (18). The literature described determinations of titanium by flame AAS of solids (19),high purity aluminum (20), ferrosilicon alloys (21),and iron and steel (22). In the past few years, matrix effects encountered with flameless AAS devices have been investigated by several authors (23-34), but little information about matrix effects of germanium, vanadium, and titanium have been described. T h e following kinds of interferences have been observed (25, 35): (1) physical interferences due to retention by occlusion in a n excess of less volatile matrix compounds or covolatilization with more volatile matrix compounds, incorporation of the element into graphite and nonspecific absorption; (2) chemcial interferences caused by the formation of compounds of different volatility or carbide formation; (3) deionizing effect of the elements easily ionized in high temperatures. All kinds of interferences result in an increase or decrease of the absorption signal. Consequently they may lead to erroneous results if the experimental conditions are not strictly controlled. 0003-2700/80/03521762$0 1.OO/O
EXPERIMENTAL Instrumentation. A double-beamInstrumentation Laboratory atomic absorption spectrometer Model 251 with hydrogen background corrector, a graphite furnace IL 455, and a Dohrmann Envirotech recorder Model SC 1200 were used. It was necessary to check and correct for the blank values on all reagents used. The germanium, vanadium, and titanium contaminations were controlled in all reagents used and were below the sensitivity of the determinations. To discriminate against furnace emission, a slit height reducer placed inside the monochromator was used. Germanium. Experimental Conditions. Sample volume, 25 /*L;drying 7 5 O C , 20 s, 225 OC, 20 s; ashing 600 "C, 15 s, 900 OC, 15 s; atomization 3500 O C , 10 s; wavelength 265.1 nm; gas argon flow 4 L/min. Preparation of Solutions. Solutions of 0.1 and 0.5 ppm Ge in demineralized water containing O.ooO1-1% v/v acids, 50,100,250, 500,1000 ppm "&lo4, NH4N03,NH4Cl,(NH4)$04, NH4HzP04 and Mg2+,Ca2+, K+, Na+ chlorides, 25 mmol/L 2-pyridylphosphinic acid were prepared. Preparation of Calibration Graph for Germanium. To a series of six calibrated containers add succesively 0.1 mL of the solution of 10000 ppm magnesium chloride, 0.4 mL of concentrated nitric acid, and 0, 0.1, 0.2, 0.3, 0.4, 0.5 mL of the solution of 10 ppm of germanium. Dilute quantitatively to 10 mL. Directly inject 25 pL of sample into the carbon furnace and determine germanium. Vanadium. Experimental Conditions. Sample volume, 25 /*L;drying 7 5 O C , 20 s, 225 " C , 20 s; ashing 1000 OC, 25 s, 1200 OC, 25 s; atomization 3500 O C , 10 s; wavelength 318.5 nm; gas argon flow 4 L/min. Preparation of Solutions. Solutions of 0.1 and 0.5 ppm V in demineralized water containing O.ooO1-1% v/v acids, 50, 100,250, 500,1000 ppm ammonium salt, and Mg2+,Ca2+,K+, Na+ chlorides, 25 mmol/L 2-pyridylphosphinic acid were prepared. Preparation of Calibration Graph f o r Vanadium. To a series of six calibrated containers add successively 1mL of the solution of 10000 ppm potassium chloride, 0.1 mL of 1% v / v phosphoric acid, and 0, 0.1, 0.2, 0.3, 0.4, 0.5 mL of the solution of 10 ppm of vanadium. Dilute quantitatively to 10 mL. Inject directly the 25-pL sample into the carbon furance and determine vanadium. Titanium. Experimental Conditions. Sample volume 25 pL; drying 7 5 OC, 20 s; 225 "C, 20 s; ashing 1000 "C, 25 s, 1200 "C, 25 s; atomization 3500 "C, 10 s; wavelength 364.3 nm; gas argon flow 4 L/min. Preparation of Solutions. Solutions of 0.1, 0.4,0.5 ppm Ti in demineralized water containing O.ooO1-1% v/v acids, 50,100,250, 500, 1000 ppm ammonium salts, Mg2+,Ca2+,K+, Na+ chlorides, 25 mmol/L 2-pyridylphosphinic acid were prepared. Preparation of Calibration Graph f o r Titanium. To a series of six calibrated containers add, successively, 0.25 mL of the solution of loo00 ppm potassium chloride, 0.1 mL of concentrated hydrochloric acid, and 0, 0.1,0.2, 0.3,0.4,0.5 mL of the solution of 10 ppm of titanium. Dilute quantitatively to 10 mL. Inject directly 25 pL of sample into the carbon furnace and determine titanium. Germanium, vanadium, and titanium stock solutions were delivered by Central LaboratoTy of Material Standards "Wzormet" Warsaw, Poland.
RESULTS AND DISCUSSION T h e interactions are expressed as percentage of the peak height absorption signal obtained for the germanium, vana0 1980 American Chemical Society
ANALYTICAL CHEMISTRY, VOL. 52, NO. 11, SEPTEMBER 1980
Table I. Percent Interaction on Germanium Signal as a Function of Concentration in 2 v/v of Sulfuric Acid; 0.1 and 0.5 ppm Ge, 100 ppm Magnesium Chloride, 0 . 6 M Nitric Acid, 0 and 25 mmol/L of 2-Pyridylphosphinic Acid (PPA) 0.1 ppm Ge % vlv sulfuric acid
0.1 0.01 0.001 0.0001
-
without PPA 27 36 144 50
100
132 96 96 132 93
Table 11. Percent Interaction on Vanadium Signal as a Function of Concentration in % v/v of Nitric Acid; 0.1, and 0.5 ppm V, 1000 ppm Potassium Chloride, 0.01 7% v/v Phosphoric Acid, 0 and 25 mmol/L 2-Pyridylphosphinic Acid (PPA)
0 . 5 ppm Ge
25 25 mmol/L without mmol/L PPA PPA PPA 31 46 54 60
100
33 25 32 29 47
dium, and titanium in the absence of the interfering substance. Perchloric acid, nitric acid, and phosphoric acid increased the signal of germanium in the range 0.1-1% v/v. Perchloric acid increased the peak height most. Sulfuric acid and hydrochloric acid decreased the signal of germanium for 1% v / v of acids. Phosphoric acid in the range 0.0001-0.01% v/v decreased the signal of germanium (minimum for 0.001% v/v). Nitric acid in a wide range caused depression of the peak height of vanadium. Perchloric acid in the range 0.0001-0.001% v/v decreased the signal but in the range 0.1-1 % increased the signal of vanadium. Phosphoric acid in the range 0.001-0.1 7’ v/v increased the signal but hydrochloric acid and sulfuric acid depressed the signal of vanadium. Nitric acid in the range 0.0001-0.1% v/v increased the signal of titanium but for 1 % v/v caused depression of the signal. Perchloric acid decreased the signal of titanium in the range 0.001-1% but for 0.0001% increased the signal. Phosphoric acid in the range 0.0001-0.01 o/c increased the signal of titanium. Sulfuric acid for 1% decreased the peak height of titanium most, but hydrochloric acid for 1% increased the signal of titanium most. Ammonium salts of these acids in the range 50-1000 ppm in general changed the signal of the investigated elements similarly to the acids. Only for high concentrations ammonium sulfate increased the signal of germanium and vanadium contrary to sulfuric acid and ammonium phosphate decreased the signal of germanium and vanadium contrary to phosphoric acid. For titanium, ammonium sulfate also increased the signal contrary to sulfuric acid. For high concentrations, ammonium perchlorate increased the signal of titanium contrary to perchloric acid. Magnesium, calcium, potassium, and sodium chlorides caused a nonspecific absorbance for the 265.1-nm wavelength (germanium) (36). T h e nonspecific absorbance can be removed by an increase in ashing temperature and addition of ammonium nitrate, nitric acid, or sulfuric acid (37). Nitric acid, 0.6 M, is sufficient to remove the nonspecific absorbance. Magnesium chloride most enhanced the germanium signal in the range 100-250 ppm (maximum for 100 ppm MgC12). Only sodium chloride in the range 1oCt250 ppm decreased the signal of germanium; other investigated chlorides increased the signal of germanium. Potassium chloride most enhanced the signal of vanadium and titanium (maximum for titanium, 250 ppm). For vanadium, a negative interference is observed when 50 ppm of MgC1, is added; while for 1000 ppm, a signal enhancement is obtained. Calcium chloride most decreased the signal of vanadium in the range 5&100 ppm. Sodium chloride increased the signal of vanadium and titanium. Calcium chloride most increased the signal of titanium in the range 500-1000 ppm. T h e addition of 0.001% v/v of phosphoric acid and 1000 ppm potassium chloride reduced the influence of ammonium nitrate on the vanadium signal. T h e working range for the investigated elements for the optimal conditions is linear up to concentration of approxi-
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0.1 ppm V
76 v/v
nitric acid
0.1 0.01 0.001 0.0001
-
0 . 5 ppm V 25 25 without mmol/L without mmol/L PPA PPA PPA PPA 133 95 75 103 100
24 1 288 37 7 27 0 280
90 90 95 97
100
82 113 120 126 3 01
Table 111. Percent Interaction o n Titanium Signal as a Function of Concentration in 5% v/v of Perchloric Acid; 0.1 and 0.5 ppm Ti, 250 ppm Potassium Chloride, 1% Hydrochloric Acid, 0 and 25 mmol/L 2-Pyridylphosphinic Acid (PPA) 0.1 ppm Ti 25
% v/v
perchloric acid 0.1 0.01 0.001
0.0001
-
0.5 ppm Ti 25
without mmol/L without mmol/L PPA PPA PPA PPA 28 56 57 57
100
36 20 56 47
18
71 64 81 78 100
31 58 72 43 23
mately 0.4 ppm. T h e sensitivity (1% absorption) is about 0.015 ppm for germanium, 0.03 ppm for vanadium, and 0.08 ppm for titanium. Interference studies must be done varying the concentrations of the analytes. In Tables I, 11, and 111, effects of the varying concentrations of the acids which most decreased the signal at optimal conditions are described. The investigations were carried out for 0.1 and 0.5 ppm of the examined elements. Phosphoroorganic complexones are the most stable organic compounds which are often used in analytical chemistry (38). An attempt to take advantage of 2-pyridylphosphinic acid (39) in carbon furnace AAS was made. The addition of 25 mmol/L 2-pyridylphosphinic acid caused depression of the signal germanium but the effect of sulfuric acid for both concentrations was reduced. For vanadium, the addition of 2-pyridylphosphinic acid enhanced the signal but for 0.001% nitric acid a maximum occurred for 0.1 ppm V. For titanium, the addition of 2-pyridylphosphinic acid decreased the signal. The addition of 1% hydrochloric acid and 250 ppm potassium chloride was sufficient to reduce interferences caused by perchloric acid. In this case, the addition of 2-pyridylphosphinic acid did not, diminish the impact on the signal of perchloric acid.
CONCLUSIONS The experiments performed allow the following conclusions to be drawn. Acids strongly influence the germanium, vanadium, and titanium signal. Nitric acid increased the signal of germanium but decreased the signal of vanadium and titanium. Sulfuric acid decreased the signal of all examined elements. Phosphoric acid decreased the signal of germanium but enhanced the signal of vanadium and titanium. Hydrochloric acid depressed the signal of germanium and vanadium but increased the signal of titanium. Ammonium salts of these acids on the whole changed the signals of investigated elements like acids, but there are several exceptions (ammonium sulfate for germanium, vanadium, and
Anal. Chem. 1980, 52, 1764-1765
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titanium; ammonium phosphate for germanium and vanadium; ammonium perchlorate for titanium). A nonspecific absorbance for MgC12,CaC12,KC1, and NaCl was observed for the 265.1-nm wavelength (germanium) and was removed by the addition of 0.6 M of nitric acid. T h e working range of all examined elements was between 0.1-0.5 ppm. T h e calibration graphs were linear up to a concentration of approximately 0.4 ppm. The sensitivities (1% absorption) were: 0.015 ppm for germanium, 0.03 ppm for vanadium, and 0.08 ppm for titanium. T h e addition of 2-pyridylphosphinic acid reduced the interference of sulfuric acid on germanium and enhanced the signal of vanadium in the presence of nitric acid but decreased the signal of titanium.
LITERATURE CITED Hermanowicz, W.; Doiahska, W.; Dojlido, J.; Koziorowski, B. "Fizycznochemiczne badanie wody i SciekBw". Arkady: Warsaw, 1976; p 392. Rudenko. N. P. Tr. Kom. Anal. Kbim., Akad. Nauk. SSSR, 1963, 14, 209. Lyle, S . J.; Shendrikar, A. D. Anal. Chim. Acta 1965, 32, 575. Lyle, S. J.; Shendrikar, A. D. 1966, 36, 286. Alimarin, I. P.; Sokolova. I. V.; Smalina, E. V.; Firsowa, G. V. Zh. Anal. Khim. 1970, 2 5 , 2287. Alimarin, 1. P.; Sokolova, I. V.; Smalina, E. V. Vesti MGU 1668, 67. Shimomura, S.; Sakurai, H.; Morita, H. Anal. Chim. Acta 1978, 96, 69. Jakubiec, R.; B o k , D. F. Anal. Cbem. 1969, 41, 78. Ohta, K . ; Suzuki, M. Anal. Cbem. Acta 1979, 704, 293. Doll, W.; Specker, H. Fresencus' 2 . Anal. Cbem. 1956, 161, 354. Schuller, H. Mikrochim. Acta 1956, 393. Goriushina, V. G.; Biriukova, E. I. i'b. Anal. Chim. 1969, 2 4 , 580. Mulford, C. E. A t . Absorpt. Newsl. 1966, 5 , 8 8 . Zolotov, I. A.; Sizonienko. N. T.; Zolotovickaja, E. S.; Jakovenko, E. I. Zh. Anal. Chim. 1969, 2 4 , 20. Kamiya, A. EiseiKagaku 1975, 21, 267; Anal. Abstr. 1976, 3 0 , 6H9. Jakubiec, R.: Boltz, D. F. Anal. Left. 1968, 1 . 347. Sutter, E. M.; Leroy, M. J. Anal. Cbim. Acta 1978, 9 6 , 244.
(18) Kirkbright, G. F.; Smith, A. M.; West, T. S.; Wood, R. Ana/yst(London) 1969, 9 4 , 7 5 5 . (19) Katskov, D. A,; Kruglikova, L. P.; L'vov, B. V . Zh. Anal. Khim. 1975, 3 0 , 238. (20) Drwiepa, J.; Jedrzeiewska, H.; Malusecka, M. Chem. Anal. (Warsaw) 1975,-20, 539. . (21) Damiani, M.; Tamba, M. G.; Bianchi, F. Analyst(London) 1975, 100, 643. (22) Cobb, W. D.; Foster, W. W.; Harrison, T. S. Anal. Cbim. Acta 1975, 78, 293. (23) Lagas, P. Anal. Cbim. Acta 1978, 9 8 , 261. (24) Fuller. C. W. Anal. Chim. Acta 1976, 8 7 , 199. (25) C i n i , R., Mazzucotelli, A., Ononello, G. Anal. Cbim. Acta 1976, 82, 415. (26) Frech, W.; Cedergren, A. Anal. Cbim. Acta 1976, 82, 83. (27) Smeyers-Verbeke, J.; Michotte, Y.; Van den Winkel, P.; Massart, D. Anal. Chem. 1976, 4 8 , 125. (28) Walsh, P. R.; Fasching, J. L.; Duce, R. A. Anal. Cbem. 1976, 48, 1014. (29) Woodis, T. C., Jr.; Hunter, G. B.; Johnson, F. J. Anal. Cbim. Acta, 1977, 90. 127. (30) Yasuda, S.;Kakiyama, H. Anal. Cbim. Acta, 1977, 8 9 , 369. (31) Nakahara, T.; Chakrabarti, C. L. Anal. Chim. Acta, 1979, 104, 99. (32) Geladi, P.; Adams. F. Anal. Cbim. Acta 1978, 9 6 , 229. (33) Johansson, K.; Frech, W.; Cedergren, A. Anal. Cbim. Acta 1977, 9 4 , 63. (34) Studnicki. M. Anal. Chem. 1979, 57, 1336. (35) Syty, A. CRC Crit. Rev. Anal. Cbem. 1974, 4(2), 155. (36) Pritchard, M. W.; Reeves, R. D. Anal. Cbim. Acta 1976, 8 2 , 103. (37) Frech, W.; Cedergren, A. Anal. Cblm. Acta, 1977, 88,57. (38) Szczepaniak. W.; Siepak, J. W a d . Cbem. 1975, 2 9 , 193. (39) KarmiAski, W.; Studnicki, M., unpublished results, NMR 'H HP 5.58 ppm, JHp884 Hz, 31P NMR -2.1 ppm (solvent H,O, reference standard mp 410 OC, dec. 480 OC. H,PO,), Present address: Sllesiau Technical University, Institute of Chemistry and Organic Technology, 44-101 Gliwice, Poland.
Marek Studnicki' Polish Academy of Science Institute of Environmental Engineering 41-800 Zabrze, Poland
RECEIVED for review February 8, 1979. Resubmitted December 11, 1979. Accepted February 25, 1980.
Comment on the Prediction of Gas Chromatographic Retention Behavior with Mixed Liquid Phases Sir: Recently Pecsok and Apffel ( I ) demonstrated that the Kovats' Retention Index of a particular solute on a binary stationary phase I ( @ )could be reasonably estimated by
I(@) = M ( @ )log [@AIO(*Ao+NA)/MA+ @s10(Iso+Ns)/ Ms 1 -N($) (1)
M ( @ )= 100
=
100 log (@AK&(z),A + @sK&(z),s)
-
@AK&Z+I),A+ @sKk(z+i),s log @AK&(Z),A + @sK&(z),s
looz
may be justified. The simplicity of Equation 4 is quite appealing as it requires only the stationary phase composition and the retention indices of the solute on each pure solvent. Comparison of Equations 1and 4 does not readily reveal when the two expressions are identical. The "apparent" success of Equation 4 is perhaps better understood when the partition coefficients in binary systems are described with a realistic thermodynamic model. Acree and Bertrand (2) expressed the partition coefficient of a solute (at infinite dilution) in noncomplexing binary systems as
(3)
where $A and @srefer to the volume fraction of pure phases A and S, respectively. I
