absorption of the 8-quinolinolinium ion in the ultraviolet region. Interferences. For the type of sample discussed here, the interference caused by plutonium only needs be considered. However, sometimes the components of stainless steel may be present as contaminants. Potassium cyanide does not prevent the precipitation of the aluminum, and it eliminates the interference of 200 pg. of nickel, copper, and cobalt, respectively. The filtrate and washings containing potassium cyanide should be treated with hydrochloric acid in a well ventilated hood before disposal. RESULTS
Recovery data for this method were obtained by carrying aluminum through the suggested ion exchange-precipitaLion procedure in the absence of plutonium. The amount of aluminum was
varied from 100 to 400 p g . The absorbances were measured a t 360 to 390 mp, The relative standard deviation was less than 2% over the various measured wavelengths. In the analysis of six Pu-A1 samples, repeat analyses on the same samples had a range of slightly less than 2 pg, with a sample which contained approximately 200 Mg. of aluminum. LITERATURE CITED
(1) Cleveland, J. M., Nance, P. D., U. S. Atomic Energy Comrn. Rept, RFP-53 (1955). ( 2 ) Darbey, A,, Am. Dyestug Reptr. 42, 453 (1953). (3) Deterding, H. C., Taylor, R. G., IND.ENG. CHEM.ANAL.ED. 18, 127 (1946). (4)Evans, H. B., Bloornquist, C. A . , Hughes. J. P.. ANAL. CHEM.34, 1962 (1982).' (5) Harvey, B. G., Heal, H. G., Maddock, A. G., Rowley, E . L., J . Chem. SOC. 1947, p' 1010.
(6) Hollingshead, ,R. G. IT.,"Osine and
Its Derivatives, T'ol. 1, Butterworths, London, 1954. ( 7 ) Jones, I. G., Phillips, G , , UKAEA, AERE-R-2879 (1960). 18) ~, Kraus. K . A , . Xelson. F.. Proc. Intern. Conf. Peaceful 'Uses At: Energy, Geneva, 1955 Vol. VII, P/837, United Sations Pub., New York, 1956. (9) Miner, F. J., Degrazio, R. P., Forrey, C. R., Jones, T. C., -4nal. Chim. d c t a 22. 214 11960). (10) 'Motojima, ' K , Hashitani, H., Bunseki Kagaku 8, 526 (1959j , (11) Patton, It. L., "The Transuranium Elements," part 1, p. 853, McGrawHill, Sew York, 1949. (12) Phillias. J. P.. Merritt. L. L.. J . Am. C&m: SOC. 71, 3984 (i040). H. B. Evass HIROSHIH . 4 S H I T A S I ' Chemistry Division Argonne National Laboratory Argonne, Ill. WORK performed under the auspices of the U. S.Atomic Energy Commission. 1 Present address, Japan Atomic Energy Research Institute, Tokai, Ibaraki, Japan
Comparison of Electron Capture and Hydrogen Flame Detectors for Gas Chromatographic Determination of Trace Amounts of Metal Chelates SIR: Various detectors-e.g., hydrogen flame ionization (3, 4),thermionic emission ionization (g), argon ionization ( I ) , thermal conductivity (9),electron capture ( 7 , 8))and flame photometric (5)-have been used for the gas chromatographic determination of metal chelates, primarily acetylacetonates and fluorinated acetylacetonates. Although quantitative aspects of these detectors have been studied, especially of the electron capture ( 7 , 8) and flame ionization detectors (3, 4), investigations of their relative performances have been limited. The present investigation comprised a comparison of the electron capture and flame ionization detectors, and lower limits of detection were determined for both detectors for trifluoroacetylacetonates of chromium(II1) , aluminum(II1) , copl)er(II), and chromium(II1)-acetylacetonate. Satisfactory accuracy and
precision for both detectors were demonstrated by analyzing known mix. tures. EXPERIMENTAL
Preparation of Samples. Trifluoroacetylacetonates (tfa) were synthesized by published procedures (1, 9). hcetylacetonates (aa) were obtained from the MacKenzie Chemical Works, Inc. Stock solutions were prepared b dissolving 0.1 gram, accurately weighel of chelate in benzene ( 7 ) and diluting to 50 ml. in volumetric flasks. Dilutions to give concentrations of to 10-8 gram per ml. were made with benzene. Apparatus. An herograph .I-90 chromatograph equipped with a n herograph electron capture detector (concentric design) was used with a variable cathode voltage. T h e detector was operated with a n electrometer input impedance of 107 ohms
Table I. Lower Limits of Detection for Metal Chelates" Hydrogen flame, amt. detectable Electron capture, amt. detectable Com__________ pound Moles Moles/sec. Moles hloles/sec. 1 2 x 10-10 5 9 x 10-13 1 1 x 10-14 4 1 x 10-13 Cr( aa )3 3 7 x 10-10 9 3 x 10-13 1 3 x lo-'@ 3 1 x 10-1' Cr( tfa j 3 1 7 x 10-10 7 2 x 10-13 1 2 x 10-14 1 2 x 10-13 Al(tfa)n 16 X 3 2 x 10-12 2 0 x 10-1" 2 0 x 10-12 Cu(tfa)s Column temperature mas 160' C for Cr(aa)3and 110' C for trifluoroacetylacetonates; nitrogen carrier gas flow rates were 60 and 50 nil /min for the electron capture and hydrogen flame detectors, respectively
2034
ANALYTICAL CHEMISTRY
and a I-mv. recorder. At conditions for optimum sensitivity the noise level of the system was about 2 X ampere. Detector voltages for Cr(aa)b, Cr(tfa)3, and Cu(tfa)* were 35, 30, 35, and 40 volts, respectively. The hydrogen flame detector wac of conventional design and was operated with an electrometer input impedance of 108 ohms and a 10-mv. recorder. At conditions for optimum sensitivity the noice level of the system was about 2x ampere. Columns of borosilicate glass tubing (3 feet long by l/s-inch i d . ) were packed with glass microbeads (60- to 80- mesh) coated with 0 2% silicone oil (Dow Corning 550). Traces of iron particles were removed from the glass beads with a magnet before coating. General operating conditions mere similar to those described by Sievers et al. (9). Procedures. Calibration curves relating peak areas (planimetered) to weight c ; were obtained by an internal standard technique (n-hexadecane as the reference compound) for the flame ionization detector and by a constant volume technique for the electron capture detector. Some electron capture analyses were made with chloroform (8) or carbon tetrachloride ac an internal standard; however, the high electron affinities of these compourids necessitated large dilutions (with increased possibilities for errors) to obtain desired sample to ctandard ratios. For this reason the conytant volume method was generally preferred.
I
I
i - 1
I. Y E N Z E N E S O L V E N T 2. A l ; T F A ) , . O 21% 3. n C 1 6 - 3 4 , I N T E R N A L S T A N D A R D , 0 2 0 ' X
I
2 . A l ( T F A l ~, 1 7 0 O P P B
3. C r ( T F A I )
, 70
PPB
COL.TEMP.= 12O'C FLOW= 60rnl/min
4. Cu ( T F A ) 2 , 0 5 7 % 5. Cr ( T F A 1 3 , 0 '9%
81
I
i
I , B E N Z E N E SOLVENT
W
W v,
v)
z
z
2
0
v)
ln
W
W
a
D:
IL
0 -Iu W I-
[r
0 IV W IW
W
0
n
I 0
1
I
I
I
I
4
8
12
16
20
R E T E N T I O N TIME , M I N U T E S
Figure 1 . detection
Separation
of trifluoroacetylacetonates with hydrogen flame
RESULTS A N D IDISCUSSION
The limits of detection determined for chelates of Cr, A1, and Cu are shown in Table I. The minimum detectable amount of sample was taken as that required to give a pe:ik twice as high as the noise level, which was 1 to 2 mm. Ivith both instruments. The sensitivity in moles per second was calculated by dividing the minimum detectable amount by the peak width in seconds (6). The limits of detection for electron capture are significantly lower than those for flame ionization, mainly because of the high electron affinity of the fluorinated ligands, although the role of the metal ion is also significant (7). With flame ionization the effects of fluorine and the metal ion are also evident, but to a smaller degree. Fluorine atoms diminish sensitivity lowering the effective carbon number of the moleculc ( 4 ) . (Jomparison of the limits of detection for Cr(tfa)a and
Table 11.
Mixture
.41(tfa)3 shows the effect of the metal ion upon sensitivity. The aluminum chelate exhibits a lower limit of detection, which is in reverse order of the respective limits of detection obtained with electron capture. For electron capture, the concentrations a t which linear response was obtained varied widely with the type of compound-e.g., t o IO-$ gram for Cr(tfa)r and lO-"J to lo-* gram for Al(tfa)3. With flame ionization, the linear range was much wider-e.g., lo-* to 1 0 - ~ gram Cr(tfa)3. Calibration curves for the flame detector, though linear, usually did not pass through the origin (4). This abnormal behavior apparently is a peculiarity of the combustion process, because calibration curves obtained with the electron capture detector passed through the origin. The reproducibility and relative error of the chromatographic method. are indicated in Table 11. Chromatograms
Analysis of Mixtures
Found _~ ___
16
Component Al(tfa), Cu(tfa)z Cr( tfa), .41( tfa)s
Added
Av.a
Av. dev. &0 01 +0 04
% Rel.
error 0 20YG -4 6 0 2170 - 20 0 57% 0 46% 0 19% 0 2057 f 0 01 +5 0 2c 1700 p.p.b. 1600 p.p.b. f100 -5 6 Cr(tfa)a 70 p.p.b. 60 p.p.b. =!= 10 - 14 Av. of four determinations. Hydrogen flame detection. Electron capture detection. No.
+I
I RETENTION
3
I 4
I 5
T I M E , MINUTES
Figure 2. Separation of trifluoroacetylacetonates with ele-tron capture detection
of the respective mixtures are illustrated in Figures 1 and 2. Analyses for chromium and aluminum were generally satisfactory. Copper recoveries, misture 1, were low, however. The reason for this is not known, but it may be due partly to the incomplete separation from chromium (Figure 1). The separation might be improved with a longer column and with temperature programming. The scope and speed of an analysis could be extended by combining both detectors in a single chromatographic run. I n this way, the advantages of both detectors could be utilized and both trace and major components could be determined on a single sample-e.g., a few parts per billion of chromium in the presence of a few per cent of aluminum. LITERATURE CITED
(1) Berg, E.
W.,Trueniper, J . T., J .
Phys. Chem. 64, 487 (1960). (2) Biermann, 51'. J., Gesser, H., AXAL. CHEM.32, 1525 (1960). (3) Brandt, W. W., Heveran, J. E., 142nd Meeting, ilCS, Atlantic City, N . J., September 11162. ( 4 ) Hill, R. D., Gesser, H., J . Gas Chromatog. 1, s o . 10, 11 (1963). ( 5 ) Juvet, R. S., Ilnrbin, R . P., Ibid., No. 12, p. 14. (6) Landowne, 11. A , , Lipsky, S.R., AXAL. CHEM.34, 726 (1962). (7) Ross, W. I)., Zbitl., 35, 1596 (1963). ( 8 ) Ross, W. I)., Wheeler, G., Ibid., 36,
266 11964). (9) Sievers, R. E., Ponder, R . W., Morrisj 11.L., Moshier, R. W., Inorg. Chem. 2 , 693 (1963).
D. K E K D A L L ALBERT Research and Development Department American Oil Co. Whiting, Ind.
VOL. 36, NO. IO, SEPTEMBER 1964
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