second-dimension chromatographic stage were omitted, this compound would be included with a-tocopherol. The transformation may be comparable with the conversion of ubiquinone to ubichromenol by Florex XXS reported by Crider, Alaupovic, and Johnson (3). Tests were done with other batches of Floridin and with other eluting solvents, and complete blanks. The loss of tocopherol was variable, of the order of 3 pg. or more. On the other hand benzene, or mixtures of light petroleum with ethyl alcohol, acetone, methylene chloride, or other solvents, when passed through columns of Floridin, extracted reducing substances approximately equivalent to 3 pg. of tocopherol. Hence 100% recovery could be simulated, even though part of the tocopherol had been lost. Although in this example the gain balanced the loss, both are variable and not always similar. The loss of tocopherol increased only slightly with the amount applied to a column; in other words, the percentage recovery improved with the amount used.
In methods such as the Analytical Methods Committee's (1) in which 1000 pg. or other large amounts of tocopherol are chromatographed, and only a small aliquot is used for later stages, a loss of a few micrograms might pass unnoticed. With other materials than seed oils or concentrates, much smaller amounts of tocopherol may have to be taken through all stages. In such cases small losses represent large percentages, which would be detected if other reducing substances were eliminated.
LITERATURE CITED
(1) Analytical
Society for
Methods Committee, Analytical Chemistry,
Analyst 84,356 (1959). (2) Bro-Rasmussen, F., Hjarde, W., Acta Chem. Scand. 11,34 (1957). (3) Crider, Q. E., Alaupovic, P., Johnson, B. C., J . Nutrition 73,64 (1961). (4) Djcks, M., Feedstufls 1960,92. (5) Diplock, A. T., Green, J., Edwin, E. E., Bunyan, J., Biochem. J . 76, 563 (1960). (6) Edisbury, J. R., Gillow, J., Taylor, R. J., Analyst 79, 617 (1954). (7) Green, J., Marcinkiewicz, S., Watt, P. R., J . Sn'. Food Agr. 6,274 (1955). (8) Hobson-Frohock, A., Analyst 84, 567 (1959). (9) Kjolhede, K. Th., 2. Vitaminfwsch. 12,138 (1942). (10) Lambertsen, G., Braekkan, 0. R., Analyst 84, 706 (1959). (11) Lehman, R. W., Methods of Biochent. Anal. 2, 153 (1955). (12) Quaife, M. L., Dju, M. Y., J . Biol. Chem. 180, 263 (1949). (13) Rindi, G., Intern. Reu. Vitamin Research 28,225 (1958). (14) Werner, E. A,, Analyst 58, 335 (1933). RECEIVEDfor review July 11, 1960. Resubmitted April 19, 1961. Accepted May 3, 1961.
CONCLUSION
Two-dimensional paper chromatography has advantages over other methods of purification, in that the tocopherol can be more certainly identified. The results above emphasize another advantage-that artifacts introduced during determinations can be eliminated. The possibility exists that alternative methods are not as good as recovery tests suggest.
Flame Photometry Using Oxycyanogen Flame J. W. ROBINSON Esso Research laboratories, Baton Rouge Refinery, Humble Oil & Refining Co., Baton Rouge, La.
b Many more metals exhibit line spectra in oxycyanogen flames than in oxyhydrogen flames. Of 40 metals examined, 29 emitted useful line spectra. These metals were contained in Groups I and II of the Periodic Table and the transition elements. The composition of the flame--.e., either oxycyanogen or oxyhydrogen- determined whether a metal exhibited line spectra or a continuum. However, the type of solvent determined the intensity of this excitation, whether it was line spectra or continuum. Important variables noted were feed rate, fuel-oxygen ratio, relative position of the flame in the inlet slit of the monochromator, burner design, and a steady flow of fuel-oxygen mixture to the burner. Use of this type of flame should considerably broaden the application of flame photometry and result in cheaper and faster trace metal analyses in samples for which the more expensive spectrographic equipment is now used.
I
1955 Baker and Vallee (1) demonstrated that a flame made from oxygen and cyanogen could be used as a source in flame photometry. The advantage of this flame was the temperatures reached-of the order of
4500' C., whereas the temperatures
reached in conventional oxyhydrogen or oxyacetylene flames are of the order of 3000" C. Further excellent work by Gilbert (4) has illustrated the potential of this high temperature flame. The object of this study was to define how much these developments have extended the usefulness of flame photometry and to obtain information on instrumental and fundamental advantages and limitations involved in this system. The principles involved are exactly the same as in conventional flame photometry. The variable which affects the intensity of emission is the number of excited atoms in the system. This is dependent on a number of variables, such as rate of feed, type of solvent used, and the combustion pattern in the flame. These factors are discussed later. Recent work (6) has shown that ambient
ultraviolet light in a flame appears to have a major effect on the intensity of emission spectra. It is probable that the ultraviolet light increases the number of excited atoms in a given atom population over and above those excited thermally. EQUIPMENT
The equipment used was a DK-1 spectrophotometer, 1P28 detector, a burner designed for use with this fuel, and an all-metal fuel line. Metal Fuel Line. Cyanogen is usually obtained as a liquid contained under pressure in metal cylinders. Unfortunately, it does not flow in a steady rate and this seriously affects the type and stability of the flame. It was necessary to control this irregular flow by inserting a constant pressure valve between the cylinder and the burner. Another difficulty
To Pilot Flame
Cyonogen
N
1226
ANALYTICAL CHEMISTRY
TO Main
Oxyprn
Flame 20' i8/8 Steel 0.085'l.D.
0.125. O.D. Coiled 2-1/2 Inches
i" Stainless 1.0 Steel I - 5ie'o.o.
Figure 1.
Metal fuel line
Pilot Flame Fuel Chamber
Main Flame And Sample Aspiration
(g#@&-O*/[CN,2
Sample
Figure 2. Schematic diagram of oxycyanogen burner
with this fuel is its slow rate of diffusion into the oxygen. This causes local pockets of cyanogen and gives rise to an unsteady flame. These difficulties were overcome by premixing the oxygen and cyanogen. Also, inasmuch as flash back and explosions were encountered when rubber tubing was used, an all-metal fuel line was fabricated. The oxygen and cyanogen were mixed by passage through a small cylinder filled with glass wool; the mixed gases were then passed to the burner. With the metal line, in no case was the flash back experienced. A schematic diagram is shown in Figure 1. The advantage held by this design over other published systems is that a single mixing chamber is used. This ensures that the fuel to the pilot flame and to the main flame is constant in composition. Further, the apparatus was simpler to construct and use, inasmuch as it included fewer regulators and mixing chambers.
res VAVXLUWS (IILLXIXCRONI)
Figure 3.
I 101
Burner. The problem of flame blowout was overcome by introducing a pilot flame fitted onto a Beckman burner with the hydrogen port removed. Under these conditions the main jet could be operated a t high fuel - oxygen flow rates, and satisfactory aspiration of the sample was effected. A diagram of the burner is shown in Figure 2. Experimental work showed thabover a wide range the relative rates of introduction of fuel to the pilot flame and main flame of the burner seemed to be unimportant. The rate of flow to the pilot flame was adjusted so that the flame would just remain kindled. The rate of flow of fuel mixture to the main burner was then operated a t any convenient flow rate. For this work the flow rate of the pilot flame was 1 cu. foot per hour and to the main flame 4 cu. feet per hour of the stoichiometric mixture of (CN)2 02. Difficulty was encountered in trying to duplicate the results obtained with other burners mentioned in the literature (2). Sample aspiration a t right angles to the direction of flow of the fuel mixture caused the flame to be unsymmetrical and to vary with sample feed rate. Also, the critical adjustment of the sample inlet capillary and the fuel line was a continuous source of trouble. No doubt, in the hands of a skilled operator
Spectrum of iron in oxycyanogen flame
Iron lines (solid) superimposed on oxycyanogen flame spectrum Cyanogen flame with excess oxygen generates no ultraviolet light or iron spectrum although the temperature of bath flames was equal
40
u
0
10
100
1000 5000
10
0
'Oak
C
..-UI
IC0
1000 5000
D
&
Li and K 40
0
10
100
1000 5000
0
Interfering Element, P.P.M.
+
Figure 4.
IO
100
1000 5000
Interfering Element,PP M
Effects of lithium and potassium on sodium emission Relative emission of sodium 5 8 9 0 Blank reading. N o = 0
A.
Unmasked flame (total flame) Na. 10 p.p.m. Li (1 0,000 p.p.m.). 26 divisions K (10,000 p.p.m.). 6 divisions
C.
Tip of inner cone (masked flame) Na. 10 p.p.m. Li (1 0,000 p.p.m.). 2 divisions K ( 1 0,000 p.p.m.). 0 division
6.
Inner cone (masked flame) No. 10 p.p.m. Li (1 0,000 p.p.rn.). 23 divisions K (1 0,000 p.p.m.). 6 divisions
D.
Unmasked flame (total flame) Experiment a t N a concentration of 500 p.p.m. Li (1 0,000 p.p.m.). 3 divisions K (1 0,000 p.p.m.). 0.5 division Sensitivity lower than in previous experiments
VOL. 33, NO. 9, AUGUST 1 9 6 1
1227
this burner would be satisfactory. However, the modifled Beckman burner used for this work was easy to make and virtually trouble-free. The burner was carried in a support which could be moved in the vertical or both horizontal planes. This enabled easy optical alignment of the burner and also enabled studies to be made of the intensity of emission from various parts of the flame. Using two different burners under the same operating conditions did not produce spectra of equal intensity. No doubt, differences in atomization of the sample (drop size) and the ratio of sample to flame components contribute most to the differences in spectral intensities observed. Flame Structure. In general, there are three main parts to the flame: the inner cone, the interconal gases, and the outer mantle. I n an oxycyanogen flame the inner cone is intensely brilliant. With different burners operating under similar conditions, the height of these different zones varied considerably. This is, in itself, an undesirable feature, since reproducible results are obtained only when the same relative position of the flame is examined in each case. Experimental work showed that the intensity of emission from these different parts of the flame varied greatly and confirmed findings published earlier (6). For most metals, the best region for analytical use was immediately above the inner cone. Although the intensity of sample emission was lower from this part of the flame, the background intensity and noise level were more acceptable. Fuel Ratio. The ratio of cyanogen to oxygen had a very large effect on the intensity of the emission from a given solution. This effect was brought about by two subsidiary effects: the temperature of the flame and the nature of the flame. The hottest temperature of the flame is obtained when the stoichiometric mixture of oxygen and cyanogen is used. With excess cyanogen the inner cone expanded until it became almost the whole flame. Its color changed to a deep purple, and emitted a high intensity of ultraviolet light. These changes in flame type come about with very small changes in ratios of oxygen to cyanogen. This makes it impractical to preset the oxygen and cyanogen pressures in order to get a stoichiometric mixture and steady flame. Consequently, the burner is best set by visual inspection. Unfortunately, the different types of flame described above show very different emission spectra for the same metal (Figure 3). The fuel ratio has a profound effect on the production and intensity of emission lines. Premixing of the oxygen and cyanogen overcame this problem to some 1228
ANALYTICAL CHEMISTRY
extent, since it eliminated local areas of excess cyanogen or excess oxygen in the flame. This, in turn, reduced the signal and background noise and allowed more reproducible results to be obtained. Interference from Other Metals. At this point, very limited work has been carried out on the interference from other metals in oxycyanogen flames. However, i t has been observed t h a t with nickel, comparatively large quantities of alumina, silica, iron, vanadium, and molybdenum did not
interfere with the intensity of,emission from the nickel. Since these metals tend t o give high background and, cause interference in nprmal flame photometry, it indicates that interference effects using the- Qxycyanogen flame would probably be somewhat less than with the conventional oxyhydrogen and oxyacetylene flames. ALKALI METALS. The effects of lithium and potassium on sodium emission were also studied. The emission intensity of sodium was measured a t
Table 1.
Limits of Detection by (Expressed in p.p.m. of metal
Element A1 B Ba
Ca AS
Cd Ce
A,
Flame Oxycyanogen Aqueous Organic6 A. solvent solvent
Oxyhydrogen, organic* solvent N.D. N.D. N.D.
Solvent Used n-Heptane +Heptane Ethanol Ethanol
3944 3961
10 20
300 300
2497
5OOo
15 5
20 0.5
3501 4534 4554 5535 4426
0.05 0.5 0.5
1 10
50 1.0
10
0.5
300
N.D. N.D. High background N.D.
N.D. N.D. N.D.
n-Heptane
N.D. N.D.
Acetylacetone Acetylacetone Benzene Benzene n-Heptane n-Heptane Benzene Benzene %-Heptane n-Heptane
1890 2288 2288 3466 3561
30
N.D.
N.D. N.D. N.D. N.D. 300
N.D.
Ethanol Ethanol Benzene
Acetylacetone
3577 5523 3405 3474
300 4 6
100 0.5 0.6
4 6
CU
3247 3274
2 2
0.3 0.1
0.5 1.0
Cr
3578 4254
0.1 0.1
0.5 0.1
Ga
4172 4300
7 5 2
0.1
2.0
AU
2427 4837
Fe
3581 3719 3737
6 6
5 1 1
50 2 2
Pb
2170 2393 4057
N.D. N.D.
N.D. N.D.
N.D. N.D.
15
1
100
Li
3232 4603
25 30
0.5 0.5
6
Mg
2852 4994
N.D. N.D.
70 70
N.D. N.D.
Mn Mo
4030
0.2
0.03
0.05
3798 3864 3902
N.D. N.D. 300
Hi3
2536 4536
N.D.
N.D. N.D.
n-Heptane
N.D.
Ni
3414 3524 2909 3301
10 1
0.3 0.3
1.5 0.3
Benzene Benzene Benzene Benzene
co
os
N.D. N.D. N.D. N.D.
N.D.
250
N.D. N.D. N.D.
N.D.
N.D. N.D. N.D.
N.D.
N.D.
Acetylacetone Acetylacetone Acetylacetone Benzene Benzene Benzene n-Heptane %-Heptane Benzene Benzene n-Heptane
three parts of the flame, when varying quantities of lithium or potassium were added. The results are shown in Figure 4. The results indicate that interference took place at lower sodium concentration more than a t higher concentration. The extent of interference is affected by the part of the flame examined, and the extent of interference by lithium and potassium was not related when different parts of the flame were examined. I t can be concluded that the niutunl
interference effect of alkali metals noted in conventional flame photometry still pertains in high temperature flames.
RESULTS SAFETY PRECAUTIONS
Using premixed cyanogen and oxygen as a fuel involves two hazards-i.e., the toxicity of the cyanogen and the explosive nature of the cyanogenoxygen mixture. Precautions should be taken a t all times to minimize these sources of danger. The explosion haz-
Emission Flame Photometry
in solution being examined)
Element Pd Pt Si
4% Na
Ti
w U V
Zn Sr
Sn Bi
Zr Tlz
SI)
Be
Flame Oxycyanogen A ueous Organic“ x, A. soPvent solvent 3242 3404 342 1 2659 2830 2922 2506 2516 2528 3280 3282 3302 5890 4981
50 0.5 200 N.T).
499 1 4999
20) Inner cone 20) 1000) Outer cone
4008 4294 4302 4680 3552 3672 424 1 3183 4379 2183 4215 4607 2840 3175 3262 2898 3067
N.D. N.D.
4722 4689 2571 2432 4661 3232) 3267) 28781 2769) 2068) 3321) 3130) 3131) 2349)
N.D. N.D. N.D. N.D. N.D.
3 4 15 0.01
N.D. 6 N.D.
N.D. N.D.
3 10 N.D. 0.1 0.03 100 500
N.D. N.D. N.D. N.D.
Oxyhydrogen, organic“ solvent
1.0 0.2 2.0
50 2.5 10
N.D.
S.D. X.D. N.D. N.D. N.D. N.D.
N.D. N.D. N.D.
N.D.
N.D. 0.8 0.8 2 0.005 15
12 12
N.D. N.D. N.D. 2 30
N.D. 0.03 0.005 3 5 5
X.D. High background
200 loo0 1000 300
30 10 100 50
N.D. N.D. N.D. N.D. N.D.
N.D. N.D.
N.D. N.D. S.D.
ard was minimized by using the metal fuel line described above.
3 3 5 0.01
High background S o lines
N.D. N.D. N.D. N.D. N.D. N.D.
Solvent Used Ethanol Ethanol Ethanol Benzene Benzene Benzene Benzene Benzene Benzene Ethanol Ethanol Benzene Benzene n-Heptane n-Heptane n-Heptane
Acetylacetone Benzene
N.D.
n-Heptane n-Heptane n-Heptane n-Heptane n-Hep tane n-Heptane Benzene Benzene
N.D. N.D. N.D. N.D. N.D. N.D. N.D. N.D. N.D. N.D. N.D. N.D.
Benzene n-Heptane n-Heptane n-Heptane n-Heptane Benzene Benzene Benzene Benzene Benzene Ethanol Ethanol
0.5 0.02
N.D. N.D. N.D. N.D.
Solvents were chosen because of convenience and ease of solution. made to find the best solvent.
No attempt was
Forty elements were examined in oxyhydrogen and oxycyanogen flames for comparison purposes. Recently, attention has been paid to the effect of organic solvents on the intensity of flame spectra. It was therefore felt desirable to obtain information on limits of detection for these elements when organic solvents were used in oxycyanogen or in oxyhydrogen flames. The results are shown in Table I. Detection Limits. N.D. in Table I indicates “not detected” in solutions containing 1000 p.p.m. of the metal being examined. Other detection limits were measured by successive dilutions of the original solution containing 1000 p.p.m. The detection limit denoted the metal concentration which gave a signal equal to two thirds of the noise level at that wave lengthi.e., the smallest concentration which could be measured directly. No extrapolation from more concentrated solutions was made. The feed rates were as follows:
Solvent Water +Heptane Acetylacetone Benzene Ethanol
Feed Rate, G./Min. 0.8 1.41 1.10 1.80 0.80
Of the 40 elements examined, 29 exhibited line spectra in the oxycyanogen flame. This compares to 17 in the oxyhydrogen flame. When an organic solvent was used, there usually was an enhancement of signal. In a number of cases the combination of oxyhydrogen flame and organic solvents produced more intense spectra than the combination of oxycyanogen flame and aqueous solvents. At the operating feed rates the temperature of the latter combination was considerably higher than the temperature of the former. This indicated that the solvent used had a more pronounced effect on the intensity of spectrum than the temperature of the flame. A possible explanation of this observation has been advanced (5). VARIABLES
During this work it was found that certain variables had a profound effect on the intensity of emision obtained from a given solution of metal. Sample Feed Rate. An account of the effect of feed rate on emission intensity from an oxycyanogen flame is given by Fuwa, Thiers, Vallte, and Baker (S), who show how the intensity of the emission goes through a maximum VOL. 33, NO. 9, AUGUST 1961
1229
Table
II.
Relative Emission Intensity of Nickel
Stock solution. Nickel naphthenate (spectrographically pure dissolved in benzene) (500 p.p.m. Ni) Solvent solution. 10% stack solution90% other solvent Relative Intensity, Ni 3414A. Feed (Corrected Rate, for Feed Solvent G./Min. Rate) Acetone 1.86 18.3 %-Heptane 1.41 18.5 Methanol 1.28 18.6 Methylcyclopentane 1.60 14.0 n-Hexyl ether 0.46 19.5 Nitrobenzene 0.54 30.0 To1u ene 1.87 16 Ethyl octane 1.50 19 Cyclohexane 1.13 25 Acetylacetone 1.10 20 Ethyl chloride 1.40 17 Monochlorobenzene 1.60 i4 Xylene 1.70 17 Chlorobenzene 1.0 27 Methyl ethyl ketone 1 . 7 16 Benzene 1.8 19 Carbon tetrachloride 1 . 6 14 Ethanol 0.8 19
and then decreases rapidly as feed rate is further increased. This is attributed to a fall off in flame temperature a t increased flow rates. Similar results were obtained in our laboratories.
It is also probable that, a t high feed rates, the energy liberated by the flame per unit weight of sample is low. Much of it may be used in evaporating the solvent instead of exciting the metal atoms. This would muse a profound decrease in emission intensity. However, it is apparent that careful control over feed rate is essential. The feed rates used in this work, shown in Table I, were measured directly by weighing the sample and container before and after aspiration for a known period of time. The optimum feed rate found was approximately ten times as great as that reported previously. This may be due to differences in burner design. Solvents. As can be seen from Table I, organic solvents in many cases enhance the intensity of emission for a given metal when introduced into the flame. It was observed t h a t different organic solvents affect the intensity of the emission differently. This is illustrated in Table 11, which gives the relative emission intensity exhibited by nickel in different solvents. If flame temperature alone controlled the intensity of emission, all organic solvents would give similar enhancement effects. Since this is not the case, it seems that the efficiency of producing the emitting species is a t least as im-
portant as the flame temperature (3). Physical properties of the solvent which can cause B change in emission include stability in the flame, the ease of combustion and liberation of the excited metal atoms, drop size, and ease of evaporation. No doubt some of the variation in the intensity of signal between different organic solvents can be explained by variation in aspiration rates for a given flame condition. ACKNOWLEDGMENT
The author thanks the Humble Oil & Refining Co. for permission to publish this work and S. A. Bartkiewicz, who designed the burner used. LITERATURE CITED
(1) Baker, M. R., Vallee, B. L., J . Opt. SOC.Am. 45, 773 (1955). (2) Fuwa, K., Thiers, R. E., Vallee, B. L., ANAL.CHEM.31, 1419 (1959). (3) Fuwa, K., Thiers, R. E., Vallee, B. L., Baker, M. R., Ibid., 31, 2039 (1959). (4) Gilbert, P. T., “Oxy-Cyanogen Flame Photometry,” Beckman Instrument Co., Fullerton, Calif. (5) Robinson, J. W., Anal. Chim. Acta 23, 479 (1960). (6) Robinson, J. W., “Encyclopedia of Spectroscopy,” G. L. Clark, ed , Reinhold, New York, 1960. RECEIVED for review October 24 1960. Accepted May 15, 1961. Divihon of Analytical Chemistry, 138th Meeting, ACS, New York, N. Y., September 1960.
Liquid Scintillation Techniques Applied to Counting Phosphorescence Emission Measurement of Trace Quantities of Zinc Sulfide J.:D.
LUDWICK and R. W. PERKINS
General Electric Co., Hanford laboratories Operation, Richland, Wash. ,An analytical procedure is based on electronically counting the individual phosphorescence photons following light-excitation for the measurement of scintillation grade zinc sulfide particles on molecular air filters. The zinc sulfide was collected on these filters during meteorological studies of particle dispersion. The analytical procedure involves dissolving a zinc sulfide laden filter in an ethyl alcoholethyl acetate solvent, exposing the sample to a fluorescent lamp, allowing the sample to decay (in the dark) for a predetermined time, then counting the phosphorescence photon emission. The counting equipment requirements are similar to those commonly used for
1236
ANALYTICAL CHEMISTRY
counting tritium. The conditions of excitation and measurement yielded a sensitivity of about gram. A sensitivity improvement of one to two orders of magnitude could probably be obtained by minor procedural changes. The precision of the zinc sulfide measurements on clean and dirty filters is about &3% and f6% standard deviation, Corrections for loss in counting efficiency on dirty filters are made from absorbance measurements with a colorimeter.
Z
(fluorescent pigment, No.’2210, U. S. Radium Corp., Morristown, N. J.) is used as a tracer in studying down-wind parINC SULFIDE POWDER
ticle concentrations under different meteorological conditions. An aerosol generator discharged the finely divided material into the atmosphere, and collectors, using molecular filters (Membrane filter No. AM-1, Gelman Instrument Co., Chelsen, Mich.), are spaced around the generator for sampling. The ZnS is commonly measured by visual counting techniques under ultraviolet light; however, recently an instrument was designed (8) using alpha excitation for its measurement. Although this instrument appeared to be satisfactory for measurements of “clean” filters (6),it was not capable of measuring ZnS in the presence of dust, soot,
