mium solution and determined by solution in HNOs and titration with a standard thiocyanate solution. Cadmium can be determined by precipitation as CdNH4POd and conversion to CdZP20.I. Cadmium is separated from zinc by adding the sodium borohydride with constant stirring to the mixture of the +2 ions a t the initial p H 2, and adding 3N NaOH, after reduction, to dissolve the zinc compound(s). After warming on the hot plate for a half hour to increase the particle size of the cadmium precipitate, the hot mixture is filtered. The cadmium precipitate is presumed to be metallic cadmium. For analysis the separated elements may be converted to the pyrophosphates. Results obtained using one reprecipitation are as good as or better than those obtained by the hydrogen sulfide method after a third or fourth precipitation. However, the results obtained as described in the experimental part are not as satisfactory in this case as for the other mixtures studied. The separation of lead and zinc is effected by adding the sodium borohydride with constant stirring to the mixture of the f 2 ions a t initial p H 5.0 to 6.0, and adding ammonia solu-
tion after reduction to dissolve the zinc compound(s). The lead is filtered from the Einc solution, and the filtrate is adjusted to p H 5.6. A second NaBHd reduction is carried out on the filtrate and the resulting lead precipitate isolated as in the first reduction step. The lead from the two reductions may be dissolved in nitric acid, and determined by precipitation as the sulfate. Zinc can be determined by precipitation as ZnNH4P04and conversion to Zn2Pe0,. Excellent results are obtained by this procedure involving a second reduction of lead. To determine whether these methods are adaptable to mixtures with concentration ranges and relative concentrations different from those used in these studies, further experimental work is required. ACKNOWLEDGMENT
The authors thank the National Science Foundation] which helped support the work described. The application of aqueous sodium borohydride for the development of a general inorganic analytical scheme was conceived by G. W. Schaeffer, and the
National Science Foundation Grant was made to support this work on the basis of the proposal prepared by Schaeffer. Work reported in this paper was continued under this grant following the death of Schaeffer, along the general lines suggested by him. LITERATURE CITED
(1) Hillebrand, W.F., Lundell, G. E. F., “Applied Inorganic Analysis,” p. 182,
Wiley, New York, 1953. (2) Hyde, E. K., Hoekstra, H. R., Schaeffer, G. W., Schlesinger, H. I., “Some Properties of Aqueous Sodium and Lithium Borohydride]” Division
of Physical and Inorganic Chemistry,
110th Meeting, ACS, Chicago, Ill., September 1946. (3) Kramer, M., Ph.D. dissertation, Saint Louis University, 1954. (4) Lundell, G. E. F., Hoffman, J. I., “Outlines of Methods of Chemical Analysis,” p. 105. Wiley, New York, 1938. (5) Schaeffer, G. W.]Miniatas, B. O., “Reactions of Aqueous Sodium Borohydride. Reduction of Platinum(1V) and Palladium(II),” Division of Inor anic Chemistry, 138th Meeting, AES, N ew York, September 1960. RECEIVEDfor review May 24, 1961. Accepted August 8, 1961. Presented in part before Division of Inorganic Chemistry, 138th Meeting, ACS, New York, September 1960.
Flame Spectrophotometric Study of Barium JOHN A. DEAN and J. C. BURGER’ Department o f Chemistry, University of Tennessee, Knoxville, Tenn,
T. C. RAINS and
H. E. ZITTEL
Analytical Chemistry Division, Oak Ridge National laboratory, Oak Ridge, Tenn.
Flame emission characteristics of the barium ionic doublet at 455.4 and 493.4 mp, the atomic resonance line at 553.6 mp, and the BaOH and BaO bands at 488 and 513 mp were studied. A prism flame spectrophotometer (Beckman DU), superior in work with bands, and a grating type (Jarrell-Ash Ebert), superior in work with lines, were used. Barium concentrations ranged from 1 to 10 pg. per ml. (Jarrell-Ash Ebert) and 10 to 100 pg. per ml. (Beckman). Effects of flows of oxygen and fuel (hydrogen and acetylene), ratio of these flows, different regions of flame mantle viewed, organic solvents, and various cations and anions were determined. With anionic interferences, the oxygenacetylene has advantages over the oxygen-hydrogen flame; otherwise not. Spectral, condensed-phase, and radiation type interferences were investigated. Several elements interfere seriously. Flame spectrophotome-
1722
ANALYTICAL CHEMISTRY
try is rapid and is more sensitive and accurate than other methods for barium in the concentrations studied.
T
HE flame spectrophotometry of barium has been studied to a limited extent only (4, perhaps because the flame emission intensity of barium is less than that of magnesium, calcium, or strontium. However, of the methods available for the determination of barium in concentrations greater than 2 pg. per ml., flame spectrophotometry has a number of advantages. Watanabe and Kendall (16) have presented a complete flame spectrum of barium. The spectrum consists of an ionic doublet a t 455.4 and 493.4 mp, an atomic resonance line a t 553.6 mp, and a series of BaOH and BaO band structures within the regions from 450 to 610 mp and from 730 to 1000 mp. The 553.6mp line and the 488-mp band are used
most frequently for the flame spectrophotometric determination of barium. Although use of the 553.6-mp line provides the greatest sensitivity, several elements, especially calcium, interfere because they also radiate a t this wave length. The 5 1 3 - u band was used by Shaw (14) in the indirect flame spectrophotometric determination of sulfate. However, if any organic material (solvent) is present, this band cannot be used because there is a strong Co band a t 516 mp, Hinsvark, R i t t wer, and Sell (9) used the 873-mp band to determine milligram quantities of barium in the presence of calcium and strontium. The 873-mp band is not very intense, and a correction must be made for the radiation interference of CaO a t 873-mp. The influence of hydrocarbon solvents on the emission in1 Present address, Electronic Tube Division, Westinghouse Electric Corp., Elmira, N. Y.
of barium were studied: flow of oxygen The relative emission intensities of and fuel, ratio of these flows, regions of the barium lines and of the BaOH band a t 488 mp for the two instruments used the flame mantle observed, organic solin this study are presented in Table I. vents, and the presence of various anions and cations that are commonly asSince, among other things, the maxsociated with barium. The nature of imum emission intensity of any line or band is a function of the response of the working curves was critically exthe electron multiplier phototube and amined. of the slit width, it is not feasible to Spectrum. A flame that contains establish the maximum emission inbarium shows a series of BaOH and EXPERIMENTAL DETAILS BaO band structures within the region tensity that can be obtained. A more Reagents. Standard solution of practical emission intensity, as recorded from 450 to 610 mp and from 730 to barium, 1.00 mg. per ml., was prepared in Table I, was determined by setting 1000 mp. Prominent heads of band by dissolving 1.78 grams of BaClz 2Hz0 the wave length of the monochromator systems attributed to BaOH are located i n 0.1111 HC1 and diluting the resulting a t the wave length of the line or a t the a t 488, 513, and 527 mp. The molecular solution to 1 liter with 0.1111 HC1. energies of dissociation for the molecular wave length of the crest of the band and Nore dilute standard solutioiis of barium were prepared from this standband systems are 5.4 i~ 0.5 electron by setting the slit width a t a selected ard solution by appropriate dilutions volts (e.v.), whereas the excitation value (for lines: 0.030 mm. for the Beckwith 0.1X HC1. energies are listed from 2.0i to 2.90 e.v. man instrument and 0.05 mm. for the All othcr solutions used were prepared Jarrell-Ash spectrometer; for bands: (8912). from ACS-approved grade chemicals. The atomic line a t 553.6 mp is nestled 0.10 nim. for the Beckman instrument). Apparatus. FLAME SPECTROamong the emissions from the BaO The corresponding spectral band widths PHoTohiETERS. Jarrell-Ash Ebert molecular systems; the excitation enare included in Table I. Next, the scanning spectrometer, together with dynode voltage of the electron multiergy for this line is 2.24 e.v. Although flame attachment and the modified plier phototube (RCA IP28 for both the excitation energy of the atomic 0RXL18872k power supply (10). The instruments) was increased until the characteristics of the monochromator line is low, the emission intensity of the are: focal length, 500 mm.; grating, fluctuation of the recorder pen (noise line is not particularly high. One 1200 lines per mm. over a 52 X 52 mm. level) equaled 1% (0.1 mv.) of fullreason is the greater ease of ionizaruled area hlazed Tor 5000 -4.; effective scale deflection. Finally, a standard tion of barium atoms as compared with aperture, f, 8.5; linear dispersion a t the lighter alkaline-earth elements. solution of barium was aspirated into exit slit, 1 G -4.per mm.; spectral range, the flame, and the emission intensity For the singly ionized barium atom, the 2000 t o SO00 A. in first order. The ionization energy required is 5.21 e.v. was determined for the particular line -mve Icngth drive shaft-sine bar mechor band. If necessary, suitable supAn ionic doublet appears a t 455.4 and anism is iotated by a motor and 493.4 mp; the energies of excitation of pressor controls were used to keep the reduction gear system, mhich provides a pen on the chart. Under these operatthe lines of this doublet are only an smooth scanning rate zt eight different speeds within the range from 2 to 500 A. ing conditions, the Jarrell-Ash instruadditional 2.72 and 2.51 e.v., respecper minute. The instrument is proment gave the higher emission intentively. Consequently, the ionic doublet vided with interchangeable fised slits. sity for the barium lines, whereas the will be observed with comparatively Matched 50-micron entrance and exit Beckman instrument excelled for the good sensitivity in oxygen-fuel flames. slits were used in this study. The flame background emission is band systems. The superiority of the Beckman Nodel DU flame spectrograting instrument probably is due to constant and free from significant band photometer. Data were recorded on a less stray light and to better resoluspectra in the vicinity of the 455.4mp 10-mv. Bristol recorder, having a z/’g ionic line. The background reading tion, and thereby to the application of second pen response, by means of the Rcckmnn energy-recording attachment a larger dynode voltage to the photocan be taken a t 450 and/or 460 mp. (ER.4). The Beckman integral atomBy contrast, the ionic line a t 493.4 mp tube before the phototube noise exceeds izer burner was used throughout the and the atomic line a t 553.6 mp are 1%. When the same voltage was apstudy. plied to the phototube of each instrunestled among the emissions from the The following instrument settings molecular band systems. A background ment, the emission intensities of the were used, unless otherwise indicated: barium lines were identical. reading can be made only by the baseJarrellWorking Curve. ,4n oxygenline method. Although only the enBeckman Ash hydrogen and an oxygen-acetylene velope of the band systems is observed Sensitivity conflame possess sufficient energy to with the optics of the Beckman introl, yo adjust 50 (ERA) High strument, the fine structure is resolved ionize barium atoms. From the Saha Selector switch. with the Jarrell-Ash spectrometer. equation and the assumption that the position 0 1 High Multiplier phototube resistor, megohms 22 5 Multiplier phototube (RCA Table I. Emission Intensity of Barium Lines and Bands 1P28). volts (Standard solutions, 1 to 10 pg. of barium per ml.) 60 75 per dinode 0.03 0.05 Slit, mm. Slit Width Sensitivity, 0 60 0.08 Spectral band n-o.,n Jarrell-Ash Beckman DU Mv. .ue./M1./0.1 -, , -width, mp at Length, Spectral, Spectral, Jarrell500 mp Asha Beckman hIP AZm. m/l Mm. ml.c ROTAMETERS.Brooks Rotameter 455.4 0.05 0.08 0.03 0.5 0.06 0.7b Co., Lansdale, Pa., Sho-Rate -Model 493.4 0.05 0.08 0.03 0.6 0.08 0.8b 1356 was used to regulate the flow of 0.05 0.08 0.03 0.8 0.03 0 . 13b 553.6 the fuel gases. 488 0.05 0.08 0.1 1.9 1 0.17 513 ... ... 0.1 2.1 ... 0.3c RESULTS AND DISCUSSION Volts/dynode, 90. b Volts/dynode, 75. The effects of the following experic Voltsjdynode, 65. mental variables on emission intensity
tensity of the 873-mp band has been reported by Curtis, Knauer, and Hunter (9). The objective of the present investigation was to study the complex spectrum of barium and the effect of experimental variables on the emission intensity of barium.
I .
_I_
VOL. 33, NO. 12, NOVEMBER 1961
0
1723
rooo:
,
,
,
,
I
7
,
-
m
, ,,,
,
,
, ,,
line a t 553.6 mp has a slope (emissionfactor) of 0.97 for barium concentrations from 60 Mg. per ml. up to a t least 1000 pg. per ml. (Figure 1). At lower concentrations the slope (log emission plotted us. log concentration) decreases as a result of ionization. Even a t high concentrations of barium, self-absorp-
,
I I
100 1000 COQCENTRATION OF BARIUM, pg per ml 10
Figure 1 . barium
Log-log calibration curve for
partial pressure of metal atoms in the flame is 10-6 atm., the degree of ionization for barium is calculated to be 0.086 a t 2450" K. (net oxygen-hydrogen flame) and 0.428 a t 2800" K. (wet oxygen-acetylene flame) (7'). Any appreciable ionization will have a pronounced effect on the strength of the atomic lines and the ionic doublet of barium and on the shape of calibration curves based on emission intensity from the excited states of neutral atoms or the excited states of ionized atoms. A fundamental assumption in quantitative analysis is that, under given conditions, the intensity, I , of an emitted line within a flame is directly proportional to the concentration, C, of emitting atoms or
I = kC log I = log k
+ log c
A plot of log I log C should produce a curve of unit slope if complicating factors, such as self-absorption and ionization, are absent. When working curves do not satisfy the ideal relationship, they frequently satisfy the relationship tis.
I
=
kCn
Or
log I = log k
+ n(l0g C)
where n is sometimes referred t o as the emission factor (1). For relatively low concentrations of barium, an increase in flame temperature causes an exponential increase in the ionization. The consequence is a depletion of the number of available neutral atoms that can be excited to an upper-energy level, with the results that the intensity of the atomic line a t 553.6 mp is weakened, whereas the ionic lines a t 455.4 and 493.4 mp are strengthened, Consequently, the working curves for both classes of lines are nonlinear oyer the lower concentration ranges. In logarithmic coordinates and a t optimum instrument settings for an oxygen-acetylene flame, the atomic 1724
ANALYTICAL CHEMISTRY
01
0.2
0.3 0.4 0.5 RATIO OF OXYGEN FLOW TO HYDROGEN FLOW
the emission lines are approximately equal to those in oxygen-acetylene.
Effects of Flow of Oxygen and Hydrogen on Emission Intensities. The variation of the emission intensity as a function of the ratio of oxygen flow to hydrogen flow for several fixed oxygen flows is shown in Figure 2. For the ionic doublet of barium, the maximum emission intensity occurs when this ratio is 0.27. The value of this ratio is also 0.27 for the molecular band system that crests a t 513 mp, By contrast, the emission intensity of the atomic line does not exhibit a maximum a t any of the hydrogen flows investigated but continues to increase as the hydrogen flow increases. The particular burner and flowmeter combination that was used did not permit higher hydrogen flows. The relationship of emission reading, uncorrected for background emission, to the background emission follows the same trend as does the relationship of emission reading, corrected for background emission, t o the background emission. Effects of Flow of Oxygen and Acetylene on Emission Intensities. The variation of the emission intensity as a function of the ratio of oxygen flow to acetylene flow for several fixed oxygen flows is shown in Figure 3. The molecular band systems of barium, as represented by the crests a t 488 and 513 mp, were not studied because of the intensity of the flame background due to C:! band systems that appear in this portion of the spectrum. For the ratios of flow of oxygen to flow
Figure 2. Barium emission intensity as a function of ratio of oxygen flow to hydrogen flow 1 cu. ft./hr.
= 0.472 liter/min.
tion poses no problem when work is done with the atomic line, but ionization precludes the use of this line for concentrations of barium less than 60 pg. per ml., unless a radiation buffer is employed to repress the ionization of barium. By contrast, the ionic doublet of barium exhibits a complementary behavior. In logarithmic coordinates, its slope slowly decreases because of a diminishing degree of ionization with increasing concentration. For concentrations of barium between 80 and 100 pg. per ml., the slope becomes constant and has a value of 0.57. The emission intensities of the two lines of the ionic doublet parallel each other over the entire concentration range investigated. Measurements in oxygen-hydrogen, although hampered a t low barium concentrations by low emission intensity, showed that the logarithmic slopes for
.5..
---_-
I
s.5
2.0 2,5 3.0 RA-,O CiF OXYSEN FLOW 7'2 ACErY_ENE FLOW
Figure 3. Barium emission intensity as function of ratio of oxygen flow to acetylene flow 1 cu. ft./hr.
= 0.472 liter/min.
I
-OXYGEN-HYDROGEN FLAME
1
Table II.
Effect of Other Elements on Emission intensity of Barium in an OxygenHydrogen Flame
Barium Recovered, % Interferent Concn., Element rg./ml. 10 -4luminum 50 100 -4mmonium 1000 Boron 10 Calcium
10 U P . of Ba per -ML0 455.4 553.6 mfi mlr 63 62 41 50 36 30
Iron
Lead
Lithium
Magnesium
Sodium
Strontium
Thorium Titanium Zinc
25 100
25 100
...
...
... ...
...
... ...
1
100
1000 10 100 1000 100
81
59 50 93 76 55
...
e
... ... ...
...
106
109 114 124
C C
c
90 90 57
... ... ...
...
...
...
...
... ...
...
... ...
...
... ...
10
100 100 93 87 96 80
100 100 96 88 100 101
... ... ...
31 100 98 92 90 92 89 101 98 91
109
50
10
100 1000 10 100 10 100
88
71 29
1000 10 100 500 1000 10
...
50 100
75
500 100 1000 10 100 100 1000
a
Jarrell-Ash.
c
Direct spectral interference.
5
92 63 16 96 69 45 89 70
...
45
...
100
98
...
106 90 91 91 98 94 84 107 126 131 102 104
...
132 102 104 113
...
85 70
31
30
... ...
...
9
8
...
c
100
100 500 1000
100
C
c
94 65
...
100 105
... ...
100 100
... ...
...
...
75
...
...
98 80
...
500
500 1000 10 100 500 1000
.... *.. 80
...
...
... ...
...
93 67 ... 54
100
...
...
...
...
111
... ...
1000 10 100
...
...
72 ... 100 72 100 98 95
500
1000 Potassium
34
100
500
Nickel
...
... 100
1000 Molybdenum
...
...
1000 Lanthanum
... ... ... ...
500
Copper
513 mp
95 84 101 112 128
97 97 86
553.6 mp
mk
...
50 100
Chromium of acetylene investigated, emission intensities of the atomic and ionic lines increase continuously. However, the line-to-background emission intensity ratio passes through a maximum at ratios of oxygen flow to acetylene flow between 1.9 and 2.1 for a slit width of 0.030 mm. The emission intensity as a function of the flame region viewed for the several barium lines and one band system is shown in Figure 4. I n order t o observe the barium emission from different regions of the flame, the burner \\as mounted on a racking mechanism. At each setting (called burner height) a rectangular section within the flame mantle is viewed. The vertical dimension of the rectangular region is 6 mm. Thus, the designation of a position as being 10 mm. above the tip of the burner implies that a region of the flame mantle which extends from 10 to 16 mm. above the burner tip was viewed; this is the normal flame region that is viewed with the Beckman flame spectrophotometer. When an oxygen-hydrogen flame is used with the Beckman instrument, the normal position of the burner permits one to observe the region of maximum emission intensity. The emission intensity of the ionic doublet decreases markedly as the region viewed approaches the inner cone. For an oxygen-acetylene flame, the region of maximum emission intensity occurs immediately above the inner cone for both the atomic and the ionic lines; on the other hand, emission intensity decreases rapidly as a region higher in the flame mantle is viewed. Lundegardh (11) reported a similar phenomenon for the air-acetylene flame. However, the optimum line-to-background emission intensity ratio does occur at, or only slightly lower than, the normal position of the burner. Interferences. The extent to which other elements interfere with t h e barium emission is given in Tables
100 pg. of Ba per MLb
455.4
96 81
10
Figure 4. Effect of flame region viewed on emission intensity of barium
of Ba per M1.b 488 mp
...
5 HEIGHT AaOVE BASE OF F L A M E , mm
-- 119. 25
...
*..
...
... ... ... ...
88 80 78 100 100 100 ...
...
...
... ...
75 49 35
...
*.. 102 105 110
100 95
... C
c
84 53 c
C
...
96 59
87
80 76 96 104
100 100 98
103
...
...
...
... ... ... 90 94 100 ... 100
... ... ... ... 100 110
119
...
124
c
c
...
...
...
*.. ... ...
... ...
...
...
...
... ...
...
... ... ... ...
... ... ... / . .
...
... ... ...
...
35
... ...
...
... ...
...
...
... ... ... 133 .
.
I
...
77 29 28
100 103 101
...
...
...
55
100 108
114 130
...
... ... ... ... ... ... ...
... 79
...
... ... ...
...
100 100
100 95
...
, . .
... ... 135 ... ... 115
...
...
...
...
...
c
...
...
... ...
...
100
100
* Beckman DE.
VOL. 33, NO. 12, NOVEMBER 1961
1725
Table 111.
Effect of Other Elements on Emission Intensity of Barium in OxygenAcetylene Flame
Instrument, Beckman DU Concentration of Ba, 100 p g . per ml. Barium Interfered Recovered, % ' Concn., 455.4 553.6 Element pg./ml. mp m/l Aluminum 100 51 32 500 100 500
Calcium Chromium Iron
,,,,,.I ,
! ,,,,,,!I , ,, .L, , u] 601 " " ' I i 0.0001 0.00( O.O( 0.1 1.0 CONCENTRATION, M
Lanthanum
Figure 5. Effects of anions on recovery of barium in oxygen-hydrogen flame A.
Jarrell-Ash [Ba+2], 10 pg./ml. W a v e length, 553.6 m p Slit width, 0.05 mm. E. BeckmanDU [Ba+*], 100 pg./ml. W a v e length, 553.6 mp Slit width, 0.03 mm.
a
I1 and 111. Serious spectral interference is encountered from calcium, magnesium, and sodium a t 563.6 mp; from chromium, copper, iron, magnesium, and manganese in the region of the band system that crests a t 513 mp; and from magnesium a t the 493.4ml.c ionic line. A partial list of specificity factors for the band systems that crest at 513 and 873 mp has been published ( 5 ) . The ionic line a t 455.4 mp is markedly free from direct spectral interferences. Condensed-phase interference is observed with a number of elementsnamely, aluminum, chromium, iron, thorium, and titanium. When these elements are present, the use of releas-
Table IV.
Wave Length, M p
455.4
88 64 90 83 95 81 78 73 25 51 72 45
100 500 100 500 100 500 100 100 100 500
Organic Solvent Concn. (V,/V,), 70 Acetone 1. 9 3.8 6.4 11.a 21 . 0
488
10 30 50 70 90
553.6
10 30 50 70 90
+
Enhancement Factor Methanol Ethanol 2-Propanol 1,bDioxane 1.6 2.7 3.8 2.4
1.7 1.5 1.6 2.1 3.8
1.9 1.5 1.3 1.5 2.9
1.5 1.8 1.9 1.9 4.4
1.7
1.5 2.2 2.7 4.8 10.0
1.8 2.1 2.4 3.6 7.5
2.1 2.3 2.3 2.8 6.6
1.8 2.2 2.8 3.9 7.5
13.4
ANALYTICAL CHEMISTRY
.
~
l
l
1 IWLJ
~ ""1
0.01
O\
1.0
Jarrell-Ash [Ba'*], 10 pg./ml. W a v e length, 553.6 mp Slit width, 0.05 mm.
ing agents or protective chelating agents is recommended. Self-standardization (standard addition) in the higher concentration ranges may overcome the difficulties but a t the sacrifice of considerable emission intensity. Repression of the ionization of barium in the flame-Le., Ba" = Ba+ e--is the cause of the inhibition of the ionic lines and the enhancement of the atomic line and of the molecular bands when calcium, lithium, potassium, sodium, and strontium (presumably, also cesium and rubidium) are present. Each of these elements is easily ionized; the ionization of barium is thereby repressed with the consequent brightening of the atomic line and of the molecular band systems a t the expense of the emission intensity of the ionic lines.
1.5 I .8 2.0 2.9 8.6
~
Figure 6. Effects of anions on recovery of barium in oxygen-acetylene flame
Direct spectral interferences.
1 . *5 2.0 2.5 4.4 15.4
l
1111
0001
CONCENTRATION, M
136 116 123 145
5.3 7.9 10.9 16.9
90 c
80' 0.000i
e
5.7 6.5 8.8 14.1
3.9
0
m
80 67 100 86 97
4.8 6.2 9.1 16.2
7.6
W
>
a
(1
3.1 4.8 7.8 14.7
2.4
'zo:
12 (I
Enhancement of Barium Emission Intensity by Various Organic Solvents
10 30 50 70 90
1726
Potassium Sodium Strontium
24
CH3COOH
The trends of the data for the 493.4mp ionic line (not shown in Tables I1 and 111) parallel the trends of the data for the stronger 455.4-mp ionic line. A comparison of the results presented in Tables I1 and I11 indicates that an oxygen-acetylene flame has no advantage over an oxygen-hydrogen flame. The cooler oxygen-hydrogen flame seems to give consistently superior results and less interference, particularly from repression of the ionic lines. The effect of the common anions on the barium emission intensity is summarized in Figures 5 and 6. In general, the interferences of the anions on the atomic and ionic lines are significantly different from each other only in the anion concentration range from 0.1 to 1.OM. Chloride (as HC1) and nitrate (as " O s ) were innocuous in concentrations of 0.1M and less. Acetic acid enhanced the barium emission intensity in both flames. Contrary to the findings of Baker and Johnson (2) in their study of calcium, perchlorate (as HC104) failed to enhance the barium readings. In fact, a small depressive effect was observed for the oxygen-hydrogen flame; this effect has also been observed for elements other than barium (6, l a ) . The depression caused by phosphate is not unexpected and is an example of condensed-phase interference. In the hotter oxygen-acetylene flame, the phosphate interference is less and can be easily overcome by self-standardiaation. Effect of Organic-Aqueous Solvent Media. The emission intensity of barium is considerably enhanced when organic solvents are contained in the test solution (Table IV). The ionic lines are enhanced the most, the bands the least. When the organic-aqueous
solvent mixtures are used, the depth of immersion of the capillary of the burner into the test solution appears t o be critical. It is recommended that the emission readings be taken within the time interval of 10 to 15 seconds after initiation of aspiration and that the beaker which contains the test solution be refilled to the original level before a reading is repeated. Of the solvent mixtures tested, 1,4 dioxane-water (1 to 1 by volume) provided the most reproducible flame conditions. Although the enhancement achieved is less than that obtained with acetone-water or methanol-water in similar volume ratios, slight variation in the volume ratio of 1,4-dioxanewater is not as critical. Higher volume ratios of organic solvent to water provide larger enhancements, but the solvent composition is very critical because of the steep slope of the curve showing the emission intensity us. sol-
vent composition; also the consumption of the test solution is very rapid. ACKNOWLEDGMENT
The authors acknowledge the assistance of Helen P. Raaen in the preparation of this paper. LITERATURE CITED
rem, L. H., “SpectrochemicalAnalp. 78, Addison-Wesley, Cambridge, Mass., 1950. (2) Baker, G. L., Johnson, L. H., ANAL. CHEM.26,465 (1954). (3) Curtis, G. W., Knauer, H . E., Hunter, L. E., Am. SOC. Testzng Materials, Spec. Tech. Publ. No. 116, 67 (1951). (4) Dean, J. A., “Flame Photometry,” Chap. 14, McGraw-Hill, New York, 1mn. -I--. (5) Ibid., p. 211. (6) Dean, J. A., Burger, J. C., ANAL. CHEM.27,1052 (1955). (7) Foster, W. H., Jr., Hume, D. N., Ibad., 31,2033 (1959). (8) Gaydon, A . G., “Dissociation Energies “ks$’
and Spectra of Diatomic Molecules,” 2nd ed., pp. 201-3, Chapman & Hall, London, 1953. (9) Hinsvark, 0. N., Wittmer, S. H., Sell, H. M., ANAL, CHEM.25, 320 (1953). (10) Kelley, M. T., Fisher, D. J., JoneB, H. C., Ibid., 31, 178 (1959). (11) Lundegardh, H., Lantbruks-Hoqskol. Ann. 3, 49 (1936). (12) Mavrodineanu, R., Boiteux, H., ILL’AnalyseSpectrale Quantitative z a r la Flamme,” Chap. 14, Masson et le, Paris, 1954. (13) Menis, O., Rains, T. C., ANAL. CHEM.32, 1837 (1960). (14) Shaw, W. M., Ibid., 30, 1682 (1958). (15) Watanabe, H., Kendall, K. K., Jr., A p p l . Spectroscopy 9, 132 (1955). RECEIVEDfor review May 25, 1961. Accepted August 11, 1961. Taken in part from a portion of a dissertation submitted by J. C. Burger t o the Graduate School of the University of Tennessee in partial fiilfillment of the requirements for the degree of doctor of philosophy. Presented at Pittsburgh conference on Analytical Chemistry and ilpplied Spectroscopy, March 1957.
Quantitative Study of Factors Influencing Sample Flow Rate in Flame Photometry J.
D. WINEFORDNER and
H. W. LATZ
University o f Florida, Gainesville, Flu.
A variation in solution flow rate during flame photometric analysis produces a change not only in metal atom concentration in the flame but also in flame temperature which will result in a change in population of the excited energy levels. Therefore ,it is desirable to know the factors affecting flow rate and the extent of their effect. Flow rates of various liquids through total consumption atomizer burners are studied in relation to viscosity, surface tension, density, temperature, ionic strength, capillary radius, atomizing gas flow, fuel gas flow, and driving force. It was found that flow rate is mainly dependent on viscosity, the driving force, and the capillary dimensions. A smaller effect has been attributed to solution composition that results in slipping and turbulence during flow, Although the main factors affecting flow rate are those used in the Poiseuille equation for capillary flow, obedience to this equation was found only for high viscosity liquids with low flow rates. Sources of error due to variation in solution flow rate are discussed on the basis of this study.
F
LAME photometry is widely used for the rapid and accurate determination of trace quantities of sodium,
potassium, calcium, and magnesium. The accuracy, however, is greatly dependent on a number of experimental variables that influence the photometric response. The ultimate instrumental measurement which is related to the concentration of the salt in the sample of concern depends upon the method of sample introduction into the flame source, the dispersion of sample solution droplets, the evaporation of any water of solvation to produce a dry salt mist, the dissociation of the salt particles t o produce metal atoms and nonmetal atoms, the excitation of the metal atoms by means of the thermal energy of the flame source, and the emission of radiation as the excited metal atoms drop back to a lower level. The spectral response is indeed related to the number of excited metal atoms per unit volume of flame gases and therefore related to the metal atom concentration in the lower (usually the ground) state, which is related to the metal atom concentration in the original sample solution. This relationship is dependent on any equilibria involving the metal atoms in the flame gases, on the self-absorption of the emitted radiation by the cool atomic vapors surrounding the flame, on collisional losses of energy, and on other broadening phenomena. A number of papers (3, 6, 9, 14, 16), theses (1, 8 ) , and books (7, 10, 13) have
considered several of the above-mentioned variables in relation to spectral intensity (actually photometric response). However, in view of the large number and complexity of the variables, it is extremely difficult and usually meaningless to study the effect of one variable on photometric response, since the latter may be dependent on several other variables which are also changing. This paper concerns the quantitative study of the factors affecting one variable-sample introduction into the flame. Changes in sample flow rate into a flame will directly affect the flame photometric response. The most frequent errors in flame photometric analyses probably occur as a result of changes in sample flow rate which are due to changes in sample composition and/or atomizer characteristics. I n this paper the variations of solution properties, atomizer characteristics, and atomizing gas pressure are studied for total consumption atomizers to determine their effect on sample flow rate. The results are analyzed in terms of the effect of each factor on sample flow rate. It is shown that the simple Poiseuille equation for flow or the usual modification of the Poiseuille equation does not accurately or adequately describe the type of flow which occurs in atomizer capillaries used in flame photometry. VOL. 33, NO. 12, NOVEMBER 1961
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