V O L U M E 23, NO. 1, J A N U A R Y 1 9 5 1 Table 111.
Test NO.
Effect of ~ ~Antimony, ~ and~ ~ on Selenium Recovery Element -4dded
Element Added
brsenic llrsenic -4rsenic Arsenic Arsenic Arsenic Arsenic .4ntiinony -4ntimony .Intimony Antimony Antiinony ‘I’ellurium Tellurium Tellurium
0.04 0.04 0.04 0.40 0.40 0.40
Selenium Added
% 1 2 3
2 6 7 8 !4
10 11 12
13 14 15
% 0.0100 0.0100 0.0100 0.0100 0 0100 0.0100 0.0100 0.0100 0.0100 0 0100 0.0100 0.0100 0.0100 0.0100 0.0100
0.40
0.003 0.003 0.030 0 030 0.030 0.003 0.003 0.030
StarchIodide Reagent Added MI.
5 I 5 2 1
!
5 1
1
1 1
?
125 ~ ~l
Selenium Found
% 0.0102 0.0102 0.0100 0.0123 0.0114 0.0110 0.0113 0.0100 0 0100
0.0109 0.0103 0,0102 0.0100 0.0100 0.0102
l
during the distillation and reprecipitate when the hydrobromic ~ i acid~ is ~ iexpelled. ~ , , The ~ air-inlet hose should be provided with a bleeder to prevent possible suck-back of distillate. Titration. Remove the receiving beaker from the distillation assembly, and add 2.5 ml. of 90% formic acid and approximat.ely 3 grams of urea. Heat to dispel bromine. Neutralize with sodium hydroxide (1 pound per liter of water), using phenolphthalein indicator. Add 13 ml. of 18 N sulfuric acid and 2 ml. of 6% potassium cobalticyanide and cool the solut,ion to 20” C. Add 5 ml. of starch-iodide reagent (1 gram of potassium iodide in 100 ml. of 0.1% wheat starch paste) and titrate immediately wit,h 0.005 to 0.01 1%’ sodium thiosulfate solution. The end point is indicated by a color change from violet to pink which persists a t least seven seconds. Standardize t.he sodium thiosulfate solution against a selenite or selenious acid solution carried through all the steps leading to the titrat,ion. Run a reagent blank to establish the purity of new lots of chemicals. CONCLUSIONS
point to dissolvr any residual sulfur. Evaporate as described for copper metal, cool, and add 1.0 ml. of perchloric acid (60%) and 5 ml. of water. Distillation. Assemble the digestion flask and distillation head after coat,ing the ground joints with silicone grease. Clamp the neck of the flask to a ring stand or place in a special rack, allowing space for a Bunsen burner below the flask. Immerse the outlet, L , in 50 ml. of 0.170 aqueous hydrazine sulfate solution contained in a 250-ml. Bereelius beaker. Cool the beaker in a 6-inch evaporat.ing dish containing cold water. With the stopcock closed, introduce compressed air (or carbon dioxide) into tube J, a t such a rate that 2 o r 3 bubbles per second rise from L. Introduce 5 ml. of 48% hydrobromic acid into the sample through the funncl, I . Heat the flask gently with the Bunsen burner. Withdraw bromine vapor from the surface of the covered receiving beaker by means of a hooked glass tube connected to a water aspirator. When the solution in the flask becomes green, increase the flame and start 10 ml. of hydrobromic acid flowing into the eamplc a t the rate of 0.75 to 1 .O ml. per minute, keepin! the solution dark green. Maintain a vapor temperature of 123 to 130” C. Heat the thermometer well, E , occasionally t o remove condensate. The precipitate of copper sulfate will dissolve
Tiic method dcscrihcd is successfully used in the analyscs of copper bullion, mattes, and pyritic samples. The accuracy and reproducibility of the results are within the acceptable limits for control work. To avoid possible loss of a small amount of selenium, care should he taken not to fume the samples unnecessarilp during digestion. LITERATURE CITED
Y., Analyst, 67, 346-51 (1942). (2) Hoffman, J. I., and Lundell, G. E. F., J . Research Natl. Bur. Standards, 22, 465-70 (1939). (3) Jennison, H. C., and Smith, C . S., “Metals Handbook,” pp. 1389-95, Cleveland, Ohio, Ainericsn Society for Metals, 1939. ( 1 ) Evans, R.
( 4 ) McNulty, J.
S.,ANAL.CHEM.,19, 809-10
(1947).
(5) Pavlish, A. E., and Silverthorn, R. IT., J . Am. Ceram. Soc., 23, 11+18
(1940).
(6) Scherrer, J. A., J . Research S a t l . Bur. Standards, 16, 253-9 (1936).
(7) Scott, W. IV., “Standard Methods of Chemical Analysis,” 5th ed., pp. 388-9, New York, D. Van Nostrand Co., 1939.
RECEIVED .4ugust 8,
1950.
Impurities in Catalyst Materials Quanti t a t ive Spec t roscop ic A nalys is Usi ng A 1te r na t i ng Cu r re nt Spark DUANE D. HARMON
AND
RAYAMONDG . RUSSELL, Gulf Research & Development
co.,Pittsburgh, Pa.
The use of catalysts requires constant checking on the catalytic activity and the content of certain of the inorganic ions present. A method of checking that was quick and reasonably accurate was desired. -4 spectrographic method has been developed which will give results precise to within *loyo of the amount present of any of the desired cations. This method has been applied to the determination of iron, vanadium, nickel, and sodium in catalyst materials, the entire analysis taking less than 4 hours for a group of samples. This method should be applicable to any nonmetallic sample which can be put in powdered form. I t will give more information in a s h r t e r time than is possible by ordinary chemical methods. It utilizes the alternating current spark form of excitation and a briquetted pellet.
M
A N Y catalyst materials used in the oil industry are composed of an aluminum silicate matrix containing several minor impurities. During the life of the catalyst its activity decreases to the point where it is no longer economically feasible to continue its use, and a t the same time an increase in metallic impurities occurs. This “pickup” can be attributed either t o the metals present in the oil, or to the equipment used to handle the catalyst.
To determine these impurities by wet chemical methods is laborious and time-consuming, and the chemical determination of elements present in amounts less than 0.1% is relatively inaccurate. Inasmuch as spectrographic methods are usually more rapid and more accurate in these ranges, a spectrochemical method was developed for iron, nickel, vanadium, and sodium which were elements of particular interest a t this time. Several methods have been proposed for the analysis of im-
126
A N A L Y T I C A L CHEMISTRY
purities in refractory base nonmetallic samples (I, 3, 9). Those using the direct current arc were discarded because in the authors’ experience, and with their direct current arc source, they were relatively nonreproducible and not suited to nontechnical personnel. Other methods might have been satisfactory, but this investigation was carried out with the alternating current spark. The method developed use8 a briquetted sample as a flat upper electrode and a hemispherically tipped graphite rod as the lower counterelectrode. INTERNAL STANDARD (6)
The composition of the catalyst to be analyzed was approximately: silica 85%, alumina 12%, magnesia 1 to 275, and impurities. Two approaches were available for the selection of an internal standard. rln element could be added in constant amount9, or an element present in the sample in constant amount could be used. An element to serve as an added internal standard must be readily available in a highly pure form, at least with regard to the elements to be analyzed; it must have a relatively simple spectrum, so as not to interfere with any of the analysis lines, but must have a sufficient number of lines of varying intensities to facilitate 5election of an internal standard line; it must not be present in the sample in large and varying amounts; and it should have excitation conditions similar to the elements being determined. Several elements were considered. Copper was not used because all the copper oxide available contained small amounts of nickel. Chromium was not used because i t was expected that the method would have to be extended to cover the analysis of chromium. Molybdenum had far too complex a spectrum. Cadmium did not have sufficient lines of proper intensities. Other elements could have been tried, but it was decided to attempt to find an element in the sample itself. Of the elements native to the sample, the choice fell between silicon and aluminum. Because the silicon content was the highrst, any variation in it would cause a smaller variation in the intensities of the lines than would a similar variation in the aluminum content. Silicon was tested and found to be satisfactory for the method. Of the lines of silicon in the wave-length range desired, only one, Si1 2970.347, was of the proper density for densitometry with the exposure necessary to bring the lines ut the trace elements to a proper density. A slit width of 30 microns on the B & L. large quartz Littrow spectrograph served to resolve it from FeI 2970.105, the only poPsible interfering line encountered. For instrunients of lower dispersion it should be possible to use Si1 2987.648 as in internal standard line providing suitable step filters were available. Another analysis line for iron would also b e necessary. FeI 2981.446 should be usable in the unfiltered portion. Because no usable silicon lines exist in the 5900 A region, it became necessary to add an internal standard. Lithium was chosen because its line 6707.8, like Na 5889.9, derives from the first resonanc’e transition of the neutral atom. The potentials for the tramitions giving rise to these lines are 1.85 and 2.1 volts, respectively, for the lithium and sodium lines (8). EXCITATION CONDITIONS (TABLE I)
Capacitance. On the high voltage spark source used, capacitance and power were controlled by a single switch. It was found by experiment that for the determination of iron, nickel, vanadium, and sodium in the region 2550 to 3500 A. the maximum power available was needed to give proper line intensities without I e3orting to extremely long exposure times. This made the use of the maximum capacitance available, 0.021 pf., mandatory. To have used the same value for the determination of sodium in the 5900 A . region xTould have necessitated an extremely short ex-
Table I.
Excitation Conditions
(Large quartz Littrow spectrograph) Fe, Ni, V, Na Range, 4 . 2550-3500 Plate Spectrum analysis No. 1 Input voltage volts 230 Voltage drop :cross transformer 75 input, volts 2 Power kv.-amp. Ca acjtance, rf. 0.021 Infuctance, mh. 0.18 5 Prespark, seconds Exposure seconds 70 Gap lengih, mm. 3 Upper electrode 1/2 inchbriquetted pellet Lower electrode 1/4 inch graphite rod with hemispherical tip
Na 3700-8000
1L 230 75 4’03.014 0.36 5 25 3
Table 11. Effect of Inductance on Reproducibility Element (X) I z / I s i Mean Mean Deviation, %
MD
=
Fe V Na Ni
0.18-mh. inductance, 15 determinations 135 1.48 125 1.80 62 1.72 49 1.63
Fe V Na Ni
0.36-mh. inductance, 15 determinations 135 1.03 97 2.62 61 1.75 44 2.73
= ’ N
used for computing mean deviation ( 4 )
where M D = mean deviation ZZ = numerical value of term A mean = arithmetical average 1Zi A = absolute value of individual deviation N total number of terms = 15 MD % mean deviation = - X 100 A
--
posure time. For that reason, 0.014 pf. was chosen for the longer wave-length region. Inductance. The following inductance values, all that were available, were tested for iron, nickel, vanadium, and sodium in the 2550 to 3500 A. region; residual inductance, 0.09, 0.18, and 0.36 mh. As the first two did not give a high enough ratio of line to background, they were discarded. Table I1 shows the reproducibility studies carried out to test the latter two values of inductance. As a result of these studies 0.18 mh. was chosen as the inductance value giving the more reproducible results. For sodium in the 5900 A. region, 0.36 mh. inductance was chosen because it gave the most arclike discharge possible with the authors’ source. .4n arclike discharge was felt to be necessary because both Na 5889.9 and Li 6707.8 are arc lines resulting from the 2 5 1 / 2 - 2 P 3 / 2energy transitions of the neutral atom ( I O ) , and therefore more easily excited under more arclike excitation. Prespark. Sparking off studies were made using a modified moving plate technique. The plate, instead of moving continuously, was moved stepwise, standing stationary for 10 seconds, then dropping to the position for the next 10-second exposure. These studies indicated that neither the presparking nor the exposure t,imeswere critical within the accuracy required ( * 10%). A 5-second prespark time was chosen to enable the spark to reach electrical stability and to clean off any electrode surface contamination before exposure. Exposure. Exposure times x-ere chosen t o bring the line density into the proper intensity range. PREPARATION OF ST4NDARDS
As no chemically analyzed standard samples were available, synthetic standards had to be prepared. For these, a relatively pure catalyst of the type to be analyzed was employed as a base matrix, and to it Kere added knoFn amounts of impurities in thr form of sdts.
127
V O L U M E 23, NO. 1, J A N U A R Y 1 9 5 1 A standard was prepared by adding to the base matrix the following percentages of impurities: iron 1.0%, sodium 1.0%, vanadium 0,05%, and nickel 0.05%. This standard Nas then successively diluted with the base material to form a series of four standards with the following known percentage concentrations: iron and sodium 1.0, 0.6, 0.3, and 0.15; nickel and vanadium 0.05, 0.03, 0.015, and 0.0075. A fifth standard containing only base matrix was included to enable the correction for residuals to be made, and to provide the lowest standard of the series. Once the standards had been prepared and ignited a t 500" C. for 2 hours, they were mixed Kith natural graphite. Natural graphite was necessary to serve as a binder for briquettirlg and to act as a conductor for the electric current. The following proportions proved satisfactory: de-ashed natural graphite 2.5 gmms, standard 1 gram. Mixing was done with a mortar and pentle. 'rhe mixed standards were then briyuetted in a die 0.5 inch in diameter on a briquetting press a t 20,000 pounds per square inch plunger pressure.
The lines listed in Table I11 were then read on the densitometer and their transmittances obtained. CURVES
The emulsion calibration curve was constructed by the two-line method ( 2 ) . Tests taken over a period of time have shown that this curve remains usable throughout the life of one emulsion lot number within the accuracy required. This is, of course, dependent on a routine method of plate processing.
PREPARATION OF SAMPLES
Samples to be analyzed were either pelleted or "fluid" catalyst. The fluid catalyst, because it already was a finely divided powder, nedded no processing prior to ignition. The pellets had to be ground to approximately 100-mesh before ignition. Ignition was done at 500" C. for 2 hours, for the purpose of removing most of the carbonaceous matter, which ivould serve as a diluent, and water which, in addition to serving as a diluent, had been found to cause the 1)riquetsto explode when sparked.
w
e
IO
---
m
I1 z
2 20 I-
:" 50
--
Figure 2.
1Iethod of Constructing Transmittance Scale for Slide R u l e Calihration (:urve
I
I
I I
I I
I
I
I
I I I I I I l l 3oioso 100 RELATIVE INTENSITY I
I
20 I
I
I
-
1
I
1
005
1
1
1
1
1
.01 ,015 .02 PERCENT V
I
I
200 300 I
1
.03 .04
Figure 1. Method of Constructing Concentration Scale for Slide Rule Working curve
The samples were permitted to cool in tightly closed weighing bottles (bottles made of borosilirate glass were used to hold the sample during ignition), then weighed, mixed, and briquetted in the same manner as the standards. I t \vas found advisable to store both standards and samples in a drying oven a t 110" C. until ready to make the exposures. This prevented moisture pickup, which would cause the briquets to explode when sparked. PROCEI)URI.,
Three briquets of each of the five standards plus three briquetof a sample, to serve as a secondary standard for curve shift correction, were sparked on each of tv,o plates taken on different
days, using the conditions in Table I. The plates were developed in D 19 developer for 4 minutes, rinsed in dilute acetic acid for 30 seconds, and fixed in E.K. acid fixer until clear. They were then washed in running water foi 15 minutes and dried on a plate dryer.
The perwritage coiicentratiom of the impurities were plotted against the relative intensity ratios of the analysis lines, as obtained from the calibration curve, on a calculating board to obtain preliminary working curveb. The values used for relative intensities were the average of the six evposures for each element in each standard. The values used for percentage concentrations were the known amounts of impurities added above, and had to be changed to allow for residuals in the base matrix. This was done by the method of successive approximations described by Duffendack and Wolfe (.5) until a straight-line working curve rewlted.
Table 111. Analysis Line FeI 2970.105 V I1 3102.299 NaI 3302.323 NiI 3414.765 NaI 5889.953
Lines Used for .&nalysis(8) Internal Si1 Si1 Si1 Si1 LiI
Standard Line 2970.347 2970.347 2070.347 2970.347 6707.844
PREPARATION OF SLIDE RULE
In order to simplify the calculation procedure, a slide rule, as described hy Harmon ( 7 ) , was preparc?ti. By refrrring to each of t'he working CUI'VFW, it was possible to find for each value of relittivr intensity :i corresponding percentage concentr:it,iori. From a srvii,s of t h i w concentration values :I concentration scale \\-as cwnstruc.tcd corresponding to the relative intensity (11) (Figure 1 ) .
ANALYTICAL CHEMISTRY
128 The calibration curve as prepared had log transmittance as the ordinate and log relative intensit,y as an abscissa which could be moved in a direction parallel to itscilf. By immoliilizing the relative intensity scale i t was possible to find for etich v:tlue of relative intensity a corresponding value of transmittance. From these values a transmittance scale vias plotted corresponding t,o relative intensity (Figure 2). However, because the relative intensity scale was immobilized only for the purpose of constructing the transmitt,ance scale, the latter scale h n d to be madc so that it would operatr in slide rule faPhion with the former ( 2 ) .
___ Table TV.
Reproducibility Studies (Sample S-551)
% re
Plate N o 1685 1692 1706 1713 1721 1728 1733 1740 1744 1752 1761 1766 1770
0.64 0.64 0.64 0.62 0.62 0.64 0.64 0.62 0.64 0.60 0.63 0.63 0.63
Mean l f e a n deviation, yo
Cheniical
0.64
76
% V 0.025
pi1
0.027 0.028 0.026 0.027 0.022 0.026 0.022 0,032 0.021 0.02s
0.012 0.012 0.012 0.013 0 012 0.010 0.009 0.012 0.012 0.011 0.010 0.010 0.011
0.63
0,025
0.011
1.5
7.4
9.1
0.027
0.025
Table V. Reproducibility Studies (Sample 5-571) RELATIVE INTENSITY 6 7 a 9
$0 ro
do
20 do
410 do
11
12
idoo
13 I14 1 7 1 6 7 1i 8n 1 9 2 00
cbb
Zb 20
'
% Na
I
% Na
TRbNSMITTAHCE
I Figure 3.
I
I
Slide Rule
4 Referenre
mark
By this method a slide rule was prepared having t,he trausmittance scale on the base and the relative intensity scale plus a concentration scale for each element on the slide (Figure 3). In use, the index (log Iz/Zi8= 1 ) ( 2 ) wm placed over the transmitt,ance of the internal standard line by moving the slide. T h e indicator was then moved to the transmittance of each analysis line, and the percentage of each element was read from its respect,ive scale from under the hair line. Curve shift was corrected for by analyzing a sample of sinii1:ir composition in which the percentage concentrat,ion of the irnpurities was known. With the indicator a t the percentage otitained, a reference mark was drawn in pencil on the indicator at the correct percentage concentration, and was used during subsequent analyses t.0 indicate the correct percentages (see Figure 3). A new transmittance scale must, be made each time the emulsion is recalibrated. S0DIU.M
Sodium could be determined simultaneously with iron, nickel, and vanadium, using Si 2970.3 as the internal standard line and Na 3302.3 as the analysis line except in the presence of interfering elements. Zn 3302.6 interfered with S a 3302.3 to such an estent that when zinc was present, even in small aniount9, another line of sodium had t o be used. N a 3303.0 also has zinc interference. None of the other lines of sodium in t,he 2550 to 3500.4. region had adequate sensitivity for the analysis. Ka 5889.9 and Na 5895.9 were t,he only other lines of sodium having the sensitivity necessary for the analysis. S a 5889.9 was chosen as the analysis line because i t was the more intense, Lithium 6707.8 A. was chosen as the internal standard line. I~kperimentat~ion showed that only minute amounts of 1it)hium (0.1yo)could be tolerated in t>he littiiuni-graphite-saniple mistme. Therefore, 1.2 grams of lithium csrl)onate were added to 1 pound (453.6 grams) of de-asheri natural graphite and niised in a ball mill overnight. The mising problem then became one of niising 2 grams of the graphite-litliium carbonate misturr with 1 gram of the sample with a mortar pestle. The mixtures were then briquetted and sparked using a 1L plate in the region 3700 to 8000 A. I'kcitation conditions used are shown in Table I. Densitometry, establishment, of the working curves, and finally the construction of a slide rule and its usagc~were rarried
Mean
0.18
hleandeviation, %
7.4
out as for the preceding technique. Katurally, a separat,e emulsion calibration curve and transmittance scale were necessary for the 1L emulsion. DISCUSSION
Reproducibility figures are presented in Tahle I V for iron, nickel, and vanadium. No chemical dat,a were available for nickel and vanadium in the orders found, so reproducibility values only are shown. 4 chemical analysis was available for iron and is shown in Table IV. Reproducihilit,y figures are shown for sodium in Table 1'. The method here shown is slow compared to many spectrographic met,hods using self-elect'rodes, but i t is much more rapid than chemical methods. h sample can be analyzed in about 4 hours after receipt. The slowness is a result of the ignition necessary. IIowever, from five to ten samples can be analyzed in very little more time than necessary for one, so the time per sample decreases with the number of samples analyzed. ACKNOWLEDGMEST
The authors desire t o express their appreciation to P. D. Foot,e, esecutive vice president of Gulf Research B: Developmpnt Co., for permission to present this paper, and t,o D. Imogene Nison for her nssist,ance in the experimental portion of this work. LITERATURE CITED (1) Burdett. R. A . , and .Jones, L. C . , ANAL.CREM., 19, 238 (1947).
(2) Churchill, J. R.. IND.ENG.CHEM.,-4s.4~.ED.,16, 653 (1944). (3) Churchill. .J. R.. and Russell, R . G., Ihid., 17, 24 (19G). (4) Davis, H. T., and Nel30n, JV, F. C., "Elements of Statistics," 2nd ed., pp, 74-7, Bloornington, Ind., Principia Press (1937). ( 5 ) Dnffendack, 0. S.,and Wolfe, R. A., ISD. ESG. C H E M . b, s . 4 1 . . E D . , 1 0 , 1 6 1 (1938). 16) Gerlarh, TV., Z. anorg. Chem., 142, 383 (1925). 17) Harmon, D. D., Ax.41,. CHEM.,22, 1227 (1950). (8) Harrison, G. R . , "M.I.T. Wavelength Tables," Yew Tork. John TViley Bi Sons, 1939. (9) Hels, A . IT.., and Scribner, B. F., J . R e s m r c h S a t l . Bur. Standa r d s . 38, 439 (1947). (IO) hleggcrs. W.F., J . Optical SOC..4ni., 31, 39 (1945). (11) Owens, J. S., M d u l s cold rll/q/s, 9, 15 (1938). R E C E I V E AIay D I.?. 19SO.
