Rapid identification of poisons and their relative degree of potency for any type of catalyst. The analyzer could be used, before a plant is designed, as a screening device for testing all gaseous foreign materials that might possibly enter the process. Determinaticm of the activity of many other types of catalyst (hydrogenation, alkylation, polymerization, etc.). Suitable strongly adsorbed substances would be used for each type of catalyst. As a research tool for studies on the mechanism of catalyst poisoning, com-
petitive reactions, effects of changes in the physical and chemical properties of the catalyst, and behavior of homologous series of reactants on a given catalyst; for developing methods for catalyst reactivation, and determining carbon content of fouled catalysts. LITERATURE CITED
(1) Conn, 34. E., Connolly, G. C,, Ind. Eng. Chem. 39, 1138 (1947). ( 2 ) Mills, G. A., Boedeker, E. R., Oblad, A. G.. J . Am. Chem. SOC.72, 155460 (1950).
(3) Mills, I. W., Oil & Gas J. 46, No. 28, 237-41 (1917). (4) Scheumann, Ibid., 46, KO. 28, Iv*, 231-2 Rescorla, (1947). A. R . p
(5) Stone, R. L., J . Am. Ceram. Soc. 37, 46-7 (1954). (6) Stone, R. L., Ohio State Univ., Eng. Expt. Sta. Bull. 146 (1951). ( 7 ) Stone, R. L. Rowland, R. A., Natl. Research douncil, Pub. 395 (1955). (8) Thomas, C. L., Ind. Eng. Chem. 41, 2565 (1949). RECEIVEDfor review June 21, 1956. Accepted April 29, 1957. Work done with apparatus in Department of Ceramic Engineering, University of Texas.
Internally Standardized General Spectrographic Method A. J. FRISQUE Research Departmenf, Standard O i l Co. (Indiana), Whiting, Ind.
b A rapid general spectrographic method has been developed that is capable of determining a large number of elements in a wide variety of matrices within 25%. Its basis i s the use of a mixture of germanium dioxide and graphite as internal standard, buffer, and diluent. Use of a single matrix for these purposes and of a fast convenient procedure for preparing samples minimizes analysis time. The high purity, rarity in samples, medium volatility, and favorable excitation characteristics of germanium dioxide make it a superior internal standard. RAPID general method having moderate accuracy is important to n spectrographic. laboratory handling nonrepetitive samples. Methods for malyzing diverse samples with a single set of standards are less accurate than specific methods where standards and wnples are closely matched and xcuracy is limited only by precision. General methods simulate the matching of standard and sample by the gross dilution of both with a common buffer nnd, in addition, frequently require a coninion reference element. The usefulness of a general method depends heavily on the ease n i t h which these additions can be made to samples. For nonrepetitive samples, the elimination of imperfectly undmtood matrix effects with matched standards is impractical and the general approach remains a necessary compromise between speed and accuracy.
Sumerous general methods hare been reported. Harvey's method (3) assumes working curves having unit slope and interpretation of the results is based on line t o background ratios; absence of an added reference element saves time. Jaycox (7) favors accuracy by adding two separate reagents to unknown samples-germanium dioxide as a diluent and copper oxide as internal standard. The rapid semiquantitative method of AIitteldorf and Landon (9) brackets the intensity of an unknonm element line with standards of known concentration. An acceptable compromise in the general approach is sufficiently important to be under study by Group VI, Subcommittee I1 E-2 of the American Society for Testing Materials which has summarized the methods and listed features important to a general method (1). A general procedure that does not incorporate an added element should be fastest, but accuracy may be much lower than that obtainable with specific methods. A procedure which incorporates a sample diluent in addition to the internal standard can maintain a constant sample plus diluent weight and should offer best accuracy. Sample handling time, however, is increased proportionately and if the added element is one frequently determined, a qualitative check of the sample may be necessary to check the applicability of a procedure. A need was felt for a rapid method based upon the addition of an uncommon reference element of medium volatility and excitation char-
acteristics and which offered a marked increase in accuracy relative to the increased time required for the reference element addition. Because the accuracy required for the elements is frequently not known until the elements themselves are known, elaborate sample preparation techniques are not justified in a preliminary analysis. When a suitable reference element can be conveniently added, however, the time saved by not having to repeat analyses may outweigh the time spent reporting an occasional result more accurately than necessary. Strock (10) suggested elemental germanium as an internal standard of suitable rarity with favorable excitation characteristics. The high purity of available reagent grade germanium dioxide, as well as its medium volatility ( 7 ) ) offer further advantages in its use as an internal standard. Commercially available germanium dioxide is as free from contaminants as the electrode graphite. These features plus reasonable cost prompted development of a method employing it as a reference element. Speed was gained by an improved powder-handling technique. APPARATUS AND REAGENTS
Mixing apparatus consists of a Wig-LBug dental amalgamator ( 5 ) and accessories (Spex Industries, 80-56 230th St., QueensVillage 27, N. Y.). Spectrographic equipment consists of a Bausch & Lomb large Littrow spectrograph (5 A. per mm., 3200 A.), an ARL multisource power supply, an ARLVOL. 29, NO. 9, SEPTEMBER 1957
1277
Dietert comparator-densitometer, and other conventional equipment. Suib able excitation conditions are summarized in Table I. Spectra are recorded in SA2 plates without condensing lens with a rotating sector set for 65% transmittance. The photographic emulsion is calibrated by standard ; semiquantitative elecmethods (4 trodes (3) are used. The standards are Spec-Pure oxides, nitrates, and carbonates (Jarrell-Ash, 26 Farwell St., Newtonville 60, Mass.). The internal standard is 99.99% germanium dioxide (Eagle Picher, 1 North Michigan Ave., Chicago, Ill). Electrodes are high purity graphite. Suitable internal-standard and element lines, with approximate lower detectable limits in micrograms are shown in Table 11. Sample dilution prevents exceeding upper limits for any line* chosen. POWDER HANDLING
The use of plastic rather than glass or metal equipment in critical parts of the procedure avoids contamination. Reducing the particle size of low concentration elements provides the required number of particles for accurate sampling. The dental amalgamator permits rapid and thorough mixing of powders, graphite, and germanium dioxide. Plastic rather than metal sieves are necessary for the germanium dioxide. Trace percentages of contaminants from metal sieves in the high concentration germanium dioxide are a significant fraction of a low concentration standard. Plastic rather than glass vials were found t o be necessary for containing the powders during mixing on the amalgamator. Significant contamination from elements in glass was observed when glass vials were used for mixing samples. Mixing and diluting the powder standards with the amalgamator gave precise working curves only a t the high concentration levels. Lack of precision for the low eoncentration levels was traced to relatively coarse particle standards. Because the calculated intensity of a single spherical 100-mesh particle of a sensitive element is significantly higher than background, a low concentration standard can tolerate only a few such relatively coarse particles. Precision is accordingly limited by the difficulty of accurate sampling. Element standards passing 325 mesh eliminated this difficulty. The germanium dioxide is several orders of magnitude more concentrated than the element standards and a coarser powder can be used. A check of the particle size shoived that only a small fraction did not pass 100 mesh. Particles larger than 50 mesh were removed with a plastic sieve. Particles coarser than 325 mesh are
1278
ANALYTICAL CHEMISTRY
PROCEDURE
Table 1.
Suitable Excitation Conditions
Voltage Current, (short-circuit) amperes CaDacitance. microfarads Inductance, 'microhenries Resistance, ohms Exposure time, seconds Slit width, microns Analytical gap, mm.
300 14 60 480
18
90 30 9
permissible with samples as with the dioxide because the total amount arced is also high compared to a lon- concentration standard. Though a single particle of sample may contain all of the elements in the sample mixture, a single particle of a synthetic powder standard cannot. For these reasons and because considerable time is spent in sample preparation relative to standards which are prepared only once, sample particle size is not routinely determined. Fineness of samples remains an objective but is not as critical as irith the standards. Before the analysis sample is inixed with matrix, the bulk of the sample is mixed and broken up on the amalgamator. Infrequent samples with particles too hard for breaking in plastic may be ground in a steel amalgamator attachment. Usually, however, such samples are ground in an agate mortar to avoid possible contamination of iron and other metals composing the steel capsule, which could obscure the measurements of these elements. The dental amalgamator mixes the powders, graphite, and germanium dioxide with speed and thoroughness not possible by mortar and pestlr.
Table II.
Element Germanium Aluminum
Angstroms 2829.0 3082.2 2568.0
0 9
3071.6 2497.1 3179.3
i0
Chromium
2849,8
3
Cobalt
3044.0
1
Copper
3274.0 2961.2
u
3020.6 2973.2 2804.5
0.5
Lead
8,. &.
s,
=
ins. of staiidard
df,
=
in dilutions 1, 2,.. n mg. of matrix in dilutions 1, 2, . . .n
ml, w 2 . . .m,
=
MI, d12
mg. of matrix used to dilute (SI MI) (82
++ M+M2),. (8, n) ,
Suitable Spectral Lines for Analysis
Detectable Limit, y
Barium Boron Calcium
Iron
Master standards, each containing four to six analysis elements as the pure oxides, nitrates, or carbonates, are first prepared from 325-mesh powders. Four or five such master standards cover the elements of interest. Approximately 30 mg. of each master standard are mixed with 400 mg. of a 1 to 3 germanium dioxide-graphite matrix to make up the reference standards of highest concentration. Fivefold dilutions of each of these first reference standards with the matrix are made to the detectable limit of the most sensitive element in a master standard. Because the matrix containing the internal standard is also thr diluent, the internal standard concentration is constant and at a maximum (25% germanium dioxide) only after several fivefold dilutions of a reference standard. Increases in the matrix (internal standard) concentration with decreasing element concentration are accounted for in the calculations. Designating:
0 1 5
Element Lithium Magnesiiini
Angstroms
Detectable Limit, y
3232.6 2779.8
6 4
hlanganrw
2798.3 2949.2
0.2
Molybdeniim Nickel
3170.3
0.8 0 9
Phosphoruc
2534.0
Silicoii
2881.5 2987.6
Sodium
3302.3
Tin
3175.1
Titanium
3242.0
03
3050.8 3002.5
200 0 6
For the above initial weights of master standard and matrix (30 and 400 mg., respectively), the ratio of standard to matriy for the first dilution is:
Table 111. Precision and Accuracy Present Found Brass NBS Sample 157 CII
72.1 17.9 9.7 0.14
Si
Zn CO
Addition of 50 mg. of (&+AIl) to an additional 200 mg. of matrix gives, as the ratio for the second dilution:
s n _-
M(n-1)
S(n-1)
MgO
x
Si
(3)
The fraction of each element present in a master standard times the successive S/M values gives the quantity “milligrams of element per milligram of matrix” for each dilution. This quantity, plotted logarithmically against the intensity ratio, gives the n orking curve for each element. If the fraction of each element present in a master standard is the same, calculations on the dilutions are kept a t a minimum. Powdered samples for a n d ) 91s are treated much as a master standard. About 5 mg. of the dried and powdered sample are mixed with 100 to 150 mg. of matrix in a disposable plastic vial on the amalgamator. Diluting this mixture with five to ten times more matrix extends the concentration range. Sample calculations are identical to those for the standards the concentrations. in this case, being expressed as “milligrams of sample per milligram of matrix.” Three electrode cups are filled with each reference standard and arced. Intensities are corrected for background, and working curvcs. to be used for all nonrepetitive samplcs, are plotted as indicated above. One or more cups of each sample are filled and arced. After correcting for background, the quantity “milligrams of elenicrit per milligrarii of matrix” convsponrling to each measured intensity ratio for the sample is read from .t \!orking curve.
7celement
=
sample, mg. element, mg. x loo/matrix, mg. matrix, mg Analysis results arc olitained in the usual manner. Columns 2 and 3 of Table I11 list, respectively, individual analysis results obtained from single arcings and the average of the individual results. Individual values in column 2 are generally within 25% of the true value. Values in column 3 average within 12% of the accepted value for the 14 elements tested. 4 n ash from a sulfated (6, 8)
19.1 8.9 2.95 1.13 0.68
Si 110
x Wen-11 + m(n-i)[S(n-~) + !44(-1)1
32, 32, 2 i 2.8. 2.1. 2.0 2.5; 2.8;2 . 7 0.39,O.46,O. 46 0.15,O. 2 6 , 0 . 3 1
Stainless Steel XBS Sample 160 17, 17, 16
c: r
11- 1 t - l )
58,58, 55
54.7 37.i 2.4 2.2 0.58 0.27
CaO
=
____
Error, %
63 17 11 0.13
12 5 13 7
57 30 2.3 2.7 0.44 0.24
4 25 4 22 24 11
17 7.4 3.2 1.2 0.77
12 16 8 6 16
44 34 10 2.0 0.24
0 10
Burnt Refract,ory NBS Sample 76
so that, in general: .If,
66. 63. 60 18; 17: 16 12, 11, 10 0.15,O. 13,O.11
AV.
>rtk
8.0.6.7.7.4 3 . 4 ;3 . 2 )3 . 1 1.2,1.2,1.1 0.78,O. i 8 , O . i 5
C!alcium Zeolite“ Si02
49, 44, :39 35. 34. 34 lo) lo; 11 2.0,2.1,1.8 0 . 2 4 , 0 . 2 4 , 0 23
43.8 37.8 11.8 2.7 0.26
ri1.0,
15 26 7
Furnace Ileposit‘ FC 0
5!t, 65
tiO.6
ti2
2
Anlolint present determined by conventional wet chemical analysis.
petroleum sample was analyzed spectrographically by the general method, based on the powdered oxide, nitrate, and carbonate standards, and by a specific method, based on the sulfation of metal organic standards and a cobalt naphthenate internal standard. The results indicated negligible anion affects:
General Specific
2.8 ‘3 3
8.8 9 9
23 23
For many ash samples, analyses as oxides total close to 100%. The large amount of buffer required to minimize interelement effects limits the sample size and, therefore, the sensitivity of general methods. The inorganic elements of greatest interest in nonrepetitive samples, however, are likely to be those present in the greatest concentration. Fortunately, these elements can be buffered and still remain within the required sensitivity limits. The procedure has been extended t o samples of low inorganic content by concentrating them. Samples suspected of containing volatile metallic compounds are first sulfated or extracted (2, 6 , 8). When the approximate inorganic content is known, the matrix may be added before concentrating. When not known, the inorganic content is first visually estimated. For results based on weight of solids rather than total sample
weight, matrix is added to the residue from the ash determination. The germanium dioxidegraphite matrix is weighed a t times of reduced sample load. The only subsequent weighing required is that of the analysis sample. This single weighing is necessary even in procedures without an added reference element. Elapsed analysis times are, therefore, not extended over noninternally standardized methods. LITERATURE CITED
A S T X Bull. 216, 29-32 (1956). Barney, J. E., A N A L . CHEW27, 1283 (1955).
Harvey, C. E., “Method of SemiSpectrographic Quantitative Bnalysis,” Applied Research Laboratories, Glendale, Calif., 1951. Harvey, C. E., “Spectrochemical Procedure?,” A plied Research Laboratories, olendale, Calif., 1951. (5) Helz, A. W., Scribner, B. F., J . Research Natl. Bur. Standards 38, 439 (1947). (6) Horeczv, J. T., Hill, B. N., Walters, A. E., Schutze, H. G., Bonner, W. H., ANAL. CHEM. 27, 1899 (1985). (7) Jaycox, E. K., Ibid., 27, 347 (1955). (8) Milner, 0. O., Glass, J. R., Kirchner, J. P., Ynrick, A. N., Ibid., 24,1728 (1952). (9) Mitteldorf, A. J., Landon, D. O., A p p l . Spectroscopy 10, 12-14 (1956). (IO) Strock, L. W., Ibid., 7, 64-71 (1953).
RECEIVED for review Xovember 7 , 1956. Accepted April 29, 1957. VOL. 2 9 , NO. 9 , SEPTEMBER 1957
1279
