adsorption. It can uroceed a t the same time and on the same column with liquid-liquid partitioning. I t is a type Of adsorption and Occurs when a partition column is not loaded to capacity with stationary phase. The 2,4-DNPH's that can be separated or purified on the three columns are not limited to those listed in Table 1. Any 2,4-DNPH that has a polarity between the n-butanal derivative and the bis derivative of glyoxal should partition on one of the three columns.
ACKNOWLEDGMENT
The author expresses his sincere thanks t o Earl Hammond of Iowa State University and Daniel Schwartz of this laboratory for supplying of the bis(2,4-dinitrophenylhydrazones) needed for this studv.
LITERATURE CITED
(1) Corbin, E. A,, Schwartz, D. p.1 Keeney, Mark. J. Chromatog. 3, 322 (1960).
( 2 ) Duin, H. van, Xatwc 180, 1473 (1957). ( 3 ) Duin, H. van, Reports from the Netherlands Institute for Dairy Research (N.I.Z.O.), No. 54, May (1961). (4) Meigh, D. F., Chem. Znd. (London) 1956, 986. (5) Wolfrom, 14. L., Arsenault, G. P., h A L . CHEM. 32, 693 (1960).
RECEIVEDfor review March 28, 1962. Accepted July 16, 1962. The use of trade names is for the purpose of identification only, and does not imply endorsement of the product or its manufacturer by the C. S. Department of Agriculture.
Direct Spectrographic Determination of Trace Impurities by High Purity Platinum A. J. LINCOLN and J. C. KOHLER Research & Development Division, Engelhard Industries, Inc., Newark, N.
b A direct optical emission spectrographic method for the quantitative determination of 27 impurities in platinum covering the range from 0.1 to 800 p.p.rn. has been developed. The technique utilizes a d.c. arc operating at 300 volts and 12 amperes with an atmosphere of 70% argon-30Yo oxygen in a Stallwood jet. The preparation of standards and the capped pellet technique used to prepare samples are described in detail. The analytical lines and internal standard lines used for the various impurities are tabulated. Working curves for some of the elements are shown. The precision of the method is 10% :xpressed as relative standard deviation.
T
CONTROL of trace impurities in high purity platinum used for thermocouples, certain e!ectronic components, catalysts, and a variety of other atomic age products has in recent years become extremely important. T o meet this need, a direct optical emission spectrographic method for the quantitative determination of 27 impurities in the range 0.1 to 800 p.p.m. has been developed. The earliest reported method for the quantitative and semiquantitative determination of impurities in platinum was described by Raper and Withers (7) using globules of platinum in a shallow electrode crater operated at 6 amperes and 200 volts. Standards were prepared by the addition of impurities as solutions to pure platinum powder which was then evaporated t o dryness and ignited in a n atmosphere of hydrogen. Hawley and coworkers ( 4 ) described a method for the quanHE
I.
titative determination of gold, silver, copper, iron, nickel, palladium, and rhodium in platinum sponge. Standards and samples were converted to platinum black by reduction with high purity aluminum filings in either a n acid or alkaline medium. A multisource spark-like discharge was used to excite the sample mounted as a pellet. Other previous work in the field of platinum spectroscopy by various investigators has been reviewed by T n y m a n (12) and Hauley and coworkers (4). Initial studies of various types of excitation for platinum indicated that a direct current arc technique would be necessary for the low level. impurity detection required in this study. The use of platinum sponge in both deep and shallow electrodes resulted in extremely poor precision which was attributed to excessive wandering of the arc on the metallic bead that was formed during arcing. Capped pellet techniques reported by R a r k (IS) and by Hodgkin and Hanson ( 5 ) were investigated to determine if arc wandering could be minimized and precision improved. Initial studies indicated that considerable improvement in precision could be achieved by using a pellet technique. Best results were obtained when platinum x a s mixed with graphite, formed into a pellet containing a backing of graphite, and burnt in a friction fitting undercut type electrode. Thiers (11) and Hamniaker and coworkers (3) have shown that controlled atmospheres in a direct current arc excitation can be used to suppress cyanogen bands, reduce background interference, and increase sensitivity. Techniques using a Stallwood jet (IO)
nith various atmospheres h ve been reported by Rupp and coworkers (8) and Shaw and coworkers (9) to increase both precision and sensitivity in direct current arc techniques. These techniques when applied to platinum improved both precision and sensitivity. Studies using argon and mixtures of argon and oxygen in the Stallwood jet indicated that the most satisfactory data were obtained using 70y0 argon30% oxygen. Because available analytical techniques do not permit accurate determination of most elements in platinum below 100 p.p.m., the preparation of chemically analyzed standards was not possible. The preparation of suitable synthetic standards was then investigated. The most satisfactory standards were obtained by impregnating ammonium platinum chloride with the required elements as chloride solutions wherever possible. The resulting product ww dried at low temperature, thoroughly blended, and reduced in an annealing gas atmosphere. PROCEDURE
Apparatus. The equipment used in this study is tabulated in Table I. It consisted primarily of commercially available equipment. T h e pelleting die and press assembly was designed and constructed in our own laboratory using standard components wherever possible. Preparation of Standards. The spectrographic standards were prepared from a selected lot of platinum sponge having a purity of 99.999+%. The platinum was dissolved in aqua regia, then the excess nitric acid was removed by evaporation with dilute hydrochloric acid. The platinum mas then precipitated as ammonium platVOL 34, NO. 10, SEPTEMBER 1962
e
1247
0.1 5 7 "
Figure 1.
Typical pellet
Table 1. Apparatus Spectrograph Applied Research Laboratories 2 meter with 24,400 lines per inch grating; dispersion, 5.2 A./mm. Excitation -4RL Multisource Model No. 5700 Densitometer ARL Model No. 5400 Mixer mill h e x Industries Model No.
'm
Roll mill Pellet press and die assembly Stallwood jet
Englehard Industries Englehard Industries
Flowmeter
Brooks Rotar R-2-l5C witksteel ball
Spex Industries Model No. 9014
Table 11.
Impurities Added to Platinum Standard Group A Group B
Cadmium Calcium
ZYY
Iridium Iron Lead Magnesium Molybdenum Palladium Ruthenium Silicon Tellurium Tin
Table 111.
Aluminum Antimony Arsenic Bismuth Boron
Chromium Cobalt Manganese Nickel Osmium Rhodium Silver Zinc
Excitation and Photography
Voltage Current S ectral region SPit width Analytical gap Filter system
300 V. d.c. 12 amperes d.c. 2180-4600 A. 20 cc 3 mm.
Exposure Atmosphere
camera position with selected lines independently filtered 30 seconds 70% argon-300/, oxygen at 4 I./min. Eastman SA-1 D-19, 5 minutes at 65' F. Eastman X-ray
Emulsion Development Fixer
1248
Primary filtering at slit-
split field 50T/100T at
ANALYTlCAL CHEMISTRY
000 MODIFIED
BUEHLER
STOKES
PELLETINO DIE
M E T A L L U R G I C A L PRESS
Figure 2.
Pelleting press and die assembly
inum chloride by the addition of ammonium chloride. All impurities were then added to the ammonium platinum chloride as chloride solutions, with the exceptions of iron, which was added as ferric nitrate; boron, as boric acid; silicon, as sodium silicate; and silver, as silver nitrate. Twenty-seven elements were added as impurities to the platinum standard prepared for this study. The large number of impurities involved made it necessary to add them in two separate groups (Table 11); the elements were selected for each group to minimize line interference as much as possible. The standards were prepared in concentration ranges from 0.1 to 800 p.p.m. Standards u p to and including the concentration level 10 p.p.m. all contained the combined impurities shown in Groups A and B, Table 11, in a single standard. For concentrations above 10 p.p.m., a separate standard was made a t each level for the impurities contained in each of the above groups. A weighed portion of ammonium platinum chloride ww transferred to a polypropylene bottle, and solutions containing the various impurities were added. The combined mixture was dried in the bottle at 110" C. After the standard was completely dry, the bottle was capped and placed on a mixer mill for 10 minutes to ensure that all salts adhering to the walls of the bottle were removed and blended into the standard. The dried ammonium platinum chloride containing the added impurities ww then milled on a rotary mill with a platinum baffle for a minimum of 72 hours to ensure homo-
geneous distribution of the impurities. The thoroughly blended ammonium platinum chloride was then transferred to a quartz boat and reduced at a temperature of 200" C. for 2 hours, 300' C. for 1 hour, and 600" C. for 0.5 hour in a n atmosphere of 7% hydrogen93% nitrogen a t the flow rate of 14
J-
y7+ 0.002 0.000
0
0.242"
Figure 3.
High purity graphite electrode
liters pcr hour. The resulting platinum sponge was then reduced to a powder using a mixer mill for 10 minutes. Sample Preparation. All samples of platinum sponge are converted to a powder in a polyethylene vial containing a polyethylene ball using a niiser mill for 60 seconds. .4 200-mg. portion is platinum is added t o 50 mg. of National Special Spectrogrnphic Graphite Powder (Grade SP-1) and thoroughly mixed in a miser mill for 60 seconds. From the previously prepared mixture of platinum and graphite, a 50-nig. portion of weighed and transferred into the pelleting die. A 100-mg. portion of high purity graphite powder is now placed in the pelleting die on top of the previously added 50-mg. portion of platinum and graphite mixture. A pressure of 40 tons p s i . is then applied to the combined material in the pelleting die. Figure 1 shows a typical pellet obtained by this procedure. Figure 2 is a schematic arrangement of the pelleting press and die assembly used to prepare pellets. \Vhile the procedure described here was designed primarily for platinum sponge which can be readily converted to a powder, the technique may be applied to platinum that has been melted and worked into bar stock, wire, sheet, and other fabricated forms. Samples may be taken from platinum in these forms by the use of a No. 0 jeweler saw blade or a S o . 5 file, using the saw blade or file only once for each sample to prevent cross contamination. Only samples having a particle size of -100 mesh should he used. Samples obtained in this manner are boiled in a 1: 1 solution of hydrochloric acid for 1 hour to remove iron introduced during sampling, after which the solution is decanted by repeated washings with distilled water. Electrode System. T h e pellet is inserted into the precision machined crater of a high purity undercut type electrode similar to t h a t shown in Figure 3. T h e crater in t h e electrode is designed to permit a friction fit between the pellet and t h e electrode. Looseness between the pellet and the electrode can have a marked effect on the precision. The electrode with the pellet inserted is placed in a Stallwood jet which forms the lower electrode (anode) in the system. The upper electrode consists of 11/2 X inch diameter flat face high purity graphite. Prior to operation, the Stallwood jet system is flushed with a mixture of 7Oy0 argon-30yo oxygen for 1 minute. During excitation, the argon-oxygen flow is 4 liters per minute. Excitation and Photography. T h e conditions for excitation a n d photography are tabulated in Table 111. DATA AND DISCUSSION
The line pairs used for the 27 impurities in this project are listed in Table IV together with the concentration ranges covered. The filter
Table IV.
Element Ag
A1
Au As B Bi Ca Cd co Cr CU Fe
Ir Mg
Mn Mo Ni
os
Pb
Pd Rh
Ru Sb
Si
Sn Te
Zn
Line Paiirs and Analytical Ranges
Analytical Line A. 3382.9 3382.9 3961.5 2373.1 2676.0 3122.8 2349.8 2497,7 3067.7 4226.7 4226.7 3466,2 3453.5 3395.4 4254.3 4254.3 2762.6 3247.5 3247.5 3020.6 2788. J 3220.8 2924.8 2802.7 2779.8 2801.1 2801.1 3132.6 3493.0 3437.2 2909.1 2802.0 2802.0 3404.6 2447.9 3434.9 3396.9 3498.9 2678.8 2311.5 2881.6 2528.5 2840.0 2840 0 2385.8 3345.0 3345.6
io
20 10 10 10 2 10 10 2 20 10 10 10 1 10 10 10 10 10 10 20 10 10 10 10 10 20 10 10 20 10 2 10 10 20 10 10 20 10 20 10 10 Table V.
B
Cd Fe Mg
Mo
os Pd
Ru Si Sn
Internal Std. Line A. P t 3110.1 Pt 3110.1 Pt 3110.1 Pt 2578.4 Pt 2578.4 Pt 3110.1 Pt 2578.4 Pt 2578.4 Pt 3110.1 Pt 3110.1 Pt 3110.1 Pt 3110.1
10 1 10 20 10
Analytical Line Element A. Au
Filter,
Filter, % Transmission
2676.0 3122.8 2497.7 3466.2
Pt Pt Pt Pt Pt Pt Pt Pt
Pt Pt Pt Pt Pt Pt Pt Pt
3110.1 3110.1 3110.1 3110.1 2814.0 3110.1 3110.1 3110.1 2814.0 3110.1 2814.0 2814.0 2814.0 2814.0 2814.0 3110.1
Pt 3iio.i
Pt Pt Pt Pt Pt
Pt Pt
Pt Pt Pt Pt Pt Pt Pt Pt Pt Pt Pt
3110.1 2814.0 2814.0 2814.0 3110.1 2578.4 3iiO. 1 3110.1 3110.1 2578 4 2578.4 2814.0 2578.4 2814.0 2814.0 2578.4 3110.1 3110.1
70
Transmiasion
Concentration Range, P.P.M.
10 10 10 20 20 10 20 20 10 10 10
0.1-10 10-400 1-20 20-160 0.5-20 10-160 20-400 4-100 5-40 0.1-5 1-80 10-160 0.5-10 10-800 0.5-10 5-20 20-80 0.1-1 1-20 2-20 20-160 10-160 80-800 0.1-10 10-160 0.5-10 1-40 10-160 1-10 10-80 80-800 5-80 40-400 1-10
10
10 10 10 10 10 10 10 10 10 ~. 10 10 10 10 10 10 10 10 10 10 10 10 10 20 10 -.
10 10 20 20 10 20 10 10 10 10 10
10-400 0.6-10 10-80 5-40 40-800 20-800 5-25 10-160 2-25 10-100 40-800 10-80 80-800
Interfering Lines
Interfering Line and Concentration Level Element A. P.P.M. 400 Ru 2676.1 400 Cr 3122.6 400 Ru 2497.7
3020.6 2802.7 2779,8 3132.6 2909.1 3404.6 2447.9 2678.8 2528.5 2840,O
factor used for each analytical and internal standard line is also included. A list of interfering lines together with the concentration level at which interference occurs is shown in Table V. The log relative intensity ratio for each line pair was obtained by standard
Fe CO _.
Cr
co
Rh
Fe
Cr Fe
Fe
i 2
Sb Cr
3465.9 3465.8 io20 7 2802.7 2779.5 3132.5 2909.1 2908.9 3404.3 2447.9 2678.8 2528.5 2840.0
800 40 10 160 400 800 1000 1000 1000 1000 40 40 40
spectrographic procedures using an emulsion calibration curve (1). Working curves were constructed by plotting the log relative intensity ratio us. the corresponding log concentration. Background corrections were made whenever necessary. VOL 34, NO. 10, SEPTEMBER 1962
1249
t
ai
I
I
I
I
I I I I I
IO
0.1
1
1
I
I
I
I
l
l
,
04
I
I
I
I l l 1
I
!
1
I
I
I
!
,
I
L
10
PARTS PER MILLION
Figure 4.
Typical working curves (Ag, Rh, Pd, Au)
Residual impurities in the platinum blank were estimated by standard spectrographic techniques (2, 6) and are listed in Table VI. Typical working curves for some of the elements covering the various concentration ranges are shown in
Table VI. Residual Impurities Contained in Platinum Blank
Zn3345.0 (101
= -
Concentration, P.P.M.
Element A1 Ca
2.0
cu
