provides a very sensitive assay, allowing a peak of only 1 or 2 pmoles of carbonyl compound to be readily detected. The presence of 0.13f (or greater) bisulfite in all fractions and throughout the resin bed stabilizes carbonyl compounds as the bisulfite complex. This allows separation and quantitative recoveF of volatile compounds as a-ell as ones which tend to polymerize or oxidize readily. The method described should be useful for stabilizing, separating, and q u a -
titating micromole amounts of nldehydes and ketones fornied in biological systems. particularly where it is clesirable to recover these compounds for isotopic degradative studies or for further characterization. LITERATURE CITED
(1) GabrielJon, G., Samuelson, O., .J& C h m . Sm@, 6 , 7‘29 (19.52). (2) Zbid., p. 138.
(3) Gabrieleon, G., Samuelson, 0..S w m k . K ~T &~k . 62, , 211 ( 1 9 j ~ ) , (4) Zbid., 64, 150 (19.52).
( 5 ) Huff. E., Rudney, H.. J . R i d . Ciirr i i
,
2 3 4 ~low (lgjY’,
(6) Perkin. K. H., J. C‘hsui. SOC. 59, 766 (1691). ( 7 ) Rudnej-, H., .irch. Biociienl. 23, 67 (1949 j. ( E ) Samuelson, O., Pjostrom. E., Sr,t t i $ / ; . Kem. Tidskr. 61, 305 (1952). (9) Pamuelson. O., Westtin, .\.. Ihid., 5 9 , 2 U (1947). (10) Sjostrom, E.. Trans. C h n i f w r s Zlnir. 136, 8 (195311. (11) Thornton. B. J., Speck, J. C., .\SAL, CHEU.22, S99 (195Oj. RECEIVED for reiiew Soveniber 10. 1958. -1ccepted July 16, 1959.
X-Ray Fluorescence Analysis of Stainless Steel in Aqueous Solutions R. W. JONES and R. W. ASHLEY Chemistry and Metallurgv Division, Chalk River Project, Atomic Energy o f Canada Ltd., Chalk River, Ontario, Canada
b Nickel, chromium, molybdenum, and niobium have been determined in aqueous solutions of stainless steels by x-ray fluorescence spectrometry. Nickel, chromium, and molybdenum are determined directly in solution, while niobium is separated by conversion to NbzOj and determined after briquetting with cellulose powder. The method is considerably faster than conventional wet-chemical techniques and gives results which are more precise and accurate than those from previously reported x-ray methods. The standard deviation for all four elements is better than 1% of the amount present in the concentration range of interest. Agreement between chemical and x-ray fluorescence results on standard steel samples is within 1%.
S
steels have been analyzed by s-ra!- florescence spectrometr? for several years I 2 . 4 . 5 ) . Such analvses have been genernliy perfornied on solid samples having a uniform surface area and finish ( 4 ) .and are not readily adaptable t o other s n i p l e fornis such 3 s drillings and turnings. .inother disadvantage of using solid samples is the existence of “absorption-enhancement” effects which often lead to serious errors ( 4 ) . Sherman ( S ) , Soakes (y), and Mitchell (6) have treated the problem mathematically with good results, and Burnham, Hower. and Jones (3) worked out a general scheme of analysis based on the equations of Sherman by altering and extending the Original equations. They were able t o adapt their method t o a great variety of sample shapes and forms. and t o reduce the amount of mathematical computations involved by the use of graphical methods. TAISLESS
Silverman and Houck (9) worked out a scheme for the determination of iron. chromium. and nickel in aqueous solution, but the accuracy was t o onl!- about 3ycof the amount present. The present paper describes a somen-hat different aqueous method which results in greater accuracy. and also permits the deterniination of niobium and niolyhdenuni to be camed out on the same saniple. In this work, which was intended specifically for the analysis of the 1S5; chromium, 8% nickel series of stainless steels, no attempt was made to determine iron. because this element is generally obtained by difference. If required, the method could ensill- be estended t o include the iron deterniination. The method should also be rendily adaptable to anslyses of other steels and alloys. EXPERIMENTAL
Instrumentation. A Philips, threespecimen s-ray 5uorescence spectrograph, Model 52254, with specimen spinner and helium path attachments was used. Conditions were as follows: X-ray tube Philips F.\-60 W target .inalyzing cyatal LiF (L’d = 4.028 -\. Collimation Primary. 5 X 4 inch parallel plnte Secondary, 0.005 X 4 inch parnllel plate Detector Philips. Type 5224.5, scintillation counter (Sa1 crystal I Pulse height .itomic Instrument Co., Model 510; analyzer single channel, modified to allow 3-fold increase in available channel width Chemical Procedures. Becausc niobium is difficult t o maintain completely in solution in the common mineral acids, it was decided t o carry
out a cheniical separntinn of tiitniobium from the ma j o r con s t it u e n t 5 of the steel by the sulfurous aci,! hydrolysis method ( 1 ) . -kn addition:d advantage of this separation is that the concentration of the niobiuni in the niobium fraction is greater than that in t h t original steel sample, thereh;: giving increased sensit.ivity. This is desirablr. because the niobium content of the steels is generally less than 15;.
A O.5-gram s m p l e of eke; is diesolved in 10 ml. of aqua regin. \\-hen solution is complete. ’7 ml. of concentrated sulfuric acid are added and the solution is tnken t.o d y n e s . The s l t s 3re then taken up in about 50 ml. of water. and 25 ml. of 3 saturated solution of sulfur dioxide and n little filter pulp rre added. The solution is heated nearly to boiling and digested for to 1 hour, after which it is filtered and the precipiiste ~ 3 s h e dKith :ipprosimately 200 mi. of distilled n-nter to which 1 to 2 drops of sulfuric wid nre added. The filter paper and precipitnte are ignited a t ahnut SOO” C. :ind the ignited residue is then mixed \ \ i t h 1.00 gram of cellulose powder (\VhAtman ashless cellulose pon-der for c!iromstography. stmdard gnde! nnd hriquetted into n !-inch diameter pellet a t 60,OOO-pound pressure ir: an .kRL briquetting machine (>lode1 44.51 The filtrate is concentmted to t.\;nctl!. 50 nil. and thr m o i ~ ~ h d c n u mvliro. niiuni, and nickel cieterniinntions :ire made on 3 10-ml. aliquot of this solution. Preparation of Standards. Siobiuin standards n-ere prepared by taking aiiquots of a soiution of Johneoi!. Matthey and Co., Ltd.. “spec-pure” niobium and carrying them through the hydrolysis and briquetting steps. A different series of standard solutions prepared for the molybdenum determination than for nickel ana chro’1.
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1629
miuln. For molybdenum, only iron was added in an amount corresponding to the expected total iron, chromium, and nickel content of the samples. For the nickel and chromium standards, varying amounts of iron, chromium, and nickel were used to cover the range 5 to 15% nickel and 15 to 25y0 chromium while keeping the total concentration of the three elements constant, The sulfuric acid concentration of the standards was kept identical with that of the samples. X-Ray FluorescenceM easurement s For the niobium determinations, the x-ray tube was operated a t 30 kvp. and 35 ma. and intensity measurements were made on the niobium K , line a t 28 = 21.35’. The times for a minimum of 256,000 counts for the niobium peak and for 64,000 counts for the background at 28 = 19.50” were recorded. Samples were rotated during irradiation and duplicate counts takcn on both sides of the specimen. Since the sample holders for the spectrogrnpli are 13,” inches in diameter and the sample briquets only 1 inch, polyethylene adaptcrs wcre uscd to keep the samples centered in the x-ray beam. For the x-ray intensity measurements on the remaining elements, 10-ml. sample aliquots were placed in the sample holders. The sample holders were the standard type supplied with the instrument, fitted with 0.00025inch Mylar windows. For molybdenum the x-ray tube was operated a t 60
kvp. and 25 ma. All measurements were made on the molybdenum K , line. A minimum of 128,000 counts was accumulated and all counting measurements were made in duplicate. A “blank” steel solution free from molybdenum was measured to correct for background, the pulse height and’
/ /
.
Table 1.
I ,c
1 20
MILLIGRAMS
I ,o NiOBlUH
IN
I
I
40
50
SAMPLE
Figure 1. Calibration curve for the determination of niobium in stainless steel
Chemical Values Sample and Ta BCS 246 0.82b
X-Ray Fluorescence
Values, yo Nb‘
7’ Ta 0.02
It was found experimentally that the use of helium in the “optical” path of the spectrograph resulted in both higher over-all intensities and improved peakto-background ratios (by a factor of 2) for the chromium measurements. Use of the pulse-height analyzer also increased the peak-to-background ratios by a factor of approximately 3. Background corrections proved unnecessary, as no significant differences were observed either between sampies and standards or from day to &I.. 3upljcate counting times for ZL minimum of 128,000 counts were recorded and counting rates calculated.
Figure 2. Calibration curve for the determination of molybdenum in stainless steel
Niobium in Standard Steel Samples
7% Nb
alyzer being uscd to reduce the background of scattered radiation by a factor of approximately 2. On account of the higher concentrations of the chromium and nickel in the solution, the x-ray tube was operated a t lower power levels for the determination of these elrments-40 kvp., and 40 ma. were used for the measurement of the Cr K , intensity, and 30 kvp. and 30 ma. for the nickel K,.
0.770 0.761 0.760 0.761 Av.= 0.763
UILLIGRIIYS
MOLYBDENUM
PER 5 0 ML
SOLUTlW
RESULTS AND DISCUSSION
Table 111. Calibration Data for Chromium and Nickel Determinations
NBS 444 0.21
Unknown
0.178 0.174 0.179 Av.c 0.177
“ Individual values obtained by analysis
Nickel Chromium Concn. in Concn. in standard standard soln., Counts/ soln., Counts! mg./50 ml. second mg./50 ml. second
of separate samples.
* Standard deviation 0.027”.
Sample
BCS 246
n
50 0 75 0
Standard deviation o.oI)370.
Table II.
25
2710 5025 7220
75.0 100 0 125 0
3260 4125 4970
Niobium in Synthetic and Spiked Samples Added 0.202 0.202 0.404 0.604 1.008
Niobium, 7% Found by x-ray anal. 0.960 0.966 0.578 0.606 1.000
(by diff.)
Av. X-Ray Value from Table I
0.758 0.764 0.174
0.763 0.763 0.177
In sample
NBS 444 A (synthetic)“ ... ... B (synthetic)” ... ... a Prepared from standard solutions of Nb, Fe, Cr, and Ni to simulate solutions of niobium-containing stainless steels. 1630
ANALYTICAL CHEMISTRY
Determination of Niobium. Figure 1 shows the calibration curve used for the niobium determination. The limit of detection using a 0.5-gram sampie would be about O.Ol%, assuming this small amount of niobium could be recovered quantitativei:; from solution. The results obtained on three standard steel samples supplied bj’ the Bureau of Analyzed Samples, Ltd., Yorks, Engiand (BCS sampies), and the Nationai Bureau of Standards, Washington (NBS sampiesj, are shown in Table I. The precision of the results by the xray method is obviously very good, the standard deviation being 0.003% niobium. The difference between the chemical and x-ray values can be attributed a t least partly if not completely t o tantalum (which is difficult t o separate chemically from the niobium). In general, results of chemical analysis of
Table IV. Molybdenum in Standard Stainless Steel Samples
Sample NBS 444
NBS 845
NBS 846
BCS S.S. 4
BCS S.S. 5
BCS 246
Nominal % Mo 0.22
0.92
0.43
l.W
1.41d
2 . 8gd
Table V.
Chromium and Nickel in Standard Stainless Steel Samples
Nominal
NBS 121b
17.68b
NBS 846
18.37
0.47 0.44 0.44 A V . 0.45 ~
NBS 847
23.73
1.30 1.29 A V . ~1.29
BCS 246
18.8
BCS 261
17.20f
0.20 0.20 Av. 0.20 0.95 0.93 0.95 A v . ~0.94
1.44 1.42 1.44 A V . ~1.43 2.91 2.86 2.86 A v . ~2 . 8 8
Individual values obtained by analysis
of separate samples.
Standard deviation 0.02%. Standard deviation 0.04yo. Standard deviation o.0370.
stainless steel are reported as percentage of niobium plus tantalum, whereas the x-ray method gives niobium alone. The chemical values reported in Table I for the British chemical standards are averages based on determinations carried out at ten dif€erent laboratories. However, the tantalum values were supplied by only one laboratory and may be regarded with some uncertainty. To check on the efficiency of the niobium separation, a group of synthetic and "spiked" samples was analyzed for niobium. The results (Table 11) suggest that the x-ray values are, i n fact, accurate. Determination of Molybdenum, Chromium, and Nickel. The calibration for the determination of molybdenum is shown in Figure 2. Table 111 lists the counting rates obtained on chromium and nickel standard mmples. These data give linear calibration curves. The molybdenum calibration covers the range 0 to 5% and the chromium and nickel calibrations cover the ranges 15 to 25 and 5 to 15%, respectively. These were chosen as representative of stainless steels such .as Types 304,316, and 347. A variety of NBS and BCS samples
70 Nickel
yo Chromium Sample NBS lOld
X-Rsy Fluorescence, % Moa
18. 68b
X-ray0
Nominal
18.91 18.49 15.43 A v . ~18.61 17.59 17.54 17.58 A v . ~ 17.57 17.94 17.73 17.71 A v . ~17.79 23.50 23.45 23.35 A v . ~23.43 18.52 18.68 18.73 18.72 A v . ~18.66 17.14 17.11 17.12 17.18 A v . ~ 17.14
9.05'
11.14C
9.10
13.26
12.1
13.0&
X-ray' 9.07 8.98 9.01 Av: 9.02 11.12 11.10 11.12 Av.' 11.11 9.14 8.96 8.98 Av.* 9 . 0 3 13.28 13.25 13.22 AV.~13.25 12.36 12.30 12.29 12.27 Av: 12.30 13.10 13.13 13.09 12.88 Av: 13.05
Individual values obtained by analysis of sgparate samples. Standard deviation o.0370. Standard deviation 0.02'70. Standard deviation 0.12y0. * Standard deviation o.07y0. f Standard deviation 0.04yob. Standard deviation o.0570.
was analyzed by the proposed procedure (Tables N and V). These results compare very favorably with the accepted chemical analysis values. The average difTerence between chemical and x-ray values for 2% molybdenum or greater is less than 1% of the amount present. For chromium and nickel the average differences between chemical and x-ray results are 1 and 0.5% of the amount present, respectively.
determined). Preparation of the necessary standards is a simple matter. The specific method described waa used only for the 18% chromium8% nickel types of stainless steel, but the general method could easily be applied to any type of stainless steel or other alloys of iron, chromium, and nickel. All t.hat is required is a suitable set of standards, which are easily prepared by solution techniques. LITERATURE CITED
CONCLUSIONS
An accurate, precise, and relatively rapid x-ray fluorescence method for the determination of niobium, molybdenum, chromium, and nickel in stainl p steel samples has been developed. It is considerably faster than the usual wet-chemical methods employed. While the direct determination of these elements on a solid sample is even more rapid, the procedure used here offers certain advantages over the direct method-i.e., absorption-enhamement effects are negligible, the samples can be in any form or shape and much smaller samples can be utilized (as little as 0.1 gram if niobium is not being
(1) Bagshawe, B., Elwell, W. T., J . SOC.Chem.Ind. 66,398 (1947). (2) Brissey, R. M., Chase, G . A., Am. Machinist 97, No. 9, 132 (1953). (3) Burnham, H. D., Hower, J., Jones, L. C., ANAL.CHEM.29, 1827 (1957). (4) Dodds, D. J., von de Veld, L., N o r e h Reptt. 2, 87 (1955). (5) Gillam, E., Heal, H. T., Brit. J. Appl. Phys. 3 , 353 (1952). (6) Mitchell, B. J., ANAL. CHEM. 30, 1894 (1958). (7) Noakes, G. E., ASTM Spec. Tech. Publ. 157, (1953). (8) Sherman, J., Zbid. (9) Silverman, L., Houck, W. W., U. S. Atomic Energy Comm., Rept. NAA-SR1788.
RECEIVEDfor review April 9, 1959. .4ccepted June 26, 1959.
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