Spectrophotometric Determination of Beryllium in Aluminum with Sulfosalicylic Acid It. V. MEEK1 A ~ DCHARLES V. B4NKS Institute f o r -4tomic Research and Department of C h e m i s t r y , Iowa S t a t e College, .4mes, Iowa
A method of determining small amounts of beryllium in aluminum depends upon the fact that the beryllium-sulfosalicj late complex has an absorption maximum at a longer wave length than does the sulfosalicylate alone. The optimum wave length is 317.0 m p . The procedure is designed to accommodate the range of 0.0015 to 0.23% beryllium in aluminum, but may be conveniently changed to accommodate much higher o r lower ranges. Inter-
THE
spectrophotometric determination of metals by virtue of the characteristic absorpt,ionof their “colorless” complexes in the ultraviolet region of the spectrum has long remained almost nonexistent. In the course of extending the analyticd chemistry of beryllium to include at least one method of analysis based on such absorption it was discovered that the sulfosalicylate complex of beryllium is amenable to this type of application. A detailed study of the beryllium-sulfosalicylate complex with respect to its identity and the magnitude of its dissociation constant has been reported ( 4 ) . In that study it was shown that the optimum range of pH for the formation of the complex is from approximately 9.2 to 10.8, even when the mole ratio of sulfosalicylate t o beryllium is as low as 2 to 1, and that the mole ratio of sulfosalicylate to beryllium in the complex ion is 2 to 1. Titrimetric evidence showed that both hydroxylic hydrogen atoms of the two sulfosalicylate ions are replaced in the formation of the complex ion. Hence the beryllium-sulfosalic.ylate comples ion is best represented as Be(C,H,So,OCO,),----. The magnitude of the dissociation constant of the complex ion a t the optimum pH to give simple sulfosalicylate ions, C&30sOHCO?--, and an unknown beryllium species, Be,, vas shown to be npprosimately 2.1 X 10-9 a t 25” * 1 ’. At the rather high ionic strengths commonly present during actual analyses the value of k” is more nearly 2 X 10-10. In this work the deterniiriation of verj- small amounts of beryllium in aluminum was deliberately chosen as representing one of the most challenging analytical applications of the method. The range of approximately 0.0015 to 0.23% ber?-lliuni in :duniinum \vas somewhat arbitrarily rhosen as a very useful range :ind is not to he construed as a limitation on the method.
ference b! the aluminum-sulfosalicylate complex is eliminated by complexing the bulk of the aluminum with N,N,N’,N’-tetrakis-(carboxymeth y1)-ethylenediamine and by adding approximately the same amount of aluminum to the standards as is present in the samples. Copper and iron, particularly the latter, must not be present in more than trace amounts. Interference by iron is eliminated b? extraction with (2, bis 2’-chloroethyl) ether.
grade sulfosalicylic acid from either of two commercial bour(w proved satisfactory for this work. It has been reported (4) that this acid is really 5-sulfosalicylic acid or, a t least for the purpose of complex formation with beryllium, behaves as the 5-sulfosalicylic acid. X , S , aV‘ , S ’ - Tetrakis - (carboxvmethyl) ethylenediamine [(ethylenedinitrilo)tetraacetic acid, ethylenediamine tetraacetic acid] is available commercially in the form of the free acid or the various salts, or solutions of the salts, under the trade names of Sequestrene -4.4, Versene, Trilon B, etc. In the present work the acid was purified by the addition of reagent grade sulfuric acid to solutions of the sodium salt of the acid to give a pH of ca. 2.8. The acid, precipitated in this manner, Was separated by filtration m d digtqted for several hours in a large volume of distillcd \later
-
IO0
I
-
REAGESTS
In general, only reagent grade materials were used in this study. Care was used in selecting only those lots of materials containing a minimum of iron, because it WRE knoivn t,hat the presence of iron was particularly undesirable (5). The source of bervllium m s triply sublimed beryllium basic acetate, Be4O(CzH3O2),,which contained a total of only ca. 100 p.p.m. of manganese, magnesium, silicon, calcium, and aluminum as determined spectrographically. Other elements were not detected. The average of five gravimetric analyses as the oside indicated a purity of 100.08%. Stock solutions of beryllium xere prepared by fuming accurately weighed quantities of the basic acetate in covered 500-ml. Erlenmeyer flasks with excess reagent grade sulfuric acid and diluting with tlistilled water in appropriate volumetric flasks. Reagent 1
041-
0
1
I
0
I
I
I II
PH
Figure 1. Effect of pH on Observed Absorbancies at Constant Sulfosalicylate Concentration (5 X lo-‘ M) Using Beckman instrument. 1. 1.00 x i o - S M 2. 1.00 X 10-4 .M
Preaent address, Prooter and Gamble Company, Ivorydale, Cincinnati
17, Ohio.
1512
Beryllium concentration: 3. 2.00 x 10-4 M 4. 2.50 X 10-4 .M
V O L U M E 22, NO. 1 2 , D E C E M B E R 1 9 5 0
15 13
on a steam bath. The acid was again separatcd by filtration, washed with hot distilled water, and dried. The material thus obtained was very white, melted a t 245-246' (not corrected), and g w e clear, water-white solut.ions on diePolution with sodium or ammonium hydroxide. Stock solutions of this material were prcpared by weighing the appropriate amounts of the free acid, dishydroxide Rolvingi n the proper amounts of sodium or to give a pH of about 9, and diluting in volumetric flasks.
thali *0,007 ;ttlsorballl.y unit \yerc (jtlfic.l.vrd for the ranges indicated above. Elimination of Aluminum Interference. It, was necevsary to adopt a systematic8 procedure of analysis using specified amounts of aluminum and other reagents to arronimodate some choseii range of beryllium roncentration. It \vas somewhat arhitraril\.
2
000 280
2 90
300
WOIO
Figure 2.
320
310 Ienpth
330
340
4bsorption Spectra of Solutions
in Table I, u 4 n g Cary instrument and distilled water reference *elution. 4,s. 6 . 7 , and 8 eorrerpond to solutions 1, 2, 3, 4, 5 , 6, 7, 8, respectivel? , In Table I
Solutions prepared
io
, mp
8% dewribed
Standard nluminum solutions w r e prcyxired from reagent gradr aluminum sulfate octadecahydrate. Traces of iron vere rrmoved by precipitating a part of the aluminum along with the iron by the addition of reagent grade sodium hydroxide. The solutions were then analyzed gravimetrically by the method of Willard and Tang (6). A solution of aluminum was also prepared from the most nearly pure aluminum metal currently available, kindly supplied by J. R. Churchill of the Aluminum Company of .imerica. The spectrographic analysis supplied by Churchill indicated only 6 p.p.m. of iron, and beryllium as not det,ected. Thc solution \vas prepared by dissolving a weighed quantity of the inc3tal in dilute wagent grade sulfuric acid and diluting in a volumrtric flask. IN STRIJMENTS 111 the spectrophotometric studies Cary recording spcrtrophotometer (lfodrl 12) and a Brckman quartz spectrophotomliter (Model DU) were employed. Matched silica cells, 1.000 cm. in thickness, were used with the Cary instrument,, and pimilar nrlls, 0.998 cm. in thickness, were used with the Beckman instrument. Reckman glass electrode pH meters (hlodels H-2, XI, and G) were used for the pH measurements, depending on the accuracies tlrsired and the availability of the instruments. Appropriate sodium ion corrections r e r e made wherever accurate lino\vledge of pH was desirable.
EXPERlM ENTA L
Effect of pH. In order t o test the quantitative effect of pH on ahsorhancy, solutions containing sulfosalicylic acid and beryllium sulfate were adjusted t o various p H values by the addition of dilute reagent grade sodium hydroxide solution and compared nith a reference solution which was 5 X Ai in sulfosalicylic :wid, and adjusted to a p H of 9.87. Figure 1 graphically represents the dependence of observed absorbancy on the pH. So long as the p H \?as between 9.2 and 10.8 the absorbancies remained within 0.01 absorbancy unit of each other, except in the vase of the most dilute beryllium solution. I n the case of very dilute beryllium solutions the p H should be adjusted to between 9.2 and 10.5to give a range of no more than 0.01 absorbancy unit. In general, for the best duplication it is advisable to keep the solutions as near t>hesame pH as possible, but departures of no more
Curves I, 2,3,
decided to standardize upon the use of 0.200 gram of aluminuni 50.0 ml. of 0.50 Ji ethylenediamine tetraacetic acid, 10.0 ml. of 1.00 X 10-2 JI sulfosalicylic acid, and a final volume of 200.0 ml. Under these conditions thc mole ratio of ethylenedianiine tetraacetic acid to aluminum is approximately 3.4 to 1.0 and amounts of beryllium up to about 0.45 mg. are determinable. This is equivalent to approximately 0.22% beryllium on the nig. of beryllium present, aluminum basis. n l t h 3.0 X equivalent to 0.0015% beryllium in aluminum, an absorbancy of ca. 0.01 is observed with an estimated error of approximately 50%. I t is necessary to complex the aluminum for a t least two reasons. In the absence of a suitable romplexingagent the aluminum simply precipitates at the pH demanded by the analysis. Sulfosalicylate complexes aluminum, hut is present in very small amounts cornpared to the aluminum. The fact that aluminum is c.omplexed by sulfosalirylate alters the spertral properties of the solutions a t the wave length of interest and makes necessary t'he rllimination, or at least the minimization, of aluminum roniplexation by sulfosalirylate. Table I indicates the composition of solutions used to show the minimization of aluminum interference by the addition of rthylenediamine tetraacetic acid. Filtered, concentrated reagent grade ammonium hydroxide was used in the adjustment of pII in these solutions because p H is more easily adjusted with it than with alkali solutions; furthermore, the purity is generally better in the case of the ammonium hydroxide solutions. The solut,ioris described in Table I were scanned on the Cary instrument at a temperature of 25" * 1'using a distilled water reference solution. The absorption spectra obtained are s h o ~ v nin Figure 2. Curve I , Figure 2, show that solutions 0.125 M in ethylenedianiine tetraacetic acid a t a pH of 10.05 absorb only in amounts of about 0.01 absorbancy unit in the n-ave-length range of 290 to 350 mp. At 317.0 mp the absorbancy \vas 0.009. Curve 2, Figure 2, shows that solutions 0.125 111in ethylenediamine tetraacetic acid and containing 0.2000 gram of aluminum per 200.0 ml. of solution a t a pH of 10.04 also absorb only in amounts of about 0.01 absorbancy unit ovw thr range of wave Irngths. At. 317.0 mp the absorbancy a - u0.012. Obviously the aluminum-
ANALYTICAL CHEMISTRY
1514 _____
Table I. Composition of Solutions for Spectrophotometric Examination (In attempt to eliminate alnminrini interference by ethylenediamine tetraacetic acid) 0.2287 M 1 . 0 0 X 10-sM 0 . 5 0 M EthylpH (BeckSoluAluniinurn Beryllium 1.00 X 10-2 .If man Model enediamine tion Sulfate Sulfate tetraacetic SulfosaliFinal H-2 So. Added Volume Instrument) Added Acid cylic Acid Y1. M 1. M1. 211. M1. .... 200.0 10.05 1 .... .... 50.0 2 32.4 .. . 50.0 .. . 200.0 10.04 3 ... .... 50.0 10.0 200.0 10.07 4 32.4 .... 50.0 10.0 200.0 10.06 R .... 25.0 50.0 10.0 200.0 10.08 6 32.4 2.5 , a ao, 0 10.0 200.0 10.08 7 ... ... .... 10.0 200.0 10.28 8 25 0 .... 10.0 200.0 10.20
__ etliylenrdiumine tetra:icetatr complex does not absorl) a t , o r near, 317.0 mp, the wave lrngth of interest. Curvr 3, Figure 2, shows the absorption due to a solution 0.125 K in ethylenediamine tetraacetic acid and 5.00 X 10-4 M i n sulfosalicylate at a pH of 10.07. At 317.0 mp the absorbancy was 0.341. Curve 7, Figure 2, tvhich represents absorption due to a .If in sulfosalicylate at a p H of 10.28, was solution 5.00 X virtually identical with c u r w 3 and differed from it by no more than 0.010 absorbancy unit anywhere in the wave-length range of 290 to 350 my. The absorhancay observed a t 317.0 mp for curve 7 was 0.338. This comparison shows that the presence of ethylenes appreciably interfere x i t h the diamine tetraacetic wid t l ~ not ici ahsorption of' sulfosalicvlste solutions a t or near 317.0 mp. c u r v e 4, Figure 2, s h o w the ahsorption of a solution 5.00 X 10-4 A4 in sulfosalicylate, 0.125 JI in ethylenediamine tetraacetic acid, and containing 0.2000 gram of aluminum a t a pH of 10.06. This curve does differ appreciat)ly, 0.045 absorbancy unit, from curve 3 and this differrnco was presumed to be due to the presence of a small amount of the aluminum-sulfosalicylate complrs. The absorbancy observed for curve 4 a t 317.0 mp was 0.386. Curves 5, 6, and 8, Figure 2, show the changes in a1)solbancy brought about when solutions exactly like solutions 3, 4, and 7, respectively, Table I, are ni:ttlc 1.25 X AI in beryllium. The absorbancies a t 317.0 mp for C U I ' V ~ S5, 6, and 8 were 1.133, 1.178, and 1.122. I t was thus shown that the increase in absorbancy for the constant amount of 1)erylliuni added was essentially the same in the presence of aluniiiiuni and rthylenediamine tetraacetic. acid as in their absenr:e.
parts per million of beryllium on the aluminum basis, may be plotted along the abscissa.
Recommended Procedure. Obtain the aluminum ana beryllium in the form of the sulfuric, perchloric, or hydrochloric acid solution in avolume of about 100 ml. The solution should contain 0.2000 * 0.0200 gram of aluminum. The excess of acid should be kept as small as conveniently possible to minimize the amount of base subsequently required for neutralization. Add to the solution 10.0 ml. of :rpproximately 1.00 x 10-2 AT reagent grade sulfosalicylic acid and 50 nil. of approximately 0.50 M sodium or ammonium ethylenediamine tetraacetate of pH 8 or 9. Very accurate measurement of the volume of the latter solut,ion is not required. (Unless the etliyleiir.tliainirie tetraacetic acid used is pure as indicated by melting point and ahility t,o form a clear, waterwhite, sodium or ammoriiuni salt solution, it should t)e purified by recrystallization as describtsd above.) Adjust the pH of the solutiori to between 9.2 and 10.8 with filtered. concentrated reagent grade aninionium hydroxide. Dilute the solution to exactlg 200.0 ml. with distilled water and measure the ntlsorbancy a t 317.0 mp against a reference solution prepared in exactly t,he same manner as the sample solution, omitting the sample. The final pH of this solution should not be greater than 10.5. Read the corresponding beryllium concentration from a calibration curve prepared by using known amounts of beryllium and 0.2000 gram of pure aluminum and the same amount of sulfosalicylic acid and ethylenediamine tetraacetic acid as was used in the actual analysis. For the most accurate work it is hrst to keep the p H of the sample and standard solutions as nearly the same as possible. This is not inconvenient because of the buffering action supplied by the ethylenediamine tetraacetic acid in tht: pH range of interest. A pEI of 10.0 is very caonvrriient.
Sodium hydroxide may he suhstituted for ammonium hydroside, but in general sodium hydroside solutions are not as free of contamination, particdarly iron, as are amnionium hydroxide solutions. The use of sodium hydroside does not permit the ease of pH adjustment the ammonium hydroxide affords. In the absence of aluminum the ethylenediamine tetraacetic acid need not be used. However, this acid does effectively complex a large number of metallic ions a t the pH range of interest and may he used profitably where such complesing is desirable.
A series of solutions !vas prepared to test the degree of aluminum interference throughout the determinable beryllium range. All these solutions and the blank solution were 0.125 JI in ethylenediamine tetraacetic acid, 5 X 10-4 M in sulfosalicylic acid, adjusted to a pH of 10.50 * 0.15 with sodium hydroxide, and had a final volume of 200 ml. Some solutions also contained beryllium, while others contained beryllium plus 0.2000 gram of aluminum. The ahsorbancies were read on the Beckman instrument using the blank solution as the reference. These data are shown in Figure 3. Although the aluminum interference was not caornpletely removed hy complexation with ethylenediamine tetraacetir acid, it was reduced t o a relatively small amount. At most, under the conditions stipulated, the interference is about 0.05 absorbancy unit. In order to eliminate errors due to the presence of aluminum i t is only necessary to add approximately the same amount of aluminum to the beryllium standards as is present in the samples. A difference of 20% in the aluminum content should bring about only 0.01 unit difference in the observed ahsorhancy. For extremely accurate work, particularly in the very low beryllium range, the aluminum content of samples Figure 3. Absorbancies Observed at 317.0 mp and standards should be more nearly equivaUsing Beckman instrument for various eoncentrations of beryllium 1. 0.2000 gram of purified aluminum present lent. As a matter of convenience actual beryl2. No aluminum present lium concentrations in solution, rather than Q 0.2000 gram of aluminum from Aluminum Company of America
V O L U M E 2 2 , NO. 12, D E C E M B E R 1 9 5 0
OJO
t
1515
Yl -5tondord
0 IO
040
-
030
-
amount of precipitate collected in the bottom of the flasks containing the cerium, zirconium-hafnium, and tin contaminants. When these solutions were re-examined after decantation .3 days after their preparation, the absorbancics observed were 0.!182, 0.973, and 0.972, respectively. The dcpart.urcs from the standard value of 0.985 were small enough to be considered irisignificant for the range of concentration of berylliuni used. Of the cations examined, only cupric ropper and ferric: iron offered highly objectionable interferences. The interference by ropper \vas not considered a serious problcn~bwause it could he eliminated by removing the copper t)y electrodeposition ( 2 ) . The interference hy iron could probably IIC removed by electrodeposition at the mercury cathode (6)01'by the separation of ferric chloride from beryllium by extraction a i t h arnyl acetate or diethyl ether ( 7 ) . The extraction of iron by bis(2,2'-c~hloroethyl) ether ( p , p'-dichloroethyl ether) was described hy Aselrod and Swift ( I ) ; it appeared that the hydrochloric acid concent1.ation was prrhaps less critical in this method than in the others, provided that the acid c.onc*entration was greatrr than 7 formal. This mrthod was essentially the onc used in removing thr iron interference in the present work. I
I
20
1 10
1
?' ,-s""d"$
COnfemin~fmp I O " ,
Figure 4.
Relative Interferences in Sulfosalicylic Acid Method for Beryllium in Aluminum
1.0% of each indicated contaminating ion as determined using Beckman spectrophotometer. Low beryllium range, 90.2 p.p.m. beryllium i n aluminum
The beryllium-sulfosalicylate complex is formed immediately and is stable for a t least 2 months. Temperature control is important only where there is no or only a slight excess of sulfosalicylic acid present. Under these conditions the temperature of the sample solution and the standard solutions should be nearly the same. Cation Interferences. Figures 4 and 5 graphically indicate the degree of interference brought about by the presence of various cations a t moderately low and moderately high concentrations of beryllium in aluminum, using the method outlined above. In each case 0.0020 gram or 1% of the contaminating cation was used. T h e vation sourres iwre various reagent grade metals, salts, and salt hydrates. After 48 hours had elapsed, the solutions for the low beryllium range R hich contained the cerium, zirconium-hafnium (Zr-Hf ea. 98 to 2), and tin contaminants contained slight, definite precipitates. These solutions were decanted and re-examined in the Beckman instrument. A noticeable reduction in the degree of interferrnce a a s brought about by the roagulation of the precipitates. The absorbancy values observed for the decanted solutions were, respectively, 0.131, 0.124, and 0.116. Comparison of these values with the standard value.: 0.112 indicated that the interferences a-rre almost completely eliminated. In the case of the higher ber)llium range (Figure 5 ) , a small
b C ~ n l o n l n ~ l l nion. ~
Figure 5 ,
Relative Interferences in Sulfosalicylic k i d Method for Beryllium in Aluminurn
1.0yo of each indicated contaminating ion as determined using Beckman spectrophotometer. High beryllium range, 1353 p.p.m. beryllium i n aluminum
Duplicate samples for the same two previous (*oncentrationsof hrryllium examined were prepared as indicated in Table 11, along vrith a blank solution and two standards, one for each of the hervllium concentrations. For solutions 1, 2, 3, and 4, the iron, beryllium, and aluminum solut,ions were placed in 250ml. beakers. Three dropsof concentrated Table 11. Solutions Used in Removal of Iron by Extraction with reagent grade nitric acid were added to 0, p'-Dichloroethyl Ether each to ensure the complete oxidation of 0.50 .If EthylCorrected the iron t,o the trivalent state. To each 1.00 X 1 0 - 3 .If +u1.00 X 10-2 .If enediamine pH (BeckSolution Iron Berylliiini minuni Sulfosalitetraacetic Vinal man Model solution were nddcd approximately 30 ml. cylic Acid Acid Volurne H-2) No. Added Added Sulfate of concentrated reagent grade hydroM1. M1. 311. Mg. G. -If 1. chloric acid and the solutions were evapo... 30.0 10.19 Blank ,.. 10.00 200.0 rated to near dryness on a hot plate. T o 200.0 Control 1 . .. 30.0 0,2000 10.00 50.0 10.25 each solution were added 40 ml. of con10.22 60.0 Control 2 ., . 2.00 0.2000 200.0 10.00 1 2.00 po.0 200.0 9.98 0.2000 10.00 30.0 centrated reagent grade hydrochloric acid 10.07 2 2.00 30.0 0.2000 10.00 JO.0 200.0 and 10 ml. of distilled water. Each solu200.0 2.00 3 2.00 10.00 50.0 9.98 0.2000 4 2.00 2.00 9,95 200.0 0.2000 10.00 60.0 t,ion was then extracted with three 25-1311. portions of freshlv distilled B,B'-
1516
ANALYTICAL CHEMISTRY
It was concluded that the P,P’-dichloroethyl et,her extraction sucTable 111. Determination of Beryllium after Removal of Iron with @,@’-Dichloroethyl Ether (Solution numbers correspond t o Table 11) Observed Abso! bancy
Solution Control 1 Control 2 1
2
3 4
Table I\’.
0.998 0.114 0 992 0.996 0.122 0.118
Beryllium Taken P.p.m. 1350 90.2 1350 1360 90.2 90.2
Beryllium Found P.p.m. 1350 90 1360 1370 100 95
Anion Interferences in Sulfosalicylic hcid Method for Beryllium in .4luminum (Low beryllium range)
Solution No. Blank Control 1 2 3 4
Nature and Amount of Anion Contaminant
....
....
1 ml. coned. reagent grade nitric acid 1 ml. reagent grade glacial acetic acid I-ml. reagent grade sirupy phosphoric acid 1 g. reagent grade sodium fluoride
Observed Absorbancy at 317.0 nib
Berylliuiii Taken P.p.m.
Berylliuni Found P.p.m.
o:ii6
....
90.2
...
0.437
90.2
560
0 124
90.2
105
92
0.063
90.2
20
0,115
90.2
92
cessfully removed the iron interference.
Anion Interferences. I t had already been shown that large amounts of perchlorate, chloride, and sulfate ions did not interfere in the proposed method. Table I\- indicates the identity and quantity of other contaminating anions examined, together n-ith the degree of interference which was found for each in the low heryllium range. Fluoride, in the amount used, offered no interference. However, a crystalline precipitate, presumabl), ammonium fluoride, was noted. Acetic acid interfered \Fer)slightly. Large interferences were noted for nitrate and phorphate ions. KO interference was observed from the carbonatc normally present in sodium hydroxide or from the carbon dioxide absorbed by the solutions after they had been adjusted to p H of 10. LITERATURE CITED
.Ixelrod, J., and Swift, E., J . Am. Chem. SOC.,62, 33-6 (1940). (2) Baskerville, E., .~NAL.CHEM..21, 1089-91 (1949). (3) Foley, R., and A4ndeison, R., J . Am. Chem. SOC.,70, 1195-7 (1)
(1948). (4)
Meek. H. V., and Banks. C. V., submitted for
publication
ill
J . Am. Chem. SOC. (5) Slomin, G., “Rapid Quantitative Electrolytic Methods of Analysis,” C h i c a g o , E. H. Sargent and Co., 1943. (6) W i l l a r d , H., and Tang, S . ,IND.ENG.CHEY.,A N ~ LED., . 9,357-63 (1937).
(7) Young, R.. J. Chem. Edttcntion. 26, 357 (1949).
dichloroethyl ether, observing the usual extraction techniques. Each solution was evaporated t o near dryness, to avoid the necessity of later neutralizing tzn excessive amount of acid, the solutions were diluted to about 125 ml. each with distilled water, and the analysis was carried out in the usual manner. Table I11 indirates the observed absorbancies and-corresponding parts per inillion of beryllium on the aluminum basis n hich w r e ohtnined.
RECEIVED h l a y 5 , 1950. Contribution 98 from Institute for Atomic Research and Department of Chemistry, Iowa State College. Based on work performed in the Ames Laboratory, Atomic Energy Commission. .4bstracted from a dissertation submitted by Homer V. Meek t o the Graduate Faculty of Iowa State College in partial fulfillment of the requirements for the degree oi doctor of philosophy, 1950.
Multipurpose Method of Spectrographic Analysis Sodium Nitrate Matrix and Alternating Current A r c Excitation V. G. PERRY, W. M. WEDDELL, AND E. R. WRIGHT Texas Division, The Doto Chemical Company, Freeport, Ten. A quantitative spectrographic technique of general applicability is based on sodium nitrate as a common matrix. The method is particularly useful in the analysis of sodium hydroxide, brines, and other sodium salts which are converted to sodium nitrate prior to spectrographic analysis. Other types of samples are analyzed by suitable preliminary chemical preparations. Forty-two elements may be determined with an accuracy approaching 5 % of the amount present.
T
HE value of a quantitative spectrographic technique is considerably enhanced if it is capable of general application to a wide variety of substances. The method herein presented represents an extension of the sodium nitrate method recommended by Hess, Owens, and Reinhardt ( 3 )and adapted by McClelland ( 4 ) . T h e method in brief consists of suitable chemical treatment, so that the sample is converted into, or taken up in, a 20% sodium nitrate solution, followed by spectrographic analysis using a 2.2ampere alternating current arc discharge for excitation. In general, samples handled by this method fall into four classes: (1) sodium compounds such as sodium hydroxide or sodium chloride brines, which are easily converted to sodium nitrate: ( 2 ) other inorganic materials soluble in nitric acid; ( 3 ) organic mate1 ials which can be iyet-ashed; and (4) refractory materials 1 equiring fusion or other extended chemical treatment. The method is particularly applicable to the alkali industry, where a significant fraction of the total analytical load consists of sodium salts easily converted to sodium nitrate.
SPECTROGRAPHIC CONDITIONS
Spectrograph. A.R.L. grating spectrograph, Model 2060. Excitation Source. A 2200-volt, 15 kv.-amp. transformei is used with 220 volts on the primary and 950 ohms ballast resistance in the secondary in series with the analytical gap. Because the arc-gap resistance is small compared with the ballast resistance, fluctuations in the arc current are negligible. Electrode Stand. A slight modification of that of Duffendach and Wolfe ( 2 ) , with a 1-nim. pitch screw to adjust electrode separation and water-cooled electrode clamps. Auxiliary Optics. Light from the source is focused upon the grating through a &inch (12.5-em.) spherical quartz lens. BJ means of a 3-inch quartz lens and front surface mirror placed behind the source, the intensity of light reaching the grating ma! be increased by some 807, when necessary. Safety Hood. The entire optical bench, the electrode stand, and the source leads are enclosed within a safety hood which is equipped with limit switches on the doors. Opening the hood while the arc is in operation automatically shuts off power to thc transformer. The hood also protects the operator’s eyes from ultraviolet radiation, and has an exhaust fan for fume removal.
