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 ( 1 9 4 9 ) . (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 ( 1 9 4 9 ) .
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 ) . The 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.
V O L U M E 22, NO. 12, D E C E M B E R 1 9 5 0 Graphite Electrodes. These are 0.25 inch in diameter by 1 inch in length with a 0.125-inch end dressed back 3 / 1 ~ inch. United Carbon Products Company spectrographic Grade A graphite is used for general purpose work. The more economical spectrochemical grade is used for analyses in which electrode impurities will not interfere with the determination. Film Handling. Film (35-mm., Eastman spectrum analysis S o . 1) is developed by standard procedures and air-dried under :i fan. Line intensities are measured with an A.R.L. densitom('ter and a calculat'ing board ( 6 ) is used to compute log intensity i,:itios. Film Calibration. Film calibration is accomplished b y a method similar to that of Churchill ( I ) . A spark discharge bctween mild steel pins is photographed through a four-step rotating sector, the steps of which have a 1-2-4-8 intensity relationship. A preliminary curve is drawn by plotting the densitometer iwding of each stcp against that of the next succeeding stcp. From this preliminary curve a plot of densitometer reading :igainst log rt~l:rtiyr~ intensity giws the film response curve. PROCEDURE
Class I, Sodium Salts. Pampl consistiug largely of sodium hydroxide, sodium carbonatcl, or dium chloride are converted i o sodium nitrate by simple evaporation n i t h nitric acid. Other sodium .;alts are converted t o nitrates by more lengthy chemical treatment 0 1 ' :ire' handlcd by dilution with sodium nitrate as in c*l:tss11. Class 11, Nitric Acid-Soluble Materials. These include carbonate m i n c d s , oxides, w-ater-soluble chemicals, metals and :illoys, and thcb likc. A small sample, usually 50 mg., is dissolved i l l nitric avid, evaporated to remove volatile constituents, and of sodium nitrate in the form of diluted with 20 times its weight :I 2OYOsolution. Class 111. Oreanic Materials. These are net-ashed. usually n i t h nitric, 'sulf;ric, and perchloric acids, and arc then taken up i n 20Y0 sodium nitrate solution. Class IV, Refractory Materials. Suitable chemical methods niust br used to effect solution. Silicates may be fused with sodium curbonate, followed by evaporation with hydrofluoric and nitric acids. In any case most of the silica must be removed and the sample finally tnkcn up in a sodium nit,rate solution containing sodium nittxte r:quivdent to 20 times t,he weight of original s:imple. In the case of niatrrials in class I, a sample equivalent to 2 grams of sodium nitrate is weighed ink a 50-ml. Erlenmeyrr flask and dissolved in wntrr. The solution is treated with d nitric acid and evaporntcd to rrmove the excess. To thcx dr due are added definite volumes of a molybdenum solutio1 :illy 1 nil. containing 1 mg. of molybdenum) which is used as int,ernal standard, and distilled nitric acid, and the sample is then tliluted to 10 nil. By means of a glass stirring rod, a drop of solution is placed upon the flat 0.125-inch ends of a pair of graphite talrctrodcs which have been previously impregnated with clistilled kerosrnc.. The electrodes are dried by placing in :in upright, position on :i hot plate, drying being by conduction. Duarc prepared for each sample and dupliplicatr pairs of t~lect~rodes (.ate samplw are malJ-zcd, so that a total of four pairs of electrodes is used for each detrrmiriation. The remaindrr of the procvdure follows standard spectrographic t,echniqueF. Standardization rurves for rach clement are made by carrying known mixtures in sodium nitrate through the above process. ( 'oncentrations of thr stctndartliziition curves are e trims of pwtx prr niillion of the elcnic,nt in question in tiitrat?.. Background corrections are applied when necessary I)>- the irxthod of Picrce snd Sachtrieb (6). .I veri pure grade of sodium nitrate can be prep:ircd from sodium chloride purified by precipitation from solution with hydrogen chloride. The sodium chloride so precipitated is filtered off, washed with a little water, and convertrd to nitrate by hrating with nitric acid. Excess nitric acid arid water are removed l)y evaporation and fusion of the dry salt. All reagents must h e examined for impurities before use. IVhen nrcrssary, acids (othrr t.han hydrofluoric) can be purified I)? distillation i n an all-glass still. DISCUSSION
The choicc of a common matrix material is based on several c30nsidri.ations. Akfter esperience with a number of other salts, the authors selected sodium nitrate because (1) it burns very uniformly in the alternating current arc, giving excellent reproducibility of successive spectra; ( 2 ) continuous spectral background is low: ( 3 ) pure sodium nitrate is easily prepared; (4)
1517
inany sodium salts can easily be converted to the nitrate; and (5) solutions of the salt dry easily and are nonhygroscopic. The alternating current arc was selected for the source of escitation because of its excellent reproducibility and high sensitivity. A current of 2.2 amperes was chosen as that current giving lowest continuous background consistent with stability of arc and intensity of radiation. It is characteristic of this arc that, burning t,akes place on a relatively small area of the salt cap at any one instant and slowly consumes the whole salt cap. Therefore, the area of the electrode should be small enough so that light from any portion will strike the grating. Electrodes 0.125 inch in diameter were chosen because experiments showed that this is the largest size of electrode that will allow all the light to strike the grating. An arc gap of 0.75 mm. proved to be the optimum rlectrode separation t o give a stable arc with sufficient intensity. Thirty seconds of burning are enough tirnc for the arc to cover the entire salt cap without noticeable burning of the gr:tphite. llolybdenum in the form of sodium molybdate was chosen as the internal stand:trd element, after consideration \vas taken of the melting and boiling points, the twitation potential, and the availability of sufficient, but not exccqsive, spect'ral lines of varied states of ionization in convriiient regioiis of tho spectrum. Where it is necessary to tletemiine niol\-bdenum, bismuth is used as an internal standard. calibration curves for 42 c~lenients hsvc I)ern tlrt clrinineti. Data related to a few elements are shown in Tablc I. In actual practice, the range of :inalysis is limitctl to a fairly narrow one, from the limit' of sensitivity to a valuc approsiniatrly 20 times as great, a t which point the line becomes too dark for an accurate reading. K h r n the conccmtration of an element to be tletermined falls abovc thr rangr of analysis covered by thc stand-
1'able 1.
Sensititity of Line Pairs
Wave Length of Impurity Line A.
Calciiiin
Coppei Iron Potassiuni Magnesium
Sickel I'hosplrorui Lead Silicon Strontium Zinc
"
3962 3093 3082 2573 3934 3968 3934 3968 3274 3248 302 1 4044 4047 2706 2803 2780 3337 3415 2336 2553 2833 2882 1078 4078 334: 3343
Wave Length Limit of Control Line Sensitivity" .4. P.p.m. .\Io 4070 1 N o 3112 .\lo 3112 >Io 2816 100 110 4OiO 1 .\Io 4070 1 2 .5 .\Io 3903 .\Io 3903 2.5 310 3112 .i .\Io 7112 ! .\Io 3112 zoo M o 4070 .\lo 4070 1000 310 2816 1 110 2816 2 >Io 2816 .i0 .\Io 3383 .io00 .\Io 3112 2 310 2816 500 .\Io 2816 1000 110 2816 10 .\Io 2816 10 1 110 4070 .\Io 3903 20 2.5 310 3112 Bi 298c) 23
,
I n SaSOa.
Table 11. Reference Line Transniittancy 48.5 46.0 41.0 48.5 31.5 41.5 39.5
Ar. of 28 4 4 . 5 .4\.. deviation, %, 11 Std. deviation, yo, 13
Range o', Analysis P.p.m.
1-30 6-50 7-100 100-1000 1-40 1-50 2.5-300 2.5-500 5-25 !-lo .>-IO? 300-0000 1000-10,000
-I -9n _"
2-50
.~O-lOOO
0000-50,000 5-100 500-10,000 1000-20,000 10-200 10-200
-I -Rn "-
20-500 2R-500 25-500
Reproducibility of Spectra Magnesium P.p.m. 6.1 6.0 5.8 6.0 6.2 .i ,9 5.9 6.0 2.3 3.6
blagnesirirn (Av. of 4 Arcing?) P.p.m.
6.0 5.9 5.9 6.0 6.0 6.0 6.1 Av. of seven series 6 . 0 0.7 1.1
ANALYTICAL CHEMISTRY
1518 ardiztition, the sample is diluted \\-ith sodium nitrate solution containiiig internal standard a n d the arialj-sis is repeated. Table I1 illustrates t,he i.eproduribility of successive spectra. Twenty-eight pairs of electrodes Twre loaded from :L solution ot sodium nitrate roritaining 0 p.p.m. magnesium and processed i n the usu:il fashion. T h e first column is the dmsitometer reading of the wference line, which is used to illustratt. the rtJproducihility of the general intensit). levrl of successive spwti.:i. Thc second column illustrates the :malyticul results from e:Lch electrode pair. The last two columns show thr v d u e of duplicate arcings on duplic:itcJ samples, a pr:ict,ice recommended as stand:ird analytical procedure. T h e average devi:ttioii i n this case is s r d deviation is 1.1yo. )I(, I1 rc.pi,cwint reproducildity of th(1 method undtlr the hest of c~onditioris. In actual prttctice, iri most :tn:ilj,PRS, the wsult of any detrriiiinatioir will nearly al\vays liv within 5 % of the true ~ d i i c if~ supl)iwsiori , effects are ahsc,nt or c.oiwcted fOl~.
I n any commoii m:iti,ix niratliod, interfcrence or rupprossion efferts due to the presence of suhstancrs not present during standardkition must lx guai.dd ;ig:iinst. The effect of such foreign materials varies with the natuw of the impurity arid the element being determined. As :in example, T:tl)le I11 shows the result,s of sodium niti~ite for five inetitllic obtained i n the an:il, constituents, w h m eac f sevetxl coninion salts was : I c l t i t d i n :I, c~~nceiitration of 5% of t h r \\eight of the sodium nitratc,. Conclusions drn\vrr froin the dttta in Table I11 are :IS follon-s: The coninion anions, sulfate, phosphate, and perchlorate, have little, if any, effwt at concentrations of 5% (as sodium s:ilts) of the sodium nitrate: thr determination of calcium, aluminum! and magnesium appears to be affecatcd to a somewhat greater degree th:iri that ot copper and iron. So suppi'ession effert le:diiig to high resu1t.q (positive ( ~ r i ' o r )hiis yet I ) t ~ n found. This fact, along with :I study of the :il)solute inttbiisitieu of the l i n w , indicates that the effect is one of suppressing the aii:rlytical liiiw i,:lthei, th:ii~eriIi:tiice~irieritof the internal stnnd:ird liiicu. Tilc possibility of suppression effects must I)(% IccJpt in . When supprcssioii eKects mind in \voi.k of highest accui are suspected, rorrcactioiis can he made in a simple niaiiner t)>a.dding krio\vn concciitratioiis of (~lcnieritssought to the U I I ICIIOT~IIsample dissolved i n sodium nitrnte solution, or: less xiinplj-. hy making u p new stxrid:u~di~:itio~i curves i n the ~ I ~ I W I I ~ofC ~ interfering elements.
Salt Added"
Ca
Cu Fe I'arts pe,. million 6.3" 1 Bh 39!' 6.4 I G 39 1 ,,j 38 6.2 6 5 1 .? 39 5.9 1 .> 36 4 9 1.5 34 -41
...
5.3 r, . 7 6.0 2.8 IL
1,
1.4
...
34 34
1.5 1.3 1.3
37 37
nig
5.0" 4.9 3 .0 4.7 5 .0 3.3 4 2 4 !I 4.8
4.0
I n concentration of 555 of weight of SaNOs. Known conrentrations added to ~ i w r i a l l yvurified SiiYOi.
Table IV. Known coinposition 16 88 211 424
Calcium in Sodium Chloride Brine
Calciriin. P.P.N. Chemical analyzis
Spectrographic
Error of Spectrographic Detn., 5% 4.3
44
41 86
92 223 420
21i 430
4.5
6.1 0.9
Table 1'. Calcium i n \Iagnesiiim Compoiitids 70 5%
Sample Synthetic magnesite I Synthetic magnesite B Crude 34% RIgCll liquor
Table \.I. Sodium IIydroxide Alulriiniiiii Calciiiui Chroiuiiirii Cobalt Copper Iron Lead Magnesiu in Manganese Nickel Potassiuin Silicon Silver Strontium Titanium Zinc Zirconium a
Chemical 0.48 0.34 0.063
Flint Clay Present" Found ~~
70
R 20.5 0.072 0.OJ.l
...
0,003
o.6oi.i
0.00014 0.00023 0.106 0.13 0 , 000i7
... ... ...
0.48
0.36 0,073
Other Applications
0 0003i 0,004
0.000:~
Spectrographic
%-
Wheat Straw
% 0.027
19
0.08 0.10
0.43
0.002 0.68
0.00? 0.66
0.0001 0.013
0.16 O,001(i
0.16
0.13 0.0062
...
...
...
... ... ... ... ...
1.44
1 :i
0.'l'sti
0 18
...
0.4:
20.0
...
,
.
...
Oyster Shellh
54
... ... 0.000007 0.00012
...
0 0000~6
, . .
0.000013
4.6 0.42 0.0033
...
... ...
0.000003
...
0 . Li0011
Bureau of Standards sainple 97. By preliminary separation with dithizone
Trthle 1. shows it coriipai~iwiiof chemical and spectrographic detei~minatioris of calciuni iii maguesium-base compounds. The spectrographic mrthod possesses the advantage of greater speed and particularly of grentclr sensitivity in the case of samples containing a high r:ttio of mngriesium to calcium. Such matcrials are w r y difficult to :tn:ilyze chemically for calcium. Four additional esariiples of analyses :ire shown in Tahle \-I, l3ureau of Standards sample DT is :in esample of the an:rl? R silicate rniiieral. This s:imple was treated l)y iusioii sodium cai,tionate and evapoi,:ttiori of the sodium c:uhonate melt n-it11nitric and hydi,ofluoric ticid, so t,hat a sodium niti.at,ematrix of xticxt stixw is listed as :til ex:imple of resulted. The an:ill :in analysis of :til oiginic m;it,eri:tl. In this case the sample is wet-ashed with nitric, sulfuric., and perchloric acids and firi:dlj~ taken u p in a sodium nitwte solution. The arialysis of a dithizonr estract of oystei, shell is an example of the si:nultaneous determination of miriutr concentrations of several metallic elemeiits. In addition to tlithizone exti,ac>tion,other concentration procedures :ire :tlso applicable. Sevrral ex:iniplrs of applications have heen given iri order to illustrate the vei,s:itility oi the method. Although this spectrographic techniqur \voultl not normally b e used in strict.ly routine l o r ewrnple-because of time consumed in tinnlysis-metals, rht~inicalpreputitioris, the n-ide applicahility of the methotl makes it useful for mmiy noiii~outine:inalysc.s.
API'LICATION S
L I T E K T U R E CITED
Table I\' shows :L conip:Lrison of chemical and spectrographic methods i n the aiivlysis of saturated sodium chloritlc I)rine samples contairiing known aniounts of calcium. The a g e e merit is considered satisfactoi,y. This is a useful iip[)lic:itioli of the spectrographic method, inasmuch as the conimmr iinpui,ities calcium and inagiiesium m:iy lie detei,minrd rapidly arid with good sensitivity. The limit of sensitivity of the spectrographic. method for calcium in this r w e is about 1 p.p.m. arid for migiiesium is ahout 0.5 p.1i.m.
(1) Churchill, J. I
