segment of the copper-zinc titration, which dcterniines the point of demarcation between the cadmium and zinc titrations, is rclatively short in the former cnse. The difficulty in locating the cadmium end point prevents the attainment of the desired accuracy, although the titration conditions appear f n i oi xble a t first glance. The prediction from stability constant data of conditions for strict cotitration of two metals is a t present impossible. The maximum difference in effective stability constants which permits a linear photometric titration is about 0.1 log K unit, while the various equilibria which must be considered in establishing the effective stability constant of a metal chelonate are often uncertain by 0.5 log K unit. Although in some cases it may he possible to adjust conditions empirically to obtain linear titration plots, the limited advantage to be gained over approximate
attainment of cotitratioii conditions docs not appear to warrant the effort involved. The most promising application to cadmium-zinc determinations seems to be the sclecti\-e determinxtion of one or the other when present as a minor constituent of a binary mixture in conjunction with a separate detcrmination of the sum. Under such conditions the decreased accuracy would not be a serious problem. As separation or masking techniques are least efficient under such conditions, this technique should effectively complement conventional chelometric methods. LITERATURE CITED
(1) Hollonay, J. H., Reilley, C. N., ANAL. CHEM.32.249 11960). (2) Laitinei, H . ~.4., Sympson, R. F., Ibid., 26, 556 (1954).
(3) Mdmstadt, A. V., Gohrbandt, E. C., Ibid., 26, 442 (1954).
(4) Pribil,
K.,“Komplexometrie,” Chemapol, Prague, 1954. 1. 5,) Ramaiah, N. A. Vishnu, 9nal. Chim. Acta 16, 569 (1957). (6) Heilley, C. N., Porterfield, W. LV., ANAL.CHEM,28,443 (19561, ( 7 ) Reilley, C. S . , Schmid, R. W., Sadek, F. S.,J . Chem. Educ. 36, 555 (1959). (8) Sadek, F. S., Schmid, R. W., Reillcy, C. PIT., Talanta 2, 38 (1959). (9) Schwarzenbach, G., Gut, R., Anderegg, G., Helv. Chim. Acta 37,937 (1954). (10) Sweetser, P. B., Bricker, C. E., A i i . 4 ~ . CHEY.26,195 (1954). (11) Underwood, A. L., I b i d . , 25, 1910 (1953). (12) Ibid , 26, 1322 (1954). (13) Welcher, F. T., “Analytical Uses of Ethglenediaminetetraacetic Acid,” p. 163, Van Nostrand, Princeton, N. J., 1958.
RECEIVED for review February 13, 1061. Accepted August 25, 1961. Research supported by the United States Air Force through the .4ir Force Office of Scientific Research, Air Research and Development Command, Contract No. AF 49(638)-333.
Improvements in the Fluorometric Determination of Submicrogram Quantities of Beryllium CLAUDE W. SILL, CONRAD P. WILLIS, and J. KENNETH FLYGARE, Jr. Health and Safefy Division, U. S. Atomic Energy Commission, ldaho Falls, ldaho
b A recently published procedure for the fluorometric determination o f beryllium using morin has been improved significantly, and its application has been extended. Stabilization o f alkaline solutions of morin toward air has been accomplished without use of stannite or other reducing agents. Use of diethylenetriaminepentaacetic acid in place o f (ethylenedinitril0)tetraacetic acid prevents formation o f fluorescent complexes of morin with scandium, yttrium, and lanthanum, and increases the selectivity greatly. A new combination of primary and secondary filters produces a threefold increase in the ratio of net beryllium fluorescence to blank fluorescence while requiring an instrumental sensitivity only one fourth that obtained with the previous combination. Since the exciting wave lengths are entirely in the visible region of the spectrum, errors produced b y colorless ions that absorb in the ultraviolet are eliminated. One o f the most important discoveries was the extensive adsorption o f beryllium from alkaline solution on the glass walls of the container. The fluorescent species contains beryllium and morin in a mole ratio of 1 to 1. Detailed procedures are presented for the determination o f beryllium in metallic thorium, zirconium, uranium, copper alloys, and
aluminum, in rare earth oxides and phosphates, and in silicates such as beryl and clay that are not decomposed completely b y either pyrosulfate fusion or hydrofluoric acid. Beryllium can b e determined in air dusts a t concentrations well below the maximum permissible levels without separations o f any kind in approximately 30 minutes.
I
P; a
previous publication, a procedure for the fluorometric determination of heryllium using niorin (2’,4’,3,5,7pentahydrosyflavone) was described (‘7). The procedure is very sensitive and precise, but suffers from three important disadvantages. Preparation of the solution for fluorometric measurement is rather tedious when many samples are being analyzed. The procedure is less selective than is desirable as thorium, yttrium, zirconium, scandium, lanthanum, and lithium each produce bright yellon-ish green fluorescence in descending order of sensitivity under the conditions used. Also, anomalous results are obtained occasionally that, for some unknon-n rea?on, are clearly inconsistent with the usual high precision. The present procedure is more rapid and sensitive than before and all sources of anomalous results have been identified and corrected.
~ i ~ t l i y l ( ~ n c t r i u i n i n e ~ e ~ i t a a cwid etic (DTPA) is very similar to (Pthylene(EDTA) diniti~i1o)tetraacetic acid both structurally and in its reactions with metals to form strong water-soluble complexes of the same type and wit’hthe s a m ~met,als. In general, the DTPA romplexes have formation constmts that are 10 to 1000 times larger than the corresponding complexes with EDTA\(1-3). As shown by the data of Table I, DTI’A increases the selectivity of the fluorescence procedure by forming complexes with yttrium, scandium, lanthanum, and lithium of such increased stability that much laiger quantities of the metal are required t o produce significant fluorescence in comparison to the previous method using EDTA. I n contrast, the beryllium c*omplex with niorin is completely unaffected. Unfortunately, the niorin complexps of thorium or zirconiuni are d s u affected very little by DTPX. -4 iia1ytic:il 1iim:edures for these elements ai’(’ currcntlj. bcing developed to take iitlwntnge of the exceptional sensitivity :ind stability of the morin complexes. Most procedures for the fiuorometric clctcrinination of heryllium, using niorin, einploy a solution of sodium stannite to stabilize the fluorescence by preventing the xir osidation of morin. If EDTA is added, the fluorescence is stable for over VOL. 33,
NO. 12, NOVEMBER 1961
0
1671
3 hours without stannite even in the presence of 1 mg. of copper ( 7 ) . Apparently, the direct reaction between oxygen and morin is very slow, and the primary cause of instability is due to the catalytic effect of traces of copper present in distilled water and reagents. However, when a buffer solution composed of l’iperidine, hydrazine, and EDTA as added, the fluorescence again decreased with time and stannite had to be retained. Hydrazine was known to increase the long-term stability t o air in the presence of stannite, and the inqtability was erroneously attributed to traces of pyridine in the piperidine. It has now been found that hydrazine and other compounds such as hydrosylairiinc that are generally used as reducing agents are capable of oxidizing moiin in alkaline solution in the absence of stannite. If all compounds capable of oxidizing morin directly are escluded and either EDTA or DTPA is used to complex copper and other metallic ions capable of catalyzing the air osidation of morin, alkaline solutions of morin are stable in air and the procedure can be simplified considerably. FILTERS, LIGHT SOURCES, AND PHOTOTUBES
Most proccdures for the fluoroinctric determination of beryllium using morin specify ultraviolet light. However, no systematic investigation has been made of the optimum combination of light source, primary and secondary filters, and phototube. White and coworkers (9, 10) have shown that fluorescence emission is increased greatly by irradiating the sample with light a t about 430 mp. Furthermore, the ratio of the fluorescence of beryllium to that of the blank can be increased considerably by using a mercury light source with a primary filter to ihoiate the 436-mp line (8). The fluorescence of the blank has long been one of the principal factors limiting the ultimate sensitivity of the procedure. Optimum combination of both primary and secondary filters
Table 1.
Element Blank Be Th Zr
SCd
could undoubtedly reduce both the fluoresccnce of the blank and its subsequent effect on phototube response. Other equally important advantages result from using light a t longer wave lengths for escitation. Production of fluorescence from other metal complexes, impurities in reagents, etc., or from cuvettes, filters, ctc., mill be reduced or eliminated in many cases. The longer-wave light Fill be absorbed less in general than ultraviolet, and errors due to absorption of the irradiating light will be decreased markedly. For example, impurities in reagents such as EDTA, triethanolamine (TEA), etc., tend to be yellow in color, but are much less absorbent in the blue than in the ultraviolet. Hence, requircments for reagent purity in fluorometric procedures become much less stringent. The iron-triethanolamine complex is completely nonabsorbent in the visible. but begins to absorb strongly in the ultraviolet. Therefore, the metal that is one of the most serious interferences from the standpoint of light absorption and frequency of occurrence becomes tolerable in relatively large quantities nhen blue irradiation is used. To choose between tungsten and mercury for the light source and to obtain specific filter recommendations for each, the ratio of net to blank fluorescence mas determined n i t h over 50 different eombinations of primary and secondary filters. Transmittance spectra of these and many other filters have been published ( 5 ) . Absorption, escitation, and emission spectra of morin and the beryllium complex (4) were guides in the selection of the ones to be tested. Other important characteristics such as scattered light levels and relative instrumental sensitivity required ere also measured for each combination. Escept for a few interference filters from other sources, Corning glasses ryere used in standard thickness unless specified to be otheraise. With a tungsten source and a Dumont 6291 multiplier phototube, a conibina-
Fluorescence of Metal Complexes of Morin in Alkaline Solution
Quantity,
Fluorescence,a Sc. Div.
...
0.250 0.50 1.00 1,000 1,000 1,000 10,000
10.0 86.2 3.8 3.1 5.4 2.9 0.2 1.2
Sensitivity, pg./Sc. Div. DTPAb EDTAc
0: 00290
0.13 0.32 185 345 5,000 8,000
_.
0.00545 0.25 (5 pg.) 0.88 ( 5 pg.) 9 . 1 (5 pg.) 6 . 5 (10 pg.) 0 . 6 9 (5 p g . ) 1,600 (10 mg.)
La Y Li Corrected for blank. * Instrumental sensitivity that used with 0.25-pg. standard. Values redetermined with e Instruniental sensitivity that used n-ith 0.5-pg. standard. smaller quantities of metal indicated in parentheses and corrected for increased sensitivity over that previously reported (7). Larger quantities may produce highly fluorescent crystalline d Sensitivity erratic. precipitate which appears to be sparingly soluble complex with EDTA or DTPA with adsorbed scandium-morin complex to produce the fluorescence. 5
1672
ANALYTICAL CHEMISTRY
tion of Nos. 3387(443) and half-standard thickness 5113(472) for the primary and NOS. 3384(490) and 5031(562) for the secondary gave the lowest blank and highest ratio of beryllium to blank fluorescence with no detectable scattered light and very moderate instrumental sensitivity. For comparison, the filter combination of Nos. 5860(376) and 4015(476) recommended in the previous publication ( 7 ) requires four times the instrumental sensitivity and gives a ratio only one third as large, besides producing much greater interference from other absorbing or fluorescent species. The figures in parentheses give the wave length in millimicrons a t which the transmittance of the individual filter is 10% and are given to identify the filters actually used more precisely ( 5 ) . Because of the lack of significant energy in the mercury spectrum betreen 436 and 546 mp, no filter combination gave as high a ratio of beryllium fluorescence to blank fluorescence with a mercury source as was obtained with a tungsten source. However, a combination of 3389(418)-5543(4SO) for the primary and 3355(454)-5031(562) for the secondary gives escellent rcsdts with a medium-pressure mercury lamp. It is unlikely that a 1P2S phototube would give significantly different results than those obtained with the 6201. After most of the present work had been completed using a 0.5-pg. beryllium standard and the filter combination recommended above, the results were discovered to be nonlinear a t 0.5 pg. by about 3 to 4%. KO error was introduced in the data reported because the results were always compared against a standard containing the same quantity of beryllium. However, the procedure published previously ( 7 ) using a N o . 5860 filter for the primary !vas nearly linear at 1 pg. Careful redetermination showed a n error of about 570 a t this level. To determine the effect of other primary filters on the linearity of the procedure, two solutions of beryllium were prepared using the same pipet and 1- and 2-liter volumetric flasks so that quantities of beryllium could be taken that differed by a factor of exactly 2. The corrected reading from the halfstandard was then multiplied by 2 and compared with that from the full standard. Because of the additional errors introduced by multiplication and subtraction, deviations larger than about 1% may not be real. The results can be interpreted by comparison to the absorption spectra of morin and the beryllium comples (4) and the transmittance spectra of the filters involved ( 5 ) . The absorbance of morin and its beryllium complex a t equal concentrations is the same at 368 and 421 mp, with morin being the more absorbent between the two wave lengths. Accordingly, filters transmitting in this region
will produce a positive deviation from linearit'y in certain concentration ranges because of the increased intensity of the exiting light resulting at higher beryllium concentrations from conversion of the more absorbent morin to the less absorbent complex. Ultraviolet filters transmitting around or above the isoabsorbance point at 368 mp result in greater rangc of linearity than is obtained a t wave lengths greater than 421 mp. The Corning 5874 gives results that are only 3% low a t 1 pg. because its transmittance band occurs a t a slight'ly longer ware length and requires only one third the instrumental sensitivity t h a t is necessary with the 5860. A combination of 7380 and half-standard thickness 59iO transmits a t a slightly longer wave length, and results are within lY0 of linearity a t 1 kg. However, with all the ultraviolet filters, the blanks are two or three times higher and the sensitivity is correspondingly less. Furthermore, the interference of as little as 0.1 mg. of iron as the T E A complex is serious when the ultraviolet filters are used. A 418-mp interference filter gives the best linearity over the greatest range. The results are only 3% low a t 1 pg. and are not affected by a t least 1 mg. of iron. However, the 3387-5113(',/2) combination, used in the present work, is still recommended because it results in greatest sensitivity and general freedom from interference from fluorescent or absorbing species. -40.25-pg. beryllium standard should be used to keep nonlinearit'y less than 2%. The results will be about 3 to 4% low a t 0.5 p g . and 13% low a t 1 pg. ADSORPTION OF BERYLLIUM FROM ALKALINE SOLUTION BY GLASS
Since the beginning of these studies several years ago, a n unknown source of error has evaded all efforts a t identification and has persisted to the present time despite the best procedure that could be devised including the use of buffers, fluorescent standards, complexing agents, etc. Several consecutive beryllium standards would agree with each other to a few-tenths per cent, then one would be several per cent low without any apparent reason. Occasionally, a standard would produce fluorescence several per cent higher than was thought possible in view of the standard calibration curves and the normal values obtained from day to day. After stannite was successfully eliminated in the present procedure, it was apparent immediately that the net fluorescence of a given quantity of beryllium is always greater in a solution containing stannite than in one without. The buffers in both procedures had been balanced very carefully to eliminate the effect of the estra alkali present in the
Table
II.
Effects of Stannite
on Adsorption of Beryllium from Alkaline Solution by
Glass and Polystyrene Stannite Present
Container KO.
s ~ div. ,
Fluor.,
Be on wall, 70
Glass Plastic
1 3
7.1
7.2
2.8 0.02
Glass Plastic
5 7
99.9 106.Zb
2.8
Glass Plastic
11
Norm.0 fluor.,
so. div. Blanks
No.
2
Stannite Absent Norm.4 Fluor., Be on fluor., sc. dlv. wall, % sc. div. 5.2 5.2
7.3 0.2
6 8
95.2 101.8
0.1
10
5.3
12.3
4
0.5-kg. Be Standard
9
6.9 7.1
0.08
95.5 99.1b Blanks
4.0
0.2
12 5.3 0.5-pg. Be Standard Glass 13 96.1 3.1 92.1 14 86.0 Plastic 15 99.1 0.1 92.1 16 99.8 Gross fluorescence corrected for blank then divided by fraction present in solution. * Value too high; reason unknown.
stannite. Furthermore, no trace of beryllium, thorium, or zirconium or any material affecting the absorption in the visible region of the spectrum could be detected in the stannous chloride used. Although its significance was not recognized a t the time, the presence of aluminum also increased the fluorescence of a 0.5-pg. beryllium standard greatly, even though aluminum is knonn to produce no fluorescence with morin under the condition used. While using beryllium7 as a tracer, activity remeined in the volumetric flask after the alkaline solution from the fluorometric measurement had been discarded. The quantitj deposited on the walls of the flask amounted to as much as 15% of the total beryllium present. Preci:iitation of beryllium hydroside from 0.5 p g . of total beryllium seemed highly unlikely in the presence of DTPA at the alkalinity employed. Furthermore, the deposition was much more reproducible than one would espect if it were caused by precipitation of beryllium hydroside. This evidence would seem to indicate that some sort of anion exchange process was taking place with the glass. Solutions of both blanks and 0.5-pg. beryllium standards were prepared for fluorescence measurement both nith and without stannite in both borosilicate glass volumetric flasks and polystyrene vials. About 2 X lo6 c.p.m. of beryllium-7 containing 1 X gram of natural beryllium was added to each test as tracer. After measurement of the fluorescence, the solutions were discarded and the containers were rinsed once with water. Each container was then rinsed thoroughly with strong hydrochloric acid, and the acid solutions were counted in a sodium iodide well counter. The data in Table I1 present the gross fluorescence in arbitrary scale
7.0
96.8 96.7
0.5
13.9
93.7
0.4 94.9 of total beryllium
divisions, the percentage of the total beryllium that was present on the container walls, and a normalized fluorescence. The latter value represents the total fluorescence that would have been obtained if the adsorbed beryllium had reacted to the same estent as that in the solution. It was calculated by correcting the gross fluorescence for the appropriate blank and dividing by the fraction of the total beryllium present in the solution. Because of one anomaly in the first set of data, the entire esperiment was repeated after having soaked the glass flasks in strong hydrochloric acid for about 3 days. Several interesting conclusions can be drawn from the data of Table 11, some of which are of very fundamental and far-reaching consequences. First, except in tests 15 and 16, the gross fluorescence is greater in the presence of stannite than in its absence n i t h either blanks or standards in either glass or plastic. The percentage of the total beryllium found on the walls of the flask is correspondingly less. Apparently, stannite occupies anion exchange centers that otherwise would be occupied by beryllate. I n the exceptions mentioned, the presence or absence of stannite would be espected to make little difference because of the scarcity of anion exchange centers on the polystyrene. However, such eschange capacity of polystyrene is apparent in every case but a t a very low level compared to glass. Second, the gross fluorescence of the standards is always greater in plastic than in glass, the difference being much greater in the absence of stannite. The blanks are the same in glass as in plastic but are greater in the presence of stannite in either case. Obviously, since the blanks contain too little beryllium to produce VOL. 33, NO. 12, NOVEMBER 1961
1673
detectable fluorescence, the adsorbed beryllium is without visible effect, However, the percentage beryllium adsorbed from the blanks containing 1 x gram of beryllium agrees very closcly with that from the standards containing 0.5 kg. under the same conditions. Third a decreace in fluorescence of the standards is paralleled by an equivalent increase in the quantity of beryllium present on the sides of the container. This can be observed most clearly by comparing the normalized values for "total" fluoiescence. It is sonieR hat surpriring that as much as 14% of the total 0 5 kg. of beryllium present was on the walls of the glass flask, and that such a large loss could be accounted for so exactly by a decrease in fluorescence of 14 scale divisions. The difference in the norinalized values of tests 14 and 16 is only 1.2 scale divisions, a t least part of which n ould certainly have been caused by greater losses during washing the flask from the 14% adsorption than from the 0.4% In the presence of stannite, tests 13 and 15, adsorbed beryllium on the glass was only 3%, and the normalized values agree exactly. The normalized values of tests 13 and 15 are slightly loner than those of tests 14 and 16, and the blanks are dways greater in the presence of stannite than in its absence. Both effects could be accounted for by a slight turhdity of hydrolyzcd stannate or by a slight reqidual fluorwwnce knoir n to be
Table 111.
con-
tainer Plastic Glass
produced with quadrivalent tin and morin a t a slightly lower alkalinity. The very significant increase in adsorbed beryllium obtained on the second set of experimcnts is of particular import'ance. rlpparently, soaking the flasks extensively in strong hydrochloric acid cleaned all nnion exchange centers in the glass from ions that' had built up through previous use sucli as beryllates, stannite, stannate, EDTA anions or anionic complews with metals, etc. The chloride ions are then inore easily replaced by beryllium species. Furthermore, there is definite evidence of estensive penetration into the glass wall. The longer an alkaline beryllium solution is allowed to remain in contact with the glass surface, t,he longer the flask must be soaked in strong hydrochloric acid to remove the beryllium. The increase obtained on the second set with polystyrene is likely due to an increased wettability on using the second time. Because of the difficulty of pouring from polystyrene vials and the lower precision attainable from their use as volumetric equipment', some other method of minimizing or eliminating t'he adsorption of berylliuni on glass volumetric flasks was desired. While rechecking the effect of various metals on the revised procedure aft'er elimination of stannit'e, 5 mg. of aluminum was found to produce an unexpected and unexplained increase in fluorescence of nbout 1070 n-ith a 0.5-pg. beryllium
Effect of Aluminum on Adsorption of Beryllium from Alkaline Solution by Glass Aluminate Absent Aluminate Present, 4 hlg.A1 Yorm. Norm. fluor., Be on fluor., Fluor., Be on Fluor., w l l , yo sc. div. No. sc. div. wall, yo sc. div. NO, sc. div Blanks 1 0.6 ... 2 4 8 5 5 ... 5.3 ... 0 4 ... 4 8 4.4 5.3 0 8 . . 4 4 8 5.7 3 ... 5.2 5 2
Plastic
5
Glass
7
Glass
9
102 3 100 2 100.1 100.1
0 7
4 8
6.2
...
98.0 97.8 94.2 94.7
0.4 0.2 4.9 4.5
93.5 93.2 94.0 94.1
...
0.5-pg. Be Standard 6 0.2 97.2 0.2 95.1 96.1 8 1.2 96.1 1.3
In presence of: Plastic
10
Glass
11
12 13 14
100.1 100. 1 102 0 101 2 101 8 101 9 100 7 100 8 100.9 101.0
0.8 0.9 0.2 0 2 0 6 0 6 1 1 1.0
6.5 5.4 5.4
0.5 0.3 0.3
.o
1
1.1
95.7 95.8 96.4 95.6 96, 6 96.7 96.0 96.0 96.1 96.2
1 mg. Fe
2 mg. addn. A1 2 mg. addn. A1
2 mg. addn. 41; 1 mg. Fe 2 mg. addn. Al; 1 mg. Fe; 1 mg. Y 1 mg. Fe; 1 mg. Y
Blanks 15 16
17
1674
ANALYTICAL CHEMISTRY
1.1
2 mg. addn. Al; 1 mg. Fe; 1 mg. Y 2 mg. addn. Al; 1 mg. Fe 2 mg. addn. A1
standard. Yo such effect was present in the procedure employing stannite (7). Because other anions could be expected to act similarly to stannite in occupying the nnion exchange sites, the effectiveness of aluminum in preventing the adsorption of beryllium was investigated. As shown by the data of Table 111, 4 mg. of aluminum is more effective in preventing adsorption of beryllium than the stannite used in the previous met'hod. These data are very similar to those of Table I1 in ot,her respect's, homever. The quantiby of beryllium on the sides of the container is much greater in glass in the absence of aluminum than either in its presence or in plastic wit'h one esception. The exact quantity depends entirely on the condition of the glass surface and has been as high as 15% of the quantity present depe,nding on the previous use of each flask. The adsorption in the absence of aluminum appears to decrease Ivith increased use of the flasks in t'he present procedure containing aluminum. As s h o w by the data of test 2, bhe quantity of beryllium found on the sides of plaat'ic vials used extensively is essentially the same as that found on the glass flasks. This m s not true in t,hc stannite data of Table 11,when the polystyrene vials were newv,and indicates that polystyrene will develop some anion exchange capacity with continued use. However, in all cases, the fluorescence increases in direct proportion t'o the decrease in adsorpt'ion and the normalized values agree remarkably well. The precision of the data obtained in polystyrene vials is less than that using volumetric flasks because of the inherent limitations of the vials. However, the normalized values are about 2 scale divisions higher in the presence of alurninum than in its ahsence in either plastic or glass indicating that some small source of error other than the adsorption of beryllium on the glass is still present. The concentration of triethanolamine used in the present procedure is known to have decreased the fluorescence of a 0.5-pg. beryllium standard by about 2.5 scale divisions, apparently owing to the formation of a competing beryllium-TEA complex. Since aluminum also forms a comples with TEA, it appears logical to espect the relatively high concentration of aluminum employed to displace the beryllium and make it available to produce the fluorescent complex with morin. The blanks are slightly higher in presence of aluminum than in its absence because of the presence of a trace of beryllium in the aluminum. Inclusion of aluminum in the procedure thus increases the precision and reliability by decreasing the t'otal quantity-and therefore the variabilityof the beryllium present on the glass. The error caused by aluminum in the nonstannite procedure is also made
negligible since a n additional 2 mg. of aluminum mill produce a n error of not more than l%, The procedure is not affected significantly by 1 mg. of iron and 2 mg. of aluminum, either alone or in combination, although 1 mg. of iron will enuse decolorization of the solution on standing overnight. The results also indicate that the presence of iron or aluminum nil1 not restore the interference of yttrium significantly by reducing the concentration of uncombined DTPA. One milligram of yttrium produces a n error of only 1 scale division even in the presence of 1 mg. of iron and 2 mg. of additional aluminum (total 6 mg. of Al). Because of the high sensitivity of the present procedure toward beryllium and because the exchange adsorption of beryllium on the glass will be significant evtn in the presence of aluminum in comparison to a blank, special attention must be given to cleaning the volumetric flasks after use. It is recommended that the flasks be emptied within a n hour or so after the measurement of fluorescence is completed, rinsed with tap water and stored in 2M hydrochloric acid. Otherwise, subsequent blanks or lon-level samples might be contaminated by adsorbed beryllium from flasks used previously with high-level samples. Significant penetration of berylliuni into the wall will also be observed if the solutions are allowed to remain in the flasks for more than a fern hours. When ready to be used again, the flasks should be given such other cleaning as is required to remove grease, etc. Kew flasks have shown serious adsorption of beryllium even in the presence of aluminum until they were cleaned in cleaning solution or strong alkali. BERYLLIUM-MORIN REACTION
Although the reaction with morin has been used for many yc-rs for both detection and determination of beryl”um, the identity of the fluorescent species does not appear to have been established. To obtain informaticn concerning the reaction involved, .ne composition of the beryllium-morin complex was determined by the method of continuous variations (11). Both absorbance and fluorescence measurements were used to follow the formation of the complex. In the absorptiometric method, X nil. of a n 8 X lOP5JIsolution of morin nas mixed with 10 - X ml. of an equimolar solution of beryllium under the recommended conditions and diluted t o a total volume of 25 ml. One solution also contained 10 ml. of the morin solution and 100 pg. of beryllium (14 moles of beryllium per mole of morin) to produce a solution of the maximum concentration of morin entirely in the form of the beryllium chelate. This solution
MOLE
Figure 1.
FRACTION
OF
BERYLLIUM
Composition of beryllium-morin complex by method of continuous variations
The curve obtained at 3 9 5 m p actually has a minimum but is shown with sign reversed for convenience of presentation.
was used to determine the wave lengths
at which the difference in absorbance between morin and the complex mould be greatest. Absorption curves were determined on each solution using a Cary Model 14 recording spectrophotometer and 1-cm. silica cells matched carefully a t all wave lengths. Absorbances were then read from each curve at each of several wave lengths. The calculated absorbance that each solution would have had a t each wave length if no reaction had taken place was subtracted from the observed absorbance. The resulting Y-values (11) were plotted against the mole fraction of beryllium as shown in Figure 1. Because the absorption curves of morin and the berylliummorin complex are very similar in shape and a t most are separated by only 16 mp ( 4 ) , the Y-values obtained were never larger than 0.117 absorbance unit and were obtained in every case as the difference of two larger numbers. Despite the small values of l’, all of the curves indicated unmistakably the formation of a 1to 1 chelate. In the fluorometric adaptation of the method of continuous variations, the solutions were prepared in exactly the same way as for the absorptiometric method except that 1.4 x 10-5X solutions of both beryllium and morin were used. The fluorescence measurements were corrected for the calculated contribution of the unreacted morin in each solution to its total fluorescence. The maximum correction Tws only 3.3 scale divisions. The corrected values were then plotted against mole fraction of beryllium as shown in the upper curve of Figure 1. The results again indicate formation of a 1 t o 1 chelate. Because there is a much greater difference in fluorescence between morin and its beryllium complex than there is between their absorbances, much larger values are obtained and the fluorometric
method in this case is more precise. However, fluorescence measurements are attended by certain inherent difficulties not encountered with absorbance measurements. When the concentration of any absorbing species is varied in the method of continuous variations, the intensity of the light producing the fluorescence also changes as the light passes through the solution if the absorption becomes sufficiently large. Consequently, a change in fluorescence is produced that is not related to a change in the concentration of the fluorescent complex. If fluorescence measurements are to be used to indicate the extent of formation of the complex, the concentrations of the absorbing species must be kept small so that the deliberate variations emrloyed will not change the intensity of the exciting light significantly. To determine if the error from this source would be significant a t the morin concentration used, the continuous variations experiments were repeated using fivefold smaller concentrations of both beryllium and morin. Polystyrene vials were also used to minimizp adsorption of beryllium. The results were identical to those obtained a t the higher concentration. Because the solutions were essentially colorless a t the 1017 er concentration, proof of a 1 to 1 complex is felt to Le as unequivocal from fluorescence data in the present application as from the absorbance data. The mole ratio method was also employed using. both absorbance and fluorescence measurements. The morin concentration was kept constant a t 2.48 X mole in 25 ml. in a n attempt t o determine the ex%ent of complex formation under the conditions used in the analytical procedure. Even with a 5em. cell, differences in absorbance between morin and the beryllium complex were too small to be meaningful, but fluorescence measurements again indiVOL. 33, NO. 12, NOVEMBER 1 9 6 1
1675
cated a 1 to 1 complex. However, this answer must have resulted in part from a fortuitous cancellation of opposite effects. Fluorescence of the berylliummorin complex is not a linear function of its concentration throughout the range covered so that the higher concentrations are not as fluorescent as they should be in relation to the lower ones. On the other hand, the higher concentrations are more fluorescent in the presence of excess beryllium than with excess morin because of the absence of the additional light absorption of the latter. However, the fact that the fluorescence was still increasing significantly a t a ratio of 3 moles of beryllium to one of morin indicates that the complex is not completely formed under the conditions used in the analytical determination. This is further substantiated by the fact that the linearity of the procedure can be increased somewhat by increasing the concentration of morin. When the mole ratio experiment was repeated using a 25-fold lower morin concentration, the fluorescence was still increasing significantly a t a 500-mole ratio of beryllium to morin indicating that the complex is highly dissociated a t such low concentrations. The incompleteness of the reaction undoubtedly accounts for the serious effect on the fluorescence of variations in pH, morin concentration, salts, etc. I n view of the alkalinity employed (pH 11.5) and the strong tendency of beryllium to form hydroxylic compounds, it seems likely that the second valence bond of beryllium is occupied by a hydroxyl group. The expected competition of hydroxyl ion for beryllium in alkaline solution might be expressed by the reaction HzO = BeMrOH HBe02- Mr2 0 H - where Mr-is the morinate anion although the final equilibrium distribution is undoubtedly much more complicated.
+
+
+
RECRYSTALLIZATION OF DTPA
Commercial diethylenetriaminepentaacetic acid contains impurities that absorb both ultraviolet and visible light, produce bright blue fluorescence under ultraviolet light, and react under certain conditions to produce a bright yellow fluorescence. It can be recrystallized from water conveniently in excellent yield and adequate purity. Add 100 grams of DTPA to SO0 ml. of boiling water and heat until boiling is resumed. Add 2 teaspoonsful of decolorizing carbon and mix thoroughly. The decolorizing carbon must be of high quality or more colored material will be added to the product than is removed. Darco G-60 of the Atlas Powder Co. has been found excellent for the purpose. Filter with suction on a Eiichner funnel using a hardened retentive paper. Transfer the clear filtrate to a clean 1-liter beaker and stir vigorously with a glass stirring rod. DTPA shows a strong tendency to supersaturate, and the stirring rod 1676
ANALYTICAL CHEMISTRY
should be allowed to scratch the sides of the beaker gently to induce the initial crystallization. Scrape the crystals off the sides as they form and stir them vigorously to induce crystallization throughout the solution. Cool thoroughly in a bath of cold running water. Filter on a hardened paper with suction removing as much water as possible, and dry a t 110" C. for several hours with frequent stirring as required to prevent formation of hard lumps. If most of the water is not removed by suction before heating, a partially liquified slurry will be obtained that is difficult to dry and will set to hard lumps. If there is any uestion of the cleanliness of either the rying oven or the laboratory air, dry the recrystallized material in a vacuum desiccator. Yield is about 95%.
3
Morin, 0.0075%, Dissolve 7,50 mg.
of pure anhydrous morin in 40 ml, of 95% ethyl alcohol and dilute to 100 ml.
with water. Analytical grade morin of excellent qualit is available from Dr. Theodor Schuciardt, Munich, Germany, and from Fluka AG, Buchs SG, Switzerland. Aluminum. Dissolve 4.9 grams of A12(SO~)~.18H20 and 1 ml. of 72% perchloric acid in 50 ml. of water and dilute to 100 ml. One milliliter contains 4.0 mg. of aluminum. Standard Beryllium Solution. Dissolve 0.1964 gram of beryllium sulfate tetrahydrate in water, add 10 ml. of 72% perchloric acid, and dilute to 1 liter. Dilute 5.00 ml. of the stock solution and 1 ml. of 72y0 perchloric acid to 1 liter. One milliliter contains 0.0500 fig. of beryllium.
INSTRUMENTATION
PROCEDURE
Instrumentation used has been described previously (7) and includes a Beckman DU spectrophotometer equipped with a fluorescence accessory and a Dumont 6291 multiplier phototube, a constant-temperature bath with provision for circulating the water around the cell compartment of the spectrophotometer, a 100-watt Type BH4 ultraviolet lamp for visual examinations, and permanent glass standards. A combination of Corning filters Nos. 3387(443) and half-standard thickness 5113(472) was used for the primary and Nos. 3384(490) and 5031(562) for the secondary with a tungsten source. A mercury source or other filters can be used as described above to obtain greater linearity or range of application a t the expense of sensitivity and increased interferences.
To the 0.5 ml. of 72% perchloric acid resulting from oxidation of the acetylacetone extract ( 7 ) ,or to other beryllium solution from which all interferences have been removed, add 1 ml. of aluminum solution followed by 3.00 ml. of sodium hydroxide-DTPA-TEA solution and 3 drops of O.Olg;l, quinine solution in 1% perchloric acid. Neutralize by adding 72% perchloric acid dropwise until a brilliant blue fluorescence is produced when the solution is examined under ultraviolet light. Add 1 drop excess perchloric acid and roll the solution gently around the sides to redissolve all beryllium hydroxide. Transfer the solution quantitatively to a glass-stoppered, 25-ml. volumetric flask and add liV sodium hydroxide until the fluorescence is extinguished. Add 5.00 ml. of piperidine buffer, mix well, and rinse the sides of the flask with a little water. Add 1.00 ml. of morin, mix, place in the water bath for a few minutes to adjust the temperature, and dilute carefully to the mark. Insert the glass stopper, mix thoroughly, and place in a constant-temperature bath for about 20 minutes before measuring the fluorescence. Adjust the temperature of the bath to within 1' or 2' C. of the prevailing room temperature ( 7 ) . Prepare and measure a blank and a beryllium standard vith each group of samples using 5 ml. of water and 5 ml. of the 0.05 pg. per ml. of beryllium solution, respectively. If greater range is desired, use a higher standard with one of the other filter combinations for the primary as described.
REAGENTS
Sodium Hydroxide - DTPA - TEA. Dissolve 60 grams of sodium hydroxide and 320 grams of anhydous sodium perchlorate in 250 ml. of water and filter through a double 7-em. glass fiber filter in a No. 2 Biichner funnel. Dissolve 13.0 grams of recrystallized diethylenetriaminepentaacetic acid and 10.0 ml. of 20% triethanolamine in 50 ml. of water and about 20 ml. of the sodium hydroxide solution. When all solid material has dissolved, add the remainder of the sodium hydroxide, dilute to 500 ml., and store the solution in a polyethylene bottle. Acidify a small portion and test for the presence of hypochlorite or chlorine. Any oxidizing capacity must be eliminated by treatment with small portions of sodium sulfite. Piperidine Buffer. Transfer 15.0 grams of purified DTPA to a 500-ml. volumetric flask with about 200 ml. of distilled water. Add 75.0 ml. of redistilled piperidine, stopper the flask, and swirl under a stream of cold water until cool. Add a solution of 20 grams of anhydrous sodium sulfite in 150 ml. of water and dilute to 500 ml. Store in a tightly stoppered bottle with a polyethylene-lined screw cap.
DETECTION LIMIT AND PRECISION
The detection limit is defined a t the 95y0 confidence level as that quantity of beryllium that is equal t o twice the standard deviation of its determination. To determine its value and the precision obtained with larger quantities of beryllium, ten blanks and ten 0.25-pg. standards were analyzed under the recommended conditions. The mean and its standard deviation was 9.8 =t0.05 scale divisions for the blanks and 94.8 f 0.2 scale divisions for the standards.
The data indicate a detection limit of 0.5 mkg. in a 25-ml. volume and that 0.25 pg. can be determined with a precision of about 0.5% both a t the 95% confidence level. Whether such sensitivity and precision can be maintained on actual samples depends on how well the sources of error are controlled, particularly when separations are not used, as in analysis of air dusts. Because of the serious effect of small changes in alkalinity on the fluorescence, large buffer capacity is desirable to minimize not only direct errors in adjustment of pH but also indirect errors resulting from elements that consume hydroxyl ion. Particularly, ammonium ion resulting from oxidation of organic matter with nitric acid or amphoteric elements in the sample will produce a significant decrease in alkalinity. The buffer capacity of the present procedure is much greater than that of the previous one, and the equivalent of 2 ml. of 1N acid or base can be added without producing a n error greater than about 1%. However, because of competing reactions between beryllium and aluminum each for DTPA, TEA, hydroxide, glass anion exchange centers, and morin, maximum precision will be obtained if the samples are analyzed as nearly like the standards and blanks as possible. This includes temperature and timing of addition of reagents and measurement of fluorescence. Kormal variations will affect the maximum precision only slightly. EFFECTS OF OTHER ELEMENTS
I n the previous procedure, about 1 mg. of cerium, praseodymium, neodymium, or samarium caused seriously low results with either blanks or standards. Each of the remaining rare earths except promethium have been tested individually since and have been shown to react similarly. The low results obtained were caused by consumption of most of the morin by the rare earths to form slightly or nonfluorescent complexes even in the presence of EDTA. Absorption bands of rare earths or their complexes with EDTA are not strong enough a t the concentrations used to cause error as was reported erroneously in the previous publication. Because of the presence of DTPA, no interference of any kind could be detected in the present procedure with 1 mg. of any of the rare earths except cerium on either blanks or standards. High results were obtained a t first but were shown to have been caused by traces of thorium in the rare earths even though rare earth oxides of purity greater than 99.9% were used in the tests. A few representative tests with rare earths are shown in Table IV. Cerium originally produced seriously low results even in the presence of DTPA by oxidizing the morin reagent. When the solution is made strongly alkaline, part of the
Table IV. Q
Element
Effects of Other Elements ~ ~ Error, ~ Sc. - Di17.~
tity, Mg.
Ce
1
Pr
0.83
Nd
0.86
Sm
0.86
Fe Bi
1 1 1 1
Hg
% Ni
1
Blank
0 . 5 pg. Be
f 0.2
f 0.5
+ 0.1 (f27.3) -
0.2
(0.0) 0.2 (t 8.11 (+ . . 8.1) 0.0 0.0’ (+ 1 . 1 )
+
+ 00.0 .1 0.0
+ 00 .. 30 -
0.1
- 0.4 ($20.9) 0.1 - 0.6) 0.1 6.0) 0.3 1.3) 0.4 0.3 1.2 5.0 - 2.8
+ + ++ +++ -
1 0.2 - 0.9 1 0.3 - 5.7 co 1 - 4.0 -75.9 U 0.1 - 2.3 9.9 U 1 0.0 - 0.2 Mo Blank = 5.1 Sc. Div.; 0.5-pg. Be Standard = 93.0 Sc. Div. Values in parentheses are results obtained without removal of thorium impurity in rare earth.
-
cerous hydroxide is oxidized rapidly by air to ceric hydroxide. The ceric ion formed on acidification is partly stabilized on addition of DTPA-TEA, and the resulting complex is capable of oxidizing morin in alkaline solution. If present in the quadrivalent state, 1 mg. of cerium will oxidize the small quantity of morin completely in a few seconds. If a few milligrams of sodium sulfite is added after the alkaline solution has been reacidified to reduce ceric cerium, addition of DTPA-TEA will stabilize the trivalent state and prevent reoxidation of cerium by air when the solution is again made alkaline. Under these conditions, 1 mg. of cerium produced no error if the fluorescence is measured within about 1 hour. Some catalytic activity of cerium on the air oxidation of morin is still present as indicated by the noticeable decrease in fluorescence and color that occurs in a few hours. Trivalent iron forms a complex with triethanolamine in alkaline solution that is completely nonabsorbant to light in the visible region. Since both the exciting light and the emitted fluorescence are entirely in the visible region, error from iron is eliminated. However, the quantity of triethanolamine used in the procedure is sufficient to complex only about 1 mg. of iron. TEA forms a weak complex with beryllium under the conditions used, resulting in a slight decrease in fluorescence that is approximately proportional to the quantity used. Larger quantities are therefore undesirable and unnecessary in most applications. Iron is preferentially complexed by DTPA in acid or mildly alkaline solution to give an intense yellow color t h a t is a convenient indicator of its presence and quantity.
The yellow DTPX complex is then transposed to the colorless TEA complex when the pH is raised by addition of the buffer . The error produced by interfering ions has changed somewhat from that shown in the previous publication owing to differences in absorbance a t the new wave lengths being used for excitation and emission and to lower instrumental sensitivity. However, most of the interferences in the older procedure are still present in the present one although possibly in somewhat different degree. Many of the elements that did not interfere in the previous method were not retested because interference seemed unlikely in the present procedure considering the changes that were made. In addition to simplifying the procedure, the elimination of stannite from the procedure has eliminated the interference produced in the presence of mercury and bismuth because of their reduction to the metallic state. However, the absence of a powerful reducing agent restores the possibility of oxidation of morin by agents not inactivated by D T P A . Accordingly, measurements were repeated after about 2 hours on all solutions used in interference tests to identify those elements causing increased rate of disappearance of the beryllium fluorescence. Solutions containing thorium, cerium, uranium, and, to a lesser degree, zirconium were decolorized faster than normal in the presence of EDTA, but their effect is inhibited by a high concentration of DTPA. The error is of little concern, however, since the catalytic effect is slow and a much more serious error will already have been produced due to fluorescence or light absorption as the case may be. Direct skylight or sunlight or other intense light sources such as a 100-watt projection lamp a t a distance of a few inches will cause rapid fading of the fluorescence. Other environmental conditions such as windows or less intense light sources should be investigated if significant fading of fluorescence is encountered. The laboratory air must be kept free of all oxidizing agents. Halogens and ozone might be espected to give the most trouble in this respect. Distilled water supplies should be examined carefully to make sure that traces of chlorine or other oxidants have not carried though the distillation. Low pressure mercury lamps or other arcs that produce radiation in the short ultraviolet should not be operated in the laboratory because of production of ozone. Both blanks and standards tend to increase in fluorescence by about 0.5 and 1.0 scale divisions during the first half hour and more slowly thereafter. If time permits, samples should be allowed to stand for about 20 minutes VOL 33, NO. 12, NOVEMBER 1961
1677
before measurement, but in any case, the time of standing of both samples and standards should be kept as constant as possible for maximum precision. Also, salts cause an increase in fluorescence of the beryllium standard and a decrease of the blank. Approximate values are +2% and -4%, respectively, per gram of sodium perchlorate and about twice as high for sodium sulfate a t the 0.5-pg. beryllium level. Ethyl alcohol also causes a n increase in fluorescence of the blank but not of the beryllium standard. SAMPLE PREPARATION
Detailed directions for determination of beryllium in urine, bone, air dust and smears, ores, and steel were given in the previous publication ( 7 ) . However, those directions given for the extraction for precise work can be simplified considerably for routine application by eliminating both the second extraction and the extraction of the aqueous wash solution. If the main extraction and the ivash are allowed to settle for a few minutes, better than 987, recovery will be obtained routinely with a single extraction. Because of the excellent characteristics of beryllium as a neutron reflector and moderator in nuclear reactor technology, beryllium is being used increasingly as a component either in the fuel element cladding or directly in the fuel element itself. Accordingly, the determination of beryllium in metallic uranium, thorium, zirconium, and aluminum is required. Pyrosulfate fusion dissolves both thorium and zirconium either as the metals or as refractory oxides quickly and easily, and at the same time assures complete dissolution of any beryllium that might be present as its refractory oxide. Use of sulfuric acid and sodium sulfate to dissolve metallic zirconium is particularly noten-orthy in that the dissolution is accomplished rapidly and completely without the addition of hydrofluoric acid or other compounds of fluorine that are objectionable later in the analysis, and whose removal is both difficult and time consuming. A procedure is also included for the treatment of refractory silicates that are not decomposed by either pyrosulfate fusion or hydrofluoric acid. This procedure should be particularly useful in geochemical investigations. Determidation of beryllium in pure thorium and zirconium provides a Earticularly severe test of the adequacy of the separations because of the high sensitivity of the reaction of these two metals with morin producing fluorescence similar to that produced by beryllium. Separation factors of 5 X lo7 and 1 X lo7are required when samples of 1 gram of thorium and 0.5 gram of zirconium, 1678
ANALYTICAL CHEMISTRY
respectively, are used. To achieve such separation, the original acetylacetone extracts must be decomposed and the extraction repeated. KO method has been found that will remove either metal from the extract completely other than by complete decomposition. X separation factor of lo5is required with 1 gram of uranium and can be obtained easily in a single extraction. Sodium dithionite is used to reduce sexivalent uranium to the quadrivalent form which is not extracted significantly by acetylacetone in the presence of EDTA as is the case with sesivalent uranium. However, the small quantity (ea. 0.01%) of the quadrivalent uranium acetylacetonate that distributes into the chloroform cannot be removed with acid or dithionite as is the case with sesivalent uranium. It can be removed easily by oxidation with hydrogen peroxide during the wash. Evidence for the sensitivity, precision, and reliability of each procedure given later is derived entirely from internal sources but is felt to be completely unequivocal. Standard beryllium samples are not available, and existing methods are believed to lack both the sensitivity and precision necessary to test the masimum capabilities of the present procedure. This is particularly true in view of the large variety and complexity of the materials analyzed and the extremely small concentrations of beryllium detected. Each type of sample was spiked with a known quantity of natural beryllium and analyzed by the appropriate procedure. An identical sample was also analyzed without added beryllium to permit correction for any beryllium present originally. An exact quantity of beryllium-7 tracer containing about 2 X lo5 c.p.m. was also added to both the spiked and unspiked samples to determine the physical recovery of beryllium and to identify and eliminate all steps in which significant loss of beryllium occurred. Each fraction obtained in each procedure was counted and compared against a counting standard containing the same original quantity of beryllium-7 so that a complete material balance of the activity could be made. All fractions and the standard were counted in a 75-ml. thallium-activated sodium iodide well counter under the same conditions and a t the same time so that the counting efficiency would remain constant and decay corrections would cancel. A counting time of 5 minutes was used so that the statistics of lo6 total counts would permit the total activity t o be determined with a standard deviation of O.l%, and all beryllium could be accounted for precisely. Experimental standard deviations have shown repeatedly the absence of significant errors a t this level other than those due to the statistics of counting. The
acetylacetone extracts ( 7 ) containing the beryllium were then analyzed fluorometrically to prove the absence of any substance interfering n ith the chemical determination of the recovered beryllium. K h e n potassium fluoiide fusion was used, losses due to spattering for the entire decomposition including the transposition to a pyrosulfate fusion were approximately 0.5% and could be kept to about 0.2% with sufficient care. With this single ehception, complete material balances of 100 0 =t0.2% were obtained in every case from the tracer studies confirming the absence of significant losses of beryllium from other sources such as volatilization, adsorption on container walls, hydrolysis, etc. Nore than 99.8% of the tracer was present in the combined acetylacetone extracts. Less than 0.1% was present in any original aqueous solution after the eytraction and less than 0.02% in the solutions from a repcat extraction or in any aqueous wash solution. Because of thcii natural radioactivity, the aqueous solutions from the tests on uranium and thorium were examined for unestracted beryllium-7 with a 256channel gamma srectroineter rather than by gross gamma counting in the well counter. The physical recovery of beryllium through the sample decomposition and separations v a s shown by the tracer nork to have been bptter than 99.8%. The data of Table V show that the recovered beryllium can be determined precisely by the fluorometric procedure. Elimination of interfering elements is obvious from the remarkable consistency and sensitivity of the data. Exen when considerable beryllium was present originally, added quantities could be determined by difference with a n error less than 1% for the entire procedure. The percentage recovery of the spike shown in the last column was obtained by correcting the total beryllium obtained fluorometrically from the spiked sample for that present in the unspiked control. When significant beryllium was present originally in the sample being analyzed, aliquots of a prepared solution of the sample were used to ensure homogeneity. The sensitivity values given a t the bottom of the table show the increased sensitivity and linearity that result when the instrument is adjusted to give full scale reading with a 0.25-pg. beryllium standard. The slight nonlinearity obtained when a 0.5-pg. standard was used does not affect the validity of the results shown since the recovery of beryllium from the spiked sample was always compared with a standard containing the same quantity of beryllium. Test 1 shows that thorium does not carry through the double set of extractions in detectable quantities. Small
positive values were obtained until the practice of degreasing and cleaning the stopcocks of the separatory funnels before making the second set of extractions was initiated. Acetylacetone was again added to the thorium solution, and the ex%raction was repeated, making, however, only one set of extractions. The result of test 3 indicates the magnitude of the error that can be produced by thorium that carries through the original eytraction and wash. A similar set of data is shown for zirconium which is the only other element showing sensitive production of fluorescence \+ith morin under the present conditions. The large concentrations of beryllium relative to the sensitivity of the present procedure found in reagent grade aluminum oxide and the smaller concentrations in metallic aluminum nere interesting and noteworthy. Relatively large concentrations were also found in some natural silicates such as talc, asbestos, and particularly in aluminum silicates such as kaolin. The most important conclusion t o be derived from these data, however, is the ease and simplicity with which highly sensitive and precise analyses can be made on such generally intractable materials. The use of fusion with potassium fluoride followed by transposition to a pyrosulfate fusion is a very elegant method for the decomposition of siliceous refractories with complete elimination of both fluoride and silica (6). The results with kaolin verify the prediction made in the previous publication ( 7 ) that interference with the dircct determination of beryllium nithout separation nould most likely come from traces of thorium or zirconium. 'lhe slightly high result obtained in test 21 when separation was not employed wis proved by both gamma ray spectroscopy and chemical separation to have been caused by the presence of a small quantity of thorium in the kaolin. As qhown in Table I, the sensitivity of the present procedure toward thorium is exceptional and investigations are now in progress to develop this reaction into :i quantitative procedure for thorium. Several conclusions are demonstrated by the results obtained with beryl. A maximum of only 10 pg. of total sample could be used for the analysis because of the high concentration of beryllium; the same result was obtained by direct measurement as vas obtained after separation, and the accuracy is probably better than can be obtained by conventional macro procedures. I t should also be noted that complete recovery was obtained by the present method even though 4 mg. of beryllium was present during the extraction. The kaolin and beryl samples nere not spiked with natural beryllium because of the small sample size permitted by the beryllium already present.
Table V.
1
2 3
4 5 6
7
8
9 10 11
12
Recovery of Beryllium by Recommended Procedures
Thorium Th metal, 1 gram Th metal, 1 gram, plus 0.5 pg. Be Reoeated single extn. on Th soln. after e x t n . 2 test 1 Zirconium Zr metal, 0.5 gram Zr metal, 0.5 gram, plus 0.5 pg. Be Repeated single extn. on Zr soln. after extn. of test 4 Uranium U metal, 1 gram U metal, 1 gram, plus 0.5 pg. Be Bronze Bronze, 0 . 5 gram Bronze, 0 . 5 gram, plus 0 . 5 pg. Be Aluminum A1 metal, 0 , 2 5 gram A1 metal, 0.25 gram, plus 0.25 pg. RP
Instrument Corrected Reading, for Blank, Sc. Div. Sc. Div.
Be Found,
%
