Detection of minute amounts of tungsten with thiocyanate and tin(II) using anion-exchange resin beads

MICROCHEMICAL JOURNAL

9, 465-476 (1965)

Detection of Minute Amounts of Tungsten with Thiocyanate and Tin(lI) Using AnionExchange Resin Beods'" YUKIO NAKATSUKASA AND MASATOSHI FUJIMOTO S

Department 01 Chemistry, College 01 Foreign Students, Chiba University, Yayoi-cho, Chiba, Japan; and Department 01 Chemistry, Faculty 01 Science, The University 01 Tokyo, Hongo, Tokyo. Japan Received April 20, 1965

INTRODUCTION

The "resin spot test" is a newly developed micro- or ultramicrodetection technique that uses tiny beads of an ion exchanger as reaction media . The recent advances of this technique are reviewed by Fujimoto (3, 4) with many examples, which also include some organic applications (20) . Some of the merits of this method should be mentioned here. The most outstanding advantage is the high sensitivity, which is not attained in conventional spot tests. The volume ratio of the two liquid phases inside and outside of the exchanger beads reaches some thousands to hundred thousands (14); the high K d value of the component in very low concentrations favors the increased concentration in the exchanger phase , which enhance the sensitivity of the spot tests (Fig. 1). The characteristic colorations which are observed only in the ion exchanger phase' also increase the visual sensitivity of the resin spot tests. 1 Paper presented at the International Symposium on Microchemical Techniques -1965, held at The Pennsylvania State University, University Park, Pennsylvania, U.S.A., August 22-27, 1965. 2 Paper XXIV in the Series "Microanalysis with the Aid of Ion Exchangers;" Part XXIII: see Ref. (13). 3 Temporary address: Max-Planck-Institut fiir Physikalische Chemic, Gottingen, West Germany. 4 These characteristic colorations can be attributed to one or both of the following factors : (a ) the extremely high concentration of the reagent components in the exchanger phase, as shown in the case of Co(II )-NCS--anion-exchange resin system (sky blue) (5, 6, 8, 14) ; and (b) the strong polarizing effect of the charged functional groups of the resin upon the adsorbed ionic species. This effect is noted in the charac-

465

466

YUKIO NAKATSUKASA AND MASATOSHI FUJIMOTO

The second advantage of the method is the enhanced selectivity. Cationic (or anionic) interferences can be avoided easily by the use of an anion (or a cation) exchanger and of some reaction forming characteristic anionic (or cationic) species. Intensely colored or highly turbid sample solutions con(ST)

01-/1,~.\

\l) R

(a)

\LJ R.'

(b)

FIG. 1. Localized reactions in the resin spot tests (RST) as compared with reactions in the usual spot tests on the spot plate (ST). (a) Color reaction; (b) precipitation reaction.s 51' 52' 5)l: Drop of the solution; R, R' : Resin beads. Coloration or precipitation is shown with shading.

taining some metal ions or biological materials could also be used; the resin beads loaded with the desired component can be separated for the test by removing the outer solution. Other advantages of this technique are the stabilization of the unstable colored products in the exchanger phase [as shown in the case of Cr (VI)H 202-anion-exchange resin system (7) 1, increasing color intensities of the resin phase with time (14), and the possibility of saving the test result by drying the colored resin beads (for example, 8). The slowness of the color development in the resin phase depends mainly on the relative slow diffusion of the ions in the network of the exchanger phase (14). This has been partly overcome by the application of modified techniques, such as the use of finely-divided ion exchanger powders in the resin-flotation method (11) and the resin-centrifuge method (12), or the use of noncross-linked liquid ion exchangers (16). teristic coloratic n of the strongly basic exchangers upon adsorption of colorless ions such as OH- (dark ocher), 5H- or 52 - (dark green or dark grayish blue-green) and I - (yellow). These will be discussed in detail elsewhere. :; It is interesting to note that the precipitation occurs either (i) in the pore liquid of the exchanger or (ii) in the adjacent outer liquid phase, depending on the conditions or the nature of the precipitation reactions (Fujimoto, M., and Mizumachi, K., unpublished observations).

DETECTION OF TUNGSTEN USING RESIN BEADS

467

Some microscale devices and wide varieties of ion-exchanging media for the resin spot tests are detailed in the recent reviews (3,4). The present paper provides a further extension of the principle of the resin spot test to the detection of tungsten (VI). Anionic thiocyanato complexes of tungsten (V), formed in a reducing medium such as an acidic solution of tin(II) chloride (1,19), are strongly adsorbed on a strongly basic anion-exchange resin. The greenish-yellow to yellow color developed on the pale-colored resin beads interferes seriously with the detection for molybdenum(VI) under similar conditions (9). It can be used, however, as an excellent resin spot detection test for nanogram amounts of tungsten (VI), the details of which will be described below. MATERIALS AND METHODS

Reagents Stock solution oj tungsten( VI). A calculated amount of tungstic acid prepared from analytical grade sodium tungstate(VI)-dihydrate, was dissolved in a minimum excess of dilute sodium hydroxide to prepare a slightly alkaline stock solution containing 1.00 mg \V (VI) per milliliter. This solution was diluted with 0.01 F sodium hydroxide when necessary. Ammonium thiocyanate stock solution. A 100/0 aqueous solution was used. Tin(ll) chloride solution. Ten per cent SnCl 2 in concentrated HCl was prepared as a stock solution immediately before the test. Other reagents. Hydrochloric acid and chloroform were distilled and acetylacetone of Dotite analytical grade (Dojin Pharm. Labs.) was used. All other reagents were of analytical grade . Ion -Exchange Resins The following pale-colored, strongly basic, anion-exchange resins were given a preliminary treatment (15) and used in the chloride form: Dowex I-Xl , -X2, -X4 and -XIO, and Dowex 2-X2. The strongly acidic cationexchange resin Dowex SOW -X8 was also used in the free acid form or the ammonium form for the column separation of interfering ions. Dropping Capillary Pipettes Capillary pipettes were drawn from a glass tube (3) . These pipettes delivered 40 ± 2 ul per drop.

468

YUKIO NAKATSUKASA AND MASATOSHI FUJIMOTO

Procedure

After some trials the following general procedure was applied to determine the best conditions for the test: On a white spot plate a drop of the slightly alkaline test solution is mixed with several grains of an anionexchange resin in the chloride form. After a few minutes' standing, one drop of tin(II) chloride solution in concentrated HCI is added followed by one drop of dilute aqueous ammonium thiocyanate. After 20 to 30 minutes a greenish-yellow color (or yellow color, depending on the concentration of tungsten) appears on the resin phase and is observed under magnification of about X 20. The use of a fluorescent lamp and some prior practice are recommended to enhance the detection of the yellowish color tone. RESULTS AND DISCUSSION

Determination of the Best Conditions and the Limit of Identification

A sample solution containing 40 ng W(VI) per drop [i.e., 1.0 ppm. W(VI)] was used for this purpose. Effect of the RCl concentration in the tin (II) chloride solution. The concentration of hydrochloric acid in the tin(II) chloride solution affects the color intensity and the tone on the resin beads. The color intensity with 10% SnCI2 decreases as the concentration of HCI decreases. The greenish color is diminished with HCI concentrations lower than 3 F; with 1 F HCI the color is almost yellow. Thus the solution in 12 F HCI was used. Effect of the SnCl! concentration. A series of freshly prepared reagent solutions in 12 F HCI containing 0.1, 0.3, 1, and lOro SnCl2 were tested. The same intense coloration was observed for the last three concentrations. The 10% SnCl2 solution was adopted, since the coloration was somewhat better than others and the deterioration of the reducing power on standing in the air is thus avoided. Effect oj the Nll 4NCS concentration. Under the best conditions with the SnCb solution the color intensities of the resin beads decreases as: 10% ~ 3ro > 170 ~ 0.3% ~ 0.1% NH 4NCS. The 3% solution gave the best apparent coloration. Effect oj the neutral salt concentration. The presence of the indifferent salts in the reaction mixture influences the ion-exchange distribution of the trace component, which often affects the apparent color intensity of the resin phase. The increasing concentration of the neutral salt such as sodium chloride gave a less greenish coloration, but did not affect seriously the reaction sensitivity.

DETECTION OF TUNGSTEN USING RESIN BEADS

469

Effect of resins and limits of identification. Under the best conditions as determined above, the limit of identification of the test was determined, after 1 hour of standing with various ion-exchange resins, as follows:" Dowex I-Xl , 10 ng ; -X2, 10 ng; -X4, 16 ng ; -X 10, 16 ng; and Dowex 2-X2, 16 ng; i.e., 1O-!1l gram-atom amounts of tungsten(VI). The coloration at the identification limit was less greenish. If the temperature is too low, the spot plate should be warmed on a water bath to accelerate the reaction. When the same conditions were used as above without added resins , the positive test was given by a pale yellow coloration of the solution. This appeared slowly after 20 to 30 minutes standing only with the test solutions containing more than 2 flg of tungsten (VI) . Thus the limit of identification of the test is enhanced about 200 times by the addition of several grains of a strongly basic resin of low cross-linkage. Influences of Foreign Substances These are summarized in Table 1 together with the limiting proportions. Milligram to 100-flP; quantities of the following ions do not interfere with the detection of 1O -2_~lg quantities of tungsten (VI) (i.e., the limiting proportions are in the order of magnitude of 104): La(III ) , Ce(IV ), Zr(IV) , Th (IV), 1\1n(II), Fe(III) , Ni(II), Zn(II), Cd(II) , Al(III) , Ga(III) , In(III), Ge(lV), Sn(IV) , Pb(II) , Sb(III), Bi(III) ; F- , Br-r , 1- , NO a- , 50:12 - , S04 2 - , HP0 42- , B40 72 - , HCOO - , C:!04 2 - , tartrate and citrate. The following readily reducible ions interfere with the test seriously: Pd(II) , Pt(IV) , Ag(I) , Au(III), Hg(II) , As(V), Se(IV), and Te(IV). Most of these ions were removed as precipitates prior to the test ; masking was not as effective as in the conventional spot test because of the much higher sensitivity of the present resin spot test. Pd(II) and Au(III) were readily reduced with a small amount of zinc dust to a metallic precipitate. Hg(II), As(V), Se(IV) and Te(IV) were reduced with SnCl2 in concentrated HCl to form a precipitate. Ag(l) and TI(I) were precipitated with a drop of 10% NH 4NCS. The precipitates were filtered off using a micro layer of glass wool or of filter paper pulp (Fig. 2); the filtrate was then evaporated to a small volume on a spot plate and subjected to the test. The interference of platinum(IV) could not be removed by simple pre6 To assure the definite positive test near the limit of identification, no more than five grains of resin beads should be add ed and a blank should also be run .

La(N0 3)3 Ce(S04)2 TiOS0 4 ZrO(NOa)z Th(NO a)4 NH4VOa KCr(S04)2 K 2Cr04 Na 2Mo04 UOz(OAc)z MnS0 4 FeCl a

La(III) Ce(IV) Ti(IV) Zr(IV) Th(IV) V(V) Cr(IlI) Cr(VI) Mo(VI) U(VI) Mn(1I) Fe (III) Co(II) Ni(Il) Pd(1I) Pt(IV) Cu(Il) Ag(l) Au(III) Zn(II) Cd(1I) Hg(II) AI(II1)

NiCl2 PdCl z HzPtCl o CuS0 4 AgNO a HAuCl 4 ZnS04 CdS04 Hg(N03 ) Z KAl(S04)z

csci,

Added form

Foreign ion 0.017 0.017 0.1 0.017 0.017 0.1 0.017 0.033 0.4 0.033 0.017 0.025 0.05

270 270 64 270 510 400 53 1300 800 530 1300 40 1000 100 640 800 1300 1300 400 1300 1000

nel nel nel (Ye) nel nel nel (Ye) ncl-plGrn nel-ltBI nel (Or) nel (Ye) nel nel-plYe nel(BI) nel-grn\Vh nel (reYe) nel (Ye) nel (Wh, ppt) nel (Wh, ppt) ncl (Blk-Vlt) nel nel nel (BIk-Gry) nel 0.02 0.04 0.02 0.02 0.05 0.017 0.025 0.025

0.025

1000

200

o.ozs

Amount of detectable W(VI) (lA-g)

Amount of foreign ion (ug)

Coloration of the resin phase«

1:8'103

1:1.6'104 1:7.6'104 1:1.6·10a 1:2'104 1:4'103 1:3.2 '104 1:2'104 1:6.5'104 1:6.5 '104 1:8'103 1:7.6'104 1:4'104 1:4'104

1:4'103 1:3'103 1:4'104 1:2'103

1 :1.6'104 1: 1.6 '10 4 1:6.4'102 1: 1.6'104 1:3'104

Limiting proportion

TABLE 1 INFLUENCES OF FOREIGN SUBSTANCES ON THE DETECTION OF TUNGSTEN(VI) WITH AMMONIUM THIOCYANATE AND TIN(II) CHLORIDE BY THE RESIN SPOTTEST

c::

k

!'.::

i,»

0

>-l

0

i,e

"l

....c::... !'.::

0

>-l

'" > :5'"

)-

fI,C

s,«,»

k

fI,C

b,c,d,k

b,c,d.k

)0-

Z

t, e

e

)0-

'"

)0-

~

c::'"

>-l

)0-

~

Z )0-

~

...0

><

e

k

b,c,d,k

Remark

~

..... 0

C 6H507 -

Br 1NOa S032 S04 2HP04 2 B40 72 H COOC20 42 C4H406 2 -

F-

Ga(III ) In (III ) TI (I) Ge (IV ) Sn (I V) Pb (II) As(V) Sb (IIl ) Bi (III ) Se (lV) Te(lV)

Foreign ion

SbC13 Bi(XO a) a H 2S eOa K 2T eOa KF KBr KI KNO a Na2S0a K 2S04 Na2 HP 0 4 Na2B407 NaOOCH (NH 4 ) 2 C204 Rochelle sal t Ammonium citrate

~a2HAsO~

SnCI 4 Pb (X03 ) 2

~a2Ge03

In (1I:0a ) 3 TI2S04

csci,

Added form

1300

0.017

1300

neI

nel

0 .017

800 1300 270

800

0 .017 0.025 0 .05 0.01 0.017 0.01 0.01 0.01 0.025 0.05 0.05 0.Q25 0.Q25 0.025 0.025 0.017 0.Q25 0.025 0 .01 0.017 0.017

W(VI) (I! g)

Amount of detectable

260 130 400 100 270 53 720 320 200 400 400 1000 1000 200 1000 1300 600

Amount of foreign ion (ug)

nel nel nel (Wh, pp t ) nel nel nel nel (Ye) nel plYe nel (Re-Br, pp t) ncl (Blk-Gry ) nel nel nel nel nel nel nel neI nel nel

Coloration of the resin phase«

TABLE 1 (Continued)

1: 7.6 ' 104

1: 7.6'10 4

1: 1.5'104 1:5.2' 103 1:8 '103 1:1 '104 1: 1.6 '104 1:5.3 ' 103 1: 7.2 '104 1:3.2 '104 1 :8 ' 103 1:8' 103 1:8' 103 1:4 ' 104 1 :4'104 1:8 -103 1:4'10 4 1: 7.6 '10 4 1: 2.4"10 4 1:3.2 '10 4 1 :8 '104 1 :7 .6'104 1: 1.6 ' 104

Limiting proportion

t, » ;, e

i,»

(, e

Rem ark tl t'l

'-l .-

-l>-

en

>tl

tll t'l

Z

IJ>

....

t'l

III

0

Z

c:: ....IJ>

Z

t'l

0-,1

IJ>

0

Z

c::

0-,1

"'J

0

Z

0

0-,1 ....

o

t'l

0-,1

n The colorations of the resin beads caused by the large excess of interfering ions are given in parentheses, Colors not in parentheses are caused by the remaining forei gn ion itself, in th e absence of tungsten, under conditions identical to those used in determining the limiting proportion. Color code: nel, no coloration; pI, pale; It, light; BI, blue; Blk, black ; Br, brown; Grn, green, grn, greenish; Gry, gray; Or, orange ; Re, red; re, reddish; Vlt , violet; \Vh, white; Ye, yellow ; cf. also Refs. (3,4 ). II A drop of dilute ~aOH was added to pr ecipitate the bulk of int erfering substa nces. C The precipitate was filtered off using a micro layer of glass wool or filter paper pulp (Fig. 2). d Th e remaining traces of interferin g substances were removed using a micro column (9) of Dowex SOW-X8 in the NH,,-form. The effluent was evaporated to a small volume prior to the test . " The out er solution was rem oved with a capillary or a small filter paper strip pr ior to the test , to elimin ate the interference by the intense color of the outer solution. f The test solution was warmed with a drop of 3% H~02 in 1 F H~S0-l on a water bath to reduce Cr(VI) to Cr(lll). II A small amount of zinc dust was added to reduce the interfering substances. If Cu(II) was reduced to Cu(I) with a drop of 10% SnCI in 6 F He!. 2 I A drop of 10% NH 4NCS was added prior to the test to precipitate the interfering substances. j The test solution was warmed after adding a drop of 10% SnCl 2 in concentrated HCI to reduce the interfering substances. k For details, see the text.

TABLE 1 (Continued)

Cl

o

~

C

...

:I:

... ..,

ClVI

>

> VI

~

> VI > > Z c

:0::

C

>oj VI

~

>

z

a

:0::

C

<

~

........

DETECTION OF TUNGSTEN USING RESIN BEADS

473

cipitation methods; the resin beads turned yellow upon mixing with the filtrate and the reagents. The anion-exchange separation by Kraus (17) was very efficient in removing the last traces of platinum(IV) . A micro column of a strongly basic resin in the chloride form (9, 10) was condi-

o 2

F

3 em FIG. 2. Micro filters. F : Filter wad of glass wool or of filter paper pulp.

tioned with concentrated Hel and the test solution containing concentrated HCl was passed through. Tungsten(VI) was eluted selectively with 1 F HCl onto the spot plate, Pt(IV) being held quantitatively in the column . Upon addition of the reagents to a solution containing vanadium (V) , V (IV) complexes were formed which imparted a yellow color to the resin beads . Therefore, vanadium(V) was first reduced with oxalic acid to vanadium (IV) and taken up on a micro column? (9) of a cation-exchange resin in the H-form conditioned with 0.1 F HF. Tungsten(VI) was eluted easily with 0.1 F HF while vanadium(IV) was retained at the top of the column as a green band (2) . It is to be expected that other metal ions will also be retained in the column upon elution with 0.1 F HF as shown by Fritz etal.(2). Molybdenum(VI) interferes with the test most seriously, imparting to the resin beads an intense orange color of anionic 1\Io(V) complexes (9). Most separation procedures, such as xanthate extraction, sulfide precipitation or various column separations, were unsuccessful. The extraction of molybdenum(VI) as the acetylacetone complex (18) was found to be most efficient for the present purpose. The test solution was first acidified to 1-2 N in sulfuric acid. It was then shaken in a ZS-ml separatory funnel with two 2-ml portions of acetylacetone-chloroform (1 : 1, v/v) , and finally 7

In this case a glass tube could be used lor the column; see Ref. (2).

474

YUKIO NAKATSUKASA AND MASATOSHI FUJIMOTO

with 2 ml of chloroform to remove the bulk of acetylacetone from the aqueous phase. The aqueous phase was passed through a small disk of moist filter paper to remove chloroform droplets, and evaporated in a small porcelain crucible to a small volume. The concentrated solution was heated further with concentrated HN0 3 to destroy the last traces of organic component (otherwise, the pale yellow decomposition products color the resin beads). The colorless solution thus obtained was ready for testing. Some transition metal ions form intensely colored thiocyanato complex anions which interfere with the test. Thus uranium (VI) imparts an intense yellow color (6), and cobalt(II) a blue color (6) to the resin beads. The bulk of these ions was first removed as the hydroxide precipitates with a drop of dilute NaOH and the remaining traces were removed from the filtrate on a micro column (9) of a cation exchanger in NH 4-form. The interference of titanium (IV) could be eliminated in the same manner. TABLE 2 LIMITING PROPORTIONS IN THE PRESENCE OF SERIOUSLY INTERFERING IONS

Interfering ion Ti(IV) V(V) Cr(VI) Mo(VI) U(VI) Co(II) Pd(II) Pt(IV) H~(II)

T1(I) As(V) Se(IV) Te(IV)

Amount of interfering ion

Amount of detectable tungsten (VI)

(p,g)

(!1g)

1.3

0.04 4 0.64 0.13

0.017 0.1 0.1 0.01 0.01

Limiting proportion

Remark

1:76 1:0.4 1:40 1 :64 1:13 e

0.11 2.7 5.3 0.13 1.0

0.017 0.033 0.017 0.033 0.017

1:6.5 1:82 1:310 1:4 1:60

a Ti(IV), V(V) and Pt(lV) interfere with the test so seriously that the eluate from a careless column separation still gives a faint yellow color to the resin beads. The limiting proportions were estimated to be as low as that for Mo(VI). b After the development of the color the outer solution was removed, a few drops of concentrated HCI were added and the coloration of the resin beads was compared with that of a blank test. C As little as 0.04 /Lg Pd(II) gives a pale reddish yellow color in the resin phase.

DETECTION OF TUNGSTEN USING RESIN BEADS

475

After evaporating to a small volume, the effluent from the column was subjected to the test. Table 2 shows the minimum amounts of tungsten(VI) detected in the presence of small amounts of these seriously interfering ions, together with the values of the limiting proportion. SUMMARY A sensitive resin spot test for tungsten(VI) with ammonium thiocyanate and tin ( II ) chloride is proposed by the application of several grains of pale-colored strongly basic anion-exchange resins in the chloride form . The resin beads assume a gr eenish-yellow to yellow color in the presence of tungstent Vl} . Under the best conditions the limit of identification, after 1 hour of standing, is 10 ng W (VI) (l : 4 '10 6 ) with a resin of low cross-linkage. The sensitivity is about 200 times higher than that of the usual spot test (2 Itg W(VI); 1: 2'10"'). The interferences of 46 ions are investigated. The removal of the following ions, which give serious interferences, is described in detail: Pt(IV), V(V) , Mo(VI), U(VI) and Co(ll) . General aspects of the resin spot techniques are also briefly surveyed. ACKNOWLEDGMENT We wish to thank Mr. Yoshitaka Kadoya for his assistance. REFERENCES

1. FEIGL, F ., "Spot Tests in Inorganic Analysis," 5th ed., pp. 120-121. Elsevier, Amsterdam, 1958. 2. FRITZ, J. 5., GARRALDA, n. n., AND KARRAXER, S. K., Cation exchange separation of metal ions by elution with hydrofluoric acid. Anal. Chern. 33, 882-886 (1961). 3. FUJUfOTO, M ., Ion exchange resins as reaction media for microdetection tests . Chemist-Analyst 49, 4-10 (1960). 4. FUJIMOTO, M ., Recent advances in resin spot tests : 1960-1964. Chemist-Analyst 54, 58-62, 92-95 (1965). 5. FUJIMOTO, M ., Studies on the cobalt ClI) thiocyanato complexes. On the blue compounds adsorbed on the anion-exchange resins. Abstr. Ann. Meet . Chem , Coordination Compounds, 4th, Tokyo, 1954, pp. 3-5 . 6. FUJIMOTO, M., Microanalysis with the aid of ion-exchange resins . I. Detection of minute amounts of cobalt with ammonium thiocyanate. Bull . Chrm , Soc. Japan 27,48-50 (1954). 7. FUJIMOTO, M., Microanalysis with the aid of ion-exchange resins. II. Detection of minute amounts of chromium with hydrogen peroxide. Bull. Chem, Soc . Japan 27,347-350 (1954). 8. FUJIMOTO, M., Direct measurement of the state of complex ions adsorbed on the ion-exchange resin phase with ion-exchange membranes. Bull. Chern. Soc. Japan 29, 285-287 (1956). 9. FUJIMOTO, M ., Microanalysis with the aid of ion-exchange resins . V. Detection of trace amounts of molybdenum with ammonium thiocyanate and tin ( I!) chloride. Bull . Chem, Soc. Japan 29, 595-600 (1956).

476 10.

11.

]2.

13.

]4.

15.

]6.

]7. 18. 19. 20.

YUKIO NAKATSUKASA AND MASATOSHI FUJIMOTO

FUJIMOTO, M., Microanalysis with the aid of ion-exchange resins. XII. Detection of nanogram amounts of nickel with rubeanic acid. Bull. Chem, Soc. Japan 30, 274-278 (1957). FUJIMOTO, M., Microanalysis with the aid of ion-exchange resins. XV. Adsorption of the finely divided particles of strongly basic anion exchanger on the interface of two liquids and its microchemical applications. Naturunssenschajten 47, 252 (1960). FUJIMOTO, M., Microanalysis with the aid of ion-exchange resins. XVI. Development of the resin spot tests by the use of centrifugation of finely divided ion exchangers. Bull. Chem. Soc. Japan 33, 864-866 (1960). FUJIMOTO, M., AND IWAMOTO, T., Microanalysis with the aid of ion exchangers. XXIII. Resin spot test for the detection of nanogram amounts of heavy metals with 1-(2-pyridylazo)-2-naphthol (PAN) or 4-(2-pyridylazo)-resorcinol (PAR). Mikrochim. Ichnoanal. Acta 1963, 655-667. FUJIMOTO, M., AND KORTUM, G., Diffuse reflexion spectra of heavy metal complexes and of methylene blue cations enriched on ion-exchange resins. Ber, Bunsenges. Physik. Chem. 68, 488-496 (1964). FUJIMOTO, M., AND NAKATSUKASA, Y., Microanalysis with the aid of ion-exchange resins. XIX. Detection of nanogram amounts of iron(III) with ferron. Anal. Chim. Acta 26, 427-4'>3 (1962). FUJIMOTO, M., AND NAKATSUKASA, Y., Microanalysis with the aid of ion exchangers. XXI. Modifications of the resin spot test with high molecular weight amines. Anal. Chim. Acta 27, 373-376 (1962). KRAUS, K. A., AND NELSON, F., Anion-exchange studies of the fission products. Proc, Intern. Coni, Peaceful Uses Atomic Energy, Geneva 7, 113-125 (1955). MCKAVENEY, J. P., AND FREISER, H., Analytical solvent extraction of molybdenum using acetylacetone. Anal. Chem, 29, 290-292 (1957). SANDELL, E. B., "Colorimetric Determination of Traces of Metals," 3rd ed., pp. 886-889. Wiley (lnterscience), New York, 1959. TSUJI, A., Microchemical detection using ion-exchange resins. Resin spot tests. Kagaku no Ryoiki 16,780-794 (1964).