Spectrophotometric determination of palladium with pontachrome azure blue b

79

SPECTROPHOTOMETRIC I’ONTACHROME AZURE

DETERMINATION BLUE B

OF

PALLADIUM

WITH

Many organic rcagcnts for the spcctrophotomctric dctcrmination of palladium based on the piillildiunI have been rcvicwcd by Bcamish ‘. Marc rcccntly. proccdurcs complexes with 2,2’-dipyridylkctoximc’. 2.1,,7-bcnzosclcnadiazol~~. chromuzurol hiivc been suggested. Pontachromc a%urC S*. and tropacolin 0 and its ilniIlO~UCS’. (,“-dichloro-4’-hydroxy-3.3’-dimcthyIfuchsor~c-5.S’-dicarboxyl;~tc: blue B (sodium-“‘. Color

In&x

43830).

;I triphcnylmcthanc

dye. has been

used ;LS il spcctrophotomctric

for hcryllium”. iroii(lll)“. coppcr(Il)“. uri~rliUm(VI)~. ii!ld SCilIIC~ilIIllH. It hiis bun found Ihat microgritm i\mounts of pillladium illso rc;lct with this rc;lgcnt in ii \vcilkly ilcicfic mdium to form iI complex. This pitper dcscribcs iI method for the dctcrmilliltioll of pilllildillm hilSCd 011 tllc form;ltion of il colored complex Of pi~lli~dium with pontrrcllrornc;Izur~ hluc 13.Scveritl conditions under which microgram illTl0l~IltS of pilllildium c;lfl bc dcturmincd. the influcnccs id Jivcrsc ions illltl thC wmposition of the complex arc discussed. The proposed method for pillliIdium offers the rC;lgCllt

atId high precision without ild\‘ilnlil~CS of simplicity. good sensitivity. cxtr;lltiotl ; rcusonitblc sclcctivity ci111 bc ;1chi~vd by mc;ltls of makillg

All

absorbance

mcasurcmcnts

clcctrodc

All

the tlccd for iIycntS.

pi-l mctcr.

model

M-5.

wcrc of analytical-rcagcnt pulladiut~~ soltttion. A standard stock solution was prepared by dissolving palladium distilled water, and then adding small amounts of hydrochloric palladium content of this stock solution (I.1 7 mg ml - ‘) was established gravimetrically solutions were made by suitable dilution of this stock as Pontctchronw solution. Pontachromc azure blue B (E. 1. du Pont dc Ncmours & Co. Inc.. U.SA.) was further purified by recrystallization from Ar~ul.Cilia Acttr. 60 (1972)

80

K. Ul:Sl:Gl.

M. TAHUSHI

-I’. StIIGISMATSU.

methanol bcforc USC,and iin ayucous 0.2’,‘(, (w/v) solution wils prepared. stable for ilt Icast 3 weeks. BuJJ&r solulion (pfl 5.5). 0. I M Potassium dihydrogcnphosphatc 0.1 M disodium hydrogcnphosphatc solution wcrc mixed.

The solution

WAS

solution

and

Transfer the sample solution containing 2.5-60 c(g of palladium to a 25-ml volumetric flask. Add 2.5 ml of the rcagcnt solution and 5 ml of the phosphate buffer solution to ildjust the pH to 5.5. If the pH of the resulting solution is not bctwccn 5.2 and 5.7, it may bc prcncutritlizcd with hydrochloric acid or sodium hydroxide solution. Dilute the solution to the mark with distilled water and mix. After IO min. me;isurc the absorbance itt 605 nm ilgainst i1 rcfcrcncc solution containing the same iltYlOllntS of rCilgCntS. CillCUliltC tllC pillliK!iUm conccntriition Of ttlC SilmplC solution by means of i\ calibriltion CIITVC. I~t:SUI.‘l-S

AND

I~ISC’IJSSION

The absorption spectra of pontachromc il%urc blue B hitvc been presented previously”: maximal itbsorbi~ncc occurs at 480 nm below pH 4.5, at 430 nm over the pH range from 5.5 to 10. itnd iit 590 nm above pH 10.5. The absorption spectra of pontachromc ;lzurc blue B and its palladium complex arc presented in Fig. I ; the solutions wcrc adjusted to pH 5.5 with the phosphate buffer solution. The maximal

06r-------.-----

Wawicngth

Fig. 40

I. Absorption spectra or pon1;lchrorr.c p.p.m.: Pd: (I) 0. (2) 0.9. (3) I.H pp.m.

Fig. 2. Absorption

;IZUW blue

B and

spcctril of pahdium cnmplcx iII various (3) 6.0. (4) 7.0. (5) 8.0. (6) 10.0.

pH: (I) 4.0. (2) 5.2-5.5.

its pi~lhdium

pt1 values.

Rcapcnt

(nm

)

complex

at pH

200 p.p.m.;

5.5. Rcagcnt

Pd I.17 p.p.m. :

PALLADIUM

WITH

PONTACHROME

AZUHE

BLUE

81

B

absorption of the palladium complex is found at 605 nm, at which point the reagent does not absorb appreciably. In order to observe the spectral changes on varying the pH. absorption curves for the palladium complex were prepared at different pH values (Fig. 2). These curves were obtained by measuring the absorbance of colored solutions containing 1.17 p.p.m. of palladium and 200 p.p.m. of pontachrome azure blue B at various pH values against a reagent blank containing the same amount of reagents_ Below pH 7.5. the maximal absorbance of the complex was found at 605 nm; above pH 8.0, maximal absorbance was shifted to shorter wavclcngths. Below pH 3. the complex partly precipitated. Effect o/‘pH The effect of pH on the color dcvclopmcnt of the complex was examined by measuring, at 605 nm, the absorbance of a solution containing palladium and the reagent at different pH value from 3.5 to 8.0. Maximal absorbance of the complex was observed between pH 5.2 and 5.7 and a pH of 5.5 was, thcrcfore. maintained in subsequent work. The reagent curve was obtained in the same manner, with the same amount of the rcagcnt. A 0.1 M phosphate buflcr pH 5.5 w;\s found to be satisfactory. The volume of the buffer solution &cd \vils found to have no C~~CC[011 the absorbance of a 0.9-p.p.m. palladium solution over the range 3-10 ml. The order of addition of the buffer and the reagent had no effect on the intensity of the complex color.

Fig. 3. Effccct of pH on color dcvclopmcnt. blank ; (3) rcfcrcncc: rcagcnt blank.

Stability

Rcagcnt

200 p.p.m. : Pd 0.9 p.p.m. ; (I) rcfcrcncc

: wiltcr. (2) rcugcnt

of color

The color of the complex was fully developed in a few min after mixing, and an essentially constant absorbance reading was obtained over a period of at least 2 h. Effect of reagent concentration The effect of the reagent And.

Chinr.

Acta. 60 (1972)

concentration

was

examined

by measuring

the

K.

x2

Ul:SUCil.

‘I-. St1 IGEMATSIJ.

M. TAUIJSIiI

i\bs(>rb:tncc at GO5 nm of solutions

containing a constant concentration of palladium itnd varyingumountofthcrcagcnt.A 15fold molurcxccssofthc reagcntovcrpalladium wils rcquircd in order to obtain maximal itbsorbilncc. With Only it smiill cxccss of rCilgCfIt. the colored complex was slow to dcvclop. Large amounts of the rcagcnt, CA/. 35-molar cxccss,did not affect cithcr the rate or the color intensity of the complex. The Optimill amount of the rcagcnt was 2.5 ml of a 0.2’%, reagent solution in 8 final volume of 25 ml, which sufficed for less than 2.5 p.p.m. of palladium.

The ilbsorbancc was indcpcndcnt of the tcmperaturc of the color development gritduillly dccrcascd with rise of over the range 10-40”. Above 40”. the absorbance tcmpcraturc. I-lcncc, normal laboratory tcmpcrilturc chilngcs introduce no error. ;l%llrC blue 13 complex obeys Hccr’s Iitw over the 0. I to ill Icast 2.5 p.p.m. of pilllildiUfIl (2.5-62.5 Jig per 25 ml). The optimitI working rilngc W;LS itbout 0.2-,2 p.p.m. of pilllildium. At 605 nm the sensitivity molar absorptivity wits 4.79 * I OJ I molt-- ’ cm- ‘. The spcctrophotomctric was cstimatcd to bc 2.2. 10-’ jig Pd cm-“. The sensitivity of the prcscnt method is compared with those ofother methods in Table I.

The

concentration

‘1’Al~l.l:

pilllildil~m~. rilIlgc

pontilchrc>r~lc

Of

I

C’OMI’AI~ISON

WI’I’II

O-l’t Ilil<

I
I.OR

Sc~f.\iril-ir,l (. IO .’ jf{/

I’AI.I.AI>IUM

C’f)l ‘)

x.3 (425 nm) x (427 nrn) 7 (63s wn) 5.x (590 rm1) 5

(3W

5

(450 ntn)

11111)

4

(51X tim)

I .9 (330 nm)

2.6 (410 nm) 7.2 (605 nm)

_

2.6

4.70 ..--.

_

_. _

In a test of the reproducibility of the method, 10 samples, each containing 1.0 p.p.m. of palladium. wcrc prepared according to the standard procedure and mcasurcd i\t GO5 nm. The uvcragc :tbsorbancc was 0.425, with a standard deviation of 0.005 absorbance unit or I .2”/,.

PALLADIUM

WITH

PONTACI+ROME

AZUKE

BLUE

83

H

Beryllium. coppcr( I I). iron( I II), uranium(VI), scandium, aluminum, yttrium. and rare earth clemcnts also form colored complexes with pontachrome azure blue B in weakly acidic solutions ‘-“. Thcsc ions were thereforc included in a study of possible interference with the determination of palladium. Some common ions, including these cations. were added individually to a solution containing 29.2 pg of palladium, and their effect was examined under the conditions of the standard proccdurc. The results arc summarized in Table II. It can be seen that some diverse cations, especially aluminum. beryllium. copper( I I). and iron( III), interfered seriously with the determination of palladium. Scandium, uranium(V1). yttrium. and rare earth clcmcntsdid not form colors in it phosphate-buffcrcd solution. Chloride. sulfntc. and fluoride wcrc without cffcct cvcn in large amounts. acctatc. nitrate. phosphate. The following metallic ions did not intcrfcrc up to IO p.p.m.: magnesium. calcium, strontium, barium, cadmium. Icad. zinc, mcrcury(I1). cobalt(l1). and nickel. Cyanide and EDT/\ prcvcntcd the formation of the palladium complex.

taken : 2Y.2 pg)

(I’;rll;ldium

.

_. Irw

Acltlctl (/If/)

.

_

I3cryllium(ll) Coppcr( I I) Iron(lll) Aluminum(lll) Scandium(lll) Yttrium(lll) L;lnthrrnum(lll) Ccrium(lll) Ncodymium(lll) Gudolinium(ll1) Dysprosium(ll Erbium(lll) Ruthcnium(lll)

I)

I’d

fimncl

._ _ 20 30 30 60 IO 30 I00 loo IO0 IO0 100 IO0 I00 IO0 IWO

-

_. 6X.2 45.Y 2Y.4 36.7 30.5 52.H 2Y.0 28.8 28.7 2H.O 28.‘) 28.6 29.0 29.2 2Y.O

-

._

-

PC/ finolcl (/I!/) . _ -

(jog) Rhotlium(lll) Gold(lll) Platinum( IV) Gcrm;lnium(lV) ‘T’it;lnium(lV) Urilnium(VI) Molybdcnum(VI) l-luoridc Sulfiltc Chloride Phosphate Acct;rtc Nitrate ED-I-A

IOU)

low low I(X) lo0 loo loo 2OwO loo0 IWJ loo0 1000 IMKJ lo(K)

28.Y 2Y.0 28.9 29.0 283 29.2 28.9 29.2 29.2 2X.9 29.3 28.7 2X.9 20.3

Fluoride was invcstigatcd as a masking agent for the more seriously ofTcnding ions.Aluminumandberyllium wcrecffcctively masked by fluoridcand can be tolerated without further separation (Table III). However, the interlerencc by copper and iron(I11) cannot be eliminated by the addition of fluoride. Therefore these ions must bc separated completely, by ion exchange”, solvent extraction’“, or other suitable procedures. Complex formcttion The method of continuous variations’” was applied ; a series of solutions was prepared front equimolar concentration of palladium and pontachrome azure blue B. The color was developed and measured in the usual way. A plot of absorbance at A~rcrl. Cili,n. Aclu. 60 ( 1972)

84

K. UESUGI.

TABLE

M. TABUSHI

111

EFFECT

OF

(Palladium

FLUORIDE

taken:

AS A

29.2 erg; fluoride --

/on added (jq)

MASKING added:

AGENT

5 ml of 0.1 M NnF solution)

Pd fclund (pg)

Error (“4)

28.9 29.2 38.9 29.0 28.8 29.3 34.5

-

___--Bcryllium(I1)

250 500 30 250 500 30 50

Copper Aluminum(lIl) Iron(I11)

0

+ + +

0.3 0 33.2 0.7 1.4 0.3 18.2

--

-

0

T. SHIGEMATSU.

0.2

Fig. 4. Continuous

0.0

variation

__

0.6

method.

08

1

pH 5.5; [Pd]

+ [Rclgcnt]:

(1) 4.4.

IO-’

hf. (2) 2.2. lo-’

M.

605 nm against mole fraction of palladium is shown in Fig. 4. The maximum corresponds to a 1:2 reaction ratio between palladium and pontachrome azure blue B. These results were confirmed by the mole ratio method”. Similar relations were also observed for the beryllium6-, copper(II)6-, and scandium-pontachrome azure blue B complexe$’ formed in a slightly acidic medium. The formation constant of the palladium complex was determined spectrophotometrically. The conditional formation constant for the complex at pH 5.5 and 25O was calculated, from the curves of the continuous variation, to be 5.0*1010. It is expected that this reagent will find many applications where a highly sensitive reaction for palladium is desired. The present work was supported in part by a Grant for Scientific Research from the Ministry of Education, Japan Government. A~ul.Cilinl.

Accu. 60 (1972)

PALLADiUM

WITH

PONTACHROME

AZURE

BLUE

85

B

SUMMARY

A new spectrophotometric method for the determination of palladium with pontachrome azure blue B (Color Index 43830) as reagent is described. The palladium complex has maximal absorbance at pH 5.2-5.7 and at 605 nm. Beer’s law is obeyed ; the molar absorptivity is 4.79. lo4 1 mole- ’ up to at least 2.5 p.p.m. of palladium and cm-’ and the sensitivity is 2.2. lo-’ ~18 Pd cm- ‘. The mole ratio of palladium reagent in the complex is estimated to bc 1 : 2. The formation constant of the complex is 5.0. 10” under these conditions. Only copper(l1) and iron(IlI) interfere with the determination of palladium when sodium fluoride is used as a masking agent.

Une nouvellc mkthodc spectrophotomttrique cst d&rite pour Ic dosage du palladium. au moyen de Bleu pontachromc azuri: B (index 43830). L’absorption maximale se situe Q 605 nm, au pH 5.2-5.7. La coloration suit la loi dc Beer jusqu’h 2.5 p.p.m. dc palladium; cocfficicnt d’cxtinction molairc. 4.79. 10“ I molt - ’ cm .. ’ ; sensibilitit, 2.2 - lo- 3 jig Pd cm - ’ : constantc de formation du complexc, 5.0. IO”. En pr&scncc dc fluorure de sodium, sculs cuivrc(I1) ct fcr(Ill) gencnt. ZUSAMMENFASSUNG

Es wird eine neue spektrophotometrische Methode fi_jr die Bcstimmung von Palladium mit Pontachromazurblau B (Farbindex 43830) als Reagenz bcschrieben. Der Palladiumkomplex hat eine maximale Extinktion bei pi-I 5.2-5.7 und 605 nm. Das Beersche Gesetz ist mindestens bis 2.5 p.p.m. Palladium erfiillt ; der Extinktionskoefflzient ist 4.79 - lo4 1 mol- ’ cm - ’ und die Empfindlichkcit 2.2. lo- 3 pg Pd cm- ‘. Das Molvcrhfltnis von Palladium und Reagenz im Komplex wurde zu 1 : 2 ermittelt. Die Bildungskonstantc des Komplcxes ist untcr diesen Bedingungen 5.0’ 10”. Wenn Natriumfluorid als Maskierungsmittel verwendct wird, stijren nur Kupfer(l1) und Eisen(II1) die Bestimmung von Palladium.

REFERENCES 1 2 3 4 5 6 7 8 9 10 I1 12 13 14

F. E. Bcamish. Tulunro, 12 (1965) 743. W. J. Holland and J. Bozic. Anal. Chem.. 40 (1968) 433. T. G. Bunting and C. E. Mcloan, A&. Chem.. 40 (1968) 435. R. Ishida. Bull. C/tern. Sot. Jap.. 42 (1969) 101 1. K. K. Saxcna and A. K. Dcy. And. Cltena.. 40 (1968) 1280. Y. Krrtsubc. K. Ucsugi and J. H. Yoc, Bull. Chem. SW. Jop., 34 (1961) 72. Y. Krrtsubc. K. Ucsugi and J. H. Yoc. Bdl. Chem. Sot. Jop.. 34 (1961) 826. T. Shigcmntsu. K. Ucsugi and M. Tnbushi. Jnp. Anal.. 12 (1963) 267. A. 1. Vogel. A Text-book of Quanrirative Inorgunic Anu1ysi.s. 3rd Ed., Longmans 1961. p. 511. A. Gocminnc, M. Herman and Z. Ecckhaut. Awl. Chim. Acru. 28 (1963) 512. W. D. Jacobs, Anul. Chem., 32 (1960) 512. A. Kawasc, Jap. Atd.. 12 (1963) 714. 0. Mcnis and T. C. Rains. Anal. C/rem.. 27 (1955) 1932. W. D. Jacobs. C. M. Whclcr and W. H. Waggoner. Taluntu. 9 (1962) 243.

And.

Cl:irn. Ado. 60 (1972)

Green.

London,

K.

86 15 10 17 IH IO 20

M. N. A. K. I’. J.

Ut:SUGl.

01orno. /h/l. C’/I~~I. SUN.. Jup.. 36 (lY63) XX‘). C’. Sogani xnd S. C. l3tlilltitCtliIryil. /ltIU/. <‘/lc*I~l.. 20 (lY57) 397. Ci. Marks and t’. 13. thlmish. Atrcrl. C/IOH.. 30 (1958) 1464. I,. Chcng. And. C’hcw.. 26 (lYS4) I UO4. Job. AII~I. Chiw. Y (1028) 1 13. t 1. Y oc ;Ind t.1. I.. JO~ICS. Id. fC,~f/. C/IC~I.. AIIC~/. Ed,. IO (lY44)

‘1’. St+IGllMAI’SU.

I I.

,%I. TAUUSHI