Spectrophotometric determination of beryllium with chrome azurol s

Sl:‘ECTROPHOTOME-MIMIC CHROME AZUROL S

I3>E’I’ERMINATION

01’ BERYLLIUM

WITH

azurol s (3”-sLllpllo-2”, 6”-clicl~loro-3,3’-dimetl~yl-4’-l~yclr~~~~~fuchsons,g’-dicarbosylic acid) has been used for the detection of bcryllium~~~, and has been applied widely for tile spcctropl~otometric determinatic)n of Ixryllium~~-*‘*p 2’ 922; it has also been suggested as indicator in titrations of beryllium solutions”“. The composition axurol S formed in solution and properties of the beryllium complexes with clmm~ were Linccrtain for a long tirne~~~“~~~~1.1and widely different conditions have been prescribed for the sl’e”tropllotornetric clctermination of beryllium with clu-omc azurol S. In tllc present p%pcr, several procedures for this determination are descrilxxl; tllcsc are based on a detailccl stucly of the reaction of beryllium(I1) with chome azurol SIG, wllicli sliowccl that three different complexes of beryllium with chrome azurol S are possible. It is shown that polyvinyl alcohol has a favorable effect on the optical propertics of tlie reaction system in slightly acidic nicdium and that the use of calcium polyaminopolycarboxylic acid chelates as masking agents allows the estabiisluncnt of sensitive and selective procedures. Cllromc

Berylli~wn stnurlnrd. Solutions containing 0.4506 mg Be/ml were prepared from London) ancl standardizecl gravimeberyllium nitrate (Specpure ; Johnson-Matthey, trically as beryllium ammonium phosphate. Cltro,rlze azzrrol S. Teclmical products (J, R. Geigy, Basel) contained kaccs of Ca, Mg, Si, Fe and 15.3:/’ sodium (theor. for pure trisodium salt: 11.4%). Colourccl spots with XF values of o.SG and 0.6s were detected by descending paper cllrornatogra: water mixture as (60 : 30 : IO). The Geigy product was phy from acetic acid : ethanol acicl purified by the method of Langmyhr and Klausen 10, The less soluble tetrabasic dihydrate of chrome azurol S was twice precipitated from hydrochloric acicl (I : I), dried at 30-50” and stored over phosphorus pentoxide. The contents of the active product (G3HteOoSC1, ~.zHzO) in two purificcl samples were 93.57% and 95.4’3/0, evaluated by elemental analysis and by differential potentiometric titration with 0.1 M sodium hydroside; 3 protons of the reagent are titratablc. Aqueous solutions of the reagent were stable for at least two days at pH 1-13. All the chemicals used were of analytical-reagent grade. Various buffer solutions were prepared by mixing I M solutions of the required salt and corresponding .Il?ral. CJ~irn. Actn,

44

(xgGg)

333-344

ncicl: formate (pFI4.t35), acctntc (pH4.8 ors.o), plltllalatc (pH4.75) and citrate (13~4.75). Pyricline-nitric acid buffer (pH 5.0) was prcpwecl from 81.3 ml of twice-distilled pyridi1x2 and 42 ml of conccntratecl nitric acid (rl = 1.39) dilutecl to I 1 wit11 water. Pyriclinc, l~cxan~etl~ylcnctetraminc, tricthanolamine or tris(llydroxymethyl)aminomethanc (sufficient to give I kT solutions on dilution) were dissolved in a little water and the pr-1was acljustccl to 6.7 -+ 0.3 wit11 I M percllloric or nitric acicl before dilution wit11 water to I 1. Polyvinyl alcollol (Mowiol, Germany) wit11 cu. 12 o/o unllydrolysecl acetate groups was used as a 4”k1 (w/v) solution in water.

A I
EQUILIISRIA

OF

l~BRSLLIUM(II)

WITH

CHROME

AZIJROL

s

As was sllown previously 16, tllree different complexes, T3eRl-I -, l3eJ<~~-- and I3eIX(OI-I),Y-, are formed stepwise in solutions containing a lilnitecl csccss of reagent, as a function of pr-r; the three complescs are forniccl between the pH intervals 4.S-5.0. G.4-7.0,9.7--x0.3, respectively. Detergents sucll as polyvinyl alcol~ol, cetylpyriclinium bromide or cetyltrimethylal~itiioniun7 bromide consiclerably increase the apparent molar absorptivity at 11~5.5-8.0 as well as batllocln-omically shift tile absorption masima of the berylliumchrome azurol S complescs (Fig. I). Similar observations liave been made in other systems containing nictal cl.lelates with llighly negatively cliargccl dye anionsl7-10 and in the system uranyl-chrome aaurol S”‘). The particular colour changes are inclicatecl in Table I, which sliows the cliffcrcnces in absorption masima between the particular ligancl forms and the beryllium complcses.

IIowever, the transition of tile reel I-I&“--form to tile yellow HR:‘--form of the reagent can greatly affect measurements below pEr 5, if excess of reagent is present, unless tile pr-r is strictly controlled in both tile standard ancl sample solutions. T RBLE SOhIT<

I:

DATA

ON

UER~LlJ.lM(~~)

CliELATES

\VITII

Cl-IROiGIS

A%UROL

s

_---.pr

COl,tplC.%f

-1.8

6.7 10.0

;;:‘;;

Bd
568

AJ.,IW

l?enge~ut

/OYMI I-1213?-

;c;; 499

BczRe”-

540

I-IR3-

+29

BcR(OI-I)xy-

490

I-II<“-

-129

Gr5m

a’ In the prescncc

of 2 0.5%

polyvinylalcohol.

(um) 69 III

18Ga 61

SPECTROFI~OTOXIETI~IC

T)B?‘EIZ;\IINr\‘L’ION

OF

RC

335

The l,Ir interval 6.5-xo.0 is inore suitable for the determination of beryllium, since the yellow I-II<+-- form of the ligaud which alone exists under these conditions, absorbs only slightly (cJ the clissociation constants of particular l&and formsl”). l)E?‘ISI~RIINATION

Effect

OF DBIZYLLIUM

of the reiprlt

4,9 rf.:0.1

AT pH

corrceutration

urrrl ionic

stw.r@lt

Almost constant absorbmcc is obtained when a 3-5-folcl escess of the reagent is present (c~=z.o~xo--GM; c1~=7*10 -6&f), but a ro-fold e.scess is recommended for ‘I’he concentration of the reagent iu solution is liimitecl by its solupractical purposes. bility and by its absorbance at the wavelength of niasiinuin absorbance of the UeRHcomples (566 nm). ‘I’hc theoretical molar absorptivity for tile 13&Hcomplex of a~=51,300 at 56S nm, earlier calculated for solutions with a large csccss of metal ion, could not bc acliicved w11cn escess of ligantl was present. Molar alxorptivitics lxtwcen 19,500 1_ 300 and 21,q.oo * 250 were oldninecl for reagent concentrations ol I.0 - 2.4. * Io--‘l M ancl metal concentrations of 2.0 * Io-5 Min 0.1 M sodium perclllorate am1 nitrate media, respectively, the sensitivity limits being 4.6-4.2. ng 13e/ml, respectively. Tile influence of ionic strength on the absorbance was negligible for ,u = 1.1 (sodium perchlorate) at pi = 4.9 f. 0.1. However, the alxorbancc considerably increased above an ionic strength of 2, where partial precipitation of tlw red-violet beryllium (II) species and of the esccss of dye occurs. Y’lte mdidity II/‘ J3eer’s law ad the illfhemx of b~lffdY.s 73eer’s law was strictly obeyed for solutions containing IO-&O 116 Be/ml at 56s nm when tlie reagent concentration was more than Io-‘1 M. For solutions without buffers, the absorbance was always interl~olatecl frOli1 nbsorbancc-pIr plots for the pH requested; all the berylliuni(I1) concentrations were taken in account. ‘13ctween the above limits, the absorbance-beryllium concentration plots were always linear even in

________.-_-.__..-_-_.

..-.._

.

Ullf/e,

____---.-_c,

@I

-----_ 5.0 5.0 4.80 4.85 4*75 4.75

hcctatc~ Formatcc

Phtllalatc!~~

n b c cl

Scusitivity limit ia xg Be/cm”

_-.

Pyridinc-nitmtcn+”

CitratcC Pyridinc Acctatc

__-----

(568 WU)

-j- EDTAI~~(~ + EDTA a.“

--__

4.99

CR = 2.4.10-4 Al; CM = 3.0.10-6 0.0~~-0.20 M buffer. CR = IO-’ i,f, CsI = 2 * IO-’ &f. Containing 2.5 - 10-3 M EDTA.

1,1,,335 & 200 19,795 rt: 200

4.05 4.G

1g,ooo

4.0

&

200

“-0,750 & 200 4,950 * 50 2,150 z!.z 50

5.01

--lvr.

fou A = O.OI

18.745 17,200

rt 270 & 300 ____------

4.25

18.4

42.0 4.8 5.25

-

L. SOMMER,

336

V. ItUI3k;

presence of a constanto.o2-0.11 M concentration of various buffers such as pyriclinc, acetate, formntc, phthalate or citrate in the PI-I interval 4.8-5.0. I-Iowever, the apparent molar :Lbsorptivity n1a.y decrease; the interfering effect of buffers increased in tllc order : pyritlinc < acetate N formate -z phthalate -K citra.te (Table II). Pyricline and acetate buffers wcrc used in o.x M concentration to minimize interfcrcnce in the prcsencc of 2.5' ro-‘lM rcagcnt.

tlw

‘l’l~ limiting concentrations causing a relative clevintion in absorbance of & 2% are given in Tables III and IV. The interfercncc of various cations was considerably rcclucccl at 11~ 49 in the lxescncc of 2.5 *IO-:I M EDTA. EDTR is the only suitable masking agent, but a special calibration plot must lx usecl for tile concentration of ED’I’R usccl, since tile absorbance of the ‘I3clCFI- complcs is slightly affectecl by EDTA.

LIhlItINC;

RATIOS

(C,( =: __ _____

2.5’ IO-,’ M; _- .__.._ -____,-.-

.-I gc!uf -... _._^

012

ANIONS Cll” _......._

AND

AGISN’L‘S

AGhlNST .

.._...__..

CT/C I,,.” . ..-. .-...._

CJ./CI,~P . .._. ._......_..... _......._

.._

hlhSI
10-S M) . ._ .._^ _-..._

_^_ .

_. . .._____-

.*I gcn1 .._- .--..-_.-

.

Nitrxtc C.l~loriclc

.1_80

1 PO

Trwtratc

600

1200

0s;rlntc

S11lpl1atc

270 60 5”

150 ‘5 0.5 1500

NTR 15I n-f\ C IYL‘A

Carl.nIiatc l’l10spl1;1tc l-krcll IOKL~C 2500 - _.._..-._. _...._._.._... -.-_ ..._.... 1’ 1311=

4.85;

11~II = ri.(io; TA13l.x =

0.

I

n4 TItlS

.

_._. _ _....-_.._...-_._

-___.. .-

_._ _ ..____

CT/C Ill!” _...-..._ -. . ..-.- ._...

.-._

cz/c Id’ _..__ -- ..-_....._.

I?,0

“5

9

‘5 IO

35 70 25

7 (J

._.. _ ___....._._. -._- .-_..___^.____ _._.__ _.... _.__

Iniffcr.

1 \r

LIhlI’L’INCi (Cl(

-.... _ -.__ .._-.__..__ -... 0.1 AT ClCC!tiltChrfcr.

13151~YLLIUhl

RATIOS

2.5. Io-.i

Cnliou _..-.-.

01’

CATIONS

M;

G,,,, =

c*

/c

I\,.”

AGAINS’I‘

13ILI
10-n fw) Cr/Cllr””

CT/C

C.+I,,*‘?

I,‘?““1

-.._..._. ^ ___._.._.______ ..._ ____._.___.._.______ im 0.0.5

.,_..._ _..._.___ -. . _. -. 1.o

_ -_ ..___._-. 50

)\,\1W

0.1

‘P

0.

t

80

C,I

‘2

25

0.

I

1ocl

0.

t

10

0. I

20

I:@+ “-1.

%t.l\

0.5

I.JCh”+

I

hJi2.t A

5

]3i :I+ 1DClB-t

10

2 ;rmlr 100

I

I”5 50

C;;,“‘t

2

200

Ln:‘+

I.5 3 I

I

y:,.t

<:r:a-t

20

p1,‘+

%ll”f n’lg”-tCa”+, Bn’+

35 300 500

5 5 0. 0.2

I”-5 500 I

.tocl

0.1

100

0.5

500 5oo 5.50

0.2

100

20

500 650 5oo -

300 1’20 I.50

11pit = O.Go; 0.1 MTRIS buffer. 11With ‘2.5.10-3 Af EDTA and 3. IO-3 IW Ca. 0 ~II = 4,90; o.I nf zrcctatc buffer. ‘1 With 2.5.10-3 MEDTA. 0 In tlic prcscncc of 0.05% hyclroxylnminc l~yclrocldoridc. A~nnl. China.

Actn,

4.50

44 (1969) 333-34.t

sooo 2000 -

SI’~CTROI’HOTOhlETIZIC

I’)ETT:I(RlINA’rION

OF

I’3C

337

Recontmenrled pvoccdure azurol S tetrahasic acid Pipette 5 ml of 2.5.10-3 &I (cu. 0.15’;/0 w/v) of chrome solution into a so-ml volumetric flask containing 25 ml of slightly acidic sample solution (IO-2Yo ng Rc). Add 5 ml of 1 III pyridinc-nitric acid or acetate buffer of pr-r 5.0 and dilute to the mark with water. Check the pH of this solution (4.9 * 0. I) and niensure the absorbance at 568 nm after 20 min against a reagent blank preparccl under tlic same conditions. The coefficient of variation was +o.S’):, at tlic cj5%, conficlence level for 1o determinations on solutioils without interfering ions or masking agents in the conccntration interval go/zoo ng k/nil.

Effect

of reagent conce~~itvatiort and ioh strw,@h Only the RezR@-- for111of the chelatc is formed at l>EF6.7 ko.2. Masimal absi)rbance is obtained with a more than two-fold cscess of reagent in pure solution, but a IO-fold excess is rccommendcd. In solutions wit11 an ionic strength exceeding I. I, tllc beryllium chclate flocculates and tl1c dye coprecipitatcs ; tliis can also bc observctl if insufficient reagent is present.

Beer’s law was obcyecl over the same range at pH 6.7 and 4.9 (x0-zS0 ng I3c/nil) when measurelnents were made at 540 and 56s nm, rcspectivcly, for solutions with c1l=2.5* IO-‘1, However, at pH 6.7 less strict pH control was needed. Tile vnluc of tile apparent inolar absorptivity &Z founcl at pi-16.7 f o.2 ( E22= 14,350) was considerably lower than the theoretical molar absorptivity for the clinuclear complcs ~22= 70,350 for 540 mn estinlatecl earlier (822 - 2~3~= 2S,700) 15. Tile sensitivity was 6.3 ~ig/cni~ for A ==O.OI The buffers examined were pyridinc, l1cxan1cthylcnetetran1ine, triethanolan1ine, tris(hyclroxyn1ethyl)an1ino111etl~ane (TRIS) ancl acetate. Acetate clccrensccl the absorbance of the l3e~R~4--chelatc solution as its concentration increased from 0.005 M to 0.2 M, whereas the other buffers tested increasecl the absorbance slightly as their concentration increased. Triethanolamine gave brown-reel colloidal precipitates of colloicl solutions in more than 0.06 M concentrations. The sensitivity for A = 0.01 was G.S ng 13e/cn1” when TRIS buffer was used, conlpared to sensitivities of 7.3-7.5 with other buffers at 0.1 M concentrations. Apparent n1olar absorptivities (Fz) arc between

1.14 and

1.33.10”.

Effect

of varbrcs ions and mashing agents The limiting concentrations of various ions and masking agents causing a rclative absorbance deviation of &-2% are listed in Tables III and IV. Masking agents such as NTA, EDTA, CyDTA, oxalate and 2,3-din1ercaptopropanol decreased the absorbance of the BesR#- complex solutions above PH 6.5 even when a IO-fold excess of reagent was present. Such reagents had less effect above PH IO, but at these pi values the yellow nm,

RH3--form pK,d=rx.?g) However,

of the reagent which the

begins

strongly

calcium(II)-EDTA

to dissociatk

affects

to tile violet

the sensitivity chelate

W*--form

(A,,,

= 596

of the method.

in the presence Allal.

of a slight

excess

Cllilrt. rlcta. 44 (rg6g)

of

333-344

I. .

338

SOhIhIISR,

v.

IaJBliij

calcium(I1) proved to he a suitable masking agent for various ions at per 6.54.~~ Any beryllium boundby m-ni is rcplacecl by calcium(I1) or barium(II), but the latter ions did not affect the absorbance of the BedC2 “---chelate even at Be :Ca(Ba) ratios of I : 500. The recommenclecl proportion for masking is Ca: EDTA = 1.25 : I for 2.5 *IO-~ M EDTA solutions. The limitingconccntrations of various ions with and without calcium(II)-EDTA are shown in Tables III and IV. ‘I’lle rcconlmcncled procedure is similar to tllat given for pry 4.9, except that I M TRIS buffer is adclecl illstead of 1 k? acctatc buffer, and the absorbance is nieasurcd at 540 nm. Uncler tlicse conditions, tlic coefficient of variation was found to Ix + I ‘j/o.

A cliffercnt absorption maximum for the ~IkIi:!“chclate at 6x5 nm, and a consiclerable increase in molar absorptivity wcrc observccl at pH 5.+23.0 in the prcsence of cletcrgents such x.s polyvinyl alcohol, cctyltrimctliylai~i~i~~~niu~~~ bron~iclc ancl cetylpyriclinium broniicle (Fig. I). The bromides were unsuitable bccausc the beryllium chclate tenclecl to form colloiclal solutions. In the presence of polyvinyl alcoliol the violet solutions turned blue if escess of metal was present ; with escess of reagent prewith consiclcrable dicliroic sent, the yellowish-orange colour became brown-green effects.

4

5

6

7

8

9

'fi

&?I-/

Fig. I. pli-nbsorbancc curves in the system beryllium--chrome azurol S for solutions with or without polyvinyl alcoliol (PVR) (rcagcnt blank suldxw2tccl). ,L = 0.1, cIL= 1.0. x0-‘AT, cat 1.0.10-5 Af. Mcasurctl after 30 min. Cut-w I. Grs nm, 0.5% PVA, p 40; curve 2. 615 nm, 0_5”/~ PVA, ,11-r o, tncnsurcd after z min only; curve 3. 5GS nnl, without PVh; curve 4. 540 nni, without PVh; curve 5. 500 nm, without PVA.

The absorbance maximum of the beryllium chelate solutions clepenclecl on the concentration of polyvinyl alcohol but reachecl a constant value of 615 nm above 0.5 0/o (w/v) polyvinyl alcohol; this is a shift of 75 nm comparecl to the wavelength of masimum absorbance in the absence of polyvinyl alcohol. The alcohol had little effect on the absorption spectrum of the lXH3--form of the reagent. .&ad. Chint. Ada, _tL#(rgG9) 333-344

The lm-absorbance plot lmd plateaux which clcpenclecl on the wavelengtl~ for solutions wit11 a ro-fold excess of reagent, i.e. at 1’13 6.1~6.9 for 6x5 nm, pH 4.+-5.0 at $23 nm, or plr 9.S--10.4 for q.c)o--$58 nm. The largest incrcnsc in molar absorptivity was observed at pr-r -6.0.

Tlie alxorl3anc.e at 615 nm and at pH 6.6 rcacl~ccl its maximum after 20-30 min and tlzn remained constant for 5 11. Above a o.50/O (w/v) concentration of polyvinyl alcohol, tlw alc01wl conccntratim did not affect the absorbance ; a ~I.S~/~ conccntmtion was used. Maximum absorbance \vas acllievcd with a ro-folcl cscess of reagent conditions. (CR= 10-‘1 M) uncler the

I%xds IZLWwas obeyed over the range 5-130 ng 13e/iiil at par 6.6-6.9 and at 615 nin in solutions containing I.Io-‘l hd rcagcnt and o.S% (w/v) polyvinyl alcolwl. The absorbance was always incasured against a reagent blank at the same 1x4 value. The apparent molar absorptivity values under thcsc conditions was 52,000, giving a sensitivity of I.75 ng Re/cin~ for A =o.oI. Nitrate and chloride in concentrations corresponding to ~=0.2-1.0 had a ncgligiblc effect 011 the absorbance. Sulpliate precipitated tlie beryllium cliclate from 5 * Io-zi M concentrations, and percl~lorntc decreased tlic absorbance cvcn at p 20.02. Various buffers such as triethanolamine (T&4), tris(l~yclrosyinctliyl)aniinomethane (TIPIS), pyricline and l~exametl~ylcnctctraminc (HMT) were tested ; llesamine had the least. effect on tlie absorbance at px G.6-6.9. Apparent niolar alxorptivities arc compared for various concentrations of buffers in Table V. Hexaminc buffer of pi-i 6.60 in 0.x A4 concentration was selected for practical use. TEA in low conccntrations increased the absorbance but decreased it at higlier concentration; moreover, tlic calibration plot showecl a change in slope at cu. 40 ng 13e/inl (Fig. 2).

hI’PAIZ&N~E‘ AlOLAliAl3SORI’TlVITllZi (Cl10

=

I3ttffcr

5’

ro-”

iv;

CI’VA

1-IMT TRlS Pyritlinc ---

o.q,

(w/v);

VARIOUS CR

=

E,, * IO.’ (G I5 1wt) -__...--__---.-

fir-1

CONCENTR,\TlONS lo-‘1

0.15 ns

6.50

6.01

6.60

‘t.95 *I*PO 4 JJ7

5.85 4.93 .t.Go _t..t8

5.‘@ *t*94 .t . ‘1I 4.36

6.60 6.60 -_--_.-

----~---

-__-

13UFFIsRS

. . _._ .-_

.___--

0.1 nr

--

OF

M)

0.02 nf

__..-__..-._.-_. TEA

=

FOR

0.20

n’r

_-

4.87 ‘1.88

‘+.I 1 .t.25

-..-----___

Effect of interfering

i0lZ.s Current masking agents considerably interfered witll the clielste formation at PH 6.5-7.0 (Table VI), but tile calcium-EDTA ch.elate could again be used for masking the csccss of calcium was not wllen the ratio of EDTA to calcium was 1:1.2-1.3; critical. Tile limiting ratios of diverse ions for a + 2% deviation from the tlieoretical absorbance are sllown in Table VII. Awal.

Chinz. .4cln,

44 (rgGg)

333-344

34”

r

T-

AA

1.0-

TABIX

VI.

LIMITING

RATIOS

_____ .-I &WJt

OF

ANIONS

-__.__-

Sulpl1ntc

sonIl’:

-.-.-

M,\SICING

ACY
.__. -_..-_____

C,ll:no” ___~__..__.__._

C.r/CIlO” .._.. --..--._

_----_-

-

AND

__._.__

.._. ---

, _.__.__.___._

.4 gc71 t --____.

____^.....

5-Sulpllosnlicylat~ Citrntc kxtatc NTA 12DTA CDTA l.~l~Ioriclc

1000

100

AT pII 6.65 ANI> 9.85 -.-.-_.--. ___._.__. __.__. __..- ..__. _.....__ _______

0.2

1000 ‘too0 I’crchlorntc d.+aoo Chloritlc 2550 ‘to00 .*ooo Nitrntc 50 1~110sphatc 15 12.5 Cwlwn;Ltc 30 Tnrtmtc 3.5 200 Oxnlatc 20 -.- ._._ --...-.-._. - .._.._. -___. -.----.I_---.-.. - -...._._-- .-----..--- .___ .___.._ 1’ 13116,C,5 in prcscticc of 0.8O/” polyvinyl ;ilc~liol (0. I M 2wI.s); tlL == 1’ 1’11().&j; c1L=2. 5. IO-” fir: f-ar=10-” Ad.

LIhlITING OF

RATIOS

0.8’;/,

(IO-~

A4

(W/V)

Bc.

FOR

CATIONS

I’OLYVINYL

AGAINST

IO-.’ M rcagcnt,

SC”+

G

y3+ -f&an+

4

22

3 0.2

50

0.1

3-t

“5 30 30

%Il?.’

n&p I_T&W

r\13+ GnJ+In”” ZrIv 2%“’ pb””

2’

4 ; 25

0.1 Ad TICIS,

Cltittt.

Acta.

AT

1X4

6.65

IN

TIIIS

UC&~“’ Ain”+ ]7cW

50 0.5 z? IO 0.15

160 /tz? zt r.to

CO 1-t.

12

160

v’v Cr3.I.

Cd

?+

TiI V Bi3-t Ca’2+ Ba2+ Rqg”;

;: 3 25 60

.++ (~gGg)

615 ntn)

Ni 3+ .1’<12+

20

n Without Ca-EDTR misturc. b With Ca-EDT.4 mixture. .-lmbl.

1 I)

2.5 ‘OS 200 20 15 0. I

ALCOI-101,

85 135 270 305 55

cu

R11RYLLIUhl(

333--3-t.+

15 2 30 2 I 3ooo 1500

---

C+lk.” -._-._.....- --

32

170 310 305 IO 20 -

I’IIl~SI3NCIL

--

CI/Cd’ __..___ -._.--20


acid (PH s--O), IO ml of aqueous Add =j ml of IO- 3 M chrome azurol S tetrabasic 49$ (w/v) polyvinyl alcohol solution and the slightly acidic sample solution containing 5-130 ng I3e to a 50-1111volumetric flask. Dilute with water and add 2.5 ml of 0.1 M disodium-ED?‘A solution and 3 nil of 0.1 M calcium nitrate solution. Shake carefully, and clilutc to the mark add 5 ml of I M hesamethylcnetctran1inc buffer (T>Ir ~6.6) with water. Check that the PH is between 6.4 and 6.7 and measure the absorbance at 615 nm after 20-30 min against a reagent blank. If water is used as reference, subtract the absorbance of tlic reagent blank from the total absorbance. The coefficient of variation was found to be _t 1.5?{, at the q5’){, conficlcnce level, calculated from I0 pure solutions containing IO--x00 ng T3c/nil. l~&TERMINATION

OF RERYI,I.IUhl

.AT PH IO.O+O.Z

at pH 97-10.4 in solutions with a Only the T3el<(OM) xy- chelate is fornicd sniall escess of reagent. l’he cliffcrcntial curve sliowecl *;iaxiniuni absorbance at 490500 nm. Rcer’s law was obcycd over tllc range lo--r&) ng T3e/n11at l>~r 10.0 +o.2 with The apparent molar absorptivity was 25,300 + 200 a 2.5.x0--” 1M reagent solution. (500 nm, estrapolatecl value), giving a sensitivity of 3.6 ng Re/cmz for A =o.or.

IZffcct of ionic

strength,

blrffe~s and diverse

ions

The amn1onia-an1n1onium chloride buffer used to adjust the pH had very little effect on the absorbance; the apparent molar absorptivity increased fro111 25,900 for 0.02 M buffer to 27,100 for 0.2 M buffer. Inert salts such as nitrate or perchlorate had no effect up to /~=2, but further increase in concentration caused the formation of colloiclal solutions or precipitates. Masking agents again interferccl seriously (Table VI), but the calciun1(11) and barium(II) chelates or NTA, EDTA or CDT.4 did not interfere even at ratios CC,,/CIW or TABLE

VI I 1.

LIhlITING (IO-~

RATIOS nr

Bc,

-_--._-____ Catio?b ____-_--_..._._

Ca”+ 13.22.t X11?+

Ccl2+ I-r&p+

ChTIO.NS

AGAINST

13lSRYLLIUXI

_ _._. __..___-_-_-.--~-----_-.-

CZIC

cu2+

Mg”+

OF

2.5. 10 -4 nd rcagcnt. 0.1 M buffer IlC __..__.

0.03

30 50 100

I

2.5 I 2 :!

C*IC13P ..-----_--._ 90

.too 6.50

Tn3+ %rlv Th” PL,‘-’

260

\rr \’

3’0 25 35 I6 *7

0.15 2

;;

Pcl’+

7.5

550

ISa+ Cr”f 1J&“f Mnz+ I;c”f CO”+

Ni2.t

pII

9.85

.._____ -.__--- ---- ---_-

Cdio,r _._.. ..__._. ___

so0

Sc3.t yac La=rAl”-+ Gas+

0.2

___.__

AT

; 500 nm)

CS/CIl~? _.._ -_---.-

2 0.1

4

0.1

I0 2

0.15 ? 2.5 0.4 7.5 7.5

..-...-

-.--

-

CrIC nu” . . -.. .-_---_

3.10 4

‘S 75 185 50 3 I*- 5 ” ro;soc I62 IGO

-t50 900

----_____---* In the prcscncc of cclr = 3 - 10-s AI; CCDT,~ = 2.5. x0-3 M. h In the prescncc of o.or”/J BAL. c In the prcscncc of o.o05O/~ hydroxylamine hydrochloride. Awcl.

CJrinz.

.*f ctn,

44 (rgGg)

333-344

CDTA and calcium nitrate in tlie ratio I : 1.2 were of 50 or 100, respectively. USCCIto mask various intcrfcring ions at tllis pry (TableVIII). Hyclroxylamincdecrcascd ant1 2,3-dimcrcaptopropanol decreased that of the in tcrfcrcncc of urnnyl ion, cl~ron~iuni(III). cllrr/cIl~!

To 5 ml of 2.5. IO-:' M chrome azurol S tctrabasic acid rcaffcnt in a so-n11 volumetric flask, add 20 ml water, tlic sliglltly aciclic or neutral solution of sample containing 10-IS0 ng Be, 5 ml of 2.5 *Io-3 M CIYl’A, 5 ml of 3 * xo-3 A!! calcium nitrate ancl 5 ml of 1 PI ammonia-ammonium cllloricle buffer. Dilute to tbc mark with wntcr. and nicasurc tlie almnkmcc at 500 nni after 20 min Cllcclc tliat tlic lm is 9.S-x0.1 against a rcqent l>l;ml<. ‘I’lle cocfficicnt of variation was & 1 .sr%, for 10 pure s!)lutions containin,q so150 ng lk/llll.

In their work on tlic determination of beryllium with chrome amrol S, Srx,vrzlcSIIII~I_EIZ:~~‘* suggcstecl that lm 6.0 (pyridinc buffer) was optimal. A similar 1X-LWas rccolnmclldcd by SINHA ANL‘,DE\‘“, but changes in the px-rinterval 4,0-G.S were said not to be critical. WOOI,‘” earlier recotnnieticlccl pH 7.0 (anitiioniuni acetate), KA1’sum ct al.’ 1. ions pE-L5.S (acetate buffer) while Uhllmo*rozl suggested alkaline nicclium. Interfering were separatecl by osinntc precipitation or by anion cxcliangers. On tllc otlm- hand, preferred pi 4.4-4.6 in the presence of acetate buffer and EDTA MLK~.WIN cl czZ,‘~~l(J as masking agent, ADnnrovIE et ad. *‘I pH 4.5, and l’1\lCALNS7~*pH 4.6 in tlie presence of acetate, HDTA and ascorbic acid. As is shown above, chrome azurol S is one of tile most promising reagents for tile spectropliotometric cleternlination of beryllium but tile conditions of tile imcthod tnust be carefully controlled. At pH 4.9ho.1 in tile presence of liniited concentrations of EDTA, the determination of bet-yllitnn is reasonably selective, but tile absorbance is consiclerably affectecl by various buffers or sligllt PI-r changes and tile absorbance of the H&“--fornl in escess of the reagent consiclerably increases tile total absorbance Pyricline-nitric acicl or acetate buffers (0.1 AI) of the beryllium con~plex solution. of pH 4.9ko.1 arc suitable. Beryllium in the range IO-2So ng may be cletcrmincd at 56s nm under these conditions with a relative error of less than & I.oO/~. The spectropl~otonietric sensitivity is 4.G5.3 ng Be/cm” for A = 0.01. The cleterniination of berylliutn at pH 9.S-10.1 in tile presence of anitmoniaatmtnoniutn chloride buffer or in unbuffered solutions is also possible when interfering ions are screenecl by tile calcium(II)-CDTA chelate. Beryllium in tile range IO-ISO ng may be cleterminecl wit11 a + 1.50jo error at 490-505 11111. The spectrophotometric sensitivity is 3.S ng Be/cm” for A =O.OI .The strongly absorbing R”--form of the reagent may seriously interfere if tlie prescribed PH is overstepped. The nlost protnising procedure is at PH 6.5~6.9 in tile presence of ca. o.S% (w/v) polyvinyl alcohol and 0.1 M l~exan~etl~ylenetetran~ine buffer. Beryllium in tile range 5-130 ng tnay be cleternlined at 6x5 nnl wit11 a + 1.5% error with the best sensitivity (1.75 ng Be/cm” for il = 0.01). Triethanolamine tnay also be used as buffer ~1.4~ ANI,

A?&. Cl&z.

.4&z,

44 (r&g)

333-344

ST’ISC1’ROPHO’I’O~IE-MIMIC

I.)I~l’EHhfINATION

OF

l!k

343

but a slope change is then observed on the calibration plot at 40 ng Fk/ml. A similnr observation has been nxdc for tllc clctermination of beryllium wit11 crioclwomcynninc of various ions can be remwccl by the R (C.I. Mordant Blue 3)5’. The interference calcium--EDTA chclate. Without polyvinyl alcol~ol at pH 6.5-6.9, ineasurcmcnts can be made at 540 nm in tile lw2scncc of 0.1 M tris(l~ydrosy~netl~yl)nminomctlianc buffer, but tlic sensitivity is lower (6.S ng 13c/c1nz for R =o.oI).

Tlw well-known clctermination of beryllium with clironie azurol S may 1x2 carried out at pEr 4.9 + 0. I (pyridine or xctate), at pki 6.7 &- 0.2 (‘flond to tile sole presence of presence of polyvinyl alcol~c-A. three

particular

vinyl

a.Icol~ol,

nni. EDTA, proccclurcs.

coniplcses tlic

of

Ca--1SDT.A

lx~rylliuni

wit11

cln-omc

muI-

S.

In

prcscnce

of

polJ’-

1.75 ng 13c/nll for an absorlx~~cc of 0.01 at 6x5 and Ca-CD’fA are cffectivc masking agents in tlw different

sensitivity

Ixacllcs

La cl&x-mination bicn connuc clu b&yllium avcc le chronic-azurol S peut Gtre faitc clans diffckcntcs conditions: rl un l)H de 4.9 + 0.x (pyriclinc ou ac6tatc), (i un pI_1 A un pkr de xoto.2 en solution aqueusc, h un dc 6.7 +o.z (.SO1u t ion dc tampon TRIS), p1-Lde 6.5 ko.4 (l~~sanii?ti~ylc\nc t
Die wolilbekannte 13estinimung van Beryllium mit Clirolnazurol S kann bci den drei pH-Wcrten 4.9, (5.7 uncl 10.0 entsprccliencl clcn drei besondcren I
5 S. N.

SINHA AND A. Ii. DEY, J. Idiau Chew. Sot., 39 (rgb) 4Gg. 0 S. C. SRIVASTAVA AND A. Ii. DEY, J. Iuorg. N,ucl. CJleru., 25 (1962) 72. (rg63); ~VUC~. Ski. Abstv., 7 1’. PAKALNS, .~~zrstr. At. Emrgy Co~rzru. .4~Bc/Tn~-r~~

17 (1963)

No.

14132.

Amzl.

CJrim.

Acta,

44 (r&g)

333-344

344

I-. SOILIMEIZ,

V.

KUBti~