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Spectrophotometric determination of aluminium with chrome azurol s
ANALYTICA
CHIMICA
ACTA
SPECTROPHOTOMETRIC CHROME
AZUROL
57
DETERMINATION
Or;
ALUMINIUM
WITH
S
I’. PAKALNS
Aust~dian (Received
Aiosn’ic E?~rgy Cotnnhsiota, 1964)
RescirrcJr Esiablishmed,
tatccrs Heiglrts,
N.S. W. {Arrstralia)
&lay 1xtl1.
Methods commonly used for the spcctrophotomctric determination of aluminium ilavc been summarized by SANDELL 1. The most important reagents are aluminon, eriochrome cyanine R and 8-hydr~xyquin~~n~. The aluminon method is based on the formation of a coloured lake with aluminium and has the disadvantage that heating is required, and that experimental variables must bc carefully controlled to ensure reproducible results. The 8-hydroxyquinoline method is often too lengthy for routine use. Eriochromc cyaninc R is more than three times as sensitive as aluminon, but can be used only under very rigid cxpcrimcntal conditions. ICASHKWSKAIA A?~;D MUSTAFIE;~ used chrome azurol S (C.I. No. 723, also known as solochrome brilliant blue B, and polytrop blue R, or sodium salt of 3”” sulfa-z”,G’‘-clichloro-3,3’-dimethyl-4-hydroxy fuchson-5,5’-dicarboxylic acid) to determine aluminium in steels and aluminium bronzes. They measured the absorbance of the aluminium-chrome azurol S lake at 530 rnp, where Beer’s law is not obeyed. By choosing a wavelength of 567.5 rnp for absorbance measurements, the aluminiumchrome azurol S complex was found to obey Beer’s law from o to 1.2 ,ucg Al/ml. Chrome azurol S reacts with aluminium at room temperatures, thereby eliminating the heating needed with some other lake-forming reagents. The present investigation shows that chrome azurol S is a fairly sensitive reagent for the determination of aluminium, and is superior to aluminon and criochrome cyaninc R for the direct spectrophotometric determination of aluminium in mixtures of diverse ions. EXPERIMENTAL
Ap@watus
and reagents
A Unicam SP Goo spectrophotometer with I-cm glass cuvettes was used in all experimental work. Clrro?j,teuzttrol S sol&ion, 0.165%. Dissolve 0.165 g of chrome azurol S (Geigy (A/sia),Pty.Ltd.) in water and dilute to zoo ml. Acetate btcffer soWion, @? 4.60. Dissolve 238 g of sodium acetate trihydratc in 500 ml of water, add x02 ml of glacial acetic acid, and dilute to I 1 with water. When 5 ml of buffer solution was diluted to 25 ml the PH was 4.6. Standard alumi?tiz~m sohtio?t, IO pg/nrl. Dissolve o.ozoo g of pure aluminium foil in 20 ml of 2 M hydrochloric acid by heating gently, and dilute with water to 2 1 in a volumetric flask. Anal. Chint.Acta, 32 (rgGg) 5743
58
I'.PAKALNS
Recomnrended pvoceduve Transfer an alicluot of the slightly acid sample solution (1-35 pg Al) to a z5ml volumetric flask. On a separate aliyuot determine the amount of 10% sodium hydroxide required to neutralise the free acid to methyl orange indicator. Add 1.0 ml of IO/, ascorbic acid and 5.00 ml of acetate buffer solution. Add the predetermined amount of roe/, sodium hydroxide. Dilute to about 20 ml with dater. Add x.0 ml of 2% sodium thiosulphate solution, zoo ml of 0.165"/~ chrome azurol S and dilute to volume. Measure the absorbance within IO min against a blank at 567.5 rnp in I-cm cells. If more than 2 rn6 of copper, 4 mg of iron, or molybdenum, thorium, titanium, tun@en and vanadium is present, special precautions must be taken (see Shrdy of intc7fe7emcs). DISCUSSION
Sensitivity
a?ad stability
of the method
The aluminium-chrome nzurol S lake when measured against the blank, has maximum absorbance at 545 rnp (Fig. I). However at this wavelcn@h the absorbancc-wavelength curve does not pass throu@ the origin. It was found that when a wavclcn@ of 567.5 rnp was used, a curve was obtained which did pass tluou&h the . . origin. At 567.5 rnp the molar absorptivity of the lake is 2r.G * 103 (200), corrcspondin6 to 0.00125 pg Al/cm2 on the Sandcll scale. Beer’s law is obeyed to at least 1.2 pg Al/ml, but at 1.6 pg Al/ml there is a 2% deviation. ‘I’hc absorptivity varies considerably with change in pH, concentration of chrome azurol $5, and buffer. When only
Fig.
I 0.7-
L
O530
t 540
I
I
550
560
WAVELENOTH
(mp
l:ig. 1. A\1>Yorb;mcc-wnvclcliKth (U) blank vwsw
water.
1
I
570
590
cIIrvcs.
I%xd
)
Dig. 2. Absorbuncc-pH Curve. to&dg ml, at 5Go rnp, t-cm cuvcttcn.
25
A ML Clrirn.
Acta,
J
590
32 (1965) 57-63
Al, 0.05
volun~c 25 ml, I -cm cuvcttcs.
ml
lmffcr.
2 1111o.r6s'~0
chrome
(I\) Ala+ VCVS~~S blank, nzurol S, final volume
DETERICIINATION OF Al WITH CHROHE AZUROL S
59
0.05 ml of buffer solution i= ., used, the molar absorptivity increases to 38.4 - 103 (0.0007 rug Al/cm* on the San&l1 scale). At the specified pH of 4.6 the aluminium-chrome azurol S lake is formed instantly. The absorbance decreases slowly on standing (2% per hour), but is somewhat less stable when interfering ions are present. The stability of the lake was tested in the temperature range 15” to 35” and found to be stable. The absorbance decreases by I y. for each x0 rise in temperature, when measured against the blank. of varying reagent concentrations A decrease in the concentration of the buffer solution increases the absorbance of the lake. A change from 5 ml to z ml of buffer solution increases the absorbance by 20%, and a change from I ml to z ml of the reagent increases the absorbance by 55%. However it was impracticable to raise the dye concentration above o.or4°/0because of the high blank absorbance (0.510 at o.ox~~/~ dye). Effect
Choice
of pi-f
The absorbance of the aluminium-chrome azurol S lake increases gradually with increasing PH and reaches a maximum at pH 5.8, after which the absorbance drops very sharply (Fig. 2). KASHKOVSKAIA AND MUSTARIK~ used an ammonium acetate buffer solution of PH 5.12. The pH value of 4.6, which is in the middle of the sodium acetate-acetic acid buffer range, was selected in the present work to minim& any PH changes caused either by free acid or free alkali. Additions were made to solutions containing 2 ml and 5 ml of buffer solution, and from the results obtained (Table I), it was decided to use 5 ml of buffer solution. In addition, the interference of iron(II1) was much larger at pH 5.x than at pH 4.6.
RECOVRRY
017
111 AND
Added
CHANGISS
5
-_--._._ Nil 0.x ml IO M &-ICl O. I ml IO nr N.IOH
OP
1M
ADDITIOS
Al’TRR
ml buffer
OlJ
2
PRIZE
ACID
ml buffer
AND
Al forcnd (pg)
pt1 _-.-
20.0
4.60
21.0
4.49
20.0 22.3
4.63 4.35
---_-
19.5
Interference by diverse ions Many elements form strong Cu2+, Fea+, Th4+, Ti4+, and Zr4+. various masking agents (Table II). The interference of iron(II1) ascorbic acid is sufficient to mask solutions which contain more than
j-69
x8.3
ALKALI
__.--
PH
Al found (pg)
FRILI!
4.90
colours with chrome azurol S, for example, Bcs+, Many interferences can be minimiscd by using can be masked by ascorbic acid. One ml of 1% 4 mg of ferric ion. To determine aluminium in 4 mg of iron, proportionately more ascorbic acid Anal. Chinr. Acta, 32 (xgGg) 5743
Bon+
20.0
Bin+
20
C.hz+ aa+ COW Cr3+ Cm*
20.0
I+3
20.0
20.2
20.0
20.0
20.0
19.3 r8.g
32-7 .O
20.0
2.0
20.0
10.8
1.0
20.0
10.0
10.0
F&PI.
Mlla+ Mo(VI) Mo( VI) Mo(VI) MO(W)
10.8
-
I().8
--I
.).C
20.0
20.0
S-0
20.0
1H.c)
10.0
20.0
18.8
10.0
-
20.0
-2
30.0
0
20.0
2=
0.5
10.0
I.0
20.0
-
3c 20
1.0
10.0
-
3c
2.0
20.0
19.7
2.0
20.0
20.0
2.0
20.0
20.0
G* 5
20.0
18.2
0.5
‘20.0
22.2
11
0.5
10.0
12.2
22
‘10.0
Z‘f.‘i
22
X0.0
0.2
20,O
2.0
20.0
2.0
20.0
1cJ.cJ
‘L.0
20.0
1.0
20.0
iQ.44.
0.2
20.0
2 ‘) . I
0.019
20.0
II.2
1:-
0.038 0.09s 0.5 1.0 2.0
l?O4”-
20.0
G,t
20.0
2.0
20.0
19.8 19.0 lg.0
20.0 20.0
--------.-a BuIIcr ncldcrl lxlorc ;rucurbic acid; 5 1n1 of .z(;/,, N&i&a. 11 2.5 In1 of I 0/0 ascorbic acid atlclcd. 0 0.5 mg PO43- rrcldr:d to wcnlcly acid solution. d 0.5 ing POda- nddccl. 0 Without: ascorbic ncid. f 1) nrg Cal+ acldcd. And.
Chim.
Acta,
32 (1965)
5743
-2 0 0 -9
Id~.‘~
20.3 lg.G 20.6 3G.o lg.8 lg.8
I
2;-
l’O,jJ -
Gb
2.0
1.0
PO.1" -
G’J
005
0.
p -
;‘a
-
2.0
‘ri4
W(VI) ZllSk
1.
-
10.0
‘1’1, 4 I.
U(VI) V(V) V(V)
1 OB
20.0
1.0
C
-
10.0
2.C)
hIKa”
20.0
21 -42
- 70 -go I
-2 --5
DETERMINATION
OF
Al
WITH
CHROME
AZUROI.
s
61
should be added, and it is necessary to prepare standard aluminium solutions which contain an amount of iron equivalent to that in the sample aliquot. Copper can be complexed satisfactorily with sodium thiosulphatc. One ml of 2% sodium thiosulphate is sufficient to complex 2 mg of copper( and proportionately more of the sodium thiosulphate solution should be used for larger amounts of copper. In slightly acid solutions ascorbic acid has a tendency to reduce Cu”+ to Cu+ forming a precipitate. The maximum amount of copper(I1) which can be tolerated in the recommended procedure is 2 mg. It was found that at pH 4.6 copper(I1) is not reduced by ascorbic acid, and by changing the order of addition buffer solution followed by ascorbic acid - it was possible to determine aluminium in solutions containing larger amounts of copper. Molybdate ion interferes seriously, but the interference can be overcome by procedure should be used: to the complexing with phosphate ion. The following slightly acidic solution (1)~ x.5) add 0.5 mg of phosl~hatc ion and let it stand for 5 min. Add x.0 ml of I(/,, ascorbic acid, shake, and immcdiatcly add 5.00 ml of buffer solution. Continue as in the rccommcnded procedure. Thorium interferes to a large extent, and the interference is proportional to the amount of thorium present. Titanium forms a strongly coloured complex with chrome azurol S. The interference in the microgram range can bc masked by the addition of 0.5 mg phosphate ion. Tungstate reduces tile alurninium absorbance, but the addition of calcium makes the interference negligible. Vanadium(V) interferes slightly, but vanadium(IV), which is formed by reduction with ascorbic acid, interferes seriously. ‘I’hc interference of various neutral salts was stutliecl at the 20 pug of aluminium lcvc!l, by measuring the absorbance against the stanclard blank (Table III).
Rcfivoducibility of the method Ten replicate dctcrminations were maclc at the 20 ,ug of aluminium level using the recommended procedure ; the relative standard deviation was -& 0.4%. COMPARISOS
cyanine ferences
BETWEISN
CHROME
AZUROI.
s,
ERIOCHROMII
CYANIND
13,
AND
ALUMINON
The procedures used for the determination of aluminium with eriochrome li ancl aluminon have been described prcviously”fQ. A comparison of interin the 3 methocls is given in Table IV. The results show that the eriochrome A~ad.
C/rim.
Ada,
32 (r9G5)
5743
I’.
62
COSll’hl~1SO.N n1: ISTl?HI~I~I
__-__-
__.. _-_-
. . . . . . ._---.
--
.._. -_
crrw
Ilclativc
_- _ _-_.Clitwtir uziwol (20 pg/2s ml) ._..
..--...--_____ -
HIPAC.IZNTS ---_
._---
--
(IO /lR/5fl .___ - ___.
_-.... -...-
-,
+
--.-_--..--..
--
.
Nil
1
ml
.
.-...-
c1r
I
iv
I-I(‘.1
I ml of I III Nat )1-l _-____....._.-.-. _.._--
-.
..-
20
-!-
too Ho
>.
.+.
1rm
>
-I-
ran
-t- 25 + 5 .-_ 4
-I-
-
(J IO
0
-I-
2
4
-
(J
7 .I- I ‘)
j..dZ .__ 1
.I-
-
-t_--
I 2
-....
._
.(.O ‘I.5
4.7 .__..._
.
_.._._ - .._...
t,
II
70
_, _.._._., ___._.__.. _.
.
.-
._
3
.___.____ ..__. _
_.,._.____.__.
I:‘rioi*hromc
p-1 . _. .._-.
10.0
10,s .._.. --.-.-
-
tr11)
t 8 -+ I 1 .t- 5
;!I
.o
-.......-..
/.&/so
-
rcziirof S __ _ _
-.
._--._.
(20 -__---_-__
_-
_....
PU -.- . -...
WI)
I
..___ ..-.__.
C~?irr~~~if
.___ -__ ___._- ..__- --__ cyutiitae It .Iluttiir~o~i
0
.
.-...
_-_-__
--
1
..-..
--
--
0
.-.. -----
.. .
0
I
- I . .. 2
A tltlrrl
---
-. -
(%,) _......____._____~ S Iivioclitvmre
0
- -..__ -
PAKALNS
cyci?iirit* It
. _. __.....-- _.-_._ pfi PC ..___-__ .___._._. _..- .._ . _ f-J.0 I0.C)
13,” fJ.0 .._____.________
5.7 CJ.7 .._.- ._.. .___..-__
cynninc 12 nnd alunlinon mcthocls iirc subject to large crrws by many foreign ions, in particular clwomium ancl cobalt, whicl1 must Ix complctcly rcmovcd. Even small amounts of phosl~liatc intcrfcrc seriously in tlic criochromc cyimitlc R mcthocl. Small amounts of free wicl or free alkali produce ncgligiblc errors in tlw chrome neurol S mctlwcl, but very Iargc errors with criochromc cyanine 1C (Table V) wl1ich rccluircs prccisc p1r wljustmcnt. For tliis reason, tlic criochromc Cplillc 12 procedures recon-micnclctl for tlw clctcrmination of :iluminiuni in magnesium iLllOyS”, zinc metal(~, and iron orw3 , all USC strictly controllccl amounts of acid for dissolution and slxcified sample aliquut sizes. On tl1c basis of sclcctivity , simplicity, and rapidity, cln-omc uzurul S appears to bc tlic most suitnblc rcngcnt yet lxop&xl for tlw routine spectrophotonictric determination of aluminiuni. even tliougli it is less sensitive than eriocliromc cyanine I<. As an exnmplc of tlic versatility of the chrome azurol S sp”ctrophotomctric metllocl, aluminium was dctcrmined directly in a permanent magnet ulloy (13.C.S. Sample 233, C0-23.7’j/~, Ni-rI.z’j/,, Al-G.gSo/o,Cu-~.r~~,,Ti-O.8~/,,Mn-o.2o/o,Si-o.~o/o, Fc-51.2%). The result found was 7.04 & 0.03% Al, wl1icl1 comprcs favourably with
L)ETERMINATION
OF
Al
WITH
CHROSIE
A%UROI,
s
63
the certificate value of 6.98% Al. Both the criochrome cyanine R and aluminon methods failed when applied directly to this alloy, because of the interference of cobalt. SUMMARY A comprehensive investigation of the spcctrophotometric determination of aluminium with chrome azurol S is clcscribccl. No heating is required for colour formation, and the method is considerably more reproducible and selective than either the eriochrome cyanine I< or aluminon methods. In the presence of suitable masking of agents, only 13@+, %r4+, and F- cause serious interference. A molar absorptivity 21,500 at 567.5 rnp was found for the aluminium-chrome azurol S lake, with a relative standard deviation of -& 0.4% at the 20 pg Al level. I3ccr’s law is obeyed from o to 1.2 ,ug Al/ml.
L’auteur dbcrit une mC_thodc de dosage de l’aluminium au moycn de chrome azurol S. Ce 1xocCdC ne trCccssite pas de chauffage; sa rqxoductibilitc5 et sa shlcctivitb sont mcilleurcs clue cellcs dcs mCthocles A l’&iochrome cyaninc R ou i‘l l’aluminon. En pr&encc dc r&ctifs dc masquagc approl>ri&, seuls 13e”+, %r’l+ ct l;- @nent s&-icusemcnt. La loi de I3cer s’applique de o h 1.2 pg Al/ml. ZUSAMMENI’ASSUNG
Eine ausftihrlichc Untcrsuchung dcr spektrall~hotometrischen 13estimmung cles Aluminiums mit Chromazurol S wircl bcschricbcn. Fiir die beniitigtc Farbbildung ist kein ErwZrmen erforderlich. Die Mcthoclc bcsitct cinc lxssct-c ICeprocluzierbarkeit und ist sclektiver als die Eriochromcynnin R- oclct Aluminon-RIethodc. In Gegcnwart von brauchbarcn maskiercnclcn Rcagenticn veruxsachen nur 13e”+, %r4+ und I;ernsthafte StBrungen. Die molarc Estinktion fiir den Aluminium-Chromazurol SLack betrug 21500 bci 557.5 rnp, die rclativc Standarclal>wcichung 0.4% bci 20 pg Aluminium. Das Iseerschc Gesetz wircl von 0-1.2 pg Al/ml befolgt.
E.
13. SANVELL,
Colorin~elrir
I~elernrinulio~r
of Traces
of dlclais,
Irltcrucicmx.
N*‘cw York,
1959,
1’. 2 rg.
I.. C.
IKENHIJHRY
hNV
A.
‘lb40~hS.
flwd.
C/rcw2.,
23 (1951)
18of1, /Irriil. Cirim.
Actrc,
31 (1965)
57-63
CHIMICA
ACTA
SPECTROPHOTOMETRIC CHROME
AZUROL
57
DETERMINATION
Or;
ALUMINIUM
WITH
S
I’. PAKALNS
Aust~dian (Received
Aiosn’ic E?~rgy Cotnnhsiota, 1964)
RescirrcJr Esiablishmed,
tatccrs Heiglrts,
N.S. W. {Arrstralia)
&lay 1xtl1.
Methods commonly used for the spcctrophotomctric determination of aluminium ilavc been summarized by SANDELL 1. The most important reagents are aluminon, eriochrome cyanine R and 8-hydr~xyquin~~n~. The aluminon method is based on the formation of a coloured lake with aluminium and has the disadvantage that heating is required, and that experimental variables must bc carefully controlled to ensure reproducible results. The 8-hydroxyquinoline method is often too lengthy for routine use. Eriochromc cyaninc R is more than three times as sensitive as aluminon, but can be used only under very rigid cxpcrimcntal conditions. ICASHKWSKAIA A?~;D MUSTAFIE;~ used chrome azurol S (C.I. No. 723, also known as solochrome brilliant blue B, and polytrop blue R, or sodium salt of 3”” sulfa-z”,G’‘-clichloro-3,3’-dimethyl-4-hydroxy fuchson-5,5’-dicarboxylic acid) to determine aluminium in steels and aluminium bronzes. They measured the absorbance of the aluminium-chrome azurol S lake at 530 rnp, where Beer’s law is not obeyed. By choosing a wavelength of 567.5 rnp for absorbance measurements, the aluminiumchrome azurol S complex was found to obey Beer’s law from o to 1.2 ,ucg Al/ml. Chrome azurol S reacts with aluminium at room temperatures, thereby eliminating the heating needed with some other lake-forming reagents. The present investigation shows that chrome azurol S is a fairly sensitive reagent for the determination of aluminium, and is superior to aluminon and criochrome cyaninc R for the direct spectrophotometric determination of aluminium in mixtures of diverse ions. EXPERIMENTAL
Ap@watus
and reagents
A Unicam SP Goo spectrophotometer with I-cm glass cuvettes was used in all experimental work. Clrro?j,teuzttrol S sol&ion, 0.165%. Dissolve 0.165 g of chrome azurol S (Geigy (A/sia),Pty.Ltd.) in water and dilute to zoo ml. Acetate btcffer soWion, @? 4.60. Dissolve 238 g of sodium acetate trihydratc in 500 ml of water, add x02 ml of glacial acetic acid, and dilute to I 1 with water. When 5 ml of buffer solution was diluted to 25 ml the PH was 4.6. Standard alumi?tiz~m sohtio?t, IO pg/nrl. Dissolve o.ozoo g of pure aluminium foil in 20 ml of 2 M hydrochloric acid by heating gently, and dilute with water to 2 1 in a volumetric flask. Anal. Chint.Acta, 32 (rgGg) 5743
58
I'.PAKALNS
Recomnrended pvoceduve Transfer an alicluot of the slightly acid sample solution (1-35 pg Al) to a z5ml volumetric flask. On a separate aliyuot determine the amount of 10% sodium hydroxide required to neutralise the free acid to methyl orange indicator. Add 1.0 ml of IO/, ascorbic acid and 5.00 ml of acetate buffer solution. Add the predetermined amount of roe/, sodium hydroxide. Dilute to about 20 ml with dater. Add x.0 ml of 2% sodium thiosulphate solution, zoo ml of 0.165"/~ chrome azurol S and dilute to volume. Measure the absorbance within IO min against a blank at 567.5 rnp in I-cm cells. If more than 2 rn6 of copper, 4 mg of iron, or molybdenum, thorium, titanium, tun@en and vanadium is present, special precautions must be taken (see Shrdy of intc7fe7emcs). DISCUSSION
Sensitivity
a?ad stability
of the method
The aluminium-chrome nzurol S lake when measured against the blank, has maximum absorbance at 545 rnp (Fig. I). However at this wavelcn@h the absorbancc-wavelength curve does not pass throu@ the origin. It was found that when a wavclcn@ of 567.5 rnp was used, a curve was obtained which did pass tluou&h the . . origin. At 567.5 rnp the molar absorptivity of the lake is 2r.G * 103 (200), corrcspondin6 to 0.00125 pg Al/cm2 on the Sandcll scale. Beer’s law is obeyed to at least 1.2 pg Al/ml, but at 1.6 pg Al/ml there is a 2% deviation. ‘I’hc absorptivity varies considerably with change in pH, concentration of chrome azurol $5, and buffer. When only
Fig.
I 0.7-
L
O530
t 540
I
I
550
560
WAVELENOTH
(mp
l:ig. 1. A\1>Yorb;mcc-wnvclcliKth (U) blank vwsw
water.
1
I
570
590
cIIrvcs.
I%xd
)
Dig. 2. Absorbuncc-pH Curve. to&dg ml, at 5Go rnp, t-cm cuvcttcn.
25
A ML Clrirn.
Acta,
J
590
32 (1965) 57-63
Al, 0.05
volun~c 25 ml, I -cm cuvcttcs.
ml
lmffcr.
2 1111o.r6s'~0
chrome
(I\) Ala+ VCVS~~S blank, nzurol S, final volume
DETERICIINATION OF Al WITH CHROHE AZUROL S
59
0.05 ml of buffer solution i= ., used, the molar absorptivity increases to 38.4 - 103 (0.0007 rug Al/cm* on the San&l1 scale). At the specified pH of 4.6 the aluminium-chrome azurol S lake is formed instantly. The absorbance decreases slowly on standing (2% per hour), but is somewhat less stable when interfering ions are present. The stability of the lake was tested in the temperature range 15” to 35” and found to be stable. The absorbance decreases by I y. for each x0 rise in temperature, when measured against the blank. of varying reagent concentrations A decrease in the concentration of the buffer solution increases the absorbance of the lake. A change from 5 ml to z ml of buffer solution increases the absorbance by 20%, and a change from I ml to z ml of the reagent increases the absorbance by 55%. However it was impracticable to raise the dye concentration above o.or4°/0because of the high blank absorbance (0.510 at o.ox~~/~ dye). Effect
Choice
of pi-f
The absorbance of the aluminium-chrome azurol S lake increases gradually with increasing PH and reaches a maximum at pH 5.8, after which the absorbance drops very sharply (Fig. 2). KASHKOVSKAIA AND MUSTARIK~ used an ammonium acetate buffer solution of PH 5.12. The pH value of 4.6, which is in the middle of the sodium acetate-acetic acid buffer range, was selected in the present work to minim& any PH changes caused either by free acid or free alkali. Additions were made to solutions containing 2 ml and 5 ml of buffer solution, and from the results obtained (Table I), it was decided to use 5 ml of buffer solution. In addition, the interference of iron(II1) was much larger at pH 5.x than at pH 4.6.
RECOVRRY
017
111 AND
Added
CHANGISS
5
-_--._._ Nil 0.x ml IO M &-ICl O. I ml IO nr N.IOH
OP
1M
ADDITIOS
Al’TRR
ml buffer
OlJ
2
PRIZE
ACID
ml buffer
AND
Al forcnd (pg)
pt1 _-.-
20.0
4.60
21.0
4.49
20.0 22.3
4.63 4.35
---_-
19.5
Interference by diverse ions Many elements form strong Cu2+, Fea+, Th4+, Ti4+, and Zr4+. various masking agents (Table II). The interference of iron(II1) ascorbic acid is sufficient to mask solutions which contain more than
j-69
x8.3
ALKALI
__.--
PH
Al found (pg)
FRILI!
4.90
colours with chrome azurol S, for example, Bcs+, Many interferences can be minimiscd by using can be masked by ascorbic acid. One ml of 1% 4 mg of ferric ion. To determine aluminium in 4 mg of iron, proportionately more ascorbic acid Anal. Chinr. Acta, 32 (xgGg) 5743
Bon+
20.0
Bin+
20
C.hz+ aa+ COW Cr3+ Cm*
20.0
I+3
20.0
20.2
20.0
20.0
20.0
19.3 r8.g
32-7 .O
20.0
2.0
20.0
10.8
1.0
20.0
10.0
10.0
F&PI.
Mlla+ Mo(VI) Mo( VI) Mo(VI) MO(W)
10.8
-
I().8
--I
.).C
20.0
20.0
S-0
20.0
1H.c)
10.0
20.0
18.8
10.0
-
20.0
-2
30.0
0
20.0
2=
0.5
10.0
I.0
20.0
-
3c 20
1.0
10.0
-
3c
2.0
20.0
19.7
2.0
20.0
20.0
2.0
20.0
20.0
G* 5
20.0
18.2
0.5
‘20.0
22.2
11
0.5
10.0
12.2
22
‘10.0
Z‘f.‘i
22
X0.0
0.2
20,O
2.0
20.0
2.0
20.0
1cJ.cJ
‘L.0
20.0
1.0
20.0
iQ.44.
0.2
20.0
2 ‘) . I
0.019
20.0
II.2
1:-
0.038 0.09s 0.5 1.0 2.0
l?O4”-
20.0
G,t
20.0
2.0
20.0
19.8 19.0 lg.0
20.0 20.0
--------.-a BuIIcr ncldcrl lxlorc ;rucurbic acid; 5 1n1 of .z(;/,, N&i&a. 11 2.5 In1 of I 0/0 ascorbic acid atlclcd. 0 0.5 mg PO43- rrcldr:d to wcnlcly acid solution. d 0.5 ing POda- nddccl. 0 Without: ascorbic ncid. f 1) nrg Cal+ acldcd. And.
Chim.
Acta,
32 (1965)
5743
-2 0 0 -9
Id~.‘~
20.3 lg.G 20.6 3G.o lg.8 lg.8
I
2;-
l’O,jJ -
Gb
2.0
1.0
PO.1" -
G’J
005
0.
p -
;‘a
-
2.0
‘ri4
W(VI) ZllSk
1.
-
10.0
‘1’1, 4 I.
U(VI) V(V) V(V)
1 OB
20.0
1.0
C
-
10.0
2.C)
hIKa”
20.0
21 -42
- 70 -go I
-2 --5
DETERMINATION
OF
Al
WITH
CHROME
AZUROI.
s
61
should be added, and it is necessary to prepare standard aluminium solutions which contain an amount of iron equivalent to that in the sample aliquot. Copper can be complexed satisfactorily with sodium thiosulphatc. One ml of 2% sodium thiosulphate is sufficient to complex 2 mg of copper( and proportionately more of the sodium thiosulphate solution should be used for larger amounts of copper. In slightly acid solutions ascorbic acid has a tendency to reduce Cu”+ to Cu+ forming a precipitate. The maximum amount of copper(I1) which can be tolerated in the recommended procedure is 2 mg. It was found that at pH 4.6 copper(I1) is not reduced by ascorbic acid, and by changing the order of addition buffer solution followed by ascorbic acid - it was possible to determine aluminium in solutions containing larger amounts of copper. Molybdate ion interferes seriously, but the interference can be overcome by procedure should be used: to the complexing with phosphate ion. The following slightly acidic solution (1)~ x.5) add 0.5 mg of phosl~hatc ion and let it stand for 5 min. Add x.0 ml of I(/,, ascorbic acid, shake, and immcdiatcly add 5.00 ml of buffer solution. Continue as in the rccommcnded procedure. Thorium interferes to a large extent, and the interference is proportional to the amount of thorium present. Titanium forms a strongly coloured complex with chrome azurol S. The interference in the microgram range can bc masked by the addition of 0.5 mg phosphate ion. Tungstate reduces tile alurninium absorbance, but the addition of calcium makes the interference negligible. Vanadium(V) interferes slightly, but vanadium(IV), which is formed by reduction with ascorbic acid, interferes seriously. ‘I’hc interference of various neutral salts was stutliecl at the 20 pug of aluminium lcvc!l, by measuring the absorbance against the stanclard blank (Table III).
Rcfivoducibility of the method Ten replicate dctcrminations were maclc at the 20 ,ug of aluminium level using the recommended procedure ; the relative standard deviation was -& 0.4%. COMPARISOS
cyanine ferences
BETWEISN
CHROME
AZUROI.
s,
ERIOCHROMII
CYANIND
13,
AND
ALUMINON
The procedures used for the determination of aluminium with eriochrome li ancl aluminon have been described prcviously”fQ. A comparison of interin the 3 methocls is given in Table IV. The results show that the eriochrome A~ad.
C/rim.
Ada,
32 (r9G5)
5743
I’.
62
COSll’hl~1SO.N n1: ISTl?HI~I~I
__-__-
__.. _-_-
. . . . . . ._---.
--
.._. -_
crrw
Ilclativc
_- _ _-_.Clitwtir uziwol (20 pg/2s ml) ._..
..--...--_____ -
HIPAC.IZNTS ---_
._---
--
(IO /lR/5fl .___ - ___.
_-.... -...-
-,
+
--.-_--..--..
--
.
Nil
1
ml
.
.-...-
c1r
I
iv
I-I(‘.1
I ml of I III Nat )1-l _-____....._.-.-. _.._--
-.
..-
20
-!-
too Ho
>.
.+.
1rm
>
-I-
ran
-t- 25 + 5 .-_ 4
-I-
-
(J IO
0
-I-
2
4
-
(J
7 .I- I ‘)
j..dZ .__ 1
.I-
-
-t_--
I 2
-....
._
.(.O ‘I.5
4.7 .__..._
.
_.._._ - .._...
t,
II
70
_, _.._._., ___._.__.. _.
.
.-
._
3
.___.____ ..__. _
_.,._.____.__.
I:‘rioi*hromc
p-1 . _. .._-.
10.0
10,s .._.. --.-.-
-
tr11)
t 8 -+ I 1 .t- 5
;!I
.o
-.......-..
/.&/so
-
rcziirof S __ _ _
-.
._--._.
(20 -__---_-__
_-
_....
PU -.- . -...
WI)
I
..___ ..-.__.
C~?irr~~~if
.___ -__ ___._- ..__- --__ cyutiitae It .Iluttiir~o~i
0
.
.-...
_-_-__
--
1
..-..
--
--
0
.-.. -----
.. .
0
I
- I . .. 2
A tltlrrl
---
-. -
(%,) _......____._____~ S Iivioclitvmre
0
- -..__ -
PAKALNS
cyci?iirit* It
. _. __.....-- _.-_._ pfi PC ..___-__ .___._._. _..- .._ . _ f-J.0 I0.C)
13,” fJ.0 .._____.________
5.7 CJ.7 .._.- ._.. .___..-__
cynninc 12 nnd alunlinon mcthocls iirc subject to large crrws by many foreign ions, in particular clwomium ancl cobalt, whicl1 must Ix complctcly rcmovcd. Even small amounts of phosl~liatc intcrfcrc seriously in tlic criochromc cyimitlc R mcthocl. Small amounts of free wicl or free alkali produce ncgligiblc errors in tlw chrome neurol S mctlwcl, but very Iargc errors with criochromc cyanine 1C (Table V) wl1ich rccluircs prccisc p1r wljustmcnt. For tliis reason, tlic criochromc Cplillc 12 procedures recon-micnclctl for tlw clctcrmination of :iluminiuni in magnesium iLllOyS”, zinc metal(~, and iron orw3 , all USC strictly controllccl amounts of acid for dissolution and slxcified sample aliquut sizes. On tl1c basis of sclcctivity , simplicity, and rapidity, cln-omc uzurul S appears to bc tlic most suitnblc rcngcnt yet lxop&xl for tlw routine spectrophotonictric determination of aluminiuni. even tliougli it is less sensitive than eriocliromc cyanine I<. As an exnmplc of tlic versatility of the chrome azurol S sp”ctrophotomctric metllocl, aluminium was dctcrmined directly in a permanent magnet ulloy (13.C.S. Sample 233, C0-23.7’j/~, Ni-rI.z’j/,, Al-G.gSo/o,Cu-~.r~~,,Ti-O.8~/,,Mn-o.2o/o,Si-o.~o/o, Fc-51.2%). The result found was 7.04 & 0.03% Al, wl1icl1 comprcs favourably with
L)ETERMINATION
OF
Al
WITH
CHROSIE
A%UROI,
s
63
the certificate value of 6.98% Al. Both the criochrome cyanine R and aluminon methods failed when applied directly to this alloy, because of the interference of cobalt. SUMMARY A comprehensive investigation of the spcctrophotometric determination of aluminium with chrome azurol S is clcscribccl. No heating is required for colour formation, and the method is considerably more reproducible and selective than either the eriochrome cyanine I< or aluminon methods. In the presence of suitable masking of agents, only 13@+, %r4+, and F- cause serious interference. A molar absorptivity 21,500 at 567.5 rnp was found for the aluminium-chrome azurol S lake, with a relative standard deviation of -& 0.4% at the 20 pg Al level. I3ccr’s law is obeyed from o to 1.2 ,ug Al/ml.
L’auteur dbcrit une mC_thodc de dosage de l’aluminium au moycn de chrome azurol S. Ce 1xocCdC ne trCccssite pas de chauffage; sa rqxoductibilitc5 et sa shlcctivitb sont mcilleurcs clue cellcs dcs mCthocles A l’&iochrome cyaninc R ou i‘l l’aluminon. En pr&encc dc r&ctifs dc masquagc approl>ri&, seuls 13e”+, %r’l+ ct l;- @nent s&-icusemcnt. La loi de I3cer s’applique de o h 1.2 pg Al/ml. ZUSAMMENI’ASSUNG
Eine ausftihrlichc Untcrsuchung dcr spektrall~hotometrischen 13estimmung cles Aluminiums mit Chromazurol S wircl bcschricbcn. Fiir die beniitigtc Farbbildung ist kein ErwZrmen erforderlich. Die Mcthoclc bcsitct cinc lxssct-c ICeprocluzierbarkeit und ist sclektiver als die Eriochromcynnin R- oclct Aluminon-RIethodc. In Gegcnwart von brauchbarcn maskiercnclcn Rcagenticn veruxsachen nur 13e”+, %r4+ und I;ernsthafte StBrungen. Die molarc Estinktion fiir den Aluminium-Chromazurol SLack betrug 21500 bci 557.5 rnp, die rclativc Standarclal>wcichung 0.4% bci 20 pg Aluminium. Das Iseerschc Gesetz wircl von 0-1.2 pg Al/ml befolgt.
E.
13. SANVELL,
Colorin~elrir
I~elernrinulio~r
of Traces
of dlclais,
Irltcrucicmx.
N*‘cw York,
1959,
1’. 2 rg.
I.. C.
IKENHIJHRY
hNV
A.
‘lb40~hS.
flwd.
C/rcw2.,
23 (1951)
18of1, /Irriil. Cirim.
Actrc,
31 (1965)
57-63