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Extraction-spectrophotometric studies on the reactions of manganese(II) with dithizone
An~lytfca Chlmica
Acta
Elscvier Publishing Company, Printed in The Ncchetlands
,:
469
Amsterdam
,. :,.
,‘..
,’
EXTRACTION-SPECTROPHOTOMETRIC OF MANGANESE(I1) WITH .DITHIZONE
STUDIES
ON THE REACTIONS
‘., ZYGMUNT
Department (Received
MARCZENKO
of Anulyticul 6th November
AND
Chemistry,
MIROStAW
Polirechniku.
ivlOJSK1
Wursaw (Polund)
1970)
Dithizone (cliphenylthiocarbazone) is a very important reagent for the calorimetric determination of- metals, but its reaction with manganese(I1) has not been fully studied. Akaiwa and Kawamoto’ were the first to note the synergic effect of pyridine on the extraction of manganese by dithizone (H,Dz) and to utilize this analytically. They showed that the extractable species had the composition ‘Mn(HD&Py,,, the value of n being unestablished. In the work described here, these results were extended, and practicable methods were developed for the determination of manganese( II). EXPERIMENTAL
Apparatus Several spectrophotometers were used, depending on the purpose of the measurement ; unless otherwise stated, l-cm glass cuvettes were used. pH values were measured with a Ridan compensation pH-meter, and a glass-saturated calomel electrode pair. ,1
Reagents Spectroscopically pure, hydrochloric .acid, nitric ‘acid, and sulphuric acid, and an ammoni&olution prepared by .saturating,twice-distilled water with gaseous ammonia were used. ,Twice-distilled water’ was. used .throughout.: St&dard,. m&gane$e sdluth, 0.1. M. Dissolve ,7.5460 .g of manganese(1.I) .; sulphate (dried at i 50” and’calcined at 400’) in water,containing 1,ml of concentrated sulpburic.,acid and, dilute.’ to 500 ml with.water.’ ‘, ” i( ‘. ‘,’ ‘. . >’ : .: Dithizo& (H&z); 5 - ,l O-PM CnCCZ, (or in CHC13). Dissolve p.0320 g of purified dithizone’, in .darbon tetrachloride and dilute to 290 ml with the solvent. Dilute this stock solution suitably ‘~,.with.: the :appropriate solvent Ito ,obtain working solutions. ‘, ‘. :,,Fyridin’e. Commercial ,.(C.P.) pyridine was purified by distillation. through a laboratory column to.,collect the fraction of b.p. 1 15.5°~~1~15.60. ; ..I :.:H~dr&c>latiine,~.2 M’ soliith. Dissolve 14 g of hydroxylammonium chloride in 100 ,ml of water; neutralize ,with aqueous sodium hydroxide (PH. cu. 7) and purify with dithizone. :,Ij ‘,I ,. : :: i : : ‘,, : .,;, , / ‘, : ,.. 1. tartrate, 20% solution. Purify with dithizone at ,pH ca. 8.5. ., (. ~Potassiu&,sodium ,- ‘. .Ammonia .buffer, pH,,9&. Dissolve 21. g of ammonium chloride in water, purify the,solution. with dithizone, add :120 ,ml of concentrated ammonia; 1.4,g of potassium cyanide, and 200 ml of pyridine,‘and dilute to 1 1 with water; :: , ‘: ” , Anal. Chim. Acta., 54 (1971y469-474
470
Z. MARCZENKO,
hi
MOJSKI
Distribution oj’manganese Distribution coefficients were calculated from measurements of manganese in the aqueous and organic phases, manganese being stripped with 1 M hydrochloric acid from the organic phase. The manganese was determined, either calorimetrically with formaldoxime3 or spectrophotometrically by the procedure described below. Direct
determination of’mar~gunese To less than 5 ml of a solution at pH 2-3 containing below 10 pg of manganese add 1 ml of the hydroxylamine solution. Shake the resulting solution (pH 6.5-7.0) with portions of 0.003% dithizone in carbon tctrachloride until the colour of dithizone does not change. To the aqueous solution, add 1 ml of the tartrate solution and 2.5 ml of the buffer. Dilute to cu. ,lO ml with water and 4hake the mixture for 1 min with exactly 10 ml &f,0.003°/o dithizone in carbon tetrachloride. Measure the. absorb,‘, ance at 510 nm against a blank solution. .“..
Determination of manganese by reversion : Follow the direct method’ until the extract ‘of the manganese complex ,in carbon tetrachloridel is obtained. ,Halve,the extract and shake one portion for 1 min with 10 ml of 1 M hydrochloric acid. Measure the absorbance of the carbon tetrachloride solution shaken with acid at 620 nm with the portion unshaken with hydro‘/,’ chloric acid in the reference cell, +SULTS :_
AND .“,.
DlSC~SSION . ’
:, Manganese(Il)-dithizone system ‘. In chloroform solution dithizone reacts with manganese(II) at pH 9-11 to yield a violet complex which can be extracted into the organic phase. Hydroxylamine .‘, I. was added to keep manganese in the correct oxidation state. .?The’ Complex shows maximum absorbance at 515 nrn ;’ it decomposes on standing. to regenerateidithizone. The coinposition of the complex was’ established by determining the manganese, calorimetrically with bformaldoxime, and the dithizone by :its absorbance. at 605 rim: Whether’ dithizone or, manganese was ‘in ‘excess, the complex, was :found’ to, be’,a ,primary dithizonate;‘,Mn(HDz);. r .. I’, Maximal extraction of nianganese(I1) occurs over the pH range 9.5-l 1; but the ieaction:,is:~,i~~omplete. ‘For [Mn] : [HiDi] ,.ratios of 1 ‘f2.5, 1 i 125 and, 1: 50, the pertientage extracti&‘of inanganese is 38; 45 and :58%, respectively.,With a lOOO-fold excess of:manga,nese~,overdithizone~~only ‘about -60”/0:of’the latter, is used. ~ ‘, ‘: ‘1’ : ,’ .’ ,When .ohldroforni wasreplaced by the less ljolar solvent carbon fetraohloride, the primary manganese(I1) dithizonate Separated as ai red-brownish solid at the inter; face. The, composition, .ofcthe’ complex :was ,established by filtering, off the ‘solid and washing.it: before ;decomposition,zwith 0.1. M:sulpliuric a&in ,the .presericd’of,tiilver, ions and carbon tetrachloride ; dithizone was determined by measuring the.absorbance of silver ,‘dithizonate’: in carbon (.tetrachloride, and manganese i ,with. : formaldoxime. With: carbon tetrachloride;: maximal, extractio’n’~was obtained, within the pH range 9.*10;3; but ai ,viiith: chloraform’percentage extra&ion .was’ l&,5 indicating thelow stability of ihe complex.:,f Anal;. C/tfm.-ii&;
54 (1971) 469474
(:.
! :
.,
,. ” ’
:
.I
‘..‘.._
;’
.,_,
REACTIONS OF MANGANESE(I1)
471
WITH DITHIZONE
Mcrnganese(.II)-dithizone-pyridins system ., ,’ ‘, ‘0 In, the’ presence, of pyridine, manganese(H) reacts’ with dithizone in carbon tetrachloride to.yield an extractable complex Mn(HDz)&, with maximal.absorption at 510 nm’. Absorption curves for this complex and for dithizone in carbon tetrachloride solutions are presented in Fig. 1. The absorbance of the complex is stable for 10 min. Hydroxylamine was added to the aqueous phase to ensure the. presence of manganese(U), and 0.005 M cyanide was added to mask heavy metal traces, without affecting the manganese-dithizone reaction.
Fig. 1. Absorption spectra of a solution of Mn(HDz),Py, (2) and dithizone (I) in CC.&. [H,Dz] a2.5. 10-j M, [ Pya =0.62 &I, [Mn] = 1.1 0e2 M. pH = 8.7. Fig+ 2. Coefficient of extraction (E) of manganesc(l1) in relation to concentration of pyridinc in the organic phase. (1) [H,Dz]==Z.S~ 1O-J M, pH=8.7; (2) [H,Dz]=8. lO-s M, pH=9.5.
.The value of n wasostablished by plotting the ~i~trib~ti~n ratio E=‘X[Mn],,, 1 erent Foncentrations of pyridine, Plots’ of ,log. E against log [Py] [Mn’.+ J, for ,d’ff at a. fixed. Condentration of dithizone and, fixed pH were linear over the ran’ge’O.OS-Q.40 M:pyridine (F&2) and the’sloije,of 2 indicates the composition Mn(HDz),Py, for the extradited complex. The. equilibrium. coucentrations of iyridine were calculated from the:known initial concentrations, taking into account the partition between the t,%d. phas$s, and,'using,'the value:. P =, [ P&&J[Py] =.1.7 ? measured’ acidimetri&ally, for.:0.1~:~[rjl]~lt.2M: ‘I. ,,’ ‘, ,: ,@iear plots (not’ &produced) of slope 2, were ,also obtained for, plots of log E against log [H,Dz] foi’f Py]_ =0.39 M ,and’at pH 8..6 and 9.2, and for plots ‘of log E agai$,‘p@ for [P~&.~=00.39 ,M. and .[H2Dzl10,=8’:, lo-’ M and [Py]i,,30.08 M and [H&Z],,, +,2’* lfl-4 ,M. T,h esd results establish couclusively the composition of the .synergi,oally, extracted, species. ’ ‘_.,,.Fxtractlon of manganese can be represented ,by’ ,’ I>:.,
Mn2+2
(H,Dz),,,$_2(Pyj,,b
----L(Mn(HDz),Py,),,,+2
H+
hence. K,,
:.,” “.,
=’
[Ii.+]” CMr!(HDz),lPy,l,,,CH+12 = E_ .CMn’.‘lCWW~r~C.P~],2,,.. icH2D$&J~~]&, Anal. Chinr; Actn, 54 (1971) 469-474
472
Z. MARCZENKO,
M. MOJSKJ
The extraction constant, K,,, was measured at ionic strength I=O.2 ‘(NaCl) with [,CN’],,,,=0.005 M; the pH.value lay in the range 7.2-8.7, where both protonation of pyridine (pK = 5.22) and hydrolysis of mariganese(I1) (pK = 10.52) are negligible. The, complexing action of pyridine, chloride and ammonia, on manganese(U) in the aqueous phase could be ignored ; any error thus introduced would be lower than that I inherent in measuring E, [H2D~],,B, and pH:
0
-2.0
-40
-do
c b
ao
Fig. 3. Graphical dcterminution of the extraction I = 0.2 (N&I), [CN-] =0.005 M. Fig.4. Percentage~xtrnctionoTmungunese(II)in 1*1O-s M.
constant
relation
8.0
for Mn(HDz),Py,
to pH. [HzDz]
40,o
into carbon
4to
H
P tctrachloride.
= I - 10e4 M. [Py] ==0.62 M, [Mn] =
The plot of log e us. log [H,Di&,[Py],,,1[H,+] is linear and of the predicted of.2. Extrapolation. giyes log KiX= -_6.5 (Fig., 3). The effects ‘of &dnbentratipns of the reagents”arid of pH on the absorban& of the ‘extracts’ were ~&&&&~~ ‘Absorbancesl-of cart&n tetrachloride solutidns’,bf &&G (HDz)2Py& we’re, measured’ with reference to a blank: except’wben the effect of manwas’:studied; ‘when’‘cai~o~.‘tkt~aChloride’was used., Increase in ganesedoncentratitin th$ prri,~ine,.:~dnc~nt~afion incr&&d, tl$absorbance.‘of the’ organic ‘extra& ‘up to ,a concentration of 6.4 M, tibove whichthe absorbanck remained~con~stant,‘for [H&j =1 ,l* 107.” M, [+J:?] 7.J * JO-,’ M and,pH e?.g..Por [Mn’T] -i *JO-y;M and,.[Py].= 0.62;M at(pH 9.2 or‘ 9.8, the per&ntage &xtractionlof ‘i&&ganese(II)‘incr&sed .as the dithizS~~~~~nc~ntration in&eased; ‘up ‘to ‘a &olar excess ,of’,l’o’i i,.after which ,it’r& mained ‘$onstant. Dithiione &a&d ~completely, with:inanganese’,when, the “concentra’tion’of ihe.latter was’at h&t 200 times’as’ high as that ‘&fthe fornier. .Witn the adopted concentrations,of dithizone and pyridine at pH 8,;siO.2; the' ptirtientage extra’&io,n’of manganese was ~.about 95o/0 (Fig; “4)‘.,Above pH 10.2,‘tho $e&entage extraction was reduced by hydrolysis of manganese’and almost complete passa’ge:of,dithizofie from the ,organic into, the aqueous phase. ‘, :’ ,. 1,“. ., ,..’ I.. Use:of the complex i%f~(HD&Py,~for. the detkrtii~ation of tiarqjciri~sk ” The studies described .above indicate that’, the ternary complex should be slop
it,tal.’C/rltn;~Acta, 54 (1971) ‘469474
REVCkNS
OF MANGANESE(U)
473
WITH DITHIZONE
useful in providing a sensitive extraction-spectrophotometric method for the determii );’ I’. nation of manganese. However, at the pH values necessary for almost quantitative extraction’of manganese; a’considerable portion of dithizone passes into the aqueous phase, and it is ‘therefore essential to maiqtain a high concentration of dithizone in the organic phase. Unfortunately, this ,leads’to an unfavourably high blank value. Free dithizone cannot be washed out of the carbon tetrachloride extract containing M~(HDz)~P~,, because the complex is then partially decomposed. In Fig. 5, the blank absorbance value is plotted against the pH of the aqueous phase.
Fig. 5. Blank absorbance TABLE
in relation
to pH. [H,Dz]
= 1. 10s4 M, [Py] =0.62
M.
I
DETI~RMINATION
Material
NaCl,p:a.
High-purity tin
01: MANGANI~SE
IN SODIUM
Method
Mn found” (%I
CHLORIDE
P.A.
AND
IN ‘HIGH-PURITY
TIN METAL
deviation, s
Mn added (%I
Total it411 found (%)
1.10-S
2.4.10-’ 2.2.10-5 ’ 2.4.10”’ 2.3.10-5 1.6. 1O-4 1.6. 1O-4 1.7.10-4 1.6.10~*
Standard
Dire&t
1.5.10-’
7.10-7
Reversion
1.4.10-5
4:
Direct
7.4*10-s
3.4.10-6
1.10-4
Reversion
7.5. lo-”
2.8.10-6
1.10-4
10-7
l.lO-’
o The averoke of G.determinations. .’
If it is assumed that the manganese concentrations are of the order of 1,.10W5M (maximum 1 pg ml- I), .the’ following reagent concentrations are recommended : 0.Q03°/; (w/v) dithizone in .carbon tetrachloride, 5% ,(v/v) pyridine in water, and a pH values of 9.8. Addition of hydroxylaminc ensures the presence of only manganese(II), ,whcreas addition of cyanide reduces the blank value.. ., j/ Two .procedures are: suggested, the, direct procedure and the reversion procedure4. In the latter, the absorbance of a dithizone solution obtained after. the complex has been’ decomposed is measured, 1 M hydrodhloric acid acting as the reversion . ,. , agent. In the direct procedure, the molar absorptjvity (8) is 57QOO(specific ‘absorp; tivity!, 4 = &/(at.wt. - lOOO)= 1.02) at 510 nm, and in the ‘reversion pro,cedure E,= 64v ,, ,‘. ,‘,,/ ,’ (a=1.17) at’ 620 nm; : ., ‘The proposed method for the determination of ma&an&e is.highly selective. Anal. Chirn; Acta, 54,(1971) 469-474
z.
474
MARCZENKO,,
M. MOJSKI
Under the conditions adopted and with various metals removed by prior extraction with dithizone at pH 7, thallium is the only interference. I ,’ This dithizone-pyridine method was used todetermine manganese in analytical reagent-grade sodium; chloride and in, high-purity tin: After the samples had, been brought into.solution, manganese ‘was separated’by using a lanthanum carrier?. The analytical data, listed in Table I indicate the good precision and accuracy of the method employed ;’ the reversion method, affords the better precision. sUtiARY
”
Manganese(H) can be extracted as the primary dithizonate Mn(HDz), over the optimal pH ranges 9.5-11.0 (CHC13) or 9.0-10.3 (Ccl,). Even with the dithizone in large excess only Xl-60% of manganese is extracted. Synergic enhancement, in. the presence of 0.6 A4 pyridine leads to extraction of the complex Mn(HDz),Py., over the pH range 8.5-10.2 provided that a lo-fold excess of dithizone is present. ,The extraction constant, for Ccl4 is 3 * 10’ 7. Direct and reversion procedures for the spectrophotometric determination of manganese(H) are described and applied to the determination of manganese in sodium chloride (p.a.) and high-purity. tin. Only thallium(I) interferes. R&SUM&
.),.
. Le manganese(H) peut Qtre extrait comme dithizonate primaire, Mn(HDz),, aux pH 9.5 h 11.0 (CHCl,) ou9.0 a 10.3 (CC14). On ne peut extraire que 50 A 60% de manganese, meme, en presence d’un grand exces de dithizone. Une addition de pyridine 0.6 M conduit i une extraction du complexe’Mn(HDz),Py, aux pH de 8.5 it 10.2, avec un excbs de.10 fois de dithizone. La constante d’extraction pour Ccl4 est de 3 *lo- 7. Des methodes sont proposees pour le dosage spectrophotometrique du mangantse(II)‘avec application dans le chlorure de sodium (p.a.) et l’etain tres pur. Seul le. thallitim(I).g&e., ,, :
.’
. ZUSAMM~FASSUNG
:,
Mangan(II)‘kann als primares Dithizonat Mn(HDz), in den optimalen pHBereiohen 9.5-l 1 .O : (CHCIJ) oder 9.0-10.3 (CC14) extrahiert.. werden. Auch .mit Dithizon in grossem ljberschuss werden nur 50-600/, des Mangans extrahiert. Die synergetische Steigerung%r Gegenwart von 0.6 M, .Pyridin ftihrt ,zur Extraktion des Komplexes Mn (HDz)=Py, im pH-Bereich ‘8.5-1,O.a; ‘vorausgesetzt dass ein 10:father Dithizoniiberschuss’ vorhanden, ist.. Die Extraktionskonstante ftir CC14, ist 3 * 10’ ?; Es~werden+~unmittelbareund*~Umkehrverfahren fur die,.spektrophotometrische Bestimmung .von Mangan (II) ,beschrieben und, auf,die: Bestirnmung,.von Mangan in Natriumchlorid, (p.a:) und:,hochreineni’ Zinn angewendet; Nur . Thallium(I) stiirt. .,’ ‘, ,‘.‘(’ R&ERE,N\ICES‘,. : : : .. .!’ : -: ” : ., ‘, ‘. .,! -.,/ ,’ ,::, ,:,,‘,” ., .‘. I FL;,AKAIWA AND H.’ KAWAMOTO, Anal. Ck’t~t. Acfu, 40 (1968) 407.
4, I-1: M. ?RVING AND’E; J: BIJTLBR,Ai;afjst; 78 (1953) 571. ‘, ’ 5 %. ,H. AYRES r~~i) B. D, NARANU, Anti/. ,Cltim. Ada; 24 (1961) 241. 6. Z.;MI\R?XQNRO!.I\ND M:MOJSKI, CYtem.. ~Attctl. (Wursnw); 12 (1967) 1155;
AiraL %XirnL’Acta;’ 54 (1971) 469-474
’
:
’
‘,
j
Acta
Elscvier Publishing Company, Printed in The Ncchetlands
,:
469
Amsterdam
,. :,.
,‘..
,’
EXTRACTION-SPECTROPHOTOMETRIC OF MANGANESE(I1) WITH .DITHIZONE
STUDIES
ON THE REACTIONS
‘., ZYGMUNT
Department (Received
MARCZENKO
of Anulyticul 6th November
AND
Chemistry,
MIROStAW
Polirechniku.
ivlOJSK1
Wursaw (Polund)
1970)
Dithizone (cliphenylthiocarbazone) is a very important reagent for the calorimetric determination of- metals, but its reaction with manganese(I1) has not been fully studied. Akaiwa and Kawamoto’ were the first to note the synergic effect of pyridine on the extraction of manganese by dithizone (H,Dz) and to utilize this analytically. They showed that the extractable species had the composition ‘Mn(HD&Py,,, the value of n being unestablished. In the work described here, these results were extended, and practicable methods were developed for the determination of manganese( II). EXPERIMENTAL
Apparatus Several spectrophotometers were used, depending on the purpose of the measurement ; unless otherwise stated, l-cm glass cuvettes were used. pH values were measured with a Ridan compensation pH-meter, and a glass-saturated calomel electrode pair. ,1
Reagents Spectroscopically pure, hydrochloric .acid, nitric ‘acid, and sulphuric acid, and an ammoni&olution prepared by .saturating,twice-distilled water with gaseous ammonia were used. ,Twice-distilled water’ was. used .throughout.: St&dard,. m&gane$e sdluth, 0.1. M. Dissolve ,7.5460 .g of manganese(1.I) .; sulphate (dried at i 50” and’calcined at 400’) in water,containing 1,ml of concentrated sulpburic.,acid and, dilute.’ to 500 ml with.water.’ ‘, ” i( ‘. ‘,’ ‘. . >’ : .: Dithizo& (H&z); 5 - ,l O-PM CnCCZ, (or in CHC13). Dissolve p.0320 g of purified dithizone’, in .darbon tetrachloride and dilute to 290 ml with the solvent. Dilute this stock solution suitably ‘~,.with.: the :appropriate solvent Ito ,obtain working solutions. ‘, ‘. :,,Fyridin’e. Commercial ,.(C.P.) pyridine was purified by distillation. through a laboratory column to.,collect the fraction of b.p. 1 15.5°~~1~15.60. ; ..I :.:H~dr&c>latiine,~.2 M’ soliith. Dissolve 14 g of hydroxylammonium chloride in 100 ,ml of water; neutralize ,with aqueous sodium hydroxide (PH. cu. 7) and purify with dithizone. :,Ij ‘,I ,. : :: i : : ‘,, : .,;, , / ‘, : ,.. 1. tartrate, 20% solution. Purify with dithizone at ,pH ca. 8.5. ., (. ~Potassiu&,sodium ,- ‘. .Ammonia .buffer, pH,,9&. Dissolve 21. g of ammonium chloride in water, purify the,solution. with dithizone, add :120 ,ml of concentrated ammonia; 1.4,g of potassium cyanide, and 200 ml of pyridine,‘and dilute to 1 1 with water; :: , ‘: ” , Anal. Chim. Acta., 54 (1971y469-474
470
Z. MARCZENKO,
hi
MOJSKI
Distribution oj’manganese Distribution coefficients were calculated from measurements of manganese in the aqueous and organic phases, manganese being stripped with 1 M hydrochloric acid from the organic phase. The manganese was determined, either calorimetrically with formaldoxime3 or spectrophotometrically by the procedure described below. Direct
determination of’mar~gunese To less than 5 ml of a solution at pH 2-3 containing below 10 pg of manganese add 1 ml of the hydroxylamine solution. Shake the resulting solution (pH 6.5-7.0) with portions of 0.003% dithizone in carbon tctrachloride until the colour of dithizone does not change. To the aqueous solution, add 1 ml of the tartrate solution and 2.5 ml of the buffer. Dilute to cu. ,lO ml with water and 4hake the mixture for 1 min with exactly 10 ml &f,0.003°/o dithizone in carbon tetrachloride. Measure the. absorb,‘, ance at 510 nm against a blank solution. .“..
Determination of manganese by reversion : Follow the direct method’ until the extract ‘of the manganese complex ,in carbon tetrachloridel is obtained. ,Halve,the extract and shake one portion for 1 min with 10 ml of 1 M hydrochloric acid. Measure the absorbance of the carbon tetrachloride solution shaken with acid at 620 nm with the portion unshaken with hydro‘/,’ chloric acid in the reference cell, +SULTS :_
AND .“,.
DlSC~SSION . ’
:, Manganese(Il)-dithizone system ‘. In chloroform solution dithizone reacts with manganese(II) at pH 9-11 to yield a violet complex which can be extracted into the organic phase. Hydroxylamine .‘, I. was added to keep manganese in the correct oxidation state. .?The’ Complex shows maximum absorbance at 515 nrn ;’ it decomposes on standing. to regenerateidithizone. The coinposition of the complex was’ established by determining the manganese, calorimetrically with bformaldoxime, and the dithizone by :its absorbance. at 605 rim: Whether’ dithizone or, manganese was ‘in ‘excess, the complex, was :found’ to, be’,a ,primary dithizonate;‘,Mn(HDz);. r .. I’, Maximal extraction of nianganese(I1) occurs over the pH range 9.5-l 1; but the ieaction:,is:~,i~~omplete. ‘For [Mn] : [HiDi] ,.ratios of 1 ‘f2.5, 1 i 125 and, 1: 50, the pertientage extracti&‘of inanganese is 38; 45 and :58%, respectively.,With a lOOO-fold excess of:manga,nese~,overdithizone~~only ‘about -60”/0:of’the latter, is used. ~ ‘, ‘: ‘1’ : ,’ .’ ,When .ohldroforni wasreplaced by the less ljolar solvent carbon fetraohloride, the primary manganese(I1) dithizonate Separated as ai red-brownish solid at the inter; face. The, composition, .ofcthe’ complex :was ,established by filtering, off the ‘solid and washing.it: before ;decomposition,zwith 0.1. M:sulpliuric a&in ,the .presericd’of,tiilver, ions and carbon tetrachloride ; dithizone was determined by measuring the.absorbance of silver ,‘dithizonate’: in carbon (.tetrachloride, and manganese i ,with. : formaldoxime. With: carbon tetrachloride;: maximal, extractio’n’~was obtained, within the pH range 9.*10;3; but ai ,viiith: chloraform’percentage extra&ion .was’ l&,5 indicating thelow stability of ihe complex.:,f Anal;. C/tfm.-ii&;
54 (1971) 469474
(:.
! :
.,
,. ” ’
:
.I
‘..‘.._
;’
.,_,
REACTIONS OF MANGANESE(I1)
471
WITH DITHIZONE
Mcrnganese(.II)-dithizone-pyridins system ., ,’ ‘, ‘0 In, the’ presence, of pyridine, manganese(H) reacts’ with dithizone in carbon tetrachloride to.yield an extractable complex Mn(HDz)&, with maximal.absorption at 510 nm’. Absorption curves for this complex and for dithizone in carbon tetrachloride solutions are presented in Fig. 1. The absorbance of the complex is stable for 10 min. Hydroxylamine was added to the aqueous phase to ensure the. presence of manganese(U), and 0.005 M cyanide was added to mask heavy metal traces, without affecting the manganese-dithizone reaction.
Fig. 1. Absorption spectra of a solution of Mn(HDz),Py, (2) and dithizone (I) in CC.&. [H,Dz] a2.5. 10-j M, [ Pya =0.62 &I, [Mn] = 1.1 0e2 M. pH = 8.7. Fig+ 2. Coefficient of extraction (E) of manganesc(l1) in relation to concentration of pyridinc in the organic phase. (1) [H,Dz]==Z.S~ 1O-J M, pH=8.7; (2) [H,Dz]=8. lO-s M, pH=9.5.
.The value of n wasostablished by plotting the ~i~trib~ti~n ratio E=‘X[Mn],,, 1 erent Foncentrations of pyridine, Plots’ of ,log. E against log [Py] [Mn’.+ J, for ,d’ff at a. fixed. Condentration of dithizone and, fixed pH were linear over the ran’ge’O.OS-Q.40 M:pyridine (F&2) and the’sloije,of 2 indicates the composition Mn(HDz),Py, for the extradited complex. The. equilibrium. coucentrations of iyridine were calculated from the:known initial concentrations, taking into account the partition between the t,%d. phas$s, and,'using,'the value:. P =, [ P&&J[Py] =.1.7 ? measured’ acidimetri&ally, for.:0.1~:~[rjl]~lt.2M: ‘I. ,,’ ‘, ,: ,@iear plots (not’ &produced) of slope 2, were ,also obtained for, plots of log E against log [H,Dz] foi’f Py]_ =0.39 M ,and’at pH 8..6 and 9.2, and for plots ‘of log E agai$,‘p@ for [P~&.~=00.39 ,M. and .[H2Dzl10,=8’:, lo-’ M and [Py]i,,30.08 M and [H&Z],,, +,2’* lfl-4 ,M. T,h esd results establish couclusively the composition of the .synergi,oally, extracted, species. ’ ‘_.,,.Fxtractlon of manganese can be represented ,by’ ,’ I>:.,
Mn2+2
(H,Dz),,,$_2(Pyj,,b
----L(Mn(HDz),Py,),,,+2
H+
hence. K,,
:.,” “.,
=’
[Ii.+]” CMr!(HDz),lPy,l,,,CH+12 = E_ .CMn’.‘lCWW~r~C.P~],2,,.. icH2D$&J~~]&, Anal. Chinr; Actn, 54 (1971) 469-474
472
Z. MARCZENKO,
M. MOJSKJ
The extraction constant, K,,, was measured at ionic strength I=O.2 ‘(NaCl) with [,CN’],,,,=0.005 M; the pH.value lay in the range 7.2-8.7, where both protonation of pyridine (pK = 5.22) and hydrolysis of mariganese(I1) (pK = 10.52) are negligible. The, complexing action of pyridine, chloride and ammonia, on manganese(U) in the aqueous phase could be ignored ; any error thus introduced would be lower than that I inherent in measuring E, [H2D~],,B, and pH:
0
-2.0
-40
-do
c b
ao
Fig. 3. Graphical dcterminution of the extraction I = 0.2 (N&I), [CN-] =0.005 M. Fig.4. Percentage~xtrnctionoTmungunese(II)in 1*1O-s M.
constant
relation
8.0
for Mn(HDz),Py,
to pH. [HzDz]
40,o
into carbon
4to
H
P tctrachloride.
= I - 10e4 M. [Py] ==0.62 M, [Mn] =
The plot of log e us. log [H,Di&,[Py],,,1[H,+] is linear and of the predicted of.2. Extrapolation. giyes log KiX= -_6.5 (Fig., 3). The effects ‘of &dnbentratipns of the reagents”arid of pH on the absorban& of the ‘extracts’ were ~&&&&~~ ‘Absorbancesl-of cart&n tetrachloride solutidns’,bf &&G (HDz)2Py& we’re, measured’ with reference to a blank: except’wben the effect of manwas’:studied; ‘when’‘cai~o~.‘tkt~aChloride’was used., Increase in ganesedoncentratitin th$ prri,~ine,.:~dnc~nt~afion incr&&d, tl$absorbance.‘of the’ organic ‘extra& ‘up to ,a concentration of 6.4 M, tibove whichthe absorbanck remained~con~stant,‘for [H&j =1 ,l* 107.” M, [+J:?] 7.J * JO-,’ M and,pH e?.g..Por [Mn’T] -i *JO-y;M and,.[Py].= 0.62;M at(pH 9.2 or‘ 9.8, the per&ntage &xtractionlof ‘i&&ganese(II)‘incr&sed .as the dithizS~~~~~nc~ntration in&eased; ‘up ‘to ‘a &olar excess ,of’,l’o’i i,.after which ,it’r& mained ‘$onstant. Dithiione &a&d ~completely, with:inanganese’,when, the “concentra’tion’of ihe.latter was’at h&t 200 times’as’ high as that ‘&fthe fornier. .Witn the adopted concentrations,of dithizone and pyridine at pH 8,;siO.2; the' ptirtientage extra’&io,n’of manganese was ~.about 95o/0 (Fig; “4)‘.,Above pH 10.2,‘tho $e&entage extraction was reduced by hydrolysis of manganese’and almost complete passa’ge:of,dithizofie from the ,organic into, the aqueous phase. ‘, :’ ,. 1,“. ., ,..’ I.. Use:of the complex i%f~(HD&Py,~for. the detkrtii~ation of tiarqjciri~sk ” The studies described .above indicate that’, the ternary complex should be slop
it,tal.’C/rltn;~Acta, 54 (1971) ‘469474
REVCkNS
OF MANGANESE(U)
473
WITH DITHIZONE
useful in providing a sensitive extraction-spectrophotometric method for the determii );’ I’. nation of manganese. However, at the pH values necessary for almost quantitative extraction’of manganese; a’considerable portion of dithizone passes into the aqueous phase, and it is ‘therefore essential to maiqtain a high concentration of dithizone in the organic phase. Unfortunately, this ,leads’to an unfavourably high blank value. Free dithizone cannot be washed out of the carbon tetrachloride extract containing M~(HDz)~P~,, because the complex is then partially decomposed. In Fig. 5, the blank absorbance value is plotted against the pH of the aqueous phase.
Fig. 5. Blank absorbance TABLE
in relation
to pH. [H,Dz]
= 1. 10s4 M, [Py] =0.62
M.
I
DETI~RMINATION
Material
NaCl,p:a.
High-purity tin
01: MANGANI~SE
IN SODIUM
Method
Mn found” (%I
CHLORIDE
P.A.
AND
IN ‘HIGH-PURITY
TIN METAL
deviation, s
Mn added (%I
Total it411 found (%)
1.10-S
2.4.10-’ 2.2.10-5 ’ 2.4.10”’ 2.3.10-5 1.6. 1O-4 1.6. 1O-4 1.7.10-4 1.6.10~*
Standard
Dire&t
1.5.10-’
7.10-7
Reversion
1.4.10-5
4:
Direct
7.4*10-s
3.4.10-6
1.10-4
Reversion
7.5. lo-”
2.8.10-6
1.10-4
10-7
l.lO-’
o The averoke of G.determinations. .’
If it is assumed that the manganese concentrations are of the order of 1,.10W5M (maximum 1 pg ml- I), .the’ following reagent concentrations are recommended : 0.Q03°/; (w/v) dithizone in .carbon tetrachloride, 5% ,(v/v) pyridine in water, and a pH values of 9.8. Addition of hydroxylaminc ensures the presence of only manganese(II), ,whcreas addition of cyanide reduces the blank value.. ., j/ Two .procedures are: suggested, the, direct procedure and the reversion procedure4. In the latter, the absorbance of a dithizone solution obtained after. the complex has been’ decomposed is measured, 1 M hydrodhloric acid acting as the reversion . ,. , agent. In the direct procedure, the molar absorptjvity (8) is 57QOO(specific ‘absorp; tivity!, 4 = &/(at.wt. - lOOO)= 1.02) at 510 nm, and in the ‘reversion pro,cedure E,= 64v ,, ,‘. ,‘,,/ ,’ (a=1.17) at’ 620 nm; : ., ‘The proposed method for the determination of ma&an&e is.highly selective. Anal. Chirn; Acta, 54,(1971) 469-474
z.
474
MARCZENKO,,
M. MOJSKI
Under the conditions adopted and with various metals removed by prior extraction with dithizone at pH 7, thallium is the only interference. I ,’ This dithizone-pyridine method was used todetermine manganese in analytical reagent-grade sodium; chloride and in, high-purity tin: After the samples had, been brought into.solution, manganese ‘was separated’by using a lanthanum carrier?. The analytical data, listed in Table I indicate the good precision and accuracy of the method employed ;’ the reversion method, affords the better precision. sUtiARY
”
Manganese(H) can be extracted as the primary dithizonate Mn(HDz), over the optimal pH ranges 9.5-11.0 (CHC13) or 9.0-10.3 (Ccl,). Even with the dithizone in large excess only Xl-60% of manganese is extracted. Synergic enhancement, in. the presence of 0.6 A4 pyridine leads to extraction of the complex Mn(HDz),Py., over the pH range 8.5-10.2 provided that a lo-fold excess of dithizone is present. ,The extraction constant, for Ccl4 is 3 * 10’ 7. Direct and reversion procedures for the spectrophotometric determination of manganese(H) are described and applied to the determination of manganese in sodium chloride (p.a.) and high-purity. tin. Only thallium(I) interferes. R&SUM&
.),.
. Le manganese(H) peut Qtre extrait comme dithizonate primaire, Mn(HDz),, aux pH 9.5 h 11.0 (CHCl,) ou9.0 a 10.3 (CC14). On ne peut extraire que 50 A 60% de manganese, meme, en presence d’un grand exces de dithizone. Une addition de pyridine 0.6 M conduit i une extraction du complexe’Mn(HDz),Py, aux pH de 8.5 it 10.2, avec un excbs de.10 fois de dithizone. La constante d’extraction pour Ccl4 est de 3 *lo- 7. Des methodes sont proposees pour le dosage spectrophotometrique du mangantse(II)‘avec application dans le chlorure de sodium (p.a.) et l’etain tres pur. Seul le. thallitim(I).g&e., ,, :
.’
. ZUSAMM~FASSUNG
:,
Mangan(II)‘kann als primares Dithizonat Mn(HDz), in den optimalen pHBereiohen 9.5-l 1 .O : (CHCIJ) oder 9.0-10.3 (CC14) extrahiert.. werden. Auch .mit Dithizon in grossem ljberschuss werden nur 50-600/, des Mangans extrahiert. Die synergetische Steigerung%r Gegenwart von 0.6 M, .Pyridin ftihrt ,zur Extraktion des Komplexes Mn (HDz)=Py, im pH-Bereich ‘8.5-1,O.a; ‘vorausgesetzt dass ein 10:father Dithizoniiberschuss’ vorhanden, ist.. Die Extraktionskonstante ftir CC14, ist 3 * 10’ ?; Es~werden+~unmittelbareund*~Umkehrverfahren fur die,.spektrophotometrische Bestimmung .von Mangan (II) ,beschrieben und, auf,die: Bestirnmung,.von Mangan in Natriumchlorid, (p.a:) und:,hochreineni’ Zinn angewendet; Nur . Thallium(I) stiirt. .,’ ‘, ,‘.‘(’ R&ERE,N\ICES‘,. : : : .. .!’ : -: ” : ., ‘, ‘. .,! -.,/ ,’ ,::, ,:,,‘,” ., .‘. I FL;,AKAIWA AND H.’ KAWAMOTO, Anal. Ck’t~t. Acfu, 40 (1968) 407.
4, I-1: M. ?RVING AND’E; J: BIJTLBR,Ai;afjst; 78 (1953) 571. ‘, ’ 5 %. ,H. AYRES r~~i) B. D, NARANU, Anti/. ,Cltim. Ada; 24 (1961) 241. 6. Z.;MI\R?XQNRO!.I\ND M:MOJSKI, CYtem.. ~Attctl. (Wursnw); 12 (1967) 1155;
AiraL %XirnL’Acta;’ 54 (1971) 469-474
’
:
’
‘,
j