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Oximidobenzotetronic acid
343
OXIIUIDOBENZOTETRONIC A NEW
REAGENT
FOR
THE
ACID
SPEC-~IIOPHOTOrVIE;TRIC OF Il~Ox(II)
DI.Yl’ERMIN.4TIOI\
WENCER AND DUCKEKT~ have made a critical study of various organic reagents recommended for the colorimctric determination of iron. In the past few years, a large number of compounds have been suggested for the! calorimetric and spcctrophotometric determination of iron. Some of these arc : ~-ll~clrosybiphctI_vl-3-carbos?rlic acid’, ethyl n-isonitrosoacctoacctatc”, nitroso I<-salta, s,G-l~cnzoc~uin:~lcliic xicl5, xpicolinic acid and quinalclic acid (l.7, nt-mctliosy-o-nitrosophenolH, iodosinc”, f,7-clihyclrosy-r,ro-phcnanthrolinc’“, 2-fluorobcnzoic aciclll, z-ucctvl-p~.ritlinc osirnel2, 4,7cliphcnyl-r , xo-plienanthrolinel:~ , 3-hc*clrosy-2-naphthoic acidid, q-uinolinic acicll~, picolincdio,simc*O and o-c,lianisiditic!l7. 13ut all these reagents suffer from the disadvantage that a strict pH control is necessary, and in many cases organic solvents arc necdcd either to keep the complcs in solution or to estract the colourcd complcs; also in many cases foreign ions interfere in the calorimetric dctcrmination. SASI)EI_I.~* has clescribccl and reco~mcnclctl wrious reagents for tllc colorirnctric clcthninntion of iron. o-Phcnanthroline~~ is good, but has certain clisadvantnges: silver and bismuth give precipitates with the reagent, and the mctliocl cannot give accurate results when large amounts of metal ions like zinc, trmgstate, nickcl,cobalt and tin are present with iron. Although the thiocyanate mcthocl~‘~ is cstensivcly used, the method suffers from the following drawbacks: a large csccss of the reagent is ncccssary for complete colour clevelopmen t, the method can be used only within a narrow p11 range, fluoride, phosphate, osalnte, vanaclatc, molylxleniim and tungsten intcrferc and the colour fades rapidly with time. During the course of our studies of certain derivatives of benzotetronic acid as analytical reagents”0-“2, it has been observed that osimidobenzotetronic acid (or dcisonitrosobcnzotetronic acid) can be successfully employed for the spcctrophotometric determination of iron(I1). ANSCHOTZ” LJ first prepared this compound and after analysis of its silver salt gave CuH404NAg as the molecular formula for the salt. This author also reported the formation of a blue colour when an aqueous suspension or alcoholic solution of the reagent was treated with an aqueous solution of iron chloride. We have now observed that when a freshly prepared alcoholic solution of this reagent is treated with an aqueous solution of iron( R cleep blue water-soluble complex is instantaneously produced. Although a similar reaction is seen with iron(III), we have studied only the former reaction, as it is more sensitive and the colour development is instantaneous. The iron(complex is quite stable Anal.
Ckirn.
Ada,
25
(196x)
343-347
344
A.
N.
IJHAT,
13. I).
JAIS
and the intensity of 4l1e colour remains unchanged between the wide PH range of obeys Lambert-Beer’s law between the concentration 2.5 and x0.o. The comples range of 0.54-5.4 p,p.m. of iron and the optical density is unaffected within the for iron; only cobalt, temperature range of IO-_SoO. The reagent is quite selective nickel, ccrium(IV) and zirconium give coloured complexes but they interfere only when present in quantities more than fifty times that of iron.
4-Hyclrosycoumarin, an easily available substance was prepared by the mcthocl of into oximidobenzotetronic acid by the et dz4, and was reaclily converted action of nitrous acid as dcscribccl by ANSCMYKP. The strength of the solution of osimiclol~en~otetroni~ acid in alcohol employed was 1.0. x0-3 M. STAHMAN
Ferrous ammonium suiphatc (pro aaalysi) w;Ls used. Hydrosylaminc llydrochloride was used as the reducing agent to ensure that all iron was in the clivalent state. All other reagents wore of .B.W.H. (AR.) or Merck pro annlysi quality.
A Hi&r U.V. Spcctrophotomctcr wns employed for the absorption spectrum of osimidobenzotetronic acid. All other spectrophotometric measurements in the wavelength range of 370 m/c-750 my4 were made with the Unicam Spectrophotometer Model SP Goo; x-cm absorption cells were used. All PH rne~~s~~rerne~~tswere made with the help of a I3cckmann PH Meter Model H z.
The absorption spectrum of osimidobenzotetronic utrrtviolct as well ~1s in the visible region. Maximum
Wavelength
acid was asccrtainecl in the absorption was observed at
mp
Arrcd. Cltim.
Actu.
25 (1gGr)
343-347
345
OSIMIDOBENZOTETHOSICt\CID
249 m,u and 334 m/t, the former being more pronounced than the latter (Fig. I), and no absorption maximum was observed in the visible region. The absorption spectra of the iron(osimidobenzotetronic acid complex was determined at various PH values between 2.0 and 10.0, pH adjustments being made with dilute solutions of hydrochloric acid and sodium hydroside. The comples exhibited maximum absorption at 625 rnic in every case (Fig. 2), which indicated that only one type of comples was produced under these conditions of PH. The comples after partial estraction with chloroform exhibited the same absorption maximum. A 50% (v/v) ethanolic solution of the complex also had the absorption masimum at 625 m/l; the absorption clue to the reagent
Wovclcngth Pig.
2.
t\lJS(JI@cJll
l at pH 10.0;
I
In rnp
spectrum of ircm( I I)-r)ximidobcnzotctronic acid complex. at I)H 8.0 and 6.0; 0 at pH 4.0; A at pll 2.0; r-1in chhxwform: cthannl.
at this wavclcngth was found to be ncgligiblc. chosen in the subsequent investigations.
The wavelength
625
lmnx = Gz5 mp >( in 50% (v/v)
m/l was, thcrcforc,
The optical densities at 625 m/c of a series of solutions containing osimidobenzotctronic acid and iron(I1) in the molar ratio of 0.5 : I to g : I were determined. A plot of the results showed that maximum density was reached at the molar ratio of For the determination of iron, however, the 4 and remained constant thereafter. molar ratio of the reagent to iron was maintained at IO in the subsequent studies. Effect of fiH on the ojdical density
of iron(oximidobenzotetroltic
The stock solution of the complex was 6.6.10-6 M with of this solution was taken in a 25-ml measuring flask and the mark using dilute solutions of hydrochloric acid and sodium resultant solution to a PH value within the range of 2.5-10.
acid coq%?4m respect to iron: IO ml volume made up to the hydroxide to bring the It was found that the
A wti. Clrirn. Ada,
25 (IgGi)
343-347
A. N. BHAT,
346
B. D. JAIN
absorption by the complex is at a maximum and remains unchanged over this wide PH range. The PN of each of the solutions was determined using a suitable glass electrode. Stllhility 0j th? colollr o/ tile comp1cx The colour of the complex was found to be stable and no change in the optical density could bc observed even after keeping the complex for 36 h. The effect of temperature on the optical density of the complex was also studied using a thermostat for tcmpcraturcs above 25O and a refrigerator for lower temperatures. No change in tllc optical density of tllc comples was observed between xo” and 50”. ‘I’!Ic colour of tllc complex is, however, destroyed on continuous heating at Ioo”. The complex was found to obey Lambert-Beer’s law in the concentration range of 0.54-5.4 p,p.m. of iron and in tlic pri range of and 10.0.
.“___, .,__ _-. _.. ___. _ .._. _
___... _-_..__.._ -_
..
._
-
rruku,cII.5
IOIl
p.p.w.
.I._
-....__--._-._--
lolmdlr’tf .--
I’trtirssill~ll
S;Llt
’ PfJ
GOV
Sodium
sidt
Soclium Sodium
salt Sillt
X00
~~JC~illlll
Sillk
#loo
2000
800 /(OO
720 500 GO0 I500
MolylJclcnulll Nickel Silvct Thorium ‘I’itnnium
I Q.200 200 .I00 I200
AnimcJniuni Sulpl1cltc N i trntc Nitrate I’cJt.
titallyl
Scdiuni
\vlJlfriilll
400 72“
inolylJtlatc
LOO
.+00
tuiqstntc
.?OO
Urmiiiln(
,iOO
Yttrium
t_Jranyl nitrntc Nitrate
%irconiuni
(>xychkJridc
Zinc
S11Ipha_!
IOZO
N i triltc
I\niinonium
.tOC’
iii1r;rt.c:
200
Oxdl~tc
Nitrxtc
\’ 1)
gro
I .I.&0
S111pl1atc:
~~liloritlc
I LOO 300
3600 I20 I
I ICI
I 00 I 00
Slll~~l1iltC! .
Iderlerence
Sulpl1atc Sulpl1ntc Nitrate Nitrate Strlpllatc Chlrwitlc
GVO
Sillt
Allilnc~l~iilm
.-__
dare to foreign. ions
The stoclc solution of the complex was I * IO- 4 M wit11 respect to iron, and the molt ratio of the reagent to iron was 10. 10 ml of this solution was transfcrrecl to a 25-ml standard flask and mixed with a known amount of a solution of a foreign salt, and the volume was made up to 25 ml with water. The optical density was determined within IO min of mixing. The concentration of the foreign salt in the complcs solution was progressively increased till the optical density changed by 2% from the theoretical values. The concentrations of the ions testccl which caused ,no interference are given in Table I. No interference was causecl by tin(I1) or sulphitc. Hyclroquinone was used as the reducing agent when the interference of silver was studied.
OSIblIDOBENZOTETRONIC
Reconnnended
AClD
347
procedure
The
given iron solution at pH 2.5-10.0 containing 0.54-5.4 p.p.m. of iron is with a fresh solution containing a ten-fold amount of the reagent in the minimum amount of alcohol within the temperature range 10-50~. The optical density at 625 m/l of the ferrous complex so produced is measured and the concentration of iron deduced from a standard calibration curve obtained under similar conditions.
treated
ACKNOWLEDGEMENTS The
authors
I)cpartment,
of Atomic
are grateful to Prof. T. R. SESHADRI, F.R.S., Head of the Chemistry for his kind interest and helpful discussions, and to the Department Energy, Govt. of India, for financial assistance.
Oxilniclol,cnzotctronic acid is l~roposcd for thu spcctro~‘l~utomctric estimation of iron. A frcshl? l~rclXLrc!d ZdcOhdic Sdllti(Jn Of thC rcagcrlt ~NdllCCs il deep MLIC water-soluble complcs with an ac~ucwus solution of iron( Il). ‘I’hc conil~1c.x is stable ant1 its optical density is constnnt nt 1114 2.5-10. I,ambcrt-I3ccr’s 1~1~ is followxl from 0.54-5.4 11.p.m. of iron nt G25 nip; tcmpcraturc hns no effect bctwccn IO” ant1 $50~. ‘I’hc rwgcnt is highly sclcctivc for iron.
cst proposd p’our Ic dOSilKC spcctrophotoUn nouveau rdactif, l’aciclc oxitnitlol,cnzotbtronicllrc, niJtricluc clu fcr( I I). Cc rCactif cst tr&s sdlcctif ct clonnc un coml~lcxc blcir tr& stable.
%ur sI’cktrol’hot~)Inctrisclicn Ijcstinlmun~ Van I’c-(I I) wirtl Oxi;~~itlc~~~nzotctrolis~llrc ~~orp2sclila~cri, tlas mit Fe-(II) cincn stabilcn, I~lnu gcftirbtcn I~onil~l~~ bilclct.
;ds licqpnz
ID I:. D. SNIS1.LANV C. 1’. SNI:LL, Colorirmfric Methods of Atiulysis, Vol. II, 3rcl Eel., trand, New York, 1954, p. 307, 2” h. N. UHAT AND U. 1). JAXN, l‘ctfartlu, 4 (1960) 13. “1 r\. N. Ibit\T AND 13. I>. JAIN, ‘I’ccb~frc, 5 (1g60) 271. 22 A. N. ISHAT ANIJ 13. D. JAIN, hoc. Indiun Acud. Sci., 53h (1961) 147. 23 R. ANSCHC~TZ. Awr. C/IP)~., Liebigs, 3G7 (rgog) r6g. w M. A. SThlInlhN, I. WOLFF AND I<. 1’. k.NK, J. Am. Chetti. sot., 65 (1943) 2285. Aw~l. Clriw.
Ada.
2’5
(I~GI)
\‘an Nos-
343-347
OXIIUIDOBENZOTETRONIC A NEW
REAGENT
FOR
THE
ACID
SPEC-~IIOPHOTOrVIE;TRIC OF Il~Ox(II)
DI.Yl’ERMIN.4TIOI\
WENCER AND DUCKEKT~ have made a critical study of various organic reagents recommended for the colorimctric determination of iron. In the past few years, a large number of compounds have been suggested for the! calorimetric and spcctrophotometric determination of iron. Some of these arc : ~-ll~clrosybiphctI_vl-3-carbos?rlic acid’, ethyl n-isonitrosoacctoacctatc”, nitroso I<-salta, s,G-l~cnzoc~uin:~lcliic xicl5, xpicolinic acid and quinalclic acid (l.7, nt-mctliosy-o-nitrosophenolH, iodosinc”, f,7-clihyclrosy-r,ro-phcnanthrolinc’“, 2-fluorobcnzoic aciclll, z-ucctvl-p~.ritlinc osirnel2, 4,7cliphcnyl-r , xo-plienanthrolinel:~ , 3-hc*clrosy-2-naphthoic acidid, q-uinolinic acicll~, picolincdio,simc*O and o-c,lianisiditic!l7. 13ut all these reagents suffer from the disadvantage that a strict pH control is necessary, and in many cases organic solvents arc necdcd either to keep the complcs in solution or to estract the colourcd complcs; also in many cases foreign ions interfere in the calorimetric dctcrmination. SASI)EI_I.~* has clescribccl and reco~mcnclctl wrious reagents for tllc colorirnctric clcthninntion of iron. o-Phcnanthroline~~ is good, but has certain clisadvantnges: silver and bismuth give precipitates with the reagent, and the mctliocl cannot give accurate results when large amounts of metal ions like zinc, trmgstate, nickcl,cobalt and tin are present with iron. Although the thiocyanate mcthocl~‘~ is cstensivcly used, the method suffers from the following drawbacks: a large csccss of the reagent is ncccssary for complete colour clevelopmen t, the method can be used only within a narrow p11 range, fluoride, phosphate, osalnte, vanaclatc, molylxleniim and tungsten intcrferc and the colour fades rapidly with time. During the course of our studies of certain derivatives of benzotetronic acid as analytical reagents”0-“2, it has been observed that osimidobenzotetronic acid (or dcisonitrosobcnzotetronic acid) can be successfully employed for the spcctrophotometric determination of iron(I1). ANSCHOTZ” LJ first prepared this compound and after analysis of its silver salt gave CuH404NAg as the molecular formula for the salt. This author also reported the formation of a blue colour when an aqueous suspension or alcoholic solution of the reagent was treated with an aqueous solution of iron chloride. We have now observed that when a freshly prepared alcoholic solution of this reagent is treated with an aqueous solution of iron( R cleep blue water-soluble complex is instantaneously produced. Although a similar reaction is seen with iron(III), we have studied only the former reaction, as it is more sensitive and the colour development is instantaneous. The iron(complex is quite stable Anal.
Ckirn.
Ada,
25
(196x)
343-347
344
A.
N.
IJHAT,
13. I).
JAIS
and the intensity of 4l1e colour remains unchanged between the wide PH range of obeys Lambert-Beer’s law between the concentration 2.5 and x0.o. The comples range of 0.54-5.4 p,p.m. of iron and the optical density is unaffected within the for iron; only cobalt, temperature range of IO-_SoO. The reagent is quite selective nickel, ccrium(IV) and zirconium give coloured complexes but they interfere only when present in quantities more than fifty times that of iron.
4-Hyclrosycoumarin, an easily available substance was prepared by the mcthocl of into oximidobenzotetronic acid by the et dz4, and was reaclily converted action of nitrous acid as dcscribccl by ANSCMYKP. The strength of the solution of osimiclol~en~otetroni~ acid in alcohol employed was 1.0. x0-3 M. STAHMAN
Ferrous ammonium suiphatc (pro aaalysi) w;Ls used. Hydrosylaminc llydrochloride was used as the reducing agent to ensure that all iron was in the clivalent state. All other reagents wore of .B.W.H. (AR.) or Merck pro annlysi quality.
A Hi&r U.V. Spcctrophotomctcr wns employed for the absorption spectrum of osimidobenzotetronic acid. All other spectrophotometric measurements in the wavelength range of 370 m/c-750 my4 were made with the Unicam Spectrophotometer Model SP Goo; x-cm absorption cells were used. All PH rne~~s~~rerne~~tswere made with the help of a I3cckmann PH Meter Model H z.
The absorption spectrum of osimidobenzotetronic utrrtviolct as well ~1s in the visible region. Maximum
Wavelength
acid was asccrtainecl in the absorption was observed at
mp
Arrcd. Cltim.
Actu.
25 (1gGr)
343-347
345
OSIMIDOBENZOTETHOSICt\CID
249 m,u and 334 m/t, the former being more pronounced than the latter (Fig. I), and no absorption maximum was observed in the visible region. The absorption spectra of the iron(osimidobenzotetronic acid complex was determined at various PH values between 2.0 and 10.0, pH adjustments being made with dilute solutions of hydrochloric acid and sodium hydroside. The comples exhibited maximum absorption at 625 rnic in every case (Fig. 2), which indicated that only one type of comples was produced under these conditions of PH. The comples after partial estraction with chloroform exhibited the same absorption maximum. A 50% (v/v) ethanolic solution of the complex also had the absorption masimum at 625 m/l; the absorption clue to the reagent
Wovclcngth Pig.
2.
t\lJS(JI@cJll
l at pH 10.0;
I
In rnp
spectrum of ircm( I I)-r)ximidobcnzotctronic acid complex. at I)H 8.0 and 6.0; 0 at pH 4.0; A at pll 2.0; r-1in chhxwform: cthannl.
at this wavclcngth was found to be ncgligiblc. chosen in the subsequent investigations.
The wavelength
625
lmnx = Gz5 mp >( in 50% (v/v)
m/l was, thcrcforc,
The optical densities at 625 m/c of a series of solutions containing osimidobenzotctronic acid and iron(I1) in the molar ratio of 0.5 : I to g : I were determined. A plot of the results showed that maximum density was reached at the molar ratio of For the determination of iron, however, the 4 and remained constant thereafter. molar ratio of the reagent to iron was maintained at IO in the subsequent studies. Effect of fiH on the ojdical density
of iron(oximidobenzotetroltic
The stock solution of the complex was 6.6.10-6 M with of this solution was taken in a 25-ml measuring flask and the mark using dilute solutions of hydrochloric acid and sodium resultant solution to a PH value within the range of 2.5-10.
acid coq%?4m respect to iron: IO ml volume made up to the hydroxide to bring the It was found that the
A wti. Clrirn. Ada,
25 (IgGi)
343-347
A. N. BHAT,
346
B. D. JAIN
absorption by the complex is at a maximum and remains unchanged over this wide PH range. The PN of each of the solutions was determined using a suitable glass electrode. Stllhility 0j th? colollr o/ tile comp1cx The colour of the complex was found to be stable and no change in the optical density could bc observed even after keeping the complex for 36 h. The effect of temperature on the optical density of the complex was also studied using a thermostat for tcmpcraturcs above 25O and a refrigerator for lower temperatures. No change in tllc optical density of tllc comples was observed between xo” and 50”. ‘I’!Ic colour of tllc complex is, however, destroyed on continuous heating at Ioo”. The complex was found to obey Lambert-Beer’s law in the concentration range of 0.54-5.4 p,p.m. of iron and in tlic pri range of and 10.0.
.“___, .,__ _-. _.. ___. _ .._. _
___... _-_..__.._ -_
..
._
-
rruku,cII.5
IOIl
p.p.w.
.I._
-....__--._-._--
lolmdlr’tf .--
I’trtirssill~ll
S;Llt
’ PfJ
GOV
Sodium
sidt
Soclium Sodium
salt Sillt
X00
~~JC~illlll
Sillk
#loo
2000
800 /(OO
720 500 GO0 I500
MolylJclcnulll Nickel Silvct Thorium ‘I’itnnium
I Q.200 200 .I00 I200
AnimcJniuni Sulpl1cltc N i trntc Nitrate I’cJt.
titallyl
Scdiuni
\vlJlfriilll
400 72“
inolylJtlatc
LOO
.+00
tuiqstntc
.?OO
Urmiiiln(
,iOO
Yttrium
t_Jranyl nitrntc Nitrate
%irconiuni
(>xychkJridc
Zinc
S11Ipha_!
IOZO
N i triltc
I\niinonium
.tOC’
iii1r;rt.c:
200
Oxdl~tc
Nitrxtc
\’ 1)
gro
I .I.&0
S111pl1atc:
~~liloritlc
I LOO 300
3600 I20 I
I ICI
I 00 I 00
Slll~~l1iltC! .
Iderlerence
Sulpl1atc Sulpl1ntc Nitrate Nitrate Strlpllatc Chlrwitlc
GVO
Sillt
Allilnc~l~iilm
.-__
dare to foreign. ions
The stoclc solution of the complex was I * IO- 4 M wit11 respect to iron, and the molt ratio of the reagent to iron was 10. 10 ml of this solution was transfcrrecl to a 25-ml standard flask and mixed with a known amount of a solution of a foreign salt, and the volume was made up to 25 ml with water. The optical density was determined within IO min of mixing. The concentration of the foreign salt in the complcs solution was progressively increased till the optical density changed by 2% from the theoretical values. The concentrations of the ions testccl which caused ,no interference are given in Table I. No interference was causecl by tin(I1) or sulphitc. Hyclroquinone was used as the reducing agent when the interference of silver was studied.
OSIblIDOBENZOTETRONIC
Reconnnended
AClD
347
procedure
The
given iron solution at pH 2.5-10.0 containing 0.54-5.4 p.p.m. of iron is with a fresh solution containing a ten-fold amount of the reagent in the minimum amount of alcohol within the temperature range 10-50~. The optical density at 625 m/l of the ferrous complex so produced is measured and the concentration of iron deduced from a standard calibration curve obtained under similar conditions.
treated
ACKNOWLEDGEMENTS The
authors
I)cpartment,
of Atomic
are grateful to Prof. T. R. SESHADRI, F.R.S., Head of the Chemistry for his kind interest and helpful discussions, and to the Department Energy, Govt. of India, for financial assistance.
Oxilniclol,cnzotctronic acid is l~roposcd for thu spcctro~‘l~utomctric estimation of iron. A frcshl? l~rclXLrc!d ZdcOhdic Sdllti(Jn Of thC rcagcrlt ~NdllCCs il deep MLIC water-soluble complcs with an ac~ucwus solution of iron( Il). ‘I’hc conil~1c.x is stable ant1 its optical density is constnnt nt 1114 2.5-10. I,ambcrt-I3ccr’s 1~1~ is followxl from 0.54-5.4 11.p.m. of iron nt G25 nip; tcmpcraturc hns no effect bctwccn IO” ant1 $50~. ‘I’hc rwgcnt is highly sclcctivc for iron.
cst proposd p’our Ic dOSilKC spcctrophotoUn nouveau rdactif, l’aciclc oxitnitlol,cnzotbtronicllrc, niJtricluc clu fcr( I I). Cc rCactif cst tr&s sdlcctif ct clonnc un coml~lcxc blcir tr& stable.
%ur sI’cktrol’hot~)Inctrisclicn Ijcstinlmun~ Van I’c-(I I) wirtl Oxi;~~itlc~~~nzotctrolis~llrc ~~orp2sclila~cri, tlas mit Fe-(II) cincn stabilcn, I~lnu gcftirbtcn I~onil~l~~ bilclct.
;ds licqpnz
ID I:. D. SNIS1.LANV C. 1’. SNI:LL, Colorirmfric Methods of Atiulysis, Vol. II, 3rcl Eel., trand, New York, 1954, p. 307, 2” h. N. UHAT AND U. 1). JAXN, l‘ctfartlu, 4 (1960) 13. “1 r\. N. Ibit\T AND 13. I>. JAIN, ‘I’ccb~frc, 5 (1g60) 271. 22 A. N. ISHAT ANIJ 13. D. JAIN, hoc. Indiun Acud. Sci., 53h (1961) 147. 23 R. ANSCHC~TZ. Awr. C/IP)~., Liebigs, 3G7 (rgog) r6g. w M. A. SThlInlhN, I. WOLFF AND I<. 1’. k.NK, J. Am. Chetti. sot., 65 (1943) 2285. Aw~l. Clriw.
Ada.
2’5
(I~GI)
\‘an Nos-
343-347