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The heterometric microdetermination of mercury with mercaptobenzthiazole in the presence of an excess of foreign metals
VOL. 13 (1955)
72
THE HETEROMETRIC MICRODETERMINATION MERCAPTOB~NZTHIA~OOLE IN THE PRESENCE OF FOREIGN METALS 31. UUUTELSl
AND
E.
OF MERCURY WITH OF AN EXCESS
JUNGREIS
INTRODUCTION
In a previous investigation’ the conditions ncccssary for the determination of mercury in acidic, neutral or alkaline solution wcrc given. Tn this paper we deal with the same determination but in the presence of large cxcesscs of foreign metals. The amount of mercury rcquircd for the analysis remains the same (r~ 5-ro-QM, or r~ 2 mg Hg in 20-30 ml solution). Ln the presence of many cations, especially in the prcscncc of trivalent cations the maximum density values obtained are lower than in the blank but ncverthcless, the determination of mercury can be carried out without difficulty and the error in general lies between zero and 3 o/‘. Except in the presence of copper and bismuth, the mercury could bc dctcrmined directly without making USC of complcxing agents. An aclucous solution was used which had been acidified with acetic acid. In most casts the mercury content in the foreign metal could bc reduced to less than one percent of the total metal content and thcrc was no limit to the amount of foreign metal which could be present. Each titration took, on the average, 20-30 minutes. Special consideration was given to the determination of mercury in the prcscncc of excesses of copper or bismuth, for which methods were clahorated which pcrmittcd a precise dctcrmination of mercury in the presence of ‘L 98 (yO of the former metals. EXPERIMENTAL
The same instruments ant1 the s;lmc working tions”. All chcmicols usccl were either analytical wcrc cat-rid out at zoo C. RESULTS
conclitions wcrc used as in the previous invcstigarcagcnts or chemically pure ragcnts. The titrations
AXD
DISCUSSION
Table I gives a compilation of titrations which wcrc carried out in acetic acid water solution. The composition and the results arc given in the table. No tiltcr whatsoever was used, even in the presence of strongly coloured solutions. This was possible so long as the colourcd cation did not participate in the reaction. The titration time remained the same as in the absence of foreign metals. ltc/ererrccs
p.
78
VOL.
13 (xqj5)
HETEROMETRIC
SfICRODETERMINATION
b .
OF
JIERCURY
73
M. BOBTELSKY,
74
Ccmposttir,n : 5 ml o.ootM (== MOT) ale. -----._-- --.._- _._.-_--_ ..- -. .E.tp. ~IcmlJrr
Hg(XO,), ____-
+
“_ ..__.__.
22
JUI’GKEIS
pl/
3.02
n-83.0
-7.0
s-3.8
VOL.
rg ml (or 25 ml) Complcmcnts - __._ --
.._ -..-
.--..-
+ x ml o.ooGGM
- ---__-__-__-_
-
Al fir x nil
13 fIQj5)
mcrcaptobenzthi
.__---_-~~~
Curnf?1zmn1s ____-
23
E.
-. _
..___. ---_-~__________
3 till 112Cl~,COOH
1 ‘I I
I#
2
,,
2
‘I
‘L9.5
2 09
‘2
,I
-9.5
2 94
2
I,
n29.5
2.97
2
,,
-9.5
2.07
-3.0 rL3.0 -7.0 -.
3*07
I.
I ml0 .zdI
+
CH~COOXiL
---
+
r
Cu(SO,),
f
3 mlo.zM
EDTA-Na,
ml o.?Jl Cti(N0.& + 3 ml 0.z.W EDTA-Sa,
.I
,I
-t- = ‘.
I,
I*
-I- -1 *,
,, XL,-cttrate
,.
9.
_f- ,L .I
,*
II
-I- 4 I,
II XI,-atratc
+ 8 ml, + 10 r
-f- 2 ml o 5~12 Cu(NC -I- 5 m -j- 2 1111 AI Cu(KO,), +
._.”
$ON
3 5
2.97
2
.I PI ,I
5
II
-I-
2
I‘
,I
i.
-!-
4 It
-i” 5 ‘I ‘I -I- 5 ,I .* _.._.---__-_-_ _.__--__P::
I‘ G5 1)‘ ------
In some cases (Ca, Bn, Al, Cr) the maximum density value is reduced. The influence of the conccntrntion of the foreign metal is not always observed and in these cases the concentration of the foreign metal may bc even more than shown in the table. In other cases a lower density value is obtained with the higher salt concentration. In the presence of trivalent cations, the concentration of the foreign cation must be greatly restricted. The limits are given in experiments x5-17. As can be seen from the table, the hcuvy foreign metals (Pb, Isa, Cd) may comprise sgg.5 %, the metals Co, Ni, Mn, Zn, > gg %, and the light metal Mg, gS ‘;/o, of the total metal content. For the trivalent metals, aluminium may comprise more than go Q/O while iron and chromium may make up more than g5 */0 of the total metal content.
(n) 1~. tire $wmnce of etirytene~~ci~~,ninetetvaacetate, Special heterometric titrations with bismuth and Ml3T wcrc carried out in the presence of EDTA-Na, in order to clear up the prr-dependency of the precipitation, One experiment had the following composition: 5 ml o.oozlld Bi(NO& (+ HNO,) + I ml o.r.ii HCl + z ml LIP CH,COOH + 2 ml X N&NO, + 3 ml o.orJl MBT + 2 ml o.o~Jl EDTA-Na, + 5 ml I-I,0 _t- x ml .ii NaOH. The result was that bismuth remained in solution at all plr’s and no precipitation occurred. An analogous esperimcnt which was carried out in the abscftcc of EDTA-Na, showed that bismuth is precipitated heteromctrically in acid solution. From our previous investigation1 WC know that EDTA, if present in acetic acid or sodium acetate Jt’eferetrces
p.
78
ni
+ 2 ml iv1 Cu(XO& ,* Kn,-citrate ml ilk. + IO ml I-I,0 (vol. = -j- 2 ml M CU(NO& -i- .I 0 ,, Xii,-ciiratc *. I. -t- 2 ,, 0 ,, IO ml ale, f 5 ml f-I,0 (vol. = + 2 ml M Cu(NO& ,I ,. -t 2 ,* ,I I. -I- 4 .* ,, Xtig-cftriit~ 15 ml ilk. (vol. - : f 3 ml 0. I Af EIITA-Na, -t_ 2 nil 0. I Al lS(P1103)3f- 7 ml *, CEI,COOl~I .I
:: -
VOL.
13
HETERONETRIC
(1955)
.t: 2.006 mg Hg
T =
20’
BIICRODETERBII~c’hTIOS
OF
MERCURY
75
C
----
_-__
---_.--_-
Inild
RCWlWkS
pmcip.a1
--_._ __-_-_-_._--___
_ - __...__ . ._ ____.._
_.
-
..
.-._
y/,
rul _
_. _..
crmr
_ _
12.7 12.7
30 32
p max. then steep drop.
G.1
12
imum, then drop.
G.I
‘5
0.0
3.oG
25
0. .I
3.00
11
00
0.Gg
0.0
x.55
30
0.0
0.71
-0.3
‘ccipitatc floats on the surface
irn line,
then slow
1.
I,
1,
,.
,,
0,
1,
,.
0
,*
drop.
20
0.4 +
I.0
I.55
15
0.0
0.75
-2.0
0,
1 55
14
0.4
0 79
-1.0
0.
r*55
*s
0.53
-1.0
4.6 I .92
35 45
0.9.1
$-a.3
I.02 _ ._
+0.7
0.4
^ .
. .
X.4)
0.0 0.2
30 -. _-_- - -
I.8
.
0.St
+2.5 -1.0
0.89
_
_
_
-..
.
.
solutions, dots not influence the hetcromctric titration of mercury with MHT. Acting on these results, WC tried to determine mercury in acetic acid solution in the l>rcsence of bismuth, by the addition of EDTA-Na,. Table II, experiments 32-34 (Fig. I) show these results. The csl~eriment number and tlic curve number correspond to facilitate
3 Fig.
1.
bismuth. References
Titrations p.
~8
of mercuric
nitrnte
in solutions
containing
ml
complcxing
agents
and
copper
or
76
XI,
BOJW.ELSKY,
E.
JUXGREIS
VOL.
13 (rc)55)
cornparison. As can 1~ seen, mercury can be determined without any difficulty in an acetate or acetic acid solution which contains sufficient EDTA to bind any bismuth. As cxperimcnt 3-1 with sodium ac~tutc shows, the initial precipitation occurs very late, only after the addition of fro ‘3/O of the MBT which was necessary for the titration. i’his is of course ;L disadvantage, but in spite of this the obtained masimum density value was as high as usunl and the error was only I~$,. Our solution contained 98 ‘/o bismuth. Hccausc of the maximum density values in the presence of EDTA and bismuth which . are high, even less mercury can be dctcrmincd. (b) 1n Ihc +WCSC)ZCC o/ tvisodiztnzcitv~~te. In the presence of excesses of citrate, in neutral or ~~lk~tlinc solutions, a precipitate was obtained with lzismuth immediately, and no titration coulcl be made.
(a) 192 I/tc ~JYCSC’I~CC a/ ethylencc~irci)z2’?tctetv~~ricLttnte. Just as in the case of bismuth, similar parallel heteromctric and prr-titrations were carriecl out with copper in the prcsencc, as well as in the abscncc of EDT.4. WC could ascertain that copper is not precipitated by the addition of M13T in the prcscncc of IXWA under any conditions of pii’s. WC used this property for the hctcrometric titration of mercury in the presence of copper. Tnblc II, cspcrimcnts 22 and 23 (Fig. I) show the results of such titrations from acetic acid or acetate solutions. As can bc seen, mercury can bc determined only in mctic u&Z solution if sufficient IXWA is added to hind the copper. (1~) In tl~..e+yL’scncc oi trisocti2lntcitvale. From our previous investigations WC know that trisodiumcitratc dots not interfere with the hetcrometric determination of mercury with MIST at any pn, and may bc present in any concentration. From other invcstigation$ WC know that copper forms a soluble very strong comples with citrate, cspecintty i?t c&zclli~a solrrlion. Acting on these results, WC carried out a series of heterometric titrations some of which are compiled in Table 11. The course of the titrations can be seen in Pig. I. As csperimcnt 24 shows, the titration cannot bc carried out without disturbances if an NQWWWG solution of mercury is titrated. A minimum amotmt of alcoltol must be prcscnt. As Fig. I shows, WC obtain, in all cases, at the analytical end-point, an optical masimum density &W and then the density drops with the further addition of MBT. The critical cncl-point is obtained by the intcrscction of the Inst part of the titration l&e with the horizontal maximum density line. As esperiments 29-31 (vol. = 30 ml!) show, escn a r~ 30 */* alcohol (by volume) does not change the value of the. mnsimum density. In 50 ‘yO alcoholic solution (cxp. 31), the masimum density value is already reduced, Apart from this, the initial precipitation onIy begins after the addition of 50 l)/v of the MBT, which was necessary for the titration. Thcrc is no limitation to the amount of trisodiumcitrate which may be present. This clcpcnds on the amount of alcohol adclcd, as the solubility of trisodi~lmcitr~~tc decreases with the addition of alcohol. The amount of copper which may be present on the other hand, clcpends on the amount of citrate and cannot be higher than I :I. In any case, the mercury makes up less than 2 o/o of the total metal content. The titration proceeds without difficulty ancl lasts 10-20 minutes. The error lies between zero and 2 “/o. i?efcseltcesp. 7s
VOL.
13
(1955)
HETEROMETRIC
MICRODETERMtNilTION
OF
MERCURY
77
METHOD
zo ml of an aqueous salt solutioil which contains 1 ml &I acetic acid and about 2 mg mercuric mercury a5 nitrate or srllphatc, arc titrntcd hctcrometrically with an alcoholic solution of o.orfiZo.oogllr meicaptobcnttliiazole. The snlutlon may contain the following cations, in a concentration of 0.2M c-t higher, as nitrates or sulphates: Ca, I3a, 316. Zn. bIn. Ni, Co and Cd Lead may not be at a concentration higher than 0.x&I. The concentration of the trivalent cations Al, Cr. Fe, may iiot bc higlicr than o.OgJZ. No colourcd filter is nccclccl in the prcscncc of colourcd cations. l’hc error is o-3 ‘:,&. 2.
Determination 1~1de pescnce
in the prcsmm
of excesses
of bismtrtl~
or copper
01 elll)lle,ledicrrtai,lelclmacelflle. (a) 20 ml of the aqueous solution of mercuric nitrate to bc analysetl, contain 1-2 mg mercury and an excess of bismuth which may constitute %98 “/{, of the metal content. Sufticicnt cthylencdiam~nctct~aacctatc salt solution to bind the bismuth 1s addctl ‘rho free strong acid wh ch is prcscnt in solutiou IY then transformed into to the solution, acetic acid by the addition of sodium acetate, which may I c present in c~xccss. The solution is brought to a volume of about 20 ml and titrated hctcromctrlcally with an alcoholic solution of o.or~Vf-o.oogjlf mcrcaptobcnztl~inzolc. An cnlar@ curve of tlic last part of the titration is clrawn. Tlic end-point is obtained from the intcrscction of the lint of the last part of the titration with the horizontal optical maximum tlcnsity line. The titration time is about 30-40 minutes. Error o-3 ojo. (b) The aclucous solution of mercuric nitrate or sulfate to bc analyscd contains x-2 mg mercury and an C.XCCS~of copper. To this solution is added sufficient cthylencdinniiuctctraacctntc salt solution, to bind the copper. The solution obtained is ncutralisctl ant1 then 3 ml Jf acctlc acid is utltlctl, since the final solution has to be acidic. The final solution is tllcn brought to a volurnc of 20-30 ml and titratccl hctcrornctrically with an alcoholic solution of o.oxfir-o.oognl mcrcaptobcnzthiazolc. The end-point of the titration is obtained from an cnlargcd curve of the last part of the titration by the intcrscction of the titration hnc with the horizontal optical maximum tlcnsity line. No Colcurcd filter is rcquirctl. The titration time is ‘L 30 minutes. Error 1-2 ?,A. 1,; I& pIese)lce oi trisodirtnrcilrale. (c) To tllc aiialysed solution which contains I< 2 rug mercuric mercury and an cxccss of copper (up to 98 “IO or more), are ad&d: x ml Jf Na-Qitratc _1- 2 ml iV NH,NO, -t_ 2 ml Al NH, + 5-10 ml nlcol~ol. The solution is brought to approximately 30 ml and then titrated hctcromctrically with an alcoholic solution of o.orM-o.oogM mcrcaptobciiztliia~olc from a microburct (0.01 ml). The minimum amount of trlsodiumcitratc which has to bc acldccl is I molt citrate per I molt copper. The pcrccntagc of alcohol in the solution must bc 15 y&-30 ‘x,, The end-point is obtained by the intcrscction of the hnc of the last part of the titration wit:1 the horizontal entllinc. No colour filter is needed. The titration lasts x0-15 minutes. Error 0-2 O/b. Pram the two methods prcscntctl the last is to bc prcfcrrcd as the concentration of copper may bc high and the titration proceeds quickly. SUMMARY I. A gcncral method is prcscntcd for the dctcrmination of I-Z mg mercuric mercury, in the abscncc of coinplcxing agents, in 20 ml solution, with an error of o-3 %. The solution may contain: Ca. Da, Mg, %n, hfn, Ni, Co or Cd as nitrate of sulphatc in a conccntration of 0.2M. The concentration of Pb should bc
1. Une mGthodc g6n5rale est proposde pour Ic dosage du mercurc(IT) (I h 2 mg dans 20 ml dc solution), avcc unc erreur de o-3%, cn l’abscnce d’agcnts complexants. La solutlon pcut contcnir Ca, Ba, Mg, Zn, Mn, Ni, Co ou Cd (sous formc de sulfates ou dc nitrates) cn concentration 0.21M. La. concentration en plomb doit Ctrc plus pctitc que 0.1fi1 ct cellc d’Al, Cr ou Fe plus pctitc que o.og&Z. Referertces
p.
7s
78
M.
BOBTELSKY,
E.
JUNGREIS
VOL.
13 (1955)
2. UIIC m6tlioclc spdciale cst proposBc pour lc dosage clu mercurc (r-2 mg clans 20 ml solution), (s g8%), en employant I’hthylhnediaminetetraac~tate. en prbscncc cl’un gros exces dc bismuth, L’crrcur cst clc o-3%. 3. Une m&ho& est proposec pour lu dosage clu mcrcure en pr6scnce de cuivre cn cxc&s, en solution cl’acidc ac&ique, runfcrmant l’btlIylbnediaminet&raac~tatc. ‘1. Une m&ho& spdciale cst proposdc pour lc closagc clc mcrcurc (1-2 rng clans 3o ml solution} en pr&cnce d’un yros cxc&s de cuivrc (>gS’%,). Lc titrage est effectub en solution alcalmc dc citrate est comprise entrc o-2fz/o. trisod~que. Cc closagc cst rapidc. L’crrcur %USABIMBNFASSUNG wc1c1~c erlaubt, 1-2 mg Quccksilbcr in 20 ml I. Einc alIgemeine Methodc wircl vorgcscklagen, I,iirung in Abwcscnhcit von komplexiercndcn Iic Pb-Konzcntration sol] 98OA,) enthhlt, XII bcstlmmcn. llic Titration wircl in dl
1
72
THE HETEROMETRIC MICRODETERMINATION MERCAPTOB~NZTHIA~OOLE IN THE PRESENCE OF FOREIGN METALS 31. UUUTELSl
AND
E.
OF MERCURY WITH OF AN EXCESS
JUNGREIS
INTRODUCTION
In a previous investigation’ the conditions ncccssary for the determination of mercury in acidic, neutral or alkaline solution wcrc given. Tn this paper we deal with the same determination but in the presence of large cxcesscs of foreign metals. The amount of mercury rcquircd for the analysis remains the same (r~ 5-ro-QM, or r~ 2 mg Hg in 20-30 ml solution). Ln the presence of many cations, especially in the prcscncc of trivalent cations the maximum density values obtained are lower than in the blank but ncverthcless, the determination of mercury can be carried out without difficulty and the error in general lies between zero and 3 o/‘. Except in the presence of copper and bismuth, the mercury could bc dctcrmined directly without making USC of complcxing agents. An aclucous solution was used which had been acidified with acetic acid. In most casts the mercury content in the foreign metal could bc reduced to less than one percent of the total metal content and thcrc was no limit to the amount of foreign metal which could be present. Each titration took, on the average, 20-30 minutes. Special consideration was given to the determination of mercury in the prcscncc of excesses of copper or bismuth, for which methods were clahorated which pcrmittcd a precise dctcrmination of mercury in the presence of ‘L 98 (yO of the former metals. EXPERIMENTAL
The same instruments ant1 the s;lmc working tions”. All chcmicols usccl were either analytical wcrc cat-rid out at zoo C. RESULTS
conclitions wcrc used as in the previous invcstigarcagcnts or chemically pure ragcnts. The titrations
AXD
DISCUSSION
Table I gives a compilation of titrations which wcrc carried out in acetic acid water solution. The composition and the results arc given in the table. No tiltcr whatsoever was used, even in the presence of strongly coloured solutions. This was possible so long as the colourcd cation did not participate in the reaction. The titration time remained the same as in the absence of foreign metals. ltc/ererrccs
p.
78
VOL.
13 (xqj5)
HETEROMETRIC
SfICRODETERMINATION
b .
OF
JIERCURY
73
M. BOBTELSKY,
74
Ccmposttir,n : 5 ml o.ootM (== MOT) ale. -----._-- --.._- _._.-_--_ ..- -. .E.tp. ~IcmlJrr
Hg(XO,), ____-
+
“_ ..__.__.
22
JUI’GKEIS
pl/
3.02
n-83.0
-7.0
s-3.8
VOL.
rg ml (or 25 ml) Complcmcnts - __._ --
.._ -..-
.--..-
+ x ml o.ooGGM
- ---__-__-__-_
-
Al fir x nil
13 fIQj5)
mcrcaptobenzthi
.__---_-~~~
Curnf?1zmn1s ____-
23
E.
-. _
..___. ---_-~__________
3 till 112Cl~,COOH
1 ‘I I
I#
2
,,
2
‘I
‘L9.5
2 09
‘2
,I
-9.5
2 94
2
I,
n29.5
2.97
2
,,
-9.5
2.07
-3.0 rL3.0 -7.0 -.
3*07
I.
I ml0 .zdI
+
CH~COOXiL
---
+
r
Cu(SO,),
f
3 mlo.zM
EDTA-Na,
ml o.?Jl Cti(N0.& + 3 ml 0.z.W EDTA-Sa,
.I
,I
-t- = ‘.
I,
I*
-I- -1 *,
,, XL,-cttrate
,.
9.
_f- ,L .I
,*
II
-I- 4 I,
II XI,-atratc
+ 8 ml, + 10 r
-f- 2 ml o 5~12 Cu(NC -I- 5 m -j- 2 1111 AI Cu(KO,), +
._.”
$ON
3 5
2.97
2
.I PI ,I
5
II
-I-
2
I‘
,I
i.
-!-
4 It
-i” 5 ‘I ‘I -I- 5 ,I .* _.._.---__-_-_ _.__--__P::
I‘ G5 1)‘ ------
In some cases (Ca, Bn, Al, Cr) the maximum density value is reduced. The influence of the conccntrntion of the foreign metal is not always observed and in these cases the concentration of the foreign metal may bc even more than shown in the table. In other cases a lower density value is obtained with the higher salt concentration. In the presence of trivalent cations, the concentration of the foreign cation must be greatly restricted. The limits are given in experiments x5-17. As can be seen from the table, the hcuvy foreign metals (Pb, Isa, Cd) may comprise sgg.5 %, the metals Co, Ni, Mn, Zn, > gg %, and the light metal Mg, gS ‘;/o, of the total metal content. For the trivalent metals, aluminium may comprise more than go Q/O while iron and chromium may make up more than g5 */0 of the total metal content.
(n) 1~. tire $wmnce of etirytene~~ci~~,ninetetvaacetate, Special heterometric titrations with bismuth and Ml3T wcrc carried out in the presence of EDTA-Na, in order to clear up the prr-dependency of the precipitation, One experiment had the following composition: 5 ml o.oozlld Bi(NO& (+ HNO,) + I ml o.r.ii HCl + z ml LIP CH,COOH + 2 ml X N&NO, + 3 ml o.orJl MBT + 2 ml o.o~Jl EDTA-Na, + 5 ml I-I,0 _t- x ml .ii NaOH. The result was that bismuth remained in solution at all plr’s and no precipitation occurred. An analogous esperimcnt which was carried out in the abscftcc of EDTA-Na, showed that bismuth is precipitated heteromctrically in acid solution. From our previous investigation1 WC know that EDTA, if present in acetic acid or sodium acetate Jt’eferetrces
p.
78
ni
+ 2 ml iv1 Cu(XO& ,* Kn,-citrate ml ilk. + IO ml I-I,0 (vol. = -j- 2 ml M CU(NO& -i- .I 0 ,, Xii,-ciiratc *. I. -t- 2 ,, 0 ,, IO ml ale, f 5 ml f-I,0 (vol. = + 2 ml M Cu(NO& ,I ,. -t 2 ,* ,I I. -I- 4 .* ,, Xtig-cftriit~ 15 ml ilk. (vol. - : f 3 ml 0. I Af EIITA-Na, -t_ 2 nil 0. I Al lS(P1103)3f- 7 ml *, CEI,COOl~I .I
:: -
VOL.
13
HETERONETRIC
(1955)
.t: 2.006 mg Hg
T =
20’
BIICRODETERBII~c’hTIOS
OF
MERCURY
75
C
----
_-__
---_.--_-
Inild
RCWlWkS
pmcip.a1
--_._ __-_-_-_._--___
_ - __...__ . ._ ____.._
_.
-
..
.-._
y/,
rul _
_. _..
crmr
_ _
12.7 12.7
30 32
p max. then steep drop.
G.1
12
imum, then drop.
G.I
‘5
0.0
3.oG
25
0. .I
3.00
11
00
0.Gg
0.0
x.55
30
0.0
0.71
-0.3
‘ccipitatc floats on the surface
irn line,
then slow
1.
I,
1,
,.
,,
0,
1,
,.
0
,*
drop.
20
0.4 +
I.0
I.55
15
0.0
0.75
-2.0
0,
1 55
14
0.4
0 79
-1.0
0.
r*55
*s
0.53
-1.0
4.6 I .92
35 45
0.9.1
$-a.3
I.02 _ ._
+0.7
0.4
^ .
. .
X.4)
0.0 0.2
30 -. _-_- - -
I.8
.
0.St
+2.5 -1.0
0.89
_
_
_
-..
.
.
solutions, dots not influence the hetcromctric titration of mercury with MHT. Acting on these results, WC tried to determine mercury in acetic acid solution in the l>rcsence of bismuth, by the addition of EDTA-Na,. Table II, experiments 32-34 (Fig. I) show these results. The csl~eriment number and tlic curve number correspond to facilitate
3 Fig.
1.
bismuth. References
Titrations p.
~8
of mercuric
nitrnte
in solutions
containing
ml
complcxing
agents
and
copper
or
76
XI,
BOJW.ELSKY,
E.
JUXGREIS
VOL.
13 (rc)55)
cornparison. As can 1~ seen, mercury can be determined without any difficulty in an acetate or acetic acid solution which contains sufficient EDTA to bind any bismuth. As cxperimcnt 3-1 with sodium ac~tutc shows, the initial precipitation occurs very late, only after the addition of fro ‘3/O of the MBT which was necessary for the titration. i’his is of course ;L disadvantage, but in spite of this the obtained masimum density value was as high as usunl and the error was only I~$,. Our solution contained 98 ‘/o bismuth. Hccausc of the maximum density values in the presence of EDTA and bismuth which . are high, even less mercury can be dctcrmincd. (b) 1n Ihc +WCSC)ZCC o/ tvisodiztnzcitv~~te. In the presence of excesses of citrate, in neutral or ~~lk~tlinc solutions, a precipitate was obtained with lzismuth immediately, and no titration coulcl be made.
(a) 192 I/tc ~JYCSC’I~CC a/ ethylencc~irci)z2’?tctetv~~ricLttnte. Just as in the case of bismuth, similar parallel heteromctric and prr-titrations were carriecl out with copper in the prcsencc, as well as in the abscncc of EDT.4. WC could ascertain that copper is not precipitated by the addition of M13T in the prcscncc of IXWA under any conditions of pii’s. WC used this property for the hctcrometric titration of mercury in the presence of copper. Tnblc II, cspcrimcnts 22 and 23 (Fig. I) show the results of such titrations from acetic acid or acetate solutions. As can bc seen, mercury can bc determined only in mctic u&Z solution if sufficient IXWA is added to hind the copper. (1~) In tl~..e+yL’scncc oi trisocti2lntcitvale. From our previous investigations WC know that trisodiumcitratc dots not interfere with the hetcrometric determination of mercury with MIST at any pn, and may bc present in any concentration. From other invcstigation$ WC know that copper forms a soluble very strong comples with citrate, cspecintty i?t c&zclli~a solrrlion. Acting on these results, WC carried out a series of heterometric titrations some of which are compiled in Table 11. The course of the titrations can be seen in Pig. I. As csperimcnt 24 shows, the titration cannot bc carried out without disturbances if an NQWWWG solution of mercury is titrated. A minimum amotmt of alcoltol must be prcscnt. As Fig. I shows, WC obtain, in all cases, at the analytical end-point, an optical masimum density &W and then the density drops with the further addition of MBT. The critical cncl-point is obtained by the intcrscction of the Inst part of the titration l&e with the horizontal maximum density line. As esperiments 29-31 (vol. = 30 ml!) show, escn a r~ 30 */* alcohol (by volume) does not change the value of the. mnsimum density. In 50 ‘yO alcoholic solution (cxp. 31), the masimum density value is already reduced, Apart from this, the initial precipitation onIy begins after the addition of 50 l)/v of the MBT, which was necessary for the titration. Thcrc is no limitation to the amount of trisodiumcitrate which may be present. This clcpcnds on the amount of alcohol adclcd, as the solubility of trisodi~lmcitr~~tc decreases with the addition of alcohol. The amount of copper which may be present on the other hand, clcpends on the amount of citrate and cannot be higher than I :I. In any case, the mercury makes up less than 2 o/o of the total metal content. The titration proceeds without difficulty ancl lasts 10-20 minutes. The error lies between zero and 2 “/o. i?efcseltcesp. 7s
VOL.
13
(1955)
HETEROMETRIC
MICRODETERMtNilTION
OF
MERCURY
77
METHOD
zo ml of an aqueous salt solutioil which contains 1 ml &I acetic acid and about 2 mg mercuric mercury a5 nitrate or srllphatc, arc titrntcd hctcrometrically with an alcoholic solution of o.orfiZo.oogllr meicaptobcnttliiazole. The snlutlon may contain the following cations, in a concentration of 0.2M c-t higher, as nitrates or sulphates: Ca, I3a, 316. Zn. bIn. Ni, Co and Cd Lead may not be at a concentration higher than 0.x&I. The concentration of the trivalent cations Al, Cr. Fe, may iiot bc higlicr than o.OgJZ. No colourcd filter is nccclccl in the prcscncc of colourcd cations. l’hc error is o-3 ‘:,&. 2.
Determination 1~1de pescnce
in the prcsmm
of excesses
of bismtrtl~
or copper
01 elll)lle,ledicrrtai,lelclmacelflle. (a) 20 ml of the aqueous solution of mercuric nitrate to bc analysetl, contain 1-2 mg mercury and an excess of bismuth which may constitute %98 “/{, of the metal content. Sufticicnt cthylencdiam~nctct~aacctatc salt solution to bind the bismuth 1s addctl ‘rho free strong acid wh ch is prcscnt in solutiou IY then transformed into to the solution, acetic acid by the addition of sodium acetate, which may I c present in c~xccss. The solution is brought to a volume of about 20 ml and titrated hctcromctrlcally with an alcoholic solution of o.or~Vf-o.oogjlf mcrcaptobcnztl~inzolc. An cnlar@ curve of tlic last part of the titration is clrawn. Tlic end-point is obtained from the intcrscction of the lint of the last part of the titration with the horizontal optical maximum tlcnsity line. The titration time is about 30-40 minutes. Error o-3 ojo. (b) The aclucous solution of mercuric nitrate or sulfate to bc analyscd contains x-2 mg mercury and an C.XCCS~of copper. To this solution is added sufficient cthylencdinniiuctctraacctntc salt solution, to bind the copper. The solution obtained is ncutralisctl ant1 then 3 ml Jf acctlc acid is utltlctl, since the final solution has to be acidic. The final solution is tllcn brought to a volurnc of 20-30 ml and titratccl hctcrornctrically with an alcoholic solution of o.oxfir-o.oognl mcrcaptobcnzthiazolc. The end-point of the titration is obtained from an cnlargcd curve of the last part of the titration by the intcrscction of the titration hnc with the horizontal optical maximum tlcnsity line. No Colcurcd filter is rcquirctl. The titration time is ‘L 30 minutes. Error 1-2 ?,A. 1,; I& pIese)lce oi trisodirtnrcilrale. (c) To tllc aiialysed solution which contains I< 2 rug mercuric mercury and an cxccss of copper (up to 98 “IO or more), are ad&d: x ml Jf Na-Qitratc _1- 2 ml iV NH,NO, -t_ 2 ml Al NH, + 5-10 ml nlcol~ol. The solution is brought to approximately 30 ml and then titrated hctcromctrically with an alcoholic solution of o.orM-o.oogM mcrcaptobciiztliia~olc from a microburct (0.01 ml). The minimum amount of trlsodiumcitratc which has to bc acldccl is I molt citrate per I molt copper. The pcrccntagc of alcohol in the solution must bc 15 y&-30 ‘x,, The end-point is obtained by the intcrscction of the hnc of the last part of the titration wit:1 the horizontal entllinc. No colour filter is needed. The titration lasts x0-15 minutes. Error 0-2 O/b. Pram the two methods prcscntctl the last is to bc prcfcrrcd as the concentration of copper may bc high and the titration proceeds quickly. SUMMARY I. A gcncral method is prcscntcd for the dctcrmination of I-Z mg mercuric mercury, in the abscncc of coinplcxing agents, in 20 ml solution, with an error of o-3 %. The solution may contain: Ca. Da, Mg, %n, hfn, Ni, Co or Cd as nitrate of sulphatc in a conccntration of 0.2M. The concentration of Pb should bc
1. Une mGthodc g6n5rale est proposde pour Ic dosage du mercurc(IT) (I h 2 mg dans 20 ml dc solution), avcc unc erreur de o-3%, cn l’abscnce d’agcnts complexants. La solutlon pcut contcnir Ca, Ba, Mg, Zn, Mn, Ni, Co ou Cd (sous formc de sulfates ou dc nitrates) cn concentration 0.21M. La. concentration en plomb doit Ctrc plus pctitc que 0.1fi1 ct cellc d’Al, Cr ou Fe plus pctitc que o.og&Z. Referertces
p.
7s
78
M.
BOBTELSKY,
E.
JUNGREIS
VOL.
13 (1955)
2. UIIC m6tlioclc spdciale cst proposBc pour lc dosage clu mercurc (r-2 mg clans 20 ml solution), (s g8%), en employant I’hthylhnediaminetetraac~tate. en prbscncc cl’un gros exces dc bismuth, L’crrcur cst clc o-3%. 3. Une m&ho& est proposec pour lu dosage clu mcrcure en pr6scnce de cuivre cn cxc&s, en solution cl’acidc ac&ique, runfcrmant l’btlIylbnediaminet&raac~tatc. ‘1. Une m&ho& spdciale cst proposdc pour lc closagc clc mcrcurc (1-2 rng clans 3o ml solution} en pr&cnce d’un yros cxc&s de cuivrc (>gS’%,). Lc titrage est effectub en solution alcalmc dc citrate est comprise entrc o-2fz/o. trisod~que. Cc closagc cst rapidc. L’crrcur %USABIMBNFASSUNG wc1c1~c erlaubt, 1-2 mg Quccksilbcr in 20 ml I. Einc alIgemeine Methodc wircl vorgcscklagen, I,iirung in Abwcscnhcit von komplexiercndcn I
1