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Micro-gravimetric determination of thallium with thionalide
VOL.
15
(1956)
ANALYTICA
MICI~O-C;IIAVIMI~‘I‘IITC
CHIMICA
I>ETEICMINA’I’ION THIONAT,T DE
213
AC-l-h
01;
‘I’HAILI’UlbI
WI’I’H
1x1 the course of our systematic starch for suitable micro-dctcrminations in the field of inorganic analysis, the existing micro-methods for the determination of thallium were reviewed. M’ithout enumerating all the references, mention must bc ma& of some of the method found, e.g. : a) - titrimctric method using cthylencdiaminc tetraacetic acid’, b) titrimctric method employing the liberation of iocline2, c) microgr;lvinletric cletermination as thallochromatc =, d) potentiometric titration by oxidation with F;LSrO$, c) potcntiometric titration by oxidation with KXInO,fi, f) various additional instrumental methocls mentioned in a recent review of detection and clctcrminntion of thullium”. After completion of the ;L.m. review, it was still considered desirilble to cvolvc an exact micro-gravirnctric method for the determination of thallium with thionalide (P-arninonaphthalicle of thioglycollic acid), this reagent having proved adequate for the micro-determination of lead ‘ea. The macro-method has been proposed by HERC;“. ‘To that end, the various factors affecting this determination, such as: I) the* amount of thallium, z) the amount of reagent and the method of its introduction, J) the wash licluids used, 4) the temperature and the time required to dry the precipitate, were studied. Based on these investigations, an exact micro-gravimetric method has been developed, applying Ea~rc~i’s~~ micro-technique and using R porcelain filterstick.
‘Thallium cation potassium cyanide
is l~recipitatcd from a sodium hydroxide solution, and sodium acetate, with an acetone solution of
The filtered and washed precipitate is dried at fro0 CF. Thallium from the weight of the precipitate obtain&d. IZcferemcs
p.
2x7
containing thionalide:
is calculated
CH.
2x4
CIMERMAN,
G.
SELZER
VOL.
15 (x956)
EXPERIMENTAL Reagents and solulions ew~ployrd I. Thallium eulphate solution (prepared by dissolving 2.470 g of pure thallium sulphate in bi-distilled water and making up to I litrc with bi-distilled water. The solution. thcrcforc, contained z mg of thallium per ml). 2. Sodium acctatc solution, 100/o. 3. Potassium cyanide solution, 20%,. .t, Sodium hydroxitlc r;olution 2N. 5, Tinonalitlc. 6. Acetone. 7, A mixture of 20 ml acctonc, 20 ml bi-distilled water and 3 ml ammonium hytlroxidc cone. (the PH of this mixture should 1~ 8.5 npprox.). 8. A mixture of 20 ml acctonc, 20 ml bi-distillctl water and one t!rcJp of sodium hytlroxidc 2N (the ptr of this mixture shoulcl IX 8.5 spprox.). 0, Acctonc-water (mixture I : I). 10. Iotlinc solution o.lN. I I. Sulplruric acid (I :5). I 2. TJi-distilled water WCLH used throughout.
Procedure
recommended
joy the micro-gruvimetric
determination
of thallium
Tlic solution containing the thallium cation (3-G my thallium in 1-3 ml) is introtlucctl into a previously dried and wcigllcd Pyrex glass micro-bcakcr (dimensions of the beaker: height 55 mm, outer diameter 18 mm). To this solution arc addctl 0.5 ml of sodium acctatc solution. ro’;/o. 0.25 ml of potassium cyanide solution, zoo/o and 0.5 ml of sodium Iiytiroxitlc 2N. The mwrobeaker is hcatetl to 80~ C approx. (tcmpcraturc of the solution) on a micro drying block”. A freshly prepared solution of 25-35* my of thionalidc in 2-3 ml of acetone IS introducctl in small drops from a pipcttc; throughout the addition of the reagent, the solution is stirrcd vigorously with a sllort stirring rod (as shown in Fig. I), particular cart being taken that no drop of
Fig. 1. Apparatus usctl for precipitation. a) dropping pipcttc b) glass stirring rod micro-bcukcr c) d) micro drying block with thcrmomctcr.
To pump Fig. 2. Apparatus for filtration.
rcagcnt falls on the sitlcs of the beaker or on the stirring rod. The mixture is cautiously hcated to boiling on tile clrying block,‘thc yellow prccipitatc allowed to scttlc and cool for 20-30 minutes. After cooling, the solution is filtcrcd. using low suction, through a porcelain Iiltcrstick** (Fig. 2). The bcalczr, stirring rod, filtcrstick and precipitate arc wnshcd with the mixture containing acetone, water. and ammonium hydroxide (rcagcnt No. 7), in four portions of 2 ml each. In this way the prccipitatc is freed from both excess thionalidc and inorganic ions prcscnt durmg _-* 25 mg of tliionaliclc for 3-4 mg tlmllium; 35 mg of thionaliclc for 5-G mg thallium. ++ The dimensions of the filterstick used wcrc: overall diameter II mm; stem diamctcr 3-4 mm; overall height 55 mm. All filtcrsticks used wcrc U.S.A. proclucc, made by Coors Porcelain Co., Golden. Rcfcrmces
p.
2x7
VOL.
15
(1956)
MICRO-CRAWMETRIC
DETERMINATION
OF
THALLIUM
215
precipitation. The last portion of wash liquid is collected into a small test tube and examined, on a spot plate for the prcscncc of thionalidc as follows: 0.5 ml of the wash liquid IS introduced into a depression of a black, glazed porcelain spot plate, one drop of sulphuric acid (I :5) and one drop of Iodine solution o. IN arc added and the mixture stirred vigorously with a glass rod. In the presence of at least IO micrograms (v) of thionalide, a white, floccular precipitate of dithionalidc is formed within two minutes; the prccipitatc is best obscrvetl In daylight. 2 C,,H,NfICOCH,SH
-k I, -+
C,,H,NHCOCH,-S-S-CH2CONliC10H,
-+ 2 HI
If no thionalide is dctcctcd, the filterstick IY detached from the suction system and the microbeaker, contaiding the precipitate, togcthcr with the filterstick and the stirrmg rod are dried in a prchentcd drying block of R~.~~DETTI-~'Ic~IL~R~~ at I IO’ Cl1 (tcmpcraturc inside the drying tube; towards that end the tomperaturc of the drying block must he xzoO C). using low suction, for 15 minutes; after that period. the drying tube containing the beaker, the filterstlck and the stlrring rod is taken out of the drying block and cooled outside the block for rg minutes, without interrupting the suction. After cooling, the beaker togcthcr with the filterstick and the stirring rod arc removed from the tube, the bcakcr and the handle of the stirring rod arc wiped, as usual, first with a clamp flannel cloth and next with two sets of chamois skins, left for 15 minutes on a ntckcl block near the micro-balance, 5 minutes on a nickel block inside the balance, and finally 5 minutes on the pan of the balance. The beaker, togcthcr with the filtcrvtick and the stirring rod, is weighed in the twenty-fifth minute. The weight of the precipitate, multiplied by the factor 0.4859’ gives the amount of thallium in the sample. The time required for one determination is 21/z hours approx. (including preparation of the bcakcr and the flltcrstick): two parallel determinations may be carncd out in about four hours. Cleaning of the filtcrstick, stirring rod and bcakcr after the detcrminatlon is cffectcd by washing them alternately with HNO,-II,0 (I : I) ant1 acetone a few times, and then 2-3 times with bi-dintillctl wati.r, using portions of 5 ml approx. each time. Drying and weighing of the utensils is carried out ah dcscribctl above under the procedure rccommcndcd for the microgravimctric tlctcrmination of thallium. Tnblc 1 shows some characteristic results obtained by the above method.
Comlusiorr As indicated lium with
by Teblc I, results arc exact (maximum relatlvc cxccss of ttiionalitlc bctwccn 4oo”/, and 8007{,.
error
f
o..(%)
for 3-G mg thal-
EMICH’S filtcrstick micro-technique’0 is best suited to this determination: a) The straight wide necked Emich beaker allows the direct introduction of the reagent into the solution. b) Adequate stirring is of extreme importance in this determination (see section 4 below). The form of the Emich beaker facilitates efficient stirring. 2. Prior to the precipitation, the sample solution is heated to 80” C. This temperature should not be exceeded, to prevent ejection losses during the subsequent precipitation caused by the ebullition of the acetone of the reagent solution. 3. Precipitation carried out at 80” C approx. gave uniformly good results. BERG’@ method of precipitation in the cold and subsequent heating did not prove satisfactory under the a.m. conditions. 4. As mentioned in section I above, it is advisable to introduce the reagent dropwise into the sample solution, with continuous stirring. In this way, settling out of excess thionalide on the sides of the beaker is avoided. The solution clears and the precipitate settles out properly. r.
* The factor given in R. BERGO~, foe. cif. p. 15 is 0.48Go. The factor 0.4859, is calculated from the International Atomic Weights of 1952. Rcfewnces
9. 2x7
given
by
the
authors,
CH.
C~MEHMAX,
G. SELZER
VOL.
15
(1956)
. _ - . _._.
^
Hclalrre CI,Ol
“h
- -0 -!-
“3 0. I
2,s
---_(I
-I-
O.L.3
-0.2 --O.L
-i-O.‘4
_‘j.OOCJ
Got0
-0 ‘3 -I- 0. , t-0.r 1-O IS +O.Zc, -0.07 -1..0 1 ‘! 4-0.36 --O.O
-i-l)*37 -t_ 0.3 --o.l~l I-0.1.5 ----I ,G ---I .H
5. The prccipitatc is filtered after the solution has cooled to room tcm1)crature. Attempts to filter immediately after precipitation invariably gave low results. 0. ‘I’hc wash liquids proposed by 13~1~~;~(water followed by acctonc) were found :iclcquatc csccpt when ttlc pkr of the distilled water dropped below 7; on those occasions slightly low results wcrc obtain&l and tracts of the dissolved prccipitatc could bc obscrvcd as they rcqmzcipitatcd in the filtrate. Use of a wash liquid composed of either XI ml acetone, 20 ml water and 3 ml ammonium hydroxide*-** cont. orzo ml iLcctonc, 20 ml wotcr and r clrop sodium hydroxide solution 2,V*** (per 8.5) cffcctivcly clirninntcd this I)hcnomenon ; uniformly exact results were obtained forthwith. 7. Esperiments proved thnt the procedure rccommcnded gave cxitct results whcncvcr iL q..ooC~~,-Hoo’,Y,, escess of rcagcnt was used, i.c. approx. 5.32-9.57 rng for each mg of thallium prcscnt. In practice it was found convcnicnt to use 25 mg of thionalide for .3-_cmg of thallium nncl 35 mg of thionalide for 5-G mg of thallium. S. As indicated in ‘Table 1, results arc exact for amounts of thallium from 3 to G mg. * ‘lk nminoniiini hydroxicle must bc absolntcly ptu-c ant1 must, on no account, Icavc a s~hca rcsiduc after evaporation. 12cli:mcc on the analysis of the rcagcnt, ns given on the label, is in iltlclluntc; the purity ol the nmmonium hydroxide must lx tcstccl cspcrimcntally, as its silica contcnt clcpcncls 011 the qunlity of the glass in which it lxka hccn ltcpt ant1 the clumtion of its slorngc~~. ++ Any ammonium hytlrosiclc left in t.hc prccipitntc is driven off during the drying period. **+ The nmount of soclirml lrydroxidc ~nvolvccl is ncgligihlc and nrctl not be removed by an ixlclitional portion of wnsh liqnd. l
p. 217
VOL.
DETERMINATION
MICI(O-Gl~n\‘IMETI(IC
15 (1956)
01’
THALLIUM
217
I~sperimcnts carried out on samples containing 2 mg of thallium ga\xz low results (Exp. No. 21-24, Table I) ; those carried out on samples of 7 mg thallium gave high results (Exp. No. 25-26, Table I). Consequently, 3-G mg of thallium were chosen as suitable limits for this determination.
‘I’hc authors have claboratctl tllillltiun~ with thionrtlirlc.
ill1
micro-gravimctric
exact
I.&s autclirs ont dlaborJ unc mxro-m~tlioclc au nroyxi clc In thionnliclc.
DIG \‘crfi\sscr haben cinc cxaktc mit ‘L+hionalltl nuapxwlwitct.
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for
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>lcthotlc
AcfJJ.
QJJnrf.
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of
Ic tlo.sagc tlu thi~llium
tics ‘l’l~alliumx
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cJJra/. C/ten1
(1955)
(1950) Ucrlin.
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$18
I II (1935)
13.
.p. (1938)
101.
597.
~dIrbltC/J cfrr il~r/~roc/ic~?rie.I. i\ufl , Vcrlay J. 1;. &rgmarin. .\luncllcn, 19rG, p. 8~. :IZrlJrogrwiclJfscJ~JaIyst~. \rcrIag J. Springa-, Wicn, 1:. ~IltCllT USD 1. l~os~u, .~~JJorgJJJJisr/Jr 1940, P 74. lL CL. I>UVAr., IJrorgnnlc ~/Jrr~JJogruvJrrrJ~trJC A tialysts, lclscvicr I’ulJlirhln): Co., hmsrcrtlilm, 1953, I’. 456. lz FISHIZR SCII!STIPIC C’o., rVcw-Sork, ll.S.1\., AfoJtc*rJJ I.a6oratory .~/J~/!N~I~cs. Cat. I I l (1952). p. 895 (Cat. No. zo-202). /‘rc~~-I’rst.~CjJJJf~ (It)LJ)) 13. b. In 1\. 13I:.~l~l~~~TTI-1’lCrlLliH, .\fl/rJ’oC/Jrt?JiC, 1:. ~IECIIT USIJ J, I>OSAL’, /or. c-It., p 103. :1 JJdysrJr. 5. Aufl.. Vcrlng S. I-lirzcl. Zdricli, ‘4 H. 131~~1,USD \\‘. I~ILTZ , A rrs/ri/ir7rtrg qm~Jtifnttvt*r~ 1947. Ps 29.
lo
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15
(1956)
ANALYTICA
MICI~O-C;IIAVIMI~‘I‘IITC
CHIMICA
I>ETEICMINA’I’ION THIONAT,T DE
213
AC-l-h
01;
‘I’HAILI’UlbI
WI’I’H
1x1 the course of our systematic starch for suitable micro-dctcrminations in the field of inorganic analysis, the existing micro-methods for the determination of thallium were reviewed. M’ithout enumerating all the references, mention must bc ma& of some of the method found, e.g. : a) - titrimctric method using cthylencdiaminc tetraacetic acid’, b) titrimctric method employing the liberation of iocline2, c) microgr;lvinletric cletermination as thallochromatc =, d) potentiometric titration by oxidation with F;LSrO$, c) potcntiometric titration by oxidation with KXInO,fi, f) various additional instrumental methocls mentioned in a recent review of detection and clctcrminntion of thullium”. After completion of the ;L.m. review, it was still considered desirilble to cvolvc an exact micro-gravirnctric method for the determination of thallium with thionalide (P-arninonaphthalicle of thioglycollic acid), this reagent having proved adequate for the micro-determination of lead ‘ea. The macro-method has been proposed by HERC;“. ‘To that end, the various factors affecting this determination, such as: I) the* amount of thallium, z) the amount of reagent and the method of its introduction, J) the wash licluids used, 4) the temperature and the time required to dry the precipitate, were studied. Based on these investigations, an exact micro-gravimetric method has been developed, applying Ea~rc~i’s~~ micro-technique and using R porcelain filterstick.
‘Thallium cation potassium cyanide
is l~recipitatcd from a sodium hydroxide solution, and sodium acetate, with an acetone solution of
The filtered and washed precipitate is dried at fro0 CF. Thallium from the weight of the precipitate obtain&d. IZcferemcs
p.
2x7
containing thionalide:
is calculated
CH.
2x4
CIMERMAN,
G.
SELZER
VOL.
15 (x956)
EXPERIMENTAL Reagents and solulions ew~ployrd I. Thallium eulphate solution (prepared by dissolving 2.470 g of pure thallium sulphate in bi-distilled water and making up to I litrc with bi-distilled water. The solution. thcrcforc, contained z mg of thallium per ml). 2. Sodium acctatc solution, 100/o. 3. Potassium cyanide solution, 20%,. .t, Sodium hydroxitlc r;olution 2N. 5, Tinonalitlc. 6. Acetone. 7, A mixture of 20 ml acctonc, 20 ml bi-distilled water and 3 ml ammonium hytlroxidc cone. (the PH of this mixture should 1~ 8.5 npprox.). 8. A mixture of 20 ml acctonc, 20 ml bi-distillctl water and one t!rcJp of sodium hytlroxidc 2N (the ptr of this mixture shoulcl IX 8.5 spprox.). 0, Acctonc-water (mixture I : I). 10. Iotlinc solution o.lN. I I. Sulplruric acid (I :5). I 2. TJi-distilled water WCLH used throughout.
Procedure
recommended
joy the micro-gruvimetric
determination
of thallium
Tlic solution containing the thallium cation (3-G my thallium in 1-3 ml) is introtlucctl into a previously dried and wcigllcd Pyrex glass micro-bcakcr (dimensions of the beaker: height 55 mm, outer diameter 18 mm). To this solution arc addctl 0.5 ml of sodium acctatc solution. ro’;/o. 0.25 ml of potassium cyanide solution, zoo/o and 0.5 ml of sodium Iiytiroxitlc 2N. The mwrobeaker is hcatetl to 80~ C approx. (tcmpcraturc of the solution) on a micro drying block”. A freshly prepared solution of 25-35* my of thionalidc in 2-3 ml of acetone IS introducctl in small drops from a pipcttc; throughout the addition of the reagent, the solution is stirrcd vigorously with a sllort stirring rod (as shown in Fig. I), particular cart being taken that no drop of
Fig. 1. Apparatus usctl for precipitation. a) dropping pipcttc b) glass stirring rod micro-bcukcr c) d) micro drying block with thcrmomctcr.
To pump Fig. 2. Apparatus for filtration.
rcagcnt falls on the sitlcs of the beaker or on the stirring rod. The mixture is cautiously hcated to boiling on tile clrying block,‘thc yellow prccipitatc allowed to scttlc and cool for 20-30 minutes. After cooling, the solution is filtcrcd. using low suction, through a porcelain Iiltcrstick** (Fig. 2). The bcalczr, stirring rod, filtcrstick and precipitate arc wnshcd with the mixture containing acetone, water. and ammonium hydroxide (rcagcnt No. 7), in four portions of 2 ml each. In this way the prccipitatc is freed from both excess thionalidc and inorganic ions prcscnt durmg _-* 25 mg of tliionaliclc for 3-4 mg tlmllium; 35 mg of thionaliclc for 5-G mg thallium. ++ The dimensions of the filterstick used wcrc: overall diameter II mm; stem diamctcr 3-4 mm; overall height 55 mm. All filtcrsticks used wcrc U.S.A. proclucc, made by Coors Porcelain Co., Golden. Rcfcrmces
p.
2x7
VOL.
15
(1956)
MICRO-CRAWMETRIC
DETERMINATION
OF
THALLIUM
215
precipitation. The last portion of wash liquid is collected into a small test tube and examined, on a spot plate for the prcscncc of thionalidc as follows: 0.5 ml of the wash liquid IS introduced into a depression of a black, glazed porcelain spot plate, one drop of sulphuric acid (I :5) and one drop of Iodine solution o. IN arc added and the mixture stirred vigorously with a glass rod. In the presence of at least IO micrograms (v) of thionalide, a white, floccular precipitate of dithionalidc is formed within two minutes; the prccipitatc is best obscrvetl In daylight. 2 C,,H,NfICOCH,SH
-k I, -+
C,,H,NHCOCH,-S-S-CH2CONliC10H,
-+ 2 HI
If no thionalide is dctcctcd, the filterstick IY detached from the suction system and the microbeaker, contaiding the precipitate, togcthcr with the filterstick and the stirrmg rod are dried in a prchentcd drying block of R~.~~DETTI-~'Ic~IL~R~~ at I IO’ Cl1 (tcmpcraturc inside the drying tube; towards that end the tomperaturc of the drying block must he xzoO C). using low suction, for 15 minutes; after that period. the drying tube containing the beaker, the filterstlck and the stlrring rod is taken out of the drying block and cooled outside the block for rg minutes, without interrupting the suction. After cooling, the beaker togcthcr with the filterstick and the stirring rod arc removed from the tube, the bcakcr and the handle of the stirring rod arc wiped, as usual, first with a clamp flannel cloth and next with two sets of chamois skins, left for 15 minutes on a ntckcl block near the micro-balance, 5 minutes on a nickel block inside the balance, and finally 5 minutes on the pan of the balance. The beaker, togcthcr with the filtcrvtick and the stirring rod, is weighed in the twenty-fifth minute. The weight of the precipitate, multiplied by the factor 0.4859’ gives the amount of thallium in the sample. The time required for one determination is 21/z hours approx. (including preparation of the bcakcr and the flltcrstick): two parallel determinations may be carncd out in about four hours. Cleaning of the filtcrstick, stirring rod and bcakcr after the detcrminatlon is cffectcd by washing them alternately with HNO,-II,0 (I : I) ant1 acetone a few times, and then 2-3 times with bi-dintillctl wati.r, using portions of 5 ml approx. each time. Drying and weighing of the utensils is carried out ah dcscribctl above under the procedure rccommcndcd for the microgravimctric tlctcrmination of thallium. Tnblc 1 shows some characteristic results obtained by the above method.
Comlusiorr As indicated lium with
by Teblc I, results arc exact (maximum relatlvc cxccss of ttiionalitlc bctwccn 4oo”/, and 8007{,.
error
f
o..(%)
for 3-G mg thal-
EMICH’S filtcrstick micro-technique’0 is best suited to this determination: a) The straight wide necked Emich beaker allows the direct introduction of the reagent into the solution. b) Adequate stirring is of extreme importance in this determination (see section 4 below). The form of the Emich beaker facilitates efficient stirring. 2. Prior to the precipitation, the sample solution is heated to 80” C. This temperature should not be exceeded, to prevent ejection losses during the subsequent precipitation caused by the ebullition of the acetone of the reagent solution. 3. Precipitation carried out at 80” C approx. gave uniformly good results. BERG’@ method of precipitation in the cold and subsequent heating did not prove satisfactory under the a.m. conditions. 4. As mentioned in section I above, it is advisable to introduce the reagent dropwise into the sample solution, with continuous stirring. In this way, settling out of excess thionalide on the sides of the beaker is avoided. The solution clears and the precipitate settles out properly. r.
* The factor given in R. BERGO~, foe. cif. p. 15 is 0.48Go. The factor 0.4859, is calculated from the International Atomic Weights of 1952. Rcfewnces
9. 2x7
given
by
the
authors,
CH.
C~MEHMAX,
G. SELZER
VOL.
15
(1956)
. _ - . _._.
^
Hclalrre CI,Ol
“h
- -0 -!-
“3 0. I
2,s
---_(I
-I-
O.L.3
-0.2 --O.L
-i-O.‘4
_‘j.OOCJ
Got0
-0 ‘3 -I- 0. , t-0.r 1-O IS +O.Zc, -0.07 -1..0 1 ‘! 4-0.36 --O.O
-i-l)*37 -t_ 0.3 --o.l~l I-0.1.5 ----I ,G ---I .H
5. The prccipitatc is filtered after the solution has cooled to room tcm1)crature. Attempts to filter immediately after precipitation invariably gave low results. 0. ‘I’hc wash liquids proposed by 13~1~~;~(water followed by acctonc) were found :iclcquatc csccpt when ttlc pkr of the distilled water dropped below 7; on those occasions slightly low results wcrc obtain&l and tracts of the dissolved prccipitatc could bc obscrvcd as they rcqmzcipitatcd in the filtrate. Use of a wash liquid composed of either XI ml acetone, 20 ml water and 3 ml ammonium hydroxide*-** cont. orzo ml iLcctonc, 20 ml wotcr and r clrop sodium hydroxide solution 2,V*** (per 8.5) cffcctivcly clirninntcd this I)hcnomenon ; uniformly exact results were obtained forthwith. 7. Esperiments proved thnt the procedure rccommcnded gave cxitct results whcncvcr iL q..ooC~~,-Hoo’,Y,, escess of rcagcnt was used, i.c. approx. 5.32-9.57 rng for each mg of thallium prcscnt. In practice it was found convcnicnt to use 25 mg of thionalide for .3-_cmg of thallium nncl 35 mg of thionalide for 5-G mg of thallium. S. As indicated in ‘Table 1, results arc exact for amounts of thallium from 3 to G mg. * ‘lk nminoniiini hydroxicle must bc absolntcly ptu-c ant1 must, on no account, Icavc a s~hca rcsiduc after evaporation. 12cli:mcc on the analysis of the rcagcnt, ns given on the label, is in iltlclluntc; the purity ol the nmmonium hydroxide must lx tcstccl cspcrimcntally, as its silica contcnt clcpcncls 011 the qunlity of the glass in which it lxka hccn ltcpt ant1 the clumtion of its slorngc~~. ++ Any ammonium hytlrosiclc left in t.hc prccipitntc is driven off during the drying period. **+ The nmount of soclirml lrydroxidc ~nvolvccl is ncgligihlc and nrctl not be removed by an ixlclitional portion of wnsh liqnd. l
p. 217
VOL.
DETERMINATION
MICI(O-Gl~n\‘IMETI(IC
15 (1956)
01’
THALLIUM
217
I~sperimcnts carried out on samples containing 2 mg of thallium ga\xz low results (Exp. No. 21-24, Table I) ; those carried out on samples of 7 mg thallium gave high results (Exp. No. 25-26, Table I). Consequently, 3-G mg of thallium were chosen as suitable limits for this determination.
‘I’hc authors have claboratctl tllillltiun~ with thionrtlirlc.
ill1
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I.&s autclirs ont dlaborJ unc mxro-m~tlioclc au nroyxi clc In thionnliclc.
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101.
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