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2,3-Naphthotriazole as a gravimetric, spectrophotometric, and fluorimetric reagent for the determination of silver
Analytica Chimica Ada Elsevicr Publishing Company,
239
Amsterdam
Printed in The Nctherlnnds
2,3-NAPHTHOTRIAZOLE AND FLUORIMETRTC SILVER
GARRY
L.
Defiavlnrenl (Rcccived
WHEELER,
JOHN
of Chentistry, March
4th.
AS A GRAVl-METRIC, SPECTROPHOTOMETRIC, REAGENT FOR THE DETERMINATION OF
ANDREJACK.
University
JAMES
of Missouri,
Kansas
I-I. WIElISMA Cily,
Ado.
64110
AND
PE’~El<
1’. LO-U-
(U.S.A.)
1969)
Gravimetric and titrimetric methods for the determination of silver with benzotriazole and its derivatives have been reviewed by I
-N
+
Ag+-
[
m+g+
A study of the determination of macro and trace amounts of silver with 2,3naphthotriazole in the presence of foreign ions is reported below. The reagent has been found suitable for the direct determination of milligram amounts of silver gravimetrically, while submilligram and trace amounts of silver are determined by spectrophotometric or fluorimetric methods.
Absorption spectra were obtained with a Bausch and Lomb 505 recording spectrophotometer. Absorbance measurements were made wit11 a Beckman DU and a Model B spectrophotometer using I.OO-cm quartz cells. Fluorescence spectra were also obtained from a Bausch and Lomb 505 recording spectrophotometer and fluorescence accessorya. Relative fluorescent intensities were determined with a Farrand Model A-z Fluorimeter, and fluorimetric titrations were performed with this instrument according to the procedure of WIERS~IA AND LOTTE. Anal.
Cl&la.
Acta,
46
(1969)
239-245
240
G. L. WHEELER,
J. ANDREJACK,
J. H. WIERSMA,
I?.F. LOT-r
Reagents z,3-Naphthotriazole was prepared by dissolving 5.0 g of z,3-diaminonaphthalene (Aldrich Chemical Co., Milwaukee, Wise.) in zoo ml of glacial acetic acid, diluting to 800 ml with water then to IOOO ml with ice. When the ice was completely melted, 2.5 ml of aqueous 1.2 M sodium nitrite was added rapidly while stirring briskly. The precipitate, 2,3-naphthotriazole, was recrystallized twice from boiling water containing decolorizing carbon. The average yield was GoO/,of the theoretical yield and the product had a melting range of Ig4°-xg7”. The material is quite insoluble in cold water and acidic solutions (except concentrated sulfuric acid). It is very soluble in basic solution and is soluble to the extent of 0.15 g/100 ml in boiling water. For the gravimetric procedure, a solution of 2,3-naphthotriazole was prepared by dissolving 2.50 g of 2,3-naphthotriazole in 30 ml of concentrated aqueous ammonia, diluting to xoo ml with water and filtering through a Reeve-Angel glass fiber filter (grade 934 AH) until no residue was left on the filter. For the spectrophotometric and fluorimetric procedure, IOO mg reagent was dissolved in IOO ml of hot water or IOO ml of 0.025 M sodium hydroxide. Reagent solutions containing x0.0 mg/ml concentration or greater were prepared daily, because considerable decomposition occurred within a week; less concentrated solutions were stable for a month when stored in the dark. Stanclard silver solution (5.00 mg/ml) was prepared by dissolving 0.7875 g of reagent-grade silver nitrate in a Too-ml volumetric flask containing I ml of nitric acid and diluting to volume with water. Fresh silver nitrate solution was prepared daily. A masking solution, 0.05 M in EDTA =and 0.05 M in sodium tartrate, was prepared by dissolving 18.6 g of the disodium salt of EDTA and 11.5 g of sodium tartrate in I 1 of water. Gmviwtetvic procedzwe To a solution containing 5-100 mg of silver, add 25 ml of masking solution, adjust to ca. PH II with aqueous ammonia, and add 2-20 ml of stock 2,3-naphthotriazole solution depending upon the amount of silver in the sample. A 50% excess of reagent is sufficient to precipitate the silver completely. Digest the samples at Go”-70~ for 15 min and allow to cool to room temperature. Then filter through a weighed Coors Gooch crucible and Reeve-Angel glass fiber filter (grade 934 AH), wash twice with 20-30 ml of hot water (as near Ioo” as possible), and dry at 1x0~ for 1-2 h to constant weight. The conversion factor is 0.3908.
Silver in the range 1-30 ,ug/ml can be determined by mcasurcmcnt of the absorbance of the silver triazole complex in basic solution. Prepare samples by adding to a series of roe-ml volumetric flasks, o-3 mg silver, 5 ml of a solution of 2,3-naphthotriazole solution (IO- mg/ml) in 0.025 M sodium hydroxide, IO ml of the masking agent solution and IO ml of PH 10.5 buffer. As ammonium hydroxide must be excluded to prevent precipitation of the’ silver comple’x, a metheneamine-sodium hydroxide buffer was prepared by adding 6g of metheneamine to I 1 of water and sufficient sodium hydroxide to adjust the solution to pH 10.5 as shown by a PH meter; the pH is critical (see below). Allow the yellow .4?Z&.C&m. Acta, 46
(196CJ) 239-245
2/J-NAPHTHOTRIAZOLE
AS A REAGENT
Ag
FOR
24f
color of the silver-naphthotriazolate complex to develop for 3-5 min, and then measure the absorbance at 436,416, or 3go nm against a reference standard containing all reagents except silver. Measurements at 436 nm are preferred as most metal-EDTA complexes do not absorb light of this wavelength. Direct fluorimetric’ procedure Silver in the range O.OZ~-0.100 ,.ug/nil can be determined by measurement of the fluorescence intensity of samples relative to a reference blank containing all reagents except silver. The direct fluorimetric procedure uses the same reagents as the spectrophotometric procedure, but no masking agents,
ANT> DISCUSSION
The results of several determinations of silver with the reagent, in the absence and presence of foreign metals are shown in Table I. Figure I shows qualitative interference tests conducted by adding IO ml of masking solution, 2 ml of concentrated ammonia solution and 5 ml of 0.05 M 2,3-naphthotriazole solution to IO ml of 0.01 M solution of foreign metal ion. The reagent is not specific for silver; however, the combination of the reagents, EDTA and sodium tartrate, make the method highly selective for silver. Of the ions tested, as shown in Fig. I, only antimony and and manganese are iodide interfered. The hydroxides of tin, titanium, beryllium TAl3LE
I
GrJ”V’METR’C
DETERMINATION
OF
SILVER
IN
THE
I’RESENCB
AND
AlK+lSNCE
OIr
METAL
NITRATES
.-.. Ilfela
added n
I
Ag tutc.5w (ins)
Ag fowd
5.00 rq.00 15.00 15.00
15.02. 19.82, 15.oG,
5.29 10.32 15.28 19.8~ 15.02
Cd(II) c0(f r) Cr(II[) Cu(II) l’e(IIi)
15.00 10.00 15.00 10.00 20.00
14,988 10.08, 15.28, 10.32, 19.98,
14.94 10.27 15.28 10.28 19.94
l-wll) Mn( II) Ni(II)
20.00 20.00 10.00
1g.g4,20.02 19.99, 20.02 TO.TG, TO.3G
Pb(l1) Zn(I1) Mixture Al(lIl),
15.00 10.00
14.94, 10.28,
Al(III)
5 0.1
5.18,
(nrg)
10.20,
20.00
consisting of Cd(IE). CO(II),
Cu(II), 19.50
6 Of CaCh TIlCtd nitrate
Fc(III),
Mn(II),
14.94 10.16
Ni(I1). Pb(I1). I>d(Il), T9.T9, 19.42, 19.50
Zn(Il)
ddcd.
Anal.
Chirn.
Acta,
4B (19Gg)
239-245
G. L. WHEELER, J. ANDREJACK, J. H. WIERSMA, I’. F. LOTT
242
Fr
Ra
AC*
+K Ele;,en!;c~;~l:
%?
t Ela&nts 90403: (3 &rtron*)
w
Pig. I. Effect tartrate.
of foreign
w
Pa
nnnnnnnnnn Sm Eu Gd Tb, DY
Pm
@
U
ions. (n)
Pu
NP
*Am
..
Cm
Ions non-interfering
Bk
Ho
Er
Tm
Yb
lu
Es
Fm
Md
No
Lr
C4
or mnsltcd by EDTR;
( 0) ions maslccd by
insoluble even in the presence of EDTA, therefore tartrate must be used to form soluble complexes. Tartratc also masks palladium. The reagent and silver form an insoluble complex with a I : I molar ratio, thus confirming the theoretical gravimetric factor of 0.3908. It was found that tempcratures of 1oo~-14o~ were suitable for drying the precipitate. The precipitate is neither llygroscopic nor light-sensitive. The silver complex is insoluble in most organic solvents (no solvent was found which would extract the complex from the aqueous layer). The complex is soluble in concentrated nitric and sulfuric acids. Cyanide readily dissolves the precipitate. The pw range is critical for the precipitation of the silver complex of naphthotriazole owing to the insolubility of the reagent in acidic solutions. Aqueous ammonia tended to coagulate the precipitate. Figure z shows the effect of pH on precipitation of silver napl~thotriazolate. The average error was less than 0.2 mg in samples containing s-100 mg of silver and IOO mg of foreign metals. No interference was found from nitrate, sulfate,
350
300
pH
l2
Pig. 2. Effect of pH and hot water washing on rocovcry hot water; (B) precipitate washed with hot water. Fig. 3. Spectra. (A) 2,3-Nnphthotriazolc, IO pg/ml, prr 10. Anal. Chim. Acta, 46 (1969)
23g-245
WAVELENGTH
of silver.
IO (ug/ml, pzx IO:
(A)
(B) silver
400 (n
Precipitate complex
450
m)
not washed
with
of naphthotriazolc,
2,3-NAPHTHOTRIAZOLE
AS A REAGENT
FOR
Ag
243
phosphate, acetate, oxide, fluoride, chloride or bromide in the gravimetric procedure, because silver in the sample was kept in solution by the presence of ammonia. S~ectro$d~otontetric
metltod
Figure 3 shows the ultraviolet-visible absorbance spectra of the reagent and the complex. Spectrophotometric results for silver in the presence of foreign metals, with a 50 ,q/ml reagent are shown in Table II. Silver (I pug/ml) can be determined in the presence of a mixture containing 5,000 pg/ml each of copper(H), cobalt(II), nickel(II), manganese(IT). and iron(III) ; these five ions are the most highly colored EDTA complexes. Since the absorbance spectrum shows three peaks, further selectivity can be achieved by proper wavelength selection. TABLE
II
SPISCTROPIIOTOMISTI1~C
Aa
DBT~RMINATIONS
Ag p,vcsl!lrC
A g foll,liz
(p./?.?n.)
(p.p.>?L)
O-5
0.5 3.3 1.0
4:::
5-o 10.0
5.79 IO.0
;:: 10.0
0.9 5.0 IO.0
20.0
20.0
LB”
Co
1.0
1.0
2-5 5-o 10.0
10.0
OF SILVRK
IN
TIIB
I’RIZSENCIS
OF OTJIER
IONS
5.:
a 50 p.p.m, each Cu(II), Co(II), Ni(‘II), Mn(II), Fc(III) nitrates prcscnt. b 100 p.p.m. each Cu(II), Co(II), Ni(II), Pb(II), Zn(XI) nitrates prcscnt, 0 5,000 p.p.m. each Cu(II), Co(Il), Ni(II), Mn(Il), Fc(III) nitrrrtcs present.
7 Fig.
4. Effect
9
of
pH
on
pH
absorbance
Fig. 5. Mole ratio study.
(A) 0.14
”
MOLE
(50 ,ug &+/ml; mM
reagents;
wavelcrlgth (B)
0.11
mM
FRACTION
SILVER
436 nm). reagents.
Al&al. Chim.
Acta,
46
(1969)
239-245
G. L.
244
WHEELER,
J.
ANDREJACK,
J.
H.
WIERSMA,
P.
F.
The PH is critical for maximal color development ancl stability (Fig. 4). A Job study (Fig. 5) showed that the ratio of silver to 2,3-naphthotriazole of the complex is 1,000. the complex was x : I. The molar absorptivity
LO-IT
in
I:larorimetric metlaod Table III shows the reSults obtained in the direct fluorimetric determination of silver in the absence of foreign metal nitrates but in the presence of chloride; a reagent solution containing 0.05 pg/ml was used. Chloride, zbromide and iodide ions were found to interfere with the procedure when present in the sample in excess of I p.p.m. Masking agents such as EDTA, triethanolamine, and tartrate were found to complex silver sufficiently to prevent complete quenching of the fluoresccncc of the 2,3-naphthotriaaole when silver was added.
DIRl3CT
FLUORIMETRIC /I&?
DETIERMINA’TIONS
~plwsc~rL1
OF
SILVER
A g fcmd
(p.p.0.)
(p.p.0.)
25 50 75 IO0 125
25, 24 49150 75175 ‘03 ‘25
A”
13’,
25 50 75
25 50 76
cc
25 50 75
24 52 74
* No interfering ions. b Go p.p.b. Cl- prcsmt. 0 Go0 p.p.b. Cl- prcsont. Filter selections for the maximum excitation and fluorescence of the reagent were determined from the spectra recorded on the Bausch and Lomb 505. The excitation maximum was observed at 362 nm and the fluorescence maximum at 406 nm. Accordingly, Corning filters number CS 7-55 and CS 3-73 were used as excitation and transmission filter, respectively. Fluorimetric titrations were also performed, with the same filters in the Farrand fluorimeter and a recorder output 4, for the determination of 0.1-2.0 ,ug of silver per ml (PH 10.5 nietheneamine buffer) with a 0.1 mg/ml solution of 2,3-naphthotriazole as the titrant. The end-point was indicated by the increase in the fluorescence intensity when excess of reagent was added. The minimum amount of silver which could be determined titrimetrically by this procedure was about IO times larger than the amount wllich could be determined by the direct fluorimetric procedure; since the titrant was added continuously, there was no time of standing to permit the reaction to go “to completion”. Both fluorimetric procedures are capable of detecting lower quantities of silver than the spectrophotometric method. And.
Cir,im.
A&,
qG (1gGg)
239-245
2,3-NAPHTHOTRIAZOLE
AS
A REAGENT
FOR
Ag
245
Attempts to increase the sensitivity of the spectrophotometric and fluorimetric methods by means of extraction were unsuccessful, since no suitable organic solvent could be found. SUMMARY
2,3-Naphthotriazole is suitable for the determination of macro- and microquantities of silver. The gravimetric (for 5-100 mg Ag) and spectrophotometric (&= I ,000; r-30 ,ug Ag/ml) methods are rapid and free of halide and foreign ion interferences; excellent selectivity is attained by means of masking agents. The fluorimetric method (0.025-0.1 ,ug Ag/ml) is much more sensitive than the spectrophotometric method but is more subject to interferences. Rl!csUMB Le z,g-naphtotriazole convient au dosage de macro- et de microquantit& d’argent. Les methodes gravimetriques (pour 5 a IOO mg Ag) et spectrophotometriques (E = I ,000 ; I A 30 ,ug Ag/ml) sont rapides. Les halogenures et ions &rangers ne gCnent pas; on peut obtenir une excellente selectivite au moyen de reactifs de La methode fluorimetrique est beaucoup plus sensible (0.025-0.1 pg masquage. Ag/ml) que la m8thode spectrophotom&rique; cependant elle prQsente plus d’interf&ences d’ions Strangers. ZUSAMMENFASSUNG
z,3-Naphthotriazol ist zur Bestimmung von Makro- und Mikromengen Silber geeignet. Die gravimetrische (5-100 mg Ag) und spektralphotometrische (e = 1,000 ; 1-30 ,ug Ag/ml) sind schnell und frei von Storungen durch Halogenide und andere lrremdionen. Eine ausgezeichnete Selektivitat wird mit Hilfe von maskierenden Reagenzien erzielt. Die fluorimetrische Methode (0.025-0.1 ,ug Ag/ml) ist sehr vie1 empfindlicher als die spektralphotometrische Methode, aber such st(iranf8lliger gegentiber Fremdionen. REFERENCES I I<. KODAMA, Methods of Quantitative Inorgak Analysis, Intcrscicnce, 2 M. ‘I?. EL-GHARMY AND R. W. FRI~I, Anal. Ghens., 40 (19GS) 19%. 3 J. I-I. WrnRsnrA AND J?. F. LOTT, Chemist-A?talyst, 55 (196G) 20. 4 J. I-I. WxERsnlhAND P. F. LOTT, Analytical Letters, I (rgG8) Go3.
New
York,
rgG3.
Anal. Ckim. Acta, 46 (19Gg) 239-245
239
Amsterdam
Printed in The Nctherlnnds
2,3-NAPHTHOTRIAZOLE AND FLUORIMETRTC SILVER
GARRY
L.
Defiavlnrenl (Rcccived
WHEELER,
JOHN
of Chentistry, March
4th.
AS A GRAVl-METRIC, SPECTROPHOTOMETRIC, REAGENT FOR THE DETERMINATION OF
ANDREJACK.
University
JAMES
of Missouri,
Kansas
I-I. WIElISMA Cily,
Ado.
64110
AND
PE’~El<
1’. LO-U-
(U.S.A.)
1969)
Gravimetric and titrimetric methods for the determination of silver with benzotriazole and its derivatives have been reviewed by I
-N
+
Ag+-
[
m+g+
A study of the determination of macro and trace amounts of silver with 2,3naphthotriazole in the presence of foreign ions is reported below. The reagent has been found suitable for the direct determination of milligram amounts of silver gravimetrically, while submilligram and trace amounts of silver are determined by spectrophotometric or fluorimetric methods.
Absorption spectra were obtained with a Bausch and Lomb 505 recording spectrophotometer. Absorbance measurements were made wit11 a Beckman DU and a Model B spectrophotometer using I.OO-cm quartz cells. Fluorescence spectra were also obtained from a Bausch and Lomb 505 recording spectrophotometer and fluorescence accessorya. Relative fluorescent intensities were determined with a Farrand Model A-z Fluorimeter, and fluorimetric titrations were performed with this instrument according to the procedure of WIERS~IA AND LOTTE. Anal.
Cl&la.
Acta,
46
(1969)
239-245
240
G. L. WHEELER,
J. ANDREJACK,
J. H. WIERSMA,
I?.F. LOT-r
Reagents z,3-Naphthotriazole was prepared by dissolving 5.0 g of z,3-diaminonaphthalene (Aldrich Chemical Co., Milwaukee, Wise.) in zoo ml of glacial acetic acid, diluting to 800 ml with water then to IOOO ml with ice. When the ice was completely melted, 2.5 ml of aqueous 1.2 M sodium nitrite was added rapidly while stirring briskly. The precipitate, 2,3-naphthotriazole, was recrystallized twice from boiling water containing decolorizing carbon. The average yield was GoO/,of the theoretical yield and the product had a melting range of Ig4°-xg7”. The material is quite insoluble in cold water and acidic solutions (except concentrated sulfuric acid). It is very soluble in basic solution and is soluble to the extent of 0.15 g/100 ml in boiling water. For the gravimetric procedure, a solution of 2,3-naphthotriazole was prepared by dissolving 2.50 g of 2,3-naphthotriazole in 30 ml of concentrated aqueous ammonia, diluting to xoo ml with water and filtering through a Reeve-Angel glass fiber filter (grade 934 AH) until no residue was left on the filter. For the spectrophotometric and fluorimetric procedure, IOO mg reagent was dissolved in IOO ml of hot water or IOO ml of 0.025 M sodium hydroxide. Reagent solutions containing x0.0 mg/ml concentration or greater were prepared daily, because considerable decomposition occurred within a week; less concentrated solutions were stable for a month when stored in the dark. Stanclard silver solution (5.00 mg/ml) was prepared by dissolving 0.7875 g of reagent-grade silver nitrate in a Too-ml volumetric flask containing I ml of nitric acid and diluting to volume with water. Fresh silver nitrate solution was prepared daily. A masking solution, 0.05 M in EDTA =and 0.05 M in sodium tartrate, was prepared by dissolving 18.6 g of the disodium salt of EDTA and 11.5 g of sodium tartrate in I 1 of water. Gmviwtetvic procedzwe To a solution containing 5-100 mg of silver, add 25 ml of masking solution, adjust to ca. PH II with aqueous ammonia, and add 2-20 ml of stock 2,3-naphthotriazole solution depending upon the amount of silver in the sample. A 50% excess of reagent is sufficient to precipitate the silver completely. Digest the samples at Go”-70~ for 15 min and allow to cool to room temperature. Then filter through a weighed Coors Gooch crucible and Reeve-Angel glass fiber filter (grade 934 AH), wash twice with 20-30 ml of hot water (as near Ioo” as possible), and dry at 1x0~ for 1-2 h to constant weight. The conversion factor is 0.3908.
Silver in the range 1-30 ,ug/ml can be determined by mcasurcmcnt of the absorbance of the silver triazole complex in basic solution. Prepare samples by adding to a series of roe-ml volumetric flasks, o-3 mg silver, 5 ml of a solution of 2,3-naphthotriazole solution (IO- mg/ml) in 0.025 M sodium hydroxide, IO ml of the masking agent solution and IO ml of PH 10.5 buffer. As ammonium hydroxide must be excluded to prevent precipitation of the’ silver comple’x, a metheneamine-sodium hydroxide buffer was prepared by adding 6g of metheneamine to I 1 of water and sufficient sodium hydroxide to adjust the solution to pH 10.5 as shown by a PH meter; the pH is critical (see below). Allow the yellow .4?Z&.C&m. Acta, 46
(196CJ) 239-245
2/J-NAPHTHOTRIAZOLE
AS A REAGENT
Ag
FOR
24f
color of the silver-naphthotriazolate complex to develop for 3-5 min, and then measure the absorbance at 436,416, or 3go nm against a reference standard containing all reagents except silver. Measurements at 436 nm are preferred as most metal-EDTA complexes do not absorb light of this wavelength. Direct fluorimetric’ procedure Silver in the range O.OZ~-0.100 ,.ug/nil can be determined by measurement of the fluorescence intensity of samples relative to a reference blank containing all reagents except silver. The direct fluorimetric procedure uses the same reagents as the spectrophotometric procedure, but no masking agents,
ANT> DISCUSSION
The results of several determinations of silver with the reagent, in the absence and presence of foreign metals are shown in Table I. Figure I shows qualitative interference tests conducted by adding IO ml of masking solution, 2 ml of concentrated ammonia solution and 5 ml of 0.05 M 2,3-naphthotriazole solution to IO ml of 0.01 M solution of foreign metal ion. The reagent is not specific for silver; however, the combination of the reagents, EDTA and sodium tartrate, make the method highly selective for silver. Of the ions tested, as shown in Fig. I, only antimony and and manganese are iodide interfered. The hydroxides of tin, titanium, beryllium TAl3LE
I
GrJ”V’METR’C
DETERMINATION
OF
SILVER
IN
THE
I’RESENCB
AND
AlK+lSNCE
OIr
METAL
NITRATES
.-.. Ilfela
added n
I
Ag tutc.5w (ins)
Ag fowd
5.00 rq.00 15.00 15.00
15.02. 19.82, 15.oG,
5.29 10.32 15.28 19.8~ 15.02
Cd(II) c0(f r) Cr(II[) Cu(II) l’e(IIi)
15.00 10.00 15.00 10.00 20.00
14,988 10.08, 15.28, 10.32, 19.98,
14.94 10.27 15.28 10.28 19.94
l-wll) Mn( II) Ni(II)
20.00 20.00 10.00
1g.g4,20.02 19.99, 20.02 TO.TG, TO.3G
Pb(l1) Zn(I1) Mixture Al(lIl),
15.00 10.00
14.94, 10.28,
Al(III)
5 0.1
5.18,
(nrg)
10.20,
20.00
consisting of Cd(IE). CO(II),
Cu(II), 19.50
6 Of CaCh TIlCtd nitrate
Fc(III),
Mn(II),
14.94 10.16
Ni(I1). Pb(I1). I>d(Il), T9.T9, 19.42, 19.50
Zn(Il)
ddcd.
Anal.
Chirn.
Acta,
4B (19Gg)
239-245
G. L. WHEELER, J. ANDREJACK, J. H. WIERSMA, I’. F. LOTT
242
Fr
Ra
AC*
+K Ele;,en!;c~;~l:
%?
t Ela&nts 90403: (3 &rtron*)
w
Pig. I. Effect tartrate.
of foreign
w
Pa
nnnnnnnnnn Sm Eu Gd Tb, DY
Pm
@
U
ions. (n)
Pu
NP
*Am
..
Cm
Ions non-interfering
Bk
Ho
Er
Tm
Yb
lu
Es
Fm
Md
No
Lr
C4
or mnsltcd by EDTR;
( 0) ions maslccd by
insoluble even in the presence of EDTA, therefore tartrate must be used to form soluble complexes. Tartratc also masks palladium. The reagent and silver form an insoluble complex with a I : I molar ratio, thus confirming the theoretical gravimetric factor of 0.3908. It was found that tempcratures of 1oo~-14o~ were suitable for drying the precipitate. The precipitate is neither llygroscopic nor light-sensitive. The silver complex is insoluble in most organic solvents (no solvent was found which would extract the complex from the aqueous layer). The complex is soluble in concentrated nitric and sulfuric acids. Cyanide readily dissolves the precipitate. The pw range is critical for the precipitation of the silver complex of naphthotriazole owing to the insolubility of the reagent in acidic solutions. Aqueous ammonia tended to coagulate the precipitate. Figure z shows the effect of pH on precipitation of silver napl~thotriazolate. The average error was less than 0.2 mg in samples containing s-100 mg of silver and IOO mg of foreign metals. No interference was found from nitrate, sulfate,
350
300
pH
l2
Pig. 2. Effect of pH and hot water washing on rocovcry hot water; (B) precipitate washed with hot water. Fig. 3. Spectra. (A) 2,3-Nnphthotriazolc, IO pg/ml, prr 10. Anal. Chim. Acta, 46 (1969)
23g-245
WAVELENGTH
of silver.
IO (ug/ml, pzx IO:
(A)
(B) silver
400 (n
Precipitate complex
450
m)
not washed
with
of naphthotriazolc,
2,3-NAPHTHOTRIAZOLE
AS A REAGENT
FOR
Ag
243
phosphate, acetate, oxide, fluoride, chloride or bromide in the gravimetric procedure, because silver in the sample was kept in solution by the presence of ammonia. S~ectro$d~otontetric
metltod
Figure 3 shows the ultraviolet-visible absorbance spectra of the reagent and the complex. Spectrophotometric results for silver in the presence of foreign metals, with a 50 ,q/ml reagent are shown in Table II. Silver (I pug/ml) can be determined in the presence of a mixture containing 5,000 pg/ml each of copper(H), cobalt(II), nickel(II), manganese(IT). and iron(III) ; these five ions are the most highly colored EDTA complexes. Since the absorbance spectrum shows three peaks, further selectivity can be achieved by proper wavelength selection. TABLE
II
SPISCTROPIIOTOMISTI1~C
Aa
DBT~RMINATIONS
Ag p,vcsl!lrC
A g foll,liz
(p./?.?n.)
(p.p.>?L)
O-5
0.5 3.3 1.0
4:::
5-o 10.0
5.79 IO.0
;:: 10.0
0.9 5.0 IO.0
20.0
20.0
LB”
Co
1.0
1.0
2-5 5-o 10.0
10.0
OF SILVRK
IN
TIIB
I’RIZSENCIS
OF OTJIER
IONS
5.:
a 50 p.p.m, each Cu(II), Co(II), Ni(‘II), Mn(II), Fc(III) nitrates prcscnt. b 100 p.p.m. each Cu(II), Co(II), Ni(II), Pb(II), Zn(XI) nitrates prcscnt, 0 5,000 p.p.m. each Cu(II), Co(Il), Ni(II), Mn(Il), Fc(III) nitrrrtcs present.
7 Fig.
4. Effect
9
of
pH
on
pH
absorbance
Fig. 5. Mole ratio study.
(A) 0.14
”
MOLE
(50 ,ug &+/ml; mM
reagents;
wavelcrlgth (B)
0.11
mM
FRACTION
SILVER
436 nm). reagents.
Al&al. Chim.
Acta,
46
(1969)
239-245
G. L.
244
WHEELER,
J.
ANDREJACK,
J.
H.
WIERSMA,
P.
F.
The PH is critical for maximal color development ancl stability (Fig. 4). A Job study (Fig. 5) showed that the ratio of silver to 2,3-naphthotriazole of the complex is 1,000. the complex was x : I. The molar absorptivity
LO-IT
in
I:larorimetric metlaod Table III shows the reSults obtained in the direct fluorimetric determination of silver in the absence of foreign metal nitrates but in the presence of chloride; a reagent solution containing 0.05 pg/ml was used. Chloride, zbromide and iodide ions were found to interfere with the procedure when present in the sample in excess of I p.p.m. Masking agents such as EDTA, triethanolamine, and tartrate were found to complex silver sufficiently to prevent complete quenching of the fluoresccncc of the 2,3-naphthotriaaole when silver was added.
DIRl3CT
FLUORIMETRIC /I&?
DETIERMINA’TIONS
~plwsc~rL1
OF
SILVER
A g fcmd
(p.p.0.)
(p.p.0.)
25 50 75 IO0 125
25, 24 49150 75175 ‘03 ‘25
A”
13’,
25 50 75
25 50 76
cc
25 50 75
24 52 74
* No interfering ions. b Go p.p.b. Cl- prcsmt. 0 Go0 p.p.b. Cl- prcsont. Filter selections for the maximum excitation and fluorescence of the reagent were determined from the spectra recorded on the Bausch and Lomb 505. The excitation maximum was observed at 362 nm and the fluorescence maximum at 406 nm. Accordingly, Corning filters number CS 7-55 and CS 3-73 were used as excitation and transmission filter, respectively. Fluorimetric titrations were also performed, with the same filters in the Farrand fluorimeter and a recorder output 4, for the determination of 0.1-2.0 ,ug of silver per ml (PH 10.5 nietheneamine buffer) with a 0.1 mg/ml solution of 2,3-naphthotriazole as the titrant. The end-point was indicated by the increase in the fluorescence intensity when excess of reagent was added. The minimum amount of silver which could be determined titrimetrically by this procedure was about IO times larger than the amount wllich could be determined by the direct fluorimetric procedure; since the titrant was added continuously, there was no time of standing to permit the reaction to go “to completion”. Both fluorimetric procedures are capable of detecting lower quantities of silver than the spectrophotometric method. And.
Cir,im.
A&,
qG (1gGg)
239-245
2,3-NAPHTHOTRIAZOLE
AS
A REAGENT
FOR
Ag
245
Attempts to increase the sensitivity of the spectrophotometric and fluorimetric methods by means of extraction were unsuccessful, since no suitable organic solvent could be found. SUMMARY
2,3-Naphthotriazole is suitable for the determination of macro- and microquantities of silver. The gravimetric (for 5-100 mg Ag) and spectrophotometric (&= I ,000; r-30 ,ug Ag/ml) methods are rapid and free of halide and foreign ion interferences; excellent selectivity is attained by means of masking agents. The fluorimetric method (0.025-0.1 ,ug Ag/ml) is much more sensitive than the spectrophotometric method but is more subject to interferences. Rl!csUMB Le z,g-naphtotriazole convient au dosage de macro- et de microquantit& d’argent. Les methodes gravimetriques (pour 5 a IOO mg Ag) et spectrophotometriques (E = I ,000 ; I A 30 ,ug Ag/ml) sont rapides. Les halogenures et ions &rangers ne gCnent pas; on peut obtenir une excellente selectivite au moyen de reactifs de La methode fluorimetrique est beaucoup plus sensible (0.025-0.1 pg masquage. Ag/ml) que la m8thode spectrophotom&rique; cependant elle prQsente plus d’interf&ences d’ions Strangers. ZUSAMMENFASSUNG
z,3-Naphthotriazol ist zur Bestimmung von Makro- und Mikromengen Silber geeignet. Die gravimetrische (5-100 mg Ag) und spektralphotometrische (e = 1,000 ; 1-30 ,ug Ag/ml) sind schnell und frei von Storungen durch Halogenide und andere lrremdionen. Eine ausgezeichnete Selektivitat wird mit Hilfe von maskierenden Reagenzien erzielt. Die fluorimetrische Methode (0.025-0.1 ,ug Ag/ml) ist sehr vie1 empfindlicher als die spektralphotometrische Methode, aber such st(iranf8lliger gegentiber Fremdionen. REFERENCES I I<. KODAMA, Methods of Quantitative Inorgak Analysis, Intcrscicnce, 2 M. ‘I?. EL-GHARMY AND R. W. FRI~I, Anal. Ghens., 40 (19GS) 19%. 3 J. I-I. WrnRsnrA AND J?. F. LOTT, Chemist-A?talyst, 55 (196G) 20. 4 J. I-I. WxERsnlhAND P. F. LOTT, Analytical Letters, I (rgG8) Go3.
New
York,
rgG3.
Anal. Ckim. Acta, 46 (19Gg) 239-245