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The separation and atomic-absorption measurement of trace amounts of lead, silver, zinc, bismuth and cadmium in high-nickel alloys
Analytica Chimica Acta, 80(1976)163-169 0 Elsevier Scientific Publishing Company,
Amsterdam
-
Printed
in The Netherlands
Short Communication _-__--_____--___-~ THE SEPARATION AND ATOMIC-ABSORPTION MEASUREMENT OF TRACE AMOUNTS OF LEAD, SILVER, ZINC, BISMUTH AND CADMIUM IN HIGH-NICKEL ALLOYS M. KIRK,
E.G. PERRY
and J.M. ARRZTT
Huntington Alloy Products Division, West Virginia 25 720 (U.S.A.) (Received
The International
Nickel
Company,
Inc., Huntington,
17th March 1975)
Accurate determinations of trace quantities (less than about 10 p.p.m.) of lead, silver, zinc, bismuth, and cadmium in nickel alloys have been difficult to achieve. Classical analytical methods are not suitable because of the complexity of the alloys and the low levels of those elements present. This communication describes a procedure that has the high sensitivity and selectivity necessary for determination of the low concentrations involved. The procedure is based on the use of an ion-exchange technique to separate the elements from the matrix. The separated elements are then concentrated to permit measurement by atomic-absorption spectrometry. Experimental Reagents Reagent-grade chemicals were used in preparation of all standards and eluants. Stock solutions (1000 p.p.m.) of Pb, Ag, Zn, Bi, or Cd were made with either the pure (99.999 %J)metal or commercially prepared solutions (J.T. Baker “Dilute-it”) that contained the elements in substrate form. Ion-exchange columns Anion-exchange columns contained BioRex 9 (100-200 mesh, Cl- form) resin in a plexiglass column. The resin bed was 14 cm deep and 2.5 cm in diameter. The column was preconditioned with 100 ml of 1.5 M hydrochloric acid. Cation-exchange columns contained BioRad AG50-X8 (100-200 mesh, H+ form) resin. The resin bed was 7 cm deep and 2.5 cm in diameter. The column was preconditioned with 100 ml of 0.1 M hydrofluoric acid. Equipment A Perkin-Elmer Model 303 atomic-absorption spectrophotometer was used. It was equipped with a three-slot burner and Perkin-Elmer hollowcathode source lamps.
164
Calibration standards Two sets of calibration standards were prepared for each element. One set was a low standard for the 10X scale, and the other a high standard for the 1X and 2X scales. The lead and bismuth contents were 1,2, and 3 p.p.m. for the low standards and 5,10, and 15 p.p.m. for the high standards. The zinc and cadmium contents were 0.25,0.50, and 0.75 p.p.m. for the low standards, 0.50, 1.0, and 1.5 p.p.m. for the high standards. Silver contents were 0.1, 0.2, and 0.3 p.p.m. for the low standards and 1, 2, and 3 p.p.m. for the high standards. Each calibration standard contained the same amount and type of acid as the final solution to be measured. Ion-exchange procedure Published data from several sources [l-6] were used in the development of the ion-exchange procedure. Figure 1 illustrates the procedure used to separate the lead, silver, zinc, bismuth, and cadmium from the alloy matrix.
Fig. 1. Elution
sequence
for the anion-exchange
column.
165
Dissolve a 10-g sample of the alloy in appropriate acids, usually a mixture of hydrochloric and nitric acids. After the reaction ceases, add 1 ml of hydrofluoric acid (40 7%)and evaporate the solution to dryness. Add 20 ml of 12 M hydrochloric acid and evaporate to dryness. Repeat the addition and evaporation of 12 M hydrochloric acid until all nitric acid is expelled. To ensure that all the salts are soluble, dissolve the residue in 50 ml of 12 M hydrochloric acid and evaporate to dryness on a steam bath. To produce the 1.5 M HF solution required for the column, add 5 ml of hydrofluoric acid (40 7%)and 100 ml of water, and heat to redissolve the salts. Transfer the HCl/HF solution of the sample to the anion-exchange column, and elute most of the matrix with 100 ml of 1.5 M HCl. Elute the lead and silver from the column with 200 ml of 8 M HCl; this fraction will also contain part of any titanium and molybdenum present in the sample, but these are later separated from the lead and silver by cation exchange. Elute the zinc with 200 ml of 0.001 M HCl. Remove any organic compounds present in this eluate by addition of 5 ml of nitric acid and evaporation to dryness. At this point in the elution sequence, elute any remaining molybdenum or any niobium that may have been partially adsorbed on the column with 300 ml of 4 M HCl-1 M HF solution; discard the eluate. Elute the bismuth and cadmium with 300 ml of 1 M sulfuric acid. Remove any organics in the eluate by adding 5 ml of 16 M nitric acid and evaporating to fumes of sulfur trioxide. Then cool, transfer to a glass beaker, and evaporate to dryness. Remove titanium and molybdenum from the lead/silver fraction by the cation-exchange procedure shown in Fig. 2. First remove any organics present in the eluate by addition of 20 ml of 16 M nitric acid and evaporation to dryness. Convert the metals to fluorides by addition of 10 ml of 40 9%hydrofluoric acid, and evaporation to dryness. Produce the 0.1 M HF solution required for the column by adding 5 ml of water and 2 ml of 40 9%hydrofluoric acid, redissolving the salts by heating, and diluting with 300 ml of
Fig. 2. Elution
sequence
for the cation-exchange
column.
166
water. Transfer the solution to the cation-exchange column, and elute the titanium and molybdenum with 300 ml of 0.1 M HF. Then elute the lead and silver with 300 ml of 4 M HNOJ. Obtain the chloride medium needed for spectrometry by addition and evaporation of 12 M hydrochloric acid until all nitric acid is removed from the eluate. The separated and concentrated elements in the three (Pb/Ag, Zn, and Bi/Cd) elution fractions can now be prepared for the 8.a.s. measurement. To determine the quantities of the trace elements that may have been introduced by the reagents, take a reagent blank through the entire procedure with the same amounts of reagents used for the sample, and deduct the reagent blanks from the sample values. TABLE
1
Flask sizes and concentration
rnnges for 10-g samples and instruments1
Element
Flask Concn. range Scale Wavelength expansion size (ml) (p.p.m.1 (um) -_ .---- --.---. -----.___-_ - --.--- ----.---.--.--c 1.6 Lead” 5 10x 283.3 1.5-7.5 2x < 0.15 Silver b 5 10x 328.1 0.15-1.5 1X Zinc” 25 < 1.9 2x 213.9 1.9-3.8 1x 223.1 5 < 1.5 10x Bismuth” 1.5-7.5 2x < 0.15 228.8 Cadmiumb 5 10x 0.15-0.38 1x ..-_. . . - _. -----_-_-_--_.-____ - - -----.- -.. ---0 Air--acetylene flame. bAir-propane flame. ‘Slit 4 corresponds to 0.7 nm, and 3 to 0.2 nm.
Atomic-absorption
measurement
parameters Slit 4c 4 4 3 4
The sizes of volumetric flasks used are listed in Table 1. If concentration ranges other than those listed are involved, dilute the samples accordingly. A chloride medium is needed for lead and silver, and the lead/silver fraction is transferred to flasks with 5 ‘36(v/v) hydrochloric acid. Zinc, bismuth and cadmium require a nitrate medium, and those fractions are transferred with 5 7%(v/v) nitric acid. The instrumental parameters used are listed in Table 1; in general, the instrument settings correspond to those recommended in the analytical methods supplied with the unit. Obtain an absorbance value for each element, and establish the concentrations from calibration curves. Figure 3 shows all the curves plotted on the same scale to indicate relative sensitivities.
167
Fig. 3. Composite
plot of calibrcltion
curves for the atomic-absorption
spectrophotomcter.
Discussion A hydrochloric acid medium could be used to separate lead, silver, zinc, bismuth, and cadmium from the matrix of simple alloys, but complex alloys required an HCl-HF medium. Distribution coefficients could not be found for silver and cadmium in an HCl-HF medium. It was observed, however, that only slight differences existed between the hydrochloric acid and the HCl-HF media for lead, bismuth, and zinc. Since silver and cadmium do not form strong fluoride complexes in the HCl-HF medium, it was assumed that their distribution ratios for that medium would parallel those for hydrochloric acid. This assumption was verified by the elution data. Eluant volumes were determined by adding lead, silver, zinc, bismuth, and cadmium to eight different nickel alloys and then applying the proposed procedure to the samples. The eluates were collected in lo-ml fractions, and the quantities of the added elements were determined for each fraction. The elution curves shown for Inconel alloy 600 (76 % Ni, 15.5 9%Cr, 8 % Fe) in Fig. 4 are typical of the results; eluant volumes for the other alloys varied by only about 10 ml. Cation exchange was chosen to separate titanium-molybdenum from leadsilver. Those eluant volumes were also arrived at by collection of lo-ml eluate
168 _____r
T
I---S;lnll,*,_
Fig. 4. Elution
‘1
_.._
_.llCj:_
5M
_
“3.
T-‘-_
_I!CL..-
curves for Inconel
_.
:
..__
.._..
r
._.
.
. _.._
+:,j
,%_o(!!..M!Ic:!..._,!_?Lx_~
alloy 600
on the anion-exchange
column.
fractions, and determination of the lead and silver in each fraction. Typical elution curves, again for the Inconel alloy 600 matrix, are shown in Fig. 5. The degree of recovery of the trace elements was determined by applying the elution sequence to samples of high-purity nickel pellets to which known amounts of each element had been added. A sample of the same material without the added elements was also taken through the elution sequence for
Fig. 5. Elution
curves
for Inconal
alloy 600
on the cation-exchange
column.
169 TABLE
2
Recovery of trace elements NBS SRM 361
from samples”
of high-purity
nickel pellets and analysis of
Nigh-purity nickel pellets NBS SRM 361 --_______-_.___----_-._.-_..-_Element Initial Amount Final Recovery Published Amount value found amount added amount (%) (*lo-’ %) found (-lo-’ %) found (P.p.m.) (p.p.m.) (p.p.m.) ---_._ __... .._..____._._.___.. . ..___ .--_ - ..-..._. - . . .._-_._._ -. .__... ._-. ._-._.._. .__.__._. 0.03 99,5 0.025 2.03 Lead 0.04 2,oo 0.34 95.9 0.40 0.96 Silver 0.001 1.00 0.17 0.10 100 5.00 5.03 Zinc 0.03 0.49 96.0 0.40 1.92 Bismuth 0.00 2.00 - b 0.0011 92.0 1,oo 0.92 Cndmium 0.00 __ -_----. -._ ._.....-.._._.. .-.. _ . nBesed on 10-g samples. bCadmium value not supplied.
comparison. The results, given in Table 2, ranged from 92.0 % to 100 % recovery. Analyses performed on National Bureau of Standards reference materials showed good correlation with the published values (Table 2). REFERENCES 1 2 3 4 5 6
F. Nelson and K.A. Kraus, J. Amer. Chem. Sot., 76 (1954) 5916. F.W.E. Strelow and C.J.C. Botkmn, Anal. Chem., 39 (1967) 595. J.A. Marinsky, Ion Exchange, M. Dckkcr, New York, 1966. J.S. Fritz, B.B. Garraldo and S.K. Karraker, Anal. Chem., 33 (1961) 882. F.W.E. Strelow, R. Rethemeyer and C.J.C. Bothma, Anal. Chcm., 37 (1965) F. Nelson, R.M. Rush and K.A. Kmus, J. Amer. Chem. Sot., 82 (1960) 339.
106.
Amsterdam
-
Printed
in The Netherlands
Short Communication _-__--_____--___-~ THE SEPARATION AND ATOMIC-ABSORPTION MEASUREMENT OF TRACE AMOUNTS OF LEAD, SILVER, ZINC, BISMUTH AND CADMIUM IN HIGH-NICKEL ALLOYS M. KIRK,
E.G. PERRY
and J.M. ARRZTT
Huntington Alloy Products Division, West Virginia 25 720 (U.S.A.) (Received
The International
Nickel
Company,
Inc., Huntington,
17th March 1975)
Accurate determinations of trace quantities (less than about 10 p.p.m.) of lead, silver, zinc, bismuth, and cadmium in nickel alloys have been difficult to achieve. Classical analytical methods are not suitable because of the complexity of the alloys and the low levels of those elements present. This communication describes a procedure that has the high sensitivity and selectivity necessary for determination of the low concentrations involved. The procedure is based on the use of an ion-exchange technique to separate the elements from the matrix. The separated elements are then concentrated to permit measurement by atomic-absorption spectrometry. Experimental Reagents Reagent-grade chemicals were used in preparation of all standards and eluants. Stock solutions (1000 p.p.m.) of Pb, Ag, Zn, Bi, or Cd were made with either the pure (99.999 %J)metal or commercially prepared solutions (J.T. Baker “Dilute-it”) that contained the elements in substrate form. Ion-exchange columns Anion-exchange columns contained BioRex 9 (100-200 mesh, Cl- form) resin in a plexiglass column. The resin bed was 14 cm deep and 2.5 cm in diameter. The column was preconditioned with 100 ml of 1.5 M hydrochloric acid. Cation-exchange columns contained BioRad AG50-X8 (100-200 mesh, H+ form) resin. The resin bed was 7 cm deep and 2.5 cm in diameter. The column was preconditioned with 100 ml of 0.1 M hydrofluoric acid. Equipment A Perkin-Elmer Model 303 atomic-absorption spectrophotometer was used. It was equipped with a three-slot burner and Perkin-Elmer hollowcathode source lamps.
164
Calibration standards Two sets of calibration standards were prepared for each element. One set was a low standard for the 10X scale, and the other a high standard for the 1X and 2X scales. The lead and bismuth contents were 1,2, and 3 p.p.m. for the low standards and 5,10, and 15 p.p.m. for the high standards. The zinc and cadmium contents were 0.25,0.50, and 0.75 p.p.m. for the low standards, 0.50, 1.0, and 1.5 p.p.m. for the high standards. Silver contents were 0.1, 0.2, and 0.3 p.p.m. for the low standards and 1, 2, and 3 p.p.m. for the high standards. Each calibration standard contained the same amount and type of acid as the final solution to be measured. Ion-exchange procedure Published data from several sources [l-6] were used in the development of the ion-exchange procedure. Figure 1 illustrates the procedure used to separate the lead, silver, zinc, bismuth, and cadmium from the alloy matrix.
Fig. 1. Elution
sequence
for the anion-exchange
column.
165
Dissolve a 10-g sample of the alloy in appropriate acids, usually a mixture of hydrochloric and nitric acids. After the reaction ceases, add 1 ml of hydrofluoric acid (40 7%)and evaporate the solution to dryness. Add 20 ml of 12 M hydrochloric acid and evaporate to dryness. Repeat the addition and evaporation of 12 M hydrochloric acid until all nitric acid is expelled. To ensure that all the salts are soluble, dissolve the residue in 50 ml of 12 M hydrochloric acid and evaporate to dryness on a steam bath. To produce the 1.5 M HF solution required for the column, add 5 ml of hydrofluoric acid (40 7%)and 100 ml of water, and heat to redissolve the salts. Transfer the HCl/HF solution of the sample to the anion-exchange column, and elute most of the matrix with 100 ml of 1.5 M HCl. Elute the lead and silver from the column with 200 ml of 8 M HCl; this fraction will also contain part of any titanium and molybdenum present in the sample, but these are later separated from the lead and silver by cation exchange. Elute the zinc with 200 ml of 0.001 M HCl. Remove any organic compounds present in this eluate by addition of 5 ml of nitric acid and evaporation to dryness. At this point in the elution sequence, elute any remaining molybdenum or any niobium that may have been partially adsorbed on the column with 300 ml of 4 M HCl-1 M HF solution; discard the eluate. Elute the bismuth and cadmium with 300 ml of 1 M sulfuric acid. Remove any organics in the eluate by adding 5 ml of 16 M nitric acid and evaporating to fumes of sulfur trioxide. Then cool, transfer to a glass beaker, and evaporate to dryness. Remove titanium and molybdenum from the lead/silver fraction by the cation-exchange procedure shown in Fig. 2. First remove any organics present in the eluate by addition of 20 ml of 16 M nitric acid and evaporation to dryness. Convert the metals to fluorides by addition of 10 ml of 40 9%hydrofluoric acid, and evaporation to dryness. Produce the 0.1 M HF solution required for the column by adding 5 ml of water and 2 ml of 40 9%hydrofluoric acid, redissolving the salts by heating, and diluting with 300 ml of
Fig. 2. Elution
sequence
for the cation-exchange
column.
166
water. Transfer the solution to the cation-exchange column, and elute the titanium and molybdenum with 300 ml of 0.1 M HF. Then elute the lead and silver with 300 ml of 4 M HNOJ. Obtain the chloride medium needed for spectrometry by addition and evaporation of 12 M hydrochloric acid until all nitric acid is removed from the eluate. The separated and concentrated elements in the three (Pb/Ag, Zn, and Bi/Cd) elution fractions can now be prepared for the 8.a.s. measurement. To determine the quantities of the trace elements that may have been introduced by the reagents, take a reagent blank through the entire procedure with the same amounts of reagents used for the sample, and deduct the reagent blanks from the sample values. TABLE
1
Flask sizes and concentration
rnnges for 10-g samples and instruments1
Element
Flask Concn. range Scale Wavelength expansion size (ml) (p.p.m.1 (um) -_ .---- --.---. -----.___-_ - --.--- ----.---.--.--c 1.6 Lead” 5 10x 283.3 1.5-7.5 2x < 0.15 Silver b 5 10x 328.1 0.15-1.5 1X Zinc” 25 < 1.9 2x 213.9 1.9-3.8 1x 223.1 5 < 1.5 10x Bismuth” 1.5-7.5 2x < 0.15 228.8 Cadmiumb 5 10x 0.15-0.38 1x ..-_. . . - _. -----_-_-_--_.-____ - - -----.- -.. ---0 Air--acetylene flame. bAir-propane flame. ‘Slit 4 corresponds to 0.7 nm, and 3 to 0.2 nm.
Atomic-absorption
measurement
parameters Slit 4c 4 4 3 4
The sizes of volumetric flasks used are listed in Table 1. If concentration ranges other than those listed are involved, dilute the samples accordingly. A chloride medium is needed for lead and silver, and the lead/silver fraction is transferred to flasks with 5 ‘36(v/v) hydrochloric acid. Zinc, bismuth and cadmium require a nitrate medium, and those fractions are transferred with 5 7%(v/v) nitric acid. The instrumental parameters used are listed in Table 1; in general, the instrument settings correspond to those recommended in the analytical methods supplied with the unit. Obtain an absorbance value for each element, and establish the concentrations from calibration curves. Figure 3 shows all the curves plotted on the same scale to indicate relative sensitivities.
167
Fig. 3. Composite
plot of calibrcltion
curves for the atomic-absorption
spectrophotomcter.
Discussion A hydrochloric acid medium could be used to separate lead, silver, zinc, bismuth, and cadmium from the matrix of simple alloys, but complex alloys required an HCl-HF medium. Distribution coefficients could not be found for silver and cadmium in an HCl-HF medium. It was observed, however, that only slight differences existed between the hydrochloric acid and the HCl-HF media for lead, bismuth, and zinc. Since silver and cadmium do not form strong fluoride complexes in the HCl-HF medium, it was assumed that their distribution ratios for that medium would parallel those for hydrochloric acid. This assumption was verified by the elution data. Eluant volumes were determined by adding lead, silver, zinc, bismuth, and cadmium to eight different nickel alloys and then applying the proposed procedure to the samples. The eluates were collected in lo-ml fractions, and the quantities of the added elements were determined for each fraction. The elution curves shown for Inconel alloy 600 (76 % Ni, 15.5 9%Cr, 8 % Fe) in Fig. 4 are typical of the results; eluant volumes for the other alloys varied by only about 10 ml. Cation exchange was chosen to separate titanium-molybdenum from leadsilver. Those eluant volumes were also arrived at by collection of lo-ml eluate
168 _____r
T
I---S;lnll,*,_
Fig. 4. Elution
‘1
_.._
_.llCj:_
5M
_
“3.
T-‘-_
_I!CL..-
curves for Inconel
_.
:
..__
.._..
r
._.
.
. _.._
+:,j
,%_o(!!..M!Ic:!..._,!_?Lx_~
alloy 600
on the anion-exchange
column.
fractions, and determination of the lead and silver in each fraction. Typical elution curves, again for the Inconel alloy 600 matrix, are shown in Fig. 5. The degree of recovery of the trace elements was determined by applying the elution sequence to samples of high-purity nickel pellets to which known amounts of each element had been added. A sample of the same material without the added elements was also taken through the elution sequence for
Fig. 5. Elution
curves
for Inconal
alloy 600
on the cation-exchange
column.
169 TABLE
2
Recovery of trace elements NBS SRM 361
from samples”
of high-purity
nickel pellets and analysis of
Nigh-purity nickel pellets NBS SRM 361 --_______-_.___----_-._.-_..-_Element Initial Amount Final Recovery Published Amount value found amount added amount (%) (*lo-’ %) found (-lo-’ %) found (P.p.m.) (p.p.m.) (p.p.m.) ---_._ __... .._..____._._.___.. . ..___ .--_ - ..-..._. - . . .._-_._._ -. .__... ._-. ._-._.._. .__.__._. 0.03 99,5 0.025 2.03 Lead 0.04 2,oo 0.34 95.9 0.40 0.96 Silver 0.001 1.00 0.17 0.10 100 5.00 5.03 Zinc 0.03 0.49 96.0 0.40 1.92 Bismuth 0.00 2.00 - b 0.0011 92.0 1,oo 0.92 Cndmium 0.00 __ -_----. -._ ._.....-.._._.. .-.. _ . nBesed on 10-g samples. bCadmium value not supplied.
comparison. The results, given in Table 2, ranged from 92.0 % to 100 % recovery. Analyses performed on National Bureau of Standards reference materials showed good correlation with the published values (Table 2). REFERENCES 1 2 3 4 5 6
F. Nelson and K.A. Kraus, J. Amer. Chem. Sot., 76 (1954) 5916. F.W.E. Strelow and C.J.C. Botkmn, Anal. Chem., 39 (1967) 595. J.A. Marinsky, Ion Exchange, M. Dckkcr, New York, 1966. J.S. Fritz, B.B. Garraldo and S.K. Karraker, Anal. Chem., 33 (1961) 882. F.W.E. Strelow, R. Rethemeyer and C.J.C. Bothma, Anal. Chcm., 37 (1965) F. Nelson, R.M. Rush and K.A. Kmus, J. Amer. Chem. Sot., 82 (1960) 339.
106.