Analysis of Pure Lead and Lead Alloys for the Automotive Lead/Acid Battery Industry by Inductively Coupled Argon Plasma Emission Spectroscopy Johnson Controls, Inc., Corporate Applied
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Analysis of Pure Lead and Lead Alloys for the
Automotive Lead/Acid Battery Industry by
Inductively Coupled Argon Plasma Emission Spectroscopy
Johnson Controls, Inc., Corporate Applied Research Center, 5757 N Green Bay Avenue, Milwaukee, Wisconsin 53209 (T.J.S., D.A.W.); and Department of Chemistry, St Olaf College, Northfield, Minnesota 55057 (J.P.W.)
Pure lead and lead alloy dissolution procedures suitable for elemental
determinations by inductively coupled argon spectroscopy are described
The group of lead types investigated consisted of pure lead, Pb-Sb alloys,
Pb-Ca-AI alloys, and Pb-Ca-Sn-AI alloys Major alloy concentrations
range up to 10% Sb, 2% Sn, 0.2% Ca, and 0.1% AI Trace impurities
from 0.5 to 10 ppm are determined in pure lead and in several lead alloys
Major and trace element determinations are routinely performed si-
multaneously with the use of five to seven matrix-matched standards for
each alloy type Accuracy and precision data for certified and internal
reference materials are reported Chemical, spectral, and metallurgical
interferences are also discussed
Index Headings: Lead; Pure lead; Lead alloys; Dissolution procedures;
Inductively coupled argon plasma; ICP
I N T R O D U C T I O N
T h e p u r p o s e of this work is to d e m o n s t r a t e t h a t in-
ductively coupled argon p l a s m a emission s p e c t r o s c o p y
(ICP) is a very precise a n d accurate tool for the analysis
of pure lead a n d lead alloys I n d u c t i v e l y coupled argon
p l a s m a emission s p e c t r o s c o p y is an ideal i n s t r u m e n t a l
m e t h o d of analysis for lead as a result of the argon p l a s m a
stability, t h e absence of major spectral interferences for
Received 11 November 1988
* Present address: Compunetics Inc., 2000 Eldo Road, Monroeville, PA
15146
t Author to whom correspondence should be sent
the lead alloys analyzed, a n d s i m u l t a n e o u s m u l t i e l e m e n t analysis capability Major alloy elements a n d trace im- purities in lead can be routinely d e t e r m i n e d w i t h o u t a n y special i n s t r u m e n t , s t a n d a r d , or sample p r e p a r a t i o n con- siderations T h e lead t y p e s of interest in this work are pure lead, c a l c i u m - a l u m i n u m alloys, calcium-tin-alu-
m i n u m alloys, a n d a n t i m o n y alloys T o t a l weight p e r c e n t
of lead in these alloys never drops below n i n e t y in routine analyses
T h e accurate analysis of pure lead a n d lead alloys is very i m p o r t a n t in the lead/acid b a t t e r y industry T r a c e impurities as well as major alloy c o m p o n e n t s affect t h e overall p e r f o r m a n c e of t h e b a t t e r y system Several ele-
m e n t s (such as Te, As, a n d Se) at trace levels ( < 2 p p m )
c a u s e s e v e r e g a s s i n g p r o b l e m s w h e n b a t t e r i e s a r e charged 1,2 Gassing is t h e generation of h y d r o g e n a n d oxygen from the electrochemical dissociation of water
T h e presence of a gassing e l e m e n t is t h o u g h t to lower the h y d r o g e n overcharge potential b y several m e c h a - nisms 1 Excessive gassing depletes the electrolyte, short- ens b a t t e r y life, a n d causes b a t t e r y case bulging Major alloy c o n c e n t r a t i o n s are i m p o r t a n t for p r o p e r b a t t e r y grid strength, corrosion resistance, a n d p r o p e r b a t t e r y grid m a n u f a c t u r i n g B a t t e r y grids provide t h e m e c h a n - ical s u p p o r t a n d electrical c u r r e n t p a t h in b o t h the neg- ative a n d positive plates of t h e b a t t e r y All of these fac- tors affect b a t t e r y life a n d performance
Trang 2TABLE 1 Description of ICP instrument
Spectrometers 1 Polychromator
Slits
Grating Dispersion Spectral range Optical path
2 Mini-monochro-
mator
3 Monochromator
Torch
transport
Spray chamber
system
Disk drives
Printer
Jobin Yvon 1.0-m Paschen- Runge JY-48P vacuum with 39 channels Thermo- regulation of polychroma- tor Modified so that ana- lyte emission can be blocked from the 182.037-
nm and 220.353-nm exit slits
Entrance is 0.020 mm and is computer controlled for background correction Ex- its are 0.039 and 0.050 ram
Holographic, 2550 groves/
mm
First order, 0.39 nm/mm
160-416 nm
Extension tube purged with argon
Instruments SA, Model H-20
Hilger-Engis, Model 1000
Plasma Therm, Model 2500, 27.12 MHz Auto imped- ance matching network with remote control
Quartz, 135 mm
MAK-10 cross-flow." Perisal- tic pump used (0.8 mL/
min)
MAK-20, glass expansion chamber with baffle."
Digital Equipment Corp
PDP 11/03
Two 8-in RX02 drives
LA 120 Decwriter
"Sherritt Gorden Mines Limited, Fort Saskatchewan, Alberta Canada
T8L 2P2
Arc emision spectroscopy, 3,4,5 f a m e atomic absorp-
tion, 4,~,6 x-ray fluorescence, 7 and wet chemical methods, 4,5
have been the methods of analysis used for trace and
alloy element determinations in the b a t t e r y industry All
of these methods are useful but have certain undesirable
features Flame atomic absorption and wet chemical
methods are very time-consuming when multielement
analysis is needed X-ray fluorescence is useful for mul-
tielement analysis of major alloy elements but does not
have the required detection limits for trace analysis Arc
emission is used extensively in the industry because of
the speed of analysis, solid sampling, minor and major
element determinations, and minimal sample prepara-
tion However, arc emission does have inherent problems
in the analysis of lead First, only the surface of the lead
sample is analyzed This will yield an accurate analysis
only if the sample is homogeneous Second, the lead is
soft, and incorrect polishing of lead disks can cause er-
roneous results due to smearing of the sample surface
Third, the limits of quantitation (LOQ) for some ele-
ments (such as Sb, Co, and Ni) in pure lead and lead
alloys are not low enough for all applications Fourth,
the lead standards which would be needed for arc emis-
sion techniques would be very difficult to prepare for the
large number of elements routinely determined by ICP
Solid calibration standards for arc emission analysis are
not certified and are usually made by the user Solution
TABLE II Routine operating conditions
Integration time:
calibration standards for ICP analysis can be traced to certified reference materials and can be compared to certified reference materials on a routine basis
Inductively coupled argon plasma emission spectros- copy is the instrumental method of analysis for pure leads and lead alloys in this laboratory T h e ICP instru-
m e n t provides the required detection limits, the required LOQ, increased accuracy and precision, simultaneous major and trace element determinations, and the use of aqueous standards Proper lead sample t r e a t m e n t will yield an accurate ICP analysis of the lead sample while minimizing homogeneity problems Sample preparation does require additional time but is justified by the gain
in accuracy, precision, and lower LOQ
Lead sample preparation techniques and i n s t r u m e n t modifications are discussed in this work Problems as- sociated with a stray light interference and element seg- regation in lead alloys will be described T h e results of
an interlaboratory sample exchange will also be dis- cussed
E X P E R I M E N T A L
A p p a r a t u s T h e ICP instrumentation used for the anal- ysis of pure lead and lead alloys is described in Table I Under normal operating conditions the mini-monochro- mator is set at 766.490 nm for K, and the Hilger-Engis monochromator is set for 588.995 nm for Na T h e Hilger- Engis monochromator is also used for element wave- lengths which are not available on the polychromator Off-peak background correction is not available with the two monochromators
T h e normal operating conditions for the analysis of pure lead and lead alloys are listed in Table II Limits
of detection (LOD) obtained under these conditions for standard calibration solutions are reported in Table III Experimental and literature LODs 8,9,1° t h a t were deter- mined in water are included in Table III for comparison
To convert the LOD (ng/L) in the lead solution to ppm
in lead, multiply the LOD in the 2 % lead solution by 0.050 Similarly the LOD in the 12% lead solution is multiplied by 0.00888 to obtain p p m in lead
R e a g e n t s House-distilled water was purified to 18 M~
by a Milli-Q water purification system (Millipore Corp., Bedford, MA) All f u r t h e r references to water imply the use of 18 M~2 water Reagent-grade nitric acid, d-tartaric acid (crystal), and glacial acetic acid were used for sample preparation ("Baker Analyzed, ''® J T Baker Chemical Co., Phillipsburg, NJ) T h e nitric acid was further pur-
Trang 3T A B L E III ICP wavelengths and limits of detection (LOD) in liquid
matrices
C h a n - Ele- l e n g t h Lit Exp
nel m e n t ( n m ) ( n g / m L ) a ( n g / m L ) ( n g / m L ) ( n g / m L )
" S e e Ref 8
~) See Ref 9
• E x t e r n a l m o n o c h r o m a t o r
d See Ref 10
ified by distillation before use Reagent-grade hydrogen
peroxide (30%, EM Science, Cherry Hill, NJ) and Pur-
atronic ® lead (II) nitrate (99.999%, Johnson Matthey,
Royston, England) were used for sample and calibration
standard preparation
Dissolution Preliminaries Lead dissolution and dilu-
tion of sample solutions were performed in an acid fume
hood Dissolutions were done on Lindberg hot plates
(Model 53202, Watertown, WI) The surface temperature
of the hot plate was measured with a surface thermom-
eter (PTC ® Model 314F, Pacific Transducer Corp., Los
Angeles, CA) All reported temperatures were the mea-
sured surface temperature of the hot plate during dis-
solution The hot plates were always preheated to the
desired temperature before use
Glassware was soaked in 10 % (v/v) hydrochloric acid,
followed by 10 % (v/v) nitric acid, and finally rinsed with
water before use All sample solutions were brought to
volume with water in class-A volumetric glassware Sam-
ples during dissolution were covered with watch glasses
Separate 150-mL beakers (Pyrex ®, Corning, NY) and
volumetric glassware were set aside for each alloy type
to minimize potential cross contamination
All samples were cast three-inch-diameter disks, one
half inch thick The disks of lead alloys and pure lead
FIG 1 D i a g r a m of a c a s t lead disk w i t h 3 saw c u t s m a d e in t h e disk Saw c h i p s are collected a n d m i x e d to o b t a i n a r e p r e s e n t a t i v e s a m p l i n g
of t h e lead disk
used in this study were sampled by using a hard steel saw (nickel chrome alloy steel, Model D-23, Disston, Danville, VA) A separate saw for each alloy type was used No measurable contamination has been seen from this saw type At least three radial saw cuts towards the center of the sample were made, and the saw chips were collected to obtain a representative sample for analysis Sawing chips were collected and mixed, and the appro- priate amount was weighed for dissolution A diagram
of a cast disk with three saw cuts is shown in Fig 1 Pig lead ears and other cast lead shapes (such as chill-cast lead) were sampled in a similar fashion A detailed de- scription of the sawing procedure and a discussion of the importance of obtaining a representative sample of lead alloys are given in the section of this article t h a t describes sample segregation
Pure Lead and CA Alloy Dissolution Pure lead and
lead-calcium-aluminum (CA) alloys were dissolved by using 30 mL of (1:4) nitric acid to treat 6.000 + 0.005 g
of saw chips The sample was heated at 130-140°C until dissolved (1-2 h) with frequent swirling Then water was added to the hot sample solution to obtain an approxi- mate volume of 40 mL The solution was mixed well to prevent precipitation of lead nitrate The sample solu- tion was cooled and diluted to 50 mL with water The resulting solutions showed no visible precipitation for four or more days after dissolution
The nitric acid concentration in the pure lead and CA alloy dissolution procedure is extremely important Neb- ulization problems occur when the nitric acid concen- tration used for dissolution is greater than 4 molar Lead nitrate will precipitate in the spray chamber and inside the ICP torch when the nitric acid concentration equals
or exceeds this concentration Lowering the amount of nitric acid used or evaporation to almost dryness are alternative methods to eliminate the problems caused by excess nitric acid But both alternative methods have undesirable effects The dissolution time will increase if the nitric acid concentration is too low Evaporation of the sample to almost dryness to remove excess nitric acid causes precipitation of lead nitrate in minutes to hours
in the sample solution, and the sample preparation time
Trang 4TABLE IV ICP recovery data for a 25-ppm (3.0 mg/L in a 12% Pb
solution) addition of each element
Result" RSD Recovery
a Average of 20 analyses (3 months)
is increased P r e c i p i t a t i o n of lead n i t r a t e in the sample
solution is undesirable because trace impurities could
coprecipitate T h e p r o c e d u r e described for dissolution
of p u r e leads a n d CA alloys works satisfactorily
R e c o v e r y results for t w e n t y different dissolutions in
the pure lead m a t r i x are r e p o r t e d in T a b l e IV One spikes
6 g of pure lead m e t a l with 25 p p m (3 m g / L in solution)
of each element This sample is t h e n t r e a t e d as an un-
known, with the use of t h e n o r m a l dissolution a n d I C P
p r o c e d u r e s for pure lead T h e c o n c e n t r a t i o n of 25 p p m
was a typical c o n c e n t r a t i o n for m o s t impurities when
present T h e low recovery for Sb m a y be due to the
instability of t h e Sb spiking solution when t r e a t e d with
t h e p u r e lead dissolution procedure Some of the higher
recoveries (i.e., Bi a n d A1) m a y be due to trace impurities
of these elements in t h e pure lead sample which was
spiked T h e recoveries are acceptable, a n d the m a j o r i t y
of t h e recoveries were 100 _+ 4%
C S A A l l o y D i s s o l u t i o n L e a d - c a l c i u m - t i n - a l u m i n u m
(CSA) alloys were dissolved b y using 50 m L of a nitric
a c i d / t a r t a r i c acid m i x t u r e (75 g t a r t a r i c acid a n d 50 m L
of nitric acid diluted to 1 L) to t r e a t 2.000 _ 0.005 g of
saw chips T h e sample was h e a t e d at 220-240°C until
dissolved (2-3 h) I t was necessary to a d d additional
nitric a c i d / t a r t a r i c acid m i x t u r e during t h e course of t h e
dissolution p r o c e d u r e to m a i n t a i n the solution volume
at a b o u t 40 mL, to p r e v e n t tin oxide precipitation Once
dissolved, water was a d d e d to t h e h o t sample solution
to o b t a i n an a p p r o x i m a t e volume of 60 mL, with t h o r -
ough mixing to p r e v e n t p r e c i p i t a t i o n of lead nitrate T h e
sample solution s u b s e q u e n t l y was cooled a n d diluted to
100 m L with water
T h i s dissolution p r o c e d u r e was used to p r e v e n t for-
m a t i o n a n d p r e c i p i t a t i o n of tin oxide from t h e high con-
c e n t r a t i o n of tin p r e s e n t in t h e CSA alloys analyzed (up
TABLE V Long- and short-term precision for WRM
Short (same day) a
I- Long (6 months) b Ele- Average RSD RSD ° Average RSD
(SB alloy) As 0.130 1.0 1.7 0.143 3.7
Bi 0.0075 2.7 0.4 0.0081 12
Cu 0.0656 3.5 3.0 0.0674 3.2
S 0.0059 6.8 2.2 0.0055 16
Sn 0.0812 2.8 1.0 0.0868 2.5
(SB alloy) As 0.0541 6.5 2.2 0.0585 3.8
Bi 0.0089 4.5 0.7 0.0092 12
Cu 0.0350 2.2 1.2 0.0351 4.2
S 0.0048 1.3 0.4 0.0045 28
(CA alloy) A1 0.0136 0.7 0.3 0.0136 1.5
Ca 0.1120 0.5 0.9 0.1120 1.7
Mg 0.0002 2.3 1.3 0.0002 18
a Average of 3 analyses (only measurable results listed)
~' Average of 45 analyses, 6/87-12/87 (W8117 18 analyses)
c Instrumental precision of one analysis (three 10-s integrations)
d Divide % results listed by 0.005 for SB alloys and by 0.000833 for the CA alloy to obtain mg/L in solution
to 2 %) T a r t a r i c acid p r e v e n t s t h e insoluble Sn oxides
f r o m forming T h e CSA dissolution time has a strong
d e p e n d e n c e on t h e particle size of t h e sample Dissolu- tion time for saw chips was a b o u t 2 h, a n d c u t pieces (up
to 1~ in in length) t o o k up to 3 h
SB A l l o y D i s s o l u t i o n L e a d a n t i m o n y (SB) alloys were dissolved b y first a d d i n g 30 m L of water to 2.000 +_ 0.005
g of saw chips T h r e e m L of glacial acetic acid a n d t h e n
15 m L of 30% h y d r o g e n peroxide were a d d e d a n d mixed
T h e reaction was allowed to p r o c e e d until gas evolution ceased (usually 15 min) T h e n 20 m L of a solution con- taining 250 g t a r t a r i c acid diluted to 1 L with water was added, a n d t h e sample solution was mixed well T h e n 5
m L of nitric acid was added, a n d t h e solution was mixed again T h e solution was t h e n h e a t e d at 220-240°C until all solids were dissolved (15-30 min) Dissolution time was increased when Sb a n d Sn c o n c e n t r a t i o n s were high
F o r example, an SB alloy t h a t c o n t a i n e d 7% Sb or 0.8%
Sn would take a b o u t 30 m i n for c o m p l e t e dissolution
A n t i m o n y c o n c e n t r a t i o n s greater t h a n 7 % in the SB al- loys require a longer dissolution time, b u t these high-
c o n c e n t r a t i o n SB alloys will be dissolved b y t h e SB alloy dissolution procedure I t is r e c o m m e n d e d t h a t sample weights be r e d u c e d for these alloys to avoid lead n i t r a t e
p r e c i p i t a t i o n p r o b l e m s caused b y dissolution times long-
er t h a n 30 minutes
T h e sample solutions were i m m e d i a t e l y r e m o v e d f r o m the h o t plate when all solids were dissolved, t h e n 5 m L
of nitric acid was a d d e d to t h e h o t sample solution,
b r o u g h t to a volume of 85 m L with water, a n d mixed
T h i s step was i m p o r t a n t in p r e v e n t i n g lead n i t r a t e pre- cipitation T h e sample solution was cooled a n d diluted
to 100 m L with water T h e reader is advised to use ex-
t r e m e c a u t i o n when mixing these solutions in t h e volu- metric glassware P r e s s u r e builds up because of the ex- cess h y d r o g e n peroxide present Solutions were mixed
Trang 5Comparison of ICP and flame atomic absorption results
for the SB alloy W R M - D (%)
Dif- fer- Ele- I C P S t a n d a r d AA a S t a n d a r d ence
m e n t average d e v i a t i o n n average d e v i a t i o n n (%)
C u 0.0100 0.0003 11 0.097 0.0005 18 3.0
° L e a d s a m p l e s p r e p a r e d b y a H B F 4 / H N O 3 / t a r t a r i c acid dissolution
procedure
gently 2-3 times and the built-up pressure was released
before the mixing was continued
The proposed dissolution mechanism occurring in SB
alloy treatment involved two parallel reactions The 30 %
hydrogen peroxide converted elemental lead to lead(II)
oxide The lead(II) oxide was then dissolved by the gla-
cial acetic acid Black elemental Sb was suspended in
solution Tartaric acid was added, and a white complex
with lead formed Nitric acid was then added to dissolve
the tartaric acid lead complex and the elemental Sb The
tartaric acid and the 30 % hydrogen peroxide prevented
insoluble Sn and Sb oxides from forming
The SB alloy dissolution procedure will not completely
dissolve SB alloys with Sn concentrations greater than
200 mg/L in solution A tin oxide precipitate, as con-
firmed by x-ray fluorescence, begins to form during dis-
solution, yielding a hazy solution caused by the fine sus-
pension of the tin oxide Sample weight can be reduced
in order to maintain Sn concentrations in the final so-
lution at less than 200 mg/L, to produce a clear solution
The final lead concentration can be matched to the stan-
dards by adding the required amount of lead(II) nitrate
at the end of the dissolution procedure It has been ob-
served that the fine tin oxide suspension does not affect
the analysis of the National Bureau of Standards Stan-
dard Reference Material 53e (0.5 g sample weight used)
The composition of this SB alloy was about 10 % Sb and
6% Sn Solutions containing the tin oxide suspension
must be mixed well before ICP analysis
Calibration Standards All standard stock solutions
were acidic aqueous solutions, and the calibration stan-
dard solutions were matrix matched to the sample with
the use of the same reagents and acids used in sample dissolution The appropriate amount of high-purity lead(II) nitrate was added to the calibration standard solutions in order to matrix match the samples Aliquots
of multielement (Inorganic Ventures, Inc., Brick, NJ), 10,000 mg/L single analyte, and 1000 mg/L single analyte standard stock solutions were used to prepare 5-7 cali- bration standard solutions for ICP analysis of the lead sample solutions
Major alloy elements contained in the standard stock solutions were compared to appropriate National Bureau
of Standards (NBS) standard reference materials (SRM) (Gaithersburg, MD) The SRMs were 10,000 mg/L stock solutions of each analyte A sulfur containing SRM was not available at the time, and the standard stock solution was compared to 1000 mg/L standard stock solutions from other suppliers
Reference Materials To date, certified reference ma-
terials appropriate to the analysis of the currently man- ufactured battery alloy are unavailable Working refer- ence materials (WRM) are internal lead lots which have been designated as a reference material and are repeat- edly analyzed in our laboratory Working reference ma- terials are prepared with each sample batch and are ana- lyzed as samples on the ICP instrument A W R M is designated for each type of lead alloy The WRMs pro- vide an additional check for the accuracy of the prepared calibration standard solutions and correct ICP operation
It is understood that this is only true if the WRMs do not change with time and that the WRMs are homoge- neous Precision data for some WRMs are provided later
in this article
R E S U L T S AND D I S C U S S I O N
Reference Materials Reference materials are a key to
providing analytical continuity for any analysis Results
of a reference material analysis yield a historical record
of instrument performance, calibration standard stabil- ity and consistency, operator differences, and sample dis- solution problems It is always a difficult process to de- termine the exact cause of erroneous results, and the analysis of an appropriate reference material will help simplify the problem-solving process Working reference materials are used for this purpose in our laboratory
TABLE VII ICP results for two SB alloy reference materials (%)
N B S S R M 53e" ,Alpha m e t a l s B M - 1 (lot A) b
0.14 0.04 0.03
" T h e s a m p l e size was 0.5 g b e c a u s e of S n a n d Sb c o n c e n t r a t i o n s L e a d n i t r a t e was a d d e d to t h e s a m p l e s
calibration s t a n d a r d s
h T h e s a m p l e size was 1.0 g b e c a u s e of Sb c o n c e n t r a t i o n L e a d n i t r a t e was also added
" T h e e l e m e n t s S, Cd, M n , a n d Ag are i n c l u d e d for i n f o r m a t i o n only
after d i s s o l u t i o n to m a t r i x - m a t c h
J
Trang 6TABLE VIII Results for newly released NBS SRM (%).a
(<0.0001) (<0.0001) (<0.0001) (<0.0005)
(<0.0005) (<0.0005) (<0.0001) (<0.0005) (<0.0005) ( < 0.0005)
(<0.0005) (<0.0005) (<0.0005)
a Certified in March 1988
~' E.U.: estimated uncertainty
° Uncertified information given by NBS in parentheses
Hence, a p p r o p r i a t e working reference materials are ana-
lyzed with each b a t c h a n d for each alloy type T h e s e
results along with sample analysis results are k e p t in
c o m p u t e r storage for on-line searching, sample tracking,
generation of formal reports, statistical analysis, and fu-
t u r e use
Short- a n d long-term averages of t h r e e W R M s are re-
p o r t e d in T a b l e V W o r k i n g reference materials W R M - A
and W R M - B are SB alloys W R M - C is a CA alloy Av-
erage results have changed v e r y little over t h e s i x - m o n t h
period T h e r e is a noticeable decrease in precision for all
elements, which can be a t t r i b u t e d to the variables of
i n s t r u m e n t p e r f o r m a n c e , s t a n d a r d stability, o p e r a t o r dif-
ferences, and dissolution problems, a n d to the possibility
of slight W R M heterogeneity I n s t r u m e n t a l precision is
included for comparison
Sulfur averages and precision are poor because of the
inability to obtain dissolution reagents totally sulfur free
for I C P analysis T h e r e is a p p r o x i m a t e l y 1 m g / L sulfur
in t h e sample solution due to t h e reagents used Useful
analytical d a t a can be o b t a i n e d b y careful p r e p a r a t i o n
of t h e samples and calibration s t a n d a r d solutions b y us-
ing the same reagents Sulfur in t h e two SB alloy W R M s
has b e e n c o m p a r e d to results for a colorimetric m e t h o d
(H2S generation m e t h o d ) T h e r e is a g r e e m e n t within the
s t a n d a r d deviation of the two methods Sulfur also seems
to be a difficult e l e m e n t to d e t e r m i n e in the lead matrix,
as described in the section of this article t h a t discusses
q u a l i t y assurance
T a b l e VI shows a c o m p a r i s o n of flame atomic absorp-
tion (AA) a n d ICP d a t a for an SB alloy which is used as
a W R M for 6 % SB alloys T h e r e is good a g r e e m e n t be-
t w e e n results, even t h o u g h different i n s t r u m e n t a l a n d
dissolution p r o c e d u r e s were used Also, the AA d a t a were
collected in 1974, while t h e I C P d a t a were collected on
t h e same lot in 1987 T h i s i n f o r m a t i o n indicates t h a t this
lot of SB alloy was fairly h o m o g e n e o u s a n d t h a t t h e two
dissolution p r o c e d u r e s yielded a c o m p l e t e dissolution of
this alloy
Tables VII and VIII contain results for four N B S SRMs
a n d one reference material from Alpha Metals All sam- ples in T a b l e VII a n d N B S S R M C2416 in T a b l e VIII were p r e p a r e d according to t h e SB alloy dissolution pro- cedure T h e weights of samples in T a b l e VII were re-
d u c e d because of t h e high Sn and Sb concentrations
R e f e r e n c e materials C2417 a n d C2418 were p r e p a r e d by the p u r e lead dissolution procedure All materials were
t r e a t e d as r o u t i n e u n k n o w n samples in p r e p a r a t i o n a n d
in the I C P analysis
T h e r e is good a g r e e m e n t between the certified values
a n d t h e e x p e r i m e n t a l I C P results All I C P results (except
As in C2417) are within t h e e s t i m a t e d error which was supplied by the NBS T h e As value is j u s t above the high
e n d of the e s t i m a t e d error supplied by the NBS An investigation of t h e high As result in N B S C2417 has n o t been done It should be n o t e d t h a t t h e S R M C2416 does
n o t have a suitable alloy composition for use as a ref- erence material for r o u t i n e SB alloy b a t t e r y lead analysis
E l e m e n t S e g r e g a t i o n E l e m e n t segregation can be a major p r o b l e m in the analysis of p u r e lead a n d lead al- loys Segregation in the samples t a k e n from t h e m o l t e n lead is caused b y t h e slow cooling of lead in the mold Some elements form oxides or sulfides, or stay in the
e l e m e n t a l form during solidification of the lead T h e s e
c o m p o u n d s and e l e m e n t s p r e c i p i t a t e out of solution a n d rise to the top of the mold because these p r e c i p i t a t e d
c o m p o u n d s have a lower d e n s i t y t h a n lead T h e precip-
i t a t e d c o m p o n e n t s will n o t have a chance to segregate when the lead sample is p r o p e r l y cooled a n d will be uni-
f o r m l y frozen in position
Major problems arise in the analysis of lead samples when I C P i n s t r u m e n t a l results are c o m p a r e d to arc emis- sion results on segregated samples T a b l e I X shows a
c o m p a r i s o n of ICP a n d arc emission results o b t a i n e d on
a segregated sample T h e r o u t i n e ICP results are ob-
t a i n e d b y t h e s t a n d a r d sawing p r o c e d u r e described be- low, which r e p r e s e n t s t h e average cross-section compo- sition of t h e cast disk T h e b o t t o m ICP results are
o b t a i n e d b y sawing across the entire b o t t o m surface of the disk to a d e p t h of a b o u t 1/~G of an inch T h i s is t h e
692 Volume 43, Number 4, 1989
Trang 7T A B L E IX Segregation" of a CA alloy sample disk (%)
ARC
Ele- emission ICP
m e n t results routine b ICP bottom ICP center ICP top
Sb 0.0002 0.0001 <0.0001 <0.0001 0.0001
Te - - 0.0013 <0.0003 <0.0003 0.0027
" Ca, A1, Cu, and Te are segregated in this CA alloy disk
b Cross-cut of bottom, center, a n d top layers
surface that faces the bottom of the disk mold and is the
machined surface routinely used for arc emission anal-
ysis The assumption being made by arc emission users
is that this surface cools the quickest and should be
representative of the sample taken Practical experience
does not support this assumption when severe segrega-
tion has occurred The center ICP results are obtained
by sawing parallel to the two 3-in.-diameter surfaces to-
wards the center of the disk The top ICP results are
obtained by sawing across the entire top surface of the
disk to a depth of about ~6 of an inch The top surface
is at the top of the disk mold and is exposed to air during
cooling Sampling the disk as described above is a simple
procedure and serves the purpose for identifying segre-
gation problems
Segregation problems can be minimized through the
sampling and sawing procedure described below A 3-in.-
diameter cast disk approximately 1/2 in thick is made by
sampling a molten pot of lead The sampling ladle must
be hot, and the mold must be at room temperature or
cooler 11 This procedure allows fast cooling of lead, which
will minimize segregation Even if segregation does occur,
it will occur symmetrically around the center of the lead
disk Hence, one can obtain a representative sample by
sawing radially through the sample disk
It can be seen in Table IX that the arc emission results
and the bottom ICP results are within reasonable agree-
ment The A1 result by ICP is still a little high, but this
may be an artifact of the deeper sampling of the disk
:_" -L :.::_-::
SHUTTER CLOSED
I] [ ::! i" ~! H
FIG 2 Side view of the digital linear actuator in the polychromator
of the ICP i n s t r u m e n t T h e open and closed s h u t t e r positions are
illustrated
Te
\ \
Pb
Cd
FIG 3 Top view of the s h u t t e r s y s t e m with the s h u t t e r closed which
is keeping the Pb emission at 220.353 n m from passing through the exit slit
surface Arc emission techniques analyze < 1 mm depth
of the lead sample surface, depending on the metal hard- ness Aluminum and calcium in the middle and top layers show severe segregation in this lead disk When the arc emission results and ICP results are in such disagree- ment, as indicated by the normal ICP results, the cause
is usually a segregation problem Other elements that show segregation in this sample are Te and Cu Similarly, trace elements such as Sb, Ni and Na have been observed
to segregate in other CA alloys Sulfur and selenium have been observed to segregate in SB alloys Element seg- regation problems have also been observed in CSA alloys for the same elements that segregate in CA alloys Interferences The wavelengths used for ICP analysis
of pure lead and lead alloys were chosen to minimize spectral interferences in the lead matrix and to provide the lowest possible detection limits Platinum (203.646 nm) does have spectral interferences from Sb (203.662 and 203.639 nm), 12 Fe (203.643 nm), 12 and Pb (about
~ , ~ s P
JOHNSON CONTROLS FOCAL CURVE TI ~ ' ~
CVerfical Scale X2 Horiz - I0 crn Ticks) ~eo ~A-~'~ ~ ~ ~ "
2 5 5 0 Grooves/ram
35 o Incidence Cd Te Pb ,,,
FIG 4 Diagram of the J o h n s o n Controls, Inc focal eurve for the polychromator installed in the I n s t r u m e n t s SA JY48P ICP
APPLIED SPECTROSCOPY 693
Trang 8E L E M E N T = TE
6 6 4 0 , -
!
[
6 2 4 0 * -
I
5 8 4 0 , -
i
5 4 4 0 , -
i
5 0 4 0 -
[
4640 -
s
!
4240, -
!
3840 -
[
r
3440 -
WAVELENGTH= 2 1 4 2 8 1 I CLOSED-BLANK
2 OPEN ~BLANK
3 CLOSED"STANDARD
!
I
I
3 I
I
/\
I I
2
12
3 0 4 0 - 2 / 2 I
! 2 ~ 2 / t 3 " ~ 2
2 - - 2 / / 3 ~ 3 I % 3 ~ 2 - - 2
3 / 3 ~ i , ~ ~ , i i i i _ i - - i - - i_.~ 3/ _i i xu3 3
2 6 4 0 + ! ! ! ! 1 - - - ! ! ! ! ! ! - ~ - 1 ! - 1 ~ 3
RELATIVE DIAL POSITION
FIG 5 Background spectra for 12% lead with the (1) shutter closed
and (2) shutter open; and (3) spectrum for 2.4 m g / L tellurium with the
shutter closed The stray light effect is eliminated with the shutter
closed
203.646 nm; the exact wavelength has not been deter-
mined) There are other slight spectral interferences in
the literature which have no effect on pure lead and the
alloy analyses discussed in this work This is because the
elements that cause spectral interferences are not gen-
erally present at concentrations that would cause a sig-
nificantly enhanced signal All of these potential inter-
fering elements are monitored, and corrections could be
made There was one direct spectral overlap interference
for antimony at 206.833 n m - - t h a t is significant enough
to be mentioned for which no literature reference was
found A 24 mg/L tungsten solution yields a false con-
centration of 4 mg/L antimony at 206.833 nm This in-
terference has not been a problem, because tungsten has
not been observed in the leads analyzed
Stray light from the intense Pb emission at 220.353
nm was identified in the secondary optics of the poly-
chromator A previously described 13 shutter system was
installed to eliminate the stray light effect The shutter
system blocks the path of the Pb emission at 220.353 nm
and prevents all light at this wavelength from passing
through the exit slit in the polychromator A channel at
220.353 nm had been installed in the polychromator ini-
tially for low-level Pb determinations in other matrixes
The stray light effect was unforeseen at the time the ICP
instrument was manufactured
Blocking of the lead emission at 220.353 is accom-
ELEMENT= CO
2 3 2 0 0 -
I
2 1 2 0 0 , -
1 9 2 0 0 , -
I
i
1 7 2 0 0 , -
I
1 5 2 0 0 -
13200
1 1 2 0 0 ,
9 2 0 0
7 2 0 0
5200
WAVELENGTH= 2265.02 1 CLOSED-BLANK
2 OPEfl -BLANK
3 CLOSED-STANDARD
2
/3 1
/ \
\2
3 ~ 3 2 / 2 ~ 2
3 2 0 0 1 ! ! ! ! ! - - - ~ - 1 ! - - - 1 ! - 1 - - I - ~ - - - ~ I - - I ! - 1 - - !
RELATIVE DIAL POSITION
Fro 6 Background spectra for 12% lead with the (1) shutter closed and (2) shutter open; and (3) spectrum for 0.3 m g / L cadmium with the shutter closed The stray light effect is eliminated with the shutter closed
TABLE X Effect of stray light from Pb (220.353 nm) on the back- ground signal from a 4% lead solution ~ and a 12% lead solution with the shutter open
Distance 4% P b 12% P b
Wavelength from Pb Increased Increased Channel Element (nm) slit (nm) signal (%) signal (%)
10, 6 b 10 b
74, 31 b 100 b
175, 120 b 350 b
7.5
See Ref 13
b Slotted sleeves placed on photomultiplier tubes
c Spectral interference from Pb
694 Volume 43, Number 4, 1989
Trang 9T A B L E XI Change in limits of detection (LOD) in 12% Pb for stray-
light-affected channels
I m -
S h u t t e r S h u t t e r prove-
W a v e l e n g t h o p e n closed m e n t
C h a n n e l E l e m e n t ( n m ) ( n g / m L ) ( n g / m L ) factor
plished by a digital linear actuator which has been in-
stalled in the polychromator of the ICP instrument Fig-
ure 2 shows a side view of the system when the lead
emission is allowed to pass and when the emission is
blocked out When the shutter is open, as illustrated by
Fig 2, the lead emission at 220.353 nm is allowed through
the exit slit; and when the shutter is closed, the lead
emission at this wavelength is blocked out (not allowed
through the exit slit) The top view of the shutter system
is shown in Fig 3 A diagram of the entire polychromator
arrangement is shown in Fig 4
Figures 5 and 6 demonstrate the stray light problem,
caused by a 12 % lead solution, as seen by the two neigh-
boring channels, which are Te 214.281 nm and Cd 226.502
nm The P b stray light interference is eliminated when
the intense lead emission is not allowed to pass through
the polychromator exit slit set at 220.353 nm Wave-
lengths from 193.696 nm (As) to 238.204 nm (Fe) have
stray light spectral interferences similar to those shown
in Figs 1 and 2 It is interesting that there is very little change in the off-peak background when the lead emis- sion is blocked out Only Te and Cd have a significant increase in off-peak background The off-peak back- ground emission for the open and closed positions of a 12% lead solution for the other elements is the same Notice that the stray light peaks have a broader base than the analyte emission peaks This result is probably due to the scatter pattern of the P b emission inside the polychromator The bandpass at half-height for the scat- tered background peak is about one and a half times that
of the analyte Te peak The bandpass at half-height for the Cd analyte and that for background peak are about the same Analyte emission is passed through the exit slit, so that the peak shape is regulated by the exit slit width and height, but the stray light can broaden as it
is scattered in the secondary optics
The effect of stray light on other surrounding channels
is shown in Table X A comparison is shown for the 4 %
P b solution between the shutter system and the use of slotted sleeves on the photomultiplier tubes 13 The stray light effect is reduced, b u t not eliminated Data for the
12 % P b solution were collected with the slotted sleeves still in place There is a slight increase in the P t channel background peak (about 2%), but the P b spectral in- terference at this wavelength makes it difficult to deter- mine the presence of a stray light effect Table XI lists the detection limits in 12% lead with the shutter open and closed All limits of detection show improvement with the shutter closed Again, the P t channel is affected
by a major interference from lead
ing reference materials and evaluating the testing pro- cedures used for lead analyses to obtain the most accu- rate results possible Another useful evaluation tool is a sample exchange program with other similar laborato- ries Table XII contains the results collected from 12
T A B L E XII Results for W R M - B as reported by different laboratories (%)
Ele-
m e n t J o h n s o n Controls a J C I 1983 b L a b # 2 L a b # 3 L a b # 4 L a b # 5 L a b # 6
Sb 2.77 _ 0.07 I C P c 2.82 I C P 2.88 A R C d 2.71 I C P 2.69 A R C 2.92 A R C 2.73 W e t °
S n 0.799 _+ 0.021 I C P 0.786 I C P 0.85 A R C 0.82 I C P 0.78 A R C 0.81 A R C 0.81 A R C
C u 0.0350 _+ 0.0016 I C P 0.0330 I C P 0.039 A R C 0.035 I C P 0.033 A R C 0.035 A R C 0.041 A R C
As 0.0578 _+ 0.0030 I C P 0.0517 I C P 0.06 A R C 0.056 I C P 0.054 A R C 0.052 A R C 0.058 A R C
Bi 0.0091 + 0.0012 I C P - - 0.0105 A R C 0.010 I C P 0.010 A R C 0.009 A R C 0.0107 A R C
Ag 0.0018 _ 0.0001 I C P - - 0.0017 A R C 0.0012 I C P 0.0011 A R C 0.0018 A R C 0.0021 A R C
S 0.0046 _ 0.0011 I C P 0.0055 I C P 0.0041 A R C 0.0040 I C P 0.0036 A R C 0.0049 A R C 0.0069 Col t Ele-
m e n t G r a n d average L a b # 7 L a b # 8 L a b # 9 L a b # 1 0 L a b # 1 1 L a b # 1 2
Cu 0.037 _+ 0.003 All 0.037 A R C 0.033 A R C 0.035 AA* 0.038 A R C 0.0586 A R C 0.043 A R C
As 0.055 _+ 0.005 All 0.055 A R C 0.05 A R C 0.06 A R C 0.05 A R C 0.0623 A R C 0.045 A R C
Bi 0.0097 _+ 0.0008 All 0.0087 A R C 0.011 A R C 0.010 A R C 0.0090 A R C 0.0092 A R C 0.0089 A R C
Ag 0.0016 + 0.0003 All 0.0016 A R C 0.0015 A R C 0.0012 A R C 0.0020 A R C 0.0011 A R C 0.0015 A R C
S 0.0051 + 0.0016 All 0.0052 A R C 0.0043 Col 0.0056 Col 0.0053 A R C 0.0093 A R C 0.0034 A R C Average a n d SD of 80 a n a l y s e s (7/87-2/88)
h J o h n s o n C o n t r o l s r e s u l t s as of 8/1/83 T h e s e r e s u l t s are e x c l u d e d f r o m t h e g r a n d average
o ICP: i n d u c t i v e l y coupled a r g o n p l a s m a
d ARC: ac s p a r k a n d dc arc emission
e Wet: titration, gravimetric
Col: colorimetric
AA: a t o m i c a b s o r p t i o n
h C a l i b r a t i o n s t a n d a r d n o t available
Trang 10i n d e p e n d e n t l a b o r a t o r i e s which r o u t i n e l y a n a l y z e lead
T h i s s t u d y was d o n e to assess t h e sources of v a r i a b i l i t y
in t h e analysis of SB alloys
A single w e l l - c h a r a c t e r i z e d a n t i m o n y alloy was sub-
m i t t e d to all l a b o r a t o r i e s to m i n i m i z e a n y v a r i a b i l i t y in
results d u e to a h e t e r o g e n e o u s s a m p l e S a m p l e s were
m a d e f r o m an SB alloy working reference m a t e r i a l which
was identified as W R M - B T h i s m a t e r i a l has b e e n used
in this l a b o r a t o r y since 1982, a n d results f r o m 1983 are
i n c l u d e d in T a b l e X I I for c o m p a r i s o n R e s u l t s for
W R M - B for t h e last 6 m o n t h s were a v e r a g e d to o b t a i n
r e s u l t s r e p r e s e n t a t i v e of c u r r e n t l a b o r a t o r y o p e r a t i o n s
S o m e of t h e i n c o n s t a n c y in results is e v i d e n t f r o m t h e
s t a n d a r d d e v i a t i o n seen within o u r r e p e a t e d l a b o r a t o r y
results T h e w o r s t case is for t h e sulfur value A large
v a r i a t i o n in sulfur results b e t w e e n l a b o r a t o r i e s is e v i d e n t
a n d was a n t i c i p a t e d b e c a u s e of t h e large s t a n d a r d de-
v i a t i o n o b s e r v e d for o u r l a b o r a t o r y sulfur results Sulfur
s e g r e g a t i o n in SB alloys a n d m e t h o d of analysis precision
c o n t r i b u t e to t h e p o o r precision seen for sulfur T h e g r a n d
a v e r a g e a n d s t a n d a r d d e v i a t i o n of all l a b o r a t o r y results
are also listed in T a b l e X I I T h e s t a n d a r d d e v i a t i o n of
all r e s u l t s is c o n s i s t e n t w i t h a n d slightly higher t h a n t h e
s t a n d a r d d e v i a t i o n of o u r l a b o r a t o r y results T h i s ad-
ditional i n f o r m a t i o n helps c o n f i r m t h a t I C P is an accu-
r a t e m e t h o d for lead analyses
A n o t h e r n o t a b l e difference in results is seen for anti-
m o n y T h e a n t i m o n y r e s u l t for this l a b o r a t o r y s e e m s to
be a c c u r a t e on t h e basis of t h e f a c t t h a t 6 d i f f e r e n t lab-
o r a t o r i e s a n d 3 d i f f e r e n t a n a l y t i c a l m e t h o d s gave results
within t h e s t a n d a r d d e v i a t i o n of t h e r e s u l t o b t a i n e d b y
this l a b o r a t o r y T h e k e y f a c t o r to this s t a t e m e n t is t h a t
t h e s a m e results were o b t a i n e d b y 3 i n d e p e n d e n t ana-
lytical m e t h o d s F u t u r e studies of this k i n d are being
p l a n n e d a n d will involve s e n d i n g o t h e r w o r k i n g reference
m a t e r i a l s to t h e a p p r o p r i a t e laboratories
C O N C L U S I O N S
T h r e e d i f f e r e n t dissolution p r o c e d u r e s for lead a n d
lead alloys followed b y I C P i n s t r u m e n t a l analysis are
now r o u t i n e l y e m p l o y e d in this l a b o r a t o r y T h e s t r a y light effect in t h e d e s c r i b e d I C P i n s t r u m e n t h a s b e e n corrected, a n d this allows lower d e t e c t i o n limits for 10
e l e m e n t s in a 12% lead m a t r i x T h e I C P m e t h o d s h a v e
b e e n shown to be v e r y precise a n d a c c u r a t e in t h e analysis
of p u r e lead a n d t h e lead alloys d e s c r i b e d in this work
E r r o n e o u s results which are c a u s e d b y s e g r e g a t i o n in lead
h a v e b e e n m i n i m i z e d in I C P analysis b y using t h e de- scribed s a m p l i n g m e t h o d s T h e r e s u l t s of a n i n t e r - l a b -
o r a t o r y p r o g r a m h a v e b e e n r e p o r t e d , which c o n f i r m t h e
a c c u r a c y a n d precision of t h e I C P m e t h o d
5, D H Collins, Ed (Academic Press, London, 1975), p 97
2 B K Mahato and W H Tiedemann, J Electrochem Soc 130,
2139 (1983)
Spectroscopy, R A Storer, Ed (ASTM, Philadelphia, 1987), 8th ed., p 715
4 European Lead Development Committee Analytical Subcom-
velopment Association, London, Great Britain, 1978)
5 European Lead Development Committee Analytical Subcom-
(Lead Development Association, London, Great Britain, 1971)
6 D Mongan, American Chemical Society Great Lakes Regional Meeting, Purdue University (1974), Paper No 14
7 C L Fillmore, A C Eckert, Jr., and J V Seholle, Appl Speetrosc
23, 502 (1969)
Coupled Plasma Atomic Emission Spectroscopy (Pergamon Press, New York, 1980), Vols 1 and 2, p 1
Interferences in ICP Spectroscopy (Plenum Press, New York, 1980),
p 10
ductively Coupled Plasma-Atomic Emission Spectroscopy, An At- las of Spectral Information (Elsevier Science Publishing Company, New York, 1985), p 272
ysis (Crane Russak, New York, 1978), p 25
12 A N Zaidel, V K Prokof'ev, S M Raiskii, V A Slavnyi, and E
1970), p 347
13 T Schmitt and J P Walters, 25th Rocky Mountain Conference, Denver (1983), Paper No 2