Anal. Chem. 1980, 52, 431-438
43 1
Inductively Coupled Plasma-Atomic Emission Spectroscopy: A Computer Controlled, Scanning Monochromator System for the Rapid Sequential Determination of the Elements M. A. Floyd, V. A. Fassel,' R. K. Winge, J. M. Katzenberger,' and A. P. D ' Silva Ames Laboratory and Department of Chemistry, Iowa State University, Ames, Iowa 500 7 7
(3) Storage in memory of a selected, ordered list of the most prominent spectral lines for each of the 70 or so elements determinable by ICP-AES. (4)Preselection of one or more of the stored analyte lines for each element to be determined. ( 5 ) Preselection of precise wavelengths at which the spectral background intensity measurement is to be made for each analysis line. (6) Computer software rearrangement of the selected analysis lines and corresponding background wavelengths in ascending wavelength to facilitate orderly measurements and to minimize the analysis time. ( 7 ) Video terminal for the visualization of difficult background situations and the goodness of fit of analytical calibration curve data. The video terminal also aids the judicious selection of the most useful lines for a particular analytical problem. (8) Detection limit routine for monitoring instrument performance. Detection limit measurements t h a t are based on signal-to-noise considerations provide a convenient and sensitive performance test of the entire system. (9) A signal measurement range of lo6 for exploitation of the wide dynamic range characteristics of the ICP excitation source. Computer controlled monochromator systems t h a t have some of the features and characteristics discussed above have been described (6-8), suggested (9), or are commercially available, b u t none of the versions previously described or marketed have possessed all of the capabilities specified above. Moreover, documentation of the analytical performance of these systems for atomic emission spectrometry has been meager; only the papers by Spillman and Malmstadt (6) and by Kawaguchi e t al. (8), provide data on simple synthetic solutions prepared in the laboratory. In this paper, we describe a monochromator system that provides all of the capabilities discussed above. The performance characteristics of the entire system as well as its application to several analytical problems are summarized.
A computer controlled, scanning monochromator system specifically designed for the rapid, sequential determination of the elements is described. The monochromator is combined with an inductively coupled plasma excitation source so that elements at major, minor, trace, and uttratrace levels may be determined via their atomic emission spectra in sequence without changing excitation source parameters. A number of distinctive features not found in previously described versions are incorporated into the system here described. Performance characteristics of the entire system and several analytical applications are discussed.
Radiofrequency excited, argon supported, inductively coupled plasmas (ICP) are being used to a rapidly increasing extent as excitation sources for the atomic emission determination of the elements a t all concentration levels (1-5). Most existing ICP-AES facilities use polychromators ( 5 ) for the simultaneous determination of as many as 30 or more elements. These instruments are well suited for the routine, simultaneous determination of the same set of elements in matrices of similar composition. However, when the analyst is faced with the determination of a broader range of elements, in samples of widely varying composition, then the limited set of lines observable in a polychromator becomes restrictive and serious spectral line interferences with the lines isolated may make certain channels unusable. I n principle, linear-scan monochromators can be used for the sequential determination of most of the elements in the periodic table, and a number of lines may be measured for each element to enhance the reliability of the determinations. However, for multielement determinations, the operations involved in a sequential scan to the spectral lines of interest and measuring t h e intensities of the lines relative to the spectral background usually require constant operator attention and lengthen the analysis time considerably, as compared to the time required for simultaneous multielement determinations with a polychromator. Automation of the entire analytical cycle is particularly attractive with ICP-AES. As the monochromator sequences from one element to another, optimization of source characteristics or other experimental parameters is normally not required (1-5). An attractive solution to this loss of versatility and automation would be an instrument that possesses the following characteristics and capabilities: (1) A computer-controlled scanning monochromator with a programmed, nonlinear scanning capability between selected wavelengths. (2) Automated peak seeking routine for determination of the peak intensity of selected lines.
EXPERIMENTAL FACILITIES A N D OPERATING CONDITIONS The experimental facilities and operating conditions utilized in this work are summarized in Table I and a block diagram of the analytical system is illustrated in Figure 1. A double monochromator was used because this instrument was immediately available for our use. Any monochromator with a computer controlled stepper motor should be adaptable. The original stepper motor, as supplied by GCA/McPherson, was used for this work. Wavelength Scanning System. In the monochromator described in this paper, an optical incremental encoder is connected t o the drive mechanism and enables the computer, through the scan controller, to monitor the wavelength. The encoder encodes the angular motion of the lead screw. To shift to a preselected wavelength, the computer loads a Binary Coded Decimal (BCD) value equivalent to the preselected wavelength into memory and the drive motor is actuated. As the motor drives the sine bar mechanism, which in turn rotates the grating toward the specified
'Present address: Iiistruments SA, Inc., 173 Essex Avenue, Me-
tuchen, N.J. 08840.
0003-2700/80/0352-0431$01 .OO/O
C
1980 American Chemical Society
432
ANALYTICAL CHEMISTRY, VOL. 52, NO. 3, MARCH 1980
VIDEO TERMlhAL
-~
F-C
DUAL-DRIVE FLOPPY
2
T-L-
~
_v _
DISK
I
---A
DOUBLE MONOCHROMATOR
spectrometer
-
YE-
A
I
1-
1-
SCAY C3NTROL 2
Table I. Experimental Facilities and Operating Conditions
\A
0.5-m GCA-McPherson (Acton, Mass.) model 2 8 5 double CzernyTurner monochromator scan controller Model 7 8 5 GCA-McPherson scan controller encoder Sequential Information Systems, Inc. (Elmsford, N.Y.) Series 25G optical incremental encoder with 2 tracks phase shifted 90” for direct i o n sensing and count multiplication. The encoder has a resolution of 0 . 0 0 1 2 5 nmiencoder pulse and a frequency response of 200 000 pulsesis. Supplied as a standard item with the GCA monochroma tor computer Digital Equipment Corp. (Maynard, Mass.) PDP-11/03 minicomputer with 24K memory interface Ames Laboratory design input /output Tektronix (Beaverton, Ore.) Model 4 0 0 6 - 1 Computer Display Terminal grating 1200 Gimm plane grating blazed for 300 nm A/D converter Analog Technology Corp (Pasadena, Calif.) Model 1 5 1 current t o frequency converter optical transfer Plasma emission focused b y a 1 6 cm focal length X 5 cm diameter planoconvex, fused quartz lens. Positioned at twice the focal length from the entrance slit and plasma center photomultiplier EM1 6 2 5 6 , spectral response S-13 R F generator Plasma-Therm Inc. (Kresson, N.J.) Model MN 2500 F generator, 27 MHz, 2500-W rating, operated at 1500-W forward power, < 3 W reflected power nebulizer 1.4-MHz ultrasonic nebulizer described by Olsen et al. ( 1 0 ) Ar flow rates plasma gas 1 6 L/min 1 L/min auxiliary gas aerosol gas 1 Limin observation height Torch positioned so that optical axis of monochromator corresponded t o a height of 1 5 mm above the t o p of the load coil. A 4-mm vertical aperture limited the observation zone to the region between approximately 1 3 and 1 7 mm above the load coil slits entrance 20 urn intermediate 100 p m exit 20 pm solution uptake rate 2.0 mL/min
sMLEp
Figure 1. Block diagram of the computer controlled monochromator
system
wavelength, the pulses generated by the encoder are fed back to the scan controller. By monitoring the BCD output of the scan controller and comparing it with the BCD value stored in memory, the computer is able to determine when the desired wavelength has been reached. Two scanning speeds, fast (500 nm/min) and slow (10 nm/min), are employed so that the wavelength selection is both rapid and precise (without overshoot). For the fast scanning speed, one step of the stepper motor is equivalent to a wavelength change of 0.005 nm. One step of the stepper motor in the slow speed is equivalent to a wavelength change of 0.0001 nm.
SOFTWARE T h e software developed for use with the monochromator is written in a high level language (FORTRAN) and segmented so t h a t changes in analytical procedures, computations, or reporting of final results can be made conveniently. Source listings for the various subroutines are available on request from the corresponding author. T h e software described in this paper consists of one main program (SURVEY), which is broken down into several smaller routines. The operator can invoke each routine by typing the first four letters of the desired routine on the video 1/0 terminal. Versatility was an important objective in the development of the control software. The main features of the control logic are summarized as follows. For all modes of operation, the operator specifies the measurement period (0.1-999 s), and either manual or automatic ranging of the current to frequency (C/F) converter t o give output measurements from to lo* A photocurrent. I n the autorange mode, the computer monitors the photocurrent just prior to the measurement period and switches the C / F converter to the appropriate range. Intensity measurements are read out directly as photocurrents (amperes). Analytical Wavelengths. The selection of analytical wavelengths is simplified by the availability from a “masterfile” on disk of the four most prominent spectral lines ( 1 1 ) of each of 70 elements. These “true” wavelengths are listed to 4 decimal places as shown in the available wavelength tables. T h e wavelengths for each element are assigned “priority” levels based on detection limits and potential spectral line interferences. For each analytical wavelength contained in the masterfile, a second wavelength, close to the analytical wavelength, is selected for measurement of the spectral background and is also stored in the masterfile. T o begin a series of sequential multielement analyses, the operator specifies the number of lines of each element whose net relative intensity is to be measured. Chemical symbols for the desired elements are entered into the computer through the video terminal. T h e computer searches the masterfile and locates the appropriate analytical wavelengths on a priority basis. If an analytical problem requires a special set of spectral lines not available from the masterfile ranking, these special wavelengths (with appropriate corresponding background wavelengths) can be entered through the video terminal. The
computer then rearranges the analysis wavelengths and the associated “background” wavelengths in order of increasing wavelength. T h e element symbols, analytical wavelengths, and background wavelengths are then stored in a user-named file on disk. Because the information is stored on disk and not in memory, the number of lines that can be measured sequentially is limited only by the number of lines in the masterfile. Wavelength Calibration Routine. Small errors may be introduced into the grating wavelength drive by such factors as thermal drift and through changes in gears for the rapid and slow scan modes. For exchange of the latter, precise stepper motor step sizes may not lead to precisely the same wavelength step sizes. These and other factors may cause a wavelength shift t h a t is not reflected by the encoder, hence the “true” and “instrumental” wavelengths may not agree. This situation is rectified by a “peak search” routine that
ANALYTICAL CHEMISTRY, VOL. 52, NO. 3, MARCH 1980 1V
E’rTER
S t A h T 3 Wl-*IU C 32 N M OF S P E C - ? A L -1NE
-”
TAKE U-EhS U E A S -R E ME PT .
U G V E MONOCYROMATOQ .G 3 3 5 NM I I
MAKE MEASUREMENT 6.
v
CY T
Figure 2. Program flowchart for the maximum intensity subroutine
determines the instrumental wavelength of each selected spectral line. After the appropriate wavelengths are chosen from the masterfile, the operator runs a reference solution that contains the elements of interest. T h e peak search routine steps across a 0.3-nm wavelength region of the spectrum centered at the analytical wavelength. Intensity measurements are taken every 0.01 nm for a total of 31 intensity measurements. The criterion used for determining if a peak has been located requires a t least five or more consecutive points with increasing intensity followed by five consecutive points with decreasing intensity. If a peak is sensed, the computer then calculates t h e instrumental wavelength of the analysis line and updates the operator’s disk file. T h e instrumental wavelengths are used for all subsequent operations. The peak search routine requires approximately 18 s to determine the instrumental wavelength for each analysis line. Maximum Intensity Routine. T h e instrumental wavelength calibration procedure just described is not sufficient to guarantee that subsequent intensity measurements a t the instrumental wavelengths correspond exactly to the peak intensity of the analysis line. This is because residual thermal a n d mechanical drift, spurious electronic signals taken as encoder pulses, and other unidentified aberrations may shift t h e instrumental wavelength off peak. A “maximum intensity” routine solves this problem. T h e computer flowchart for this routine is shown in Figure 2. The major assumptions made with this routine are that the shape of the spectral line is Gaussian in form and that the maximum error in t h e instrumental wavelengths of the analysis lines is less than 0.02 nm. This approach is also used by Applied Research Laboratories (Sunland, Calif.) in their Model 35000 computer controlled monochromator. In operation, the monochromator is scanned to within 0.02 nm of the analytical wavelength. Incremental steps of 0.005 nm are then taken until the computer determines t h a t the maximum of the peak has been crossed. If a Gaussian form is assumed for the spectral line, the maximum intensity may be calculated very precisely, even if the maximum falls between two wavelength steps. When no peak is discernible, as for a blank solution, the routine assumes that the previously determined instrumental wavelength is correct. This approach to peak intensity measurement differs from those previously described. Spillman and Malmstadt (6) utilized a rotatable quartz refractor plate to correct any errors
433
introduced by the mechanical wavelength drive. Kawaguchi e t al. (8) employed a vibrating quartz plate t o optically scan a small spectral region. The peak intensity was then found by their computer program. Roldan (12) and Spillman and Malmstadt (6) have outlined some of the errors that may be introduced when a quartz window is used as a refractor plate. As the computer starts the system for a multielement mode of operation, the monochromator is first initialized a t t h e carbon 247.856 nm spectral line. This line is used for reference purposes because i t is easily observable in the spectrum of Ar supported ICP discharges and occurs in a region possessing little background structure. T h e monochromator is then scanned to a starting wavelength which is a few nanometers less than the lowest wavelength of the lines to be measured. T h u s all data acquisition is performed with the monochromator scanning in the direction of increasing wavelengths. This procedure avoids errors caused by backlash of t h e wavelength drive mechanism. When the monochromator is scanning to higher wavelengths, the computer checks for the condition where the monochromator is 0.5 nm from the desired wavelength. When this boundry is crossed, the computer reduces the scanning speed from fast to slow and finally halts the stepper motor when the wavelength has been reached. A description of the various software subroutines follows: INITIATE. T h e INITIATE subroutine initializes the C / F converter measurement period, informs the computer of the current wavelength location of the monochromator, and sets up the input/output devices to be used. If the operator desires to measure the offset of the C / F converter, INITIATE will measure and store the offset value for later use. T h e offset of the C / F converter is the current, measured when no light is entering the monochromator. Although this current is very small A), it can cause significant errors for routines in which background corrections are not made (e.g., PROFILE). For all modes of operation, the operator has the option of storing the answers to the computer’s questions in a disk file, or answering the questions via the video terminal. If t h e former is chosen, INITIATE will assign a n operator specified file to be an input file and the computer will now operate without any interaction from the operator. DETECTION LIMITS. The DETECTION LIMIT subroutine is used to determine, from experimental data, detection limits of operator specified analytical lines. T h e detection limit is defined as the concentration of analyte required to give a net signal equal to three times the standard deviation of t h e background. While nebulizing a multielement reference solution, the average and standard deviation of the background are measured at the specified background measurement position near each analysis line. T h e average and standard deviation of the gross signal are determined next with t h e monochromator positioned a t the analytical wavelength. Detection limits determined in this manner provide a sensitive test of the analytical performance of the system. Determination of the detection limit of 25 analytes requires approximately 10 min. TAKE DATA. T h e TAKE DATA subroutine obtains data at a single wavelength in a repeat data mode. In this mode, the operator can choose the number of intensity measurements to be made in a repetitive sequence. At the end of the measuring sequence, the average and standard deviation of the individual measurements are printed. The sequence may be repeated under the initial conditions with a single key command to the computer. Precision values for sample, blank, and offset measurements are easily and quickly obtained in this TAKE DATA mode. Also, in this mode the operator has the option of printing the individual measurements of a sequence. PROFILE. The PROFILE subroutine provides profiles of emission intensity vs. wavelength on a sequential multielement
434
ANALYTICAL CHEMISTRY, VOL. 52, NO. 3, MARCH 1980
basis. Each profile consists of a small wavelength region which encompasses one of the analytical lines of interest. T o obtain a profile, the computer directs the monochromator to step across a wavelength region, taking data a t each step. When standard computer plotting techniques are employed, these data can be readily plotted on the video terminal for operator inspection. Typical profiles obtained in this work, with intensity measurements a t 3 1 wavelength positions, require approximately 90 s for each analytical line. CALIBRATE. T h e CALIBRATE subroutine allows an operator t~ construct analytical calibration curves using intensity vs. concentration data collected from reference solutions. A disk file is prepared that contains the elements of interest and the concentrations of t h e individual analytes in the various reference solutions. T h e subroutine conversationally leads t h e operator through the data acquisition procedure for his reference solutions. T h e individual reference solutions may be run in any order, may be repeated, or may never be run at all. T h e integration time is specified by the operator, and a table of background corrected, net relative intensities can be requested during calibration so the operator can monitor the performance of the instrument. The net intensities, used in the calibration and analytical routines, correspond to the difference between the calculated maximum intensities at each analytical wavelength and the respective background intensities obtained at the preselected wavelengths above or below each analytical line. This approach for background correction differs from that used by previous authors. Kawaguchi et al. (8)employed a vibrating quartz plate to produce a sinusoidal wavelength modulation. With sinusoidal modulation, the total integration time of the individual background and analyte line signals is small compared to the total measurement time. The procedure employed here allows for more efficient measurement because the monochromator can be set at a specific wavelength and halted for signal integration. Spillman and Malmstadt (6) also integrated the background signal a t a specific point. However, they used a quartz refractor plate to shift the spectrum a t the exit slit to the desired background wavelength. After the operator has calibrated the instrument, the subroutine calculates curve coefficients and prints a value for each analytical line that indicates the quality of fit of the analytical curves to the experimental points. This quality of f i t is expressed as the percent root mean square of the relative deviations of the calculated values from the observed data. The subroutine stores the element symbol, wavelength, concentrations, intensities, and curve coefficients for each analysis line in a user-named file on disk. This information forms a complete record of the entire calibration procedure for examination a t a later time, should questions concerning the analytical results occur. The analytical calibration curves are calculated as first, second, or third order polynomial equations, as specified by the operator. The operator also has the option of weighting or not weighting the data by the reciprocal of net intensity squared (13). For 25 analytical lines, the CALIBRATE subroutine requires approximately 10 min for each reference solution. ANALYTICAL. T h e ANALYTICAL subroutine performs sequential multielemental quantitative analysis of samples using analytical calibration curves prepared by CALIBRATE. Upon entering t h e ANALYTICAL subroutine, the operator specifies a calibration file containing the analytical calibration curves prepared by CALIBRATE. This subroutine accepts input of sample identification information for the individual samples. If the operator desires to use an autosampler, sample identifications can be set up in a file prior to the analyses. In that case, the analyses may be performed without operator attention. As each sample is run, the computer steps the
Table 11. Precision of Wavelength Reproducibility
element Mo P
202.03 213.62 213.86 214.44 231.60 224.27 228.62 233.38 249.77 235.61 267.72 310.23 313.04 316.34 324.75 435.40
Zn Cd Ni Ir
co Rh
B Mn Cr V
Be Nb cu
Ba a
meana true instrumental wavelength, wavelength, nm nm 202.03 213.63 213.86 214.43 231.61 224.28 228.62 233.48 249.79 237.62 267.73 310.27 313.06 316.36 324.78 465.37
standard
deviation, nm
0.007
0.007 0.008 0.005 0.007
0.007 0.008
0.007 0.003 u.004 0.008
0.010 0.00ti 0.010 0.008 0.010
Mean and standard deviation of 1 0 individual measure-
ments over a 5-dav period.
monochromator to the appropriate analysis line and background wavelengths, measures the emission intensities (for a time specified by the operator), and calculates the concentration of each element using the appropriate analytical calibration curves. T h e analytical results are printed and stored on disk immediately after each sample is analyzed.
PERFORMANCE An important requirement for computer controlled monochromators is the capability of selecting the predetermined wavelength rapidly and accurately. The reliability of wavelength selection was tested with the peak search subroutine which determines the instrumental wavelengths of the analytical lines. Ten measurements, one at the beginning and end of each day, were obtained for 16 wavelengths over a period of five days. The mean and standard deviation of these measurements, summarized in Table 11, indicates that the monochromator is relatively free from mechanical drift. The slewing time of the monochromator is given by the equations
t =
0.120(x)
t = 6(x)
+ 3.2
+ 0.1
for x
for x
> 0.5 n m
< 0.5 nm
where t is the time in seconds required for slewing x nanometers between wavelengths A and B. For example, the monochromator will slew from Zn 213.86 nm to Ba 455.40 nm in 32.17 s. Movement of the monochromator from 213.76 nm (background wavelength for Zn 213.86 nm) to 213.86 nm requires 0.70 s. Maximum Intensity Routine. T h e operation of the maximum intensity subroutine was tested by a comparison study made of the precision of maximum intensity measurements that could be achieved, with and without using this subroutine, at ten different wavelengths ranging from Zn 213.86 nm to Cu 324.75 nm. First, the instrumental wavelengths of the ten lines were determined with the peak search routine. Then the instrument was slew-scanned to each of these ten lines in turn ten different times. Intensity measurements were made for each line for each scan. Next, the same ten-line scan sequence was repeated again ten times but with application of the maximum intensity routine (as described in the section on maximum intensity routine under "Software". The results of these measurements, summarized in Table 111, show that an improvement in the precision of the intensity measurements was generally achieved when the
ANALYTICAL
Table 111. Precision of
AXIhfuhI INTENSITY
instrumental wavelength, nm
setR
Zn Cd
A
Ni
co Fe
Mn Cr J \
CU
Zn Cd
B
Ni
co Fe Mn Cr V
cu
Subroutine
monochromator scan without with maximum maximum intensity intensity subroutine subroutine
213.86 214.14 221.65 228.62 238.20 257.62 267.72 310.23 324.78
5.87 12.23 6.60 1.42 1.38 1.29 6.41 5.59 15.37
2.96 4.40 5.00 2.62 0.76 0.64 3.51 2.15 6.45
213.86 214.11 221.65 228.62 238.20 257.62 267.72 310.23 324.78
3.74 6.21 3.21 2.32 1.98 1.20 2.36 3.01 5.43
1.99 3.23 3.01 1.43 0.83 0.50 2.04 2.03 3.10
%RSD of 10 points at analyte concentrations 1 0 times the detection limit. B. 7cRSD of 1 0 points at analyte concentrations approximately 5 0 times the detection limit. a
_
X.
_
~
refer e n ce
element
standard, ngimL
As
100
Ba Be Bi Cd
100
co Cr cu Eu
Ga Ir La M 11 Mo Ni
sc Sr Ti Y Yb Zn ZI-
100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100
measured" average, nglmL 94 99 101 96 97 99 99 96 101 104 95 97 100 93 97 99 100 97 98 101 98 102
relative standard deviation, %
5.27 1.40 1.20 11.30 4.00 2.10 1.80 2.60 4.60 8.40 3.60 2.10 1.00 8.10 0.90 0.60 1.10 1.40 2.30 1.90 2.10 4.20
Reference solution was run 5 times at regular intervals during an 8-11 normal analytical seguence. maximum intensity subroutine was employed. The abnormally high values observed for the Cd and Cu lines when the maximum intensity routine mas not applied are representative of the loss of precision introduced by spurious off-peak intensity measurements. Wavelength Profiles. Wavelength profiles provide the best assessment of potential stray light or spectral interference problems ( 1 4 ) and are especially useful in the preliminary investigative stages for new sample compositions. Data obtained with the profile subroutine can easily be plotted directly on the video terminal for an immediate determination of potential sources of interferences. Typical profiles observed
VOL. 52. NO. 3, MARCH 1980
435
Table V . Detection Limits, g / L wavelength, nm A1 As
Ba Be Bi Ca Cd
co
Cr cu
DY
Er Eu
Fe Ga Gd
Ge Hf Ho
In Ir La Lu
m
Mn Mo Nb Nd Ni
Table IV. Reproducibility of Analytical Data
CHEMISTRY,
Pb Pd Pr Re Rh Ru Sb sc Se Sm Sn Sr Ta Tb Te Th Ti TI Tm
u V
U'
Y
Yb Zn Zr
308.22 197.20 455.40 313.04 223.06 396.85 214.44 228.62 267.72 324.75 353.17 337.27 420.51 238.20 294.36 342.25 265.12 277.34 389.10 230.61 224.27 394.91 261.54 279.55 257.61 202.03 316.34 430.36 231.60 220.35 340.46 330.84 221.43 233.48 240.27 217.58 361.38 196.03 359.26 235.48 407.77 226.23 350.92 214.28 283.73 334.94 351.92 346.22 385.96 310.23 207.91 371.03 328.94 21 3.86 343.82
detection limit 2. 10.
0.5 0.05 5. 0.l 0.9 2. 1. 0.4 1. 1. 0.!i 0.5 6. 4. 20. 2. 0.9 20. 0.6 2. 0.2 0.04 0.:1
6. 1. 3. 2. 20. 1 0. 3 4. 11. 8. 30. 0 .I. 70. 12. 10. 0.01 15. 1. 18. 10. 0.4 7. 3. 11. 0 , Z! 11. 0.07 0.1 0,2! 1.
range (ref. 1) 0.4-2 3-6 0.09-0.5 0.01 -0.02 3-9 0 .o 2-0.2 0.1-1.0 0.3-2 0.2-1 0.2-0.4
0.4-4.0 3-7 2-20
0.03-0.7 0.0 3-0.1 3-9 1-2 1-20 1-19
4-30 2-18 9-25 0.01-2
0.04-5 2-23 0.2-0.7 0.1-2 0.2-2
in the course of our studies are shown in Figure 3. For the Mn example in Figure 3A, it is apparent that the background changes caused by 2OOmg/L of Ca, Mg, or T i are significant a t the 0.01 mg/L level of Mn and that important analytical errors will result unless accurate background correction procedures are employed. Similar circumstances apply for other elements as well when the determinations must be performed for concentration levels near the detection limit. The profiles in Figure 3B suggest that the Ti 313.08 nm line is not likely to cause significant interference at the Be 313.04 nm line a t Ti/Be concentration ratios below 200. Stability. Table IV shows typical short term qtabilities observed for a reference sample solution that was run 5 times a t approximately equal time intervals within a normal analytical sequence of approximately 8 h. These data were acquired after a single calibration a t the beginning of the 8-h
436
ANALYTICAL CHEMISTRY, VOL. 52, NO. 3, MARCH 1980
Table VI. Analytical Results for EPA Water Samples sample 1 A1 A1
As Be
Cd Cd
co co Cr cu Fe Fe
Mn Mn Ni Pb
V V a
236.7 308.2 197.2 313.0 214.4 226.5 228.6 237.9 267.7 324.7 238.2 259.9 257.6 259.3 231.6 220.3 292.4 310.2
ALa
RSD,%
EPA
7 09 664 195 7 24 49 46 500 454 158 223 5 89 587 316
2.6 2.0 4.0 5.3 3.0 11. 3.2 5.9 5.3 1.7 1.6 0.5 1.0 2 .0 0.9 15. 1.8 1. 0
700 700 200 7 50 50 50 5 00 500 150 250 600 600 35 0 350 250 2 50 750 750
314 2 20 217 7 32 735
concentrations, p g / L sample 2 ____ AL RSD, % EPA 97
109 19 19 3 3 20 20 10 11 I$ 12
11 15 21 28 r r
I S
71
3.5 9.6 5.1 5.1 6.7 12. 6.4 8.2 13. 12. 21. 1.3 5.8 3.3
60 60 22 20 3 3 20 20 10 11 20 20 15 15 30 24 70 70
11. 8.5 14. 3.6
sample 3 AL
RSD, 93
EPA
161 162 63 185 14
1.9 1.5 7.3 0.5 21. 20. 2.0 1.9 4.1 5.3 3.3 3.0 2.6 1.8 6.6 6.0 1.2 1.0
160 160 60 180 14 11 120 120 50 70 180 180 100 100 60 80 170 170
14 127 119 54 52 179 175 94 96 66 98
I77 177
Indicates Ames Laboratory result.
Table Vll. Analytical Results f o r USGS Glasses concentrations, pigig sample GSD
sample GSC A La AS
Ba Be Bi
Cd
co Cr
cu Eu Ga Hi" Ir La Mn Mo Ni Pd Ru
SC Sr
Ti
w
Y 3%
z 11 Zi.
197 2 155 1 313 0 233 1 214 4 228 6 267 7 321 7 120 5 291.4 277 3 223 3 394.9 257 6 202 0 231 6 340 5 210 3 361.4 407 7 334 9 207 9 371.0 328.9 213.8 343.8
RSD, % 6.1 12.
39 3.5
2.6 6 11 6
12. 5.1 12. 9.8
3.0 6 7 9
215
1.3
31 8
15
AL
RSD,%
CSGS
92 40 45 28 33 14 40 54
3.8 5.3 9.8 8.4 4.2 5.2 6.2 6.7
90
330 510 512
56 16 51 212
20, 11. 4.5 4.5
4.3 1.6 2.3 5.1 1.4 0.9 1.0 2.3 5.1 20. 8.4 7.1 2.4
450 500 500 180 420 450 490 500 600 20 500
50 13
14.
3 66 J0
16.
27 11
6.2
8
6 1
12
1.8 13.
I
200
sample GSE
USGS
AL
43 3.2
___
RSD,%
USGS
11.
41 40
42 5
1(5
51Y
20
151 5,iX 59 6 ,521 507 95 96 32 ,503 499 403 501 27 506 483
17 210 54 36 3 64
4.4 7.1
41
47
3.1
18
39
