trometer. It was measured in the NORMAL mode and a total of 1024 points were obtained at a rate of 45 kHz and then outputted to a chart recorder at 7 points/s. This spectrum is identical to that obtained from a minicomputer data acquisition system for a single scan without background subtraction.The noisy baseline is due to fixed pattern noise and dark current (see reference 4). The PRETRIGGER mode is illustrated in Figures 6b and 6c. In these cases 256 and 512 points were acquired before the trigger pulse that initiates the scan of the photodiode array. It should be noted that the transient recorder cannot be simultaneously operated in both the background subtraction and PRETRIGGER
as multipliers, dividers, difference amplifiers, log modules, and log-ratio modules can perform a large variety of data processing tasks as can the single memory system presented here with synchronized feedback. Finally, it is interesting to note, that the recent development of analog shift registers in integrated circuit form is sure to have an impact on transient recorder instrumentation ( 5 ) .These devices offer the potential of replacing the major functional blocks of the transient recorder (ADC, digital shift register memory, and DAC) with a single 16-pin integrated circuit and, in fact, the construction of a high speed transient recorder using a serial analog delay line integrated circuit has already been reported (6).
modes.
CONCLUSIONS A transient recorder can add considerable flexibility to a variety of data acquisition tasks in the laboratory. Typical applications range from the measurement of transient atomic absorption signals generated by furnace and carbon rod atomization systems to stopped-flow measurements. For many minicomputer systems, it can provide a simple off-line oscilloscope refresh system or it can be used to transfer plots to a recorder, freeing the minicomputer for more important data acquisition or processing tasks. In addition, the transient recorder is a fundamental building block for more sophisticated instrumentation. Systems with dual memories or even two transient recorders combined with analog components such.
QUAN-A
LITERATURE CITED (1) N. E. Korte and M. B.Denton, Cbem. Insfrum., 5, (l), 33 (1973-74). (2) P. N. Daum and Peter Zamie, Anal. Cbem., 46, 1347 (1974). (3) H. V. Malmstadt, C. G. Enke, S. R. Crouch, and Gary Horlick, “Optimization of Electronic Measurements”, W.A. Benjamin, Menlo Park, Calif., 1974. (4) Gary Horlick, Appl. Specfrosc., 30, 113 (1976). (5)Gary Horiick, Anal. Cbem., 48, 763A (1976). (6) T. A. Last and C. G. Enke. Anal. Cbem., 49, 19 (1977).
RECEIVEDfor review May 26, 1976. Accepted November 8, 1976. Financial support by the University of Alberta and the National Research Council of Canada is gratefully acknowledged.
Computer Program for Quantitative X-ray Fluorescence Analysis
Michael F. Ciccarelli General Electric Company, Corporate Research & Development, Schenectady, N. Y. 12305
A Fortran IV program called QUAN, written for minicomputer users is now available for quantitative x-ray fluorescence analysis. The program based on a fundamental parameters model, is an extensively modified and simplified version of Stephenson’s CORSET ( 1 ) . With this approach a single effective wavelength is used to describe the fluorescing radiation rather than the actual spectral distribution emitted by the tube. The effective wavelength is that wavelength which is less than the absorption edge of the measured line and capable of maximum excitation of that line. It then becomes a simple task to calculate matrix effects and to determine emitted x-ray intensities. Reliable quantitative results were obtained on multicomponent samples even when only a single well-characterized standard containing all the elements in the unknown was used. The main drawback of CORSET is that it requires a large amount of core memory making it unsuitable for minicomputer operation. QUAN, on the other hand, requires only 12K bytes of core memory. It was developed on an Interdata 70 minicomputer equipped with B Real Time Operating System (RTOS) which has been described previously ( 2 ) .The system is supported by a number of peripheral devices including a
1.2-million word cartridge disk, magnetic tape transports, high speed line printer, etc. Since RTOS has overlay capabilities, QUAN can be stored on disk with only a portion of the program in core a t any one time. To further reduce the program size, it was necessary to fit the energies of the charcteristic lines and absorption edges. Because fitted data are used, a warning is printed out if an emitter’s line energy comes within 10 eV of the edge of an absorbing element. When this warning is printed, the operator should check to make sure the proper mass absorption coefficient is being used. Data analyzed with both CORSET and QUAN have been found to give comparable results. Three standards obtained from the National Bureau of Standards were analyzed with QUAN. The results, which illustrate the effectiveness of the program are presented in Table I. The compositions of Reni! 41 (1206-2) and Waspaloy (1207-2) were calculated from the raw data in Table 11, using Waspaloy (1207-1) as the single standard. Preliminary results on noncertified super-alloy materials indicate that a standard’s composition can vary from an unknown’s by as much as 30-50% relative, for most elements. Additional experiments are now under way to better define acceptable compositional tolerances for standards. Copies of the program are available from the author. ANALYTICAL CHEMISTRY, VOL. 49, NO. 2, FEBRUARY 1977
345
-
~~
Table I. Certified and Measured Compositions of NBS Reference Materials a Standard 1, certified
Element Mo Ni cu co Mn Fe Cr Ti Si A1
4.50 56.1 0.026 13.0 0.34 2.22 18.88 3.09 0.47 1.26
Sample 2
Sample 3
Certified
Measured
Certified
Measured
10.3 53.3 0.040
10.3 52.6 0.03 11.6 0.064 0.44 19.34 2.9 0.26 1.9
4.34 55.7 0.033 13.5 0.29 2.09 19.4 2.54 0.61 1.30
4.40 55.9 .031 13.7 .30 2.07 19.1 2.60 .60
11.5
0.030 0.46 19.17 2.9 0.21 1.7
1.28
nl. NBS Standard, Waspaloy (1207-1). 2. NBS Standard, Rene 41 (1206-2). 3. NBS Standard, Waspaloy (1207-2). Table 11. X-ray Intensity Data a Used in Determination of Measured Values Presented in Table I Standard 1
Sample 3
Element
Peak
Background
Peak
Background
Peak
Mo Ni cu
638 305 7 238 273 482 088 1061 440 3 959 495 1013 298 1024 798 3 117 753 165 133 68 688
66 334 152 128 149 100 8 213 249 128 46 384 17 996 6 463 29 766 21 384
1 374 403 7 107 008 536 511 932 193 2 399 927 215 357 975 739 2 690 396 107 056 100 330
69 110 154 535 149 911 5 300 215 934 29 282 16 212 6 208 26 748 23 288
621 582 7 150 348 469 059 1110 434 3 737 364 958 124 1047 991 2 630 838 203 290 68 636
co
Mn Fe Cr Ti Si A1 a
Sample 2
Background 66 201 151 704
146 113 6 807 242 218 49 857 18 253 6 573 31 497 20 945
Intensities corrected for dead time. LITERATURE CITED
RECEIVEDfor review August 6, 1976. Accepted September
( 1 ) D. A. Stephenson, Anal. Chem., 43, 1761 (1971). (2) M. F. Ciccarelli, W. T. Hatfield, and E. Lifshin, Siemens Rev., 41, (1974).
23, 1976.
Sampling of Metal Air Particulates for Analysis by Furnace Atomic Absorption Spectrometry B. N. Noller" and Harry Bloom Chemistry Department, University of Tasmania, Box 252C, G.P.O., Hobart 700 I, Ausfralia
MatouBek and Brodie (1,2) have described determination of lead and cadmium air particulates by furnace atomic absorption following collection on 0.22-gm Millipore GSWP filter disks inserted into modified graphite sampling cups. Woodriff and Lech ( 3 )earlier demonstrated the applicability of using graphite crucibles to sample sub-liter volumes of air to follow changes over a few minutes in lead air particulate concentrations. Applying the same principle, we demonstrated the feasibility of using the technique of Matoulek and Brodie (I) to follow ambient lead concentrations a t a number of locations in Hobart during the course of single days ( 4 ) . Following this survey and after using the existing technique ( I ) over a period of several months it became obvious that contamination of particulate samples in graphite sampling cups occurred prior to analysis. For example, as a 200-ml sample of air containing 1 pg/m3 P b was equivalent to collecting an absolute amount of 200 pg Pb, the ease of contaminating such a small quantity of lead is obvious. While contamination of graphite sampling cups within the laboratory could be monitored, the existing method of storing graphite 346
* ANALYTICAL CHEMISTRY, VOL.
racks with plastic covers proved to be unsuitable for the following reasons: 1) Although the plastic covers appeared to seal the graphite sample racks tightly, if graphite sampling cups were not analyzed immediately upon return to the laboratory, contamination caused by air leaking under the seal of the plastic cover would occur. The existing procedure was satisfactory only when samples were analyzed immediately but not if sampling cups were stored for a few days before being analyzed. 2) Up to 10 graphite sampling cups out of a total of 20 in each graphite rack were needed t o give a suitable average blank for samples taken a t any particular location. 3) The sampling cups were easily displaced from their positions in the graphite racks during transport in a vehicle, to and from the laboratory, and could not be identified with respect to sample number. 4) During collection of air particulates the graphite sampling cups were all exposed t o the atmosphere, momentarily. Extreme care was required to prevent gross contamination. Table I shows the effect of exposing sampling cups to auto-
49, NO. 2, FEBRUARY 1977
