A semi-automatic system for operation of electrical detection for a spark-source mass-spectrometer

m8lua,

1972, vol. 19. pp. 1147 to 11%. PammonRas.

RimtsdhN-blmd

A SEMI-AUTOMATIC SYSTEM FOR OPERATION OF ELECTRICAL DETECTION FOR A SPARK-SOURCE MASS-SPECTROMETER* R. J. Co NZEMIUS, W. A. RHINEHARTand H. J. S~EC Institutefor Atomic Rcwarch and Deptmcnt of Chcmhy, Iowa state university, Ames, llowa 50010, U.S.A. (Received 15 December 1971. Accepted 31 January 1972)

=-A

oemi-antcmwic control syptan has bean d+opu3 for -sourw mats-Jpectromter, whcb pcrlnita close Meracbon between the ojwtor, the tmtnmxnt eta electrical ion-detection and a computer viu tiatc-sharing (remote terminal) facilities.

ELECTRICAL detection has been shown to be very useful in detecting ion-currents with the spark-source mass-spectrometefl although photographic ion-detection is still used as the sole detector in most laboratories. However, a particular disadvantage of photographic detection is the lack of continuous knowledge of instrument response which can be interpreted and made useful immediately. The fundamental means for electrically measuring spark-source signals has hecn reported.~ This paper describes the automation of electrical detection, the&y permitting exten&e routine usage and significant improvements in the precision of analytical results. Electrical detection systems have been developed which utilize both scanning and peak-switching techniques. Here, electrostatic field scanning of relatively narrow mass ranges is used for identifying reference lines and for subsequent tuning of the instrument to a ref&renuemass. ELtrostatic peak-switching is then used to select appropriate ion-currents. It is the automation of the peak-switching mode that will he described here. Some of the guidelines for developing this automated system are as follows. Accurate

electrostatic

peak

switching

is technologically

simpler

and also

cheaper than magnetic peak-switching. Most samples analysed by electrical detection in this laboratory are of high purity, consequently their spectra have been previously characterized thus affording a preknowledge of spectral interf&rencesand the best choices for nuclide lines. Quality control programmes in pure material production are normally concerned with a limited number of impurities, thus generul surveys on samples, which can be best performed photographically, are frequently not needed. Studies involving multiple samplings (e.g., testing for inhomogeneities or concentration gradients) are also normally concerned with limited groups of elements. Control over sample volume is desirable when elemental inhomogeneities are suspected or known to exist. Instrument recalibration with an internal refkrence element should be possible at any time the operator suspects that a previous calibration is no longer valid. + Work was performed in the Ams Contribution No. 3158.

Laboratory of the U.S. Atomic Energy 1147

1148

R. J. -,

W.

A. -T

and

H. J. SVEC

Provision for ion-counting or high-sensitivity measurements should be made. Ion-currents to an electron multiplier should be controlled to eliminate needless high current amplification and to avoid impingement of high ion-currents on the llrst dynode. Measuremtnt times should be from one to several seconds in order to average short term fluctuations in the spark and inhomogeneities in the sample and yet permit reasonablt total assay times. Electrostatic field settling after switching will rquire approximately one second. Average data rates and total output per analysis will normally be less than 10 characters per second and 4000 total characters respectively, for peak-switching techniques. System design should allow for concurrent functions such that the greatest fraction of time required for analyses is due to field settling and actual measurement periods. Advantages of remote interfacing to an existing large computing facility should be used if possible. Figure 1 is a schematic diagram ilhrstrating the functions of various components of an automated systems for meeting these requirements. Figure 2 is a more detailed schematic diagram of thesysttm,referring to actual components chosen to perform the functions given in Fig. 1. The units labelled AL, were designed and constructed

at this laboratory. The usefulness of the sttpwise scanner as well as the reproducibility of the signaldetecting circuits have been described previ~usly.~*~ A detailed description of the autoprogrammer and its manual control consolt (right centre of Fig. 2) is givtn below along with a brief description of the allowable operator interaction with the computer. Specitications and operating details for the commercial units in the system are obtainable from the manufacturers’ literature.

Spark-source

mass-spectrometer

1

Autoprogr am?ner-g4Tu?ml*tims

The logic and functions performed by the autoprogrammer are given in Fig. 3. Instructions to the unit may originate from either paper tape (contains the main programme and is read by a reader under control by the autoprogrammer) or from manual control (permits the operator to perform functions independent of the main programme, such as recalibration of the instrument). The relay-operated voltage divider, RVD, can be controlled by either the autoprogrammer or the operator oiu the keyboard. The RVD controls the electrostatic-analyser voltage by imposing a variable reference voltage on the analyser-voltage supply. The ion-accelerating voltage is controlled via another reference voltage from the ela%rostatic-analyser voltage supply. The accelerating-voltage supply also has provisions for an offset voltage which corrects for the high initial energy of the ions before ace&ration. The latter permits the ion beam to remain centred at the energy-dcfming slit of the elcctrostatic analysar located near the ion-beam monitor in the field-free region between the electrostatic and magnetic fields. Maximum voltage from the electrostatic analyscr supply is 2500 V. The ion-accelerating voltage is -10 times this voltage and is limited to 30 kV. The instrument may be recalibrated as a normal function of the main programme or at the operator’s command, in which case the functions for recalibration arc shown on the left side of Fig. 3. Recalibration at the operator’s command corresponds to the “yes” route in the upper left portion of Fig. 3 and the RVD is controlled by the keyboard. Normally the operator will have preset the keyboard to the reference mass such that the field immediately begins to settle to the correct voltage as the ion beam 6

R. J. CONZEMIUS,W. A. biNZHART and H. J. Swc

is turned on. Since the optimum setting for the ratio countmeter period is usually already known, it also has been preset. Thus the first decision by the operator is whether to make continuous readings or single readings. When recalibration is completed, control is returned to the main programme. This point in the logic outlined in Fig. 3 is the “no” direction of the decision block in the lower left corner of the figum. The functions of the main programme arc indicated on the right side of Fig. 3. The “temporary hold” in the programme can be made by the operator and is indicated by the decision block in the upper right hand corner of the figure. This temporary hold permits manual functions to be performed before the automatic programme is continued. The period selection (external time base from the monitor voltage-to-fiqucncy converter) is set in the ratio countmeter according to instructions contained in the tape programme along with the number of readings (maximum of three) for each of two periods as indicated in the figure. Two different period settings with three readings per period normally provides sufkient dynamic range for selecting a proper sample volume and reproducible readings for indicating the degree of homogeneity of the sample

Figure 4 is a simpliftcd control-function diagram for the autoprogrammer. The arrows indicate the direction of information flow. In the automatic mode, a 20-level programme cycle is used. Control-function address is generated by a 20-step ring

Spark-source mass-spectrometer

FIG. 4.-Simpliikd

1151

autoprogrammer ControLfunctiondiagram.

which is synchronized with the instruction data coming from the programme tape reader. Information from the tape reader is in standard ASCII code format and utilizes only numbers for issuing instructions to the various system elements. The tape programme format with currently available options is shown in Table I. All nv coding translations, routing decisions and programme-level advance instructions are carried out in the control logic drouitry and interfacing portion of the auto-programmer. From the control logic &m&y the proper instructions are issued to the ion-beam control circuits, the ratio countmeter control circuits and the RVD. Programme-level advance instructions are determined either by an internal clock, tape instruction, or by feedback signals from the data coupler section, depending upon the operation being performed at a particular programme level. It should be noted that the RYD control data are routed into one of two avail&k memory storage systems rather than directly into the RVD. This provides for rapid parallel entry of the BCD data to all five decades of the RVD at level B of the programme. This prevents the electrostatic analyser power supply from having its refm voltage completely removed and then returned in relatively slow serial form from the programme tape input. Such a radical procedme would greatly increase the settling time required for the supply voltage, The paraBel entry format provides a single step change directly from the previous reference voltage setting to the new settings. Such a procedure requires that the operating programme be written so that the desired RVD setting for a s-g programme cycle can be read into the alternate memory storage during a current programme cycle. This is accomplished in levels C, D, E, F and G of the programme. The ratio countmeter period selection is programmabk remotely and the proper logic levels are supplied by the period-control selection circuits. The period is selected at programme level I for the first three and at kvel Q for the last three possible data reading cycles. A dual gating circuit controls the input of data passing to both the numerator and denominator inputs of the ratio countmeter. These gates are opened by programme control and closed by a feedback signal from the counter when

counter

1152

R. J. CONprmvS, W. A. R~NEEARTand H. J. Svec TULB I.-TAPE Program level

B” C D : G IH

Tape coda

PR OC3RAbME

FORMAT

System control functions with options Turn beam off. Transfer new settin to RVD and clear alternate memory storage. Read RVD dax& ! setting into memory stotage. Read RVD decade II satting into memory storage. Read RVD decade III setting into mamory stoqe. Read RVD decade IV setting into memory storage. Read RVD decade V setting into memory storage. Ckar period-control ti Set period-control flip l?op E. 1. Set period-control flip-flopNo. 2.

J E M N 0

Stop for system adjustmant if operator-sekcted. Start data-taking cyck No. 1. Start data-taking cycle No. 2. Advance without taking data. Start data-taking cycle No. 3. Advance without takiog data.

P

Q R S T

Set-+aritintrol @ipflop No. 1. Set pea&&control fthsllop No. 2. Set &hxLcontroI “’ flo$ No. 3. Start data-taking cy~ “$ No. 4. Advance without t&in data. Start data-tak@ cycle 5 o. 5. Advance with04 thin data. Start data+kiDe cvcb !l 0.6. Advows witt& &dog data.

the denominator has reached fuh count. The required number of counts is determined by the period4Wrol setting. When the data coupler has received and stored the appropriate input data from its sources it issues a signal to the pro gmmme-control logic which allows the programme to continue to its next level. In the on-line mode with a computer, the timing of the signal is determined by the computer. The tape programme may consist of as many 204evel programme cycles as desired. A programme in its entirety may be spliced in a continuous loop and thereby repeated asoftenasdesired. Manual control of the system is available to the operator through a small consoIe, of which the controls are shown in Fig: 5. The operator may interrupt the automatic mode by setting the programme selector switch to the “recalibrate*’ position. This corresponds to the “yes” direction in the upper left of Fig. 3. When the main programme cycle under way has been completed, a programme interruption will occur and control will revert to the operator. The RVD setting will be determined by the keyboard entry and the counter-period selected is determined by the countmeter period switch. In this mode, a tixed 54evel internal programme is used. The format is given in Table II.

1153

PROGRAM

SELECTOR

K&-

READ MODE

FIG.5.-Manual amtrol consok.

In the single-reading mode (“Auto”- far right of Fig. 5) the progve is held at the “home” level until the operator actuates the manual start button (“Recalibrate start”). The programme then automatically steps sequentially to the data-taking level. Upon completion of one reading, the programme returns to the “home” level and stops. The operator may initiate this routine manually as often as desired. If a repetitive-reading mode (?ount”) is selected, the sub-programme will stop at the Y level and continue making data readings under the previously determined settings until commanded to stop by the operator. These modes are useful for system adjustmentszand cahiration checks. TABU IL-MANUAL CONTROL IQRMAT control fumtioxl

prr

G X Y

BcamisofF: ma8srtkctionisdctemhd by keyboardon RVD. Buimisturnedon. start takingdata.

By returning the programme-selector switch to the “Main Programme” and actuating the “main prqramme start,” system control is returned to the main tape programme. The autoprogrammer will then proceed from the point at which it was previously interrupted. Computer interaction

One of the advantages of this system is that it can be interfaced to a large (IBM 360-65 in this case) computing facility. This permits use of high-level languages, access to large disc storage for permanent or temporary files, remote entry into a large CPU for programmes requiring greater active space, and sharing of cost and time of the computer. The programming language used for this work is a subset of PL/I. Figure 6 is a block diagram of the principal programmes used with the electrical

1154

R. J. CoNziemn, W. A. Rmrmrm~ and H. 1. SVEC

FKI. 6.-S@~

block diagram of computm intcmction with auqmpmmai -rpsctromstsa.

detection system. The “Main” programme maintains overall control and passes necessary information onto the three principal subprogrammes, “Table,” “Concentration” and “Summary.” Subprogramme “Table” permits automatic punching of paper tape programmes for the autoprogrammer as will as passing this information onto other computer programmes. Subprogramme “Concentration” accepts raw data in the form of amplifier range, intensity ratio, and electrostatic-analyser voltages, determines mass, performs referencing to tabulated information (Le., symbol, ionic charge, abundance and relative sensitivity), subtracts noise and computes signal-to-noise ratios, concentration and precislox~ The output is stored in a computer tie as well as being printed immediately at the remote terminal. Subprogramme “Summary” provides for various types of data summaries as well as a brief final report of the analytical results. Ease of programming and access to the facilities of a large computer permits easy and rapid setting up of special .&&es. Time required for data transfer (10 characters per second) or computer response (tenths of seconds up to several seconds) does not limit the overall system because these time periods occur during fieldor datareading periods which require about the same amount of time. CONCLUSIONS

Table III is an illustration of the precision afforded by the system. It shows the results of a measurement of the platinum isotopic abundances in a silver-platinum alloy, using the -Pt line as the reference. Relative standard deviations (column 4) and the pooled average deviations (column 6) as well as correlation of observed data (column 5) with reported data (column 7) indicates satisfactory agreement for sparksource determinations.

Sparkanucc

Tm

~.-hiUSION

-spectrometer

1155

OF READINCH FOR ISOTOPESOF PUTINUM IN A SILVER-PLATINUMALWY (Manual Spark Cont~$ and Adjustment)

Ave. 3readings

Run No. 195

33.80 33.80 33.80

O-8 3-O l-7

194

32-5 31-o 33.2

1.0 ’ 24 2.3

196

.

: 3 : 3

z: 24.3

: 3 2 3

Computed abundance

198

6.92 792

192

0790 O-768 O-839

190

O-0144 O-0107 09134

: 3 : 3

34.6

4.0

33.80

339

2.6

32.9

244

1.5

25.3

;:; 1-o o-2 5-O 7.13

06

7.21

O-82

3-4

O-78

0‘013

9 11.2

i:; o-7 :-: 66 OQ127

The system has been in operation for more than two years and its principal use is in determining impurities in rarearth matrices. It has also been highly useful in determining concentration gradients in vanadium-diffusion couples.

Ac&~*~ts--The authors wish to acknowledge the many individuals, especially the& colleagues, who comriiuted to this dwclapmnt. We wish especially to thank William 0. Manns whose discussions were be&ciai at the onset, Jerome E. Niebamn who provided advice concerning compatibiiity with the computer, Arthur R Anderson who suggmted improvements in programmmg, ElaineClarkwhoaidedin progrrumne &bugging, Louis Mourlam Jr. who contributed ZflY to hereand thedesignoftheauto~ andtoClanmceR.Neaswhoobtainedthedatarepo fikol+cdte8tthesystgn

Authors'mm-Chuit comp~ncnts

arc

diagmms and const~ction details of the autoprogmmmer available upon request.

dOtkAL

Z&mmn~&aEin halbautomatisches Regelsystem fib ein Massenspektrometer mit Funkenquelle wurde entwickelt. Es erlaubt eine enge Wechselbeziehung zwmzhen der Bedienungsperson und einerseits dem Ger8t tlber den elektrischen Ionennachweis, andererseits dem Rechner tlber eine AuPenstelle im Zeitwechmlbetrieb. R&m&-On a 6labor6 un systeme de contrUe semi-automatique pour un spectrom&re de masse B source d%tinceile, qui permet une interaction ctroite entre ateur, 1’ l’instrument a& la d&ection ionique 6kctrique et une tnce 010 des facilit6s (point termimd tloigne) de partage de temps. REFERENCES 1. R. J. Conremius and H. J. Svec, naee Analysis by Mass S’ctrometry, Ed. A. J. Ahearn, Chap. 5, Academic Press, New York, 1972. 2. J. S. Gorman. E. J. Jones and J. A. ’ le, Anal. Chem., 1951.23.438. 3. L. B. Furgerson, R. J. Conzemius and I% . J. Svec, Tuhtu, 1970,17, 762.

1156 4. 5. 6. 7. 8.

R. J. Comgmrs,

W. A. -

and H. J. SVEC

R. J. carraearius and H. J. Svcc, ibhi., 19@,16,365. and R. M. BUiott, Anal. Gem., 1971,43,43. R. A. B’ C. W. HYI?= , J. Maw Sprr. Ion +v., 1%9,3,293. F. A. Schmidt -on* U.S. Al. likgy Comw~.Rqr. ORNL-3528, p. 46,1963. E. J. Spiba 8P- J. R Site,