583
Anal. Chem 1980, 52, 583-585
of ~~~~l M~~~~~~ ~~~~d in various Table 11, Species of Fish by the Present and the Wet Digestion Method
no. 1 2
3 4 5
species of fish shark mackerel threadfin red fish rockcot
present method, PPm 0.086 i 0.004 0.169 I 0.008 0.194 i 0.009 0.302 i 0.014 0.479 0.016 2
wet digestion, PPm 0.091 ? 0.003 0.162 i 0.004 0.183 2 0.009 0.321 7 0.010 0.493 I0.015
tained after sample digestion is shown in Table 11. Close agreement in the values measured by the two different methods was observed. The accuracy of the proposed method was also assessed in the analysis of NRS Orchard Leaves SRM 1571 and Bovine Liver SRM 1577, which gave mercury contents of 0.152 f 0.006 pg/g and 0.016 f 0.003 pg/g, respectively. These values are in good accord with the NRS certified values of 0.155 f 0.015 and 0.016 f 0.002.
ACKNOWLEDGMENT The authors thank C. K. Chu for helpful discussions.
quantities of inorganic (as HgCl,) and organomercury (as CH,HgCl) added to a series of replicative homogenized shark meat samples was 96.0 f 3.4%. The mercury content obtained from eight determinations was 0.086 ppm and the precision expressed as the relative standard deviation of the mean value was 4.3%. Addition of cysteine has shown no effect on the reduction under the given conditions. Use of tributylphosphate was undesirable as addition of even a small amount (20 pL) tends to increase the partition equilibrium time remarkably (from 6-min increase to over 20 min). This was in fact not necessary as no foaming problem was encountered using the present setup. Comparison of results obtained by the present method in the analysis of several species of fish samples with those ob-
LITERATURE CITED (1) Poluektov, N. S.: Vitkin, R. A,; Zelyukova, T. V. Zh. Anal. Khim. 1964, 19, 937. (2) Hatch, W. R.; Ott, W . L. Anal. Chem. 1968, 40, 2085. (3) Ure, A. M. Anal. Chim. Acta 1975, 76, 1. (4) Hawley, J. E.; Ingle, J. D.. Jr. Anal. Chem. 1975, 4 7 , 719. (5) Tong, S.L. Anal. Chem. 1978, 5 0 , 412. (6) Magos, L. Analyst(London) 1971, 96, 847. (7) Magos, L.; Clarkson, T. W. J . Assoc. Off. Anal. Chem. 1972, 55, 966. (8) Matsunaga, K.; Ishida. T.; Oda, T. Anal. Chem. 1978, 48, 1421. (9) Analytical Methods Committee, Analyst i:London) 1977, 702, 769.
RECEIVED for review June 28, 1979. Accepted November 5, 1979. This work was supported by a Vote-F grant from the University of Malaya, Kuala Lumpur, Malaysia.
Determination of Mercury in Iodine Monochloride by Argon Plasma Emission Spectrometry Maurice R. Smith Olin Corporation, P.O. Box 248, Charleston, Tennessee 373 10
T o ensure t h a t the concentration of mercury in ambient air does not exceed 1 pg/m3 in mercury cell chlor/alkali plants, emissions are restricted to not more than 2300 g of mercury per day (I). Procedures for simultaneously quantitating the particulate and gaseous mercury emissions in stack gases are rigidly defined by the Environmental Protection Agency (EPA) (2-5). Briefly, the currently accepted procedure is as follows. (1)The effluent gas is scrubbed through 0.1 M iodine monochloride (ICl), a liquid oxidizing solution (6). (2) An aliquot of that solution is diluted to 50 mL using 0.1 M ICl. (3) The diluted solution is made basic with 10 M NaOH, then stirred vigorously for 3 min. (4) Hydroxylamine sulfate, 5 mL, is added to reduce mercury(I1) to elemental mercury. (5) The solution is shaken and immediately placed in an aeration system. (6) The elemental mercury formed is carried through the optical cell of an atomic absorption spectrometer set a t 253.7 nm (7,8). We and others ( 9 , I O ) have had great difficulty achieving consistent results with the hydroxylamine sulfate method. As a result, a second procedure, which has not been accepted by the EPA as of this writing, has appeared in the literature (11-13). I t retains IC1 as the scrubbing solution, but dilutes the samples with 5% H2S04and then reduces the mercury(I1) with tin(I1) chloride. While running the above EPA procedures, several synthetic samples were analyzed by dc argon plasma emission spectrometry because this method is generally linear over a wide concentration range ( 1 4 ) and is an order of magnitude faster than either EPA method.
EXPERIMENTAL All chemicals used were analytical reagent grade materials. The hydrochloric acid used to prepare the IC1 and to rinse volumetric 0003-2700/80/0352-0583$01 OO/O
flasks was distilled from quartz. The water was distilled, demineralized through a Barnstead NANOpure 4 system and finally distilled from quartz. The acid and the water were stored in acid rinsed Nalgene bottles. All glassware was cleaned by accepted procedures (15). The 1.0 M IC1 was prepared by published procedures ( I ) . The known samdes were oreDared in 0.1 M IC1 from either 100 or 1000 pg HgimL stock solition with a combination of Mohr pipets (Class A, 5 and 10 mL) and fixed volume Eppendorf pipets. The dc argon plasma emission data was obtained on a SpectraSpan I11 (Spectrametrics, Inc., Andover, Mass.) operated in the single element mode on the mercury 253.7-nm emission line. This instrument has a SpectraJet I11 excitation source, which produces an inverted Y shaped plasma, struck between a tungsten cathode and two carbon anodes. The entrance slit dimensions, which do not appear to be critical, were either 50 pm wide X 100 pm high or 100 pm wide X 200 pm high; the particular combinations are given in the appropriate tables. The exit slit dimensions were 25 pm wide X 500 pm high. The plasma source emission was integrated for three 10-s periods during each analysis.
RESULTS AND CONCLUSIONS Since argon plasma emission (APE) is generally linear over a wide concentration range, the low and high values on the working curve were set a t 1.00 and 100 pg Hg/mL, respectively. Known concentrations of mercury in 0.1 M IC1 were prepared and analyzed in order of increasing concentration (Table I). The low sample was analyzed last to determine if residual mercury was retained by the sampling system. I t was not. The initial APE results were encouraging; thus, two more sets of synthetic samples were analyzed as before, except a known sample with 130 pg Hg/mL was added to each set. These results also appear in Table I. 'The data clearly show c' 1980 American Chemical Society
584
ANALYTICAL CHEMISTRY, VOL. 52, NO. 3, MARCH 1980
~~___________ Table I. Mercury Analysis in 0 . 1 M Iodine Monochloride by APE between 1.00 and 1 3 0 g/mL prepared valuea 1.o
15.0 30.0 1 5 .O G O .0 75.0 90.0
100.0 130.0
analyzed v a l u e b , c
analyzed v a l u e b , d
analyzed value",d
0.958 i 0.017 (4.2)' 15.0 i 0.087 ( 0 . 0 ) 31.0 * 0.461 ( 3 . 3 ) 45.7 i- 0.432 (1.6) 60.8 * 0.478 ( 1 . 3 ) 75.2 I1.22 ( 0 . 2 7 ) 89.2 z 0 . 5 0 1 ( 0 . 8 6 ) 1 0 0 i 1.26 ( 0 . 0 ) N. D.
1 . 0 1 i 0.035 ( 1 . 2 )
N.D.~ 0.174 ( 4 . 3 ) N.D. 60.8 i 0.467 ( 1 . 3 ) N.D. 90.5 + 0.407 ( 0 . 5 5 ) 1 0 1 i 0.629 ( 1 . 0 ) 129 i 0.329 (0.77)
0.995 * 0 . 0 1 3 ( 1 . 5 ) N.D. 31.0 7 0.033 ( 3 . 3 ) N.D. 61.5 i- 0.151 ( 2 . 8 ) N.D. 90.0 t 0.726 ( 0 . 0 ) 102 :0.626 ( 2 . 0 ) 128 r 0.370 ( 1 . 5 )
average error (1)
average e r r o r (1)
average e r r o r ( 2 )
31.3
*
a All values are in pg/mL. These results are the average and standard deviation as obtained from t h e instrument printout Entrance slit widths 50 X 100 wm. Working curve set between 1.00 and 1 0 0 p g Hg/mL. for three 1 0 - s analyses. Entrance slit widths 1 0 0 X 200 pm. Working curve set between 1.00 and 1 0 0 p g HgimL. Percent error relative t o prepared value. f Not done.
_______
_
_
~
____
~
___ _
_____
~-
~
-~
__
Table 11. Mercury Analysis in 0 . 1 M Iodine Monochloride b y APE between 0 . 2 0 and 1 .OO pg/mL prepared valuea
analyzed valueb-d
0.20 0.40 0.50 0.60 0.70 0.80 0.90 1.00
N.D.f N.D. 0.497 ? 0.003 (0.60) 0.604 ?- 0.004 (0.67) 0.694 + 0.016 (0.86) 0.808 ? 0 . 0 1 1 (1.00) 0.906 r 0.005 (0.67) 1 . 0 2 i 0.023 (2.00) average error (0.97)
analyzed value' 0.207 0.409 0.476
?
'
0.002 (3.5)" 0.075 ( 2 . 3 ) 0.011 (4.8)
I
*
N.D.
0.676 T 0.009 (3.4) N.D.
N.D. 0.020 ( 1 . 9 ) average e r r o r ( 3 2 ) 0.981
i-
analyzed valueb
ac.f'
i 0.001 ( 7 . 5 ) 0.405 + 0.010 (1.3) 0.398 I0.013 (0.4) N.D. 0.695 :0.013 (0.7) N.D. N.D. 1.00 I 0.003 ( 0 . 0 )
0.215
average e r r o r ( 2 . 0 )
All values are in pg/mL. These results are the average and standard deviation as obtained from the instrument p r i n t o u t for three 10-s analyses. Each of these sets are individually prepared. Entrance slit widths 50 X 100 pm. W o r k i n g a
curve set between 0.50 and 1.00 p g Hg/mL. e Entrance slit widths 100 x 200 pm. Working curve set between 0.20 and 1.00 p g Hg/mL. f Not done. Percent error relative to prepared value. t h e A P E procedure, with an average error of 1% over the range of t h e analysis, t o be a good analytical method. I t is noted t h a t the 130 pg Hg/mL known samples were correctly analyzed by APE with an error of less than 2 % , which shows t h a t the working curve defined between 1.00 and 100 pg H g / m L is linear to a t least 130 pg Hg/mL. T h e EPA procedure for mercury in IC1 is reported to be valid between 0.50 and 120 pg Hg/mL (13);therefore the APE procedure in the low region was investigated. T h e working curve was first defined by 0.50 and 1.00 pg H g / m L and finally by 0.20 and 1.00 pg Hg/mL standards. Samples of known concentrations were prepared a n d analyzed in order of increasing concentration (Table 11). Again the low sample was analyzed last, and it was verified t h a t residual mercury was not retained by t h e sampling system. It can be noted in Table I1 that, although the results are acceptable on both working curves, the average error over the more narrow working range is certainly better. Finally, the stability of the APE instrument was investigated. A 30 p g Hg/mL sample was analyzed repeatedly over a period of more than 30 min without updating the working curve t o yield 30.8 f 0.268 gg H g / m L (0.9% RSD) from the following data: 30.7, 30.3, 30.8, 30.4, 30.4, 30.9, 31.0, 31.0, 30.8, 31.2, 30.8, 30.9, 30.7, 31.1, 32.3, and 31.9 pg Hg/mL. This variation is acceptable, especially since, under normal analytical conditions, this laboratory runs no more than five analyses nor more than 20 min without updating the working curve of the APE unit. T o verify that the instrument is stable over a five-sample analysis load when more dilute solutions are encountered, five repetitious analyses of the 0.60 pg Hg/ mL known were done on the 0.50 to 1.00 pg Hg/mL working curve to obtain 0.603 f 0.003 pg H g / m L (0.46% RSD) from the following results: 0.604, 0.606, 0.601, 0.599, and 0.604 pg Hg/mL. The precision of the Eppendorf pipet used to prepare t h e standard was 0.68%; thus the confidence limits of the
results are determined by the precision of the dilution rather than the APE. In summary, it has been shown t h a t dc argon plasma emission spectrometry is an excellent method for the analysis of mercury in 0.1 M IC1. T h e method is applicable over the range 0.50 to a t least 130 p g Hg/mL, on working curves defined between 0.50 and 1.00 pg H g / m L and 1.00 and 100 pg Hg/mL, with errors averaging 1% of the known "spiked" values. This wide linear range negates the necessity of diluting samples, contributing to making the APE procedure some ten times faster t h a n the standard flameless atomic absorption procedure, a factor of some concern to quality control laboratories.
LITERATURE CITED "National Emission Standards for Hazardous Pollutants", Fed. Regist., 38 (66), 8835-8845, April 6, 1973. Mitchell, W. J.; Midgett. M. R . "Methods for the Analysis of Mercury Emissions from Mercury Cell Chlor/Alkali Plants": U.S. Environmental Protection Agency: Research Triangle Park, N.C., May 1975. Rom, J. J. "Calibration and Operation of lsokinetic Source Sampling Equipment"; U.S. Environmental Protection Agency: Research Triangle Park, N.C., APTD-0576. March 1972. Martin, R . M. "Construction Details of Isokimetric Source Sampling Equipment"; U.S. Environmental Protection Agency: Research Triangle Park, N.C., APTD-0581, April 1971. "Standard Method for Sampling Stacks for Particulate Matter", "1971 Annual Book of ASTM Standards", Part 23; Philadelphia, Pa., 1971; D-2928-71. Linch. A. L.: Staizer. R . F.: Sefferts. D. T. A m . Ind. Hya. . - Assoc. J . 1968, 29 79 Poivektov, N S ,Vitkum. R A Zelyukoria. Y V Zh Anal K h m 1984, 19, 937. Hatch, W. R.; On, W. L. Anal. Chem. 1968, 4 0 , 2085. Scarinaeiii. F. P.: Puzak. J. C.; Bennett, 8. I.; Dennv, R . L. Anal. Chem. 1974-46, 278.' Baldek. C. M.: Kalb, G. W.; Crist, H. L. Anal. Chem. 1974, 4 6 , 1500. Mitchell. W . J.; Midgett, M. R . Air Pollut. Control Assoc. J . 1976. 2 6 , 674. "Method 101. Reference Method for Determination of Particulate and Gaseous Mercury Emissions From Stationary Sources (Air Streams)"; U.S. Environmental Protection Agency, Office of Air Quality Planning and
Anal. Chem. 1980, 52, 585-586 Standards: Research Triangle Park, N.C., Oct. 1977. (13) "Method 102. Reference Method for Determination of Particulate and Gaseous Mercurv Emissions From Stationarv Sources (Hvdrooen Streams)' , U S. Ehvironmental Protection Agendy, Office of Ai; Quality Planning and Standards Research Triangle Park, N C Oct 1977 (14) Fairless, C M H Am Lab 1978, 10 101
585
(15) "Methods for Chemical Analysis of Water and Wastes"; U.S. Environmental Protection Agency, Publication No. 60014-79-020, 1979: pp 4-5.
for review October
53
1979. Accepted December
39
1979.
Adaptation of the 8253 Timer as a Programmable Real Time Clock for Minicomputer Applications John C. Lennox' Department of Chemistry, University of Arkansas, Fayetteville, Arkansas
7270 1
We report here the design of a simple but versatile real time clock source based upon the Intel 8253 programmable interval timer (Intel Corp., Santa Clara, Calif.) as adapted to use with the micro NOVA minicomputer system. The design presented is functionally similar to earlier designs ( 1 , 2 ) ,but also presents reduced chip count and software overhead, certain flexibility, and potential added capabilities not available in t h e former. In its current configuration, the basic application of this clock is as a programmable interrupt source for a general purpose data acquisition system integrated into a Data General micro NOVA minicomputer. In this capacity t h e clock is capable of providing repeated interrupt requests a t time intervals ranging from 2 ps to approximately 10 min. T h e 8253 is inexpensive ($14.95, Jameco Electronics, San Carlos, Calif.), requires a single power supply voltage of +5 V a n d is fully T T L compatible. This chip is designed as a highly flexible timing circuit, primarily composed of three independent 16-bit counters which can be selected to operate in a variety of capacities: programmable width one shot, pulse generator, square-wave generator, etc. Each counter is composed of a 16-bit count register, a mode control word, and a separate input for its individual clock source. Selection of a particular operating function for a given counter is obtained by programming of the specific mode control word associated with t h a t particular counter. More detailed descriptions of the functioning of this chip are available in the manufacturer's data sheet and literature ( 3 , 4 )and will not be repeated here. In the current design, the mode control words of two counters are selected such that each operates as a square-wave generator, dividing its input clock frequency by the 16-bit count previously loaded into its internal count register. As such, each counter output will be a square wave whose period is t h e product of the period of its input clock period and the quantity stored in its internal count register. One counter of the 8253 (CLK 0) is programmed to operate as a time base generator, providing output periods in decades from 10' t o lo4 ps. This time base, initially selected under software control, is directed t o the input of a second counter (CLK 1) which is selected to multiply this base period by any number from 2 to 216. T h e output of CLK 1 (OUT 1) then provides repetitive transitions at the appropriate time interval for computer interrupt. As the O U T 1 square wave will be of a variable period from 2 p s to approximately 10 min, this clock transition is utilized t o strobe a 1.4 p s monostable (Figure 1, IC 3/21 which will set the DEVICE DONE flip flop, thereby generating the appropriate interrupt request sync pulse to the NOVA. Upon computer interrupt, appropriate action is taken by t h e interrupt handler routine for either d a t a acquisition or experimental control. If the ADC system has been enabled,
the clock timeout is also gated to strobe the sample and hold amplifiers, multiplexer, and initiate conversion of t h e ADC. Because of t h e relatively high overhead associated with the Data General Disk Operating System, modifications have been made to its interrupt handling routiries to permit acquisition rates in slight excess of 10 kHz (normally approximately 1 ms is required by their routine, limiting rnaximum interrupt rates to 1 kHz). In lieu of d a t a acquisition, interrupt software can be utilized for experimental control via direct digital output or digital-to-analog converters. Although the internal registers of this chip are 16 bits wide, the timer is primarily designed as a support chip for 8080 based microprocessor systems, t o be loaded in 8-bit bytes by memory mapped I/O. Furthermore, as t h e minimum write pulse width for the chip is 400 ns, applications in minicomputer systems which provide shorter 1/0 pulse widths must provide for these limitations with appropriate hardware and software as described below (refer to Figure 1). IC 1,hex R / S latches and IC 2, a n 8-bit latch, are loaded from t h e NOVA output bus by the instruction DOCP 0,40. Execution of this instruction applies the 16-bit contents of accumulator 0 onto the NOVA d a t a lines (DATAO-DATA151 andloads these latches by assertion of t h e J/O control signal DOC (250 ns wide). T h e 8 least significant bits of this output word (DATA8-DATA15) serve as data inputs to the count and mode control registers of the 8253, whereas t h e 6 most significant bits are used to enable counting (DAXA4), writing to the 8253 (DATAB),and to enable interrupts for this interface (DATA5). T h e signals A0 and A1 are used t o select counter or mode control word loading as described iri t h e manufacturers literature. The second half of this instruction results in assertion of IOPLS, which is directed to the 400-ns monostable (IC 3/1) whose output is gated with the write enable level, WR ENB, t o generate the appropriate width write pulse for t h e 8253. As the d a t a of the accumulator would not be present on the NOVA 1/0 bus during the entire duration of this write signal, t h e 8-bit latch (IC 2) is necessary to extend t h e appropriate signal levels t o the inputs of the 82.53. If bits 4 or 5 of accumulator 0 are not set, the clock can be disabled by execution of the instruction DOCP 0,40. Disabling is also obtained by assertion of the IORST control line, asserted upon execution of the NOVA instruction IORST and upon initial application of power t o the system. T h e clock is set by a FORTRAN call whose parameters are the clock count to counter 1 and the power of ten for the base frequency of CLK 0. As an example, CALL CLKSET (1234,4) will generate an interrupt every 1234 X lo4 ps, once the clock interrupt enable has been set. This assembly language routine (401, locations including tables), now merged into the FORTRAN Runtime Library, loads the mode control words and count into each register as required. Counter 1 is loaded with the binary
Present Greenville,
address.
Burroughs FVellcome Co., P.O. Box 1887,
N.C. 27834
0003-2700/80/0352-0585$01 OO/O
(C 1980 American Chemical Society
