Table V. Amount of Lysine in a Sample of Fish Meal Compared with the Difference in Amount of Dye Bound (Calculated as Lysine) by Untreated and Treated (Chloroformate) Fish Meal Carpenter, 'available' lysine, % Sample
A1745 1773 1820 1854 1880
Average B17273 17677 17680 17681 17275
Average Overall average B Soya meal B Cashew
Lysine, ? I , aminogram Found
5.3 6.0 4.9 4.6 4.9 5.1 4.4 4.3 5 .O 4.7 5.6 4.8 4.95 3.0 1.6
Corrected
x
1.14
5.1 5.1 3.9 5.6 3.5 4.6 4.1 4.5 4.2 3.8 3.8 4.1 4.35
5.8 5.8 4.5 6.4 4 .O 5.3 4.6 5.1 4.8 4.3 4.3 4.6 4.95
...
... ...
...
basic amino acids (LHA) and of histidine and arginine (HA), respectively. The variation is attributed to other dye-binding capacities in the particular sample of fish meal. CONCLUSION
Differential dye binding, calcd as lysine, 70
5.3 5.9 4.8 5.9 4.7 5.3 4.4 4.7 4.7 4 .O 5.5 4.7 5 .O 3.1 2.2
ty (EDBC) for fish meal protein before and after treatment with ethyl chloroformate and the molar quantity of lysine in the sample. The EDBC of the untreated and treated fish meal approximates to the total equivalents of the three
The difference in the amount of dye bound, calculated as lysine, for different fish meals, and for a sample of soya meal, before and after treatment with ethyl chloroformate is shown in relation to the amount of lysine in the sample, determined by amino acid analysis and the "available" lysine by Carpenter's method (9) without correction and with correction (10) in Table V. The agreement would indicate the use of differential dye binding capacity for the routine determination of lysine as being quicker and simpler than the elegant Carpenter's method or aminogram analysis. ACKNOWLEDGMENT The authors thank 0. A. M. Lewis (Department of Botany, U.C.T.) for all aminograms and I. M. Moodie for lysine determinations by Carpenter's method; the Director, FIRI, for permission to publish these results; and the C.S.I.R. for financial assistance. RECEIVEDfor review September 24, 1973. Accepted April 23, 1974. (9) K. J. Carpenter, Biocbem., 77, 6-04 (1960). (10) I. M. Moodie, Fishing lnd. Res. lnst., Annu. Rep., 24, 23 (1970).
Evaluation of an Ozone Photometer for Ambient Ozone Measurements Leo Zafonte, William Long, and James N. Pitts, Jr.' State wide Air Pollution Research Center, University of California-Riverside, Riverside, Calif. 92502
Recent emphasis on the development of new analytical techniques for environmental quality studies has resulted in the development of new analytical techniques for the atmospheric monitoring of ozone. Noted developments in this area were the uses of the ultraviolet absorption ( I ) and the ethylene chemiluminescent ( 2 ) and the nitric oxide chemiluminescent techniques (3, 4). In the course of investigations a t the Statewide Air Pollution Research Center, the Dasibi Environmental Model 1003A ozone photometer was evaluated for use as a routine airborne, atmospheric monitor. This report gives the results of several testing procedures which were used to determine the instrumental response, calibration, and linearity. A complete description Author to whom correspondence should be addressed. (1) Lloyd D. Bowman and Richard F. Horak, "A Continuous Ultraviolet Absorption Ozone Photometer," Paper No. 7430. Presented at the Meeting of the Instrumentation Society of America, May 1972, pp 103-108. (2) Gary J. Warren and Gordon Babcock, Rev. Sci. Instrum., 41, 280 (1970). (3) Donald H. Stedman, Eric E. Daby, Fredrick Stuhi. and Hiromi Niki, Air Poliut. Contr. Ass.. 22. 260 (19721. (4) Arthur Fontijn, .Albert0 J: Sabadeli, and Richard J. Ronco. Anal. Cbem.,
42, 575 (1970). 1872
of the actual experimental results obtained by the use of the instrument in an airborne monitoring program can be. found elsewhere (5). EXPERIMENTAL The Model 1003A ozone photometer (Dasibi Environmental 'Corp., Glendale, Calif.) used in these tests is a self-contained unit with a digital readout whose operation is based upon the physical measurement of the absorption of ultraviolet light a t 2537A by ozone in a single absorption chamber 14 inches long. This particular unit was of special manufacture for operation on small aircraft. The modifications included a sample flow rate increase to 2.7 liters per minute, higher than the standard flow rate of 1.0 liter/minute, in order to accommodate a faster measurement time. The optical bench was strengthened by the manufacturer to minimize possible susceptibility to vibration, and the circuit boards were held in place with detents to minimize slippage. Also, the absorption cell is approximately one half the length of those in units currently being produced. In other respects, this unit was identical to the standard version. '
(5) Hermilo R. Gloria, James N. Pitts, Jr., Joseph V. Behar, Gary E. Bradburn, and Leo Zafonte, "Airborne Measurement of Air Pollution Chemistry and Transport. I. Initial Survey of Major Air Basins in California, Report No. 1," T h e Statewide Air Pollution Research Center, University of California, Riv-
erside, Calif. 92502.
A N A L Y T I C A L C H E M I S T R Y , V O L . 46, N O . 12, O C T O B E R 1974
Ozone measurements with this instrument are updated every 11 seconds and are based on two half-cycle (5.5 seconds each) integration periods. During the first or reference half-cycle, atmospheric air is first passed through a catalytic scrubber to remove ozone before entering the light chamber. The scrubber consists of manganese dioxide coated on an open structure to minimize pressure drop and particulate collection. At this high flow rate, the cell is purged of previously contained gases within three seconds, after which a digital light intensity measurement is made over a total integration period of approximately one second. This integration time is accurately determined with a quartz crystal frequency source and retained in memory for the second half-cycle. The accuracy of this instrument calibration is dependent on a calibration count for the reference light measurement, which is determined by the potassium iodide technique. It should be noted that the reference integration interval is varied in such a way as t o reproduce automatically the same total integrated light measurement in each reference half-cycle. Therefore, the ozone calibration remains constant and linear at all times, depending only on the selectivity of the ozone scrubber. During the second or measurement half-cycle, the atmospheric air containing ozone is passed directly into the light chamber. After purging the cell of deozonized air from the previous halfcycle, a light measurement is made by integrating the intensity over precisely the same time period established during the first half-cycle and is retained in memory. Assuming ozone to be the only gas removed by the scrubber, the difference in the light intensity measurement can be related by Beer's law to the ozone concentration because the integration times during both the reference and the measurement half-cycles are identical. In this manner, long term perturbations (greater than 11 seconds) such as light intensity variations due to source fluctuations, window solarization, and Rayleigh scattering are cancelled out in the digital subtraction process. A t the fractional change in light measurements obtained by this technique to the Beer-Lambert law can be expressed in a linear fashion to a close approximation. Thus, ozone measurements are expected to be linear with concentration as an inherent feature of this technique.
RESULTS AND DISCUSSIONS Calibration Accuracy and Linearity. T h e instrument was calibrated for accuracy using the standard potassium iodide technique. T h e instrument was in operation for at least one hour prior t o the calibration and was often running overnight. Figure 1 gives the cumulative results of several calibrations which were run over a period of several months. T h e solid circles indicate the points which were verified against potassium iodide (a primary calibration) while the open circles give the comparative determinations by the Dasibi ozone monitor and a Mast ozone meter which were simultaneously sampling a stream of ozone (a secondary calibration). In this case, the Mast ozone meter was a bench unit routinely kept in good operating condition for such secondary calibration checks. Because of drift characteristics of the ozone source, the reliability of each calibration is 0.02 ppm. For comparison to the data, the solid line in Figure 1 has a slope of 1.00. T h e best fitted linear function t o these data has a slope of 1.016 f 0.017. These results indicate that the calibration accuracy is within the manufacturer's specifications. T h e standard error in the slope of f0.017 we feel t o be very good in view of the fact t h a t two different calibration techniques were used on several occasions over a long period of time. We feel t h a t this error is due to differences in calibration technique rather than t o nonlinearity in the actual measurement. Response Time. T h e unit was tested for its response to a step ozone input in the following manner. An ozone calibrator (Model 1505, Dasibi Environmental, Inc.) was placed on t h e input line within two inches of the inlet port. T h e UV lamp in the calibrator was turned on and permitted to stabilize for 30 min with the instrument in operation. After the warm-up period, the adjustable sleeve around the
Fl.Oo -
,
OZONE
,
,
CONCENTFlA'
,
,
,
:
!b~rf~-je~-mdI80^'
Figure 1. Calibration data for the Dasibi Environmental Model 1003A ozone photometer ( 0 )indicates the primary calibration points (KI Technique):( 0 )indicates the secondary calibration points utilizing a calibrated Mast ozone meter. A linear least squares treatment of the data points yielded a fitted slope of 1.016 f 0.017 and an intercept of -0.005 ppm
Table I. Dasibi Model 1003A Response t o a Step Ozone I n p u t Time, sec
0
11
22 33
44 55
66 77 88
A v response, Test 1
Test 2
0 .o
0 .o
0.043 0.043 0.043 0,044 0.042 0.043 0.044 0,044
0,134 0.139 0,137 0.143 0.141 0.141 0,142 0,142
Test 3
Test 4
0 .o
0.0
0.370 0.372 0.371 0.373 0.373 0.373 0.373 0.373
0.618 0.634 0.634 0.632 0.634 0.631 0.633 0.630
5%
Test 5
0 .o
0.633 0,637 0.636 0.637 0.635 0.637 0,635 0.636
00.0
98.3 99.8 99.5 100.6 99.7 99.9 100.6 100.4
photolysis lamp within t h e calibrator was closed and the ozone reading was observed t o decrease t o zero. In each test, the sleeve was quickly adjusted t o a n arbitrary setting a t the start of the 11-second measurement period (as indicated by the light on the front panel of t h e instrument) and the data given in Table I below were recorded a t each 11second interval. T h e data indicate t h a t t h e instrument had an average response of 98% within one measurement period (11 seconds) to the step ozone input. During four of the tests, the instrument response was 98% or better while the fifth test (No. 4,Table I) indicated response of 94% during this period. Further testing showed the pen-ray lamp on the ozone source t o be temperature sensitive, and t h a t ozone equilibrium was not immediately established at the time the sleeve around the quartz tube (on the calibrator) was withdrawn. Therefore, this lower response factor is most probably the result of t h e testing procedure rather than a n instrumental characteristic. Because of the two-step measurement technique used in this instrument, it is not practical to define an instrument response time; more properly, the term delay time should be used. T h e data in Table I indicate t h a t the delay time is a maximum of 11 seconds for 98% response. However, in actual practice, the difference between the time of the ozone measurement and its display is only 1-2 seconds because the measurement time falls within the later halfcycle operational mode. This time will vary only slightly because the integration time varies only slightly with each measurement and, therefore, it need not be considered for routine ground-based monitoring where changes over a period of several minutes are of interest. In airborne monitoring, however, the delay time must be known for each instrument for accurate work.
ANALYTICAL CHEMISTRY. VOL. 46, NO. 12, OCTOBER 1974
1873
Maintenance. In the course of our studies, relatively little maintenance was required to keep the instrument in calibration. The long-path cell was periodically cleaned with ethanol each month during use to minimize ozone losses within the cell, a ten-minute operation. This procedure had no effect on the calibration and served to increase the light intensity reaching the detector and thus to reduce the integration .period. 'Because an ultraviolet absorption technique is used, no accessory gases or solutions were required and thg calibration was independent of small changes in the atmospheric gas flow rate. The ozone scrubber should be periodically changed as recommended by the manufacturer to eliminate the possibility for low ozone readings. Airborne Operation. In airborne use, two important factors which must be overcome are aircraft vibration and tilt for noise-free and effective operation. With liquidbased measurement techniques, these factors tend to disrupt the flow of the measuring liquid and may cause noise excursions on the output recorder. Under the operating environment of a twin-engine aircraft (Cessna 4011, this instrument has proved itself to be insensitive to these factors except during severe turbulence after which recovery was observed to occur in one 11-second measurement period. At a ground speed of 180 mph, the ozone measurements are integrated over a distance of 0.05 mile, with new readings every 0.5 mile. Based on studies a t ambient concentrations, there were no apparent interferences due to nitrogen dioxide, hydrocarbons, or sulfur dioxide. Possible interference would depend upon such factors as the value of the absorption and scattering cross sections a t 2537A and the selectivity of the ozone scrubber. The sample intake was located in the aircraft nose approximately four feet in front of the propeller plane to eliminate exhaust-hydrocarbon interferences, and
no further interferences were observed in the course of our studies. The general agreement of the Model 1003 ozone measurements and the Mast total oxidants meter during each flight indicates that the levels of photochemically generated aerosols which were encountered did not introduce an observable change in the ozone reading. On one occasion an Os-ethylene chemiluminescent monitor was flown with the Model 1003, and readings of both instruments were generally in agreement within 0.01 ppm of ozone a t the low ozone concentrations that were encountered. CONCLUSIONS Based on the data presented in this report, the following conclusions can be made. The accuracy, repeatability and linearity of the ultraviolet absorption technique are satisfactory for atmospheric monitoring. The unit responded to within 98% of the step ozone input within one measurement period (11 seconds). The instrument proved itself to be sufficiently rugged and reliable for routine airborne operation. The use of the ultraviolet absorption technique results in a lower maintenance requirement as compared t o liquid techniques for ozone measurement and either a comparable or lower maintenance requirement as compared to ethylene chemiluminescent techniques. ACKNOWLEDGMENT The authors express their appreciation to the Ames Research Center of the National Aeronautics and Space Administration and, particularly, to Hermilo R. Gloria of NASA for the opportunity to evaluate this instrument during airborne operation. RECEIVEDfor review December 26, 1973. Accepted May 20, 1974. Specific reference to brand names of instruments does not imply endorsement by the University of California Statewide Air Pollution Research Center a t Riverside,
I CORRESPONDENCE Beryllium Content of NBS Standard Reference Orchard Leaves Sir: A recent paper ( I ) indicated the presence of volatile beryllium compounds in National Bureau of Standards Orchard Leaves (SRM 1571), and in air samples taken from a beryllium machining facility. Samples of Orchard Leaves digested with nitric and sulfuric acids in an open beaker, or dry-ashed in an oxygen plasma furnace a t 150 "C, gave only 16% and 7%, respectively, of the beryllium content found when the leaves were digested under reflux with nitric and sulfuric acids (0.11 f 0.01 ppm Be). Relatively large amounts of beryllium were detected in a Dry Ice cold trap inserted between the plasma furnace and the vacuum pump. The analytical method used involved gas chromatographic measurement of the beryllium trifluoroacetylacetone complex extracted into benzene. This report ( I ) contained several surprising results. Among these was the observation that volatile beryllium compounds were present both in Orchard Leaves and in air samples taken from a beryllium machining factory. Also, the volatile beryllium compound detected in Orchard Leaves was so inert that it distilled from concentrated mineral acid mixtures, yet apparently underwent (1) M . S. Black and R . E. Sievers, Anal. Chem.. 45, 1773 (1973)
1874
A N A L Y T I C A L C H E M I S T R Y . VOL. 4 6 ,
NO. 1 2 ,
complete chemical exchange with trifluoroacetylacetone (Htfa) when shaken for 15 min with a benzene solution of Htfa. This type of behavior is certainly unusual, and is not shown by any known beryllium compound (2, 3). For example, the beryllium complexes of acetylacetone and its fluorinated derivatives are very volatile and thermally stable, yet they are readily wet-ashed in an open beaker without any loss of beryllium (4-6). Over the past ten years. a very large number of environmental samples have been analyzed for beryllium in our laboratory, after either wet-ashing in open beakers or dryashing a t temperatures up to 800 "C (7). If undetected (2) L. E. Smythe and T. M . Florence, "Recent Advances in the Analytical Chemistry of Beryllium," in "Progress in Nuclear Energy," c. E. Crouthamel, Ed., Series I X . Vol. 3, part 6 . Pegamon Press, New York, N . Y . . 1963. (3) D. A . Everest, "The Chemistry of Beryllium," Elsevier, Amsterdam, 1964. ( 4 ) J. D. Cosgrove, J . Morgan, and P. Pakalns, Australian At. Energy Comm. Rept. AAEC/TM 87 (1961). ( 5 ) C W. Sill and C. P. Willis, Anal. Chem., 31, 598 (1959). (6) J. K . Foreman, T. A. Gough, and E. A . Walker, Analyst (London), 95, 797 (1970). (7) W . R Meehan and L. E. Smythe. Environ. Sci. Techno/.. 1, 839 ( 1967).
OCTOBER 1974
