Recording Nickel Carbonyl Detector JULIAN E. MCCARLEY, ROBERT S. SALTZMAN', and ROBERT H. OSBORN Hercules Experiment Station, Hercules Powder Co., Wilmington, D e l .
To meet the need for detecting nickel carbonyl in the atmosphere of a pilot plant area of the Hercules Experiment Station, a very sensitive, continuously recording nickel carbonjl detector was developed. R hen air, contaminated with nickel carbonyl, impinges upon a hot borosilicate glass plate, solid nickel compounds are deposited on the surface. 4 norel optical arrangement using polarized light incident at the Brews! erian angle for borosilicate glass measures the quantity of deposit. Concentrations in the range of 0.05 to 4 p.p.ni. b) rolume can be measured. At a concentration of l p.p.m. the accuracy is zt0.2 p.p.m. or 4~20'3 of the aniount present. The detector is also sensitiie to iron carbonjl and can presumably be used for other nietallo-organic vapors and gases, such as tetraeth?llead.
I
?; OXO
and carbonylation reactions using nickel as a catalyst, nickel carbonyl [iYi(CO)4]is generated in the systeni. Because of the extreme toxicity of this compound, its presence in plant atmospheres constitutes a potential health hazard to personnel. I n order to detect such hazardous conditions, an instrument is needed to continuously record nickel carbonyl concentration in the atmosphere. The threshold limit for nickel carbonyl given by the American Conference of Governmental Industrial Hygienists ( 2 ) a t the time this work was being done Kas 1 p,p.m,; this value was superseded in 1954 by H. recommended limit of 0.001 p.p.m. ( 1 ) . A very sensitive instrument is required to measure such small concentrations with any degree of accuracy. Chemical methods of analysis are sufficiently sensitive, but they are time-consuming and give only spot checks of concentration. With the hope of finding an adaptable commercial instrument, several niethods of instrumentation, including infrared spectroscopy, spark spectroscopy, and flame photometry, nere evaluated for nickel carbonyl detection. T o evaluate the infrared spectroscopy method, a commercial infrared gas analyzer was tested. Its limit of detection was approximately 4 p.p.m. by volume. The limit of detection of a laboratory-type spark spectrograph was established as 0.1 p.p.m., but to obtain this sensitivity, a 1-hour exposure of the photographic plate mas required. A flarxe photometer equipped n i t h a multiplier phototube as a radiation detector also had a detection limit of 0.1 p.p.m. The flame photometer, hovever, has tKo distinct disadvantages as a plant instrument. The rate of oxygen consumption (8 cubic feet per hour) makes it expensive to operate continuously, and the open flame makes it dangerous to operate in many plants. It was felt that none of the instruments tested would operate satisfactorily without extensive modification. rl review of some of the basic properties of nickel carbonyl led to the development of a sensitive, stable instrument based on the following three basic principles. 1. When a stream of air containing nickel carbonyl impinges on a hot surface, the nickel carbonyl decomposes, yielding metallic nickel and carbon monoxide. The nickel then reacts a i t h components of the atmosphere to give conipounds of nickel which deposit on the hot surface. I n the absence of carbon monoxide, the rate of decomposition is proportional to the concentration of nickel carbonyl in the air stream (3). 2. For small quantities of deposit, the reflectance of light from 1
the deposit is a measure of the aniount of material deposited. Although the reflectance is not a linear function of the quantity of deposit, it varies directly nith the quantity of deposit as 1or:g as the deposit remains thin. 3. When a collimated beam of light is incident upon the surface of a dielectric a t an angle whose tangent is equal to the refractive index of the dielectric (Brewster's angle), the light is completely polarized by reflection, but a t any angle of incidence other than Brenster's angle, the reflected light is not completely polarized. These three principles are employed in the following manner in the instrument. A stream of air from the plant atmosphere flows through a nozzle and impinges upon a hot borosilicate glass disk. If nickel carbonyl is present in the stream, a deposit f0rm.s on the disk directly below the nozzle. A collimated beam of plane-polarized light is incident upon the disk a t the point where the deposit, if m y , is formed. The angle of incidence of this beam is the Bremterian angle for borosilicate glass, and its plane of polarization is perpendicular to the plane of incidence. This arrangement, which corresponds to the crossing of Sicol prienis, results in extinction, so that no light is reflected from the disk. The refractive index p , and, therefore, the Bren-sterianangle (arc tan p ) , for the deposit is different from that for glass. Thus, the condition of extinction obtains only for the glass, and any light reflected from the surface is due entirely to the deposit. The intensity of the reflected light is nieasured by a recording photomultiplier photometer which is calibrated in parts per million of nickel carbonyl. DESCRIPTION OF IXSTRUMENT
The instrument consists of three principal parts: a mechanical unit, an optical system, and a detector. A photograph of the instrument is shown in Figure 1. Became the instrument described here is an experimental model, no attempt was niade to refine it. Kherever possible, components ccrrrr.on to n-.ost optical laboratories were used. Mechanical Unit. I n the mechanical unit (Figure 2) a borosilicate glass disk, 3.75 inches in diameter and 0.2 inch thick, is sandwiched betlveen two 200-watt Chromolox ring-type electrical heaters which maintain the temperature of the disk a t 350" C. These heaters are enclosed in stainless steel housings and are connected to the line through a Variac autotransformer. The lower heater housing is connected through a Transite insulator to a shaft which is geared to a clock mechanism. The clock rotates the disk one complete revolution in 24 hours. The components of the mechanical unit arc mounted in a water-cooled aluminum housing. The upper compartment of the housing, which encloses the disk, is both light-tight and air-tight. Also enclosed in this compartment is a glass nozzle from which the sample stream flon-s and impinges on the periphery of the disk protruding from betx-een the heater housings. The pressure within the compartment is maintained below atmospheric by means of a water aspirator. The difference in pressure betneen the compartment and the atmosphere causes the sample stream to floa through the nozzle. The sample f l o rate ~ is about 500 cc. per minute. If the sample stream contains any nickel carbonyl, it decomposes upon striking the surface of the hot disk and leaves a solid deposit of nickel compounds on the surface of the disk directly belo\y the nozzle. Because the disk is constantly rotating, the quantity of deposit a t any point on the peri her\ of the disk is a measure of the concentration of nickel car onJl in the sample stream a t the time that point was directly below the nozzle. The disks can be cleaned for re-use hy washing them Kith x i r m G S hydrochloric acid. Optical System. The physical arrangement of optical com-
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Present address, Chambers Works E I. du Pont de Kenlour8 8 CO.,
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881 The light rvliich is reflected from the deposit Falls upon the cathode of the photomultiplier,
the output of which is measured by a vacuum tube voltmeter-recorder combination. The intensity of this reflected light is a function of the quantity of deposit on the disk and is, thus, also a function of the concentration of nickel carbonyl in the sample stream. The recorder is calibrated in parts per million of nickel carbonyl and gives a continuous record oi the concentration of nickel carbonyl in the atmosphere. A microsuiteh can be mounted on the recorder chassis in such a position t h a t it is actuated a t any predetermined concentr& tion of nickel carbonyl. It is thus very easy t o connect an alarm bell which can be made to ring a t a predetermined set point.
n. .--
-Figure 1.
CALIBRATION
Recording nickel carbonyl detector
ponents is show-n in Figure 3. The source of illumination is a General Electric lamp, Type NA-TlOP, operating on 6 volts a t 18 amperes, sup lied by a Sole. constant voltage transformer. The light from t i e lamp is collimated by the first lens, passes through 8. limiting aperture, and is brought to a focus by the second lens. A second aperture, slightly smaller in diameter than the lamp filament, is located a t the focal point of the second lens. This aperture is adjusted so that only the light from the center of the filament asses through it. The light from this aperture is recollimated %y a third lens and passes through a wide band filter having its maximum transmittance a t 5200 A. From the filter, the light passes through an adjustable slit and a Polaroid disk and emerges as a very narrow collimated beam aE plnnepolarized, green light.
Air containing a known concentration of nickel carbonyl far calibrating the instrument is obtained from a multiple dilution system. Carbon monoxide from B cylinder is bubbled through a. test tube of liquid nickel carbonyl which is maintained a t 0" C. by m ice bath. I n bubbling through the liquid, the carbon monoxide becomes s a t u a t e d with nickel carbonyl vapor, so that the concentration, X , of nickel earbonyl in the resulting stream is given hir
X = P X IOn p.p.m. where p is the vilpor pressure of nickel carbonyl a t 0' C. and P in the total pressure of the system. Just after the saturator thcrc is a r&f valve. which consists of a elass tube inserted in a n a t atmosmeans of a sed through 0 to 58 eo. :arbon moncis stream of per minute
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and translation, so that it is possible to direct the beam to a given m i n t on the disk a t a given angle of incidence. The mirror is
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Most of the resulting stream is exhausted into a fume hood, hut
x small part af it is passed through a second siee 08 Flowrator and is mixed with a stream of air from a size 2L Flowrator. The ~~~~~~~~~~
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any particular direition is negligible. Light will, however, be reHected by the deposit, since its Brewsterian angle is different from t h a t of borosilicate glass. The light reflected by the deposit is measured by the detector unit. Detector. The detector unit consists of a Photovolt line-operated photomultiplier photometer Model 520-M, operating into a Brawn Electronik strip chart recorder.
air stream is held constant a t 25,000 ce. per minute by a sec?nd Moore How controller. Most of the resulting stream is again exhausted to the hood; only 500 cc. per minute is fed to theinBtrument n o d e as calibrating gas. The How rates through the two siae 08 Flowrators m e manuslly rontrolled by means of glass stopcocks. These flow rates de-
882
ANALYTICAL CHEMISTRY
terniine the two dilution ratios and, thus, the concentration of nickel carbon>-lin the calibrating gas. The final concentration, X,is given by
n-here p
=
P = F1 = F2 = Fa = I.'? =
vapor pressure of nickel carbonyl a t 0" C . atmospheric pressure f l o rate ~ through first 08 Flonrat,or f l o rate ~ through 01 Flowator flox rate through second 08 Flonrator flow rate through 2L Flowator
The vapor pressure, p , of nickel carbonyl a t 0" C. is 134 nini., and F, and F , are held constant a t 10,000 cc. per niinute and 23,000 cc. per minute, respectively. If atmospheric pressure, P , is take:i as 760 mm., the eqiintion rednws to
-Y = 0.000iOS F,F:j p.p.m. Carbon monoxide is used in the bubbler and for the first dilution to prevent premature deconiposition of the nickel carbonyl. Air is used for the second dilution to promote oxidation of the deposit on the hot disk. S o evidence of decomposition of nickel carbonyl in any part of the system except on the hot disk was found. DISCUSSIOS
From the basic principlea of operation, it is seen that the mininiiini concentration of nickel carbonyl that the instrunient can detect depends upon the qu;tritity of deposit that is allowed to build up on the surface of the disk. This, in turn, depends upon the rate of sample flow aiitl npon the rate of rotation of the
disk. Large saniplr floir P, hon e w r , tend to cool the surface and decrease the deposition efhieiicy, so that for given values of temperature and rate of rotation, there exists an optimum rate of f l o ~ . The optimum rate Eo1 the iristrunient described in this paper was found to be about 500 cc. per n-incite. At this flow rate, the instrument gives full-sc ale deflection a t a concentratioii of approximately 4 p.p.m. The sensitivity of the instrunLent can be increased appreciably by altering the position of the light beam mith respect to the nozzle so that a greater quantitv of material is deposited a t a given point before the reflectance at that point is measured. This, however, introduces a longer t h e lag beta een deposition and measurement. K i t h a &minute time lag (which was not considered excessive) the instrument registered a deflection of 1yc of full scale for 0.2 p.p.m. A time lag of 10 minutes results in 1% of full-scale deflection for 0.05 p.p.ni. The instrument is capable of even greater sensitivity because, with the particular nozzle which was used, the time of deposition a t any point on the periphery of the disk is approximately 40 minutes. Although the instrument described in this paper n as designed for the detection of nickel carbonjl, it is also sensitive to iron carbonyl and should be easily adapted to the detection of tetraethyllead and other metallo-organic gases and vapors. LITERATURE CITED (1) Arch. I n d . H u g . and Occupational M e d . 9, 531 (1954). (2) Chem. Processing (;lrnerican Conference of Governmental Indus-
trial Hygienists) 15, 134 (1952). (3) Garratt, A. P., Thompson, H. K., J . Chem. SOC.(Lo7ldon) 1934, 1824. R E C E I V Efor D review 11s. 2 6 , 19.53. Accepted .Ianiiar~-28, 1956.
Indicator for Titration of Calcium in Presence of Magnesium Using Disodium Dihydrogen Ethylenediamine Tet raacetate HARVEY DIEHL and JOHN L. ELLINGBOE Department
of Chemistry, lowa State College, Ames, lowa
A new indicator, designated calcein, has been prepared for the titration of calcium in the presence of magnesium with disodium clihydrogen ethylenediamine tetraacetate. No preliminary treatment is necessary be>ond dissolving the sample and adjusting the pH to a value of 12. Excessisel3 large amounts of sodium and magnesium cause the results for calciuttl to be slightly low. Interference 1)) copper and iron is obTiated by the addition of c! ankle.
A
SE\T- i.itlicatoi for the titration of calcium with disodium dihydrogen ethylenediamine tetraacetate [the disodium salt of (ethj-1enedinitrilo)tetraacetic acid] in the presence of magnesium has been prepared by condensing irninodiacetic acid w t h fluorescein. This is a procedure analogous to that employed by Schwarzenbach and others for the preparation of the so-called metal phthaleins (4). In highly alkaline solution the indicator is brown and its calciuni complex is a yellow-green. At lower pH values the free indicator is also yellow-green. Magnesium does not form a complex with the indicator. The indicator may be used for the determination of calcium in water, limestone, or other calcium compounds. I t has been given the trivial name calcein. I n the analysis of limestone or water, the total calcium and
niagtiesiuni can be deterinilied by using disodium dihydrogen ethylenediamine tetraacetate as the titrant with Eriochronie Black T as the indicator (1-3). Either the calcium or magnesium must then be determined separately and the other calculated by difference. AIagnesium cannot be determined in the presence of calcium because the formation constant of the calcium complex of ethylenediamine tetraacetate is two orders of magnitude greater than that of the magnesiwn complex. T o determine calcium directly using disodium dihydrogen et,hylenediamine tetraacetate as the titrant, the pH is niade siifficiently high so that the magnesium is largely precipitated as the hydroxide and an indicator is used which combines with calcium only. Murexide is such an indicator ( 5 , 6), but the end point with it is rather indefinite and is made worse by increasing amounts of magnesium. A sharper end point is obtained with calcein than with niurexide, and larger quantities of magnesium may be present without impairing the end point. The niagnesium may exceed the calcium by a factor of 20 to 30 without interference. Large amounts of sodium salts-2 t o 3 granis of sodium chloride, for exanipledo not affect the titration. Strontium and barium interfere and are titrated along with calcium; the end point with either alone is the same as that with calcium. Copper and iron interfere with the end point, but such interference is easily obviated by the addition of cyanide. The titration of calcium may be performed in the presence of chloride, nitrate, acetate. and sulfate.
