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Anal. Chem. 1984, 56, 1629-1632
Portable Chemiluminescence Detector for Nickel Carbonyl David A. Hikade'
Department of Chemistry, The University of Michigan, Ann Arbor, Michigan 48109 Donald H. Stedman2*
Departments of Chemistry and Atmospheric and Oceanic Science, The University of Michigan, Ann Arbor, Michigan 48109 James G.Walega2
Space Physics Research Laboratory, The University of Michigan, Ann Arbor, Michigan 48109
This article descrlbes a portable chemllumlnescent detector for Ni(C0)4 contalnlng two Innovative components, a selfcontained carbon monoxide source which provides a greater degree of portability and a thermal dlfferentiator to Improve selectivlty. The Instrument is capable of measuring partsper-billlon levels of Ni(CO),, Fe(CO),, and NO. The instrument was used to measure carbonyl concentrations in the fleld and in Cigarette smoke.
Nickel carbonyl is used as an industrial catalyst in reactions such as carbonylation, cyclization, dehalogenation, clathration, and polymerization (I), it also plays an important role in the Mond process of nickel refining (2) and has been applied in nickel plating operations (3). Since the discovery of this carbonyl in 1890 (4), over 350 cases of gaseous Ni(C0)4 poisoning have been reported with more than 20 fatalities (2). It is not known whether chronic inhalation of low levels of this species may cause cancer in man (51, however, that has been suggested based on animal studies (2,6). In addition, the teratogenic capability of Ni(C0I4 has been demonstrated (7). To help prevent exposure of industrial workers to this dangerous substance, in 1959 the American Conference of Governmental Industrial Hygienists (ACGIH) set a threshold limit value (TLV) of 1 ppb (part per billion by volume) (8), one of the lowest values established for an industrial compound. Recent studies (9) indicate that this species may not be carcinogenic to man; because of this the ACGIH raised the TLV to 50 ppb (8). Ni(C0)4and Fe(CO)6form under relatively mild conditions, at least from a thermodynamic viewpoint (9,lO). This implies that the presence of both species is not limited to industrial situations, but that they may be found where CO comes into contact with metallic nickel or iron (e.g., incomplete combustion). It is possible that even a widely available and used consumer item such as a cigarette (in so far as it contains both metals in its composition) could be a potential source of these metal carbonyls. Nickel levels in a cigarette have been found to range from 1.59 to 2.1 pg (11). Earlier studies demonstrated that 10 to 20% of this nickel is released into the mainstream smoke with over 80% being present in the gas phase (12). One researcher found that passing CO at low temperatures (20-100 "C) through tobacco removed much of the nickel present. This observation, combined with others (13), lends credence to the Current address: Owens Corning Fiberglas Technical Center, Granville, OH 43023. Current address: Department of Chemistry, University of Denver, Denver, CO 80208. 0003-2700/84/0356-1629$01.50/0
hypothesis that Ni(C0)4and Fe(C0)5are present in cigarette smoke. If true, this could have important implications in regard to cigarette smoking, although as yet there has been no definite proof that these metal carbonyls are present in cigarette smoke. As well as the apparently toxic nature of the metal carbonyls themselves, there is evidence which indicates that Ni(C0)4 may block the induction of pulmonary benzopyrene hydroxylase (14). This enzyme detoxifies the 3,4-benzopyrene which is a suspected carcinogen present in cigarette smoke. A number of analytical techniques have been applied to gaseous Ni(C0)4 and Fe(CO)6 detection within the past 30 years. Methods such as spectrophotometry (9), atomic absorption (15),chromatography (2), polarography (16), UV absorbance (17), and mass spectrometry (18)have been used; however, each technique lacks one or more of the qualities which are desirable in a portable system, namely, good sensitivity, selectivity, monitoring capability, portability, and reasonable price. Possibly the best technique which has been developed for Ni(C0I4 analysis is infrared spectrometry, the method employed in monitors by some Mond refineries (19). This technique was found to be rapid, specific, free from interferences, and accurate to within 10%. Use of multiplereflection long path absorbance cells combined with Fourier transform spectrophotometer systems permits measurement of gaseous nickel carbonyl levels down to 0.01 ppb; however, such systems are quite costly and not easily used in the field. Chemiluminescence. Chemiluminescence is the only analytical technique which has been developed within the last 12 years that has come close to satisfying all the requirements for an all purpose carbonyl detector. In this method, light emission occurs as a result of the chemical reaction between the metal carbonyl and ozone in the presence of CO. This was first observed by Morris and Niki (20) who proposed the following mechanism for Ni(C0I4 chemiluminescence:
NiO
-
Ni NiO*
--
+ O3
Ni(CO),
+ CO
+ O3 NiO
NiO
+ products
+ COz NiO* + O2
+ hu
Ni
(460-750 nm)
Fe(C0I5 was found to chemiluminesce under similar conditions, generating FeO* which emits photons of wavelengths between 560 and 680 nm. A third species, NO, was also found to chemiluminesce under the same conditions (although CO has no effect on intensity), with resulting photons emitted at wavelengths greater than 600 nm. It is therefore apparent that any chemiluminescent Ni(CO)* detector will also have some sensitivity to both Fe(C0I5 and NO, depending on specific equipment and conditions. These are the only species
8 1984 American Chemical Soclety
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ANALYTICAL CHEMISTRY, VOL. 56. NO. 9. AUGUST 1984
Table I. Calculated Thermodynamic Equilibrium Constant for the Production of Carbon Monoxide temp, k
298 800
900 1000
kp, atm
1.4
X
2.0 x 10-2
1.8 1.7
X X
lo-'
temp, k
k,, stm
1100 1200 1300
1.1 x 10' 5.2 X 10' 1.9 X lo2
loo
known to he detected with such a n instrument (21). Since the above phenomena were first observed, a number of chemiluminescent Ni(CO), detectors have been constructed, moatly by modifying existing NO detectors (21-23). For instance, in order to make a chemiluminescent Ni(CO), detector based upon a Columbia Scientific Instrument (CSI) Model 1600 NO, monitor, two modifications were required. These were to dry the sample because high water vapor content decreases the response to metal carbonyls (21) and to provide the carhon monoxide to induce the enhanced carbonyl response. The sample air was pmed through a permeation drier to remove water vapor. Pure carbon monoxide from a technical grade CO cylinder was passed through an I,/charcoal filter to remove any metal carbonyls present in the gas (24) and then added at the NO, modulation valve in the original CSI detector. This instrument had excellent sensitivity with a detection limit below 1ppb; moreover, the device was very stable and could he used as an area monitor with a response time of 1 min. Use of a modulated CO flow and measurement of the modulated signal removed any interference from NO that may have been simultaneously present (21). Also, by placing an interference filter between the reaction chamber and photomultiplier tube, this instrument could he made specific to either Ni(CO), or Fe(CO),. Unfortunately, with a weight of almost 40 kg for the basic instrument (excluding cylinders, regulators, and sample drier), this device was hy no means portable. In regard to cost, the total system was constructed for under $10000, a definite improvement over the earlier techniques. Although the instrument proved to he an excellent device under laboratory conditions, its lack of portability prevented its use in the field. It became apparent that a new instrument was required which would he more portable and yet maintain or improve upon the other characteristics. Besides size and weight, another factor which limited its transportability was the requirement of pressurized cylinders, which, in the case of CO, was also a safety and legal liability.
EXPERIMENTAL SECTION CO Source and Killer. The approach taken to provide a
self-contained CO source was to pass air over activated charcoal maintained at high temperature. The CO producing mechanism consists of the following steps: C(S) + OPC3)
-
CO,(g) + C(s)
CO,(g)
(1)
2CO(g)
(2)
Thermodynamic data were used to determine the operating temperature that would he required. The equilibrium constant for the above reactions
was calculated for various temperatures as listed in Table I. Assuming that the kinetics are fast at high temperatures, it was concluded that a significant production of CO required temperatures approaching 1000 "C. This conclusion was supported experimentally, A CO source, illustrated in Figure 1,was designed. This source eonsisted of a 4 in. length of 1 in. id. stainless steel tubing to which side arms, bottom, center baffle, and a removable top (to refill
Flgu~e1. Cutaway diagram of the thermal CO source and CO removal system. Dry air passing inside the Stainless steel reactor is forced through a bed of hot charcoal at the bottom. Pump exhaust is passed through the outer coil over an oxidation catalyst lor CO removal.
with charcoal) were added. The tube was filled with 6 g of activated charcoal. A heating tape wrapped around the tube heated the source to approximately 900 "C (upper limit of the tape). The temperature is monitored by a thermocouple and controlled electronically, When operating, dried ambient air flows down the charcoal on one side, passes under the center baffle, and up the other side. Prior to entering the reaction chamber, the CO/CO,/air mixture flows through a carbonyl filter (I,/charcoal) to remove the significant amount of metal carbonyls formed as side products within the steel CO source. Without such fdtering, a large carbonyl signal was observed. Once warmed up (90min), the CO source provides over 20% CO corresponding to a formation efficiency of almost 7%.
Incorporated in the CO source design is a CO removal system for treating the CO rich but highly oxygenated pump exhaust. This is accomplished by passing the pump exhaust through copper tubing which is coiled around the CO source (see Figure 1). The tubing contains CO oxidation catalyst (Pt on AI,O,) which is heated indirectly by the heating of the source to a temperature of 250 OC. A t this temperature, CO oxidation to CO, is >99% efficient. Thermal Differentiator. The two methods used in the past to eliminate NO and Fe(CO), interferences to the Ni(CO), measurement were optical filtering and CO modulation (21). This unit uses their relatively different thermal stabilities for species differentiation. By h e a t i i the sample inlet line to the appropriate temperature, we can remove signals due to one or both carbonyls in air. The Ni(COI4 signal was found to he completely eradicated at temperatures >120 OC, even in the presence of CO concentrations >loo0 ppm. Similarly, the Fe(CO), signal becomes negligible at temperatures >240 "C. Under the same sampling conditions, the NO signal remains stable at temperatures in excess of 300 "C. The thermal differentiator built into the portable instrument in. diameter stainless steel consists of a 4-in. length of coiled 'Ig tube surrounded by heating tape. Temperatures are regulated by a thermal probe and electronic temperature controller. A three-position switch allows the differentiatorto he set at ambient temperature where all three species are measured, at 120 "C where only Fe(CO), and NO are detected, and at 240 "C where only NO is measured. A bypass valve is included to allow signals at ambient
ANALYTICAL CHEMISTRY, VOL. 56, NO. 9, AUGUST 1984
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Table 11. Results of Cigarette Studies Using a Portable Carbonyl Detector brand
I
II
. TWLhYAL UILLER
Marlboro Filter Marlboro Filter Marlboro Filter Camel Filter Camel Filter Camel Filter Winston Filter Winston Long Pall Mall Regular
amt,d ppb Ni(CO)* Fe(CO)b 22.0 27.5 0.7 4.0
3.9 15.4 40.0
5.9 9.8
NA NA NA 5.0 NA NA ND 4.0
NA
Relative uncertainty is approximately *50%. NA, not analyzed. ND, not detected. Detection limit
