Quantitative Determination of Asbestos Fiber Concentrations D. R. Beaman* and D. M. File’ The Dow Chemical Company, Midland, Mich. 48640
By using a transmission electron rnlcroscope equipped with selected area electron dlffraction (SAED) and energy dispersive spectrometry capabilltles, it is possible to resolve many of the ambiguities that lead to incorrect fiber concentrations when the determination Is based only on morphoiogy or crystal structure or elemental composltion. It was found that 40-100% of the chrysotile fibers in water samples have distinctive tubular morphology. ldentiflabie SAED patterns were observed for about 30 and 60% of the chrysotlle and amphibole flbers, respectively, in pure standards. The losses occurring during sample preparation In a condensation washer were confirmed, quantified, found to be variable and to average about 50% for amphibole fibers and 10% for chrysotile fibers. By applylng corrections for SAED ambigulties and losses during sample preparation and by maklng allowances for the dependence of fiber composltlon on fiber 8128, It was possible to measure asbestos flber concentrations with a precision of f30%. A classlficatlon scheme was developed to establlsh maximum and minimum limits of flber concentration for each sample.
The presence of asbestos fibers in air, water, and food grade materials has become a subject of health and envir o n m e n t a l concern (1-3). While the hazards of prolonged asbestos inhalation have been well established (4),there does not yet appear to be a clear answer concerning the toxicity of ingested asbestos (4-6).T h i s report describes a method of measuring the concentration of asbestos fibers i n filterable liquids and solid matrices. The total asbestos mass in such samples is low because the fibers have small diameters (0.034-0.7 y) and the mean aspect ratio (length/ diameter) is usually less than 300. Consequently, high magnification electron microscopic techniques, which are both sensitive and selective, have evolved as the most appropriate method for determining the concentrations of small fibers i n liquids (7-14). The accuracy and precision of the microscopic techniques are affected b y the ambiguities that arise in fiber identification i n samples containing interfering nonfibrous material and non-asbestiform fibers and by the large multiplying factors used in converting microscopic data to concentrations. To reduce the ambiguities and improve the reliability of the analysis, we have used a method i n which fiber identification is based on the nearly simultaneous determination of three characteristicsnamely, morphology, elemental composition, and crystal structure. This is possible i n a transmission electron microscope ( T E M ) equipped with selected area electron diffraction (SAED) and an energy dispersive spectrometer (EDS).
EXPERIMENTAL Sample Preparation. All the water samples were prepared by vacuum filtration through 0.22-p Millipore cellulosic ester filters followed by solvent extraction of a dry filter section positioned on a carbon film on a T E M grid. The filtration was designed to retain over 99.99% of the chrysotile which has the smallest fibril diameter of the asbestiform minerals. Agitation just prior to filtration is necessary to prevent settling and promote suspension homogeneity.
Present address, Cameca Instruments, Inc., Elmsford, N.Y.
Detergent is used in samples when the fibers tend to be clumped with nonfibrous debris such as clay. After filtration, the filter is dried and 3-mm diameter circular sections are cut and placed (sample side down) on TEM grids covered with carbon-coated Formvar films. The grids are 200 mesh Maxtaform Cu. (The grids and condensation washer are available from Ernest F. Fullam, Inc., P.O. Box 444, Schenectady, N.Y. 12301.) This relatively thin grid with a carbon coating provided minimum film breakage in the washers, reduced geometrical problems, and allowed EDS work over a larger portion of each grid square than possible with standard Cu or nylon grids. The grids and filter are placed on the Ni support screen attached to the cold finger in a condensation washer ( 1 5 ) . The power to the heater is adjusted so that condensation of the solvent (acetone) occurs in the reflux column somewhere between the height of the grid and 3 mm above the grid. If the condensation level is lower, inadequate washing results while, if higher, excessive losses and nonuniform washing occur. After washing for about 1hr, the grid is ready for T E M examination. The filter was also extracted without condensation in a Jaffe washer (16) using tetrahydrofuran (THF). The T H F level is brought to just beneath the grid and replenished a t least once every hour. The duration of washing (-11 hr) in the Jaffe technique is a delicate balance between too little time, in which case filter material remains, and too much time, in which case extensive film breakage and folding occurs. The Jaffe method produces a sample with less wash-off and fiber loss than the condensation washer, but the sample is not easily counted in the TEM primarily because of retained millipore and folding of the carbon film. The low Jaffe losses are presumably due to the more gentle wash action provided by a predominantly capillary extraction in T H F as opposed to the condensation washing. In a modification of this procedure, called the Jaffe wick method, the solvent level is maintained at half the height of the screen and the solvent is transported to the screen level by filter paper. The extraction is carried out in a small ground-glass sealed bottle and requires much longer times (60-90 hr) to dissolve the filter. Ashing has not been used routinely in water analyses because the amount of organic material has generally been low and, thus, did not constitute a sufficiently serious problem to warrant the additional step. In addition, after ashing, the fibers tend to be clumped in the remnants of the ash making counting, EDS and SAED, difficult. The clumping can be diminished by ultrasonic treatment which increases the fraction of smaller fibers and the apparent fiber concentration. Kramer and Mudroch (14) found that ashing degrades fibers. It is imperative that no step in the preparation procedure alter the fiber length, diameter, elemental composition, or structure if the size distribution and fiber concentrations are to be representative of the as-received sample. Stanton ( 6 ) has indicated that fiber dimensions may be the single most important factor in determining fiber toxicity. Ultrasonification, centrifugation, grinding, ashing, or any chemical treatment should be avoided unless it can be shown that the treatment does not degrade the fibers. Insoluble solids are ashed in a plasma a t an oxygen pressure of about 10 Torr and a temperature of 100-120 OC, for 72 hr with an intermediate stirring after 36 hr. The ash is suspended in water, treated ultrasonically for 10-20 min, filtered, and subjected to filter extraction. Fifty percent caustic soda samples are initially diluted in filtered water by a factor of 50-100 and then slowly neutralized with 1 N HC1. Just before filtration is completed, an additional 500 ml of water is added to remove any NaCl that would precipitate in the filter during drying. A low magnification (200X) examination of the grid is advisable to ascertain if optimum loading and particulate distribution have been achieved and all filter material removed. Instrumentation. The transmission electron microscope was selected as the basic instrument rather than the scanning electron microscope (SEM) because of its superior imaging capabilities and suitability for searching a t 20000X and because of its excellent selected area electron diffraction (SAED) capabilities. The image in ANALYTICAL CHEMISTRY, VOL. 48, NO. 1, JANUARY 1976
101
C. Chrysotile
A. Chrysotile
7 2 0 Seconds
6 Chrysotile
7 2 0 Seconds
I.-nT..”-
d
=
340 A, D = 100 A, STEM
d = 340 A,
rw-
V r r l i l
D = 400 A, STEM
E. Cummingtonite D. Grunerite
300 Seconds
d = 340 A. D = 3000 A. TEM
F. Fayalite
120 Seconds
720 Seconds
~ d = 0 . 3 ~D . = 1700 A, TEM
d = lp, D = .5p, TEM
d = . 5 ~D , = .5p, TEM
Figure 1. Energy dispersive spectrometer (EDS) spectra for various fibers and instrumental conditions All the spectra were acquired in TEMs operated at 80 kV in the scanning TEM (STEM) or TEM mode. A, B. D. and E are fibers in potable water. Cis in NaOH. and F is a standard. The fiber type and count time are indicated above each spectrum. d is the liber diameter and D is the beam diameter. The peaks and indicated BnergieSinkeVareMgat1.25.Siat 1.74,Caat3.7.Crat5.4.Mnat5.9.Feat6.4,andCuat8.0
the TEM is not distorted by sample movement as is the acquired scanning image in the SEM. Video scan rates may be used to alleviate this problem with an accompanying loss of image quality. The tendency to lose focus with sample movement is minimized by the eucentric goniometer stage of the TEM. The excellent brightness and contrast in the TEM are easily obtained, require only simple adjustment for photographic documentation, and make the detection of the smallest fibers relatively straightforward. The concentration of asbestos in a talc sample was 500 times higher when measured with a TEM than when measured with an SEM (7). The field of view is usually larger (2-3X) in the TEM. All of these factors lead to overall ease of operation, accurate morphological identification, and nonfatiguing analysis. When using the criterion that a fiber is any particle with an aspect ratio greater than three, asbestos morphology is somewhat distinctive, but not always sufficiently so to allow nanambiguous morphological distinction hetween asbestos fibers and other materials such as: diatoms, diatom fragments, oxides (Fe, Ti, and Si are common), clays, ”on-asbestifom silicates (mica and talc fragments, ete.), metal fragments, fiber glass, synthetic fibers, cellulose, chlorides, carbonates, sulfates, bacteria, plant fragments, and other organic debris. Morphology can be degraded by overlying films and adjacent nonfibrous debris. Some investigators (8, 17) have used the distinctive tubular 01-hollow core appearance to count chrysotile, but we have found this to be an unreliable criterion because the fraction of chrysotile fibers with such an appearance varies, depending upon the chemical and thermal history of the sample. In the ease of amphiboles, the morphological ambiguities aye even more numerous, particularly when the fiber diameter approaches the ultimate fibril diameter (0.06-0.2 p). In the samples studied herein, the asbestos fiber content ranged from 0 to 100%of the total fiber content and therein arises the need far ancillary methods of identification. Because the amphibole and serpentine minerals are crystalline and have distinctive SAED patterns, an analyst can often do an admirable job of visually distinguishing between amphibole, nonamphibole, and serpentine patterns in the TEM. There me dif102
ANALYTICAL CHEMISTRY, VOL. 48, NO. 1, JANUARY 1976
ficulties, however, that lead to low measured fiber concentrations when the determination is based on SAED only. The quality of a SAED pattern depends on the fiber diameter and is degraded by adjacent materials. The SAED pattern from chrysotile, which is streaked in alternate layer lines and sharpest in the odd lines (18), is rare enough in materials of this d-spacing to be of general use in identification. However, the extent to which SAED can be used to identify chrysotile depends on the size of the fiber and the extent of thermal, chemical, and mechanical treatment. Because of these problems and the fact that the electron diffraction patterns of the various amphiboles are not readily distinguished from one another, electron diffraction data should be used in conjunction with morphological and chemical information, Energy dispersive spectrometers (EDS) can simultaneously detect x-ray photons from all elements with atomic numbers above ten (19)and can he easily adapted to most TEM’s (20) With an EDS on the TEM, we have been able to easily measure elemental intensities from fibers considerably smaller in diameter than the electron beam (Figure 1).The EDS is not a padacea and does introduce complexities that can lead to misinterpretation. In any particular TEM-EDS combination, the areas of the grid that will provide unhindered elemental data depend on the grid orientation in the sample holder, the angle of tilt, and the type of grid used. Absorption of x radiation by the grid must be avoided, because it can yield misleading results through differential absorption. Secondary x radiation generated in the vicinity of the sample by backscattered electrons and primary x rays is detected hy the EDS because it is not a focusing spectrometer and is, therefore, insensitive to the location of the source of x-ray generation (19).T o minimize such effects, the anti-contamination cold plate was either drilled out and fitted with a carbon liner or coated with a dag dispersion while the sample holder was equipped with a beryllium or carbon insert and the detector was collimated. The high energy backscattered electrons can penetrate the Be window, but lose sufficient energy in the process to not be a problem in the detection of energies above 1keV. In our experimental configuration with the beam restricted to clean, particle-free regions at least one field of view
0
0
2
m
2 d
8 +I
+I
+I
+I
+I
+I
p
s
Y
0
0
0
i
i
j
o
0
Y
ANALYTICAL CHEMISTRY, VOL. 48, NO. 1, JANUARY 1976
103
4
0 0
Y
>~ (p/p)&eral, ANALYTICAL CHEMISTRY, VOL. 48, NO. 1, JANUARY 1976
105
I,/Isi is expected with decreasing size because the relative increase in emission will be greater for the element with the larger absorption coefficient. Thus, in grunerite the reduced absorption path length leads to a greater relative increase in Si emission ((w/p)i:unerite = 1455) than in Fe emission ((p/p)F&nerite= 65) and a subsequent 25% decrease in the Fe/Si intensity ratio as the size decreases from 1.5 to 0.15 w. The magnitude of this effect decreases as the amount of Fe decreases because the Si concentration is similar (20-27%) in the minerals examined. The ratio of the intensity ratio (IX/Isi)lat one fiber radius ( r l ) to that at another fiber radius ( r z ) is given by exp ~ [ ( ( d ~ )-k(w/p)%%) i ~ ~ ~ ~ (rz ~ - rdl. When (,u/p)&,,,,i 3) according t o the following scheme: Indeterminant fibers are those fibers that cannot be classified because of their location on the grid or the presence of interfering material. Non-asbestiform fibers include the following: a) fibers with non-amphibole or non-serpentine SAED patterns, b) amorphous fibers and fibers with ill-defined SAED patterns whose intensity ratios differ from the standards, and c) fibers with nonasbestiform morphology such as distinctive diatoms. Ambiguous fibers have indistinct SAED patterns, but intensity ratios within the data scatter range of the standards. Positive fibers include: a) those with amphibole or serpentine SAED patterns and intensity ratios and b) those with chrysotile elemental composition and morphology regardless of the quality of the SAED pattern. Each ambiguous and positive fiber is classified as a particular mineral on the basis of its elemental intensity ratios. The fiber concentration corresponding to positively identified fibers represents the minimum value while the sum of the positive and ambiguous categories represents the maximum possible concentration. The number of fibers per liter, F1, is given by filter 1000 (1) Fi = c0s8 where n = number of fibers counted in z fields; z = number of fields of view examined in finding n fibers; dgrid = diameter of the filter section; dfieid = diameter of a field displayed on the viewing screen; dfiIter= diameter of the used portion of the filter; and 8 = sample tilt, Le., = the angle between the horizontal and the sample surface. With the sample tilted to permit x-ray analysis, a larger area on the specimen grid is included in each field of view relative to Oo tilt. The number of fields of view per specimen grid is the projected elliptical area of the TEM specimen grid divided by the area of a field of view, i.e., (?r/4)(dgriddgrid cos 8)/(*/4)(dfield)* where dgridcos 8 is the smaller elliptical axis. In chrysotile containing samples when the fibers are present as fibrils the mass per liter can be calculated from F I and the mean fiber length, 1. Where 1 is in microns and Fl is in millions of fibers per liter, the mass in micrograms per liter is 0.00231 FI,assuming a density of 2.55 g/cm3 for chrysotile and a fibril diameter of 340 A. Because the projected fiber lengths are measured with the_ sample in the tilted configuration, the calculated mean length, 1, is less than the true mean, 1. In the case of a random fiber orientation (all doc angles equally probable) 1/1 = (2/s)J;’* (1 - sin’ 8 sin2 where a is the angle the fiber makes with the z axis and 8 is_thetilt angle (16). Evalgation of the elliptic integral gives 1 = 1.07 1 at 8 = 30° and 1 = 1.121 a t 8 = 39O, the two tilt angles used in this report. If g is the mass in grams of dissolved solid, the number of fibers per gram, F,, is given by
(3(k) (A
I : ( (k) filter
Fg
=
cos
(2)
In analyzing 50% caustic solutions, F I is the number of fibers per liter of 50% caustic when u is the volume of 50% caustic filtered in ml. The number of fibers per gram of NaOH, F g . ~is a ~ ~ (3)
106
ANALYTICAL CHEMISTRY, VOL. 48, NO. 1, JANUARY 1976
RESULTS AND DISCUSSION Examination of the filtrate in the condensation washer revealed t h a t some fiber loss was occurring during sample preparation. A 0.01-ml water droplet containing amphibole fibers was placed o n t h e TEM grid a n d evaporated t o dryness in a protected environment. While this m e t h o d of sample preparation is appealing because t h e r e appears t o b e little possibility of loss, there are some serious disadvantages. Surface tension leads t o segregation during drying a n d subsequent nonuniform fiber distributions. T h e r e is a tendency t o concentrate the solids at t h e periphery of t h e drop, a n d t h e fibers are often found clumped with nonfibrous debris a t grid bar intersections where i t m a y n o t b e possible t o obtain good EDS spectra. Another problem is t h a t t h e volume 1.) is so small that inhomogeneities within t h e sample might become detectable. Notwithstanding these uncertainties, a comparison was m a d e with condensation washed samples a n d t h e calculated losses, assuming n o loss in t h e air dried sample, ranged from 0-98% a n d averaged 43% (43 f 38) for amphibole-containing s a m ples. Atomic absorption measurements of t h e M g and/or Na concentration present o n washed grids were used t o determine losses. Filters were prepared using particulate loadings 50-1OOX higher t h a n those normally required for successful fiber counting in order t o provide sufficient Mg a n d N a so t h a t t h e precision a n d detectability of t h e atomic a b sorption analysis would n o t b e a n i m p o r t a n t factor. T h r e e filter sections were prepared a n d washed in t h e washer with a blank. Two-millimeter diameter plugs were used t o avoid contributions from t h e rim of t h e grid, where high losses may occur. Only washed grids without film breakage were analyzed by atomic absorption. T h e loss was determined by comparing t h e M g and/or N a concentration for washed grids with t h a t of unwashed grids after applying blank corrections. T h e s e experiments revealed t h e following: 1) The amphibole loss in t h e condensation washer was variable ranging from 37 t o 60%, t h e m e a n of eight different loss determinations being 45% (45 f 8). 2) T h e chrysotile loss ranged from 0 t o 21%, t h e mean of 11 different loss determinations being 11% (11 f 6). 3) T h e loss measured with the Jaffe liquid method was consistently low (5 p ) . The mean fiber diameters for the amphibole and chrysotile samples were 0.3 and 0.034 p , respectively. In a series of 7 water samples of relatively low chrysotile concentration (1-60 MFL) between 40 and 100% (mean of 70%) of the fibers identified as chrysotile had a distinctive tubular appearance. On the other hand, between 10 and 60% (mean of 35%) of the fibers with a possible tubular appearance were not chrysotile but diatom fragments or fully leached chrysotile, etc. Table 111 indicates that the fraction
50
$
{c 30
-
CI Cell Liquor I567 Fibers)
c
6 E
20
-
;1 0 -
L
L
0
8
0
0 0
I
.1
I
I
1
1
.5
1
3 6 11 Size Range In Microns
17
23
34
78
Figure 7. The distribution of fiber lengths in CI cell liquor, filtered CI cell liquor, and Duluth tap water are shown. The histograms are composites of 6 samples of each type
of fibers that are actually asbestiform varies widely between different sample types and even within a specific sample category, e.g., in 50% caustic, 3 to 99% of the fibers were chrysotile while 19-8296 of the fibers in Duluth tap water were amphibole. Chlorine cell effluent is a nearly pure population with about 97% (97 f 3) of the fibers identified as chrysotile. These data illustrate the difficulties associated with a determination based on morphology only. The distributions of fiber lengths are plotted for chlorine cell liquor, filtered chlorine cell liquor, and Duluth tap water in Figure 7. The histograms represent composites of 6 different samples for each sample type. After filtration of chlorine cell liquor, about 90% of the fibers have lengths less than 3 p. The filtration removes over 70% of the fibers with lengths greater than 1 p. The fibers associated with caustic production are predominantly single chrysotile fibrils with diameters between 300 and 400 A. About 90% of the fibers in Duluth tap water have lengths less than 3 p , while about 90% have diameters less than 1 p and about 60% have diameters less than 0.4 p.
ACKNOWLEDGMENT The authors are indebted to T. A. Hiller and C. G. Mendoza of The Dow Chemical Company for performing the atomic absorption measurements. C. R. Knowles of the University of Idaho provided essential information concerning the mineralogy of the asbestos problem. We appreciate the critical review of the manuscript by G. H. Korfhage, H. T. Lutzac, R. J. Moolenaar, V. A. Stenger, P. A. Traylor, and F. P. van Remoortere of The Dow Chemical
ANALYTICAL CHEMISTRY, VOL. 48, NO. 1, JANUARY 1976
109
Company, and C. R. Knowles. We gratefully acknowledge permission to use data obtained for P. M. Cook of the National Water Quality Laboratory, Duluth, Minn. The work could not have been completed without the expert and tireless assistance of the following from The Dow Chemical Company who helped with the fiber counting: R. E. Cook, J. W. Edmonds, C. W. Kocher, D. L. Miller, C. K. Niemi, L. A. Settlemeyer, and H. J. Walker.
LITERATURE CITED (1) (2) (3) (4)
A. M. Langer and I. J. Selikoff, Arch. Environ. Health, 22, 348 (1971). H. M. Cunningham and R. Pontefract, Neture (London), 232, 232 (1971). Can. Res. Develop., 7 (6), 19-36 (1974). E. C. Hammond and H. Seidman, lnsul. Hyg., Progr. Rep., 8, No. 3, 1974. (5)P. Gross, R. A. Harley, L. M. Swinburne, J. M. G. Davis, and W. B. Greene, Arch. Environ. Health, 20 341 (1974). (6)M. F. Stanton, J. Natl. Cancerlnst., 52, 633 (1974). (7) W. C. McCrone and i. M. Stewart, Am. Lab., 1074, (4), 13. (8) G. H. Kay, Water Pollut. Control, 3 (5),33 (1973). (9) F. D. Pooiey, Brit. J. lnd. Med., 20, 146 (1972). (10) E. J. Chatfield and H. Pullan, Can. Res. Develop., 7 (6),23 (1974).
(11) B. Blles and T. R. Emerson, Nature (London), 210, 93 (1966). (12) W. J. Nicholson, C. J. Maggiore, and i. J. Selikoff, Science, 177, 171 (1972). (13) P. Cook, G. Glass, and J. Tucker, Science, 185, 853 (1974). (14) J. R. Kramer and 0. Mudroch, Can. Res. Develop., 7 (6), 3 1 (1974). (15) E. H. Kalmus, J. Appl. Phys., 25, 87 (1954). (16) M. A. Jaffe. in Proceedinas. Electron MiCrOsCODe Societv of America. Toronto, Sept. 1948. (17) P. Gross, R. T. P. de Trevllie, and M. N. Halier, Arch. Environ. Health, 20, 571 11970). - -, (18) L. Sturkey, The Dow Chemical Co.. Walnut Creek, Calif., private communication. (19) D. R. Beaman and J. A. isasi, "Electron Beam Microanalysis", ASTM STP 506, American Society for Testing and Materials, Philadelphia, Pa. 1972. (20) S. L. Bender and R. H. Duff, in "Energy Dispersion X-ray Analysis: X-ray and Electron Probe Analysis", ASTM STP 485, American Society for Tasting and Materials, Philadelphia, Pa., 1971, p 180. (21) A. M. Langer, I. Rubin, and i. J. Seiikoff, J. Hlstochern. Cytochem., 20 (Q),735 (1972). (22) J. Am. Water Works Assoc., "A Study of the Problem of Asbestos in Water", Sept. 1974, part 2.
.
RECEIVEDfor
review April 22, 1975. Accepted September
26, 1975.
Automated Method for the Determination of Total and Inorganic Mercury in Water and Wastewater Samples Abbas A. El-Awady," Robert B. Mlller, and Mark J. Carter U S . Environmental Protection Agency, Central Regional Laboratory, 18 19 West Pershing Road, Chicago, 111, 60609
An automated method for the determination of total as well as inorganlc and organic mercury by the cold vapor method is given. The method is suitable for the analysis of samples in a varlety of environmental water matrices. A detection limit of 0.05 pg/i. is obtained by the use of a highly sensitive spectrometer. The method Is suitable for the analysis of samples with mercury concentrations in the range 0.05-6 pgA. and a COD of less than 700 mg/i. The use of potassium persulfate, potasslum permanganate, potasslum dlchromate, and mixtures of these salts as oxldizing agents for the digestion step Is discussed, and a study of sample preservation is given. Twenty samples and/or standards per hour can be analyzed uslng this method.
These methods are highly suitable for the analysis of clean water samples and other samples with a very low content of oxidizable materials. However, for samples with a high content of particulate matter as well as for those with high concentrations of oxidizable impurities, the suitability of these methods is questionable. An automated method that addresses itself to these questions is presented in this paper. The comparability of the described method has been checked against the manual method presently accepted by EPA (14) and has been found suitable for the analysis of mercury in all types of water samples including those samples with a high content of particulate matter and oxidizable impurities.
EXPERIMENTAL In recent years, a number of methods have been introduced for the determination of mercury in a variety of matrices (1-10). The most widely used method utilizes a flameless atomic absorption technique first introduced by Hatch and Ott (10). Most of these are time consuming, however, and do not allow for the analysis of a large number of samples, such as is generally encountered by environmental laboratories. The solution to this problem has been to move in the direction of establishing automated procedures, which will allow either continuous monitoring or the analysis of reasonable numbers of samples per day. This increase in the sample analysis rate should be done without affecting either the sensitivity or the accuracy of the procedure. Recently a number of automated methods (11-13) for the determination of mercury have appeared in print. Present address, Department of Chemistry, Western Illinois University, Macomb, Ill. 61455. 110
ANALYTICAL CHEMISTRY, VOL. 48, NO. 1, JANUARY 1976
Apparatus. All glassware used in this work was borosilicate glass. Standard mercury solutions were prepared in volumetric flasks with glass stoppers, All glassware was first washed with water, soaked for 2 hr in a 1% potassium permanganate solution, soaked for an additional 2 hr in a 1:l mixture of concentrated nitric and sulfuric acids, and then washed with doubly deionized water. The glassware was then baked for 3-4 hr a t 400 "C. It was found that for subsequent use of the same glassware, a rinse with followed by several rinses with doubly deionized concd "03 water was sufficient. No traces of mercury were observed in these flasks. All domestic and industrial waste samples were stored in high density polyethylene, 1-liter screwcap bottles with polyethylene lined caps and preserved to give a final concentration of 0.5% "03. Liquid transfers for dilution purposes were made with Eppendorf pipets of 0.1,0.25,0.5, and 1-ml capacity. Instrumentation. The instruments used consisted o f 1) Spectro Products Mercury Analyzer Model HG-2; 2) Perkin-Elmer Model 56 multi-range chart recorder; 3) Harmonically smoothed voltage stabilizer; 4) Technicon AutoAnalyzer Unit consisting of a) Sampler IV, b) Proportioning Pump 111, and c) Heating bath with heating coil (20 f t long and 2.4-mm i.d.; 5) Gas-Liquid Separator; 6) A rotameter to measure the rate of air flow in the gas-liquid separator; and 7 ) High speed blender for sample homogenization.
