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Anal. Chem. 1980 52, I 784- I 787
r
I-
25 rnsec
TIME
-I
c-
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Figure 6. Ribbon voltage measured at fastest heating rate, 750 OC, and 500-ms interval
-
2 5 rnsec
TIME
Figure 7. Ribbon current measured at fastest heating rate, 750 and 500-ms interval
600 rnsec
OC,
full wave rectifier and a large capacitor in series, which initially discharged in excess of 20 A through the ribbon. Thus, the initial ribbon current,profile appears on an oscilloscope as an RC decay. In Figure 7 , this was missing because the signal was initially off-scale and appeared as a horizontal line on the signal averager. Figures 6 and 7 clearly indicate that after 13 ms the ribbon power went to zero and subsequently increased approximately 1 ms later. From Figure 4 it can be seen that 13 ms was the time required to heat t h e ribbon to the first plateau region. In fact, the temperature overshoot noted a t the beginning of the plateau in Figure 3 was caused when the current was again activated and overshot (compare the overshoot in Figure 3 and 7).
Figure 8. Ribbon current measured at rate of 20°/ms, 750 "C,and 500-ms interval The effect of contact resistance was also seen in the slower linear rates (20 "C/ms). Because the ribbon current for a 20 "C/ms rate (Figure 8) increased more slowly than that in the previous examples, the contact resistance effect was delayed; however, the same current voltage effects were observed. (A referee for this paper suggested that the cooling of the ribbon ends and accompanying heating of leads are possible causes for the observed secondary temperature rise. Based on the short, ca. 1-ms time constant for the current-voltage cycling of Figures 6 and 7, it is very unlikely that this explains the early plateau in the heating profile. However, this effect may influence the slow apprach to Teq.) The described data were collected from three different CDS Pyroprobe controllers using five different probes and certainly do not represent the quirks of a single defective unit. I t is unclear at this time whether or not the heating profile curves can be corrected by alteration of the temperature controller. Chemical Data System has been alerted to this problem and has indicated that a new design will be forthcoming which eliminates all the difficulties we have encountered (6).
LITERATURE CITED (1) Jones, C. E., Roland, Cramers, C. A., Eds. "Analytical Pyrolysis"; Elsevier: Amsterdam, 1977. (2) Simon, W.; Giacobbo, H. Chem. Ing. Tech. 1965, 37, 709. (3) Levy, R. L.; Fanter, D. L.; Wolf, C. J. Anal. Chem. 1972, 4 4 , 38. (4) Wells, G.; Voorhees, K. J.; Futrell, J. H. Submitted to Rev. Sci. Instrum. ( 5 ) Chemical Data System Pyroprobe 100 Series Operating and Service Manual CDS 073073, 43. (6) Levy, Eugene, personal communication, 1980.
RECEIVED for review January 25,1980. Accepted June 4,1980. The authors gratefully acknowledge support of this work by Department of Energy contract DEA2079LC10030.
Heavy-Liquid Separation and X-ray Diffraction Analysis of Airborne Particulates Tsutomu Fukasawa,
Masaaki Iwatsuki, Susumu Kawakubo, and Kiyoshi Miyazaki
Department of Applied Chemistry, Faculty of Engineering, Yamanashi University, Takeda-4, Kofu 400, Japan
Only a few papers (1-3) have been reported for the X-ray diffraction analysis of airborne particulates. The sensitivity of the X-ray diffraction method, however, is too low to determine minor components in airborne particulates. The heavy-liquid separation method has been applied for the isolation of crysotile from interfering material ( 4 ) . However, 0003-2700/80/0352-1784$01 . O O / O
the method has not been applied to X-ray diffraction studies of air pollution. This paper describes the X-ray diffraction analysis of the fractions of airborne particulates obtained by the heavy-liquid separation method with a series of carbon tetrachloridemethylene iodide mixtures. The analytical results for the IC 1980 American Chemical Society
ANALYTICAL CHEMISTRY, VOL. 52, NO. 11, SEPTEMBER 1980 G l Z j j
1785
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S i l v e r membrane f i l t e r can be used f o r t h e s e s t e p s too, D i f f r a c t i o n l i n e s , l o w e v e r , frorr t h e m a t e r i a l o f t h e f i l t e r may i n c i d e n t a l l y o v e r l a o w i t h t h o s e from t h e sample a n a l y z e d and d i s t u r b t h e a n a l y s i s .
Figure 1. Heavy-liquid separation scheme samples collected from office, business, and industrial districts are compared. T h e method is recommended for use in the study of airborne particulates.
EXPERIMENTAL Sample. Four homogenized samples denoted by AS-1, AS-2, AS-3, and AS-5 were used for the study. They were prepared from airborne particulates collected on filters attached to the inlets of air cleaners on the roofs of tall buildings. The sampling locations and dates are as follows: AS-1 (51, an office district in Tokyo, October 1973; AS-2 and AS-3, industrial districts in Chiba and Yokohama, respectively, October 1974; AS-5, a business district in Tokyo, January 1975. Apparatus. A 100-W ultrasonic cleaner unit was used for dispersion of airborne particulates in heavy liquid, and a 200-W centrifuge (ca. 33 Hz) to promote the separation of the dispersed samples in heavy liquid. A Rigaku X-ray diffractometer with a Cu tube and Ni filter was operated at 35 kV and 15 mA. Two 2O-slits were used for measurements of weak intensities from small samples. The sample holder for the diffraction analysis was an aluminum plate of 50 X 35 X 1.8 mm with a 16 X 20 mm window for a fractionated sample on a filter or a quartz plate with a 17 X 20 x 0.2 mm hollow, which was specially cut to give no diffraction line, for 100 mg of starting sample. A Philips semiautomatic X-ray fluorescence spectrometer was used for analysis of the organic solvent extracts from the particulates. Procedure. Figure 1 is an outline of the analytical procedure. The first 100 mg of sample is washed with carbon tetrachloride. All the washings are concentrated t o ca. 2 mL by evaporation, and loaded on a piece (1cm X 1 cm) of filter paper (Toyo Roshi No. 5C) drop by drop using a pipet. After the solvent is evaporated, the extract on the filter paper is analyzed by fluorescent X-ray spectrometry. These procedures are also conducted with n-hexane to determine the effect of solvent used. The residue, after washing with carbon tetrachloride, is transferred to a centrifuge tube (ca. 10 mL), and dispersed in 8 mL of a heavy liquid of carbon tetrachloride-methylene iodide by use of the ultrasonic cleaner unit. After centrifugation, 6 mL of the upper part in the centrifuge tube is divided from 2 mL of the lower part by use of a glass rod with a disk end: The disk end is introduced obliquely to the site just under the float, rotated there to release any floats attached to the disk, and then inserted to the position shown in Figure 2. The float in the upper part is filtered off on a membrane filter. The upper inside of the tube divided by the disk is carefully washed with small quantities of carbon tetrachloride t o transfer any remaining floats onto the filter in such a way that the carbon tetrachloride is not mixed with the heavy liquid under the disk. For the successive separation of the sediment in the lower part, carbon tetrachloride and methylene iodide are added to the liquid remaining in the centrifuge tube so that 8 mL of heavy liquid of a larger density is prepared. The same procedure as described above is repeated. The final sediment is filtered off on a mem-
~
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Figure 2. Dividing upper part from lower part in centrifuge tube brane filter. All the floats and the final sediment are washed with carbon tetrachloride and weighed after expelling the solvent. The membrane filter with a float or sediment is attached on the window of the aluminum sample holder with Scotch tape, whereas the 100 mg of starting sample was packed into the hollow on the quartz holder, and analyzed by the chart-recording X-ray diffraction method. The floats and final sediment are also examined by optical microscopy.
RESULTS AND DISCUSSION Matter Extracted with Organic Solvents. The extracts were 0.9-370 (2.0% for AS-1 and 0.9% for AS-2) for carbon tetrachloride and a smaller percentage (0.2% for AS-1 and 0.7% for AS-2) for n-hexane. They contained such elements as bromine, iron, calcium, chlorine, and sulfur. These elements were extracted more effectively with carbon tetrachloride than with n-hexane. Some differences can be seen among the extracts; for example, the extract from AS-5 seems to contain larger quantities of the elements described, and that from AS-2 smaller quantities. The following elements were not detected: lead, zinc, copper, nickel, manganese, chromium, titanium, potassium, phosphorus, silicon, and aluminum. Heavy-Liquid Separation and X-ray Diffraction Patterns. Typical examples of X-ray diffraction patterns of starting samples and their separated fractions are shown in Figure 3 (AS-1) and Figure 4 (AS-2). The background increase with 20 for the 100-mg starting sample on the quartz holder is explained as follows: The large incident X-ray beam from 2O-slits overflows from an effective sample surface (20 X 10 mm2) a t lower angles and gives weaker background a t lower angles. On the other hand, the background for each fractionated sample is explained as the sum of the low background from the small sample and the enhanced diffuse line and background from the membrane filter. T h e comparison between the patterns of the starting sample (a) and the fractions (b)-(f) in Figure 3 shows the effect of the heavy-liquid separation; Le., calcite, plagioclase, chlorite, biotite, magnetite, and hematite were easily identified in the fractions after the separation, though the minerals were incompletely separated from each other. T h e same case also can be seen in Figure 4, with Epsom salt, plagioclase, magnetite, and hematite being clearly identified after separation. Characteristic differences can be seen between the mineralogical components of AS-1 and those of AS-2; for example, AS-2 contained Epsom salt, hemihydrate gypsum, and far more quantities of gypsum than AS-1, but not halite and calcite which were contained in AS-1. Comparison among the Analytical Results of Four Samples. Figure 5 summarizes the X-ray diffraction analyses of the airborne particulates collected a t the four sites. T h e top histograms show weight percentages of the separated fraction against liquid density for every sample; minerals are shown in order of their densities. A strong diffraction line which does not overlap with any other lines was selected for the intensity measurement of each mineral. Two diffraction lines subject to the opposite effects of preferred orientation were measured for those minerals expected to orient preferentially on the sample holder; their intensities are shown by solid and dotted lines. I t can be seen from the top histograms that the fraction
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ANALYTICAL CHEMISTRY, VOL. 52, NO. 11, SEPTEMBER 1980 8o
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Flgure 3. X-ray diffraction patterns of AS-1 and its fractions separated with heavy liquids. (a) Starting sample, (b)-(f) Fractions separated with heavy liquids. Numerical values without dimension show densities (g cm3) of the liquids used. Weight in mg is sample weight used for X-ray diffraction analysis. Q: a-Quartz, G: Gypsum, Ha: Halite, C: Calcite, P: Plagioclase, H: Hematite, M: Magnetite, Ch: Chlorite, B: Biotite. Full scale: 8 X lo2 cps
0
35 24' f o r Cu Kcr
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40
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Figure 4. X-ray diffraction patterns of AS-2 and its fractions separated with heavy liquids. E: Epsom salt, S: Hemihydrate gypsum. See also the annotation of Figure 3 Tokyo Wt'
of density below 2.0 g cm-3 in AS-2 was significantly less than in every other sample. T h e fraction seems to consist of carbonaceous matters judging from its black color and microscopic observation. T h e degree of the separation of minerals achieved by the technique can be seen clearly in Figure 5 . Most of each mineral was separated into the density fraction corresponding to the mineral, although it may not be clearly separated from other minerals. Separations of Epsom salt, magnetite, and hematite were better t h a n those of quartz and hemihydrate gypsum. T h e sum of X-ray intensities of a mineral over all the fractions provides an estimation of relative quantity of the mineral in each sample. Quartz, plagioclase, magnetite, and hematite are estimated t o be present in approximately the same ratios in every sample. Gypsum, however, seems to be present in a larger quantity in AS-2 and AS-3, collected a t industrial districts, than in AS-1 and AS-5, collected a t the office or business district of Tokyo. The mineralogical compositions of AS-1 and AS-5 from Tokyo were similar to each other, and contained calcite which was not detected in other samples. The AS-2 sample from the Chiba industrial district, which contained less carbonaceous matter, was rich in gypsum, a n d contained hemihydrate gypsum and Epsom salt which were not detected in other samples. T h e AS-3 sample from the Yokohama industrial district contained a larger quantity of halite than other samples, and did not contain detectable amounts of chlorite and biotite which might be blown up from the ground. Mineralogical composition depends on the place where the sample was collected, as described above, and shows a char-
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Figure 5. Histograms of weight percentages or X-ray diffraction intensities against liquid density for the four samples. X-ray intensity unit: x102 cps
acter of the atmosphere there. T h e comparison of mineralogical composition among samples collected at different places and consideration of the origin of each mineral provide important information for the environmental problem. Phase
Anal. Chem. 1980, 52, 1787-1790
analysis of airborne particulates is greatly aided by the combined heavy-liquid separation-X-ray diffraction technique which is recommended for use in the study of the environment problem.
1787
(4) R. P. Bagioni, Environ. Sci. Techno/.,9, 262 (1975). (5) Y. Hashimoto and T. Otoshi, Environ. Sci. Techno/., 10, 815 (1976).
RECEIVED for review February 18, 1980. Accepted May 16, 1980. Presented a t t h e 26th International Congress of Pure and Applied Chemistry, Tokyo, September 1977. T h e study was supported by a Grant in Aid for Scientific Research from the Ministry of Education and trust money from the Environmental Agency, Japan.
LITERATURE CITED (1) B. L. Davis and N. Cho, Atmos. Environ., 11, 73 (1977). (2) K. Oikawa, T. Nomura, and H. Maruyama, Bunseki Kagaku, 25, 524 (1976). (3) R . L. Foster and P. F. Loff, Microchem. J . , 24, 184 (1979).
Comparison of Near-Infrared Reflectance and Photoacoustic Spectra of Grain Samples George Henderson and Melton F. Bryant’ Department of Chemistry, University of Georgia, Athens, Georgia 30602
T h e need often arises in the food and agricultural industries t o determine the oil, protein, and moisture content of various products or plants. In the mid-1960’s work was begun to investigate the use of near-infrared diffuse reflectance spectrometry (NIRS) for the analysis of these three constituents in various agricultural samples (1-3). T h e spectroscopic methods were developed t o replace the more laborious and time consuming conventional methods for these components in agricultural samples, i.e., the Kjeldahl method for protein ( 4 ) ,the NMR method for oil (5,6),and oven drying methods for moisture assay. Though the N I R S method offers simplified analysis procedures, shorter analysis time, and the ability to simultaneously quantify all three components, the method does require very careful control of sample preparation. Diffuse reflectance studies of various samples have shown t h a t i t is necessary to ensure uniform particle size between samples in order t o ensure meaningful comparisons between samples (3,7). NIRS suffers from scattering problems in cases where absorption is either very low or very high (8, 9). An alternate spectrometric technique which may offer potential for the analysis of agricultural products and crops is photoacoustic spectrometry (PAS). PAS offers the ability t o spectrally examine materials which are optically opaque, such a s those encountered in agricultural product analysis. Since a PAS spectrometer uses a pressure transducer rather than t h e conventional optical transducer, it is expected t h a t scattering effects will be less severe with PAS (9). This paper presents some of the preliminary work undertaken to investigate t h e use of PAS for the analysis of these sample types. T h e data presented can serve as a qualitative basis for comparing these two spectrometric techniques for agricultural products analysis. EXPERIMENTAL NIR Spectra. The NIR spectra were obtained with a Neotec near-infrared reflectance spectrometer ( I O ) . A totally reflecting material (Halon (Powdered Teflon) Radiometric Physics Section, Optical Physics Division, Institute for Basic Standards, NBS, Washington, D.C.) was analyzed and the spectrum was stored on magnetic tape for use later in correcting the sample spectrum for instrumental response characteristics. The spectrometer employed a 250-W tungsten source with a PbS detector and 1-Hz filtering on the output signal. A slit width of 2.0 mm (spectral band width (SBW) = 7 nm) was used as the spectrum was scanned from 1.00 pm, to 2.50 pm at 300 nm per min. The signal was sampled at intervals of 5.0 nm and the data were stored on magnetic tape. After the sample spectra were obtained, they were corrected RHdon for instrumental response by computing the log R,,,,,/log (Le. the corrected optical density, R = reflectance) at each point. 0003-2700/80/0352-1787$01 .OO/O
Finally, the spectra were plotted as optical density vs. wavelength using a Tektronix CRT 4012 Console plotter (Tektronix Inc., Beaverton, Ore.). P A S Spectra. The PAS spectra were obtained with a Gilford Instruments R-1500 double beam photoacoustic spectrometer (11). The R-1500 utilizes a 300-W xenon arc source for excitation with separate cell chambers for sample and reference. Multiple gratings are used (four gratings) to provide maximum efficiency in covering the ultraviolet-visible-near-infrared spectral regions. The near-infrared region is covered using two of these gratings. One grating is blazed for 1200 nm with a dispersion of 6.6 nm/mm and is used for the 800 to 1600 nm range. The spectral region from 1600 to 2500 nm is covered using a grafting blazed at 2100 nm with a dispersion of 13.2 nm/mm. Order sorting filters are automatically inserted by the R-1500 to reject overlapping higher order wavelengths. The spectrum for each sample was scanned from 800 to 2500 nm using a constant slit width of 2 mm, giving SBW’s of 13.2 nm and 26.4 nm for the first and second region, respectively. The spectrum was scanned a t 100 nm/min with a time constant of 3 s on the signal. The spectra were recorded using the instrument in the ratiometric mode with carbon black in the reference cell. Samples. The samples, consisting of five sunflower seed types and one soybean sample, were obtained from the Field Crops Utilization and Marketing Lab, Russell Research Center, USDA, Athens, Ga. 30601. The samples were chosen on the basis that their oil and protein content cover a range representative of these sample types. The approximate oil content had been previously determined by the NMR method and the protein content was determined by the Kjeldahl method for nitrogen determination which is related to protein content. Several seeds from a given sample lot were ground with an equal weight of CaCO, (as diluent) in a mill for approximately 2 min. For NIRS analysis, a portion of this ground sample was placed in a sample cell for subsequent analysis. PAS samples were taken from the same grinding lot as the corresponding NIRS samples. The samples were placed in sealed glass containers and sent to Gilford Instrument Laboratories, Inc., for analysis on their system. Prior to analysis, the samples were placed in a sample holder and the surface was leveled to present a uniform surface for analysis. Procedure. It was necessary after obtaining the two sets of spectra to digitize them in order to directly compare the NIRS and PAS spectra for a given sample. A digitizer constructed in this laboratory was used to effect the conversion of the data into digital form. The digitizer was constructed using an 8080 based microprocessor system (12),an Analog Devices RTI-1200 data acquisition unit (Analog Devices, Inc., Norwood, Mass. 02062), and a Hewlett-Packard Model 7004B x-y recorder (HewlettPackard, San Diego, Calif. 92101). The RTI-1200 provides 12-bit resolution on both the A/D converter and the D/A converters. The data are acquired under software control by the 8080 system and stored on a floppy-disk unit of a PDP-11/34 miniC 1980 American Chemical Society
