pears quite promising, especially as coupled with a preconcentration step using Chelex 100. Any problems associated with the matrix such as enhancement on absorption effects seem to have been corrected by the uniformity of the sample and the normalization process (with yttrium) for the elemental concentration levels normally expected for urine. ACKNOWLEDGMENT
The assistance of D. Appelgarth and G. Davidson of the Children's Hospital in Vancouver in handling biological samples is gratefully acknowledged. LITERATURE CITED (1) H. A. Schroeder and A. P. Nason, Clin. Chem., 17, 461 (1971). (2) E. J. Underwood, "Trace Elements in Human and Animal Nutrition," 3rd ed., Academic Press, New York, NY, 1971. (3) W. Mertz and W. E. Cornatzer, "Newer Trace Elements in Nutrition," Marcel Dekker. New York, NY, 1971. (4) R. W. Vilter, R. C. Bozean, E. V. Hess, D. C. Zellner. and H. G. Petering, NewEngl. J. Med., 188 (1974).
(5)M. Hrgovcic, Progr. Clln. Chem., V, 121 (1973). (6) H. H. Sandstead, Am. J. Clh. Nutr., 26, 1251 (1973). (7) J. Cecil Smith, Jr.. E. G. McDaniel, F. F. Fan, and J. A. Halsted, Science, 181, 954 (1973). (8) J. Jullan Chisolm, Jr.. Sci. Am., 224, 15 (1971). (9) F. W. Sunderman, Hum. Pathoi., 21, 549 (1973). (10) B. Searle, W. Chan, and B. Dovidow. Clin. Chem., 19, 76 (1973). (11) K. Beyermann, H. J. Rose, Jr. and R. Christian, Anal. Chim. Acta. 45, 51 (1969). (12) R. D. Giarque. F. W. Goulding, J. M. Jaklevic. and R. W. Pehl, Anal. Chem., 45, 671 (1973). (13) F. S. Goulding and J. M. Jaklevic, Ann. Rev. Nucl. Sci., 23, 45 (1973). (14) 8.P. Bertin, "Principles and Practices of X-ray Spectrometric Analysis." Plenum Press, New York. NY, 1970. (15) D. E. Porter and R. Woldseth, Anal. Chem., 45, 605A (1973). (16) C. W. Blount. W. R. Morgan, and D. E. Leyden, Anal. Chim. Acta. 53, 466 (1971). (17) D. E. Leydon, Adv. X-RayAnal.. 17, 293 (1974). (18) R. B. Bennett and J. M. D'Auria. hf.J. Appl. Radiat. Isof., 25, 361 (1974). (19) N. W. Tietz, "Fundamentals of Clinical Chemistry," W. B. Saunders. Toronto, Canada, 1970.
RECEIVEDfor review November 15, 1974. Accepted January 6, 1975. Work supported in part with funds from the National Research Council of Canada.
Determination of a-Quartz in Atmospheric Dust: A Comparison between Infrared Spectrometry and X-Ray Diffraction Techniques Alessandro Mangla lstituto di Chimica Generale ed Inorganica, Universita di Parma, 43 100 Parma, Italy
With reference to the problem of the determination of a-quartz in atmospheric dust, the results of a comparison between IR spectrometry and X-ray diffraction are reported. This comparison has been made with the aim of verifying the possibility of the use of IR spectrometry instead of the more expensive X-ray diffraction technique. IR determinations of quartz have already been reported by several authors ( 1 4 , even in the atmospheric dust (3, 4 ) , and the problems of the effects of the particle size and matrix interferences have been widely discussed (1-3, 6). The most commonly-used method involves the removing of the dust from the filter and the determination of the quartz by means of the KBr technique; nevertheless some authors ( 4 ) investigated the possibility of determining the a-quartz content of the dust directly on the filtering membrane. These authors propose to fold the filters to increase the ratio between the amount of dust and the surface of the filter and to reduce the consequences of the inhomogeneity of the dust distribution. In the present work, both the KBr and the membrane technique have been used but, in the second procedure, to improve the sensitivity of the method and to reduce the effects of the inhomogeneity, the samples were transferred from the original membrane to another one, on a surface of the same shape and dimensions of the spectrophotometric entrance port. The results of the two IR procedures have been checked by means of X-ray diffraction on the same sample of dust. EXPERIMENTAL Apparatus a n d Reagents. Quartz: particle size, 2-10 pm. KBr: mean particle size, 60 pm. Filtering membrane: cellulose nitrate, Sartorius 113.04.050. IR spectrophotometer: Perkin-Elmer model 457. Powder diffractometer: Philips PW 1050, CuKa radiation.
Procedure. The atmospheric dust was collected near a clay factory on a 50-mm diameter filtering membrane. A preliminary investigation of a sample of the dust by means of powder X-ray diffraction showed that only the a-quartz modification of Si02 was present. The samples of pure a-quartz of known particle size were obtained with the sedimentation method, using the Stokes formula to calculate the settling time (7). For the KBr technique, the normal procedure of preparing the pellet was followed and KBr of 60pm mean particle size was used. The spectrum was run three times, with a rotation of the pellet through 60" each time, and the resulting absorbances were averaged. In preparing the standards of quartz on the membrane, weighted amounts were transferred with water on 13-mm diameter filtering membranes using a Plexiglas support (Figure 11, with the filtering surface of the same shape and dimension as the spectrophotometric entrance port (the internal surface of the funnel was accurately smooth to avoid any deposit of dust particles). The quantitative transfer of the substance was controlled by means of a microscope; no loss resulted. The discs were then dried and scanned using the normal sample holder for the 13-mm pellets. A second membrane disc was used for reference; both sample and reference discs were cut from the same filtering membrane in a region close to its center (to avoid the effects of a possible difference in thickness). The same procedure was followed for the unknown samples, after ignition of the original filters carrying the collected dust, in platinum crucibles a t 500 "C. For the X-ray analysis, the standards were prepared adding to the weighted quartz, CaC03 up to 2 mg when their weights were less. The same procedure was followed for the unknown samples after their ignition a t 500 "C. Then, they were transferred onto the membranes, using the previously described support but with the filtering surface equal to the irradiated zone a t 20 = 26.70'. The membranes were then placed on the holders. In this way, strictly flat and homogeneous samples were obtained. For the direct comparison of the methods, a suitable amount of atmospheric dust was collected on a filter and, after burning in a platinum crucible at 500 OC, three portions of it were used for the two IR methods and for the X-ray control. ANALYTICAL CHEMISTRY, VOL. 47, NO. 6, MAY 1975
927
06 r
l l Figure 1. Filtration support
c3
I-
02
I
I 3
01
C2
33
C6
C5
04
07
mg
0
Figure 4. Dependence absorbance-quantity of quartz (4-6 mean size) on filtering membrane at k = 12.8 W r n
I
,
1 1
3
8
7
A L A
12
1c
1E
'C
'8 2c
2 5 32
4 :
.Vavele-ghr
Figure 2. Spectra of different amounts of quartz (4-6 p m mean size) on filtering membrane:
1
(A) = 0.04, (6) = 0.12,(C)= 0.20,(0) = 0.30 mg
'@:.A I /
60
I
A
II 12
14
16 12
B 14 Wavelength
16
(pm)
Figure 5. Effect of the particle size on the shape of the double peak 1 8
7
I
1
8
I
,
9
,
, 10
,
,
12
,
,
'4
,
, , , ,
,
,
16 18 20
25 30
Wavelength
(,urn)
(A) quartz in KBr pellet, (6)quartz on filtering membrane
, 40
Figure 3. Cellulose nitrate filtering membrane IR spectrum, air reference Upper curve: base line obtained differentially with portions of the same filter in sample and reference beam
RESULTS AND DISCUSSION In Figure 2, the spectra of different amounts of quartz (mean size 4-6 pm) on a Sartorius membrane filter are shown. The cellulose nitrate membrane can be used as support because of its high transmittance in the IR spectral region where the most useful quartz bands are observed (Figure 3). A remarkably flat base line is obtained using the differential technique (Figure 3, upper line). I t appears not necessary to wet the membrane with oil to reduce the scattering losses, as already reported (8). The dependence of the absorbance a t 12.8 pm (base-line method) from the quantity of quartz (4-6 pm mean size) is shown in Figure 4; no relevant deviation from the Lambert-Beer law is observed in the explored interval. 928
ANALYTICAL CHEMISTRY, VOL. 47, NO. 6, MAY 1975
The effects of the particle size on the absorbtivity and the relationship between absorbtivity and grinding time and method, when the pellet technique is used, have been reported ( I , 2 ) . Using the filtering membrane as support, this effect seems to be less relevant (Figure 5). Moreover, the peak a t 12.8 pm is more intense than that a t 12.5 pm, at an particle size value, while with the KBr pellets this effec is observed only for large particle size samples ( I ) . For the determination of quartz in the atmospheric dust, pellets with 0.735, 1.472, 1.917% of dust were prepared. The unknown percentage of quartz was determined using the calibration curve of Figure 6 obtained from the peak at 12.5 pm, which is free from interferences due to CaC03 and to many silicates (1-3). The particle size (4-6 pm) of the standards was chosen on the basis of the shape of the double peak of 12.5-12.8 pm given by the atmospheric dust. In the membrane support procedure (in Figure 7 , the spectrum of a sample of atmospheric dust on the membrane is shown), the addition method was used: 0.04, 0.10, 0.15,0.19 mg of quartz of the same particle size were added to four samples of 1.00 mg of dust and the absorbance at
f
50
I
08
c
I
40t
u L
x
06
30
-
20
-
10
-
n c
I
2
V 0
1 0
0
0.2
01
I
I
,
0 2
03
0 4
05
mg
0.4
Q
0.8
0.6
% 0
Figure 6. Dependence absorbance-percent of quartz (4-6 @m mean size) in KBr at A = 12.5 I.cm
Figure 9. Dependence intensity-amount of quartz with the X-ray powder diffraction
I
2ot i
L , 7
8
Y
I
1
'IC
12
Figure 10. Results of the addition method in the determination of the quartz by means of X-ray diffraction ,
, , , , , ' '
16 18 20
14
25 30
1
40
Wavelength (pm)
Figure 7. IR spectrum of atmospheric dust sample on filtering membrane
Table I. Quartz Percent a n d Relative Standard Deviation Quartz, %
0
,M
IR
I
I
K B r technique
13.80
4.3
Membrane support technique X-Ray diffraction
12.92 12.70
2.3 1.2
method was used (Figure IO), and these results are compared with those obtained by the IR techniques in Table I. From this comparison, it can be inferred that the IR method, even if it is not so specific as the X-ray diffraction, seems to be suitable in determining even small quantities of quartz, especially using the membrane support technique. The KBr technique can give valuable information about the mean size of the particles. 20
10
10
20 ba
'/*
Figure 8. Results of the addition method in the IR determination of the quartz on filtering membrane
12.8 Mm was measured. In these conditions, the matrix effects are practically constant. From the curve of Figure 4, it can be deduced that the extrapolation beyond the experimental four points towards the smaller quantities is allowed. The results are reported in Figure 8. A third portion of the same atmospheric dust sample was used to control the previous IR determinations by means of X-ray diffraction. [In Figure 9, the dependence intensityamount of quartz (mean size 4-6 wm) in samples prepared following the described procedure, is shown.] The addition
ACKNOWLEDGMENT The author thanks M. Nardelli for his interest in this work. LITERATURE C I T E D (1)W. M. Tuddenham and R . J. P. Lyon, Anal. Cbem., 32, 1630 (1960). (2)P. A. Estep, J. J. Kovach, and C. Karr, Jr., Anal. Cbem., 40, 358 (1968). (3)A. H.Gillieson and D. M. Farrell, Can. Spectrosc., 16, 21 (1971). (4)S.Z.Toma and S. A. Goldberg, Anal. Chem., 44, 431 (1972). (5) C.Fernandez, Med. Segur. Trab., 19, 39 (1971). (6)G. Duyckaerts, Analyst, 84, 201 (1959). (7)R. E. Carver, "Procedure in Sedimentary Petrology", Wiley, New York, London, 1971,p 73. (8) H.J. Sloane, Anal. Cbem., 35, 1556 (1963).
RECEIVEDfor review April 16, 1974. Accepted January 15, 1975. ANALYTICAL CHEMISTRY, VOL. 47, NO. 6, MAY 1975
929
