ANALYTICAL CHEMISTRY, VOL. 51,
NO. 9,
Polytron homogenizer EPA proprocedure tocol
std. dev., % 0.1 ppb
hexachlorocyclopentadiene
octachlorocyclopentene hexachlorobenzene
90 80 88 109
0.03 0.01
steps in procedure pieces of glassware required volume of organic solvent used, mL time to perform one extraction, min approximate cost per analysis
_--
0.02 1.0 ppb
hexachlorobu tadiene hexachlorocyclopentadiene
octachlorocyclopentene hexachlorobenzene
85 94 99 96
0.15 0.23 0.15 0.24
a
1 0 PPB
hexachlorobutadiene hexachlorocyclopentadiene
octachlorocyclopentene hexachlorobenzene
hexachlorocyclopentadiene
octachlorocyclopentene hexachlorobenzene
7
11
2 30
6 150
10
44
$9
$31
Costs will be based on individual laboratory costs.
when ultrasonic extraction techniques are used. Table I1 is a summary of the statistical analysis of the data. T h e percent recovery and standard deviation a t each concentration level and the correlation coefficients for the linearity of each compound over the range studied are given. This demonstrates t h a t the Polytron Homogenizer procedure produces results which meet or exceed the accuracy and precision requirements necessary for trace level environmental monitoring. We have used the technique with success for the determination of the four compounds discussed in both plant effluent and groundwater samples. Additionally the technique has also been used to extract chlorinated organics from soils efficiently with the emulsions formed easily broken with centrifugation. Table I11 is a summary of the time and cost analysis comparison between the EPA protocol and Polytron Homogenizer procedures for the overall analysis of chlorinated organic compounds in water.
___
125 89 119 86
0.24 0.12 0.13
correlation coefficien tb hexachlorobu tadiene
1589
Table 111. Time and Cost Comparisona
Table 11. Precision and Accuracy Dataa recovery, % compound hexachlorobutadiene
AUGUST 1979
0.997 0.995 0.996 0.996
Data represent three relicates for each compound at each concentration. Correlation coefficient represents how closely the experimental fits with the expected values and is equal to m o x / o y where m = slope of the line and o x and o y are the standard deviations of x and y array of the data points. a strong preferential solubility in the organic phase (such as the chlorinated organic compounds), extraction efficiencies of 90-100% can be obtained in one 30-s step. This makes it possible to minimize the volume of organic solvent used, greatly reducing the time required to perform the extraction. Also, by using hexane, hexane-benzene, or hexane-toluene instead of hexanemethylene chloride, the concentration step can be eliminated except for GC/MS analysis where only concentration by nitrogen purge would be required. For compounds with less favorable distribution coefficients, pH adjustments and multiple extractions might be necessary and these factors should be examined for individual cases. Because of the very short extraction time and the design of the Polytron Homogenizer, essentially no heat is transferred to the sample during the extraction process. This eliminates the potential for thermal degradation or evaporation loss of the compounds of interest, an effect occasionally observed
ACKNOWLEDGMENT The authors thank G. H. Olsen and K. F. Singley for their assistance.
LITERATURE CITED (1) T. A. Beilar and J. J. Lichtenberg, J . Am. Water Works Assoc., 66, 739 (1974). (2) "Sampling and Analysis Procedures for Screening of Industrial Effluents for Priority Pollutants", US. EPA EnvironmentalMonitoring and Support Laboratory, Cincinnati, Ohio, March 1977, revised April 1977. (3) Fed. Regist., 38 (125), Part 11, 17318-23 (1973). (4) "Extraction of Insecticides from Soil", R. Johnson and R. Starr, J . Agric. Food Chem., 20,48 (1972).
RECEIVED for review December 26, 1978. Accepted April 9, 1979.
Determination of Trace Antimony in Phosphoric Acid by Hydride Generation and Nondispersive Flame Atomic Fluorescence Spectrometry Taketoshi Nakahara, Syoji Kobayashi, and SBichirB Musha Department of Applied Chemistry, College of Engineering, University of Osaka Prefecture, Sakai, Osaka 59 1, Japan
I n our previous work ( I ) , a markedly enhancing effect of phosphoric acid on the antimony atomic fluorescence signals, the extent of which is directly proportional to the concentration of phosphoric acid, has proved to be due to the presence of a significant amount (Fg/mL range) of antimony as an impurity in the phosphoric acid used. On the other hand, present Japanese Industrial Standard (2)and American 0003-2700/79/0351-1589$01,00/0
Chemical Society (3) specifications for phosphoric acid do not include a specification for antimony. It is said that the levels of 20-30 Fg/mL of antimony as an impurity are generally found in ACS reagent grade phosphoric acid ( 4 ) . We undertook to apply a sensitive nondispersive flame atomic fluorescence method to the determination of antimony frequently present in phosphoric acid. This was carried out with
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1979 American Chemical Society
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ANALYTICAL CHEMISTRY, VOL. 51,
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AUGUST 1979
Table I. Summary of Experimental Conditions microwave power for electrodeless discharge lamp photomultiplier voltage diaphragm aperture load resistance modulation frequency RC time constant of lock-in amplifier integration time for peak-area measurement sample volume volume of KI solution amount of NaBH, acidity reaction time flame hydrogen flow rate argon flow rates
22.5 W (incident, 35 W; reflected, 1 2 . 5 W) 500 V 15 m m in diameter 470 kR 240 Hz 1.0 s
15 s 20 m L 1.5 mL 0.05 g 1.0 M HCI 60 s 1.0 Limin 1.0 L/min for carrier
gas and 4.0 Limin for auxiliary gas 5.0 cm above burner top
observation height in flame
Table 11. Dispersive Study of Antimony Atomic Fluorescence
wavelength, nm 206.8 217.6 231.1 259.8
relative atomic fluorescence intensity' dilute standard solution of phosphoric 50 ng Sb/mL acid of 2% (v/v) 75.0 48.9
77.1 49.1 100 24.1
100
23.9
' Relative to 100 for the fluorescence intensity a t 231.1 nm. All values were obtained under identical measuring conditions. Table 111. Reproducibility of Measurements antimony amount , np"
RSD,
%b
peak method
integration method
50 100 500
5.7 4.1 3.8 3.2
1000
3.0
4.6 3.5 2.9 2.5 2.3
10
a In 20-mL sample volume. plicate measurements.
Calculated from 1 0 re-
a procedure for reducing antimony t o stibine (SbH3) by the use of sodium borohydride (NaBH,) and determining the antimony by nondispersive atomic fluorescence spectrometry
using a premixed argon (entrained air)-hydrogen flame. T o the best of our knowledge, the work presented here is the first application of a hydride generation technique to the determination of trace antimony in phosphoric acid. The results obtained by the present method were comuared to those bv inductively coupled plasma-optical emission spectrometri (ICP-OES). EXPERIMENTAL Apparatus and Instrumentation. The specific components and the schematic representation of the experimental system employed in this work have been previously described ( I ) except that a more sensitive photomultiplier of "solar blind" type (R-166 UH, Hamamatsu TV Co.) was used and the use of a laboratory-made gas regulator facilitated more precise control of the flame conditions, resulting in great improvement in signal-to-noise ratio and reproducibility of the atomic fluorescence signals. For a dispersive measuring system, a monochromator (0.3-m Ebert mounting, JE-30, Nippon Jarrell-Ash Co.) equipped with another photomultiplier (R-106 UH, Hamamatsu T V Co.) was used. Reagents. All reagents were exactly the same as those previously used ( I ) except for a 20% (w/v) KI prereductant solution which provided a factor of ca. 3 improvement in atomic fluorescence intensity compared to no addition of iodide as described already in atomic absorption spectrometry (5, 6). Procedure. All experimental conditions in part different from those used in the previous work ( I ) are summarized in Table I. General procedure for generating stibine and measuring atomic fluorescence intensity was exactly identical to that previously described ( I ) with the exception of an addition of the iodide solution prior to production of stibine by NaBH, reduction. All experiments were made with the peak method and the integration method of measuring the atomic fluorescence signals for antimony. Blanks were run throughout this work and their values were subtracted from the gross values to obtain the net values, which were reported here.
RESULTS A N D D I S C U S S I O N Recently Winefordner et al. (7,8) have demonstrated that P O molecular fluorescence bands lying in the 220-275 nm region were measured and assigned in the flame fluorescence background and that a species, PO, was formed in the flame from phosphine (PH,) present in the acetylene as an impurity. Provided that any gaseous phosphorus compounds such as PH3 are produced during the NaBH4 reduction, the PO fluorescence bands may obscure the atomic fluorescence of antimony because of their spectral overlap when measured with a nondispersive system. To make sure of this, therefore, the atomic fluorescence intensities with the use of a dispersive system a t four major antimony atomic fluorescence lines were measured by using an antimony standard solution and a dilute phosphoric acid. T h e results obtained by the peak method of measuring the signals are shown in Table 11. These results (Table 11) confirmed undoubtedly t h e absence of the flame background molecular fluorescences arising from the PO molecule. This implied that the present nondispersive method described here is definitely applicable t o the determination
Table IV. Determination of Antimony in Phosphoric Acid by the Method of Standard Additions"
sample A B C D E
peak method av. value, f i g SbimL RSD, % 2.55 4.3 4.9 1.51 4. I 1.47 1.01 5.2 6.5 0.25
a Four standard additions were performed. determinations.
present methodb integration method av. value, M g SbimL RSD, % 4.1 2.47 4.8 1.75 1.46 4.2 4.5 0.97 6.2 0.21
av. recovery of added Sb, % 94.5 96.3 97.6 96.8 93.5
Calculated from 7 replicate determinations.
ICP-OES,' av. value, v g SbimL 2.45 1.55
1.42 1.02 0.27
Calculated from triplicate
ANALYTICAL CHEMISTRV, VOL. 51,
of trace antimony in phosphoric acid. The calibration curve obtained under the optimal experimental conditions shown in Table I has a linear dynamic range of about four orders of magnitude, linear up to 2000 ng of antimony. The detection limit, calculated on the basis of a signal-to-noise ratio equal to three as recommended by IlJPAC (9): was 0.5 ng of antimony, equivalent to 25 pg S b / m L for 20-mL sample volame. The reagent blank had a value of approximately 5 ng of antimony in 20 mL of sample volume. Table III depicts the reproducibilities of measurements with the use of antimony stafiriard solutions of various concentrations. From the interference study of diverse elements and inorganic acids in the antimony determination described previously (1) arsenic interference was mostly expected in the determination of ant,imony in phosphoric acid by the present method. I t has been reported that levels of less than 0.1 pg As/mL are found in ACS reagent grade phosphoric acid (10). In addition, the requirement for the arsenic content of J I S reagent grade phosphoric acid is limited to riot more than 0.5 pg As/mL (2). Such concentration levels of arsenic present in phosphoric acid as an impurity were confirmed in thifi work to give no interference in the antimony determination. For a more accurate determination, however. the method of standard additions in which each phosphciric acid was spiked with antimony in the range 5-20 rig Sb;mL (corresponding to 100-400 ng of antimony) was used in this work. All samples were obtained from several Japanese manufacturers. The results of the determinations are shown in Table 1V. These results (Table IV) show to a high degree good agreement between the proposed method and the ICP-OES. The values by ICP-OES were obtained by using a Nippon Jarrell-Ash Model ICAP-500 under the following conditions: forward RF
NO. 9, AUGljST 1979
1591
power. 1.6 kW: argon flow rates, 1.3, 0.8. and 0.4 L/min for cc:dant. plai.ma. and sample transport gases, respectively; sampie uptake rate, 1.0 m1,imin; height of observation, 15 mm above work coil; wavelength, 217.6 nm; entrance and exit slit widths, 10 pm; integration time for measuring the signals, i 0 s. Oilr data indicate that the sensitivity and precision of the method described here are quite adequate for the deterrnination of trace antimony in reagent grade phosphoric acid.
ACKNOVVLEDGMEKT The authors express their gratitude to Nippon Jarreli-Ash Co., Kyoto, Japan, for loan of an ICAP-500 optical emission
spectrometer equipped with an inductively coupled plasma and to Eiji Yoshimoto for his assistance.
LITERATURE CITED T. Nakahara, S. Kobayashi, and 3 . Musha, Anal. Chim. Acta. 101, 375 (1978). "!+osphOric Acid", JIS K-9005, Japanese Indusaial Standards Cornminee, Japanese Standards Association, Akasaka, Tokyo, Japan, 1972. "Reagent Chemicak", American Chemical soCier{ Comminee on Anatytical Reagents. 5th ed., American Chemical Society, Washington, D.C.. 1974. I May Y . C . Geological Survey, Reston. Va. 22092. personal cornmtinication. January 1978. H. D. Flenxng and R. G. Ide, Anal. Chim. Acta, 6 3 , 67 (1976). J. A. Fiorino. J. N. Jones. and S.G. Capar. Anal. Chem., 48, 120 (1976). H. Haraguchi, W. K. Fowler, D. J. Johnson. and 2 . D. Winefordner, Speitrochinr. Acta, Part A , 3 2 , 1539 (1976). W . K. Fowler anti J. D. Winefordner, Anal. Chem.. 49, 944 (1977). IUPAC Commission on Spectrochemical and Other Optical Procedures for Analysis, "Nomenclature. Symbols, Units and Their IJsage in Speckochemicai Analysis". Part 11, 4. :. Revision 1975, Pvre Appl. Chem., 45, 99 (1976). [Anal. Chem., 48, 2296 (1976); Ap,d. Spactrosc., 31, 345 (1977): Spectrochim. Acta, &rt 8. 3 3 , 241 (1978).] I. May and L. P. Greenland, kilal. Chem.. 49, 2376 (1977).
RECEIVED for review Januaiy 29. 1979. A-cc.epted Fpbruary 33, 1979.
Noncontaminating, Representative Sampling by Shattering of Cold, Brittle, Biological Tissues John A. Nichols"' Analytical Chemistry Facility, Colorado State University, Fort Collins, Co/oradc 80523
Lynn R. Hageman Department of Chemistry, Montana Stafe University, Bozeman. Montana 597 17
A general sample procedure tor plant and animal tissues must be very versatile to handle soft livers, hard bones, fibrous plant materials, etc., as well as complex cases such as whole fish. Problems with blenders are well-known. An elaborate solution to some of these problems has been described by Iyengar ( I ) , who described homogenizatiozi at liquid nitrogen temperature, using a Teflon-lined ballmill, to prepare bone for neutron activation analysis. However, a need remains, as in atomic spectrometry, for simple and inexpensive sampling procedures to match the stringent requirements of (a) minimal sample contamination and (b) reasonably representative sampling, sometimes with solid-sample aliquots of 50 mg or less. The feasibility of ultratrace metal analysis with furnace atomic absorption has made it tempting to subordinate representativeness to the desire for "minimal handling" of the Present address: D e p a r t m e n t of Chemistry, M o n t a n a State U n i v e r s i t y , Bozeman, M o n t a n a 59717. 0003-2700/79/0351-1591$01,00/0
sampie; this is acceptable only in special cases, when the analyte is known LO be deposited hornogeneously in the tissue of interest. The sample homogenization priw to subsampling can be accomplished with much less risk of contaminants being picked up if the sample is handled "dry". with the water frozen, so that no liquid transfer medium is available (2). This principle can be effectively combined with indirect delivery of energy for brittle shattering, through a clean plastic wrapper, to a sample previously chilied with liquid nitrogen until brittle. Such a procedure has been tested in our laboratories on many diverse animal tissues and assessed in terms of (a) representativeness of 5-g subsamples and (b) absence of contamination. Use of a blender with dry ice to keep the sample cold has been similarly tested, for samples requiring finer pulverization, using subsamples of whole fish down to 8 mg; blank levels for nine elements again document the 'C 1979 American Chemical Society
