search. I n this two-phase system, phthalate polyesters are hydrolyzed but, as in the maleate case, simple diesterse.g., dioctyl phthalate or dibutyl phthalate-are not hydrolyzed. On the basis of limited work, the hydrolysis of phthalate polyesters appears t o be complete. This procedure is sinipler experimentally than that of Garn and Halline. It requires less operator time, although the total elapsed time is greater. Further, the fact that simple esters do not hydrolyze in this method, but do in the method of Garn and Halline, can be used to differentiate between phthalate involved in polymerization
and phthalate esters used as plasticizers. A more complete evaluation of this technique for the determination of phthalates may be described a t some later time. ACKNOWLEDGMENT
The authors wish to express their appreciation t o Robert C. Makosky and Barbara Loeffler for willingly undertaking the task of synthesizing the resins. LITERATURE CITED
(1) Am. SOC.Testing Materials, Philadelphia, f;'&., "Official and Tentative
Methods, ASTRI D 563-52.
( 2 ) Garn, P. D., Halline, E. W.,ANAL.
CHEW27, 1563 (1955). (3) Garn, P. D., Vincent, S. RI., Gilrov, -. H. XI.,'unpublished measurements. (4) Hobart, E. W., ANAL. CHEM. 26, 1291 (1954). (5) Stafford,'R. W.,Shay, J. F., Francel, R. J., Ibid., 26, 656 (1954). (6) Syann, M. H., Ibid., 21, 1448 (1949). ( 7 ) kincent, S. RI.,. unwblished measurements. (8) \Tarshowsky, B., Elving, P. J., hlandel, J., A N ~ LC .H m f . 19, 161 (1947).
RECEIVED for review January 11, 1958. Accepted May 23, 1958. Division of Analytical Chemistry, 133rd Meeting, ACS; San Francisco, Calif., April 1958.
Spectroscopic Determination of Arsenic in Anthracite Coal Ashes RONALD
H.
HALL1 and HAROLD L. LOVELL
College o f Mineral Industries, The Pennsylvania State University, University Park, Pa.
b The determination of arsenic in coal and coke is important because of the detrimental effects of this element on products associated with the fuel, as in food production, and the use of coke in the metallurgical industry. Air pollution considerations are also significant. An emission spectroscopic procedure was developed as an improvement on the Gutzeit method. A physical enrichment process during excitation provided a tenfold increase in the detection limit, and improvements in the quantitative aspects. Following direct current arc excitation of a large sample in boiler electrodes, As 2349.84 and Sb 2 6 1 2 . 3 0 A. (internal standard line) provided quantitative data showing an accuracy and precision of 5 to 10% of the amount of arsenic present, covering a concentration range of 0.0025 to 0.04% arsenic trioxide. Other approaches, less accurate but possessing certain advantages, are described. The coals ashed a t 750' C. for 4 hours volatilize about 10% of their arsenic content, which is superior retention to longer times at lower temperatures.
I
K' RECEXT years the emission spectro-
graph has been utilized by several investigators for the analysis of coals and their ashes (1, 5,9-11,13,1~, 16-18). Much of the work published has made use of the total energy method as proposed by Slavin (ZOO), and utilized by Headlee (9) and Lorell (14). This Present address, Vanadium Corp. of America, Research Center, Cambridge, Ohio.
method, although advantageous because of its ease of development and versatility, is not as reliable as the internal standard method. The internal standard method has been utilized by Anderson and Beatty (1) for the determination of sodium and potassium in coal ashes. Lithium and rubidium were used as the internal standard elements. The method was reported to have a standard deviation of 4.3 and 4.1%, respectively, for sodium and potassium. Hawley ( 7 ) , in studying Kova Scotia coals, utilized rhodium black as the internal standard and determined the distribution of 25 elements in various coal seams. A level of accuracy was not reported. Hawley and Headlee (7, 9) reported arsenic found in some of the coals studied, but their detection limit was high. More complex chemical methods (4) do not lend themselves to control applications. Because arsenic is present in such minute amounts in coal ash and has poor spectrographic sensitivity, an enrichment process is needed for its determination. Harper and Strafford ( 6 ) , employing a chemical enrichment process, were able to determine spectrochemically as little as 0.5 p.p.m. of arsenic trioxide in foodstuff colors. This low detection limit m-as accomplished by precipitating out the sulfide along mith a large quantity of cadmium sulfide, after \yet oxidation of the sample. The sulfide mixture was collected on a graphite bed. The cadmium was employed as a carrier, and as the internal standard. A physical enrichment process for the a n a l p i s of minerals, reported by Wede-
pohl (21), and Shaw, Joensuu, and Ahrens (19), utilized a double-arc furnace-electrode for the spectrographic determination of trace constituents in geological material. One arc mas used to heat the sample in the electrode, and the other to excite the escaping vapors. Kedepohl used this system to study the geochemistry of zinc and reported increased detectability in using a furnaceelectrode. Shaw and coworkers reported that the detection limit of lead, indium, and tin was lowered. Two disadvantages were the intense cyanogen bands produced and poor repeatability. Shaw et al. attempted to reduce the cyanogen bands by buffering the sample with lithium carbonate, but this could affect the excitation of elements having a high resonance potential. The accuracy of the method n-as reported to be 3 ~ 3 0 % . Although this is poor, it offered a means of increasing sensitivity. B y employing a modified furnace electrode (boiler electrode), the possibility of increasing the spectrographic sensitivity of arsenic and improving the accuracy R as investigated. REAGENTS A N D STANDARDS
S B S plastic clay 98. A standard clay material found to contain 0.0004'% arsenic trioxide (Gutzeit method). The material was heated for 1hour a t 850" C. to remove the structure157 held water, because the unheated clay appeared t o swell and emerge as a solid maSs from the boiler electrode orifice. It was used as the base material in the preparation of the standard samples. Arsenic trioxide. h-ational Bureau Standards sample (99.9yo purity). VOL. 30,
NO. 10, OCTOBER 1958
1665
Antimony trioxide. Analytical c. P. grade. Contained less than 0.1% arsenic trioxide. Powdered carbon. Obtained by grinding the filings from the machining of the standard grade electrodes. Powdered carbon, internal standard mixture. Containing 0.4% antimony trioxide, the mixture was prepared by adding antimony trioxide to the carbon to form a sample containing 10% by weight. This sample was diluted stepwise to 4.0 and 0.4% antimony trioxide. Standard samples. Arsenic trioxide was added to the dehydrated plastic clay to form a sample containing 10% by weight. This 10% preparation was diluted stepwise to 1.0, 0.1, 0.05, 0.04, 0.03, 0.025, 0.02, 0.015, 0.01, 0.005, and 0.0025% Asz03. The substances, which were t o be mixed, were weighed on glazed paper and transferred to the plastic vial of a Wig-LBug. The vial was oscillated for 2 minutes t o accomplish preliminary mixing. The vial was removed from the Wig-L-Bug and the small plastic pestle carefully inserted. The mixing and grinding process was then continued for another 2 minutes.
brated in the 2350- and 2600-A. regions by the logarithmic step-sector method. GUTZEIT METHOD. The coal ash samples and the dehydrated NBS plastic clay were analyzed for arsenic by the Gutzeit method. The apparatus employed has been described (8). The only modification consisted of the substitution of glass wool for the 20- to 30-mesh sand in the scrubbing tube. The procedure employed was that proposed by Hertzog (la),with two modifications. Five grams of 20-mesh zinc were used in place of zinc sticks and the stains were developed with ammonium hydroxide before measurement. Samples of 0.1 and 1.0 gram were used for the analysis of the ashes and coals, respectively. The reading error of the stains was found to be equivalent to a t least 0.001 mg. of arsenic trioxide in the range of 0.001 to 0.02 mg. The accuracy of the method varied from 5 to loo%,
EQUIPMENT A N D PROCEDURES
SPECTROGRAPH.A
Jarrell-Ash (Wadsworth mounting) 21-foot spectrograph with a reciprocal linear dispersion of 5 A. per mm. in the first order. A sector mount and a rotating sevenstepped sector disk (step ratio 1 to 1.585) was used for attenuation of the exposure. EXCITATION SOURCE. ARL No. 2000 rectifier unit for direct current arc excitation. The unit has an output of 4 to 15 amperes a t 250 volts direct current. MICROPHOTOMETER.Hilger nonrecording KO, 451 microphotometer with FR-300 Galvoscale projection. The variable slit was adjusted to a width of 0.2 mm. and a slit length of 10 mm. DEVELOPIKG.ARL thermostatic developing machine and plate dryer. ELECTRODES.The electrodes were formed from standard grade spectroscopic carbon rods. The electrodes were arsenic-free in that 0.5 gram of the powdered carbon contained less than 0,001 mg. (0.0002%) of arsenic trioxide as determined by the Gutzeit method (12). YIG-L-BUG. The mixing instrument used for the preparation of powdered standards (Spex Industries, Inc.) consisted of a motor, controlled by a 0- to 60-second timer, which oscillated a pair of clips. The plastic vial containing the sample was mounted in these clips. The vial containing a small plastic pestle moved through a 6l/*O arc in a figureeight motion at 3200 r.p.m. PHOTOGRAPHIC EMULSION.Eastman Spectrum Analysis No. 1 plates. DEVELOPMENT. Kodak D-19, rocked for 4 minutes a t 20' C. Short stop, then indicator stop bath for 10 seconds. Fixing, Eastman Kodafix for 15 minutes. Washing, 20 minutes in ARL plate washer. EMULSION CALIBRATIOS.The Spectrum Analysis S o . 1 emulsion was cali1666
ANALYTICAL CHEMISTRY
WLER E L E C T R m
A
851LER ELECTRODE PLUG
WJNTER EECTROOE
B
Figure 1.
C
Boiler electrodes
All dimensions in mm.
Table 1. Optimum Excitation Conditions for Spectrographic Determination of Arsenic in Coal Ashes
Arsenic line employed 2349.84 A. Sector attenuation Total exposure Antimony line employed 2612.30 A. Sector attenuation Third step of reduction Electrode type Boiler Exposure time 40 seconds Preburn None Sample weight 100 mg. 7.5 mm. for Plug length" (distance plug inserted in eleccoal ashes, 11.0 mm. trode) for standard samples Spectral order Second Internal standard mixture 100 mg. Voltage drop 40-50 volts Current 15 amperes Electrode gap 2.5 mm. Slit width 20 microns Slit height 7.5 mm. Only first four Sector steps usedb steps employed except when calibrating emulsion Distance plug was inserted into electrode depended upon density of sample. b Each step of sector covered 1.5 mm. of slit height, or a total of 6.0 mm. for the four steps used. 1.5 mm. of slit was unsectored. This portion is referred to as the total exposure step.
depending on the amount of arsenic trioxide present. DEVELOPMENT OF METHOD
-4 systematic study was made of the spectrographic variables usually associated with the development of a procedure, and of the variables introduced by the peculiarities of this electrode. The variables investigated were electrode type, sample size, plug length, optical sensitivity, amount of buffer, current, arc gap, slit width, emulsion characteristics, sample particle size, and standard sample preparation. The optimum conditions are listed in Table I. The use of the boiler electrode (Figure l,A and B ) permitted the detection limit of arsenic to be lowered. The electrode acted as a boiler and the source of a concentrated stream of element vapor. The electrode reached extremely high temperatures rapidly TI hen the arc was struck. The large cavity in the electrode enhanced fractional distillation of the elements. The more volatile ones were evolved during the early part of the arcing. Because the spectrographic detection limit of an element depends upon the mass of the element present and not concentration, the detectability of the volatile elements can be increased by employing a larger sample. The capacity of this electrode permitted the use of a larger sample than is normally employed in emission spectroscopy. The tapered top of the electrode decreased the amount of arc wandering, and led to better reproducibility. The unusual properties of the boiler electrode required the study of sample size, plug length, and particle size. The data indicated that a 100-mg. sample n-as necessary for the required detectability and that the boiler electrode n-as ideal for handling this quantity of sample. The electrode plug (Figure 1, B ) length was found to have a marked influence on the repeatability of the esposures. This effect was probably related to free space and temperature gradient in the electrode. The spectrograph employed offered increased optical sensitivity in the second order, which was an advantage. A buffer (powdered carbon) contributed better burning characteristics to the sample and better repeatability. Current seemed to have the most effect on the volatilization of arsenic. Higher currents favored the excitation of arsenic. This was attributed to electrode temperature and the high resonance potential of this element. Electrode gap width was not related to line intensity, but was important from the aspect of repeatability and arc wandering. Slit width was important from the standpoint of background effects on line intensity. The Spectruni
Analjsis No. 1 emulsion offered a suitable medium for ease of development and sensitivity. Sample particle size was important in regard to burning characteristics; samples having large particle size exhibited uneven burning qualities, nqhile small particle-sized samples created sample volume problems. All of these variables were found to have some effect on the spectrographic method. Because antimony and arsenic have similar resonance potentials (6.0 and 6.6 e.v., respectively), and are both relatively volatile, it was felt that antimony would be a suitable internal standard. Moving plate studies showed that arsenic and antimony had similar vaporization patterns and they m-ere both completely volatilized out of the sample in 30 seconds. iintimony was also an excellent choice for internal standard, since it was rarely present in coal ashes in amounts greater than 0.005% (antimony trioxide). The concentration of antimony trioxide (0.4%) in the internal standard mixture was selected on the basis of the usual maximum limit found in coal ashes, and also on the arsenic trioxide impurity in the antimony trioxide. Using this concentration the arsenic line intensity was little affected by the arsenic impurity in the antimony trioxide and the antimony line intensity was not altered by the antimony content of the coal ashes. The 0.47, nntimony trioxide required sector attenuation t o decrease the Sb 2612.30 A. line intensity to a suitable level. This is advantageous, in that the sector may simultaneously reduce the arsenic line intensity to a readable level if high concentrations are encountered.
Table II. Spectrographic Analysis of Standard Samples by Internal Standard Method
As2O34 Content of Samples, $7, Found
0002
0005
%As,O.
OM0
0.0104 0.0103 0.0105 0.0120 0.0103 0.0100 0.0113 0.0115 0.0135 0.0126 0.0105 0.0113
0Ox)
0.0204 0.0240 0.0235 0.0195 0.0232 0.0232 0.0225 0.0212 0.0210
0.0304 0.0305 0.0285 0.0360 0.0290 0.0325 0.0400
0.0350 0.0342 0.0285 0.0290 0.0323 0.0037
0,0205
0.0215 Average 0.0220 Standard devi- 0,0011 0,0014 ation Coefficientof 9,7 6.4 11.5 variation, % 8.6 7.8 6.3 Error, % Including 0.0004% As203impurity in KBS plastic clay.
IN SAMPLE
Figure 2. Analytical working curve for arsenic in coal ashes
corrected t o I s b ratio was used for the analytical curve (Figure 2).
Q
RESULTS AND DISCUSSION
INTERNAL STANDARD METHOD. The analytical curve represented an average of at least triplicate exposures, while the standards containing 0.0025 and 0.005% arsenic trioxide were excited in quadruplicate. Background corrections were made on the arsenic line as described. The intensity ratio of the line pair is a linear function with arsenic concentration from approximately 0.01 to 0.04% arsenic trioxide. Below 0.01% the curve tended to deviate from a straight line, attributable to the low intensity level of the arsenic line, the 0.00047, arsenic trioxide residual impurity in the
plastic clay, and the major contributions of background to the line intensity. At low arsenic line intensity values the effects of the residual impurity and the background intensity were more pronounced. The precision and accuracy of the method were evaluated by analyzing three standard samples containing known amounts of arsenic trioxide (Table 11). The accuracy seems to lie between 5 and 10% of the amount of arsenic present, which is high considering the large number of variables which may affect the analysis, and the poor
PROCEDURE COAL SAhtPLEs. The coals n-ere ground to minus 200 mesh and ashed at 750' C. (unless otherwise specified) in a muffle furnace. SPECTROSCOPIC PROCEDURE. One hundred milligrams of coal ash and 100 mg. of the internal standard mixture n ere weighed on glazed paper and thoroughly mixed. The mixture was placed in the boiler electrode and gentlj packed by taping the electrode on a hard surface. A KO.0 pharmaceutical gelatin capsule was used to cover the top of the electrode to prevent loss of sample during loading and the plug was inserted. The lower electrode was made the anode. The counterelectrode (Figure 1, C) was placed in the upper holder and the two were aligned on the optic axis. The electrode gap was adjusted to be 2.5 mm., the arc was struck, and the shutter opened simultaneously. The Sb 2612.30 A. line intensity was evaluated in the third step and the As 2349.84 A. line intensity in the total exposure step. A background correction n a s made on the arsenic line by subtracting the average background intensity (evaluated on both sides of the line) from the gross line intensity. The
Table 111.
Spectrographic Analysis of Coal Ashes by Internal Standard Method
7%
A920a1
AP090 0 0 0 0 0
AP091 0 0048 0 0053 0 0061 0 0070 0 0075
0078 0075
0076 0073 0065
0 0062
Average Standgrd deviation Coefficient of variation, yo As203 in ashes (Gutzeit), % Error (assuming Gutzeit value correct), 70 As203 in coals (Gutzeit), Yo Ash in coals, yo As203 retained in ash (based on Gutzeit analysis), % a
0 0 0 0 0 0 0 0 0 0
AP092 0035
0 0 0 0 0
AP093 0 0037
OOii0
0036 0036 0031
0 0 0 0
0028
0015 0032 0028
0 0035
n
no28
0055 0076 0076
0062
0074
0072 0083
0081
0085 0073
0,66081 11.1 0.0066 10 6 0 00106 13 20 82 2
0 0061 0,00096
15.7 0.0040 52 5
0 00066 12 18
73 8
0.00021 6.0
0,0040 12 5 0 00054
12 89 95 5
0.00073 26.1 0,0028 0 0
0 00049 14 86 84 9
Value not included in average.
VOL 30, NO, 10, OCTOBER 1958
1667
Table
IV. Spectrographic Analysis of AP091 -H Coal Ash 750' C. Ashing Temperature At'mospheric Oxygen-Enriched, 6, Conditions 750 550 450 255 210 260 960 12.85 12.81 13.12 13.86 0.0220 0,0225 0.0255 0.0185 0.0190 0.0210 0,0190 0.0170 0.0225 0.0170 0.0210 0.0148 0.0237 0.0223 0.0220 0.0160 O
Total ashing time, min. Ash, 70 AslO3 in ash,
70
Average Standard deviation Coefficient of variation, 3% Ass03 in ash (carbon-free basis),
0.0218 0,0017 7.8 0.0218
0.0207 0.0022 10.6 0.0207
0.0219 0.0024 11 .o 0.0224
0.0166 0.0014 8.4 0.0180
-4sZOt in original coal (Gutzeit
in coal (calcd.), Yo
0.0028 0.0031
0.0027 0.0031
0.0029 0.0031
0,0023 0.0031
As203 retained in ash, %
90.3
87.1
93.5
74.2
70
AS203
method), 70
reproducibility usually reported for the direct current arc. The results indicate the method to be as reliable as many reported, in which the alternating current arc or spark was employed. Table 111 indicates the results of the spectrographic analysis of four anthracite coal ashes. The precision seemed to vary from 5 to 25% and the accuracy from 0 to 50% (based on Gutzeit value). Although this was not in agreement with the accuracy obtained on the standard samples, two factors must be considered. Three of the samples contained less than 0.005% arsenic trioxide, and the accuracy of this method is reduced below this amount because of background influence and the low arsenic line intensity a t the concentration level. The fourth coal ash (AP090) , having a n arsenic trioxide content greater than 0.005%, exhibited an accuracy within the 5 to 10% range. Also the error was calculated, assuming the Gutzeit values to be correct. Because the accuracy of the Gutzeit method may vary from 5 t o loo%, the Gutzeit values differ from the spectrographic values only by the approximate error of the method. Considering these two factors, the values agree reasonably well. VOLATILIZATION OF ARSENIC. On combustion of coal a varying quantity of its arsenic content is retained in the ash. The retention depends largely on the conditions of combustion and on the carbonate and chloride content of the coal (15). The arsenic content (expressed as arsenic trioxide) of 25 coals, ranging in rank from lignite to anthracite, and six cokes was determined by Duck and Himus ( 3 ) . The samples were ashed at 750" C. and the arsenic content of the ash was determined. It was found that the amount of arsenic retained in the coal ashes varied from 50 to 85% with an average of 69%. KO correlation was reported between the
1668
ANALYTICAL CHEMISTRY
rank of coal and arsenic retention. Upon ashing (750" C.) and carbonizing (820' C.) the same coal, it was found that more arsenic was retained in the ash than in the coke, and it was concluded that arsenic tended to be lost under reducing conditions, and retained under oxidizing conditions. The analysis of the four anthracitic coals (AP090 to AP093) and their ashes is given in Table 111. The data indicate that the coals retained 82.2, 73.8,95.5, and 84.901, of the arsenic upon ashing, with a n average retention of 84%. This figure is higher than the 69% retention reported by Duck and Himus ( 3 ) . However, these coals (AP090 to AP093) and 18 of the 25 coals studied by Duck and Himus contained less than 13 p.p.m. of arsenic trioxide. Considering the accuracy of the Gutzeit method a t these low concentrations, neither of these figures is reliable. Even though sufficient determinations were made on the coals (AP090 to AP093) and their ashes to minimize the error, it would appear that the arsenic content of the coals was too low to obtain reliable information concerning the volatilization of arsenic upon ashing. Because anthracite coals relatively high in arsenic \\ere not readily available for study, a bituminous coal unusually rich in arsenic and blended with an anthracite (AP091) mas utilized. The arsenic content of this coal blend (AP09l-H), as determined by the Gutzeit method, mas 0.0031% arsenic trioxide (Table 113. A shallow layer (6 grams in a 7-em. diameter silica dish) of this coal blend was ashed in a muffle furnace under different conditions. The air temperature of the furnace and the temperature of the coal bed were determined by thermocouples. The temperature of the coal did not reach a temperature greater than 5" C. above the air temperature of
the furnace. The coal was ashed a t 750" C., without oxygen, and a t 750', 550', and 450" C. x i t h oxygen passing into the furnace at a rate of 10.5 f 0.5 liters per hour. The furnace was raised to the prescribed temperature a t an average heating rate of 12" C. per minute beginning a t room temperature. The spectrographic analysis of the ashes obtained from ashing this coal at different temperatures and conditions is recorded in Table IV. The findings are contrary to expectations from vapor pressure considerations. A greater amount of arsenic was lost a t 450' C. than a t 750" C. Headlee (8, 11) attributed this behavior a t lon-er temperatures to more extensive thermal decomposition and mechanical loss of very fine ash containing higher arsenic concentrations. There is a relationship n-ith ashing time; 960 minutes were required to ash the coal a t 450' C. but only 210 minutes a t 750" C. Thus time of ashing rather than ashing temperature seems to have the most pronounced effect on arsenic retention. Passing oxygen over the coal during ashing appeared to have little, if any, effect on the arsenic content of the ash. The values obtained a t 750' C. without oxygen, and a t 750" C. with oxygen, were all within experimental error of each other. It appears that a n oxygen-rich atmosphere offers no advantage for the retention of arsenic upon ashing. These findings on one coal are not conclusive, but indicate a trend. Excluding the ash sample obtained a t 450' C. the average amount of arsenic retained in these ashes was 90.3%. More studies should be made concerning the volatilization of arsenic to validate these observations further. OTHER METHODS
Qualitative Estimation. T h e method employed was a n absolute line blackening-concentration correlation. The plotting method was a modification of t h e qualitative plots developed by Love11 (14). Triplicate standard samples of each concentration were exposed, and t h e blackening of t h e total exposure step of t h e As 2349.84 A. line was measured. The average. transmittance of the step \vas plotted against per cent arsenic trioxide on log-log paper. This curve was used for evaluating arsenic trioxide in subsequent samples. Table V summarizes the results obtained on four different samples, using this plot. The application of the direct relationship for the estimation of arsenic in standard samples indicated that the method resulted in a higher degree of accuracy than was expected. This was attributed to several factors. The samples were identical in composition to those employed for the preparation of the estimation curve, which
meant that variations caused by matrix difference were not inherent in the analysis. I n using the method for coal ashes, the matrix of the sample tended to vary, 1%hich probably decreased the accuracy of the estimation. Also, 10 determinations were made on each sample, which tended t o cancel out any extraneous variables. The relatively high accuracy obtained by this method was inherent in the conditions. Because of the tapered top of the electrode little arc wandering occurred, which tended to equalize the amount of radiant energy reaching the slit. and increased the repeatability of the exposures. Because the former two factors are not inherent in the method, lower degrees of accuracy are to be expected for coal ash analysis. The results on the coal ash sample (Table V) substantiated this concept. The arsenic content of the ash obtained spectrographically \vas in 947, error of the value obtained by the Gutzeit method. Honever, because of the extreme low arsenic line intensity a t this low concentration, and the poor accuracy of the Gutzeit method, the large error should not be taken as representative. The accuracy of the method probably lies between 20 and loo%, depending upon sample matrix, number of determinations made, and the amount of arsenic present in the sample. The method would be useful when only a qualitative estimation is needed. Total Energy Method. T h e d a t a in Table VI indicate t h a t t h e total energy method can be applied t o the determination of arsenic in samples having a n arsenic trioxide content greater t h a n 0.02’%. T h e method of application of this technique is essentially t h a t of Headlee and Hunter (9). Below this amount the intensity level of the arsenic line is lorn, and one is no longer n-orking on the linear portion of the emulsion curve. Another disadvantage of the total energy method is that the amount of arsenic present in the external standard and sample should not vary by a factor greater than 2 . The value obtained for samples containing 0.03, 0.025, and 0.02% arsenic trioxide showed a n error of 3.3, 8.0, and 150/,, respectively, n hen compared with the external standard containing 0.047, arsenic oxide (Table VI). As the concentration of arsenic in the samples deviated from 0.047,, the error increased. For reliable results the limitations of the method must be ronsidered. The qualitative estimation method would be useful for a first approximation and thus minimize the error resulting from deviations of the arsenic ratio in standard and sample. Generally, the accuracy of the total energy method varied from 5 to 20%, depending upon matrix effects, concentration of arsenic being determined, and the arsenic ratio of standard and samples.
Table
V.
Qualitative Study on Standard Samples and Coal Ash A P 0 9 0
Asz03found in samples,
Average Standard deviation Coefficient of variation, yo Error, yo a
Standard Standard I I1 0.01047, 0.02047, A S Z O ~ ~ .48203’ 0.0080 0.0230 0.0094 0,0190 0.0094 0.0250 0.0130 0,0220 0.0110 0.0300 0.0140 0,0270 0,0084 0.0225 0.0160 0.0285 0.0084 0.0270 0.0125 0.0216
Standard Coal Ash I11 AP090 0 . 0 3 0 4 ~ 0 0.0066yo ASz03’ ASZO~~ 0.0300 0.0120 0.0370 0.0190 0,0370 0.0084 0.0285 0.0185 0.0260 0.0160 0.0255 0.0225 0.0330 0 .0i30 0.0310 0.0115 0,0305 0.0093 0.0260 0.0048 0.0110 0.0080 0,0105 0.0105 0.0165
0.0110 0.0026 23.6 5.8
0.0305 0.0040 13.1 0.3
0.0246 0.0033 13 4 20.6
0.0128 0,0045 35.2 93.9
Including 0.0004% Ass08 impurity in XBS plastic clay. Value obtained by Gutzeit method.
Table VI.
Added to XBS Plastic Clay,
%
0.04 0.03 0.025 0.02 0.015 0.01 0.005
Arsenic Analysis Employing Total Energy Method
Standards Employed for Comparison 0.0404yo ASZO~ 0.02547, A S 2 0 3 0.0154% A S 2 0 3 Found, Error, Found, Error, Found, Error,
% 0:029 0.027 0.023 0.020 0.017 0.013
%
3:3’low
8 . 0 high 15.0 high 33.3 high 70.0 high 160.0 high
%
7,
%
$0
0.038 0.03
5 . 0 low
0,031 0.023 0.019 0.016
22.5 low 23.3 low 24.0 low 20.0 low
0.012 0,010
100.0 high
0 I024 0.020 0.016 0.012
LITERATURE CITED
(1) Anderson, C. H., Beatty, C. D.,
ANAL.CHEM. 26, 1369 (1954). (2) Assoc. Offic. Agr. Chemists, “Tentative RIethods of Analysis,” 8th ed., p. 396, 1955. (3) Duck, S. W., Himus, G. K., Fuel 30, 267 (1951). (4) Edgcombe, J., Gold, H. K., Analvst 80, G 5 (1955). ’ (5) Goldschmidt, V. M., Ind. Eng. Chem. 27, 1100 (1935). (6) ‘Harper, D . A., Strafford, N., J . SOC. Chem. Ind. Japan 61, 74 (1942). (7) Haa-ley, J. E., Can. Mining and M e t . Bull. 5 8 , 412 (1955). (8) Headlee, A. W.J., private comrnunication. (9) Headlee, A. W. J., Hunter, R. G., ASAL.CHEW22, 441 (1950). (10) Headlee, A. R.J., Hunter, R. G., Ind. Eng. Chem. 45, 548 (1953). (11) Headlee, A. W. J., Hunter, R. G., West Virginia Geol. Survey 13A, V, VI1 (1955). (12) Hertaog, E. S., IND.ENG.CHEM., ANAL.ED. 7, 163 (1935). (13) Hunter, R. G., West Virginia Geol. Survey, Rept. Invest. 5 (1948). (14) Lovell, H. L., unpublished research,
0.0
20: O’high 33 3 high
60.0 hiih 140.0 high
20.0 high
Mineral Industries Expt. Station, Pennsylvania State Univ. (15) ilIonkhouse, A. C., Coke and Gas 12, 363 (1950). (16) Nunn, R. C., Lovell, H. L., Wright, C. C., Trans. 11th Anthracite Conf. Lehigh Cniv. (1953). (17) Kunn, R. C., Pustinger, J., Hall, R. H., Report of Anthracite Research, Serial S o . 53, 56, 58, 60, Mineral Industries Expt. Station, Pennsylvania State Univ. (1954). (18) Rafter, T. A., Xature 155, 332 (1945). (19) Shaw, D. RI., Joensuu, 0. I., Ahrens, L. H., Spectrochim. Acta 4, 233 (1950). (20) Slavin, 11. L., ISD. EXG. CHEW, ANAL.ED. 10, 407 (1938). (21) Wedepohl, K. H., Geochina. et Cosmochim. Acta 3, 93 (1953). RECEIVED for review December 11, 1957. Accepted May 21, 1958. Contribution 57-36 from Fuel Technology Department and PlIineral Constitution Laboratories of the College of Mineral Industries, The Pennsylvania State University. Submitted by R. H. Hall in partial fulfillment for the M.S.degree in fuel technology, 1956, a t the Pennsylvania State University. VOL. 30,
NO. 10, OCTOBER
1958
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