PRECACTIONS. In the lower p H range, a hazard exists due to the possibility of a mild explosion of the hydrogen being rapidly evolved. This can be alleviated t o a large extent by purging the generation device with argon for 5-10 seconds previous t o the addition of sodium borohydride. At pH 6 . 5 , it was necessary only to start the argon bubbling immediately before adding the sodium borohydride. When these conditions were used, an explosion did not occur. LITERATURE CITED (1) K. Muller, Z. Phys., 65, 739 (1930). (2) T. T. Woodson, Rev. Sci. Instrum., I O , 308 (1939). (3) N. S . Poluektov, R. A. Wtkun, and T. V. Zelyukova, Zh. Anal. Khim., 19, 873 (1964). Anal. Chem., 40, 2085 (1968). (4) W. R . Hatch and W . L. (5) T. C.Rains and 0.Menis, J. Assoc. Off. Anal. Chem., 55, 1339 (1972).
(6) L. Magos and A. A. Cernik, Brit. J. Ind. Med.. 26, 144 (1969). (7) L. Magos, Analyst(London), 96, 847 (1971). (8) L. Magos and T. W. Clarkson, J. Assoc. Off. Anal. Chem., 55, 966 (1 972). (9) N. P. Kubasik, H. E. Sine, M. T. Sine, and M. T. Volosin, Clln. Chem., 18, 1326 (1972). (10) A. Bouchard, At. Absorp. Newsl., 12, 115 (1973). (11) D. C. Manning, At. Absorp. Newsl., 9, 97 (1970). (12) H. J. lssaq and W. L. Zielinski, Anal. Chem., 46, 1436 (1974). (13) W. F. Fitzgerald, W. E. Lyons, and C. D. Hunt, Anal. Chem., 46, 1882 (1974). (14) H.I. Schlesinger, H. C. Brown, A. E. Finholt, J. R . Gilbreath, H.R. Hoekstra, and E. K. Hyde, J . Am. Chem. SOC.,75, 215 (1953). (15) R. S. Braman, Anal. Chem., 43, 1462 (1971). (16) J. Toffaletti and J. Savory, Clin. Chem., 20, 885 (1974). (17) R. S. Braman, personal communication, 1975.
RECEIVEDfor review February 3, 1975. Accepted July 14, 1975.
Analysis s f Petroleum for Trace Metals: Determination of Trace Quantities of Beryllium in etroleum and Petroleum Products by Heated Vaporization Atomic Absorption Winston K. Robbins Analytical & Information Division, Exxon Research & Engineering Company, Linden, N.J. 07036
John
H. Runnels and
Ruth Merryfield
Research & Developnient Department, Phillips Petroleum Company, Bartlesville, Okla. 74004
Two analytical methods are described for the direct determination of beryllium in petroleum and petroleum products by heated vaporization atomic absorption (HVAA). The methods are applicable to the determination of 1 to 50 ng Be/g with a precision (relative standard deviation) of 10% at the 30 to 40 ng/g level. The methods were crosschecked in cooperating laboratories and the results indicate that reliable analyses can be obtained when the methods are applied in other laboratovies.
The toxicity of beryllium has placed this metal high on most priority lists as a hazardous environmental pollutant (I). In 19'73, the Environmental Protection Agency imposed strict emissions standards on beryllium. For stationary sources, no mole than 10 g Be/24 hours may be emitted and the ambient levels in air may not exceed 0.01 pg Be/m3 (2). The concern with these emissions into the atmosphere (3-5) has prompted a study of beryllium in petroleum. Although studies of beryllium levels in coal have been reported (6). few references have appeared for beryllium in petroleum ( 7 , 8 ) . In recent years, sensitive analytical techniques for beryllium have been extensively studied because of the increased use of this metal in industrial and space activities. This element can be detected in quantities as low as 4 X 10-' g using gas chromatography coupled with solvent extraction ( 9 ) . Even h w e r detection limits are possible with a gas chromatography-mass spectroscopy procedure ( I 0). In more classical procedures, sensitivities below 0.1 wg are attainable by colorimetric, fluorometric, or emission spectroscopic procedures ( I 1 ). Because of its low atomic number, beryllium is not risadily detected by X-ray fluorescence procedures.
Flame atomic absorption has been applied to the determination of traces of beryllium in a variety of matrices ( 4 , 12, 13). Interferences with flame atomic absorption are numerous, however, even with the nitrous oxide-acetylene flame (14). Heated vaporization atomic absorption (HVAA) has been applied to the direct determination of several metals a t trace levels in petroleum (15-18). The direct determination of manganese a t the 10 ng/g level in petroleum using HVAA has been recently reported (19). The detection limit for beryllium in aqueous media by HVAA has been extended to similar levels (20-22), and the technique has been applied to the determination of ppm levels of beryllium in silicate rocks (23). This paper describes two HVAA procedures which are capable of determining beryllium in petroleum and petroleum products a t the ng/g (ppb) level. One procedure utilizes the Varian-Techtron Model CRA-63 Carbon Rod Atomizer and the other the Perkin-Elmer Model HGA-'70 Graphite Furnace Atomizer. The procedures were developed independently in different laboratories and both were crosschecked by cooperating laboratories using samples spiked with known amounts of beryllium.
EXPERIMENTAL Standards and Reagents. All reagents and solvents were ACS reagent grade. Organic beryllium standards used in the procedures were prepared by serial dilution of Conostan 5000 f i g Be/g (Conoco, Ponca City, Okla.) reference standard. Aqueous standards were prepared in distilled water by serial dilution of F & J Scientific 1000 mg Be/ml reference standard immediately before use. Preparation of Samples for Interlaboratory Cross-Check. Oils typical of those encountered in the petroleum industry were spiked with known amounts of beryllium as the sulfonate (Conostan) and thoroughly mixed on a paint shaker or with a magnetic stirrer. T h e samples were transferred t o Teflon bottles and
ANALYTICAL CHEMISTRY, VOL. 47, NO. 13, NOVEMBER 1975
2095
Table I. Cross-Check Samples CR.4-63 p a c e d u x Sample d'rcrlpt
Benlliur- addcd.
on
N o . 2 Heating o i l E llenbe r g e r c r u d e Light Arabian crude
r:,
g
38.5 38.5 38.5
HG 4 -70 proccdurc
No. 2 F u e l oil No. 6 F u e l o i l Shale o i l p r o d u c t
35.0 38.9 32.3
Table 11. Instrumentation and Parameters CR1-63 pri?cc,durL
Analytical l i n e Background Slit Band p a s s Photomultiplier Recorder R e a d out Time constant Scale expansion A t o m i z e r tube Support electrodes Inert gas Cooling w a t e r Inj e c t ion f r e q u e n c y Sample size D r y cycle Ash c y c l e Atomize c y c l e
234.9 nm ( T e c h t r o n Be Lamp 12 mA) Continuum ( J a r r e l l Ash H, L a m p 1 3 mA) 100 bni 0.33 n m R- 106 ( H a m a m a t s u ) Speedomnx W ( L e e d s & N o r t h r u p --hhltirange) A b s o r b a n c e peak height 0.5 s e c 1OX ( R e c o r d e r 0-1 mV Range) Pyrolytic coated (Varian; U It r ac arbon) FX-9 ( P o c o G r a p h i t e ) 4 1. / m i n ( S i t r o g e n ) 4 1. / m i n 90 s e c 1 ill ( P f i z e r 644E M i c r o p.i . pette) 1 . 5 S e t t i n g . 0.004 kW: 20 s e c 6 . 5 S e t t i n g , 0.13 kW, 30 s e c 1.30 kW. 3 sec 8.5 S e t t i n g , tic 1-70P K ' C C ' i L d L
Analytical line Background corrector Slit Instrument r e s pons e Atomization volts Atomization timl? Charring time Charring cycle Furnace
Recorder Lam12 c u r r e n t
234.9 n m On 4 (0.? nm)
1 10 10 s e c Optimize for each sample
7 G r o o v e d Type ( P e r k i n - E l m e r No 040-6088) T r e a t e d with 600 g of z i r c o n i u m .and 600 g of 1anth anu m 2 mV full s c a l e Adjust t o b a l a n c e b a c k g r o u n d corrector
shipped to cooperating laboratories where both the unspiked (base) oils and spiked samples were analyzed as blind samples by the described procedure. The oils used in the cross-check program and the level of the beryllium added are presented in Table I. A p p a r a t u s a n d Operating P a r a m e t e r s . Optimum parameters for the determination of beryllium with the CRA-63 Carbon Rod Atomizer were established using a Jarrell-Ash Model 82-532 Atomic Absorption Spectrophotometer. Optimum parameters for the HGA-70 Graphite Furnace Atomizer were established using a Perkin-Elmer Modei 403 Atomic Absorption Spectrophotometer equipped with a deuterium lamp background corrector. Both the CRA-63 and HGA-70 have been described in the literature (2426). 2096
The atomizers were aligned in the optical path of the instruments so that minimum instrument responses (blanks) were produced during the atomization cycle by the furnace incandescent radiation. Optimum instrumental parameters established by this study are presented in Table 11. While these parameters provide optimum settings for the atomizers and instruments used in this study, they may not be optimum for other instruments; and it is recommended that each instrument be optimized for the determination of beryllium. The furnace elements used in the HGA-70 were of the grooved type that attain a maximum temperature of 1950 "C (27). Because of this low atomization temperature, beryllium is not quantitatively atomized with the furnaces as received from the manufacturer. As previously reported (281, beryllium can be quantitatively atomized from furnaces coated with a carbide-forming element or preferably a combination of elements. Consequently, all furnaces used in the HGA-70 part of this study were previously treated with 600 pg lanthanum followed by 600 pg zirconium. Sample P r e p a r a t i o n a n d Measurement-CRA-63. DirectStandard Addition Procedure. Weigh 2.5 grams of sample into a 5-ml volumetric flask and dilute to volume with tetrahydrofuran (THF). With a microliter syringe, place 1 pl of sample solution into the atomizer and record the beryllium response using the instrumental conditions described in Table 11. If the absorbance is greater than 0.05, prepare a more dilute solution by secondary dilution with T H F or by weighing a smaller sample into the volumetric flask. After the sample-solvent ratio has been adjusted to give an absorbance of less than 0.05 for a 1-pl sample aliquot, measure the response from three independent aliquots by injecting the aliquots into the atomizer at 90-second intervals. If the three signals agree to within &10%of their average, use the average absorbance for the beryllium response of that sample; if not, make two additional measurements and use the average of the five measurements for the beryllium absorbance for that sample. Add 5 pl of a 5 pg Be/ml (25 ng Be total) standard to the sample. Mix well and again obtain an average beryllium response by injecting the sample aliquots into the atomizer at 90-second intervals. In a similar manner, obtain an average beryllium signal after a total of 50 and 7 5 ng of beryllium have been added. Measure the background absorbance for each matrix at the beryllium absorbing line with a continuum lamp. Wet Digestion Procedure. Place 5.0 grams of oil into a 500-ml Kjeldahl flask and add 25 ml of sulfuric acid and 50 ml nitric acid. Place the flask on a heating mantle and raise the temperature gradually until fumes of sulfuric acid begin to evolve. Cool the flask slightly, add 25 ml nitric acid dropwise, and heat the solution again to white fumes. Add more nitric acid in small portions until a total of 125 ml is used. Cool the contents of the flask, transfer to a beaker, and evaporate to incipient dryness. Dissolve the salts in 5 ml of 1 N sulfuric acid and analyze for beryllium by HVAA using the methods of standard additions described above, substituting a 5 pg Be/ml aqueous standard for the 5 pg Be/ml standard in THF. Calculation. Calculate the concentration of beryllium in the original sample using the following equation: Ao - b (25ng) ng Be/g oil = -X -(i) 2.5 A1 - Ao where Ao is the average recorder signal for the sample solution, b is the signal at the non-absorbing line, i is the number of the addition, and A , is the average recorder signal after the ith addition of beryllium. The final value is calculated as the average of the values. Sample P r e p a r a t i o n a n d Measurement-HGA-70. Procedure. Weigh 12.5 grams of sample into a 25-ml volumetric flask and dilute to volume with THF. Heavy samples such as vacuum residues may require a secondary dilution to reduce the viscosity sufficiently to be handled with a microliter syringe. With a microliter syringe, place 100 p1 of sample solution into the furance that has been previously coated Kith a carbide-forming element. Initiate the heating cycle and record the response until the atomization cycle has terminated and the recorder returned to base line. If the beryllium signal is more than half scale, prepare a more dilute sample by secondary dilution or, alternately, weigh a smaller sample into the volumetric flask. Repeat the measurement two more times. Measure the beryllium response as described below and use the average of the three measurements as the beryllium response for the unspiked sample. With a microliter syringe, add 100 pl of a 1.0 pg beryllium standard (100 ng of Be). Mix well and again obtain an average response after a total of 200 and 300 ng of beryllium have been added t o the sample solution. Record a furnace blank that will be used to make background correction.
ANALYTICAL CHEMISTRY, VOL. 47, NO. 13, NOVEMBER 1975
TERMINATION OF iATOUIZATION CYCLE
-H
BLANK
B< SIGNAL
FURNACE BLANK
Figure 1. Background correction (HGA-70 procedure) 10~
T h e beryllium response is superimposed upon a positive background (blank) resp3nse that is caused by incandescent radiation from the atomizer reaching the detector of the instrument. Consequently, the background contribution to the total response must be determined to esi;ablish the net beryllium response. This is accomplished using the termination of the atomization cycle as a marker. The distance, in mm, between the termination of the a t omization cycle and the beryllium peak maximum is established (Figure 1. left). The background response at the same distance from the termination of the atomization cycle is determined (Figure 1, right), and subtracted from the total response. The difference is the net beryllium response. Some of the newer atomic absorption instruments are equipped with optical baffles that. prevent the incandescent radiation from reaching the detector of the instrument. The corrections discussed above may not be necessary for these instruments. Calculation. The Concentration of beryllium in the sample is determined using a standard additions plot. Plot the average beryllium response vs. ng beryllium added per gram of sample and draw the best straight line through the series of points. Extrapolate to the ng Be/g axis. The point of intersection is the concentration (ng Be/g) in the sample. A typical plot for a sample that contains 24 ng Be/g is shown in Figure 2 .
0.
,
/
p’,
28 24
20
, , , , 16
12
8
i
,
,
,
,
4
0
4
8
12
ng
Bela
16
20 2 4
Figure 2. Determination of beryllium
Table 111. Matrix Effects in the HVAA Determination of Beryllium with the CRA-63 Procedure P?O
