CONCLUSIONS The choice of time constant of the measurement system in flameless atomic absorption depends on the purpose. For theoretical studies, undistorted signals are required since otherwise all measurements from which conclusions will be drawn are influenced by instrumental parameters. Also, for practical purposes, the use of a fast response system is preferable in most cases because it enhances the separation of the analytical signal from the background signal, it provides a longer linear working range of the calibration curve and a higher sensitivity. It has only two disadvantages, a slightly increased detection limit and a much higher cost.
ACKNOWLEDGMENT The authors are greatly indebted to J. Balke and F. van de Vegt for their technical assistance.
LITERATURE CITED
Figure 6. Calibration curves for copper measured with different time constants of the low-pass filter Either the amplifier (curve 3) or the recorder (curves 1 and 2) determines the speed of response. Settings of the low-pass filter, cf. caption of Figure 3
signal or by reducing the noise level. In flameless AAS, the noise level can be reduced by decreasing the bandwidth of the low pass filter. This, however, results in a reduced peak height and consequently in a reduced sensitivity. It will be clear from Table 111, as might be expected from Figure 2, that the condition of optimum S/N ratio is most favorable. However, the gain in comparison with undistorted signals or highly distorted signals is small or even insignificant.
(1) J. D. Winefordner and T. J. Vickers, Anal. Chem., 36, 1947 (1964). (2) J. D . Winefordner and C. Veillon. Anal. Chem., 37, 417 (1965). (3) B. V. L'vov, "Atomic Absorption Spectrochemical Analysis", Adam Hiiger, London, 1970. (4) F. J. M . J. Maessen and F. D. Posma. Anal. Chem., 46, 1439 (1974). (5) J. P. Matousek. Amer. Lab., June, 45 (1971). (6) B. V. L'vov, in "Atomic Absorption Spectroscopy", Plenary Lectures presented at the International Atomic Absorption Spectroscopy Conference, Sheffield, 1969, R. M. Dagnall and G. F. Kirkbright, Ed., Butterworths, London, 1970. (7) J. P. Matousek and K. G. Brodie, Anal. Chem., 45, 1606 (1973). (8) Yu. I. Belyaev and T. A. Koveshnikova, "Proceedings of the XVll Colloquium Spectroscopium Internationale", p 62. (9) K. R. Spangenberg, "Vacuum Tubes", McGraw-Hill, New York, N.Y., 1948. (10) J. D . Ingle, Jr., and S.R. Crouch, Anal. Chem., 43, 1331 (1971). (1 1) J. S. Bendat, "Principles and Applications of Random Noise Theory", John Wiley & Sons, New York, N.Y., 1958, pp 55-60. (12) R. B. Bonsali. J. Gas Chromatogr.,2 , 277 (1964).
RECEIVEDfor review November 4, 1974. Accepted July 14, 1975.
Use of Sodium Borohydride for Determination of Total Mercury in Urine by Atomic Absorption Spectrometry John Toffaletti and John Savory Departments of Medicine, Biochemistry, Pathology, and Hospital Laboratories, University of North Carolina, Chapel Hi//,N.C. 275 14
Sodium borohydride is studied as the reducing agent for determination of mercury in urine. Aqueous sodium borohydride is added to a buffered urine sample, effecting the rapid reduction of inorganic, methyl, and phenyl mercury compounds. A heated quartz tube mounted in an atomic absorption spectrometer is used to detect mercury. Recoveries average 103 O h for mercury( II) and methylmercury( II) ions and 105% for phenylmercury(l1) ions added to urine. The detection limit is 1-2 nanograms and the precision of the method is 6.5% (RSD). The effects of several potentially interfering compounds found in urine have also been studied. Total analysis time including sample preparation is three minutes per sample.
Present interest in the determination of mercury has stemmed principally from its toxicity to man due to industrial and laboratory exposure, accidental or suicidal ingestions, and its presence as a pollutant in the environment.
The most commonly employed methods for determining mercury in urine and other samples have used a cold vapor atomic absorption technique, based upon the reduction of inorganic mercury by a stannous compound, followed by a process of sweeping the free mercury atoms into a quartz tube mounted in an atomic absorption unit. Sensitivity was excellent, and minimal interference was observed, due principally to the separation of mercury from the sample matrix prior to atomic absorption measurement. Muller ( I ) and Woodson (2) were among the first to utilize the high vapor pressure of mercury for its determination in air. Poluektov et al. (31,using atomic absorption, obtained an unusual enhancement of the mercury signal when stannous chloride was present in the samples. This enhancement was due to the reduction of ionic mercury to free mercury atoms which were vaporized much more efficiently. Hatch and Ott ( 4 ) used a cold vapor technique for determining mercury in rock samples in which mercury atoms present as a vapor were continually recirculated in a closed system until a peak absorbance was observed, usual-
ANALYTICAL CHEMISTRY, VOL. 47, NO. 13, NOVEMBER 1975
*
2091
ly in 2-3 min. Rains and Menis ( 5 ) modified this method by using controlled heating and a packed refluxing column during digestion to prevent losses of mercury. Interference due to water vapor in the cell was eliminated by heating the absorption cell to 200 "C. Magos and Cernik (6) reported that inorganic mercury could be determined in urine by stannous reduction without prior digestion; however, organomercurials could not be estimated by this method. In refinements of their procedure, Magos reported that the addition of a cadmium salt to the reaction mixture effected the reduction of methyl mercury as well as inorganic mercury (7, 8). Kubasik et al. (9) described a procedure for the determination of total mercury in urine and plasma. An overnight digestion was required although analysis was quite rapid after this digestion step. Bouchard ( 1 0 ) also described a procedure for analysis of mercury in urine using a 5-minute digestion with chromic acid. A review of the methods up to 1970 has been compiled by Manning ( 1 1 ) . Recent advances in the analysis of mercury include a carbon rod atomization procedure in which hydrogen peroxide was used to prevent the loss of mercury during the drying stage; however, no ashing stage for removal of protein and other organics was used in the method (12). Fitzgerald e t al. ( 1 3 ) employed a U-tube cold trap to preconcentrate mercury before analysis by atomic absorption. The mercury was eluted by controlled heating of the U-tube and measured a t levels as low as 0.2 ng. I t has been known for many years that sodium borohydride effects the reduction of a wide variety of metal ions, including mercury ( 1 4 ) . Nevertheless, it had rarely been used in analytical procedures for mercury until it was employed by Braman for the determination of mercury using a spectral emission-type detection system ( 1 5 ) . The present report describes a thorough study of the sodium borohydride reduction of mercury compounds in urine.
sponse strip chart recorder (Omniscribe 5000, Houston Instrument, Bellaire, Texas 77401). Mercury and iron hollow cathode lamps (Jarrell-Ash Division, Waltham, Mass. 02154) were mounted in the atomic absorption spectrometer. Modification of the atomic absorption unit involved replacement of the burner head with an electrically heated quartz absorption tube connected to a mercury generation system as shown in Figure 1. The absorption tube was constructed from a 1.1-X 15-cm quartz tube left open at both ends. A 6-mm X 8-cm quartz gas inlet was connected a t the center and the 11-cm central portion of the absorption tube was wrapped with asbestos covered No. 26 Chrome1 A wire (Fisher Scientific Co., Fair Lawn, N.J. 07410). A variable transformer (Staco, Inc., Dayton, Ohio) was used to apply a voltage across the Chrome1 wire. A mount for the absorption tube was cut from aluminum stock and interfaced to the absorption tube using asbestos sheet. The absorption tube was optimally aligned in the light path of the atomic absorption unit to allow maximum intensity of light to pass through its opening. A mercury generation device was fabricated from a 100-ml graduated cylinder cut a t the 30-ml division, and a No. 6 rubber stopper fitted with three holes to accommodate 6-mm glass tubing was inserted into the cylinder. The rubber stopper had provision for an argon bubbling inlet, a sodium borohydride injection port, and an outlet with a bubble trap. Argon flow was monitored with a rotameter and directed either through the mercury generation device into the absorption tube or through a bypass directly into the absorption tube by means of a 3-way stopcock. Reagents. Sodium borohydride (5% w/v) was prepared by adding 1.5 g of sodium borohydride (Sigma Chemical Company, St. Louis, Mo. 63178) to 30 ml of deionized water. This solution was used within 1-2 hr after preparation. Dow Corning Antifoam B (Fisher Scientific Company, Fair Lawn, N.J. 07410) was used as obtained from the supplier. Copper(I1) sulfate solution (1 mg/ml) was prepared by dissolving 250 mg of copper(I1) sulfate (J. T . Baker Chemical Company, Phillipsburg, N.J. 08865) in 100 ml of water. A 0.5M phosphate buffer, p H 6.5, was prepared by dissolving 35 g of sodium dihydrogen phosphate (Baker) and 20 ml of 10N NaOH (Fisher) in 500 ml of water, then titrating to pH 6.5. An aqueous standard solution of mercury(I1) chloride (500 pg/ ml) was prepared by weighing out 67.65 mg of mercury(I1) chloride (Alfa Inorganics, Beverly, Mass.), adding to a 100-ml volumetric flask and diluting to the mark with water. The methylmercury(I1) chloride standard (100 pg Hg/ml) was prepared from 12.52 mg of methylmercury(I1) chloride (ICN.K&K Laboratories, Inc., Plainview, N.Y.) diluted in a similar fashion to the mercury(I1) chloride standard. Aqueous phenylmercury(I1) acetate standard (500 pg Hg/ml) was prepared by adding 83.92 mg of phenylmercury(I1) acetate (Sigma) to a 100-ml volumetric flask and diluting to the mark. These stock standards were diluted with water to obtain 1 pg/ml working standards. A mixed standard was prepared by combining equal volumes of the three 1 pg/ml working standards. Procedure. Preparation of Urine Samples. Aliquots from 24-hr urine samples were collected in 170-ml plastic specimen containers (Superior Plastic Products, Providence, R.I. 02905) and one drop of antifoam B per 10 ml of urine was added. Analysis. A 1 pg/ml methylmercury(I1) chloride standard was used to prepare aqueous standards of mercury in the range of 10200 ng. The appropriate amount of standard was then added to the generation device followed by 1 ml of deionized water and 1 ml of the pH 6.5 buffer. Prior to analysis, several blanks were run through the system to remove mercurial contaminants and ensure a stable blank signal. Urine samples were then prepared by pipetting 1 ml of urine into the generation device, adding 10 pl of 1 mg/ml copper(I1) sulfate and 1 ml of pH 6.5 buffer. With the absorption tube heated a t 120 volts (850 "C), argon, flowing a t a rate of 200 ml/min, was bubbled through the sample just before injecting 1.5 ml of 5% sodium borohydride. After each determination, the generation device was thoroughly rinsed with deionized water and shaken dry.
EXPERIMENTAL
RESULTS AND DISCUSSION
Apparatus. The analysis of mercury was performed with a dual channel-dual monochromator atomic absorption spectrometer (Model 810, Jarrell-Ash Division, Fisher Scientific Company, Waltham, Mass. 021543, which permitted simultaneous monitoring at two wavelengths and was capable of delivering a background-corrected response. Peak areas were monitored by an integrator recorder (3380 A Integrator, Hewlett-Packard, Avondale, Pa. 19311) and peak heights simultaneously recorded by connecting a fast re-
Effect of pH and Tube Temperature. T o study the effect of p H on the reduction of mercury compounds, 0.5M buffers ranging in pH from 0.5-9.0 were prepared. One hundred nanograms of either mercury(I1) chloride, methylmercury(I1) chloride, or phenylmercury(I1) acetate were added to 1 ml of these buffers and each compound was analyzed in duplicate. As seen in Figure 2, all three compounds
n
h
detector
source
Figure 1. Diagram of mercury generation device and heated absorption tube The parts are (1) generation cylinder: (2)argon bubbling inlet: (3) sodium borohydride injection port: (4) outlet with bubble trap: (5)plastic syringe; (6) 3-way stopcock: (7)gas inlet: (8)quartz absorption tube wrapped with chrome1 wire
2092
ANALYTICAL CHEMISTRY, VOL. 47,
NO. 13,
NOVEMBER 1975
1004
o 0
1
2
3
4
L 5
6
7
8
L " I
9
DH
30
(%I
&O)
(370)
Applled Voltage [Temperature
-'c]
Flgure 2. Effect of pH with absorption tube at room temperature 0-0 100 ng rnercury(l1) chloride, 0-0 100 ng methylrnercury(l1) chloride, and 0-0 100 ng phenylmercury(l1) acetate
were essentially quantitatively reduced over the pH range studied. The rates of reduction were much more rapid in the lower pH ranges as judged by peak height measurements; however, the most striking observation was the nonuniformity in response from the three mercury compounds. Since previous work using a heated tube had shown that dimethylmercury was decomposed upon heating to a sufficiently high temperature (16), a p H study similar to that shown in Figure 2 was performed, except this time the quartz tube was electrically heated by the chrome1 wire. The results of this clearly demonstrated that, by heating the tube, the differences in response from the three mercury compounds were eliminated. The reason for such behavior was investigated by measuring the peak area from 100 ng of each mercury compound analyzed a t different tube temperatures. A pH of 6.5 was chosen as a reasonable pH a t which to work, consistent with equivalent responses from the mercury compounds and safety (See Precautions). Figure 3 shows the manner in which temperature affects the area response from the three mercury compounds. As the temperature increases, the response of both mercury(I1) ion and phenylmercury(I1) ion decrease consistent with a shortened residence time of the elemental mercury in the quartz tube. Methylmercury(I1) ion shows a similar decrease up to 60 volts (530 "C), while a t 90 volts (690 "C) there is a very distinct increase in the response of this compound. The decomposition of a volatilized compound from methylmercury(I1) chloride appears to be occurring. Similar results with diphenylmercury and dimethylmercury confirm that little of the phenylmercury compounds are volatilized previous to reduction, while a significant proportion of the methylmercury compounds are lost before reduction can occur. Interferences. Interferences from major constituents found in urine were studied a t concentrations in their upper normal range. To a solution of each of these compounds was added 50 ng of mercury(I1) chloride and the recovery of mercury was determined in each case. As seen in Table I, none of the compounds tested had a large effect upon the response of mercury(I1) ion a t their normal concentrations. Cysteine slowed the rate of reduction considerably; however, it had no effect upon the area response. The addition of copper(I1) ion at 10 pglml increased the reduction rate such that the peak height observed in the cysteine-copper(I1) ion solution was nearly the same as that seen from mercury(I1) ion in purely aqueous solution. Copper(I1) ion at very high concentrations in aqueous solutions supressed the response of mercury(I1) ion. This effect is most likely from amalgamation of mercury atoms with elemental copper which is also a reduction product of sodium
Flgure 3. Effect of absorption tube voltage (temperature) 0-0 100 ng rnercury(l1) chloride, 0-0 100 ng rnethylrnercury(l1) chloride, and 0-0 100 ng phenylrnercury(li)acetate
borohydride acting upon copper(I1) ion (17). As a result of this, no copper(I1) was added to aqueous standards as was the case with urine. Background Absorption. Our instrumentation provided the capability for simultaneous monitoring of two wavelengths and, therefore, the ability to correct for background absorption. In this study, a comparison between the 2537-A analytical line for mercury and the 2524-A line emitted from an iron hollow cathode lamp was made. At room temperatures, there was a small background absorption due presumably to water vapor. With rising temperature the 2524-A background line showed an increasing nonspecific absorption apparently from hydrogen burning in the tube. The 2537-A analytical line from the mercury lamp showed no such interference. As a result of this study, no background correction was employed in further work. Effect of Copper(I1) Ion on Response of Mercury Compounds i n Urine. One-ml aliquots of pooled urine samples were spiked with 100 ng of either mercury(I1) ion, methylmercury(I1) ion or phenylmercury(I1) ion, than analyzed a t pH 6.5 using a heated quartz tube. Figure 4 shows that while mercury(I1) ion and methylmercury(I1) ion gave very similar responses in urine, the reduction of phenylmercury(I1) ion was so slow it was not detected by our integrator. It was known that the addition of copper(I1) ion to urine samples would markedly accelerate the reduction of ~
~~
~
Table I. Summary of Mercury(I1) Interference Study Reccvely
from HzO, Species
Na+ K+ Ca2+ Mg2+
cu2+ cu2+ c1-
so42HP04'HCO3Citrate Uric acid Creatinine Bovine albumin Cysteine Cysteine + (100 kg/ml CU")
ANALYTICAL CHEMISTRY, VOL. 47,
Concentration
%
100 mmol/l. 100 mmol/l. 5 mmol/l. 4 mmol/l. 5 Wml 100 pg/ml 3.5 mg/ml 2.0 mg/ml 2.0 mg/ml 2.0 mg/ml 1.0 mg/ml 0.25 mg/ml 1.0 mg/ml 0.1 mg/ml 0.5 mg/ml 0.5 mg/ml
102 102 99 96 100
NO. 13, NOVEMBER 1975
70
102 100 100 104 102 98 102 98 98 98
2093
1004
/
1
0 50
' O V
f 20
10
00
30
50
40
Copper (ill Ion Added
(
Wid)
0-0 100 ng mercury(l1) chloride in urine, 0-0 100 ng methylmercury(l1) chloride in urine, and 0-0 100 ng phenylmercury(l1)acetate in urine
Table 11. Recovery a n d Precision D a t a Recovery Using P e a k Area, %
Mercury (11)
Subject
?dethylmerrur/ (11)
D.L. J.H. R.B. P.W. D.F.
107 97 105 102 102
113 100 103 104 97
Mean
102.6 i 3.78
103.4
D.L. J.H. R . B. P.W. D.F.
110 124 99 106 94
Mean
106.6 i 11.5
B.
Determination
105.2 i 3.42
Recoven/ Using P e a k Height, %
94 100 93 97 94
KO. of d e m s
20 20
82 94 56 71 61
95.6 i 2.88 C.
Peak area Peak height
Phenylmercury (11)
107 102 101 108 108 6.03
72.8 i 15.5
Precision .Mean
Std dev
RSD, %
102.6 ng 98.0 ng
6.63 ng 3.58 ng
6.47 3.62
mercury(I1) ion, so the effect of adding copper(I1) ion to urine samples was studied for all mercury compounds. As Figure 4 demonstrates, copper(I1) ion did accelerate the reduction of phenylmercury(I1) ion in urine to a rate similar to the other mercury compounds. At a copper(I1) ion concentration of 10 pg/ml, the area responses of the three mercury compounds were most similar and all urine samples were treated with this concentration of copper(I1) ion in further work. At levels above this, the responses of all mercury compounds tended to decrease in a similar manner as was seen in aqueous solution for mercury(I1) ion. Precision. A pooled urine sample was spiked with 100 ng/ml of mercury from a standard containing equal amounts of mercury(I1) ion, methylmercury(I1) ion and phenylmercury(I1) ion. After adding 10 pg/ml of copper(I1) ion, 1-ml aliquots of this pool were analyzed by the method. Table I1 shows for twenty replicate analyses an RSD of 6.4% was obtained when peak areas were analyzed. Analytical Curves for Aqueous and U r i n e Standards. A pooled urine sample as well as urine standards 2094
Verc. 'y
150 1
200
ngl
Figure 5. Aqueous and urine standard curves determined from peak area response 0-0
Figure 4. Response of mercury compounds in urine with addition of copper(li)ion
A.
100
Aqueous mixed standard, 0-0 Urine with mercury(l1) chloride, Urine with methylmercury(l1) chloride, and 0-0 Urine with phenylmercury(l1)acetate
*-*
containing either mercury(11) ion, methylmercury(I1) ion, or phenylmercury(I1) ion were prepared and analyzed according to the proposed method. Aqueous standardization was accomplished by using either the mixed standard or methylmercury(I1) chloride. Each of the three mercury compounds in urine gave nearly identical peak heights. Mercury(I1) ion in aqueous solution was reduced more rapidly producing a greater peak height and slightly smaller peak area (See Figure 3). Methylmercury(I1) ion reacted virtually the same in either aqueous solution or urine, and we found the greatest accuracy was attained by use of either a mixed standard or methylmercury(I1) chloride for aqueous standardization. This is most important when peak height determinations are performed. Figure 5 shows the standard curves of the three mercury compounds in urine closely paralleled the aqueous standard curve over the concentration range 0-200 ng added mercury. This demonstrated that recoveries of the mercury compounds in urine were consistent over the concentration range studied. I t further demonstrated the method gave a linear response a t least up to 200 ng of mercury. Recoveries. Five normal volunteers collected urine samples in the plastic containers. T o each sample was added 100 ng/ml of either mercury(I1) chloride, methylmercury(I1) chloride, or phenylmercury(I1) acetate, then analyzed by the proposed method. The recoveries listed in Table I1 averaged 102.6% for mercury(I1) ion, 103.4% for methylmercury(I1) ion, and 105.2% for phenylmercury(I1) ion when peak areas were used. P e a k Area vs. P e a k Height. The data in Table I1 and Figure 6 show that very good accuracy was obtained by monitoring the areas of the peaks. The use of peak areas was necessary due to the slightly slower reduction of phenylmercury(I1) ion in urine which produced a shorter, broader peak than the other compounds. There were, however, several good reasons for using peak heights to quantitate mercury levels in urine. As Table I1 shows, the accuracy obtained using peak heights was essentially quantitative for mercury(I1) ion and methylmercury(I1) ion. Because of the slower reaction rate of phenylmercury(11) ion, the apparent recovery of this species in urine averaged 73%. There would typically be small amounts of phenylmercury compounds in urine, and such inaccuracy is within acceptable limits for a clinical application. Table I1 also shows the better precision obtained from peak heights over peak areas. Finally, good electronic integrators are expensive and may not be as readily available as a chart recorder.
ANALYTICAL CHEMISTRY, VOL. 47, NO. 13, NOVEMBER 1975
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
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