can be made. Multiple scans can be performed, and the results added or a background scan can be generated and subtracted.
ACKNOWLEDGMENT We would like to thank John Decker for allowing us to use his design for the 509 slot mask. We also acknowledge
the assistance of Art Grant and his men a t the Chemistry Department Machine Shop. Received for review September 19, 1973. Accepted March 4, 1974. Research sponsored by Air Force AFOSR-74-2574. One of us (FWP) appreciates support from an NDEA Title IV Fellowship.
Determination of Zinc and Cadmium in Environmentally Based Samples by the Radiofrequency Spectrometric Source Yair Talmi Analytical Chemistry Division, Oak Ridge National Laboratory, Oak Ridge, Tenn
The applicability of the radiofrequency furnace (RFF) spectrometric source to the analysis of trace amounts of cadmium and zinc in environmental samples is described. Modifications in the original design of the system were employed to enhance sensitivity and reduce interferences. Both atomic absorption ( A A ) and atomic emission (AE) spectrometric modes have been successfully used with samples pretreated by various methods such as wet ashing, on-substrate wet ashing and Soluene solubility, and by direct analysis. Samples analyzed include coal, fly ash, bunker oil, gasoline, soil, bovine liver, orchard leaves, and fish gonad. The samples, once prepared, were analyzed at the rate of five per minute with an average overall accuracy of 6.8% and reproducibility of 5.5%. Detection limits for Cd and Zn were 5 pg with the A A mode and 6 and 8 pg, respectively, with the AE mode. Relative sensitivities are in the 0.001-0.5 ppm range. Interferences in the two operating modes are compared.
Among the various non-flame spectroscopy devices, the radiofrequency furnace (RFF) source has a unique position due to its ability to employ both atomic absorption (AA) and atomic emission (AE) modes. The fundamental processes involved in RFF analysis and the parameters by which they are governed were previously described ( I ) . A presentation of the practical applicability of the system to the direct analysis of trace elements in geological, metallurgical, a n d biological materials has also been given ( 1 ) . The present study represents the progress to date using this system for the analysis of trace amounts of Cd and Zn in various environmental samples. The natural association of zinc and cadmium in the geological and biological environment and the fact that cadmium toxicity may be largely associated with its ability to replace zinc in important metalloenzymes or other metalloproteins are the factors which promote environmental concern (2). The samples analyzed by the RFF system included both Cd donors-i. e., coal, oil, gasoline, and tobacco products-as well as Cd accumulators-i. e., soil, sediment, and biological and plant tissues. (1) (2)
Yair Talmi and G. H. Morrison,Ana/. Chem.. 44, 1455 (1972) William Fulkerson and H. E Goeller. "Cadmium, The Dissipated Element," ORNL-NSF Environmental Program Report, Oak Ridge, Tenn , 1973, p 29.
EXPERIMENTAL Reagents. Redistilled HzO and "03 were used in the standard preparation and wet ashing procedures. "Soluene-100," a quaternary ammonium hydroxide prepared as a xylene and toluene solution by Packard Scientific, or a 25% tetramethyl ammonium hydroxide-ethanol solution served as biological tissue solubilizers ( 3 ) . High purity, 5-9's, cadmium and zinc were dissolved in " 0 3 to prepare the corresponding 1000 pg/ml standard stock solutions. Tantalum Substrates. Tantalum substrates of Ys-in. to 5hs-in. diameter with volume capacities of 5-50 r l were punched from 0.005-in. thick tantalum sheets by simple dies. Such relatively shallow substrates stack very well and up to 400, Yg-in. diameter, can accumulate inside the furnace before their removal is required. To reduce zinc blank levels, the freshly cut substrates were prebaked in the RFF at 1500 "C for 15 minutes. Up to 1000 substrates can be treated simultaneously. The time required for the total procedure of cutting, cleaning, and prebaking is approximately 2 hours per lo00 substrates. Solutions at the 0.5- to 25-pl volume range were transferred to the substrates by means of a microsyringe. When highly acidic solutions were treated, Teflon-plunger type syringes were preferred to improve reproducibility and reduce blank values. Solid samples, including fine powders, were directly weighed on the tantalum substrates and then immobilized by means of 1-2p1 of a dilute collodion solution. Apparatus. The primary instrumentation utilized in this newly built RFF system (Figure 1) is similar to that used previously ( 1 , 4 ) . It includes the following modifications: A more powerful RF generator; a substantial reduction in the number of coil turns when the system is utilized for AA; a newly designed crucible; and attachment of the helium exhaust outlet t o a vacuum pump. The major components of the RFF system are listed in Table I. The graphite crucible is surrounded by a layer of carbon black for insulation, continuously heated by induction with an RF field and flushed with helium. The hot graphite crucible serves as the principal source of atomization, while excitation occurs in the helium plasma discharge located above the mouth of the crucible. By selecting the proper working conditions, such as the induction coil and crucible design, location of the crucible mouth in relation to the optical path, helium flow rate, and pressure, either the AA or AE mode can be optimized. Samples in the form of solids or evaporated solutions are deposited on small tantalum substrates which are fed to the furnace via the introduction chamber. Procedure. Direct Analysis. Liquids such as blood, oil, and gasoline at the 1- to 20-pl range and solids such as freeze-dried liver, coal, and soil between 0.1-3.0 mg were transferred t o the substrates as previously described. All organic samples were then ashed in a muffle oven a t 450-500 "C for 8-12 hours, after which they were ready for analysis. (3) A. J. Schumacher, Department of Environmental Health, University of Cincinnati, College of Medicine, Cincinnati, Ohio 45219, private communication, 1972. ( 4 ) G . H . Morrison and Yair Talmi,Anal. Chem.. 42, 809 (1970) ANALYTICAL C H E M I S T R Y , VOL. 46, N O . 8, JULY 1974
e
1005
S INL'
Figure 1. RFF apparatus for atomic absorption and emission 45mm
Table I. RFF C o m p o n e n t s
Figure 2. Modified reaction tube and graphite crucible with winDescription
CO,"pO"e*t
Induction furnace
Monochromator
.
Amplifier Recorder Induction coil
7.5-KW output Lepel R F generator model number T-7.5-3-Mc-ASV V, operating in the 3-3.5 MHz frequency range. Jarrell-Ash 0.5-meter Ehert mountux scanning monochromktor with Itn 1180 ruling/mm grating blazed to 4000A. Keithley 409 Picoammeter. Sanhom 151 dual-pen. AA measurements: 3-4 turns, 3-i diameter coil made of l/&. i. turn coil W i t h one turn above t l side arms. Consjsts of a 355.long, 30-mm i. 34-mm o.d. Vycar tube with two sic arms each 64-mm long, 19-mm o s 17-mm i.d. Reaction tube w modified to accommodate the wi dow type graphite crucible, Figure AA measurements: window tyi pyrolytic coated graphite crucibl b-t!
Reaction tube
Graphite crucible Vacuum system
Optional attachment of outlet exhau to a primary vacuum pump allo\V S operation at reduced pressures doum to 4 mm Hg.
-
..,
-
. ..
. . . .. . .. .. wec Hsnmng. r reeze-uneu omlogical matenaa, coal, OIL, and gasoline were digested with concentrated "02 and HC101. To avoid frothing and uncontrolled reactions, no more than 3 grams were dissolved in 20 ml of "01 and 30 ml of HCIOI. The HC104 was added after the digestion by HNOJ was near completion (5). The final solutions were then transferred to 50- or 100-ml volumetric flasks and diluted to volume. Simultaneously, reagent blank solutions and standard checks for recovery studies were also digested. These solutions, 1-20 PI, were transferred to the substrates which were then placed an a Pyrex plate. The loaded plate was then gradually heated to 200". Tissue Solubilizotmn in "Soluent ?-1OO." The successful appliea,I".-"..+" i" F.'.^l. tion of Soluene to the analysis of $--"- .llTlllr.llm l.elll fi.AL.Ltd tissues was ureviouslv reuorted (6). This study has further extended its applicahilfty to freeze-dried materiais. A 0.5 gram of NBS freeze-dried liver standard was dissolved in 10 ml of Solue,ne at 70 "C during an 8-hour period. Aliquots, 1-20 pl, of the clear 1
1
1
1
...
(6) A. J. Jackson, L. M. Mictlael, and H J Schumacher, Anal. Chem., 44. 1064 (1972).
1006
ANALYTICAL CHEMISTRY, VOL. 46, NO. 8. JULY 1974
in a muffle oven as described above. On-Substrote Wet Ashing. Solutions in organic solvents, such as methanol solutions of tobacco extracts, and organically based liquids, such as oil and blood, can he directly wet ashed on the sampling substrate. The procedure involves the following steps: Deposition of liquid sample on the substrate; evaporation of the solvent; deposition of a few p1 of a solution 4 3 2 in concentrated HC1O1-H&O~-HN03, respectively, onto each substrate; gradual heating of the substrates on a hot plate to 220 'C; and ashing for 30-50 minutes, to completion.
RESULTS AND DISCUSSION Induction Coil and Crucible Design, Short e a p h i t e crucibles have been reported to produce more accurate and precise results whether AA or AE spectrometric modes are used (I). Thus, crucibles used in this study were confined to the 2 to 2'L-in. length range. T o maintain these shorter crucibles a t high temperatures ( i e . , 2000-2400 "C), the number of induction coil turns had to be reduced to 3-6. The heating capability of this coil is superior t o the previously reported 12-turns coil (I, Z), and at the same time its ability to form a potent helium plasma is substantially reduced. This 3-6 turn coil, therefore, is the ideal arrangement for AA measurements (I). For AE, however, where both efficient atomization and excitation of the samples are essential, a 6-7 turn induction coil was selected as a compromise. The drilling of two parallel windows through the walls of the short crucible (Figure 2) further improved AA sensitivity and reduced molecular absorption and scattering interferences. These observations indicate that a substantial inhibition of the molecular recombination and condensation of the free atoms is achieved, probably because of the drastic reduction in the temperature gradient across the optical path. Thus, the absorbance recorded for 50-pg samples of NaCl at the 213.8-nm Zn line was reduced from 0.08 to 0.03 dnd Cd and Zn sensitivities were improved from 20 to 5 pg by employing this design. The effect was even more pronounced with less volatile elements such as copper and chromium (7). . . Finallv. " . all crucibles were coated with hiah density pyrolytic carbon to improve the reproducibility and the day-to-day reproducibility of the results. (7) Ronald Crosmun. Ph.0. Dissertation. University of Tennessee. Knoxville. in preparation.
~~
~
~~
~
~~
~~
~
~
T a b l e 11. D e t e r m i n a t i o n of C a d m i u m in E n v i r o n m e n t a l l y Based Materials
Sample
NBS, Coal NBS, Fly ash Bunker Oil Gasoline No. 1 No. 2 No. 3 Soil No. 1 No. 2 No. 2 NRS, Bovine liver NBS. Orchard leaves Fish gonad No. 1 No. 2 No. 3
Average sample size, g
3
0.0002-0.0015 2.4 0.0002-0.0015 1.5 1.8 0.005-0.01 0.005-0.01 0.005-0.01 0.31 0.25 0.32 1.5 0.5 0.0002-0.0015 1.5 0.0002-0.0012 1.3 2.7
2.0
Pretreatment procedureU
WA D WA D L WA D D D L WA WA WA
Found, ppm
AA AA AA AE AA AA AA AA AA AA AA AA AA AA AA AA AA AA AA AA
ss
D WA D WA WA WA
a WA, wet-ashing; D, direct; L, leaching; SS,Soluene solubility. flame atomic absorption, NBS, National Bureau of Standards.
Concentration of Cd
Spectrometric mode
0.23 f 0.01 0.24 i0.03 1 . 5 i 0.09 1 . 6 i0.15 1 . 2 i0.04 0.85 i0.03 0.0078 i 0.0007 0.0070 i 0.0006 0.0085 i 0.0007 0.42 f 0.02 0.95 i0.04 0 . 4 1 i 0.02 0.29 1 0 . 0 1 3 0.30 j ~ 0 . 0 1 8 0 . 3 0 I 0.025 0 . 1 3 i 0.005 0 . 1 3 i 0.007 0.73 i 0 . 0 3 0.84 i0.07 1.16 i0.04
Reported, ppm
Independent methodC
0.23 f0.03
SMS
1.43-1.46
SMS
0.83
SMS SMS SMS SMS
0.018
0.017 0.020 0.38 0.78,1.05 0.36,0.48 0.27
SMS, FAA SMS, FAA NBS NBS SMS FAA FAA FAA
0.11
0.14 0.7 0.8 1.3
AA, atomic absorption; AE, atomic emission.
SMS, spark mass spectrometry; FAA,
T a b l e 111. D e t e r m i n a t i o n of Zinc in E n v i r o n m e n t a l l y Based Materials
Sample
Average sample size, g
NBS, Coal Bunker oil Soil No. 1
3 1.8
NBS, Bovine liver
1.5 1.5 0.5 0.0002-0.0015 1.5 0.0002-0.0012 1.3 2.7 2.0
NBS, Orchard leaves Fish gonad No. 1 No. 2 No. 3
0.25
Pretreatment procedure
Spectrometric mode
WA WA L L WA WA
AA AA AA AE AA AE AA AE AA AE AA AA AA
ss
D WA D WA WA WA
Procedural Design. The analytical procedure for many non-flame techniques involves the introduction of a liquid sample to an atomization chamber, followed by a dryingashing-atomizing cycle. The fact t h a t the sensitivity and the reproducibility obtained by these techniques are dependent on the volume of the samples and the variation in their location inside the atomization chamber is a t least partially attributed to the use of this sampling procedure (8).This is not a problem with the RFF where the solvent is evaporated before the sample is atomized. The RFF analytical procedure separates this cycle into discrete analytical steps of drying, ashing, and atomizing. A few hundred tantalum substrates are loaded with samples and then dried and ashed if needed. The samples, once ready, are continuously analyzed a t a rate of 5 per minute without disturbing the operating conditions of the furnace. Thus, the analytical procedure is simple, fast, and highly adaptable to routine work and automation. In addition, it has been noted t h a t the separation of the three-step cycle will minimize the matrix interferences (9). ( 8 ) Mary Glenn e t a / . , Anal. Chim. Acta, 5 7 , 2 6 3 , (1971). (9) G. K . Pagenkopf. D. R. Neuman. and Ray Woodriff, Anal. Chem.. 44, 2248 (1972).
Independent method
Concentration of Zn Found, ppm Reported, ppm
39.0 i 1 1.9iO.06 85 i 3 . 5 89 L 6 126 i 4 134 * 5 124 i 7 134 + 10 27 L 2 28 i- 3 12 i 0 . 4 47 i 2 . 0 28 i 1 . 1
37 i 1 1.7i 0 . 0 3 87
FAA APDC-MIBK SMS
130 i 10
NBS
25 i 3
NBS
10
FAA FAA FAA
49 28
>
TIME
(
Esec)
Figure 3. Dual s p e c t r o m e t r i c m o d e of t h e
RFF
Performance. Analytical Working Curves. The analytical curves obtained for Cd and Zn by atomic absorption a t the 228.8-nm and 213-8-nm line were linear a t the tested 10- to 1000-pg range and passed through the origin. The analytical curves for Cd and Zn obtained by atomic emisA N A L Y T I C A L C H E M I S T R Y , V O L . 46, NO. 8, JULY 1974
1007
-
3 0 ~ S gAL-
30 PQ
T a b l e IV. I n t e r f e r e n c e s of Salts and-Salt Mixtures w i t h the E m i s s i o n of Zinc Concomitant“
Enhancement factor
AIC13 CaCL CdClz FeCl, KCl NaCl NdC13 NHaCl PbCl, Combined salts mixtureb Synthetic fly ashc
0.63 0.78 0.54 0.75 0.69 0.61 0.82 0.94 0.77 1.08 1.06
13’
13 To.,
All concomitants weighed 10 pg and were added t o 50 pg of ZnC12. Samples which consisted of equal portions of all nine concomitants 90 pg total weights, were added to 50 pg of ZnClz. 5 p l of synthetic fly ash solution contains 12.5 pg FeCl?, 10 pg AICla, 2.5 pg CaCh, 2.5 pg MgClz, 1.8 p g KCI, 0.5 pg NaC1, and 0.5 pf TiC13.
3 0 p g SALT
-
30 pq Z n
.-
3 c PQ
10 Tori
sion a t 326.1 nm and 305.7 nm, respectively, were linear a t the 20-pg to 1-pg range tested and also passed through the origin. This advantageous extension of the dynamic range, is unattainable by other flameless spectroscopic sources. Detection Limits, Accuracy, and Precision. The AA sensitivity, defined as the amount of the element which results in 1% absorption, is 5 pg for both Cd and Zn. The AE detection limits, defined as the amount of element which produces a signal twice the size of that obtained from distilled water blanks, are 6 and 8 pg for Cd and Zn, respectively. Four different techniques of sample pretreatment were described earlier. To evaluate the accuracy of the results obtained by these techniques, the following independent checks were performed: Flame atomic absorption following the APDC-MIBK extraction of the digested samples; spark-source mass spectrometry utilizing the stableisotope dilution technique; analysis of NBS standard samples; AA and AE measurements carried out by the RFF following the APDC-MIBK extraction of the digested samples; and intra-instrumental comparison of the AE and AA results obtained by the RFF, as demonstrated from the analysis of Cd in fly ash, Figure 3. As stated above among the non-flame techniques, the RFF is unique in its ability to operate in both spectrometric modes. This intra-instrumental check can be of great advantage when other independent sources are not available. Tables I1 and I11 summarize the results for the determination of Cd and Zn in the following samples: NBS round-robin coal and fly ash standards, bunker oil, gasoline, soil, NBS Standard Reference Material 1577 (bovine liver), NBS Standard Reference Material 1571 (orchard leaves), and fish gonad. As presentated in Table 11, the percentage accuracy for the determination of Cd varied from 0% in NBS coal standard to 16.1% in leached fly ash with an average of 6.7% if the gasoline samples are excluded. The poor accuracy obtained for the gasoline samples can be attributed to losses of the highly adhesive, low viscosity gasoline by overflowing from the substrate, or to possible losses of highly volatile organic cadmium compounds a t the room temperature drying. The poor results obtained with the fly ash indicates an incomplete extraction of Cd by the leaching method used. This observation was reconfirmed via the comparative use of isotope dilution mass-spectrometry technique. The average percentage accuracy obtained for the Zn samples was 6.8% and ranged from 0-20%. All accuracy 1008
ANALYTICAL CHEMISTRY, VOL. 46, NO. 8, JULY 1974
-#ME
(=I
Figure 4. Non-specific spectral interferences under reduced
pressure values are, however, based on the validity of the values of independent methods used or certified values which also involve unspecified errors. The average relative standard deviation for all the determinations in Tables I1 and I11 was 5.5% and ranged from 3.3-10.7%. As will be described below, the precision is poorer with direct analysis of solid micro-samples where heterogeneity of the samples may be a problem. Interferences. Non-specific spectral interferences, (i.e . , molecular absorption and scattering) are, generally, characteristic of the RFF-AA spectrometric mode, while nonspecific vapor phase interferences ( L e . , changes in the excitation parameters of the R F plasma) are generally typical of the RFF-AE mode ( I ) . RFF-AE Interferences. Generally the AE spectrometric mode is more affected by the matrix than the AA mode. The interferences of volatile salts with the emission of Cd and Ag were previously demonstrated ( I ) . Table IV compares the interferences caused by various individual salts, 10 l g , on the emission intensity of 0.05 ng of Zn with that caused by all salts combined and with that caused by a fly ash synthetic matrix. Although their effects differ in magnitude, all individual salts show a common supressive interference. Conversely, the complex matrices show enhancement interferences whose absolute values are smaller than the absolute values of the “individual salt” interference. It is obvious, therefore, that conclusions concerning matrix effects which are obtained from examination of the effects caused by individual salts may be misleading. Considering the high ratio, /matrix// (Zn2-J zz lo6, the interferences caused by the matrices are low enough to allow the quantitative applicability of the AE mode. Yet, the use of the standard addition method is strongly recommended as a general practice. RFF-AA Interferences. The interference of volatile salts with cadmium absorption was shown to be less severe than that for emission ( I ) . Thus, the addition of 20 k g Bi(N03)3, CaC12, CrC13, CuC12, HgC12, In(N03)3, KI, NaCl, NaI, NHJ. PbC12, Sn(NO3)2, and ZnC12 to 20-pg samples of Cd*f showed an average change of 5% in the absorption values. Despite the high ratio [salt]/[Cd2+] = 106, the interferences were generally low enough, in most
Table V. C o m p a r i s o n of Sample P r e t r e a t m e n t Techniques Sample preparation mode
Wet ashing
Analysis time, minutes/100 substrates
Sample deposition: Sample evaporation: Sample analysis: Total time"
On-substrate wet ashing
Sample deposition: HClO, deposition and digestion: Sample analysis: Total time
Soluene solubility Sample deposition: Sample analysis: Total timew
Direct analysis
Sample weighing: Sample analysis: Total timez
Systematic errors
Random errors
Accuracy range,
Re1 std dev,
%
R
Contamination orig- (a) Syringe sampling 2-8 inating from re(b) Fluctuations in agents and the anthe parameters of alytical procedure the RFF systems, Dilute solution inLe., temperature, stabilities helium flow rate, discharge excitation Contamination Same as above 4-9 from concentrated Cross contamination HClO.; and air between substrates (dust fall) Loss of sample particles during the ashing procedure Contamination Same as above from Soluene and air Loss of sample particles during the ashing procedure Partial loss of the volatile analyte a t the ashing temperature Contamination (a) Sample weighing from air (b) Sample heterogeneity Partial loss of (C) Fluctuations in sample particles the parameters during ashing of the RFF system as above Partial loss of volatile analyte a t ashing temperature
Re1 sensitivity, ppm
3-11
0.030.5
4-13
0.0010.003
4-9
4-15
0.020.1
3-11
6-25
0,0010.003
Analysis time does not include the time required for solution preparation, which is approximately, 2-3 hours/lO samples. Y Analysis time does not mclude the solubilization time, 8-12 hours, of the substrates. ' Direct analysis requires a larger number of substrates for each sample because of the heterogeneous nature of the sample.
cases, to eliminate the need for a background corrector (10, 1 1 ) . A related study (7) on the RFF showed t h a t the presence of 104-fold excess of common concomitants such as Ca, Mg, Al, Na, K, and Fe salts changed the absorbance of P b and Cu a maximum of A0.03 absorbance unit with 0.01 being typical. The matrix effect was more severe in the case of zinc. Figure 4a shows the molecular absorption and scattering signals obtained at the 213.8 nm Zn line from zinc-free salts a t the 30+g weight level. These non-specific spectral interferences. although still remarkably low considering the high ratio of [salt]/[Zn2+],can be further reduced by operating at reduced pressures, 5-20 Torr. This was achieved by attaching the RFF exaust outlet to a primary vacuum pump and completely stopping the helium flow. Operating at reduced pressures accelerated the removal process of the vaporized matrix from the optical path, as shown by the shorter decay times of the absorption signals, Figure 4. b and c ( I ) . The result is a reduction in the molecular recombination and condensation of the free atoms and thus a corresponding reduction in the non-specific spectral interferences. The significantly reduced absorption signals of the various salts, and the similarity be-
tween absorption values of pure Zn and the Zn contaminated samples, Figure 4, b and c, demonstrates this improvement. The fact t h a t interferences caused by highly volatile elements which are known to produce short lifetime free atoms (12, 13) ( i e . , Na, K, Mg, and Ca), are most reduced by the vacuum, is similarly explained. Comparison of Sample Pretreatment. Table V summarizes some of the pros and cons of the various pretreatment procedures. Some of the most apparent conclusions include the following: The wet ashing method provides optimal accuracy and precision, but worse relative sensitivities. The on-substrate wet ashing procedure is limited a t present to relatively low organic-content samples such as cigarette condensates. The Soluene solubility procedure serves as a n exkellent substitute for wet ashing and provides superior relative sensitivities. However, the Soluene being a non-volatile solvent has to be ashed prior to analysis. The direct analysis procedure is naturally the most a t tractive choice, and the feasibility of the RFF to such a task is shown in Tables I1 and I11 and elsewhere ( I ) . Nevertheless, the direct analysis of solid micro samples. 0.3K Fuwa and B L Vallee. A n a / Chem , 35,942 (1963) (13) Yu V Zelyukova and N S Poluektov Zh A n a / Khtm (12)
(10) H L. Kahn, At. Absorption Newslett.. 7, 40 ( 1 9 6 8 ) . ( 1 1 ) B V L'vov. Spectrochim. ACTA, Part B, 24, 53 (1969)
18, 435
(1963) A N A L Y T I C A L C H E M I S T R Y , VOL. 46, NO.
8, JULY 1974
1009
Average particle size, i20u Standard deviation, 0.496m g
+-
6 1.2
Y W
aJ 0.8
!:::I:// Average particle size, 32p Standard deviation, 0.088mg
VI
z
v)
0.4
0.4
0.06 0.12
0.18 0.24
ABSORBANCE
Average particle size, 1 5 ~ 1.6
Average particle size, L7g Standard deviation, 0.045mg
and fly ash samples was performed. To minimize matrix interferences, all coal samples were ashed in a muffle oven after they were weighed on the tantalum substrates. Special care was taken to avoid the contamination of the substrates by covering them with a Pyrex beaker. Fly ash samples which are basically inorganic in nature were only dried a t 105 "C in an oven. Since the Cd content of fly ash was too high to be determined by AA, the AE mode with its more flexible dynamic range was used. Figure 5 shows the decrease in the scatter of results, Cd response, with the decrease in the average particle size of the sample. Thus, there is a significant improvement in precision as homogeneity is improved. The slightly worse than expected scatter associated with the fly ash samples is apparently a result of other error contributions from interferences characteristic of the AE mode.
CONCLUSION
Coefficient of variation, 6.5%
, "
0'4 0.06 0.12 0.18 ASSOASANCE
Although absolute sensitivities obtained by the RFF are generally inferior to those of other non-flame systems, matrix interferences are substantially reduced and large samples can be introduced, thus improving the relative sensitivities. Relatively minimal requirements for the pretreatment of the samples significantly shorten the analysis time, while accuracy, 6.8%, and precision, 5.5%, are adequate for most practical cases. The RFF system, thus, offers considerable potential for the rapid and routine analysis of Cd and Zn in a wide variety of environmentally based materials.
40 60 20 EMISSION INTENSITY, arbitrary
Figure 5. Dependence of the scatter of results on the nature of the solid sample
10 mg, may be associated with severe random errors originating from the weighing procedure and more so from sample heterogeneity ( I ) . Since the maximum allowable weights of samples is limited to the milligram range, an improvement in homogeneity can be accomplished only by grinding the samples as finely as possible (14, 15). To demonstrate this, direct analysis of cadmium in solid coal
Received for review July 5 , 1973. Accepted March 4, 1974. Oak Ridge National Laboratory is operated for the U.S. Atomic Energy Commission by the Union Carbide Corporation. (14) H. Massrnann, "Spurenanalyse mittles Atom absorption in der Graphitkuvetten nach L'vov mit einem Mehrkanaispectrometer;" I I Internationales Sirnposiurn "Reinststoffe in Wissenschaft und Technik," Dresden, 1965 (15) A. W. Kleernan, J. Geol. SOC.Aust.. 14,43 (1967)
Luminescence Properties of Sulfonamide Drugs J. W. Bridges Department of Biochemistry, University of Surrey, Guildford, England
L. A. Gifford, W. P. Hayes, J . N. Miller, and D. Thorburn Burns Department of Chemistry, Loughborough University of Technology, Loughborough, LE1 1 3TU, England
The fluorescence characteristics of sulfanilamide are similar to those of aniline. N',-substituted sulfonamides containing a n-electron deficient heterocycle are weakly or nonfluorescent, while those containing n-electron excessive heterocyclic rings, aliphatic chains, or acyl groups are strongly fluorescent. The N4-substituted sulfonamides are found to be nonfluorescent except for N4acetylsulfapyridine. Sulfonamide phosphorescence originates from a n * n transition in the lowest excited triplet level in the aromatic nucleus. Sulfonamides are determined in serum fluorimetrically at room temperature with coefficients of variance of 2-7%. Limits of detection for the sulfonamides are given. +
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A N A L Y T I C A L C H E M I S T R Y , VOL. 46, NO. 8, J U L Y 1974
Sulfonamides are amides of p-aminobenzenesulfonic acid, and are of considerable importance as bacteriostatic agents. During studies on the metabolism of some sulfonamide drugs ( I , 2), more rapid and sensitive methods ,of estimating these compounds were sought. Since these compounds contain the aniline moiety which has pronounced luminescence properties (3, 4 ) , the fluorescence and phosphorescence characteristics of a series of sulfona( 1 ) J . W. Bridges, Ph.D. Thesis, Universityof London. 1963. (2) J. W. Bridges, M . R . Kibby, S. R . Walker, and R . T. Williams, Biochem. J . , 109,851 (1968). (3) P. Pringsheim. "Fluorescence and Phosphorescence," Interscience, New York, N.Y., 1949. (4) J. W. Bridgesand R. T. Williams, Biochem. J.. 107,225 (1968).
