stability of the reaction products and the results of continued bromination. That Reaction (R4) does occur as a minor reaction is evidenced by the fragmentation patterns of mono-, di-, and tribromosubstituted N,N-dimethylanilines found by mass spectral analysis of the ether extract residue. Reaction (R4) for bromine can be “forced” upon the system to an appreciable extent only by addition of more than two moles of bromine per mole of methyl orange. The reaction of chlorine with methyl orange occurs about 70W by Reaction (R4) and about 30% by Reaction (R3) as estimated from the ratio of the p-sulfonate diazonium ion concentrations obtained for reaction of one and three moles of chlorine per mole of methyl orange, respectively. Both reactions (R3) and (R4) would be expected to result in a large decrease in absorbance at 505 nm; reaction (R3) because of steric hindrance preventing the dimethylamino group from assuming a coplaner configuration with the aromatic ring to which it is attached (2,9), and reaction (R4) because of destruction of the chromaphoric system due to azo link cleavage. Since the reaction products can themselves be halogenated, methyl orange should always be kept in excess when the decrease in absorbance at 505 nm is used for analytical determination of bromine and chlorine, otherwise, an erroneously low value of total halogen content will be obtained. This explains
why the manner of addition of halogen to working solutions is of such importance for accurate determination of true halogen content. By considering the total absorption spectrum in the region 200 nm to 600 nm, micromolar quantities of bromine and chlorine can be analytically differentiated from each other, provided that reaction conditions are closely controlled, namely, if very clean glassware is used throughout, if doubly distilled water is used throughout, if the concentrations of bromine and chlorine are low enough (or are in aqueous solution prior to reaction with methyl orange) to make the formation of BrCl unfavorable, and if the pH and temperature are held constant and are the same for which the calibration curves were produced. ACKNOWLEDGMENT
We wish to thank Jack Chang of Eastman Kodak for supplying thep-bromo-N,N-dimethylanilineand phydroxybenzenesulfonic acid sodium salt used in this investigation and for helpful suggestions for characterization of the reaction products. RECEIVED for review October 20, 1971. Accepted January 6, 1972. This investigation was supported by fellowship AP 48,933-01, Air Pollution Control Office, Environmental Protection Agency.
Determination of Alkylbenzenesulfonate and Alkylsulfate Homologs, after Electrophoretic Separation Using Aqueous Dioxane Agarose Gels John R . Bodenmiller and Howard W. Latz Department of Chemistry, Ohio Uniuersity, Athens, Ohio 45701 Alkylbenzenesulfonate and alkylsulfate homologs were quantitatively determined after separation by electrophoresis. The electrophoresis was carried out using aqueous dioxane/agarose gels in a cell which permitted direct contact between the gel and electrolyte. The gel strip containing the separated component was removed from the cell. The sample was extracted from the gel with water and was quantitatively determined by the methylene blue method of analysis. There were no significant differences in the amount of sample recovered from the gel after runs of 5.0 minutes, 1.0 hour, and 2.0 hours for 14 pg of pure p-3-124. The amount of recovery was 88.4% with a relative standard deviation of 0.6%. The relative standard deviation for direct methylene blue analysis of the same comWhen the gel strip was accurately pound was 1.4%. selected, values within 2.0% of the correct value were obtained.
THEPROGRESS MADE by various workers in their attempts to analyze sulfonic acids was described by Siggia and Whitlock ( I ) . A pyrolytic gas chromatographic method, for the determination of arylsulfonic acids and salts, based on the measurement of sulfur dioxide or parent hydrocarbon was recently developed by the stime authors ( I ) . This method gives ac( I ) S. Siggia and L. R. Whitlock, ANAL,CHEM., 42, 1719 (1970). 926
ANALYTICAL CHEMISTRY, VOL. 44, NO. 6, MAY 1972
curate results for the determination of total sulfonate. However, this method cannot be used to determine the concentration of homologs in alkylbenzensulfonate mixtures because the alkyl group undergoes pyrolysis. The pyrolytic gas chromatographic method introduced by Lew (2) for the determination of homologs and isomer distribution of various anionic surfactants gives quantitative results within +5%. While this method is quite versatile and analysis time relatively short, it is certainly not applicable to all situations. The same can be said of the gas chromatographic method recently developed by Puchalsky (3) for determintion of alkylsulfates. Bodenmiller and Latz ( 4 ) have shown that anionic surfactant homologs can be separated for qualitative identification by electrophoresis using aqueous dioxane agarose gels. The present paper describes a method for the quantitative determination of alkylsulfate and alkylbenzenesulfonate homologs based on their electrophoretic separation with a n improved cell and subsequent analysis with methylene blue. No prior treatment of the sample is necessary because nonionic impuri~.
(2) H. L. Lew, J. Amer. Oil Cliem. SOC.,44, 359 (1967). (3) C. B. Puchalsky, ANAL.CHEW,42, 803 (1970). (4) J. R. Bodenmiller and H. W. Latz, ibid., 43, 1354 (1971).
ties are electrophoretically removed. The present limiting factor for both accuracy and precision is the selection of the gel strip containing the sample. A result of general interest is that compounds, at least of this type, can be extracted from the gel matrix with high recovery and reproducible results. The aqueous solution can then be submitted to selected analysis. EXPERIMENTAL
Apparatus. Drawings of the electrophoresis cell are shown in Figure 1. The entire cell, except the glass cooling block top and glass cover, was constructed from lucite. The glass plate was attached to the rest of the cooling block with Silastic 140, a silicone rubber adhesive (Dow Corning Corporation, Midland, Mich.). Power for electrophoresis was supplied by a Savant constant voltage source (Savant Instruments Inc., Hicksville, N.Y.). Materials. The agarose, cat. No. 5-24046, was purchased from the Fisher Scientific Company, New York, N.Y., and was manufactured by L'Industries Biologie Francaise S A . The sources of the alkylbenzenesulfonates (1-ABS) and alkylsulfates (1-AS) are the same as those given in a previous paper ( 4 ) . The borate buffer solution used in the methylene blue determination was prepared by mixing equal volumes of 0.05M sodium tetraborate and 0.10M sodium hydroxide. The methylene blue was obtained from Eastman Organic Chemicals, Rochester, N.Y. Spectrophotometric grade chloroform containing 0.25 % ethanol was used for extraction. Procedure. PREPARATION OF THE GEL. The gel was prepared by mixing 0.96 gram of agarose, 40 ml of 0.020M, p H 4.5 acetate buffer, and 40 ml of dioxane in the same manner as described previously ( 4 ) . The hot gel solution was either heated or cooled to 65-70 "C and poured o n the glass plate of the cell. The method of pouring was to start at one end and make two quick passes over the length of the plate. Immediately after pouring, a few quick passes were made with a stirring rod t o ensure even coverage. The entire pouring process was accomplished within 10 seconds. Prior to pouring the gel, the compressible rubber and glass end plates were put into position, the cell was leveled in both axial directions, and circulation of water through the cooling block was started. One to two minutes after the gel was poured, the end plates were removed and nine sample holes were prepared in the same manner as described previously ( 4 ) . The two outside holes were located 2 cm from the edge and 2 cm from the next hole,>whilethe seven inside holes were 1 cm apart. This preparation gave a gel which was 0.010M in p H 4.5 acetate, 1.2 agarose, 50 % dioxane, and 50 water, and is about 1.4 mm thick. ELECTROPHORESIS OF THE SAMPLE.The buffer vessels were filled exactly t o the level of the top of the glass plate with p H 4.5, 0.020M acetate solution. The temperature of the circulating coolant was adjusted t o 17 O C . The sample was deposited in the prepared holes with a blunt needle microsyringe and a potential of 1700 volts was applied to the electrodes. Careful agitation of the buffer solution was accomplished with a magnetic stirring bar and magnet every 20 minutes. Some agitation is necessary for dilute electrolytes when the electrodes d o not extend across the vessel. After completion of the run, the buffer solution was removed with an aspirator. A new buffer solution was used for each run. DETECTION A N D TRANSFER OF THE SAMPLE.A 3-rnm strip of gel with its outer side located 2.5 cm from the edge of the gel was removed from both sides. Pinacryptol yellow was carefully applied to precipitate the reference samples located in the outside positions. After 2 minutes, the excess pinacryptol yellow solution was removed by tilting the cell and
Figure 1. Electrophoresis cell (all dimensions in inches) a.
b.
14 in. X in. X 1 in. braces 16 in. X 6'/2 in. X in. glass plates
rinsing with water from a wash bottle. A solution of 4 M NaCl was then applied t o the reference spots. After 3 minutes, the excess was removed by the same procedure. During this I)eriod no solution was allowed to enter the 3mm slit. The fluorescent reference spots were detected under ultraviolet light and their positions were marked. A cut was made across the gel 3 mrn in front of the reference spots. A second cut was made 1.9 cm behind and parallel t o the first cut. The strip of gel thus defined was removed from the plate by carefully inserting a spatula under the narrow side and lifting in the proper manner. The gel strip was placed directly into a 100-mi beaker. A second gel strip called the gel blank of the same size was removed to a second beaker in the same manner. The gel blank was usually taken 7.5 cm behind the sample strip. EXTRACTION OF THE SAMPLE FROM THE GEL. Sixty-five milliliters of water were added to each 100-ml beaker containing a gel strip. The beaker containing the sample strip was placed above a magnetic stirrer and the contents were stirred at moderate speed for 1.0 hour. The stirring rate was such that the gel strip was broken into pieces of 9 t o 16 square mm size during this period. The solution from the beaker was poured into a hirsch funnel (Coors Porcelain 000) containing Whatman No. 40 filter paper. The solution was collected in a 125-in1 filter flask under partial vacuum. The gel was transferred to the funnel with a 10-ml portion of water followed by a 5-ml portion. The solution in the filter flask was quantitatively transferred with 10 ml of water to a previously prepared 125-ml separatory funnel. The method used for METHYLENE BLUEDETERMINATION. the determination of the samples was a n adaptation of the one described by Abbott ( 5 ) which was an improved version of
----
( 5 ) D. C. Abbott, A m l y s t , 87, 286 (1962).
ANALYTICAL CHEMISTRY, VOL. 44, NO. 6, MAY 1972
927
Table I. Typical Migration Distances for Alkylbenzenesulfonates and 1-Alkylsulfates in 50 % Dioxane/Agarose Gels. (Applied Potential, 1700 Volts; Cooling Temperature, 17 “C; and Current, 31 mA) Time, Concn, Migration, MixtureQ hr w/ml cm p-1-lo-s 3.00 0.50 32.8 p-3-12-s 3.00 1 .oo 30.3 p - 1-14-s 3.00 0.50 28.2 Mixture 1-104 2.50 4.00 33.8 1-11-s 2.50 4.00 31.9 4.00 30.2 1-12-s 2.50 1-14-s 2.50 4.00 27.9 a Contains 14% n-propanol. Table 11. Absorbance Values for the Direct Methylene Blue Analysis of p-(1-Ethyldecy1)Benzenesulfonate (Sample Size, 14.00 ~ 1 ) Absorbance Total Blank Sample 1.00 0.918 0.105 0.813 1 .OO 0.918 0.095 0.823 1 .OO 0.898 0.097 0.801 0.75 0.720 0.095 0,834“ 0.75 0.707 0.105 0.804= 0.090 0.8118 0.75 0,698 The actual values were divided by 0.75 to simulate absorbance values for 14 kg. Table 111. Absorbance Values for the Methylene Blue Analysis of p-(1-Ethyldecy1)Benzenesulfonate Extracted from the Gel (Extraction Time, 60 Minutes; Sample, 14.00 p1 of 1.00 mg/ml) Absorbance Run time, Blank Sample hr Total 2.75 0.687 0.807 0.120 0.782 0.122 0.660 2.75 0.135 2.00 0.858 0.723 0.716 0.127 2.00 0.843 0.134 0.860 0.726 2.00 0.130 0.844 0.714 1.OO 0.131 0.715 0.0833 0.846 0.131 0.844 0.713 0.0833
the method of Longwell and Maniece (6). The reader may consult these papers for complete details of these standard methods. Twenty-five milliliters of water, 5 ml of p H 10, 0.025M sodium tetraborate solution, and 2.5 ml of 0.025 mg/ml of methylene blue solution were added to a 125-ml separatory funnel. The contents of the separatory funnel were extracted three times with 5-ml portions of chloroform. The funnel was shaken for 60 seconds and the contents were allowed to separate for 2.5 minutes. After the third portion of chloroform was run off, 3 ml of chloroform were added and removed without shaking the funnel. The purified aqueous methylene blue solution was immediately acidified with 1.5 ml of 0.50M sulfuric acid. The solution to be analyzed was then added to the funnel. Three 7-ml portions of chloroform were used to extract the methylene blue adduct from the aqueous phase. The funnel was shaken for 60 seconds and the contents were allowed to separate for 2.5 minutes before the chloroform phase was (6) J. Longwell and W. D. Maniece, Analyst, 80, 167 (1955). 928
ANALYTICAL CHEMISTRY, VOL. 44, NO. 6, MAY 1972
collected in a 25-ml volumetric flask. The flask was filled to the mark and the absorbance of the solution was determined at 650 nm using a 5-cm cell in a Cary 14 spectrophotometer. The same procedure was used to determine the absorbance of the blank. The absorbance readings were taken immediately after the chloroform extraction of the blank which was approximately 3 hours from the time the gel strips were removed from the cell. One hundred per cent transmittance was set against air and the absorbance of the sample and blank were determined using air as the reference. Direct analysis of the standard dodecylsulfate (1-12-s) and p-(l-ethyldecyl)benzenesulfonate(p-3-12-~) solutions were also made. These determinations were made in order to calculate the per cent recovery of the sample from the gel and as an independent reference. The procedure for direct analysis using methylene blue was the same as that previously described. The solution to be analyzed was deposited directly into the separatory funnel with a microsyringe, and 90 ml of water was also added to maintain constant volume. A direct blank determination was carried out in the same manner. RESULTS AND DISCUSSION Electrophoretic Migration Patterns. Typical migration distances of compounds contained in mixtures, of which one component was quantitatively determined, are presented in Table I. It is believed that at least 95% of a component is located within 1.0 cm from the front of the spot, when 2 pl of 1.0 mg/ml sample is deposited. Therefore, the sample strip must be selected with accuracy when an adjacent member of the series is present for these distances of migration. This selection becomes quite difficult when the migration pattern is uneven across the cell. In the present case, the migration distances for the center samples tended to be as much as 4 mm behind the outer samples for migration distances of 30 cm. There was a monotonic transition from the central region to either side. This pattern was an indirect result of a convex distortion across the width of the cooling block. Although this distortion was not forced on the glass plate, the compensating variation in the amount of adhesive gave the center of the cell a slight advantage in heat transfer. Thus the migration rate was slightly less in the central region for this particular cell. Quantitative. ALKYLBENZENESULFONATES. The results listed in Table I1 give an average absorbance of 0.814 with a standard deviation of 0.012 for the direct determination of 14 pg of p-3-12-s. The linearity of the absorbance versus concentration curve over this range of absorbance has been well established (7, 8). To determine a practical time for the extraction of the sample from the gel, results from 40- and 60-minute extractions were investigated. These results showed the 60-minute extraction was 4 % more efficient than the 40-minute extraction. The decision to use a 60-minute extraction in all subsequent runs was based on the following criteria: An increase of 50% in the extraction time had given only a 4 x increase in recovery. The accuracy and precision of the method was not dependent on 100% recovery but only on a moderately high and reproducible recovery. Sixty minutes was considered a practical time for the extraction.
(7) K. Shirahama, M. Hayashi, and R. Matuura, Bull. Chem. SOC. Japan, 42,1206 (1969). (8) R. D. Swisher, “Surfactant Biodegradation,” Marcel Dekker, New York, N.Y., 1970, pp 47-53.
The data presented in Table I11 were obtained to determine if, or how much, sample was lost during migration. These results show there were no significant differences in the amount of sample recovered from the gel after runs of 5.0 minutes, 1.0 hour, and 2.0 hours. The low absorbance values, obtained from samples recovered from the gel after runs of 2.75 hours, were attributed to misjudgment in cutting the sample strips. These values were statistically rejected for subsequent calculations. The average absorbance for the six determinations is 0.718 and the standard deviation is 0.005. The average recovery of these samples from the gel is 8 8 . 4 z . This value was calculated by dividing the absorbance of the recovered sample by the absorbance obtained from direct analysis. The results from the analysis of p-3-12-s in two different mixtures are given in Table IV. The average absorbance for p-3-12-s in the 10,12,14 mixture is 0.725. If the value 0.718, previously calculated as the absorbance for the recovery of 14.00 p1 of 1.00 mg/ml p-3-12-s, is used as the reference the experimental value for p-3-12-s in the mixture is 1.01 mg/ml. In the same way, the experimental value for the concentration of p-3-12-s in the 10,11,12 mixture is 1.01 mg/ml. These values compare well with the theoretical value of 1.00 mg/ml. The results from a later attempt to obtain data for the recovery of p-3-12-s, after a migration time of 2.75 hours, are listed in Table V. The average absorbance value for the samples recovered from the gel is 0.644. The average absorbance value for the direct analysis is 0.738. The value of 0.829 was statistically rejected and was not included in this calculation. The recovery of p-3-12-s, based on these data, is 87.3%. This value compares favorably with the value 88.4 obtained earlier. The only explanation that is offered for the significantly lower absorbance values is decomposition of the sample. Data were not obtained for p-3-12-s in the mixtures for comparative purposes at this time because the mixtures contained 14% propanol which would have affected decomposition. The results presented in Table I11 indicate that if a pure standard is used, a run of only 5.0 minutes is sufficient for calibration. This assumes that the sample strip for the mixture is selected to include all the sample. ALKYLSULFATES. The results listed in Table VI show a significant difference in the amount of recovery between runs of 5.0 minutes and 2.50 hours. The average absorbance obtained for recovered material after electrophoresis for 2.50 hours is 0.667, while the value for runs of 5.0 minutes is 0.709. This lack of agreement with the results obtained in a similar study with p-3-12-s can be explained by the following observations. When clear aqueous stock solutions of 1-124 were diluted to concentrations of 4.0 mg/ml or less, precipitate formed within a few hours. There was a greater amount of precipitated material in the 2.0 and 1.0 mg/ml solutions than in the 4.0 mg/ml solution. This same behavior was observed often in previous attempts to solubilize 1-ABS in solutions of ABS or lauryl sulfate. It is quite probable that small amounts of the water-insoluble 1-alkylsulfonates were produced in the synthesis of the 1-alkylsulfates. The dilute 1-124 solutions were warmed to dissolve the precipitate gnd subsequently cooled to room temperature before sampling. Therefore, the determinations made on samples subjected to only 5.0 minutes of electrophoresis included this methylene blue active impurity. An attempt to accurately determine 1-12-s in a mixture of 1-10,11,12,14-s was not successful. The average for the
Table IV. Absorbance Values for the Methylene Blue AnaQsis of p-(1-EthyIdecy1)Benzenesulfonate Extracted from the %el after Separation from a Mixture (Extraction Time, 60 Minutes; Sample Size, 14.00 p l )
Concn, mg/ml
Mixture" p-3-12-s 1 .OO p-1,10,14-~ 0.50, 0.50 0-3-12-s 1 .OO p-1,10,14-~ 0 . 5 0 , 0 . 5 0 p-3-12-s 1.OO j~1,10,14-~ 0 . 5 0 , 0 . 5 0 p-3-12-s 1 .oo p-l,lO,ll-~ 0 . 5 0 , 0 . 5 0 p-3-12-s 1 .OO ,~-l,lO,ll-~ 0.50,0.50 1 .oo 0-3-12-s p-l,lO,ll-~ 0 . 5 0 , 0 . 5 0 Contains 1 4 z n-propanol.
Run
Absorbance Total Blank Sample
tine, hr
2.75
0.850 0.111
0.739
2.75
0.824 0,116
0.708
2.75
0.843 0.116
0.727
3.00
0.827 0,117
0.710
3.00
0,880 0.126
0.754
3.00
0.816 0,110
C.706
Table V. Absorbance Values for the Methylene Blue Analysis of p-(1-Ethyldecy1)Benzenesulfonate (Extraction Time, 60 Minutes; Sample, 14.00 p1 of 1.00 mg/ml)
Direct or run time, Total 0.719 0.748 0.757 0,782
hr
2.75 2.75 2.75 2.75 direct direct direct direct direct
0,808
0.846 0.823 0.921 0.806
Absorbance Blank 0.113 0.108
0.106 0.104 0.082 0,083 0,083 0,092 0.085
__
Sample 0.606 0.640 0.651 0.678 0.726 0.763 0.740 0.829 0.721
Table VI. Absorbance Values for the Methylene Blue Analysis of Dodecylsulfate Extracted from the Gel (Extraction Time, 60 Minutes; Sample, 12.00 pl of 1.00 mg/ml) Run time, Absorbance hr Total Blank Sample 0.140 0.715 0.0833 0.855 0.0833 0.820 0.117 0.703 0.112 0,668 2.50 0.780 0.660 0.792 0.132 2.50 0.110 0,673 2.50 0.783
Table VII. Absorbance Values for the Methylene Blue Analysis of Dodecylsulfate Extracted from the Gel after Separation from a Mixture (Extraction Time, 60 Minutes) Concn, Amount, mg/ml/ Mixture pl. compt 1-10,11,12,14-~ 6.00 2.00 1-10,11,12,14-~ 12.00 1.00 1-10,11,12,14-~ 12.00 1.00 1-10,12,14-~ 12.00 1.00 1-10,12,14-~ 12.00 1.00 1-10,12,14-~ 12.00 1.00 ~~~
Run time, hr
2.50 2.50 2.50 2.50 2.50 2.50
Absorbance Total Blank Sample 0,946 0.117 0.829 0,926 0.110 0.816 0.898 0.128 0.770 0.817 0.121 0.696 0.804 0.130 0.674 0.774 0.110 0.664
~~~
absorbance values listed in Table VI1 for this determination is 0.805. Using 0.667 as the reference, the experimental value for the determination of 1-12-s in the mixture is 1.20 mg/ml compared to a theoretical value of 1.OO mg/ml. The determination of 1-12-s in a mixture of 1-10,12,14-~ was more successful. The average absorbance calculated from the results listed in Table VI1 is 0.678. This gives an ANALYTICAL CHEMISTRY, VOL. 44, NO. 6, MAY 1972
929
experimental value of 1.02 mg/ml compared t o a theoretical value of 1.OO mg/ml for the determination. The large error for the determination of 1-124 in the 1-10,11,12,14-s mixture is attributed to the inclusion of a portion of 1-11-s in the gel sample strip. This was observed by applying pinacryptol yellow to the entire sample area after removal of the sample strip. As previously mentioned, the samples in the middle of the cell were behind the outsides samples by as much as 4 mm in these determinations. The results obtained for the 1-10,12,14-s mixture show, as in the case of the p 1-10,3-12,14-s mixture, that if the sample strip is accurately selected, this method of analysis is accurate and dependable.
ported system (4). The basic features in the design of this cell which have eliminated these problems are direct contact between the gel and buffer solution and direct contact between gel and the cooling surface. The slightly uneven migration patterns that were observed are due to failues in construction and materials and can be corrected. There is no reason why the length of the cell cannot be extended t o accommodate runs of longer duration. The results of this limited study demonstrate the method has potential for the separation and quantitative analysis of alkylbenzenesulfonates and similar ionic species.
CONCLUSION
The electrophoretic cell presented in this paper was developed to overcome problems inherent in a previously re-
RECEIVED for review Juiy 22, 1971. Accepted November 24, 1971.
Factors Affecting the Use of a Nondispersive System for Atomic Fluorescence Flame Spectrometry T. J. Vickers, P. J. Slevin, V. I. Muscat, and L. T.Farias Department of Chemistry, Florida State University, Tallahassee, Fla. 32306
A nondispersive atomic fluorescence system responding to radiation of wavelengths less than 2800 A is described, and the effect of the high energy throughput and broad spectral response of the system on the signal-to-noise ratio of atomic fluorescence measurements with line excitation sources is discussed. Dispersive and nondispersive measurements for Hg and As are compared to support conclusions on the utility of the system with flame atom reservoirs of low spectral radiance. THEBENEFITS TO BE DERIVED from a nondispersive system for atomic fluorescence measurements with atomic line excitation sources were recognized early in the application of atomic fluorescence to chemical analysis (1, 2). The principal benefits t o be expected have been listed as: (i) greater energy throughput (3-6), (ii) simultaneous collection of multiple lines for elements with a complex fluorescence spectrum (3), (iii) convenience of simultaneous multi-element analysis (3, 7-9), (iv) simplicity and ruggedness of instrumentation ( 4 ) . Attainment of the latter two of these would seem to be incontrovertible, but the real gain to be attained through (i) and (1) D. R. Jenkins, Spectrochim. Acta, 23B,167 (1967). (2) T. S. West and X. K. Williams, ANAL.CHEM., 40, 335 (1968). (3) P. L. Larkins, R. M. Lowe, J. V. Sullivan, and A. Walsh, Spectrochim. Acta, 24B, 187 (1969). (4) T. J. Vickers and R. M. Vaught, ANAL.CHEM.,41, 1476 (1969). (5) P. D. Warr, Talanta, 17, 543 (1970). (6) R. C. Elser and J. D. Winefordner, Appl. Spectrosc., 25, 345 (1971). (7) D. G. Mitchell and A. Johansson, Spectrochim. Acta, 25B,175 (1970). (8) D. G. Mitchell, “Advances in Automated Analysis,” Vol. 11, Thurman Associates, Miami, Fla., 1971, pp 503-6. (9) D. R. Demers and D. F. Mitchell, “Advances in Automated Analysis,” Vol. 11, Thurman Associates, Miami, Fla. 1971, pp 507--11.
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ANALYTICAL CHEMISTRY, VOL. 44, NO. 6, MAY 1972
(ii) is not so clearly established because it depends in part on the characteristics of the atom reservoir used. The ideal nondispersive atomic fluorescence system would make use of an atom reservoir which did not emit background radiation within the spectral response of the detector. Such ideal behavior has been approached in the use of a flameless system for mercury (IO), and presumably other flameless systems will have similar advantages for other elements. In a conventional dispersive flame atomic fluorescence system, the monochromator serves chiefly to limit the amount of flame background emission which falls on the detector. In nondispersive systems, several steps have been taken to circumvent the difficulties due to background emission: (i) Flames of low spectral radiance have been employed (4-6). (ii) Solar blind multiplier phototubes have been used in place of detectors of wider spectral response (3-6). The most widely used of these (HTV R166) responds only to radiation of wavelengths less than 3200 A. (iii) Bandpass filters have been used with both solar blind and broadband response detectors t o limit the amount of background emission reaching the detector (5-7). Filters with half-bandwidths of 4 to 50 nm have typically been employed. (iv) In work published since completion of the work described in this report, Larkins (11) and Larkins and Willis (12) have described a very useful nondispersive atomic fluorescence system in which the flame background emission was greatly reduced by separation of the flame by a sheath of inert gas. In this report we describe a nondispersive atpmic fluorescence system for the spectral region below 2800 A and discuss the benefits derived from the greater energy throughput and multiple line collection of such a nondispersive system. (10) V. I. Muscat, T. J. Vickers, and A. Andren, ANAL.CHEM., 44, 218 (1972). (11) P. L. Larkins, Spectrochim. Acta, 26B,477 (1971). (12) P. L. L,arkins and J. B. Willis, ibid., p 491.
