Rapid Analysis of Binary Amine Mixtures by Differential Reaction Rates Detailed Study of Synergistic Effects and Other Sources of Error RONALD A. GREINKE and HARRY
B. MARK, JR.
Departmenf of Chemistry, University of Michigan, Ann Arbor, Mich.
b The single point modification of the differential kinetic method of Roberts and Regan has been applied to the rapid analysis of mixtures of amines. The differences found in the rates of reaction of amines with methyl iodide makes possible the analysis of mixtures containing almost any combination of aliphatic or aromatic primary, secondary, and tertiary amines. The course of the reactions is followed b y automatically recording the solution conductance as a function of time. Synergistic effects which result from a solvent-reactant interaction, a change in activity coefficients, and catalysts are eliminated by employing the proper solvents and reaction conditions. Other errors resulting from solvent-reagent reaction and additional amine reactions produce a negligible error.
R
Hanna and Siggia (5) reported the use of the differential rate approach for the analysis of mixtures of amines. Their procedure followed the reaction of mixtures of amines with phenyl isothiocyanate which forms the thiourea and extrapolation of a second order rate plot which became linear after the faster reacting component had completely reacted. This technique was found to be more general than the numerous chemical methods (1, 6, 8, 17) previously used to determine mixtures of amines. However, as the reagent, phenyl isothiocyanate, does not react with tertiary amines, the analysis of a binary system of tertiary amines was not feasible. I n addition, to the limitation that the analysis time was slow, approximately 1.5 hours, the method was also laborious as point by point titrations were required to follow the course of the analysis. A rapid, less restricted, and less laborious analysis procedure for mixtures of amines is achieved by employing the single point kinetic method of Roberts and Regan ( 1 4 ) and by automatically measuring the competitive rates of reaction of amines with methyl iodide to form the ammonium salt with a direct recording conductance meter ECENTLP,
48 7 04
( I S ) . This method is more general than the Hanna and Siggia method as tertiary amines react with the reagent, methyl iodide. The selection of proper solvent and reaction conditions was found to be very important with respect to avoiding synergistic effects and is discussed in detail. EXPERIMENTAL
Method. Roberts and Regan (14) developed a kinetic method for simultaneously determining two components, A and B , reacting with a common reagent, R. If the concentrations of A and B are much greateri.e., 50 to 1 or larger-than the reagent, R, the following pseudo-firstorder rate expression for R holds:
where K* is the overall pseudo-firstorder rate constant for the competitive reaction of both species and is given by
K* =
kd[A],
+ ks[B],
(2)
where k~ and kB are the second-order rate constants of A and B , respectively, reacting with R, and [ A ] , ,and [ B ] ,are the initial concentrations of reacting species A and B (the amount of A and B that is consumed during the course of the reaction is negligible as the concentration of these species are in such great excess). The analysis is accomplished by measuring K*, [as described by Papa, et al. ( I S ) ] , by measuring k A and ka, which are obtained by reacting pure amines with methyl iodide, and by determining the total initial concentration of amines, [ M],,,by an independent method, which gives:
(3) Hence, Equations 2 and 3 are solved simultaneously for [ A ] ,and [ B],. Apparatus. The rate of the reaction is automatically followed by a direct recording conductance apparatus in the same manner as described previously (4, 16, IS). Reagents. The methyl iodide reagent solution was prepared by adding 2 grams of methyl iodide to a 100-ml. volumetric flask and diluting to volume with methyl alcohol.
The various amines (Eastman Kodak), methanol, n-propanol (Baker Chemical), acetone (Mallinckrodt), and dimethyl sulfoxide (DMSO) (CrownZellerbach) were reagent grade and used without further purification. Procedure. A water-jacketed cell 150 ml. in capacity, is connected to a circulating water bath maintained a t 25.0' i. 0.1' C. The solvent medium of DMSO and methanol and/or water (see section in results and discussion for proper solvent and/or proper ratio of solvents selection) along with the methyl iodide reagent solution and amines are placed into the water bath for a t least 1 hour prior to the analysis, so that they are a t 25' C. before mixing. Then, 70 ml. of the solvent medium are placed into the cell (equipped with a magnetic stirring motor and stirring bar) and the conductance electrodes are placed into the cell. -42-ml. sample of pure amine is injected into the cell using a hypodermic syringe. The recorder is then started and when a steady base line is maintained, a 2-ml. sample of methyl iodide reagent solution is injected into the cell using a hypodermic syringe, whose needle is immersed into the solution to avoid bubbling. The second order rate constant for the pure amine is calculated in the usual manner (16) from the resulting conductance rate curve. This same procedure is employed with the second pure amine and with the unknown mixture. The K*, the pseudo-first-order rate constant for the mixture, is calculated in the usual manner from the conductance curve and the initial concentrations of the unknowns are calculated by means of Equations 2 and 3. RESULTS AND DISCUSSION
Tables I and I1 list the results obtained for the analyses of various mixtures of amines employing two different solvent mediums (Table I, acetone or acetone-water medium, Table 11, DMSO or DMSO-methanol medium) together with the ratio of rate constants for the two amines in each mixture. The average absolute error found for all the mixtures in Tables I and I1 was 1.8%. The advantage of the single point method of Roberts and Regan, that VOL. 38, NO. 8, JULY 1966
1001
small ratios of kA to Ice can be tolerated rather easily (IO, I d , 14), is again illustrated here. Mixtures with a ratio of rate constants as low as 1.4 to 1 were successfully analyzed. A disadvantage of this method, discussed previously ( I d , I 6 ) , is that the rate constants of the reaction of the two reactants in the actual mixture may differ from those obtained with the pure compounds alone (synergistic effects) (19). Synergistic Sources of Error. Three different types of synergism were found with respect to the analysis of amine mixtures as described in this paper: interaction of the solvent medium with the reactants, a possible change in the activity coefficients (total concentration effect) of the reactants, and a change in the rate constants resulting from a catalysis effect. As other useful kinetic methods
(3, 4) are based on prior determination
of the individual rate constants of the pure compounds and as the single point method of Roberts and Regan can be applied to many other closely related organic compounds, it is worthwhile to illustrate how these three synergistic effects arose and affected the analysis of the amine mixtures. Also, details of the steps that can be taken to reduce these sources of error to a point where acceptable results are obtained would be beneficial for the other cases mentioned.
(aromatic), (secondary and tertiary), and (secondary and aromatic) amine. (Table I) in an acetone or acetonewater solvent medium. However, when primary and some secondary amines were present in the mixture large errors were observed. These errors probably resulted from the format'ion of Schiff bases : CH3 C
I
4
INTERACTION OF SOLVENT MEDIUM CH3 REACTANTS. The rate constants
WITH
for tertiary amines, pyridine, and p alkyldimethylanilines reacting with methyl and ethyl iodide in an acetone solvent medium have been reported (2, 7, 1 1 ) . Successful analyses of amines were obtained for a mixture of (tertiary),
Determination of Amines by Reaction with Methyl Iodide Using Acetone or Acetone-Water Solvent Medium"
A, % Taken Found 9.7 9.6 A. Triethylamine 63.5 63.1 B. Tributylamine 84.5 83.1 19.4 21.3 A . Aniline 81.3 80.3 B. o-Ethylaniline 28.1 28.4 A . Diethylamine 76.3 78.6 B. n-Methylaniline 6.9 6.1 A . Diethylamine 54.8 55.0 B. Triethylamine 79.3 75.6 a '%B taken as difference (Equation 3). hl ix tur e
I
4.0 1.9
Acetone Acetone-water
1.7
Acetone-water
Determination of Amines by Reaction with Methyl Iodide Using DMSO or DMSO-MeOH as Solvent Medium
Mixture A . Di-n-amylamine B. Tributylamine A . Diethylamine B. n-Amylamine A, B. A. B.
Propylamine Tertiarybutylamine Diethylamine Tertiarybutylamine
A . Methylcyclohexylamine B. Cyclohexylamine A. Methylcyclohexylamine B. Isopropylamine A . Aniline
B. N-N-dimethylanilhe A . %-Butylamine B. 2-Phenylethylamine A. B. A. B. A. B.
Isopropylamine Di-isopropylamine Isopropylamine o-Toluidine Di-isopropylamine o-Toluidine
1002
ANALYTICAL CHEMISTRY
A, % 'Taken Found 6.8 8.7 41.3 45.1 78.1 81.2 2.9 4.6 48.0 51.2 82.2 83.0 53.8 56.2 83.5 84.7 1.5 3.2 46.5 47.2 75.4 77.3 13.7 13.0 48.5 46.0 63.5 63.7 27.4 31.0 65.9 62.2 6.1 4.6 46.1 48.1 87.0 86.0 81.2 85.5 87.8 85.5 17.3 13.0 11.8 13.0 53.0 54.9
40.9
40.2
57.3
56.9
I
9.7
Solvent medium DMSO-MeOH
2.0
DMSO-MeOH
2.9
DMSO-MeOH
5.7
DMSO-MeOH
2.5
DMSO-MeOH
2.7
DMSO-MeOH
1.4
DMSO
1.4
DMSO-MeOH
7.7
DMSO-MeOH
kA/kB
137 18.0
DMSO-MeOH DMSO-MeOH
(4)
+ HzO
(5)
+ RzNH ~ 3 !
CHa
R
II
C-N I
I
/ ,
CHB 21.7
+ HzO
CH3
CHz Solvent medium Acetone
kr/kB
~~
Table II.
CH3 C=N-R
C=O Table 1.
+ RNHz
\
R
For example when a n-butylaminetributylamine mixture (7101, in n-butylamine) was injected into an acetone medium containing methyl iodide, the overall rate constant, K*, of the reaction was smaller than expected because of the slow formation of the Schiff base. Curve 1, Figure 1, indicates that K* was not constant for this mixture and actually decreased as function of time. The measurement of rate constants for pure amines was made when the ratio t, of reagent concentration [ R ] l , / [ R ]was slightly smaller than l/e, the optimum time of measurement (IO). Thus low results were obtained as the apparent second order rate constant for the pure n-butylamine, measured a t l/e, was larger than that in the mixture-Le., because the equilibria in Equations 4 and 5 are slowly reached, the second order rate constant, measured a t l / e , for n-butylamine will decrease as the concentration of free n-butylamine decreases. This interfering reaction could be circumvented in some cases by adding water to the solvent medium which shifts the equilibria given by Equations 4 and 5 to the left. The addition of 30% water to the medium resulted in satisfactory analyses for mixtures 3 and 4 in Table I. A plot of mole yo A found (faster reacting component in the mixture) us. the yo acetone in an acetone-water medium is shown in curve 1 of Figure 2 for a diethylamine-triethylamine mixture containing 60.3% of diethylamine.
14Ii 12
0 0
TIME ISEC.)
Figure 1 . Variation of K* for n-butylamine-tributylamine mixture (71.2% n-butylamine) as a function of time using three different solvent media. Reaction conditions: 5 ml. of amine, 1 X 10-2M CHJ, and 75 ml. of solvent medium Curve 1. Curve 2. Curve 3.
100% Acetone 09% Acetone-1 1 % water 70% DMSO-3Oyo n-propyl alcohol
Only 5% of water was required to sufficiently shift the equilibrium of Equation 5. However, curve 2 of Figure 2 indicates that a mixture of n-butylin n-butylamine-tributylamine (7o.3yO amine) cannot be analyzed satisfactorily. The addition of water improves the results, but K* still changes as a function of time (curve 2, Figure 1). Also, tributylamine becomes insoluble in the solvent medium when more than 20y0 of water is present. .Ilthough the reaction of amines with methyl iodide is completely general for all amines, the selection of acetone as a solvent medium thus limits the analytical application of the method to certain mixtures. Because charged species are formed during the course of the reaction, the rate of the methyl iodide-amine reaction can be increased if a polar solvent is used for a solvent medium (this decreases the time required for analysis). .Is seen previously, however, the solvent chosen also must not react with the amine. DMSO fulfills both conditions. Although quite similar in structure to acetone, DMSO is weakly basic because of an unshared electron pair on the sulfur atom and sulfoxides do not give ketone like addition products (15). CHANGEIN ACTIVITYCOEFFICIENTS OF REACTANTS.Siggia and Hanna (16 ) , employing the second order logarithmic method, observed in some systems that the rate constant of the slower
reacting component decreased in the presence of the faster reacting component. The reason given was that the activity coefficients of the amines in the mixture were different from the activity coefficients of the pure components. They also stated that this was actually an advantage with respect to the graphical method, as it increased the difference between the two slopes of the rate plot. However, this is not always the case, as the absolute value of both rate constants can be lowered leaving the ratio of rate constants in the mixture about the same as that found for the pure components. Thus, no increase in the difference between the two slopes is obtained. Although the results reported in Table I1 (DMSO or DXSO-methanol solvent medium) are analytically acceptable, many mixtures not reported gave results that were about 10% low when approximately 5oyOof each component was present. In particular, mixtures of n-butylamine and tributylamine were always extremely low. The first synergistic effect mentioned (solvent side reaction) was not the cause of the poor results for this system as solvent-amine interaction does not occur with this system. Table I11 clearly shows, however, that the activity coefficients of the reactants were changing for this particular system as a function of initial concentration of the reactants. Altering the reaction conditions from 5 ml. of amine, 5 ml. of reagent solution, and 70 ml. of solvent medium to 1 ml. of amine, 1 ml. of reagent solution, and 70 ml. of solvent medium, as indicated in Table 111, resulted in far better analyses. Essentially, the amines did not “notice each other” as much using the latter conditions because the environment of the amines in the mixture was almost the same as that found in the pure amine reactions (1 to 2 ml. of pure amine used to obtain k’s). Curve 3, Figure 1 indicates that K* for the n-butylaminetributylamine mixture, run in DMSOn-propyl alcohol solvent medium, is constant. (Methanol was replaced by
Table 111.
100 90 80 70 60 % ACETONE IN ACETONE-H20 SOLVENT MEDIUM
Figure 2. Mole % A found (faster reacting component) as a function of % acetone in an acetone-water solvent medium. Reaction conditions: 5 ml. of amine, 1 X 10d2MCHsl, and 75 ml. of solvent medium Curve 1. Diethylamine (A)-triethylamine mixture (60.3 mole % A taken) Curve 2. n-Butylamine (A)-tributylamine mixture (71.2 mole A taken)
70
(6) (6)
n-propyl alcohol since better solubility of the tributylamine was obtained.) A 5-ml. sample of amine was used in the analysis of the first eight mixtures in Table I1 while a 1- or 2-ml. sample was used for the last three mixtures. Better results were always obtained using lower concentrations of amines, which minimize the activity effect. CHANGE IN RATE COXSTANTS RESULTINGFROM CATALYSTS.Papa, et al. (12), indicated that serious errors would occur with the single point method of Roberts and Regan if variable amounts of catalysts were found in the
Elimination of Activity Coefficient Errors Using Proper Reaction Conditions
A , 70
hlixture A . n-Butylamine B. Tributylamine
A . n-But.ylamine B. Tributylamine
Taken
Found‘
kdks
30.2 30.2
25.7 25.7
9.4
63.2 63.2 92.8 92.8 30.2 30.2
55.7 91.3 90.3 30.2 29.8
63.2 63.2 92.8 92.8
61.6 60.0 91.7 92.6
55.7
8.2
Reaction conditions 5 ml. amine 5 ml. reagent solution 70 ml. DMSO+propyl alcohol solvent medium 1 ml. amine I ml. reagent solu-
tion
70 ml. DPIIS0-n-
propyl alcohol solvent medium
VOL. 38, NO. 8, JULY 1 9 6 6
1003
mixtures. However, this disadvantage can be overcome if a large amount of catalyst is placed into the solvent medium, thereby leveling the variable catalyst effect coming from the additional small amounts of catalyst in the sample. Even though precautions were taken to eliminate the possible errors that could be produced from the first two synergistic effects mentioned, poor results were obtained when a reaction medium consisting of 70% DMSO and 30% hleOH was employed for a methylamine (containing some water)-diethylamine mixture (see Table IV). Experiments showed that the introduction of small amounts of water (the catalyst in this case) to the solvent medium from the amine mixture itself altered the rate constants for both methyl amine and diethylamine. Considerably better results were obtained, however, when %yo of water is initially added to the solvent medium in place of MeOH (see Table IV). In this range of water concentration, the second order rate constants did not change rapidly with yo water in the medium (see Figure 3). Thus, the additional water added to the analyses solution from the amine mixture does not alter the rate constants significantly (% water remains essentially constant). Prior knowledge of the impurities or catalysts in the mixture is, thus, essential for obtaining good analytical results. If the catalyst is unknown, then one must resort t o the logarithmic extrapolation method where prior knowledge of the rate constants is not essential (10).
Other Sources of Error. SOLVENTREAGENT REACTIOK.Major and Hess (9) reported that methyl iodide reacts with DMSO to form trimethylsulfoxonium iodide.
DMSO solvent reacted over a 12-hour period and only 5% of 1 X 10-2M CH3I solution in a solvent consisting of 50% D?tISO40% MeOH-lO% HzO reacted over this same period), compared to the reaction of methyl iodide with amines (which in most cases, was complete in 5 minutes). Therefore, the error caused by this competing side reaction is quite negligible. However, caution must be taken when storing a solvent medium that contains the reagent. If a solvent medium containing 1 X 10-2X CH31is stored (or used over) several days, the quantity of CHJ remaining for the amine reaction is considerably decreased and the sensitivity of the method is lowered (or results are not reproducible). Because charged ions are formed in the solvent medium according to Equation 6, addition of more methyl iodide to the solvent medium after a period of several days does not increase the sensitivity significantly. However, by making a separate reagent solution in an inert solvent such as methanol (see experimental) this problem was eliminated. The rate of alcoholysis of methanol with primary halides is extremely slow (18). Therefore, the reagent, methyl iodide, stored in methanol was stable for many days. The alcoholysis or hydrolysis of methyl iodide which odcurred during the course of the amine-methyl iodide reaction is also quite negligible and did not lower the accuracy of the method. ADDITIOKAL AMINEREACTIONS. It is well known that the addition of methyl iodide to primary amines can continue until the quaternary ammonium salt is formed. R--NH~% RNH(CH3)
CHaI k ;
4 0
35i
: Y)
30t\
W
5
00
IO
20'
30
% H20 IN DMSO-MeOH
40
50
- H20 SOLVENT MEDIUM
Figure 3. Variation second order rate constant as a function of % water in DMSO-methanol-water solvent me2 ml. dium. Reaction conditions: amine, 5 ml. CH3I reagent solution, and 70 ml. of solvent medium Curve 1. Curve 2.
Methylamine Diethylamine
impurities reduces the sensitivity of the method. Water, essential for the possible elimination of the Schiff base formation and essential for leveling the catalyst effect of water, can reduce the eensitivity of the method through the following reaction: R3N
+ HIO fast_ [RaNH]+
+ [OH]-
(8)
which increases the conductivity of the system. As the equilibrium for this reaction is very rapidly attained, there is no kinetic interference in measuring the RS(CH3)3+I- (7) desired methyl iodide-amine reaction. CH3I CH~S-CHI + However, the addition of more than 30% However, because the reaction is run ll water to the solvent medium is not pseudo-first-order with respect to the 0 recommended as the sensitivity of the reagent, the probability of reaction of a CHI method is reduced significantly. second or third methyl iodide with one I Proper DMSO-MeOH Ratio for of the relatively few higher methylated CH3-S-O+I(6) Rapid Analysis. The determination amine products formed in Equation 7 is of K* for a mixture and pure amines was extremely small and was found to be CH3 made a t two times tl and tz, when [RIt,/ negligible, This would be a major [R],,(where [Rltiand [RIt,are the reproblem, however, if the reaction was The rate of this reaction, also measured agent concentrations a t time tl and tz) tried under straight second-order condiby following the change in conductance is slightly smaller than l/e, approxitions. of a CHJ-DMSO solution, was found REACTIONAFFECTISGSEKSITIVITY. mately 0.36 (4, 10). The time period t o be quite slow (approximately 60% of k - tl for the components in the mixThe presence of conducting nonreactive a 1 X 10-211f CH31 solution in pure ture can be altered considerably by the proper selection of solvent medium. The rate of the reaction is diminished considerably by the addition of methTable IV. Elimination of Catalyst Error Using Proper Solvent Medium anol and/or water to the solvent A , 70 medium. Thus, as most primary amines Mixture Taken Found h/kB Solvent medium react too rapidly in pure DMSO for an A . Diethylamine 32.3 38.0 1.7 7070 DhlSO accurate measurement with the apparaB. hlethylamine 32.3 41.3 307, MeOH tus employed here, it is necessary to add 2.3 707, DAIS0 A . Diethylamine 32.3 33.6 methanol or water. As a rule of thumb, 307, Hz0 B. Methylamine 32.3 32.1 the following solvent mediums are sug-
+
1004
ANALYTICAL CHEMISTRY
ki
gested for the convenient reaction conditions stated in the procedure. 1. Primary amines
70% DMS0-30%
RleOH 80% DMS0-2070 MeOH 3. Tertiary amines 90% DllSO-lO~o MeOH 4. Aromatic 100% DMSO amines 2. Secondary
By employing the proper solvents and reaction conditions, many mixtures of amines can be analyzed by a differential reaction rate technique based on the single point modification of the method of Roberts and Regan. However, amines with bulky aromatic groups, such as diphenylamine, and amines which contain electron withdrawing groups, such as ortho-bromoaniline, do not react with the reagent, methyl iodide. Also if the ratio of rate constants is less than 1.4 to 1, accurate results cannot be obtained. When comparing the method reported in this paper with the logarithmic method used by Hanna and Siggia (5), it is found that there are distinct advantages for each method, depending on the particular analysis problems and conditions.
The advantages of the logarithmic extrapolation method are : Prior determination of rate constants are not necessary, synergistic effects do not hamper analysis, and a mixture containing a primary, secondary, and a tertiary amine can be analyzed. The advantages of the method presented in this paper are: Method is more general, analysis is rapid, numerous titrations are not necessary, and low ratio of rate constants is tolerated. LITERATURE CITED
(1) Critchfield, F. E., Johnson, J. B., ANAL.CHEM.28, 430 (1956). ( 2 ) Davis, W. C., J . Chem. SOC.1938, 1865. (3) Garmon, R. G., Reilley, C. E.,ANAL. CHEW34,600, (1962). (4) Greinke, R. A., Mark, H. B., Jr., Ibid., 38, 340 (1966). (5) Hanna, J. G., Siggia, S., Ibid., 34, 547 (1962). (6) Johnson. J. B.. Funk. G. L.. Ibid.. 28. 1977 11956J.‘ (7)-J&on, R . PI, Krause, C. A., Proc. Nut/. Acad. Sci.,U . S . 40, 70 (1954). (8) Liu, Y. G., Reynolds, C. A,, ANAL. CHEM.34, 542 (1962). (9) Maior. R. T.,Hess. H. J., J . O w . ‘ Chem: 23, 1563 (1958): (10) Mark, H. B., Jr., Greinke, R. A., Papa, L. J., “Proceedings of Society
of Analytical Chemists Conference,”
Nottingham, England, p. 490, Heffer, Cambridge, England, 1965. (11) Korris, J. F., Prentiss, S. W., J. Am. Chem. SOC.50, 3042 (1928). (12) Papa, L. J., Patterson, J. H., Mark, H. B., Jr., Reilley, C. N., ANAL. CHEM. 35. 1889 (1963). (13)’Reilley, C. ’N,, J . Chem. Educ. 39, A 853 (1962). (14) Roberts, J. D., Regan, C., ANAL. CHEM.24, 360 (1952). (15) Ranky, W. O., Nelson, D. C., “Organic Sulfur Comoounds.” N. Kharasch. ed., .Yol. 1, Chap. 17, Pergamon Press; Oxfn rd, 1961. - ..~. (16) Si-ggia, S., Hanna, J. G., ANAL. CHEM.36, 228 (1964). (17) Siggia, S., Hanna, J. G., Kervenski, I. R.. ANAL. CHEM.22. 1295 (1950). (18) Streitweiser, A., “Solvolytic Displacement Reactions,” p. 37, McGrawHill, Sew York, 1962. (19) Symposium on Kinetic Methods of Analysis, Division of Analytical Chemistry, 150th Meeting, ACS, Atlantic City, N. J., September 1965. RECEIVEDfor review April 4, 1966. Accepted May 17, 1966. Division of Analytical Chemistry, 1st Great Lakes Regional Meeting, ACS, Chicago, Ill., June 1966. Research supported in part by a grant from the National Science Foundation, GP-4620. One of us (R. A. G.) is indebted to the National Aeronautics and Space Administration for a Graduate Traineeship in 1965 and 1966 which made possible this work.
A Study of the Feasibility of the Iron Hollow Cathode as a Multi-Element Atomic Absorption Unit C. W. FRANK, W. G. SCHRENK, and C.
E. MELOAN
Kansas Agricultural Experiment Station, Department of Chemistry, Kansas State University, Manhattan, Kan.
b A study has been made of the feasibility of using an iron hollow cathode lamp as a multi-element unit for atomic absorption spectrometry. Of the six elements studied, four (magnesium, manganese, nickel, and copper) produced sufficient absorption to have analytical value. One (barium) showed slight absorption and silver produced no measurable deflection. The sensitivities determined for magnesium, manganese, nickel, and copper are 10.0, 0.04, 0.1 0, and 0.80 p.p.m., respectively. This system is more rapid and less expensive than the conventionally used system for multi-element analysis. Other possible elements which may b e of analytical utility with an iron hollow cathode source are tabulated.
S
of atomic absorption spectrometry, great strides have been made in instrumentation. Advances in source technology, however, have not satisfied analytical needs. INCE THE ADVEKT
Recent publications indicate several approaches to solving this problem. Sebens, Vollmer, and Slavin (7) report the use of multi-element hollow cathodes, while Fassel and coivorkers (3) and the present authors (4) have used high energy continuous sources for some of their studies. Continuous sources also were used by Ivanov and Kozyreva (6) and Belchev, St. Beleva, and Dancheva ( I ) in the form of low intensity hydrogen lamps. Continuous sources of the types mentioned give a wide effective band width, thus reducing the sensitivity of the system. A hollow cathode, because of the narrow band width, shows a marked increase in sensitivity for the element being determined. Therefore a sharp line system that could be used as a multi-element source would be most desirable, Since the rapidity of analysis of different metals is decreased by the warm-up time of the conventional source, the hollow cathode, the practicality of the iron hollow cathode in determining several elements is
shown. It should be noted that the expense for this type of source is greatly decreased. EXPERIMENTAL
Apparatus. Data were obtained using a Jarrell-dsh one-half meter grating with Jarrell-Ash electronics, including chopper, a.c. amplifier, Sargent recorder (model S-72150) and a 1P28 photomultiplier as detector. The source was a Kestinghouse iron hollow cathode, No. 48-455. The sampling system used was one large bore Beckman burner No. 4090 in a single pass system. The fuels used were acetylene and oxygen, controlled by Jarrell--Ash regulators and monitored by G.I. flow meters, type KO.F 1300. Solutions. All solutions were made from the metal by reaction with HCl (where practical) or from t h e metal chlorides. Standard solutions of 1000 p.p.m. were prepared and all other solutions prepared by subsequent dilution. Procedure. The procedure is similar t o those described in current literature on atomic absorption except VOL. 38, NO. 8, JULY 1966
lo05
