The method is recommended for determining small concentrations of alkylbenzenesulfonate, perchlorate, or periodate in dilute brines or seawater, but not in mixtures of one or more of the anions. A test of Atlantic coastal seawater, diluted to 0.1M in chloride, showed an absorbance of 0.029 above the blank. It is more likely that this represents detergent than perchlorate. No satisfactory method for differentiating between anionic detergents and the other extracted ions has been developed for this method a t the present time. LITERATURE CITED
(1) Blyum, 1. A., Pavlova, N. N., Zauodsk. Lab. 29, 1407 (1963); C. A . 60, 34639 (1964).
(2) Fritz, J. S., Abbink, J. E., Campbell, P. A., ANAL.CHEM.36, 2123 (1964). (3) Iwasaki, I., Utsumi, S.,Kang, C., Bull. Chem. SOC.J a p a n 36, 325 (1963); C . A. 58, 131098 (1963). (4) Krasnov, K. S., Radiokhimiya 5 , 222 (1963); C. A . 6 0 , 4 8 6 5 ~(1964). (5) Krasnov, K. S., Kashirina, F. D., Ibid., 6(2), 191 (1964); C. A. 61, 4519c (1964). ( 6 ) Krasnov, K. S., Kashirina, F. D., Ibid., 6, 651 (1964); C. A. 62, 13921b f 196.5’). ( 7 ) Krasnov, K. S.,Kashirina, F. D., Yatsimirskii, K. B., Tr. Komis, PO Analit. Khim. Akad. Nauk SSSR, Inst. Geolchim. i Analit. Khim. 14, 59 (1963); C. A . 5 9 , 1 2 2 3 9 ~(1963). 18) Krasnov. K. S.. Yatsimirskii. K. B.. ‘ Kashirina,’ F. D.,’ Radiokhimiya 4, 148 (1962); C. A . 58 12008e (1963). (9) Zbid., p. 638; A . 58, 120089 (1963). (10) Venkataraman, K., “The Chemistry
6.
of Synthetic Dyes,” Vol. 11, p. 705, Academic Press, New York, 1952. (11) Yamamoto, Y . , Uchikawa, S., Akabori, K., Bull. Chem. SOC.Japan 37, 1718 (1964); C . A. 62, 4616f (1965). (12) Yang, Ping-Yu, Hua Hsueh Tung Pao 1964 ( l o ) , 606; C. A . 62, 11121e (1965). (13) Ibid., p. 628; C . A. 62, 11121f (1965).
C. E. HEDRICK BRUCEA. BERGER Department of Chemistry University of Pennsylvania Philadelphia, Pa. 19104 WORK supported under the National Science Foundation Undergraduate Research Participation Program NSF GE 6436. Division of Analytical Chemistry, Winter Meeting, ACS, Phoenix, A r k , January 1966.
Use of Citrate-EDTA Masking for Selective Determination of Iron With (IO-Phenanthroline SIR: I n situ masking is an effective, convenient method for eliminating interferences in the colorimetric determination of iron with 1,lo-phenanthroline. For example, such metals as AI, N o , Sb, Sn, Th, Ti, U, W jand Zr can be masked with citric acid; Bi, Cd, Cr, and Zn with EDTA; Cu with mercaptoacetic acid; and T a with tartaric acid ( 1 ) . This paper describes the use of duo citrate-ED’T.1 masking for the selective determination of iron with 1,lO-phenanthroline. With duo citrateEDT-4 masking, the selectivity and versatility of the 1,lo-phenanthroline procedure is greatly enhanced such that it can be used advantageously for the routine analyses of samples with unknown and widely varying compositions. Factors Affecting the Formation of the Iron (11)-1, 10 -Ph e n a n t h r o l i n e Complex in Citrate-EDTA Medium. The formation of the iron(I1)-1,lOphenanthroline complex is dependent on the concentrations of the 1,lOphenanthroline chromogen, the hydroxylamine reductant, and the citrate and EIlT,1 masking agents. The color developnient is also dependent on p H because changes in p H alter the effective concentrations of each of these reagents. This is illustrated by the following equilibria : Fe(I1,III)-EDTA
+ NHLOH H+ 1 2
1
c
-t
OH-
NH30H +
formation of the iron(I1)-1,lO-phenanthroline complex and the displacement of Equilibrium 1 to the right are directly proportional to the phenathroline and hydroxylamine concentrations and inversely proportional to the H2EDTA+ concentration. Equilibria 2, 3, and 4 show the effect of acidity on the hydroxylamine, H2EDTA-* and phenanthroline concentrations. Citrate, like EDTA, complexes iron(II1) and its effect on Equilibrium 1 is similar to that of EDTA. With the citrate and EDTA levels arbitrarily maintained a t 2.5 mmoles and 1.25 mmoles, respectively, and the hydroxylamine and phenanthroline levels maintained at 2 mmoles and 0.10 mmole, respectively, complete reproducible color development is obtained at p H 5.0 to 6.5 in 25 minutes at room temperature. Above or below this p H range, the color development is not complete. I n addition to the 2.5 mmoles of citrate and 1.25 mmoles of EDTA used for masking, up to 2.5 mmoles of citrate or EDTA or 1.0 mmole of oxalate or tartrate do not affect the color development. At higher levels, however, complete color development is obtainable only with heating. Heating at 60’ C. for 15 minutes, cooling, then standing for 25 minutes, is satisfactory.
Phen
1 Fe(I1)-Phen
H+13/0= Phen.H+
where Phen is the unurotonated 1,lOphenanthroline molecuie and Phen . H + is the protonated 1,lO-phenanthroline ion. \There iron is predominantly in the + 3 oxidation state, both the rate of
+ H2EDTA-+ + NP
11
H+ 4
OH-
H4 EDTA
The 25-minute standing Deriod is necessary because the iro;(iI)-l,lO-phenanthroline complex dissociates at elevated temperatures, then reforms slowly at room temperature (Figure 1). The
data plotted in Figure 1 were obtained by measuring the absorbance of the iron(I1)-1 ,l@phenanthroline complex at various temperatures as it was warmed from 20’ to 50’ C. The solution was then cooled rapidly and the absorbance of the iron complex was measured a t 5-minute intervals. Effects of Diverse Ions. The effects of diverse ions were studied by analyzing synthetic samples containing 54.6 gg. of iron and varying concentrations of cations admitted generally as the nitrate or chloride salts, and anions admitted as the acid or as the alkali metal salts. A “t”test at the 95% confidence level was used to establish interference. For a single determination, the allowable limits were 10.005 absorbance unit or ~k0.60gg. of iron.
Table 1 . Effect of Diverse Metal Ions at Ion to Iron Molar Ratios above the Maximum Tolerance Ratios
Diverse ion
Cr(II1, VI) cum) .
I
Ni(I1)
Diverse ion to iron
molar ratio 200 12.5 25 50 100 200 50 200 25 50
Interference,
-
+--
c/o
5.2 1.6 1.8 4.1 6.1 2.7 2.7 5b
2.0 -12.5 a These data were obtained with 54.6 fig. (-0.001 mmole) of iron present. A difference of this magnitude was ob-
served when the sample absorbance was measured between 25 to 35 minutes after color development; however, the absorbance decreases fairly rapidly upon standing.
VOL. 30,
NO. 6, MAY 1966
793
Of 54 elements studied, most of them at diverse ion to iron molar ratios greater than 100:1, only a few interfered. This is shown in Figure 2 which gives
0.460
0.430
-\ \ \
0.400
1 \
0.370 0 Y
z
4
0.340
2 m 0.3 I O
a280
0.250
20
30 40 SO TEMPERATURE, 'C.
5
60
IO
I5 20 TIME IN MINUTES
25
30
35
Figure 1. Effect of temperature and time on formation of the iron(l1)-1,lOphenanthroline complex Right: Formation of the iron(l1)-1,lO-phenanthroline complex a t 20' C. left: Dissociation of the iron(ll)-l,l 0-phenanthroline complex at elevated temperatures
the tolerance ratio (diverse ion to iron molar ratio) of the ions studied. I n most cases, the tolerance ratio given is the highest ratio that was studied and does not necessarily represent the maximum permissible ratio. Maximum tolerance ratios are given for the metal ions hg(I), Co(II), Cu(II), and X ( I 1 ) which are the principal interferences. The effects of these ions a t higher ratios are shown in Table I. Among the platinum group metals, ruthenium(II1, IV) was the only interference at a 30: 1 mole ratio. Its maximum tolerance level was not established Many common metal ions including Co(II), Cr(III), Cu(II), Dy(III), Ho(111), Mn(II), 110(V,VI) , Nd (I1T) , Ni (11) , Pd (II), P t (11,IV) R u (I1I,IV) , Ti(IV), U(IV,VI), and V(IV,V) are colored or form colored complexes with EDTA under the analysis conditions and must be compensated for with a sample blank. The interference of cobalt is somewhat unusual. The pink cobalt(I1)-EDTrl complex absorbs at
VALENCE TOLERANCE:
ION TO
IRON
MOLAR
RATIO
r9 I8 000
(CODE1
Figure 2. a.
b. c.
794
ANALYTICAL CHEMISTRY
Tolerance of method for diverse ions
Highest ratio studied. Iron level maintained a t 0.001 mmole Moximum permissible ratio a t or below which there is no interference See text for additional information
the 507-mp wavelength. The yellowishorange cobalt(I1)-I ,IO-phenanthroline complex, apparently more stable than the cobalt(I1)-EDTA complex, also abqorbs at 507 mp but not as much as the cobalt(I1)-EDTA complex. The net effect is that the subtraction of the sample blank results in an over-correction and, hence, a negative bias. In the presence of the ions Ag(I), Hg(II), and silicate, a precipitate forms under the recommended analysis conditions. The precipitate must be removed by centrifugation or filtration prior to measurement of the absorbance of the iron complex. Tungsten(V1) precipitates as tungstic acid in acid medium and coprecipitates iron. The precipitation is avoided by adding the citrate-EDTA reagent to the sample first, then adding the pyridine before the addition of the hydrochloric acid. EXPERIMENTAL
Recommended Procedure. Considering the factors affecting the development of the iron(I1)-1,lO-phen-
anthroline complex and the effects of diverse ions, the following procedure is recommended : Pipet an aliquot of the sample containing between 2 and 100 pg. of iron into a 25-ml. volumetric flask. Add 0.5 ml. of concentrated hydrochloric acid and swirl t o mix. If a white or yellowish precipitate forms, the sample may contain tungsten(V1). Discard the sample, pipet a new one, and continue beginning a t the next step. Add 1 ml. of 2JZ hydroxylamine hydrochloride, 5 ml. of the citrate-EDTA reagent (0.5M diammonium citrate4.25M disodium EDTA, aqueous solution) and 2 ml. of 0.05JZ 1,lO-phenanthroline (ethanolic solution). Swirl to mix, then add 3 ml. of pyridine. If the hydrochloric acid was omitted earlier, add 0.5 ml. of hydrochloric acid. Dilute to volume with water, mix well, and let stand for 25 minutes, or, if the sample itself contains high concentrations of organic complexing agents, heat for 15 minutes a t 60' C., chill to room temperature, then let stand for 25 minutes. Process a reagent blank and, when necessary, a sample blank with the sample. Measure the absorbance of the sample and the blank(s) a t 507 mp against
water in 1- or 5-em. cells. If a precipitate forms, either filter or settle it by centrifugation before measurement. Calculate the net absorbance of the sample and determine the iron concentration from a standard curve or by direct comparison with a pair of standards processed simultaneously with the sample. Reliability. The reliability of the proposed procedure is excellent. Based on more than 30 determinations over a period of 1 year a t the 27.3- and 54.6-pg. iron levels, the relative standard deviation is 1% a t the 27.3-pg. level and 0.5% a t the 54.6-pg. level. LITERATURE CITED
(1) Vydra, F., Kopanica, M., Cliemist-
Analyst 5 2 , 88 (1963).
STAXLEY S.YAMAMURA JOHN H. SIKES
Phillips Petroleum Co. Atomic Energy Division Idaho Falls, Idaho Division of Analytical Chemistry, 150th Meeting, ACS, Atlantic City, N. J., September 1965.
Trace Analysis of Fatty Amines by Gas Chromatography SIR: Gas-liquid chromatography offers a rapid, quantitative, and potentially specific method of trace analysis. Attempts to determine small amounts of fatty amines by this technique have not been successful. Use of highly polar partitioning liquids and alkali-treated column ( 2 , 6) failed to eliminate significant loss of sample by adsorption or decomposition. Horning et al. (1, 3, 7') have evaluated the gas chromatographic properties of a number of derivatives of biologically important amines. This report describes the quantitative determination of fatty amines in water as trifluoroacetyl (TFX) derivatives following extraction with n-hexane. Quantitative trifluoroacetylation was obtained within a 5-minute reaction time. Recoveries of 90 to 1 0 0 ~ owere obtained on samples of n-octylamine and n-octadecylamine carried through the procedure. Liquid-liquid extraction concentrates the sample and eliminates interference of many acidic and neutral components. The optimum procedure yields a sensitivity of 0.05-p.p.m. fatty amine in water. EXPERIMENTAL
Apparatus. An F & M Model 609 gas chromatograph equipped with flame ionization detertor was employed. The columns were 2-foot stainless steel, l/r-inch 0.d. packed with 2075 silicone rubber (SE-30) on 60- to 80-mesh Gas-Chrom CLH (Applied Science Labs). The column was condi-
4a0t 1
i
pg. N - O C T Y L A M I N E
loot/
0
,
5 IO 15 20 MICROGRAMS OF SAMPLE
25
water droplets from the n-hexane layer. The extracts were reacted with 1-ml. trifluoroacetic anhydride with magnetic stirring in a 50-ml. beaker. .Ivoid exposure of the reaction mixture to moisture because a violent reaction with anhydride will occur which may cause low results. After 5 minutes reaction time, the volume was reduced to 0.5 ml. with a dry stream of nitrogen. The solution was quantitatively transferred to a 1.0- or 5.0-ml. volumetric flask and diluted to volume with n-hexane. A 10-pl. aliquot was normally injected into the chromatograph and quantitatively evaluated by peak height measurement.
Figure 1 . Comparison of sensitivity free amine vs. TFA derivative
RESULTS A N D DISCUSSION
tioned a t 300' C. for 24 hours while it was swept with dry helium. The optimum helium flow rate in terms of column efficiency and detector sensitivity was 100 ml. per minute. Maximum detector sensitivity was obtained with flow rates of hydrogen and air of 55 and 400 ml. per minute, respectively. Other operating conditions were: detector sensitivity, 4 X ampere (range 10); injection port temperature, 300' C. detector temperature, 300" C.; column temperature programmed from 100" to 250' C. a t 10' C. per minute. Procedure. Weighed samples of aqueous solution containing 5 to 1000 kg. of Cs to CI8 fatty amines were adjusted to pH 9 to 10 with alkali and extracted with several portions of nhexane. Care was taken to remove
Comparison of the peak height response of the free amine us. the TFA derivative reveals the large increase in sensitivity obtained by this procedure. Figure 1 presents a graph of peak height response us. micrograms of n-octylamine or n-octylamine TFA sample injected, The free amine samples were chromatographed on 20% Apiezon-L coated Chromosorb W which was treated with alkali as recommended by Link et al. (4). This column gave the least amount of sample loss of those investigated for the free amine analysis. N o peak was obtained when less than 10 pg, of amine was placed on this column. In contrast, 0.05 pg. of TFA derivative can be detected and the peak height is linear with sample size. Use of the VOL. 38, NO. 6, M A Y 1966
795
