point, unknown, and nucleus of the phenothiazines, respectively.
R
= slope
k = column constant ,4nd for any subsequent point log t,,
=
(E*)
log L1
Similarly, the same may be done for the boiling point numbers except that it will be noted that i t is the cube root of the boiling point that is related to the log of the retention times. DISCUSSION
OF
RESULTS
Based on the data presented, the feasibility of predicting the order of elution of certain phenothiazines, their separation on gas chromatographic columns, and the type of derivative most desirable to resolve a nonseparable pair, when derivatives are possible, in addition to presenting a method for calculating their relative retention values, have been shown and established. In Table IV one notes that the predicted and observed order of elution of the compounds is in good agreement but that compounds 3, 4, and 5, and 9 and 10, as expected, cannot be separated. From the boiling point data, it would also be questionable to predict the separation of compounds 1 and 2, which, however, do separate. For identification purposes, the compounds shown numerically in Figure 1 cor-
respond to those numbered in Tables I and IV. In contrast to predicting the elution sequence, prediction of the relative retention values is subject to greater deviation. Nevertheless, the average deviation between the observed and calculated relative retention times is 8%. Although compounds 3, 4, and 5 could not be separated on a SE-30 column as predicted, acetylation of desdimethylchlorpromazine (compound 3) and desmethylchlorpromasine (compound 4) yields acetamides (compounds 8 and 10, respectively) that are separable. Despite the method’s possible applications and obvious advantages, there are several disadvantages. First, the equation AH, = KrBP holds true only for a small number of related compounds. Second, there is a sparsity of boiling point data available to establish valid boiling point number increments for specific atomic and/or molecular groupings. Third, this method cannot be used to make any predictions for isomeric structures. Nevertheless, it is our opinion that the method as described can be applied to various types of organic molecules when boiling point information is limited or nonexistent. ACKNOWLEDGMENT
The authors thank C. J. Carr and G. Cosmides of the Pharmacology Unit, Psychopharmacology Service Center,
National Institute of Mental Health, Bethesda, Md., for the phenothiazine samples used for this investigation. LITERATURE CITED
(1) Grant, D. W., Vaughn, G. A., J. Appl. Chem. London 6,145 (1956). (2) Gudzinowice, B. J., Alm, J., Driscoll,
J. L., Smith, W. R., Abstracts, Tenth Detroit Anachems Conference, Wayne State University October 1962. (3) Gudeinowicz, b. J., Driscoll, J. L., J. Gas Chromatog. 1, No. 5, 25 (1963). (4) Gudzinowicz, B. J., Martin, H. F., ANAL.CHEM.34, 648 (1962). (5) Haas, H. B., Newton, R. F., in “Handbook of Chemistry and Physics,” 38th ed., pp. 2121-2, Chemical Rubber Publishing Co., Cleveland, Ohio, 1956. (6) Herbrandson, H. F., Nachod, F. C., in “Determination of Orgamc Compounds by Physical Methods,” p. 16, Academic Press, New York, 1955. (7) Kinney, C. R., J. Am. Chem. SOC.
60,3032 (1939). (8) Martin, H. F., Ph.D. thesis, Boston University, Boston, Maas., 1961. (9) “Merck Index of Chemicals and Drugs,” 7th ed., p. 250, Merck and Go., Inc., 1960. (10) Ibid., p. 1065. (11) Pecsok, R. L., “Principles and Practices of Gas Chromatography,” pp. 847, Wiley, New York, 1959. (12) Sievers, R. E., Moshier, R. W., Ponder, B. W., Abstracts, p. 35M, 141st Meeting, ACS, Washington, D. C., March 1962. RECEIVEDfor review April 23, 1963. Accepted August 28, 1963. Division of Analytical Chemistry, 145th Meeting, ACS New York, N. Y., September 1963.
Work sup orted by the National Institute of Mentay Health under Contract No. PH 43-62-195.
Determination of Iron with Diethylacetic Isotope Dilution Analysis
Acid by
INARA MENCIS and THOMAS R. SWEET McPherson Chemical laboratory, The Ohio Stafe University, Columbus I 0, Ohio
b Solvent extraction, isotope dilution, and spectrophotometry are combined to determine small amounts of iron in the presence of copper. Diethylacetic acid is used as the reagent and solvent for the formation and extraction of the iron complex. Fe69is used as the radioactive tracer.
A
isotope dilution, spectrophotometry, and solvent extraction have been suggested for the determination of cobalt (3, 4). A study of the extraction of iron in diethylacetic acid indicates that the iron complex with diethylacetic acid is extracted into diethylacetic acid at p H values rn low aa 1. Before the iron is completely extracted, copper begins to NALYSES INVOLVING
1904
0
ANALYTICAL CHEMISTRY
extract. Since complete extraction of iron would lead to larger copper corrections, especially for high copper content samples, it was found convenient to use isotope dilution analysis. The absorption curves of iron and copper are shown in Figure 1. On the basis of these curves, it was decided to measure the absorbance at 345 and a t 685 mp. The amount of copper extracted can be corrected for by using a working curve which relates the absorbance of copper at 685 and at 345 mp. EXPERIMENTAL
Apparatus. The absorption curves shown in Figure 1 were made on a Cary Model 14 recording spectrophotometer. All other absorbance meas-
urements were made with a Beckman DU spectrophotometer using I-cm. matched rectangular silica cells equipped with ground glass stoppers. Solvent extractions were performed with A-8312 Duraglass bottles with 20-400 polyseal caps (Owens-Illinois Glass Co.). All radioactivity measurements were made with a RIDL Model 49-54 scaler. The detector used was a 5- X 4-inch, thallium-activated sodium iodide well crystal. Reagents. Diethylacetic Acid. Practical grade diethylacetic acid (Matheson, Coleman, and Bell) was purified by distillation. Infrared spectral analysis indicated t h a t the acid is stable for a t least 2 months. Standard Iron Solutions. High purity iron wire (99.9% Fe) was cleaned by immersion in dilute nitric acid and was
rinsed in distilled wiiter and acetone and dried. The wire was dissolved in 20 ml. of 1to 1nitric atrid. The solution was heated until brown fumes were no longer observed, transferred to a 250-ml. volumetric flask, and diluted to the mark with demineralized, double distilled water. Three sl,andard iron solutions were prepared whose molarities 4829 X 10-3, and were 4.712 X 4.8266 X 10-3M. Fe69 Activating SolJtion. An active solution containing Fe69 as Fe(II1) was prepared from a purified solution of high specific activity obtained from Oak Ridge National Laboratory. The Corn and Mnb4isotopes present in the received sample were removed by ion exchange (z?). Portions of this sample were added to aliquots of the iron standard solutions in 100-ml. volumetric flasks. Sufficient active solution was added so that after dilution to the mark, a 5-ml. portion g a m an activity of about 25,000 counts per minute. The activating solution had an estimated iron concentration of 0.01 fig. per 100 ml., which is negligible compared to the inactive iron used in the determination. Copper Solution. Copper nitrate (Baker Analyzed Rmgent) was dissolved in demineralized double distilled water to give a 0.03M solution. Buffer Solution. A solution which was 2M in sodium fulfate and 0.5M in sodium bisulfate wzts prepared, using demineralized, double distilled water. Procedure. PRXPARATIONOF WORKINGCURVES. Copper Working Curve. Various volumes of standard copper solution were added t o 100-ml. volumetric flasks. Ten milliliters of the buffer solution were added and the solution was dih ted to the mark with distilled water. Twenty milliliters of this solution were placed in a n extraction bottle, 1 drop of methyl orange indicator wm added, and the pH was adjusted to 3 to 4 using 1N HN03. The copper was extracted by shaking the aqueous phase for 10 minutes with 15 ml. of diethylacetic acid. The sample w:ts centrifuged for 5 minutes. A portion of the organic phase was removed arid the absorbance was measured at 345 and 685 mfi. us., 4 3 was ~ made. ~ ~ A plot of A straight line having a slope of 2.43 was obtained. Iron Working Curve. Various volumes of standard inac Live iron solutions were transferred to 1130-ml. volumetric flasks. Twenty drops of activating solution, 1 drop of methyl orange indicator, and 10 ml. of the buffer were added. The p H was 5djusted by dropwise addition of 5N NaOH until the solution changed from pink to yelloworange. The volumetric flask was filled to the mark with demineralized double distilled water. Twenty milliliters of this solution were transferred to an extraction bottle and the iron was extracted for 10 minutes with 20 ml. of diethylacetic acid. The sample was centrifuged for 5 minutes. Five milliliters of the diethylacetic acid layer were removed and placed in a 2-dram screw cap vial and counted for 10 minutes. Five milliliters of the ,tqueous iron solu-
350
1400
450
500 550 WAVELENGTH, m p
Figure 1. A. 8.
600
650
100
Absorption curves
Fe(lll) extract in diethylacetic acid Cdll) extract in diethylacetic acid
Table 1. Preparation of Spectrophotometric Working Curve Total weight of iron Fe Concn. of iron in in 20 ml. aqueous phase Extracted, diethylacetic acid, Absorbance, before extraction, pg. % pg./mI. at 24.0" C. corrected
44.9 96.7 97.2 85.9 64.5 94.4 98.3
1078.0 539.4 431.2 539.4 431.2 107.9 194.2 Table II.
Table 111. Total wei ht of sampfe used, grams Sample 157a
5.0165 5.0063 5.OW4 5.0072 5.0165
0.751 0.858 0.690 0.675 0.452 0.162 0.306
Analysis of Iron-Copper Samples
Total.-weight ____ Iron added, Copper added, 647.3 323.7 323.7 323.7 431.2 107.9
24.2 26.1 21 .o 23.2 13.9 5.1 0.5
Iron found,
Abs.
Rel.
432 117
1 1 - 10 -2 1 9
0.16 0 31 -3.09 -0.62 0.23 8.33
9.6 9.6
Analysis of National Bureau of Standards Samples
Percentage of iron extracted
Total weight of iron found, pg.
91.9 91.5 92.0 94 .O 95.2
8.58 8.66 8.57 8.56 8 68
Iron in sample, yo
N.B.S.
value
0.171 0,173 0.171 0.171 0.173 Av. 0372
0.174
0.397 0.396 0.396 0.396 __ Av. 0.396
0.39
Sample 671,KO.1 2.2083 2.2188 2.2i69 2.2224
81.5 93.7 97.2 97.7
tion in the 100-ml. volumetric flask were placed in a 2-dram vial and counted for 10 minutes. A portion of the organic layer was placed in an absorbance cell and the absorbance was measured a t 345 and 685 mp against a blank. Methyl orange does not extract into the diethylacetic acid. From the concentration of the standard iron solution, the concentration of
8.77 8.79 8.78 8.80
the 100-ml. diluted solution was calculated, as well as the weight of iron in the 20-ml. aliquot. Since the per cent extraction can be calculated from the ratio of the activity of 5 ml. of organic sample, measured after extraction, to the activity of 5 ml. of unextracted aqueous sample, the concentration of iron in the diethylacetic acid can be determined. A working curve was obVOL. 35, NO. 12, NOVEMBER 1963
0
1905
tained by plotting absorbance values us. the concentration of iron in the diethylacetic acid. See Table I. A straight line passing through the origin was obtained. To test this method for the analysis of iron in the presence of copper, several synthetic samples containing iron and copper were analyzed. The results are shown in Table 11. ANALYSISOF COPPER-SICKEL-ZINC ALLOY(NBS 15ia). Four 5-gram samples were weighed and placed in To each 250-ml. volumetric flasks. flask 40 ml. of 1 t o 1 nitric acid were added. After the samples dissolved, the solutions were gently heated until brown fumes !$ere no longer observed ( I ) . ilfter cooling, the solutions were diluted to the mark with demineralized double distilled rvater. Fifty milliliters of the sample solution were transferred to a 100-ml. volumetric flask. After the addition of 10 ml. of buffer mixture and 20 drops of activating solution, the flasks were filled to the mark. A 20-ml. aliquot vvas transferred to an extraction bottle. The pH was adjusted to 3.0 to 3.5 using 5N
Table IV.
sodium hydroxide solution. Indicator paper was used to detect the pH of the solution. The solution was shaken for 10 minutes with 20 ml. of the diethylacetic acid. After centrifuging for 5 minutes, an aliquot of the organic phase was removed for activity measurement and the absorbance of the organic phase was measured. The absorbance a t 345 mp, after correction for copper extracted, was used to determine the concentration of iron in the organic phase from the spectrophotometric working curve. The activity of an aliquot of the unextracted aqueous solution in the 100-ml. volumetric flask was also measured. The weight of iron, wu,in the 20-ml. aliquot of aqueous solution used in the extraction was calculated by means of the following equations : 100 Wa =
c,v,
T
where C, is the concentration of iron in the organic phase as read from the working curve, V , is the volume of the
Interference Study
270 fig. of iron added
Interfering ion Species Added, mg. 171.4 Chloride 85.7 68.6 51.4 34.3 11.76 5.88 4.70 2.35 100.2 25.14 20.11 15.08 28.49 28.37 31.61 13.04 6.52 6.52 2.61 57.38 9.18 5.74 26.56 13.28 1.73 .53
Magnesium Lead Chromium Cobalt Nickel Zinc Aluminum Tin
Manganese
Table V.
Molar ratio interfering ion/iron 1000 500 400 300 200 100 50 40 20 100 100 80 60 100 100 100 100 50 50 20 50 8 5 100 50 6.5 2
Iron found,
Abs.
error,
rg. 284 274 274 265 267 287 273 267 273 267 270 272 269 267 268 267 253 267 275 273 240 258 273 296 322 274 267
Pg. 14 4 5 -5 -3 17
3 -3 3 3 0 2 -1 -3 -2 3 17 -3 5 3 - 30 - 12 3 26 52 4 3
-
Rel. error,
%
5.18 1.48 1.48 -1.85 -1.11 6.29 1.11 -1.11 1.11 -1.11 0.00 0.74 -0.37 -1.11 -0.74 -1.11 -6.29 -1.11 1.85 1.11 -11.10 -4.44 1.11 9.65 19.30 1.48 -1.11
Effect of Tartrate on Iron Determination
hlolar
Tartrate added, mg. 71.55 39.22 31.38 23.53 15.69 7.84
1906
0
ratio Fe Fe tartrate/ present, extracted, iron Pg. % 100.0 50.0 40.0 30.0 20.0 10.0
270 296 296 296 296 296
ANALYTICAL CHEMISTRY
5.5 24.1 36.2 64.4 81.4 88.9
Aars m p 0.038 0.154 0.229 0.405 0.522 0.559
Fe found,
error
rg. 312 295 296 294 299 293
42 -1 0 -2 3 -3
Abs.
Pg.
Rel. error, % 13.47 -0.34 0 .00 -0.68 1.01 -1.01
organic phase used in the extraction, A , and A , are the activities of vu and v, volumes of the aqueous and organic phases, V , is the volume of the aqueous phase used in the extraction, and %E is the per cent extraction. The results are shown in Table 111. ANALYSISOF NICKELOXIDE (NBS 671, No. 1). Four 2.2gram samples were placed in 250-ml. volumetric flasks. Each of these samples was dissolved in 20 ml. of 1 to 1 nitric acid and 4 drops of concentrated hydrochloric acid. Without the addition of the hydrochloric acid, some undissolved material was observed even after the solution was gently heated on a hot plate for 1 hour. The procedure for the iron determination was the same as used for the copper-nickel-zinc alloy. The results are shown in Table 111. INTERFERENCE STUDY. Interference was studied by the addition of known concentrations of various ions to standard diluted iron solutions. The iron was analyzed by the same procedure as outlined previously. The concentration of interfering ion added, except for chloride, was 100 times that of the iron present. If there was significant interference, the concentration of the interfering ion was reduced until the error was about 1%. All metal interfering ions were added as the nitrates. The results are shown in Table IV. Addition of tartrate ion, even though i t caused a decrease in the extraction of iron, did not affect the iron determination up to a molar ratio of tartrate to iron of 50. The results of this study are shown in Table V. DISCUSSION
The molar extinction coefficient for the iron diethylacetic acid complex is 1.82 X l o 3 liters mole-' cm.-l From calculations using the pH prior to extraction, p H after extraction, and the amount of iron extracted, it can be concluded that the species extracted contains 3 moles of the diethylacetic acid for each mole of iron. This complex was found to be stable for at least 2 hours. This is sufficient time to carry out the extraction and t o obtain the necessary data for any sample. The sulfate buffer mixture is added to achieve quicker phase separation, even though excess salt causes a decrease in extraction. The density of the acid is 0.92 gram per ml. The interference study indicates that lead, chromium, cobalt, nickel, and zinc do not affect this analysis when present in molar concentrations up t o 100 times more than the iron present. Magnesium, aluminum, and tin were found to interfere. Chloride ion, when present in molar concentrations 500 times that of iron, showed no significant interference. Manganese is the most serious of all interfering ions. Even though it extracts only slightly at the pH of extraction of iron, it absorbs significantly a t 345 mp.
Even though the copper and iron complexes with diethylacetic acid are extracted in solvents such as ethers, esters, alcohols, benzene, and halogenated hydrocarbons, diethylacetic acid was selected as the best solvent for this determination, since it absorbs below 390 mp and the excess reagent is extracted by the other solvents. This method of andysis is accurate and rapid for the determination of iron. I t is quite convenient since no prelim-
inary separations are necessary. The method was tested by analyzing h’ational Bureau of Standards Samples. For the 157a sample, the relative error of the average of the values obtained is 1.2701,. The 671 No. 1 sample is in complete agreement with the NBS recommended value. The sensitivity, defined as the concentration of iron in diethylacetic acid needed to produce a change in absorbance of 0.005, is 0.15 pg. per ml.
LITE~ATURE CITE^
(1) Am. Soc. Testing Materials, Phila-
delphia, “ASTM Methods for Chemical Analysis of Metals.” pp. 239-40, 1950. ( 2 ) Kraus, K. A., Nelson, F., “Geneva International Conference on Peaceful Uses of Atomic Energy,” Vol. 7 , Paper 837, United Sations, N. Y., 1955. (3) Ralph, W. D., Jr., Sweet, T. R., Mencis, I., ANAL.CHEM.34, 92 (1962). ( 4 ) Sporek, K. F., Ibzd., 33, 764 (1961). RECEIVED for review March 19, 1963. Accepted August 16, 1963.
Determinaition of Hydrogen in Sodium by Isotopic Dilution with Tritium CLAYTON EVANS and JOHN HERRINGTON United Kingdom Atomic Energy Authority, Aldermaston, England
b Isotopic dilution with tritium i s an efficient method for determining hydrogen in sodium. Satisfactory recoveries were obtained using hydrogen spikes of 16 to 90 PI., corresponding to 140 to 4000 p.p.m. of hydrogen in sodium. The recovery has been shown to b e independent of concentration. Equilibrium between the added tritiated-hydi*ogen and the hydrogen in the snmple was established b y heating in a sealed borosilicate glass t h e at 420” C. for 10 minutes. The’ activity of the tritiated hydrogen scimples was determined b y Geiger counting.
E
with the liquid metalssodium and sodi Im-potassium alloy-as coolants in reactors has shown that strict control of impurities is essential. Hydrogen is one of the most troublesome, since it not only causes embrittlement of thr fuel element cans, but also precipitates as alkali hydrides, thereby causing plugging of the cooling circuits. A satisfactory method for the determination of hydrogen in these metals is therefore necessary. Ilolt (4) has discussed various methods of analysis and reported an isotopic dilution technique with deuterium employing mass spectrometry for the analysis of hydrogen-deuterium mixtures. We have shown that deuterium and mass spectrometry can be replaced successfully by tritium and Geiger counting. By using “break-seals ’ instead of taps, it was possible to imrrerse the ampoule completely in the furn:tce while carrying out the equilibration. This design prevented the sodium from distilling out of the heated zone and recombining with the hydrogen on condmsing on the unheated portion of the apparatus as deXPERIENCE
scribed by Holt (4). The equilibration ampoules mere inexpensive and were discarded after the experiment. EXPERIMENTAL
Apparatus and Procedure. The apparatus is shown in Figures 1 to 5 . The ampoule used in these experiments is shown in Figure 1. It was made from 10-mm. diameter borosilicate glass tubing, the effective length of which was 17 to 18 cni. After degreasing, cleaning, and removing the stopcock, i t was baked a t 180-200” C. for ‘ / a hour. While still warm, the greased stopcock key was replaced and the tube closed with a stopcock and B14 cone covered with a Teflon sleeve. The ampoule was evacuated and weighed on a balance having a sensitivity of 0.2 mg. It mas filled with dry argon via the 3-mm. tap, then with the gas flowing through the ampoule and the dispenser, the ampoule was attached to the dispenser and the system evacuated. Khen Ioading samples from a large stock of commercial metal in an argon-filled glove box, a modified ampoule was used. The boat and pusher were discarded and the l314 socket sealed to the end instead of the side as in these experiments.
The dispenser was loaded either with commercial grade or hydrogen-free sodium and filled with dry argon. When using commercial grade metal, the descaled lumps were inserted through the U19 socket while a stream of dry argon flowed through the apparatus. The E19 cone and tap were replaced, the argon flow stopped, and the tap closed. The metal was melted and by manipulating the taps to the argon supply and vacuum pumps the liquid metal was filtered through the sintered glass disk. When hydrogenfree metal was needed, the B19 socket was removed and a subsidiary, allglass, multiple-stage distillation system sealed to the top of the dispenser. The metal was vacuum distilled into the dispenser and filtered through the glass disk. The distillation system was then sealed off and removed. Samples of sodium were dispensed into the boat by melting the stock of sodium, and lifting the ball-bearing with a magnet. The sample was allowed to cool and then the boat was transferred to the break-seal end by means of the magnetically-operated pusher, the pusher then being returned to its original position. The ampoule was sealed off a t A (Figure 11, and the remainder of the original ampoule was
-814
SOCKET
-
PUSHER
BOROSILICATE BOAT
Figure 1. Sodium sample tube - a m
s 10
BORE
H V TAP
CONE
VOL. 35,
NO. 12, NOVEMBER 1963
1907
