Photometric Determination of Aluminum in Steel UNO T. HILL Inland Steel Co., East Chicago, Ind.
A nitrated Eriochrome Cyanide R dye is employed to determine aluminum in steel in both a direct and a separation method. An oxidized derivative of ascorbic acid complexes iron and minor amounts of interfering elements in a direct photometric determination of aluminum in carbon and low alloy steels. A caustic separation of iron and other interfering elements is made when high alloy steels are analyzed for aluminum. Addition of zinc and boron aids in the separation.
E
gravimetric and photometric methods for the determination of aluminum in steel are tedious and the numerous necessary chemical separations are frequently sources of error. Richter (3), Seuthe ( d ) , and 1kenberr)- and Thomas ( 2 ) have applied the Erioclironie Cyanine R photometric method to the determination of aluminum in steels after qeparation of iron and other interfering elements. A direct photometric method for the determination of aluminum in iron ores ( I ) employs masking agents for iron and other interfering elements but is not applicablr to the deterrnination of aluminum in steels because of the high iron-aluininum ratio. This study \\-as undertaken to develop a rapid direct photometric method for aluniinum in carbon and low-alloy steels and to improve the photometric method for alloy sterls inroll-ing a niinimum of chemical scparations. The caustic separation of iron and other interfering elements from aluminum is attractive because of its qpeed and simplicity. Peuthe (4) has shown that the recovery of aluminum is improved when the ferric hydroxide precipitate is homogenized by mechanical stirring. d check of Seuthe’s method showed that rccorery of aluminum was not complete but \vas proportional to the aluminum present in similar steels. The aluminum determination was dependent upon the complete separation of iron from aluminum hecause the ferric iron complex is nearly as sensitive as the aluminum complex at 535 mp. Vanadium in appreciable amounts accompanies aluminum and, if reduced, contributes a positive error by forming a n Eriochrome Cyanine R complex. The solubility of glass in concentrated hot caustic was a variable source of XISTISG
aluminum which could not be accurately compensated for in a blank. EXPERIMENTAL
Method A. Loss of aluminum by occlusion in the ferric hydroxide precipitate was believed preventable by introducing relatively large amounts of a n element similar in chemical behavior t o t h a t of aluminum, but nonreactive in the amounts employed R ith Eriochrome Cyanine
R. Of the elements tested, lithium, boron, and zinc improved the separation of aluminum and the combination of zinc and boron effected it completely. The addition of metallic zinc caused the needed reduction of chromium and vanadium to ensure the complete separation of chromium and most of the vanadium. Method B. I n a search for a more effective method of masking which is necessary in a direct photometric determination of aluminum in steel, ascorbic acid proved more selective in the presence of high iron concentrations t h a n the mercaptoacetate previously employed (I). This is due, in part, to the formation of an oxidized derivative which is formed when ascorbic acid is added to an acid solution of trivalent iron and other reducible clements present in steel. APPARATUS A N D REAGENTS
Method A. REAGCSTS.8-Quinolinol, 1 7 . in carbon tetrachloride. (Renew if precipitate foims when added t o the solution.) Dissolve 0.5 gram of 8-quinolinol in 50 ml. of carbon tetrachloride. Eriochrome Cyanine R. To 0.3500 gram of Eriochrome Cyanine R in a dry 250-ml. beaker, add 2 ml. of 1.20 specific gravity nitric acid. Swirl for 2 minutes a t Toom temperature until orange-red, add 75 nil. of nater and 0.25 gram of either urea or sulfamic acid, w i r l to dissolve, and dilute to 1 liter. Ammonium acetate buffer, p H 7.0, 32%. Dissolve 320 grams of ammonium acetate in water and dilute to 1 liter. Adjust the pH so that 5 ml. of the buffer will produce a p H of 5.8 in 50 ml. of the colored complex described in the procedure by adding acetic acid or ammonium hydroxide as needed. PROCEDURE. Acid-Soluble Aluminum. T o a 1.000-gram sample in a
150-nil. Erlenmeyer flask, add 25 ml. of 1 t o 1 hydrochloric acid and 15 ml. of 3 5 nitric acid. Place on a medium temperature hot plate and when the sample is in solution, add 0.25 to 0.50 gram of solid sodium persulfate to oxidize all of the carbon. Boil for a minute or two, dilute to about 75 ml., and add 0.25 gram of granular zinc. Khen the zinc is almost completely in solution, add about 0.7 gram of boric acid and heat until in solution. Pour the hot solution slowlg with swirling into a polyethylene beaker containing 15.0 grams of solid sodium hydroxide. Dilute with about 100 nil. of water, pour into 250-ml. volumetric flask, dilute to volume, and mix. Pour the solution back into the polyethylene beaker and allow to settle. Filtcr a portion through Khatman KO. 31H paper and discard the first 25 ml. Filter a second 25-ml. fraction and pipet a 5.0-ml. aliquot into a 50-nil. volumetric flask. Add 2 to 3 drops of 8-quinolinol in carbon tetrachloride and 2 drops of 1% p-nitrophenol indicator. Titrate with 3% hydrochloric acid until the color changes from yellow to colorltss and add 3 drops in excess. Add 5.0 ml. of Eriochrome Cyanine R dye, 0.035% solution, and after 2 minutes, add 5 ml. of ammonium acetate buffer. After 7 minutes or longer, dilute to volume, and mix. Obtain the absorbance against an aluminum-free iron blank, carried through all the steps of the procedure, a t 535 mp) 0.03 slit, and 1-em. cuvettes. From a previously prepared calibration curve constructed from National Bureau of Standards standard steel samples, determine the amount of aluminum present. The calibration curve may also be constructed by adding knonn amounts of aluminum to 1.0-gram samples of pure iron and processing these samples as described above. Acid-Insoluble Aluminum. To a 1.0000-gram sample in a 250-ml. beaker add 25 ml. of 1 to 1 hydrochloric acid and 15 ml. of 3-Y nitric acid. When in solution, filter on Khatman No. 42 paper with pulp and wash free of salts with hot water, dilute hydrochloric acid, and finally hot water. Ignite in platinum and fuse the residue with a small amount of sodium pyrosulfate. Dissolve the cooled melt in 10 ml. of 3N hydrochloric acid and about 25 ml. of water. K h e n in solution, carry out a caustic separation as for acid-soluble aluminum, dilute t o 100 ml. in a volumetric flask, and mix. To a 5-ml. aliquot in a 50-ml. volumetric flask add VOL. 31, NO. 3, M A R C H 1959
429
Table I.
Analysis of standard and Miscellaneous Steels by Method A
Aluminum Deviation, Type Present Found % 0 027 0 026 -0 a01 1i o Titanium bearing 0 106 0 000 106 Chromium, molybdenum, aluminum 0 106 0 003 0 003 0 000 55 c Open hearth iron 0 050 0 000 0 050a 50 b Chromium, tungsten, Panadium 0 050 0 000 153 Cobalt, molybdenum, tungsten 0 050" 5j Cast iron 0 100" 0 0'38 -0 002 21 d Acid open hearth 0 025. 0 026 $0 001 123 a 18 chromium, 11 nickel 0 000" G 0q0 0 000 a Represents residual and added aluminum. 0 Average of 3 detns , no detn deviated from another by more than 3 ~ 002v0.
Sample
Table II. Analysis of Standard and Miscellaneous Steels by Direct Photometric Method B
Sample NBS 170 50 b 123 a 153 Ingot 10 2
Aluminum Present Found 0 0 0 0 0 0 0 0 0 0 0
027 050a
050Q 090" 052b 059b
061b 076* 080b 073* OBb
0 0 0 0 0 0 0 0 0 0 0
028 050 048 093 053 060 058 075 074a 076* 076*
Deviation,
%
+0 0 -0 +O +0 $0 -0 -0 -0 +O -0
001 000 002
003 001 001 003
001 006
003 002
tiyo in excess. Boil out the oxides of nitrogen, cool, dilute to volume, and mix. To a 5-1111. aliquot in R 25-1111. volnmetric flask, add 5 ml. of 1% ascorbic acid and 5 nil. of Eriochrome Cyanine R solution. After 1 minute, add 5 ml. of sodiuni acetate buffer and let stand 2 or 3 minutes. Dilute to volume, mix, and obtain the absorbance against an aluminum-free iron blank carried through all the steps of the procedure a t 535 mw, 1-em. cell. From a calibration curve constructed from standard steel samples, obtain the percent of aluminum. DISCUSSION
Represents residual and added aluminum. Method A. RECOVERY OF ALUb Spectrographic value. MINUM. Because recovery of alumiAverage of 3 detns., no detn. deviating num is dependent upon t h e complete from another by more than ~!=0.0027~. oxidation of carbon, a small amount of sodium persulfate is added after t h e metal has been digested. The 2 drops of p-nitrophenol indicator and caustic concentration after the initial titrate to the end p i n t with 3N hydroprecipitation is not a factor in aluniichloric acid, then add 3 drops in excess. iium recovery 11hich permits dilution Proceed as described above for acidto a greater volume. This contributes soluble aluminum. to a faster filtration because of the more Total Aluminum. Proceed as for rapid settling of the precipitate. Aluacid-soluble aluminum, except to filter the solution as for acid-insoluble alumiminum is not absorbed on the filter num and, after ignition and fusion, paper; the same aluniinum content is dissolve the cooled melt in the filtrate. found in the supernatant liquid as in Evaporate the solution to 75 ml., add the filtered sample. 0.25 gram of zinc, 0.7 gram of boric acid, There is an apparent loss of aluminum and proceed as described abovc for if the caustic solution is aged for several acid-soluble aluminum. hours or overnight which may be due Method B (Direct Photometric to the absorption of carbon dioxide Method). R E ~ G E N T S .Ascorbic acid. 1% from the atmosphere or the formation solution. Dissolve 1 gram of ascorbic acid in 100 ml. of water. Prepare as of a n acid-resisting aluminate or hyneeded. drate, Aluminum from such solutions Eriochrome Cyanine R, 0.035y0. may be recovered completely by adding Sodium acetate buffer, p H 8.0. an excess of acid to the aliquot and Dissolve 400 grams of sodium acetate bringing the solution to a boil. After trihydrate in 1 liter of n-ater. Adjust cooling, the acidity is adjusted and the the p H so that 5 ml. of buffer will give a sample processed as described in the p H of 5.5 in the procedure described, procedure. It is best, however, to by adding either acetic acid or sodiuni process the sample as soon as possible hydroxide to the buffer. after dilution to volume and when the PROCEDURE. To a 0.5000-gram sample in a 250-ml. Erlenmeyer flask so precipitate has sufficiently settled for calibrated, add 25 ml. of 3 5 nitric acid. filtration. An aliquot mag' be acidified When in solution on the hot plate, boil and stored indefinitely. out the oxides of nitrogen, add a small EFFECTOF PH AND BUFFERS. The eycess of potassium permanganate (satabsorbance of the aluminum complex urated solution), and boil for a minute decreases with decreasing p H from a or two. Reduce the excess permangamaximum a t 6.3, while above this value nate with a dropwise addition of 10% the color is destroyed by either amsodium nitrite solution and a drop or
430
ANALYTICAL CHEMISTRY
monia or sodium acetate buffers. Sodium acetate has less suppressive effect on the aluminum complex as well as on the complexes of interfering elements and the color formation is faster in its presence than when ammonium acetate is employed. Because Method A is to be employed for the analyses of all types of steel, ammonium acetate is recommended for the improved suppression of interfering metal complexes. Color stability does not vary greatly between pH 5.2 and 5.8 except when ascorbic acid is employed as a masking agent, I n this case, slightly improved color stability is obtained a t pH 5.5 than a t the higher values. The extraction of vanadium would appear most favorable theoretically a t the lower pH values; but effective extraction of this element has been macle a t pH 5.8 by the dropwise addition of 8-quinolinol in the presence of ammonium acetate, especially when the reagent was added to the alkaline aliquot prior to its neutralization. The small volume of carbon tetrachloride containing the 8-quinolinol complexes of vanadiuni and iron is not separated in a separator)funnel, but is permitted to settle out in the volumetric flask. IKTERFERISG ELEMENTS.KO interfering elements have been observed in the high or low alloy steels analyzed by Method A. Vanadium in high concentration will accompany aluminum but it is readily removed by the addition of a few drops of 8-quinolinol dissolved in carbon tetrachloride. Traces of iron are also removed by this reagent, while larger amounts niay be complexed with the addition of mercaptoacetic acid and 8-quinolinol, both of \v-tiich may be added to basic solution prior to adjusting the acidity. Chromium and other interfering elements, except beryllium, reported previously (1) are removed n i t h the iron precipitate. Beryllium interference may be eliminated as described for iron ores ( I ) . Ascorbic acid has not been employed here because it reduces vanadium to its optimum valence state to form an Eriochrome Cyanine R complex. COLORSTABILITY.Complete stability has been observed for an hour or longer and the complex, once formed, is not dependent upon a dye concentration but may be diluted t o larger volume with good agreement with the Beer-Lambert law. When high concentrations of aluminum are complexed, sufficient time must be allowed for the complex to form, or slight deviations from linearity will result. These deviations niay be corrected by increased dye concentration because results with concentrations more than twice this amount have been excellent. It has been necessary, however, to dilute the aliquot to about 25 ml. before adding more dye to prevent the formation of a
strong background color from either boron or zinc. The dye concentration is kept Ion- t o minimize background cdor. Improved color stability and better chchting properties are obtained by nitrating the Eriochrome Cyanine R. The nitrous arid formed in the reaction ('GUSCS instability of the dye solut'ion by reduction of the chromophore group ( 1 ) . Sitruns :icid is removed by the addition of urea or sulfamic acid. Dj.e solutions VI trt7ated have rcniained stable for 6 months or longer. RASGI: OF ALUMISC_RICOXCESTRAT I ( I S . ( )ptimuni aluminum concentration is aliout 10 y in the cdored coniplcs, :inti 20 y give a n absorbance of 1. O n a 5-1111. aliquot. this rcpresents 0.050 and 0.1005 aluniinum, respectively. K i t h Iiiglicr ronccntrations, R minller aliquot ShCJ11ld lie processed. DISCUSSION
M e t h o d B. This method is applicable to 1017- alloy and carbon steel. I n high alloy steels, chromium when present blocks t h e formation of the aluniinuiii complex, and vanadium contributtb n positive error of 0.12y0 aluminum for lYc of mnadium present. Chromium ni:i>-lw rcnioved n-ith fuming
perchloric acid aiitl tlrp hydrogen chloride, and the needed correction may be applied for vanadium when the concentration is known, thus enabling a determination of aluminum in high alloy steels by the direct method. The formation of the complex in perchloric acid is sloner than in nitric acid, and the dye must lie added before ascorbic acid t o utilize the calibration obtained with nitric acid. RESULTS
Table I Phons tlic results obtained by the caustic separation of Method A with high and lo^ alloy steels. Because there are no suitable standards to demonstrate the applicability of the method to alloys, knonn amounts of aluminum were added to these steels as shown. Good agreement nas obtained m-ith all types of steels. Table I1 shows the results from the direct photometric method on lomand high alloy steels. Correction for vanadium was made and chromium was remoyed as described above in the Sational Bureau of Standards samples 5Ob, 123a, and 153. Table I11 shows the repeatability of the aluminum determination on a single sample carried out over a number of
Table 111.
Repeat Analyses of Electric Steel
Aluminum,
%
0 0 0 0 0 0 0 0 0 0
Dev. from >lean 0 000 0 000 -0 001 0 000
060 060 059
060 061 062 059 060
+0 001 $0 002 -0 001 0 000 -0 001 0 000
059
060 Mean 0 060 Std. dev.
0 0O09
days with Method A. Thr awrage deviation iq less than 0.001% aluminum. LITERATURE CITED A s . 4 ~ .CHEII. 28, 1419, (1956). (2) Ikenberry, L. C., Thomas, h b a , Ibid., 23, 1806 (1951). (3) Richter, F., 2. anal. Cheiii. 126, 426 (1944). (4)Seuthe, Adolf, Stahl it. Eisen 64, 493 (1944). RECEIVEDfor review 1Iarch 31, 1958. hccepted October 27, 1958. Pittsburgh Conference on Analytical Chemistry and Applied Spectroscopy, Xarch 1,158.
(1) Hill, U. T.,
Polarographic Oxidation of Phenothiazine Tranquilizers PETER KABASAKALIAN and JAMES McGLOTTEN Chemical Research and Development Division, Schering Corp., Bloomfield, )Tranquilizing drugs, derived from phenothiazine by substitution of alkyl tertiary amines a t the 10-position and containing various substituents a t the 2-position, give regular, reproducible, and well defined anodic voltammetric waves at a gold microelectrode. The voltammetric waves of 14 tranquilizers have been studied to determine their analytical applicability. The effects of pH, concentration, and temperature on the position and size of the waves as well as the effects of substituents in the 10- and 2-positions on half-wave potentials are discussed. The voltammetric oxidation of these compounds in aqueous sulfuric acid compares favorably with existing methods of analysis.
T
H.4XQUILIZISG drugs derived from phenothiazine by substitution of alkyl tertiary amines a t the 10-position may have electron-withdrawing groups at the 2-position. A common property
N. J.
is their susceptibility to oxidation, which is attributed to the phenothiazine nucleus, resulting in the formation of sulfoxides ( 3 ) . Generally, they are assaj ed by one of the following methods: ultraviolet ( 4 ) and infrared ( 5 ) absorption spectroscopy; colorimetry with sulfuric acid ( 2 ) or ferric chloride (7'); bromination (6) ; and aniperometric titration n ith tungstosilicic acid ( 1 ) . It was found in this laboratory that phenothiazine tranquilizers give oxidative voltammetric waves a t a solid microelectrode and these waves have been investigated to determine their analytical usefulness. The follon ing tranquilizers n ere examined: 10- [3-(4-p-hydroxyethyI-l -piperazinyl)propyl]phenothiazine (I); 10[3 - (4 - p - hydroxyethyl - 1 - piperazinyl)propyl]-2-chlorophenothiazine (11); 10 - [3 - (4- p - hydroxyethyl - 1 - piperazinyl)propyl]-2-acetylphenothiazine (111) ; 10- [3-(4-p-hydroxyethyl-l-piperazinyl)propyl] - 2 - (trifluoromethy1)-
phenothiazine (IT') ; 10-(3-dimethylaminopropy1)phenothiazine (T-) ; 10-[(lmethyl - 3 - piperidy1)rnethyljphenothiazine (VI) ; 10- [2-(1-pyrrolidiny1)ethyl ]phenothiazine (VII) ; 10-(2-dimethylaminopropyl) p h e n o t h i a z i n e (VIII) ; 10-(2-diethylaminoprnpyl)phenothiazine (IX); 10-(3-dimet hylaminopropyl) - 2 - chlorophenothiazine 10- [3- ('$-met hyl-1-piperaz inyl)(X) ; propyl]-2-chlorophenothiazine(XI) ; 10(3-dimethylaniinopropyl) - 2 - acetylphenothiazine (XII) ; 10- [3-(4-methyl1 - piperaziny1)propyll - 2 - (trifluoromethy1)phenothiazine IXIII) ; and 2diethylaminoethyl - 10 - phenothiazinecarboxylate (XIV).
R? = hydrogen or electronegative group. Rlo = tertiary alkyl amine. VOL. 31, NO. 3, MARCH 1959
431
