intensity may be accumulated in the first 200 channels of the memory; then, to the second 200-channel group, add the background (1 degree above and 1 degree belom the appropriate Bragg angle setting, if desired). For efficiency of operation, the dwell time for background correction may be a fraction of that time taken for the intensity measurement, depending on the peak to background ratio. The total background is then transferred to magnetic tape and from the magnetic tape in the subtract mode back into the first 200 channels. (The background data is multiplied by a coefficient suitable to correct for the difference in time of accumulation.) These manipulations of the data with magnetic tape require only seconds. Another way to obtain background correction which is perhaps the most useful technique may be described with the aid of Figure 3. The top half of the figure is of a titanium alloy, clad with iron and heat treated, and the lower half is of an untreated titanium alloy of the same coniposition, The purpose is 60 find if iron has diffused into the titanium alloy, and, if so, to what extent. Because the interest is only in the titanium alloy a t low iron concentration, the background intensity is obtained from an untreated alloy of the same composition. With the spectrometer sei at the appropriate Bragg angle, Fe K a intensity measurements are then run in the following automated sequence of events: The data from a spot on the
unknown accumulates ih thc add mode into Channel 1. The beam is then “chopped” (caused to jump down to the untreated titanium alloy) and the system is simultaneously switched into the subtract mode. Background is then subtracted for an equivalent amount of live time in Channel 1. Next the signal is addressed to Channel 2, the stepping motor is caused to advance the position of the electron beam by two microns, the beam is chopped, and the cycle starts over again in the add mode. For purposes of illustration, analytical points as observed on the electron back scatter display tube are superimposed on the metallograph by double exposure. This system of analysis is particularly convenient for the collection of data leading to the calculation of solid state diffusion rates. It has also proven useful in the determination of trace elements in uranium alloys. The technique used for trace analysis is similar to that described above for the Ti alloy-Fe system. High-purity uranium metal is used for the measurement of background intensity. Data for up to 400 individual quantitative analyses may be collected and statistically eraluated by simple computer techniques. Those channels that contain intensity measurements which are not, within preset limits. representative of the population as a whole may be eliminated. The precision of the remaining analytical points is then compared to theoretical precision as determined by
esin Spot Test for SIR: Diphenylamine is an important analytical reagent which is used in many oxidation-reduction titrations (3) and in the determination of vanadium(V) (it?, 13). It is of considerable importance in organic technology (3). A number of tests have therefore been proposed for its detection ( 1 , 2 , 5 , 6 , 7 , 11, 14. 19). Feigl’s test with fused thiocyanate (6) is too general, and similar results are obtained with almost all aliphatic and aromatic primary, secondary, and tertiary amines. It is also necessary for the success of the test that the thiocyanate should be free from moisture and no water-producing conipound should be present. Another test for diphenylamine depends upon the blue color 1%-hichit produces with sulfuric acid and an alkali nitrate (8). This color is produced by numerous other substances in addition to diphenylamine. Probably the best test developed is the oxalic acid fusion test of Feigl. (7‘) in which a blue color is obtained by heating the test substance with hy1
@
ANALYTICAL CHEMISTRY
drated oxalic acid. This reaction fails to distinguish between diphenylamine and carbazole derivatives. A sensitive and selective test for diphenylamine is described in this communication. It is based on the resin bead adsorption of the colored Schiff’s base formed by the reaction of diphenylamine with p-dimethylaminobenzaldehyde. p-Diniethylaminobenzaldehyde is a useful analytical reagent which gives an intense red color with pyrroles in cold hydrochloric acid medium (9, 18), having a free a-position [Ehrlich test ( 1 7 ) ] . With hydrazine and hydrazide it gives a yellow t o orange color (16). Primary aliphatic and aromatic amines are known to give yellow to orange Schiff’s bases with p-dimethylaminobenzaldehyde (4); this is not the case with secondary amines. It does, however, react with diphenylamine to produce a yellow color in hydrochloric acid media, which turns to green on heating. This is the basis of the test now proposed for diphenylamine.
counting statistics to test for phase homogeneity. If the data are judged to be satisfactory, the final result is calculated from the sum of the remaining values. There are many possibilities of programmed microprobe analysis through the use of the versatile multichannel analyzer. Quantitative concentration mapping similar bo that previously reported by Birks may be achieved. The crystal specbrometer of the Xallinckrodt microprobe has been driven in synchronization with the multichannel analyzer data address systems for a variety of purposes. With a little imagination and relatively simple circuitry many things will be accomplished with this type of system in the future. LITERATURE CITED
(1) Birks, L. S., Batt, A. P., ANAL. CHEX 35, 778 (1963). (2) Fergason, L. A,, “4Method for Trace Snal$is with an Electron hIicroprobe.” 14th Annual Conference of Applications of X-Ray Analysis, Denver Ke-
search Institute, Xetallurgy Division,
Denver, Colo., August 25-27, 1965. (3) Fergason, L. A, Neumann, F., Process Development Quarterly Progress Reporl, liSAEC Report MCW-1943 pp. 8-14, Kovember 1965. L. A. FCRGASON Monsanto Co. 800 N. Lindberg Blvd. St. Louis, %Io. 63166 THIS work performed under the auspices of the U. S. Atomic Energy Commission Contract N o . W-14-108-Eng-8 at hIallinckrodt Chemical Works, Uranium Division, Weldon Springs, 310.
iphenyla mine Resin beads have been used as reaction media for the detection of inorganic substances (10). Very few studies have been made using a resin spot test for the detection of organic compounds (16). The advantage in using resin beads as reaction media is not the increase in the sensitivity and selectivity of the color reaction, but it is the help in elucidation of the mechanism by indicating the charge type of the complex. EXPERIMENTAL
Reagents. A 1% solution of p dimethylaminobenzaldehyde(E. Merck, Darmstadt) was prepared in 50% ethanol. Dowex 50 W-X8 (20-50 mesh) was used in the Hf form. Diphenylamine (E. Merck, Guaranteed Reagent quality) was used as such. Procedure. A few milligrams of the test substance in alcohol and a few resin beads are added t o a micro test tube. One or two drops of p-dimethylaminobenzaldehyde solution are added. The contents are heated for 2 minutes. When diphenylamine is pres-
ent a deep yellow color appears on the resin beads at room temperature; this turns to green or bluish-green on heating. The green color on the resin beads persists if the diphenylamine concentration is high, but it may vanish on cooling if the concentration is low. Even a t low concentration, however, the color reappears on the resin beads upon heating. RESULTS
The following compounds gave no color on heating with p-dimethylaminobenzaldehyde and resin beads in the H+ form. Common aliphatic and aromatic hydrocarbons and their derivatives. Common alcohols, acids, ketones, aldehydes, ethers, nitriles, and carbohydrates. Heterocyclic bases : Pyridine and piperidine. Amides: Acetamide, benzamide, nbutyramide, formamide, nicotinamide, oxamide, and propionamide. Amines: Methyl, diethyl, and triethylamine, mono-, di-, and triethanolamine, niethylaniline, and diethylaniline. The following compounds gave characteristic colors (indicated in parentheses) when they were heated with p-dimethylaminobenzaldehyde in the presence of resin beads in the H+ form. Anilides : Acetanilide (Y) , p-bromoacetanilide (Y), carbanilide (Y), phenylurea (Y), and p - aminoacetanilide (D.Y,). Aromatic amines: Aniline (Y), oand m-nitroaniline (Y) , p-nitroaniline (R), o-chloroaniline ( Y ) , 0- and p-toluidine (Y), 1- and 2-naphthylamine (R), benzidine (R), o-phenylenediamine (D. R.), 1- and 2-aminoanthraquinone (R), and aminoacetanilide (Y). Pyrrole bases: Indole (R.V.) and tryptophan (R.V.) . Hydrazides: Hydrazine (D.Y.) and semicarbazide (No change). Derivatives of Diphenylamine: Diphenylcarbazone (Y) , diphenylcarbaBide (L.B.R.), diphenylmethane (No change), diphenylthiocarbazide (No change), diphenylthiourea (Y), diphenylurea (D.Y.), Carbazole (No change), tropaeolin 00 (P), barium diphenylamine-4-sulfonate (No change), W,N'-diphenylbenzidine (LG), and N phenylanthranilic acid (G) . Y = yellow RV = red violet DY = deep LBR = light brick yellow red R = red P = pink DR = deep red LG = light green G = green
Limit of Identification. From an alcoholic solution of diphenylamine, the limit of identification was found t o be 0.25 pg. in a limiting dilution of 1:2 x 104.
Table I.
Detection of Diphenylamine in Presence of Foreign Substances
Amount added,
Foreign substances Acetic acid Acetaldehyde
fig.
200 150 400 400 50 16 100 500 100 200 20
Acetone
Anisole Aniline Acetanilide Benzene Methanol Methyl acetate Methylamine 0-Nitroaniline 1-Naphthylamine Phenol Pyridine Sucrose p-Toluidine L = Light; BG
Diphenylamine detected, pg. 0.75 0.25 0.75 0.75 2 2 1 0.25 0.75 0.75 5 10 0.50 0.75 0.75 10
10
200 200 500 15 =
Color of resin phase" BG LBG LEG LBG BG BG BG LBG LBG BG BG BG LBG LBG LBG BG
Limiting proportion 1 : 2 x 104 1:2 x 104 i : x~104 1:2 x 104 1:2 x 104 1 : 2 x 104 1:2 x 104 1 : 2 x 104 1 : 2 x 104 1:2 x 104 i : i x 103 i : i x 103 1 : x~ 104 1:2 x 104 1:2 x 104 1 : l x 10s
Bluish Green.
Detection of Diphenylamine in Presence of Foreign Substances. The minimum amount of diphenylamine was detected in the presence of a number of foreign substances. The results are summarized in Table I. DISCUSSION
Inasmuch as the color is adsorbed on the resin beads, it is probably a positively-charged compound which results from the condensation of C6Hs-?JH2+C a s with p-dimethylaminobenzaldehyde. This assumption is confirmed by the fact that a neutral solution of diphenylamine and p-dimethylaminobenzaldehyde do not react to give either a yellow or a green product. However, if hydrochloric acid is added, a yellow color is obtained which, on heating, turns green or bluish-green. The following mechanism may therefore be tentatively postulated.
(c,H,),NH
+ RH+-
the presence of HCl, but they gave green color on the resin beads). Therefore, it is safe to assunie that the pyrrole bases will not decrease the selectivity of the test. The hydrazides of carboxylic acids also give a yellow to orange color with p-diniethylaminobenzaldehyde. The hydrazides are first saponified to hydrazine, and hydrmine then reacts with p-dimethylaminobenzaldehyde t o give a yellow to orange color. Therefore, hydrazides of carboxylic acidother than semicarbazide, which could not be tested owing to nonavailabilityare not likely to affect the selectivity of the test. The resin spot test method is very useful in distinguishing between aliphatic and aromatic amines. The aliphatic amines give a very light yellow color with p-dimethylaminobenzaldehyde which is not detected by the resin spot test method because the resin has also a slight yellow color. However, the
WC,H,),N+H,
W
Yellow (cold)
f Bluish green (hot)
The pyrrole bases give a violet color with p-dimethylaniinobenzaldehyde. This color is adsorbed on the resin beads which turn violet or reddish-violet. Because only a few pyrrole bases were available, the resin spot test could not be tried with all of them. However, in almost all cases where the resin spot test has been tried, the color on the beads is the same as in solution (surprisingly N,hT'-diphenylbenzidine and N-phenylanthranilic acid did not give any color with p-dimethylaminobenzaldehyde in
aromatic amines and the polyaliphatic amines give a deep yellow color and can be easily distinguished from the monoaliphatic amines. This difference in color is due to the fact that the first excited state of the compounds formed with aromatic amines is more resonancestabilized than that of the aliphatic monoamines. For similar reasons the test can be used to distinguish between amides and anilides. All efforts to elute the colored compound from the resin beads failed. It, VOL. 38, NO. 13, DECEMBER 1966
* 1957
therefore, appears to be a case of irreversible adsorption. A number of unknowns were also run in order to test the utility of the method, and it was found that the test is fast, reliable, and sensitive. This study also shows that an important remark is missing in the test for diphenylamine given in FeigYs handbook (8). After spotting the p-dimethylaminobenzaldehyde paper with an ethereal soIution of diphenylamine, exposure to acid vapors is necessary to yield the yellow color. ACKNOWLEDGMENT
The authors are grateful to A. R. Kidwai, Head of the Department of Chemistry, for research facilities and encouragement.
LITERATURE CITED
( I ) Bowen, H. J. AI., Art, E., Cawse, P. A., ,\-atwe 186, 383 (1960). (2) Broell, H., Fischer, G., Mikrochim. Acta 1962,249. ( 3 ) Comp. 0. Tomicek, Chemical Indicators, p. 171, London, 1951. ( 4 ) Chakravarti, S. X., Roy, hf. B., Analyst 62,603 (1937). ( 5 ) Feigl, F., Feigl, H. E., iUikrochim. Acta 1954,85. (6) Feigl, F., Goldstein, D., dnais 8ssoc. Brasil. Quim. 11, 143 (1952). (7) Feigl, F., Goldstein, D., ANAL. CHEM. 32, 861 (1960). (8) Feigl, F., “Spot Tests in Organic Analysis,” 6th ed., pp. 285, 278, Elsevier, Amsterdam, 1960. (9) Fischer, H., XIeyer-Betx, F., Z. Physiol. Chem. 75, (1911) 232. (10) Fujimoto, &I., Chemist-Analyst 49, 4 (1960). (11) Hearn, W. E., Kinghorn, R., Analyst, 8 5 , 766 (1960). (12) Hirano, S.,Murayama, H., Kitahara, M., Japan Analyst 5 , 7 (1956).
(13) XIeaurio, V. L., Ann. Chem. 23, 47 (1918). (14) XIeade, E. M., J . Chem. SOC.1939, 1808. (15) Pesex, &I., Petit, A, Bull. SOC.Chim., Francp 1947. 122. - ,~ (16) Qureihi, &I., Qureshi, S. Z., Anal. Chim. d c t a 34, 108 (1966). (17) Rodd, E. H., “Chemistrv of Carbon Compounds,” Yol. IVA, p. ‘39 Elsevier, Amsterdam, 1957. (18) Salkowskv. E.. Biochem. 2. 103. 185 (1920). “ ‘ ’ (19) Zagata; R., S’anags, G., Latvijas PSR Zinatnu A k a d . Vestis, Kim. Ser., 1961, 175.
~ I O H SQURESHI IN SAIDCL ZAFAR QURESHI
Chemical Laboratories Aligarh Muslim University Aligarh, India Thanks are due to the Government of India (PIISRCA),for financial assistance given to one of us (S.Z.Q.).
Estimation of Traces of Poly(Acry1ic Acid) and Other Poly(Carboxy1ic Acids) in Water and Salt Solutions by Complexing with Methylene Blue SIR: Our interest in the control of scale growth in evaporators led us to study the retardation of the growth of gypsum crystals by traces of poly(acrylic acid), an effect which was reported by AIcCartney and Alexander ( 2 ) . I n order to measure the amount of poly(acry1ic acid) adsorbed on gypsum seed crystals, it was necessary t o analyze water, or sea water, for less than 10 p.p.m. of poly(acry1ic acid). A method was developed which permits the detection of 2 pg. of poly(acry1ic acid), or partly esterified poly(acry1ic acid), in a 5-ml. sample of water, or a dilute saline solution. A modification of the method is required for solutions as concentrated as seawater. The method is based upon the formation of a complex (3, 4) between methylene blue and poly(acry1ic acid) ; the complex is separated from solution either by adsorption on borosilicate glass or by forming the complex in an adsorbed state on calcium carbonate. The amount of dye in the separated complex is then a measure of the amount of poly(acrylic acid). It is thought possible that other polyanions might be estimated by this method and that poly(acry1aniide) could be estimated after a hydrolysis step similar t o that used in the nephelometric method of Cruminett and Hummel (1).
pared by dilution of a l O - 3 M stock solution, Chroma-Gessellschaft highest purity dye-stuff was used, and easily adsorbed impurities were removed from the stock solution before dilution by pouring it through a borosilicate glass absorption column of the type described below. Adsorbents used were powdered borosilicate glass of size -60 +140 B.S.S.,or analytical grade calcium carbonate. Method for Water or Dilute Saline Solution. 1. Mix 5 ml. of methylene blue solution and 5 inl. of unknown sample and adjust the p H of the mixture to 6 with either dilute sulfuric acid or sodium hydroxide. 2. Allow the mixture to stand for 15 minutes. 3. Adsorb the resulting dye-polyanion complex on a column of 1 gram of powdered glass by drawing the mixture through under light suction over a period of about 30 seconds. The adsorbent is supported by a glass sinter of porosity 1 in a 12 mm. bore tube. 4. Wash the column with 10 ml. of distilled water and discard the washings. Elute the complex with 5 ml. of 2N HCI. 5 . Measure the absorbance of the complex against that of a blank determination a t either 740 or 668 mp. 6. Clean the adsorption column with 5N HC1 and repeated distilled water washings, and drain thoroughly under the same vacuum conditions as used in steps 3 and 4. 7. Compare with results obtained from standard polganion solutions having an ionic composition similar to that of the sample.
EXPERIMENTAL
In our work it was convenient to set aside some of the starting solutions, free froni polyanions, to prepare the blank and calibration solutions. The ab-
Reagents. The reagents employed were: methylene blue l O - 4 X (32 p.p.m.) aqueous solution freshly pre1958
e
ANALYTICAL CHEMISTRY
sorbance us. concentration plots were linear. The absorptivity of the eluted coniplexes was typically 400 a t 740 mp and 280 a t 668 inp. The ratio of dye to polyanion in the complexes was not determined so these absorptivities were calculated from the concentration of polyanion (in grams per liter), assuming that all the polyanion in the sample appeared in the solution of the eluted complex. The method has been found satisfactory for estimating poly(acry1ic acid) and copolymers of 70y0 acrylic with 30% iso-propyl acrylate having molecular weights over the range 10,000 to 100,000. Determinations on 5-ml. samples of solutions containing up to 3000 p.p.m. CaS04 and from 1 to 8 p.p.ni. of polyanion showed a mean error of 0.2 pap.m. However, theniethod fails with sea waters and brines because dye-polyanion complex formation is hindered by the presence of high concentrations of other ions. Borosilicate glass is specified because it was found to be a much better adsorbent than soda glass. The specified time of 15 minutes for complex formation mas adequate. High rates of flow of the solutions through the adsorption colunin influence the amount of complex which is adsorbed, so that the blank and sample adsorptions must be performed slowly under the same suction conditions. Eluted complex solutions are stable over a few days. Bbsorbance readings were obtained using 1-cm. standard silica cells which were cleaned with 5N hydrochloric
