V O L U M E 23, NO. 1 2 , D E C E M B E R 1 9 5 1 are needed. The sodium sulfate may conveniently be added from a spatula through a funnel which has a stem just long enough to prevent any sodium sulfate from sticking to the ground-glass mouth of the bottle. The 5-ml. aliquot of benzene may be removed by connecting the pipet to an aspirator or other form of automatic pipetter. A new standardization curve must be prepared for the modified method, as the results arc consistently about 10% higher than those from the regular procedure. This may be either because of reduction in loss due t o the use of a better solvent for nitrated DDT, the elimination of several steps, and the taking of an aliquot at the end, or a gain in concentration due to evaporation of the henzene. The latter would be expected to be considerably 1e.s than 10%. A larger initial aliquot of the strip solution must be used for the method as outlined, because of the final aliquoting procedure. Where the quantity of D D T is very low, greater sensitivity can be obtained by pipetting or filtering off the maximum possible quantity of benzene after the sodium sulfate treatment, measuring it, and concentrating t o 5 ml. before color development. It is usually possible to recover at least 13/ls of the sample in this way. For the slightly greater sensitivity obtainable by the UPC
1871
of all the nitrated DDT, a method such as the original Schechter technique would he necessary. COMPARISON OF RESULTS
In Table I are shown the comparative estimations of D D T rcsidues on field-treated apple leaves. Five aliquots from each sample were run by each method. The results agree well within the expected error, and the reproducibility wm essentially the same. I t was concluded that neither the accuracy nor the precision of the Schechter mpthod was reduced by the modifirntions desrribed. LITERATURE CITED
(1) Avens, A. W.,
private communication.
(2) Clifford, P. A., J . Assoc. Ofic.Agr. C h a i s h , 29, 195 (1946). (3) Davidom, B., Ibid., 33, 130 (1950). (4)
Xorton, L. B., and Schmalzriedt, B.,
.&x.~L.
CHSM.,22, 1451
(1950).
(5) Schechter, AI. S., Pogorelskin, Lf. .4., and Haller, H. L., Ibid., 19, 61 (1947). (6) Schechter, 11.S., Soloway, S.B., Hayes, R. A., and Haller, H. L., IND.ENG.CHEY.,;ZNAI.. ED.,17, 704 (1946). RECEIVED January 2 5 , 1951.
Spectrophotometric Characteristics of Determination of Titanium with Thymol JOHK \'. GHIEL'
AND
REX J. ROBIKSON, University of Washington, Seattle, Wash.
HYMOL was first reported as a colorimetric indicator for Ttitanium by Hall and Smith (6) in 1905. Lenher and Crawford (7) in 1913 selected thymol from several phenolic compounds as the most suitable reagent; they found it to be a t least t\ventj~five times as sensitive as hydrogen peroxide for the determination
- 0 2
500 600 WAVE LENGTH IN MILLIMICRONS
Figure 1. Absorption for Titanium-
Thymol Complex
purified potassium titanium oxalate, LiaTioi(rr04)2.21120,was recrystallized twice from distilled water. Then 3.ti8 grams of the air-dried salt were digested for 10 minutes with 100 ml. of concentrated sulfuric acid containing 8 grams of ammoniwn sulfate. The resulting solution was diluted to 1 liter with concentrated sulfuric acid and standardized gravimetrically. Two methods of analysis were used with cupferron (1, 1 4 ) and ammonium hydroxide (6) as precipitants. In either case the precipibte was ignited to and weighed as titanium dioxide. By analysis the titanium standard solution \vas found to contain 0.45 mg. of titanium per ml. of solution. From this stock solution a working standard solution, containing 0.0045 mg. of titanium per ml., was prepared by dilution with concentrated sulfuric acid. These solutions were stored in glass bottles which had been well aged with sulfuric acid. KO change in titanium concentration was noted during 2 years. Thymol Reagent. A 1% (by weight) solution of thymol was made by rapidly stirring into ice-cold concentrated sulfuric acid molten thymol slowly added from a medicine dropper. The resulting solution had a very pale straw color which deepened with time but was usable for about a week. If the thymol was dissolved in glacial acetic acid before the addition of sulfuric acid, as is sometimes recommended, t'he resulting solution had considerable color and darkened rapidly. Other solvents of thymol such as acetone, ethyl alcohol, etc., behaved similarly. Lenher and Crawford (7) had previously reported that. thymol reagent decomposed when exposed to light. However, it has been the experience of the authors that the color developed even when the reagent was kept in total darkness. The sulfuric acid was found to produce no c,olor with the reagent, with the exception of one lot, which was thought to contain nitrate as impurity. Fuming the impure sulfuric acid for about an hour removed the color-forming impurity. Eichler ( 3 )had reported that nit.rate and nitrite give a color with thymol. It was possible to get the same interference color when nitrate was added to the sulfuric acid. EQUIPMENT
of titanium. Although the thymol reagent has been used by a number of investigators (2,8, 10, 11, IS) for the determination of titanium, the spectrophotometric characteristics of the method have not as yet been reported. The results of such an investigation are presented in this paper.
All color measurements were made with a Beckman DU spectrophotometer. Corex cells of 1-cm. light path were used for measurements a t 400 mp or above and silica cells for wave lengths below 400 mp.
SOLUTIONS AND REAGENTS
Absorption Spectra of Thymol-Titanium Compound. Typical absorption spectra for the thymol-titanium compound are shown in Figure 1. Curve I indicates the absorption for B solution containing 5.0 mg. of titanium per liter and curve I1 for a solution
EXPERIMENTAL RESULTS
Standard Titanium Solutions. A standard titanium solution was prepared essentially as specified by Sandell (9). J. T. Baker's 1
Present addreas, Centralia Junior College, Centralia, Wash.
1872
ANALYTICAL CHEMISTRY
containing 2.0 nig ot titaniuin per liter For color development 0.25 ml. of thymol reagent \!as added to each 8 ml. of solution The solvent, with the wnir reagent concentration, mas used as a reference solution in the bpectrophotometric meaqurenient The absoiption qpectruni was investigated from 300 to 1000 nip Figure 1 shows that the maximum absorption ocwrred at 440 mp. Above 650 nip there \in& no bignificxnt absorption and below 350 mp there n as fluorescence
>
C 200v)
z
w
J
2
4
MOLAR RATIO
Figure 3.
6
THYMOL,^,
Effect of Heagent Concentration on Color Development 6 mg. Ti per liter Wave length 4-M
MICROGRAMS
Figure 2.
OF
Ti
PER
ML H 2 S 0 4
Calibration Curve for Titanium
Effect of Time upon Color Development. When observed visually the color intensity of the thymol-titanium compound never reached constancy but continued t o increase with time. This was apparently due to slow decomposition of the thymol reagent. Khen measured spectrophotometrically a t 440 mp the color reached its maximum intensity in 10 minutes and remained (sonstant for at least 2 hours. These observations were made on solutions containing 5 mg. of titanium per liter and the reagent concentration mentioned previously, which gave about a 35fold excess of reagent. With smaller reagent concentrations a longer time was needed for maximum color development-for example, when 0.0005 M solutions of thymol and titanium were mixed in equal volumes, continued increase in the color intenqity was noted even after 2 hours. Effect of Temperature upon Color Development. Lenhei and Crawford ( 7 )reported that visually the color intensity diminished with an increase in temperature, but that upon cooling the original color intensity was obtained, providing the maximum temperature had not been above about 90' C. For the present investigation the optical density of a solution containing 5mg. of titanium per liter was taken a t several temperatures between 15' and 35" C. No significant variation in the optical density at 440 mp was noted. Calibration Curves. In Figure 2 is shown a calibration C U I V ~ where optical density has been plotted against concentration. From this curve it is seen that Beer's law is valid for this determination, Previously Lenher and Crawford ( 7 ) had arrived a t the same conclusion as a result of their investigation of the method by the visual procedure. Effect of Thymol-Titanium Ratio upon Color Formation. Spectrophotometric measurements were made t o determine the effect of the reagent concentration upon the color intensity. A serieE of determinations was made with constant titanium concentration and increasing concentration of thymol. The results are shown in Figure 3. S o sharp break or leveling off to constant
mp
optical density occurred for ratios up to 6 to 1. This indic.;itc,s that the colored compound is appreciably dissociated in solution and that a large excess of reagent is required t o cause thr l e action to go to completion. Furthermore, nothing can be detrrniined from this curve regarding the compogition of the complrs because of the appreciable dissociation. The method of continuous variation as used by Voslxirgh ( 1 2 ) was then tried to get evidence regarding the composition of the color complex. Solutions of varying thymol-titanium proportions were prepared from 0.0005 M solutions of thymol and titanium. The optical densities were measured a t various ~ i n v e lengths and the results for three wave lengths in the region of maximum absorption are shon n in Figure 4. A color compound formed by the reaction of one thymol with one titanium is indicated by the fact that the maximum absorption occurred at a composition value of 0.5. The fact that the peak absorption occurred a t 0.5 for each wave length is evidence that onl) one color compound is formed. The breadth of the maximum ahsorption indicates considerable dissociation of the color complex. This confirms the desirability of having a large excess of reapc~iit present during color formation
I
I
I
0 2
04
06
J
I
oa
X Figure 4. Conlposition of Color Compound b) Method of Continuous Variation , X.
\olume of 0.0005 M thymol reagent added to (1 volume of 0.0005 M titanium solution
- X)
Y . Optical density due to wlor compound Wave lcngtha, 400 mp, 440 m G , 480 llllr
Effect of Foreign Substances. During the progress of this research it was determined that sodium silicate, ferric chloride, aluminum ion, and magnesium ion do not form colored complexes with thymol. It has been reported by Lenher and Crawford i 7 ) that phosphates and tin compounds are also without effect Substances that produce an interfering color are: hydrogen
1873
V O L U M E 23, NO. 12, D E C E M B E R 1951 peroxide, antimonl pentachloride ( I ) , and tungsten and vanadium compounds (7). Lenher and Crawford (7) stated that fluorides bleach the color when present in any amount, while water may be present up t o 20% without causing a fading of the color. LITERATURE CITED
‘1)
(2) (3) (4) (5) 6)
Bellucci, I., and Grassi, L.. dtfi. uccad. Lincei, 22 I, 30 (1913) Das Gupta, J . Indian Cheni. Soc.. 6 , 855 (1929). Eichler, H., 2. anal Chtm., 96, 17 (1934). Ekkert, L., Pharm. Ze?LtraZhnZZe, 75, 49 (1934). Hall, J., and Smith. ,J., Proc. A m . Phil. Soc., 44, 196 (1905). Kolthoff, I. M., and Sandell, E. B., “Textbook of Quantitative Inorganic Analyeis ” p. 70-1, S e w York, Macmillan (“I).. 1943.
(7) Lenher, V,,and Crawford, JY. G.. d . Ana. Chem. SOC., 35, 138 (1913).
(8)Muller. H. J., Ibid., 33, 1506 (1911). (9) Sandell, E. B., “Colorimetric Determination of Traces of Jletals,” p. 423, New York, Interscience Publishers, 1944 (10) Schenk, M., Helv. Chem. Acta, 19, 625 (1936). ;11) Shemyakin, F. -M., and Newmolotova, A., J. Gen. Chem (U.S.S.R.), 5, 491 (1935). 112) Tosburgh, K. C., and Coopei, G. R.. .J. A m . Chem. Sue., 63, 4% (1941). (13) Yoe, J. H., and Armstrong, A. R., Science, 102, 207 (1945). ’14) Yoe. J. H., and Sarver, L. -4.,“Organic Analytical Reagents,” p. 146, New York, John \Tiley & Sons, 1941. RECEJVEDDecember 2R, 1950.
Spectrophotometric Determination of Phosphorus In Limestone, Lime, Calciir m Hydroxide, Calcium Carbide, a n d Acetylene E. L. K 4CICOT, Shawinigan Chemicals, Limited, Shawinigan Falls, Que., Canada
HOSPHORUS, one of the c,hief impurities in calcium carbide, Prnust be determined with an accuracy difficult to obtain by the uwal gravimetric or volumetric procedures, because its content iri the raw materials used and in the finished product must be very low to give acetylene gas a i t h less than 0.05% phosphine by volume. Therefore, as a possihle solution, development of a photometric method o f analysip n as considered, m-hich will give both celeritv and accuracy, even R hen applied directly on calcium cnrbide. The literature reveal* t \+( I 1):i-k colorimetric procedures for phosphorus: the molybdenum blue method, applied to steel analysis by Hague and Bright (@, whereby the phosphorus is converted to the phosphoniolytdate, which in turn is reduced to the blue complex; and the niolybdivanadophosphate method where this yellow complex is ohtained by the action of ammonium vauadate and ammonium molybdate on the phosphorus. Preliminary tests showed that the conditions required for producing the yellow complex from the compounds under ronsideration are less critical than those for the blue complex, and that the former is more stable. These results are in agreement uith the findings of Kitson and XIellon (3). Therefore, the molybdivanadophosphate method &-as coIisitlrivtl the most suitable and reseurch was based on the w r h done by Brabaon, Karchnier, and K r t z (I), who adapted thic method to the determination of phosptiorus in limestone. The procedure conmtc essentially in oxidizing the phosphorus fuming with perchloric. acid, \vhich also serves to dehydrate the silic-athat must he filtered nut t)efore the yellon- molbydivanadophosphate is developed The color intensity is then measured on the spectrophotometer and the corresponding amount of phosplioius is read directly o n :L standard curve obtained b r similarly tic,veloping and measuring the color from various rnncentratinne of a solution of knomn phosphorus content. Spectral transmittance curves done with a Coleman \Iode1 11 L-iiioersal spectrophotometer o n ferric perchlorate and molyhdivanadophosphate solutions sho\red that at a nave length of 430 nip the effect on transmittance n a q a minimum for iron and a nia\imum for phosphorus. Rr&on, Karchmer, and Kata (1) recommended a 425 nip Illue filter, using a Fisher electrophotometer. Full color developriieiit o f the > ellow phosphorus coniple\ tooh approximately 20 minuter, :rftrr N hich the color remained Gtahle for at least 18hour. iddition of nitric acid ant1 50 inl. o f sodium hypochlorite (1 to 2% available chlorine) prior t o fuming with perchloric acid had no effect on the final color. Peichloric acid addition could he increased or decreased by as much as 25% of the recommended amount mithout affecting the final reaults.
I spectrophotometer or a filter photometer i s required. REAGEVTS
Ammonium Vanadate Solution. Dissolve 2.35 grams of ammonium metavanadate in approximately 400 ml. of hot water: add 17 ml. of 607, perchloric acid, cool, and dilute to 1 liter. Ammonium Molybdate Solution. Dissolve 100 grams of molybdic acid (85@;\ in a mixture of 300 ml. of water and 80 nil. of ammonium hydroxide. When dissolved, filter and boil filtrate 20 minutes; cool and dilute to 1 liter. Standard Phosphorus Solution. Determine, gravimetrically or volumetrically, the phosphorus content of a sample of anhydrous diammonium phosphate and weigh out an amount equivalent to 0. lOOOgram of phosphorus( theoretical amount of pure diammonium phosphate = 0.4263 gram). Dissolve in water and dilute to 1 liter; 1 ml. of this solution will he equivalent to 0.1 mg. of phosphorus. Sodium Hypochlorite Solution. Pass chlorine gas into a cold solution of 15mc sodium hydroxide and dilute so that the final solution contains not less than 1% and not more than 2% available chlorine when titrated with 0.1 N sodium arsenite. Saturate the portion needed with sodium bicarbonate (in excess) immediately before use. Perchloric acid, SO%, specific gravity 1.54. Concentrated nitric acid, specific gravity 1.42. RECOMMENDED PROCEDURES
For Standard Curve. Transfer five aliquots of the standard phosphorus solution, containing 0.1 to 0.5 mg. of phosphorus to 400-ml. beakers. *idd 20 ml. of 607, perchloric acid, boil to perchloric fumes, and fume gently for 5 minutes. Cool to below 100” C., add 10 nil. of ammonium vanadate solution, and stir. Let cool to room temperature and then transfer to 100-ml. volumetric flasks. h d d 7.5 ml. of ammonium molybdate solution, swirling the contents of the flasks to prevent precipitation. Dilute to the mark n-ith distilled water, mix thoroughly, and let stand 25 iiiinuteq foi full color development. Measure per cent transmittance on the Coleman ?*lode111 spectrophotometer balanced at 430 mp nave length, uiing distilled water as reference. Plot per cent ti ansmittance againqt concentration on semilog paper Thiq is a htraight line. Run a hlanh on all reagentq oii wch r i ~ vlot of reagents and make the propel caorrection. For Limestone. Transfer 0.5 to 2 grams of stone, depending on the phosphorus content, to a -100-ml. beaker. (If much organic matter is present, ignite the sample for 30 minutes at 900’ C.) Diesolve in 20 nil. of water and 20 ml. of 60% perchloric acid Boil to perchloiic fuineq, rover with a watch glass, arid fume slowly for 5 minutes. Cool to helo\\ 100” C., add 10 nil. of animoniuni vanadate solution, stir, and cool to I ooni temperature. Filter through a Whatman 41 H paper into a 100-nil. volumetric flask, washing out the beaker ell Wash paper and residue three times with &nil. portions of water. Be c:ireful that the final filtrate does not evceed 90 nil. *4dd i . 5 nil. of ammonium molybdate solution to this filtrate, snirling the contents of the flask to prevent precipitation. Dilute to the mark vith distilled water, mix thoroughly, and let stand for 25 minutes for full color development. Measure per cent
