1412
ANALYTICAL CHEMISTRY
One milliliter of 1% reagent was found adequate for 1 mg. of nickel. The color, which develops almost immediately, is stable for about 5 hours. The system followed Beer’s law from 0.5 to 10 p.p.m. a t 330 mp, and from 5 to 40 p.p.m. a t 410 mp.
overcome by precipitating the iron with cupferron and extracting the complex with chloroform, as suggested by Butts, Gahler, and Mellon (1). In this way as much as 500 p.p.m. of iron can be removed, negligible amounts of nickel being lost in the extraction.
DIVERSE IONS
RECOMMENDED PROCEDURE
The interfering diverse ions studied are listed in Table I, together with data on the extent of interference.
Procure a representative portion of the material to be analyzed and subject it to any necessary preparative treatment to obtain a solution free of ions which interfere with the color reaction. Measure a quantity to contain not more than 0.5 mg. of nickel in 50 ml. and transfer the solution to a 100-ml. volumetric flask. Add 10 ml. of a 1% solution of 8-mercaptopropionic acid, dilute to about 90 ml., and adjust the pH to 9.1 5 0.5. Dilute to volume, mix, and measure the absorbance a t 330 or 410 mp. Water may be used as a blank.
The general procedure was t o place 10 ml. of a nickel solution, containing 0.1 mg. of nickel per milliliter, in a 100-ml. volumetric flask and to add about 50 ml. of Fater. To this were added 50 mg. of the diverse ion to be tested, 10 ml. of a 1% solution of 8-mercaptopropionic acid, and nearly enough water to reach the graduation mark. The p H was adjusted to 9.1 =k 0.5, and the solution diluted to volume and mixed. The absorbance was then measured. If a change of absorbance of more than 2% (relative) was found, the procedure was repeated, with the concentration of the ion in question reduced by one half its previous amount. This process was continued until the ion caused no more than 2% relative error. In this work a blank was used containing an equivalent amount of the diverse ion. Of the ions investigated, the following do not interfere in a concentration of 500 p.p.m. : acetate, ammonium, barium, calcium, chloride, cyanide, fluoride, magnesium, nitrate, nitrite, orthophosphate, potassium, sodium, and tartrate. Among the interfering ions, copper, iron, lead, and manganese form precipitates of hydrous osides when the pH is adjusted to 9. By keeping the copper concentration below 100 p.p.m., and that of lead and manganese below 50 p.p.m., such interference is avoided. Interferencewise, this method compares favorably with the dimethylglyoxime method ( 3 ) . As little as 3 p.p.m. of iron precipitated. This difficulty \vas
CONCLUSIONS
This method for the determination of nickel has the following merits: wide concentration range, ease of operation, ease of preparation and stability of the reagent, stability of the colored system, few serious interferences, and two maxima available for reading on the spectrophotometric curve. LITERATURE CITED
(1) Butts, P. G . , Gahler, A. R., and hIellon, 31. G., Sewage and Industrial Wastes, 22, 1543 (1950). (2) Furman, N. H., “Scott’s Standard Methods of Chemical .Inalyais,” New York, D. Van Kostrand Co., 1939. (3) Mitchell, A. M., and Mellon, AI. G.. ISD. ENQ.CHEM.,ANAL. ED.,17, 380 (1945). (4) Swank, H. W., and Mellon, 31. G., Ibid., 10, 7 (1938). (5) Uhlig, L. J., and Freiser, H., . ~ N A L . CHEM.,23, 1014 (1951). RECEIVED for review December 4, 1962. Accepted May 21, 1953.
Spectrophotometric Determination of Phthalic Acid in Phthalic Anhydride 3IARY &I. AGARWAL AND FR43IK SPAGNOLO Research Laboratory, National Lead Co., Brooklyn, X . Y. spectrophotometric method developed by Shreve and THeether ( I ) for the determination of total phthalic anhydride HE
in alkyd resins and other phthalic esters has been applied after modification to the determination of the phthalic acid present in commercial samples of phthalic anhydride. Because phthalic anhydride is soluble in chloroform and phthalic acid is insoluble ( 3 ) ,separation of the two can be accomplished, and the phthalic acid then determined by its absorbance a t 276 mp. Since this investigation was completed, Siggia and Floramo ( 2 ) have published a method for titrating free phthalic acid in phthalic anhydride using a tertiary amine as the base The impurities which might be present in commercial grades of phthalic anhydride are phthalic acid, maleic anhydride, and benzoic acid. Because benzoic acid and maleic anhydride are soluble in chloroform, they will not interfere with the phthalic acid measurement. If determination of the phthalic anhydride content is desired, the absorption of the chloroform solution can be measured a t 291 mp and/or 300 mp. The presence of benzoic acid and maleic anhydride in the chloroform solution will not interfere with the determination, since their absorption a t these wave lengths is insignificant. However, the results obtained on synthetic mixtures indicate poor precision ( f 0 . 5 % ) in deterniming phthalic anhydride; therefore determination of the anhvdride by this method is not recommended where high accuracy is desired. Some thought was given to determining the phthalic acid gravimetrically. However, erratic results were obtained by weighing because the quantity of phthalic acid is so low (in the order of 1 to 5 mg,) and foreign matter may also be present. Therefore, the following spectrophotometric procedure \vas used.
MATERI4LS AND 4PP4RATUS
Spectrophotometer. Beckman Xodel DU quartz ulti aviolet spectrophotometer or other spectrophotometer covering the ultraviolet region; matched tused silica absorption cells, with 1.0-cm. light path. Calibration Standard. Baker’+ C . P . potassium acid phthalate. Synthetic Mixtures. Phthalic anhydride and acid are purified by recrystallization; benzoic acid and maleic anhydride are used without purification. .$PPI opriate mixtures of these acids are then used for analysis. ANALYTICAL PROCEDURE
Calibration. Determine the absorptivity a t 276 mp of potassium acid phthalate in 0.1 N hydrochloric acid over a range of 0.035 to 0.126 gram per liter using 0.1 A’ hydrochloric acid in the blank cell. If determination of the phthalic anhydride is planned, determine the absorptivity of purified phthalic anhydride in C.P. chloroform a t 291 and 300 mp, over a range of 0.025 to 0.055 gram per liter using C.P. chloroform in the blank cell. Either one or both of these wave lengths may then be uqed for the determination. Sample Analysis. Weigh 1 gram of the phthalic anhydride sample into a medium porosity fritted-glass crucible (30-ml. capacity), add 20 ml. of C.P. chloroform, stir to dissolve, filter R-ith suction, and repeat the addition of 20-ml. portions of chloroform three times. Remove the crucible and wash the loner rim with chloroform, adding the Tvashings to the filtrate If phthalic anhydride is to be determined, transfer the combined filtrate to a 250-ml. volumetric flask, dilute to the mark, and after making proper dilutions, measure the absorbance at 291 mp and/or 300 mp, against a blank of C.P. chloroform. To the suction-dried crucible containing the phthalic acid, add 10 ml. of boiling 0.1 AT aqueous sodium hydroxide and stir to dissolve. Filter and repeat the addition of 10-ml. portions of sodium hydroxide twice. Neutralize the combined sodium hydroxide
V O L U M E 2 5 , NO. 9, S E P T E M B E R 1 9 5 3
1413 _____
Table I. .\rialq-sis of Synthetic 7)Zixtures of Phthalic .4cid and Phthalic .4nhydride Synthetic Mixture Anhydride Acid
Error, % _ _ _ -4nhydride Acid
Found Anhydride Acid
~
.
extracts to pH 2 with approximately 3 N hydrochloric acid, transfer to a 100-ml. volumetric flask, and dilute to the mark with 0.1 N hydrochloric acid. Make appropriate dilutions of the solution with 0.1 iV hydrochloric acid and measure the absorbance a t 276 mp in 1.0-cm. cells against a blank of 0.1 N hydrochloric acid. For maximum accuracy, the absorbance should fall in the vicinity of 0.4 absorbance units. Calculations. Calculate the concentration of phthalic acid in grams per liter, C p , of the final diluted solution by the following equation : cp = A / u , where A is the measured absorbance and up is the absorptivity value found for pure phthalic acid in the calibration. Calculate the percentage of phthalic acid in the original sample from the following equation: C p X aliquot factor X 100 acid, % weight of
Table 11. Determination of Phthalic Acid i n Commercial Phthalic 4nhydride _
Acid, %
Sample Source A Lot 1 Lot 2 Lot 3 Source B Source C Source D Lot 1 Lot 2
0 20 0.17 0 16
Average.
0 26 0 24 0.12
0.23 0.21 0.14
0.17 0.13 0.21
0.18
0 . 9 5 0.86 0.33 0.27
0.91 0.30
0.18
cc
0.l i
Calculation of phthalic. aiihydride ma)- be made by the same formulas, substituting the valurs found for phthalic anhydride. Results obtained from analyses of both synthetic and commercial samples (Tables I and 11) show that the standard deviation of a single determination, as calculated from differences between duplicate determinations, was 0.045%. LITERATURE CITED
(1) Shreve, 0. D., a n d Heet,her, AI. R., . ~ N A L .CHEM.,23, 441 (1951). ( 2 ) Siggia, S., a n d F l o r a m o , PI'. A . Ibid., 25,797 (1953). (3) Vogel, -4. I., "Practical Oryanir Chemistry," p. 491, Ken- York, Longmans. Green :nid Co.. 194R. R E c R i w n March 20, 19.53.
Arrepted .June A. 1953.
Preparation of Water Samples for Deuterium Analysis in the Mass Spectrometer FRANCIS P. CHINARD AND THEODORE ENNS Departments of Medicine and of Physiological Chemistry, The Johns Hopkins I riirersif>.School of Medicine, Baltimore. Md. of the distribution oi heavy water in animal organI isms, . the limiting factor in the number of deuterium analyses N STUDIES
is the reduction of the separate, water samples rather than the actual measurements in the mass spectrometer. Use of conventional zinc reduction trains (2) with transfer of the gas into a sample tube by means of a Toeppler pump is tedious and time-consuming [Other procedures involving reaction of water with methyl magnesium iodide (4)or n i t h dirthyl zinc. ( 1 ) arc not suited to routine analysrq 1
+-5cm.-
Zn DUST
PYREX WOOL
fore thc thickened constriction is made. Approximately 2 grams of zinc dust are added to each tube. The tubes are then heated in a drying oven a t about 120" C. overnight and allowed to cool in a desiccator over calcium chloride. The pipets to be used for introducing the samples into t'he tubes are similarly treated. A jig, such as is shown in Figure 2, is advisable. The st,op cock is initially in position 11, and a sample tube is connect'ed to the vacuum system by means of vacuum tubing. (The end of t,he sample tube is made to touch the end of the stopcock side arm so that the exposed surface of rubber is kept to a minimum.) The cock is turned to position 111; the calcium chloride tube is thus connected t o the sample tube. The sample tube is then gently heated with a small flame in order to drive off residual water. The cock is then t'urned to position I. The sample tube is allowed to cool in place while the sample (approximately 0.01 ml.) is taken up in a pipet. The stopcock is now turned to position 11, and the sample tube is disconnected.
Figure 1. Sample Tuhe Because of the large volume and surface of the apparatus, considerable care is required to avoid contamination of the samples and to ensure complete reduction of the water (2). I n addition, improper packing of the zinc and the progressive oxidation of the zinc may result in incomplete reduction of the water samples. The surface and volume of the apparatus may be considerably reduced, and the tedious inconvenience of renewing the zinc may be eliminated by heating the water samples in the presence of zinc in individual sample tubes. The number of samples which can be processed a t one time is limited only by the size of the available muffle furnace. EXPERI\IE\T&L
The sample tubes are shown 111 Figure 1. The seal of the guard tube of the capillary end need not be perfect if the entire tube is introduced into the mass spectrometer system. The borosilicate glass wool is used to prevent gross contamination of the mass spectrometer with zinc dust; it should be inserted be-
TO PUMP
-
,"-&-
rubber
I
IS AMPLE c A
h
U
SOLID C 0 2
PYREX
I
WOOL CaC$
II
m
POSITION
Figure 2. Diagram of Jig The sample is introdured while the tube is a t a temperature between 45" and 50" C. The sample tube is now quickly reconnected to the rubber tubing and the cock is turned to position 111. The pressure in the sample tube is thus reduced and most of the atmospheric moisture removed. The sample is then frozen by the application of solid carbon dioxide to the outqide
