graphic methods has greatly facilitated our analytical work and it has provided a precise and sensitive method applicable to the anal) ber of samples. The mean and range of results obtained by this method are compared with values reported by other. for normal subjects in Table 11-. It will be seen that the mean values for magnesium. copper, and zinc are very qimilar to result. that have been obtained by other.. The normal range for magnesium, coppw. and zinc is smaller than that reported by Paixao and Yoe who employed an emiksion spectrographic method for the analysis of blood cells. The mean calcium concentration is much lower than the values reported preT. ioii4y. It would appear that previous workers have neglected to correct their results for the relatively high concentration of calcium in trapped plasma. ACKNOWLEDGMENT
We are grateful to G. AI. I3rown for his helpful advice and criticism and we are indebted to Eleanor Paulson and Miriam I3enson for their assistance.
LITERATURE CITED
(1) Albritton, E. C., Standard Talues in Blood, p. 119, USAF Tech. Report 6039, 19.51. (2) Carubelli, R., Smith, W. 0.)Hammernten, J. F., J . Lab. Cltn. N e d . 51, 964 (1958). (3) Chaplin, H., Mollison, P. L., Blood 7, 1227 (1952). (4) Feldman, C., Ellenburg, J. Y., ANAL. CHEM.30, 418 (1958). ( 5 ) Fisher, R. A., “The Design of Experiments,” p. 49. Oliver and Boyd, London, 1951. ( 6 ) Holt, J. M., Lux, IT.,T-alberg, L. S., Can J . Biochem. Physaol. 41, 2029 (1963). (7) Jarrell. It. .4., “Encyclopedia of Spectroscopy,” p. 138, Reinhold, Sew York, 1960. (8) Kagi, J. H. It. It., TTallee,B. I,., ASAI,. CHEW.30, 1951 (1958). CHEM. (9) Keitel, H. G., Brrman, H., Jones, H., MacLachlan, E.. MacLachlan. E., Blood 10, 370 (1955 1 1955jJ,. (10) Koch, H. J., Smith, E. R.,Shimp, N. F., Connor, J., J., Cancer 9, 499 49b (1956). (1956): (11) MacIntyre, I., Biochem. J . 67, 164 i 1 M-T \/. (12) Morris, J. M.,Pink, F. S..ASTM Special Technical Publications S o . 221, p. 39, Am. Soc. Testing ?*later., Philadelohia. 1957. (13) husbaum, R. E., Butt, E. hl., Gilmour, T. C., Dinio, S.L., Am. J . (“Zin. Pathol. 3 5 , 44 (1961). (14) Pagliassoti, J. P.,i l p p l . Spectry. 9,153 (195.5). \ -
5 ) Paixao, L. ?*I., Yoe, J. H., Clin.Chim. Acta 4, 507 (1959). 6 ) Rozsa, J. T., Zeeb, L. E., Petrol. Process. 8 , 1708 (1953). 7) Shields, G. S., Markowitx, H., Klas-
sen, W. H., Cartwright, G. E., Wintrobe, 11. ?VI.,J . Clzn. Incest. 4 0 , 2007
ilc)6l\ .. . (18) Smith, I. L., Yaeger, E., Kaufman, 3 ., Hovorka, F., Kinney, T. I)., A.M.A. Arch. of Pathol. 5 2 , 321 (1951). (I!)) Stitch, S. R., Biochem. J . 67, 97 j .
i19,i7)
(20) Talbot, T R , Ross, J. F , Lab Invest. 9, 174 (1060) 121) Thiers. R E , Methods Baochem .Inaly. 5 , 273 (1957). ( 2 2 ) Tipton, I. H., “PIIetal-Binding in Medicine,” p. 27, J. B. Lippincott Co., Philadelphia, 1960 (23) Yallee, B. I,., Gibson, J. G., J . Rzol. Cheni. 176, 435 (1948). (24) IVallach, S., Cahill, L. X., Rogan, F. H., Jones, H. L., J Lab. Clin. Jfed. 59, 195 (1962). ( 2 5 ) Wallacah, S.,Zemp, J. IT-.,Cavins, J. A , ,Jenkins, L. J., Bethea, M.,
Freshette, L., Haynes, L. L.. Tullis, J. L., Blood 2 0 , 344 11962). (26) Zink, T. H., Appl. Spectry. 1 3 , 94 (1959).
RECEIVEIIfor review October 7 , 1963. Accepted January 17, 1964. This nork was supported by a grant from the Medical Researrh Council of Canada.
Spectrophotometric Determination of Traces of Peroxides in Organic Solvents DlLlP K. BANERJEE and CLIFFORD C. BUDKE Research Division,
U. S.
Industrial Chemicals Co., Division of Nafional Distillers and Chemical Corp., Cincinnati, Ohio
b A sensitive spectrophotometric method for the determination of traces of organic peroxides in organic solvents is described. The sample is diluted with a mixture of acetic acid and chloroform and treated with potassium iodide after deaeration. The iodine liberated is measured spectrophotometrically a t 470 mp in 1 -cm. cells. Active oxygen in the range of 5 to 80 p.p.m. can be determined. By using 1.5-cm. cells and a wavelength of 410 mp for the absorbance measurements, the range of the method can be extended to cover 0 to 5 p.p.m. of active oxygen. Quantitative results have been obtained with 17 commercial peroxides of varying reactivity. N o reaction was obtained with di-ferf-butyl peroxide and dicumyl peroxide. The method was satisfactory for the determination of peroxides in benzene, chloroform, 2-propanol, methanol, pentane, hexane, toluene, ethyl ether, acetone, vinyl acetate, and ethyl acetate. It should b e applicable to organic solids which are soluble in a mixture of acetic acid and chloroform. 792
ANALYTICAL CHEMISTRY
colorimetric procedures have been deqcribed for the determination of organic peroxides. Martin (,9) reviewed a large number of these and pointed out their limited applicability. Kolthoff and Medalia (7’) summarized the disadvantages of ferrous ion methods which have been widely used for the determination of peroxides in gasoline, fats and oils, ethers, and rubber. The leucomethylene blue method of Sorge and Ueberreiter (14) has been used for hydroperoxides and diacyl peroxides, but the reagent is difficult to prepare and relatively unstahle. Eiss and Geisecke (5) recommended benzoyl leuco-methylene blue as an alternative reagent because of its stability in air. However, it has to be protected from light and its reaction rate with peroxides is relatively slow without the use of metal accelerators. I n the past three years there has been considerable interest in the qualitative identification and determination of traces of peroxides in solvents and other organic materials. Dugan (2. 3) used S,N-p-phenylenediamine sulfate to determine traces of UMEROUS
lauroyl and benzoyl peroxide in polymers and for the qualitative detection of peroxides in ethers. The possibility of extending this rapid method to the determination of other peroxides was mentioned, but its range of applicability \\as not determined. I n his most recent nork (+$) Dugan demonstrated that the reagent reacted with several other peroxides in benzene solution but also noted that a specific peroxide tended to react a t different rates and occasionally yielded a different end color a i t h a change in solvent. Ryland ( 1 1 ) investigated the use of N,Ndiphenyl-p-phenylenediamine, A‘,A’-dimethyl-p-phenylenediamine sulfate, and N , S , S ’ , X ’- tetramethyl - p - phenylenediamine hydrochloride as colorimetric reagents for peroxides and pointed out their advantages and disadvantages. No quantitative data were obtained. Hydroperoxides have been determined by measuring the absorbance of the colored complex formed between titanium and the hydrogen peroxide produced by the strong acid hydrolysis of the hydroperoxide (IO,15). I n general. the reagents used in the titanium
methods were not affected by atmospheric oxygen but lacked the sensitivity of some of the other organic reagents that have k e n used. Heaton and Uri (6) developed an improved iodometric procedure for the determination of traces of lipide peroxides. A 2 to 1 mixture of acetic acid and chloroform was used as a solvent mixture under continuous deaeration instead of the 3 to 2 mixture suggested by Lea (8). The higher polarity of the former apparently reduced any tendency toward continued autoxidation, catalyzed oxidation, or induced oxidation and permitted the use of larger quantities of water in the reaction mixture. ‘The ionic species determined aas the triiodide complex. Although an absorbaiice maximum was noted z t 362 mu, measurements were made at 400 mp, sinccb fewer compounds interfered at the higher wavelength. Calibration curves with linoleic acid peroxide and pure iodine were identical and Beer’s law was obeyed for concentrations of peroxide helow 5 X l O - 4 M . Application of this procedure t o other commercially availatlle peroxides was not demonstrated. I n preliminary work in this laboratory the methods of PobiIier (IO), Eiss and Grisecke ( 5 ) , and Hcsaton and Uri (6) were investigated, sirice they appeared to be the most promising of those reviewed. Pobiner’s method was limited to hydroperoxides in hydrocarbon solutions and the method of Eiss and Geisecke (5) was unsiitable because of the large numher of experimental difficulties encountwed. Modified methods based on Heaton and Uri’s work and developed in this laboratory were found to be applicable to a wide range of peroxides of varying reactivity. With these relatively simple methods, quantitative rewlts were obtained with 17 commercially avrtilable peroxides. No color formation was observed with di-tert-butyl peroxid(: and dicumyl peroxide, which are among the least reactive of all peroxides. EXPERIMENTAL
Apparatus. A Bec kman Model D U spectrophotometer was used for all the absorbance measurements. For the range of 0 t o 400 pg. of active oxygen per 25 ml., matched 1-em. cells were used. Because of rektively high blank values and other experimental difficulties experienced with conventional Beckman 5-cm. and 10-cni. cells, a special cell was drsigned for the range covering 0 to 40 pg. of active oxygen per 25 ml. The cell body conristed of a Coleman precision absorption tube of approximately 1.5-cm. path I?ngth. The tube waq fitted with a standard taper joint from which a glass capillary extended to the bottom of the absorption tube for purging with nitrogen in situ. The glass capillary was so positioned that
L
5
5
u
u
-
1
Figure 1. Absorption cell for low active oxygen
it was out of the light path and had no influence on the absorbance measurements. .ill transfers of solutions between color development and measurement were completely eliminated. The regular Beckman cell carriage was replaced with the attachment provided for the measurement of absorbance in test tubes whenever the special cell was used. Details of the cell design are shown in Figure 1. Reagents. The source a n d purity of t h e commercial peroxides a n d peroxy compounds used in this study are shown in Table I. Values for per cent purity, listed in parentheses, were supplied by the manufacturer or determined by assay methods generally used for different peroxide types. Solutions of known concentration were prepared by dissolving known weights of these peroxides in a solvent mixture of 2 to 1 acetic acid and chloroform and diluting to 100 ml. The following reagent grade solvents were xsed: methanol, 2-propano1, pentane, hexane, chloroform, benzene, toluene, ethyl ether, acetone, ethyl acetate, and vinyl acetate. A11 other reagents were of the best grade available. Procedure for High Active Oxygen Range. For t h e range of 0 to 400 pg. of active oxygen per 25 ml., prepare a calibration curve as follows, using pure iodine. Dissolve 0.1270 gram of iodine in 2 to 1 acetic acid-chloroform and dilute to 100 ml. in a volumetric flask. This solution contains 1.27 mg. of iodine per ml., which is equivalent to 80.0 pg. of active oxygen per ml. Pipet 0-, I-, 2-, 3-, 4-, and 5-ml. aliquots of this solution into 25-m1. volumetric flasks and dilute to volume with the acetic acid chloroform mixture. Purge the solutions with nitrogen for 1 to 11/2 minutes, add 1 ml. of freshly prepared 50% K I , and continue purging for 1 minute. Measure the absorbance immediately at 470 mp, using 1-cm. matched cells and a water reference. Plot absorbance against micrograms of active oxygen per 25 ml. This calibra-
tion curve is identical to that obtained using aliquots of a solution of 5 grams of 30% hydrogen peroxide in 1000 ml. Such a solution contains 700 pg. of active oxygen per ml. Determine the peroxide content of a solvent sample as follows: Pipet a 5-ml. aliquot of the solvent into a 25-ml. volumetric flask and dilute to volume with acetic acid-chloroform. Insert a hypodermic needle or a glass capillary to the bottom of the flasks and purge with a tine stream of nitrogen for 11’* minutes. Add 1 ml. of fresh 50y0 K I solution and continue purginq for an additional minute. Remove the hypodermic, -topper the flask5, shake, and let them stand in the dark for one hour. At the end of this time, meacure the absorbance of the solutions a t 470 mp, using covered I-cm. cells and \vater as a reference. Measure the absorbance as rapidly as possible to minimize the effect of any air oxidation. Sitbtract the absorbance of a blank run through the entire procedure Determine the niicrograms of active oxygen in the sample bv reference to the calibration curie. Convert the microgramii of active ouygen to parts per million of active oxygen in the solvent Peroxides in Golid sampleq can also be determined if they are soluble in the acetic acidchloroform solvent Ii a specific peroxide is known to he preqent, convert parts per million of active ovygen. to parts per million of peroxide by using an appropriate factor. Procedure for Low Active Oxygen Range. Prepare a calihration curve covering the range of 0 to 40 p g . of a h \ - e osypen as follow: Prepare a standard iodine solution in 2 to I acetic acid-chloroform containing 63.4 pg. of iodine per ml., which is erlui\alent to 4.0 pg. of active oxvgen per ml. Pipet 0, 1. 3, 5, 8, and 10 ml. of this solution into 25-rn1. volumetric flasks and dilute to volume with acetic acidchloroform qolvent containing 4% water. Transfer a portion of each qtandard to the special absorption cell and purge slowly with nitrogen for 3 minutes. Add 5 drops of freqhlv prepared, deaerated, 507, KI through the standard taper joint and replace the stopper loosely. Continue purging with nitrogen for an additional 3 minutes. Tiqhten the stopper and close the nitrogen inlet so that the qolution is under a slightly positive nitrogen pressure. Meaqure the absorbance immediately a t 410 mp, wing water in another matched Coleman absorption tube as a reference. (-4s shown in Figure 1, each abqorption tube is provided with a glass em for reproducible positioning before absorbance measurements.) Subtract the absorbance of the blank and plot absorbance against micrograms of active oxygen per 25 ml. Determine the peroxide content of a solvent sample by diluting a 5 m I . sample to 25 ml. with 2 t o 1 acetic acid-chloroform containing 4% of water. Develop the color as described above and allow the solution to stand in the dark for 1 hour before the absorbance is measured. After correcting for the VOL. 36, NO. 4, APRIL 1 9 6 4
793
absorbance of a blank carried through the entire procedure, obtain the micrograms of active OxJ'Ren Present in the sample from the calibration curve and convert to parts per million in the solvent.
The ranges of absorbance values for both the high and low range Calibration curves are shown below.
RESULTS A N D DISCUSSION
Standard Curves. Identical straightline calibration curves with good reproducibility were obtained for the high active oxygen range, using either iodine and potassium iodide or hydrogen peroxide for standardization.
Table 1.
reagent H202
I7-M 1;-KI
Active oxygen range,
Absorbance
pg./25 ml. 0-384.1 0-389.0 0-40
range 0.016-0.830 0.003-0.797 0 . 0 -0.850
Quantitative Reaction of Classes of Peroxides
Compound tert-Butyl hydroperoxide
Type Hydroperoxide
p-Methane hydroperoxide 2,5-Dimethylhexane-2,5-dihydroperoxide Cumene hydroperoxide
Laiiroyl peroxide
Diacyl peroxide
Myristoyl peroxide Benzoyl peroxide
Diaroyl peroxide
2,4-Dichlorobenzoyl peroxide tert-Butyl perbenzoate
Perester
tert-Butyl peracetate Di-tert-butyl diperphthalate tert-Butyl peroxypivalate tert-Butyl peroxyisobutyrate Cyclohexanone peroxide
Standardizing
Ketone peroxide
Methyl ethyl ketone peroxide Succinic acid peroxide
Source and 7c purity Lucidol (94.6) Lucidol (59.0) Lucidol (73.2) Hercules (81.3) Lucidol (96.8) Lucidol (96.6) Lucidol (98.0)
Lucidol (41.1) Lucidol (96.6)
Lucidol (75.1) Lucidol (51.5) Lucidol (51 . O ) Lucidol (73.9) Lucidol (89.3) Lucidol (61.8) Lucidol (98.4)
Hydroxylheptyl peroxide
Lucidol (98.0)
Di-tert-butyl peroxide
Lucidol (98.0)
Dicumyl peroxide
Hercules (99.6)
Active Active Sample 0 2 0 2 size, present, found, p.p.m. p.p.m. ml. 154.0 2 152.0 4 152.5 154.0 2 105.1 99.0 4 105.1 97.0 2 94.0 98.0 4 94.0 96.0 3 67.3 74.0 5 67.3 73.2 3 40.0 42.7 5 42.7 40.8 3 61.0 59.3 5 61 . O 58.8 3 76.4 73.3 76.4 73.2 5 4 34.8 34.7 66.0 64.6 4 4 86.5 85.1 3 84.3 86.0 84.3 83.8 5 3 72.8 78.0 72.8 78.0 5 45.0 48.8 5 66.0 70.8 5 84.4 90.0 5 3 69.4 79.3 5 69.4 74.0 2 138.5 141 . O 3 142.7 138.5 61 . O 2 51.5 4 51.5 62.5 2 88.0 107.0 88.0 4 109.0 161.5 157.0 2 161.5 3 161.6 87.8 3 94.0 87.8 94.4 5 3 73.3 79.1 79.1 5 75.2 40.7 4 39.2 4 76.2 79.3 4 73.5 78.3 54.0 5 54.0 84.6 5 84.6 119.6 5 120.0 91 .O None re5 covered after 24 hr . 5 54.6 None recovered after 24 hr.
794
ANALYTICAL CHEMISTRY
Heaton and Uri (6) also demonstrated that calibration curves obtained with linoleic acid hydroperoxide and iodine with KI in 2 to 1 acetic acid-chloroform were identical. The use of iodine for standardization under the specified conditions is recommended, since the volumetric assay of hydrogen peroxide is eliminated and absorbance measurements can be made immediately. Heaton and Uri ( 6 ) purified commercial oxygen-free nitrogen by passing the gas through three wash bot,tles containing 15yo sodium hydrosulfite, 10% sodium hydroxide, and 0.2% sodium anthraquinonesulfonate as indicator. However, n e found that the laboratory supply of nitrogen wa? satisfactory for deaeration without purification, even for the 0- to 10-p.p.m. active oxygen range. The special cell shown in Figure 1 was designed for use in the low active oxygen range. By eliminating the transfer of solutions from reaction flasks to the absorption cell, the effect of any oxidation by air was minimized. hlolar absorptivity values of 845 at 470 mp and 5700 a t 410 mp were obtained for active oxygen, in agreement with the values reported by Heaton and Uri ( 6 ) . As shown by Heaton and Uri ( 6 ) , the absorbance ciirve for triiodide showed a continuous increase in nbsorhanre with a maximum at 362 mp with a decrease in wavelength. Although the absorbance maximum for triiodide occurs a t 362 mp, absorbance measurements were made a t 410 and 470 mp, as fewer compounds interfere a t the higher wavelengths. Quantitative Reaction of Peroxide Classes. The primary objective of this work was the development of a simple quantitative spectrophotometric method for traces of peroxides. To determine whether t h e described procedure was applicable to a range of peroxide types, solutions of known concentration prepared from 19 commercial compounds belonging to the hydroperoxide, diacyl, diaroyl, perester, dibasic acid, and ketone peroxide groups were analyzed. The active oxygen present in the solutions was calculated from the assay values shown in Table I and the results obtained are shown in the same table. I n evaluating the data, allowance should be made for errors in the assay procedures used, many of which leave much to be desired. Satisfactory recoveries were obtained for 17 of the compounds. No color development was observed in the case of ditert-butyl hydroperoxide and dicumyl peroxide, which are two of the most resistant organic peroxides known. Observation indicated that color development was fairly rapid in all cases, although some differences in rate were noticed. tert-Butyl perbenzoate appeared to be the slowest reacting of
the compounds. The rate of color development with ten’-butyl perbenzoate is shown in Figure 2. Color development reached a maximum in one hour. To eliminate any eff :et of rate of color development on atisorbance, all the samples were allowed to react in the dark for one hour before absorbance measurements were ,nade. The polarographic half-wave potentials serve as an indication of the bond strength of the --0-0groups in the various classes of peroxides (IS). If this criterion is used, the order of decreasing bond strength is di-tert-butyl peroxide > dialkyl peroxides > tert-butyl peresters > hydroperoxides > diacyl peroxides > peracids. Di-tert-butyl peroxide is not reduced over the normal polarographic range. I n the data shown in Table I, di-tert-butyl peroxide and dicumyl peroxide, which has a similar structure, were the only two compounds that did not react a t all. All the compounds belonging t c the other classes reacted quantitatively in spite of the wide variation in peroxide bond strength. No peracid was included, but compounds in this group should react quantitatively if the bond strength correlation is valid. Silbert (12) pointed o u t that this order is :tlso followed in the reactivity of these classes of compounds toward iodide ion, although no significant differences in reactivity toward iodide was noted for most of the compounds used in this study. The active oxygen concentrations varied from to 10-4M. The rapid rate of reaction in the 2 to 1 acetic acidchloroform solvent was not a function of the concentration of potassium iodide. This was varied from 0.012 to 0.12M without affecting either the rate or reaction or the intensity of the color obtained. Altshuller ( 1 ) has pointed o u t the importance of p H in determining the reaction rate of iodide with compounds like peraretic acid, succinic acid peroxide, cume ?e hydroperoxide, di-tert-butyl peroxidt:, and hydrogen peroxide in the 10-4 to 10-6M concentration range. T l i e extremely slow reaction rates in alkaline medium were ascribed to a decrease in the rate of an intermediate reaction in which iodate is formed from hypoiod ,te. Furthermore, in alkaline medium a decrease in absorbance was often observed a t later stages of the reaction of iodide and hydrogen peroxide. This was due to the conversion of triiodide to iodide, a reaction which also takes place with other organic peroxides in alkaline solution. I n acid solution, however, peroxy acids, acyl peroxides, hydroperoxides, and hydrogen peroxide will react rapidly with iodide even a t concentrations as low as L to 10 pg. per ml. I n view of Altshuller’s findings, the most plausible explanation for the rapid quantitative reaction obtained with the com-
‘4
Figure 2. Reaction rate curve for tertbutyl perbenzoate and iodide ion 350 pg. active oxygen present
pounds used in our work is the fact that the color-forming reaction was carried out in a highly acidic medium. The 2 to 1 acetic acid-chloroform mixture used in the methods described gave a p H of 1 when diluted 20% with water. Heaton and Uri (6) indicated that a small quantity of water is necessary for solution of the KI in the reaction mixture. Our work indicated that up to 5 ml. of water had no effect on the absorbance obtained after one hour. Determination of Peroxides in Solvents. There has been considerable interest in the determination of traces of peroxide in various solvents used in the laboratory or in chemical processes. These are often present as impurities or are formed by autoxidation on standing. T o determine whether the method was applicable to peroxides in solvents, synthetic samples containing known weights of either benzoyl peroxide or hydroxylheptyl
peroxide in various solvents were prepared and the solutions diluted to volume with 2 to 1 acetic acid and chloroform before analysis. Satisfactory recoveries were obtained using the high range method. as shoan in Table 11. The volumes of solvents used were completely miscible with the 2 to 1 acetic acid-chloroform solvent mixture. Since extrernely low levels of peroxide are often encountered in some solvents, three of the solvents used to check recovery in the high active oxygen range were chosen and synthetic samples prepared containing from 2 to 8 p.p.m. of active oxygen. The recoveries obtained using the sensitive low range procedure are shown in Table 111. By maintaining a positive nitrogen pre,w i r e over the sample during the reaction time and eliminating the transfer of solutions from reaction flask to absorption cell, the effect of air oxidation was minimized. Low blank values of < 2 pg. of active oxygen were obtained. KO colored solutions containing peroxides were analyzed. No difficulty should be experienced with such solutions if a correction is made for the absorbance due to color a t the wavelength of measurement. Because of the limited time available, recoveries from solvents of all the peroxides used in this study could not be checked. However, since the other peroxides were quantitatively recovered in the absence of solvents, it is safe to assume that similar recoveries would result in the presence of solvents. Even if some of the peroxides reacted with the solvents used or decomposed, the methods described could be used to
~~
Table
II.
Recovery of Peroxides from Organic Solvents
(High active oxygen) Peroxide added Benzoyl peroxide
Hydroxylheptyl peroxide
Table 111.
Solvent Hexane Methanol Toluene Ethyl ether Acetone Ethyl acetate Pentane %Propanol Vinyl acetate
Active 02 in solvent, p.p.m Present Found 71 71 71 71 71 65 65 65 65
2 2 2 2 2 8 8 8
8
71 72 73 73 72 64 63 64 64
6 4 2 2 4 8 6 6 6
Recovery of Peroxides from Organic Solvents
(Low active oxygen)
Solvent Benzene
Peroxide added Succinic acid peroxide
Ethyl ether
Benzoyl peroxide
Hexane
tertButy1 hydroperoxide
Active oxygen in solvent, p.p.m. Present Found 2.5 2.8 2.5 2.8 5.1 4.7 1.4 1.5 4.1 4.4 6.9 7.4 2.4 2.5 4.9 4.8 7.3 7.2
VOL. 36,
NO. 4, APRIL 1964
795
ACKNOWLEDGMENT
Table IV.
2: 1 HAC-CHC18 present, ml. 25 20 15 25
Effect of Acid Concentration on Peroxide Recovery
Solvent Benzene
Present, ml.
Chloroform
20
0 5 10 0 7
10
15
25
2-Propanol
20 15 10 5
0 5 10 15 20
Active Present
02,
420 420
rg.
Found 431 43 1
K o t miscible 329 329
323 326
43 1 431 43 1 43 1 43 1
438 445 438 448 43 1
S o t miscible
The authors thank the Lucidol Division, Wallace & Tiernan, Inc., and Hercules Powder Co. for supplying the samples of commercial peroxides used in this study. The assistance of A. E. Mertes with some of the analyses reported here is also appreciated. LITERATURE CITED
(1) Altshuller, A. P., Schwab, C. >I., Bare, M., ANAL.CHEM.31, 1987 (1959). (2) Dugan, P. It., Ibid., 33, 696 (1961). (3) Ibid.. D. 1630. (4) Ibid.; i5, 414 (1963).
(5) Eiss, M. E., Geisecke, P., Ibzd., 31,
determine the active oxygen levels at a n y particular time. Effect of Acidity. T o determine whether variations in t h e acid concentration of t h e reaction mixture had a n y effect on peroxide recovery in t h e presence of solvents, t h e rccovery of active oxygen from solutions containing known amounts of hydroxyheptyl peroxide and varying amounts of 2 t o 1 acetic acid-chloroform was checked (Table IV). All the solutions were made u p t o volume with the solvent under test. The ratio of acetic acid-chloroform and solvent can be varied between fairly wide limits without affecting the quantitative recovery of active oxygen. The main limitation on the volume of sample that can be used is its miscibility with the
acetic acid-chloroform mixture. I n almost all cases, 5 ml. of the solvents tested were miscible with 20 ml. of acetic acid-chloroform. Recovery of peroxide was quantitative when as little as 20% by volume of acetic acidchloroform was present in the solvent mixture. It should therefore be possible to determine peroxide groups on polymers and other organic solids if the solution of the material is compatible with the minimum amount of acetic acid-chloroform required for the reaction of the peroxide with iodide. Attempts to determine di-tert-butyl peroxide by using HCl to increase the acidity were unsuccessful. Ten milligrams of this peroxide gave a pale yellow 2 hours after solution in 1 to 1 HCl and the addition of KI.
1558 (1959). (6) Heaton, F. W., Uri, K.,J . Sci. Food Agr. 9, 781 (1968). (7) Kolthoff, I. L l . , Xedalia, A. I., AN.41,. CHEM. 23, 595 (1961). (8) I,ea, C. H., Proc. Rou. SOC.108B, 17n (1931).
(9) Martin. A. J., “Organic Analysis,” Yol. 4, p. 3, Interscience, New York, 1960. (10) Pobiner, H., ANAL. CHEM.33, 1423 (1961). ( I 1) Ryland, A. L. , Division of Analytical Chemistry, 142nd Meeting ACS, .4tlantic City, zi. J., September 1962. (12) Silbert, L. S., J . .Ana. 022 Chemists’ SOC.39,480 (1962). (13) Silbert, L. S., Witnauer, L. T., Swern, D., Iticciuti, C., J . =Im.Chem. SOC.81, 3244 (1959). (14) Sorge, G., Ueberreiter, K., Angew. Chem. 68, 352 (1956). (15) Wolfe, W. C., ANAL. CHEM. 34, 1328 (1962). RECEIVED for review Xovember 21, 1963. Accepted December 30, 1963.
Simultaneous Spectrophotometric Determination of Calcium and Magnesium with Chlorophosphonazo 111 JERRY W. FERGUSON, JOHN J. RICHARD, JEROME W. O’LAUGHLIN, and CHARLES V. BANKS lnstitute for Atomic Research and Department of Chemistry, lowa State University, Ames, lowa
b A rapid and sensitive spectrophotometric procedure for determining calcium and magnesium with Chlorophosphonazo 111 is described. Either calcium or magnesium may b e determined a t p H 7.0 in the range of 0.1 pg. per 25 ml. (0.004p.p.m.) to 10 pg. per 25 ml. (0.4 p.p.m.). In mixtures of calcium and magnesium, calcium is determined a t pH 2.2 a t a wavelength of 667.5 mp. The magnesium is then determined by difference a t p H 7.0 and 669 mp, where the absorbances due to the two metal complexes are additive. Milligram amounts of the alkali metals can b e tolerated but most other metals interfere.
A
spectrophotometric procedure for the determination of trace amounts of calcium and magnesium was needed for a study of the SENSITIVE
796
ANALYTICAL CHEMISTRY
extraction of the alkaline earths with organophosphorus compounds. Reagents used for the spectrophotometric determination of calcium include murexide (22, 23, 24, 26, 27, Sf),ocresolphthalein complesone (23), chloranilic acid (6,29),and Eriochrome Black T (32). Most of these reagents have fairly low sensitivities and are not stable. Their use requires very close control of experimental conditions for reliable results 4 recently suggested reagent for calcium is glyoxalbis-(2hydroxyanil) ( 8 , 12). It is sensitive and small amounts of magnesium are reported not to interfere. The spectrophotometric determination of magnesium with lake-forming reagents such as Titan Yellow (7, 10, I S , 14, SO), Thiazole Yellow (11, 18, f9), and Brilliant Yellow (28) has been reported. These reagents are fairly sensitive but, like most such lake dyes,
require estremely close attention to experimental details for reliable results. Eriochrome Black T has been used for the determination of magnesium (4, 9, 26, 23, 32) and for the simultaneous determination of calcium and magnesium (32). A recently reported reagent for magnesium, Magon (1, 16, l y ) , is sensitive and forms a fairly stable complex with magnesium. The use of 2,7-bis-(4-chloro-2-phosphonobenzeneazo) - 1,8-dihydrosynaphthalene-3,6-disulfonic acid (Chlorophosphonazo 111) as a sensitive reagent for both calcium and magnesium is reported here. The synthesis and use of this reagent for the spectrophotometric determination of uranium were reported by Nemodruk et al. (20). Chlorophosphonazo I11 has also been used for the spectrophotometric determination of titanium, zirconium, thorium, and scandium ( 5 ) , quin-
