496
ANALYTICAL CHEMISTRY
of Standards certificate of 0.56%. yielded 0.55, 0.55, and 0.55%.
The three determinations
permits the athinment of a sensitivity of 0.05 microgram of cadmium. The procedure is proposed for general use because of its great freedom from interferences and its simplicity.
DISCUSSION
Failure to obtain the orange color of excess dithizonein theaqueous phase after the first extraction ordinarily indicates that the 100microgram limit of the procedure for cadmium has been exceeded. In unusual cases, it may indicate the presence of more than 100 niicrograms of mercury or thallium. Mercury may be recognized by the orange color of the chloroform extract. The analysis may be completed in these cases, if required, by using additional dithizone and washing with chloroform after an excess has been attained. I n the case of unusually large amounts of other interfering metals exceeding the combining power of the 50 mg. of potassium cyanide used in this extraction, the best procedure is to repeat the analysis on a smaller portion of the ashed sample. 4 preliminary extraction with dithizone a t p H 2 map be used to remove excessive amounts of mercury, silver, and copper. In the final extraction, the absence of the yellow color of escess dithizone in the aqueous phase and the obtaining of a darker extract indicate that an excessively large amount of cadmium has been taken in the aliquot. If more of the sample is not available, all of the cadmium may be readily recovered by shaking with additional dithizone and chloroform. The conibined extracts are stripped with tartaric acid and the latter may then be aliquoted and the final extraction repeated in the usual mnnner. The proper estimation of the aliquot to be used requires some experience. A wide variety of types of samples may ordinarily be treated without complication. The colorimetric system as described
ACKNOWLEDGMENT
The author is grateful to D. €1. Byers and H. E. Stokinger, under whose direction the w-oil; was rarried out, for their review and criticism. LITERATURE CITED
(1) Cholak, J., and IIubbnrd, D. RI., ISD.Esn. CHEM.,.Is.AI.. ED., 16, 333 (1944). ( 2 ) Church, F. JJ’., J . Ind. Hug. Tu.rico?., 29, 34 (1947). ( 3 ) Klein, il. K., J . Assoc. Ofic.Agr. rhemists, 30, 455 (t947). (4) Ibid., 32, 349 (1949). (5) I b i d . , 33, 592 (1950). (6) Klein, A. IC., and Wichman, H. J., Ibid., 28, 257 (1945). (7) Salteman, B. E., ANAL.CHEM.,24, 1016 (1952).
(8) Sandell, E. B., “Colorimetric Determination of Traces of Metals,” pp. 170-7, New Tork, Interscience Publishers, 1944.
(9) Sandell, E. B., IND. E x . CHEW,SAL. ED.,11, 364 (1939). (10) Setterlind, A. S . , and Krause, -1,H., “llicroanalysis of Cad-
mium by the Diphenylthiocarbazone (Dithizone) Rlethod,” Dept. of Public Health, State of Illinois, January 1943. (11) Shirley, R. L., Benne, E. +J,, and JIiller, E. J., ASAL.CHGY., 21, 300 (1949).
(la) Stein, C., J . Assoc. Ofic. A g r . Chemists, 34, 417 (1951). (13) Ftrafford, S . , W y a t t , P. F., and Kershaw, F. G.. .4!ld&
70,
232 (1945). (14; (15)
JVelcher, F. J . , “Organic Analytical Reagents,” Vol. 3, pp. 536-9, New York, D. Van Nostrand Co., 1947. Wichman, H. J., .I. Assoc. O ~ C-4gr. . Chemists, 32, 343 (1949).
R E C E I ~ for E Dreview AIay 2 6 . 10.52. Accepted Ijoveniber 17, 1952.
Determination of lindane in Air IRWIN HORNSTEIN AND W . N. SULLIVAN Bureau of En toninlog?. a n d Plant Qtrarantine, C‘nited Stares Departmpnt os Agricrcltrrre, Beltscille, .Md. I\DI\E
is being used to kill insects by its fumigating effect,
L and devices for dispersing lindane vapor have been placed in pulhc p l a c ~ sto control flying insects. KO adequate procedure
has Iwen dvailable for determining small amounts of lindane in air. In the method described in this paper lindane is collected either in acetic acid or preferably 011 an alumina column and determined colorimetrically. As little as 0.1 miciogram of lindane per liter of air can be determined. This method should prove useful in entomological and toxicological investigations. The gamma isomer is the insecticidal component in technical benzene hexachloride. Lindane, which contains a t least 99% of the gamma isomer, has a high enough vapor pressure, approximately 10-5 mm. of mercury a t 30” C. ( I ) , to kill insects by its fumigating action (3, 4, 6). Vapor-pressure measurements of lindane were obtained in a private communication (2). Various methods are used to disperse lindane vapors in air. Thermal generators heating lindane to just below its melting point are available. Burning lindane-impregnated papers and blowing air through lindane-coated screens have also proved effective. Determination of the amounts of lindane that are thus disseminated in the air is extremely important, because of the toxicity of this insecticide to man and animals. There is always the possibility of contaminating foodstuffs that may be exposed to the vapors in stores and warehouses. In addition, information of this nature is essential in entomological studies. The lindane concentration in air ha5 been previously estimated from total chlorine determinations ( 3 ) . In the procedure described in this paper the colorimetric method for determining benzene lieuachloride, recently described by Schechter and Horn-
stein (5) has been adapted to the determination of lindane in air. In brief, this procedure involves the dechlorination of benzene hexachloride or lindane to benzene and its subsequent nitration to ?n-dinitrobenzene, which after extraction is reacted with methyl ethyl ketone in the presence of strong alkali. The violet-red color that develops is measured photometrically. As little as 5 micrograms of lindane can be determined in this manner. Although in this procedure all the isomers of benzene hexachloride are reported as lindane, no error is involved, since insect control is achieved by vaporization of lindane alone. Two methods for obtaining the desired air sample have proved satisfactory. In one, the air sample is drawn through gaswashing bottles containing acetic acid, and the amount of lindane ahorbed in the acetic acid is determined. In the other, the air sample is pulled through an alumina adsorption column, and the adsorbed lindane is washed off the column with acetic acid. The second procedure requires a minimum of equipment and is considerably more rapid than the first. The results are precise and are in agreement with those obtained by the acetic method. For all practical purposes adsorption on alumina is the more useful method. In the dispersal of lindane vapor by heat it is to be expected that, when the vapors become cool, solid partisles of lindane may lie distributed in the air. Thus the amount of lindane reported in a given analysis would actually be the lindane in the vapor phase plus a random number of lindane particles that might be collected in the adsorption train. The average of several determinations in an enclosed space would give a good indication of the total amount of lindane in the air. To avoid partirle formation and thus learn how precise this
V O L U M E 2 5 , NO. 3, M A R C H 1 9 5 3
497 _ _ _ ~
-
-
__
tion coiitainnig 10 grams of lindanc. A funnel was suspended through a hole in the top of the cabinet so that the air inLindane Yapor Cubic Feet side could be sampled without opening reniperature, Pressure, of Air Saiiipling h l i c r o g r a t n ~ ‘70 the doors. The cabinet was left open for Panipleq Collc.ctrd c. Micron Sampled Time, Nin. liter iatiiration 24 hours to ensure complete removal of 1.18 90.7 On d u n i i n a 27 0.076 2.5 10 13 1.21 93.3 the acetone, and then kept closed for one 1 .20 92 3j week to let the lindane concentration iii 1.16 84 . 1.16 89.5 the air attain equilibrium. Some air ex1, 20 02 r, change was possible through seepage 1.10 91.0 around the doors, as no attempt was 1.10 !I1 0 made to have the cabinet completely 1.08 00.0 airtight. When the lindane was col. lected in acetic acid, the air was sampled by pulling out 3 cubic feet of air at the rate of 1 cubic foot per hour through gas-\\-ashiiig hottles. The rate of adsorption on alumina was RS method of analysis might be, thc xnalyscs were made in a closed high as 0.2 cubic foot per minute. cabinet, in which the walls had been treated with lindane and Under Nonequilibrium Conditions. For applying Sullivan’s equilibrium attained in the enclosed air space. When the sample ( 7 ) method of lindane dispersion a Peet-Grady chamber 6 X 6 X G was collected in acetic acid, an average of 1.1 micrograms of feet was used, S o attempt was made to have the chamber completely airtight; some air exchange could take place around the lindane was found per liter of air (Table I). This corresponds to door. Eight and three-tenths grams of lindane in 200 nil. of a .‘relative lindane saturation” of about 91 % based on the theoacetone were sprayed as a fine mist on a fiber glass filter 6 X 6 X 1 retical value calculated from vapor pressure measurements. inches, which had a coating of oil to help retain the lindane crysWhen alumina was used as an adsorbent, 1.19 micrograms of tals. The filter was fastened to the guard of a &inch fan. Operation of the fan caused an air current to flow through the filter and lindane was found per liter of air. This also corresponds to a disperse the lindane vapor. The air stream was directed from one “relative lindane saturation” of about 91 %. corner of the floor diagonally across the chamber and slightly upNo material other than glass should precede the adsorbents. ward. The sampling setup was placed on the floor a t right Lindane vapor appears to be readily adsorbed, as was well angles to the air stream. Sampling. When acet>icacid was used as a collector, the air to illustrated in an unexpected manner. When a piece of rubher be analyzed was pulled through two gas-washing bottles in tubing about 1 foot long was used to connect the funnel outlet of series, equipped with fritted-glass gas dispersers, each bot,tle conthe cabinet to the adsorption train, no lindane was found in the taining about 125 ml. of glacial acetic arid. Almost all the acetic acid bottles, but n hen all-glass connections were used, allindane was absorbed in the first bottle. The absorbers were followed by a purifying jar filled with a 50-50 mixture of granular most theoretical valucs, based on vapor pressure measurements, soda lime and silicic acid t o remove traces of acetic acid. This were obtained. soda limesilicic acid mixture had to be renewed from time to The precision of the method appears to be about 4=2”/0 time, as it had a tendency to clog. This jar was connected t,o a Although no definite statement as to accuracy can be made, the calibrated gas meter followed by a diaphragm-type compressor equipped with a bleed valve to regulate the flow t,hrough the abresults obtained are good when compared to theoretical values sorbers. that can be calculated from known vapor pressure measurements. The air was pulled through this sampling apparatus a t the rate Sullivan ( 7 ) has described a method for dispersing lindane of about 1 cubic foot per hour. Three cubic feet gave an adequat,e vapors by blowing air through an oil-coated fiber glass filter sample (50 to 100 micrograms of lindane). The acetic acid was washed into an Erlenmeyer flask equipped with a 24/40 joint, treated with lindane. A number of runs were made lsith this the acid in the second bottle being used as a wash for the contents method to see how reproducible the results might be under more of the first bottle; an inner 24/40 joint about 150 mm. long was usual conditions. The values olitaincd, as shonn i n Talde 11, attached to the flask to minimize losses by splashing, and the acid fell within a narrow rangr. The precision olitained was about was then concentrated to about half its volume on a hot plate to remove traces of volatile materials, such as benzene, that might 3=6%. interfere in the analysis. The lindane analysis was run on the concenbrate as described by Schechter and Hornstein (5). A P P A I ~i~ u s For adsorption of lindane on an alumina column, a borosilicat,e glass test tube was provided with a hollow stem; a wad of glass Two ga5-v ashing bottles, with fritted disks and ground-glass wool was placed at the bottom of the test tube, and 20 grams of stoppers, 250 ml. capacity, rimilar to Fisher Xo. 3-038. 80 to 200 mesh alumina were used as the adsorbent; another wad Purifying jar, wide neck a t top and tubulature a t bottom. of glass wool was placed on top. It is preferable to pack the colBorosilicate glass test tube, about 25 mm. in diameter and 200 umn by applying suction. This adsorption tube was connected mm. long, n i t h attachcd bottom stem about 90 mm. long (for directly to the vacuum side of the compressor through a tightly alumina adsorbent). fitted rubber stopper set in a suction flask to act as a holder during Gas meter, calibrated, 15 (.t-test or mechanical (diaphragm) the run. The gas meter was attached to the pressure side of the type. Diaphragm-type compressor, hp., similar to Searscompressor. -4n air sample containing 50 to 100 micrograms of Roebuck paint spraver No. 99D-01858. lindane was pushed through the meter a t rates as high as 0.2 Specially designed all-glass digestion and nitrating apparatus cubic foot per minute by adjusting the bleed valve on the i-:tcuuni described in (6) but with a 24/40 rather than a 19/38 joint. Any suitable photometer.
Table I.
Lindane Deterniinatioris tinder Equilibrium Cotidi tioris
~
REAGENTS
Glacial :icetic acid ldsorption alumina (similar to grsdc availablc from Fisher Scientific Co.), 80-200 mrsh Soda lime, approximately 8 mesh Silicic acid, approximately 8 mesh Reagents for colorimetric procedure as described by Schechtcr and Hornstein ( 6 )
Table 11.
Samples Collected On alumina
Lindane Deterniinations i n Peet-Grad>- Chamber (.4ir saiiiple 3.0 cubic feet) Yapor Temprraturc, Pressure, Sarnplinr: C. Micron Tinie. l l i n . 30 0.11 67 60 60 79 21
PROCEDURE
Under Equilibrium Conditions. +4cabinet 2.5 X 2.5 X 4 feet with the doors and walls made of glass and the top and bottom of wood was painted on all inside glass surfaces with an acetone solu-
Lindanr .\IicrograinP/ O0 liter saturation 1.10
61
1.33 1.13 1,17 1.17
63 65 65
70
498
ANALYTICAL CHEMISTRY
side. With the outlet of the gas meter thus open to atmospheric pressure, regardless of the rate of flow, a partial vacuum cannot form inside the gas meter container and cause the sides of the gas meter to buckle. The adsorbed lindane was removed from the adsorbent by washing with successive portions of glacial acetic acid (about 150 ml. total volume). If some h e aluminum oxide is carried through, no harm is done. The filtrate was washed into an Erlenmeyer flask with acetic acid and, as in the first procedure, the acid was concentrated to about 100 ml. The lindane analysis was run on this concentrate. To the Erlenmeyer flask containing the lindane-acetic acid concentrate, zinc dust and malonic acid were added, and the flask was connected directly to the dechlorination and nitration apparatus. The flask was then heated in an oil bath a t 150" C. for about 3 hours. The exact details of the procedure are given in ( 6 ) . IVhen the colorimetric method is used to determine lindane, it is first necessary t o prepare a calibration curve employing a standard glacial acetic acid solution of lindane (6). COKC LUSIOK s
The concentration of lindane in air under optimum conditions can be determined with a precision of about &2% by the Schechter-Hornstein colorimetric method. Adsorption on an alumina column provides a rapid, simple,
and precise method for sampling air containing lindane. Sampling can be made a t the rate of 0.2 cubic foot per minute. In an endosed space, n i t h very little air interchange, lindane concentrations of about 90% of saturation calculated from known vapor pressure measurements were found. ACKNOWLEDGMENT
The authors are grateful to R. A. Fulton of the Bureau of Entomology and Plant Quarantine for valuable suggestions. LITERATURE CITED
(1) Balson, E. W., Trans. Faraday Soc., 43, 54 (1947). (2) Ethyl Corp., Detroit, Mich., private communication. (3) Fulton, R. A . , Nelson, R. H., and Smith, F. F., J . Econ. Entomol., 43, 233 (1950). (4) Hoffman, R. A , , and Lindquist, *4.W., J . Econ., Entomol., 42, 436 (1949). ( 5 ) Schechter, M. S., and Hornstein, Irwin, A S ~ LCHEM., . 24, 544 (1952). (6) Slade, R. E., Chemistry & Industry, 40, 314 (1945). (7) Sullivan, W. N., J.Econ. Entomol., 44, 126 (1951). RECEIVED for review Bugust 16, 1952. Accepted October 15, 1952
Colorimetric Determination of Magnesium with Eriochrome Black T AUBREY E, JURYEY, JR., J . fir. KOMARMY, AND G. AT. WYATT University of .Irkunsas, Fuyetteville, Ark. colorimetric methods for the determination of S magnesium are available in the literature (5, 6, Some methods depend upon the formation of color lakes and EVERAL
9-11),
others upon an indirect determination of magnesium t)>.a suitable colorimetric method. In all these determinations n o method involves a true solution of a colored magnesium complex in which the color intensity is directly proportional to the magnesium concentration. This paper presents a spectrophotometric method for the determination of magnesium using the reagent Eriochrome Black T, 1 - (1 - hydroxy 2 naphthylaxo) - 2 - hydroxy - 5 - nitro - 4 naphthalenesulfonic acid. The Versenate (disodium salt of ethylenediaminetetraacetic acid) method for the titration of total hardness of water ( 2 ) employs Eriochrome Black T as :in indicator a t the pH of 10.1. In the p H range of 7 to 10 t'his reagent forms a very slightly dissociated, soluble, intensely red coinples with magnesium. The reagent itself in unbuffered methanol solution has a deep reddish black color; a t a pH of 10.1it is blue. Interferences from copper, manganese, iron, aluminum, cobalt, and nickel were reported by Diehl, Goete, and Hach (Z'), who gave procedures for eliminating these int,erferences and limiting concentrations, Calcium was found to complex with the dye almost as readily as magnesium, giving an absorption curve similar to that of the magnesium complex. It is shown in the present investigation that the calcium ion may be removed prior to the determination of magnesium.
- -
reagent dye solution in absolute methanol was prepared. These solutions were prepared by dissolving 0.5000 or 0.1000 gram of dye in methanol and diluting to 100.0 ml. Standard Magnesium Solution. This solution was prepared by dissolving 8.3636 grams of reagent grade magnesium chloride hexahydrate, RlgClz.6H20, in distilled water and diluting to 1 liter. Magnesium was determined gravimetrically by weighing as Mg2P20, and its concentration in the solution was found to be 1.000 mg. per ml. More dilute solutions were prepared from this solution by careful dilutions with distilled water. Buffer Solutions. The buffer solution of p H 10.1 was prepared according to the directions of Diehl, Goetz, and Hach (I) by mixing 6.75 grams of reagent grade ammonium chloride with 57 ml. of C.P. concentrated ammonium hydroxide and diluting to 1 liter with distilled water. 0 5
EXPERIMENTAL
Instruments. A Beckman quartz spectrophotometer, Model DU, with 10-mm. Corex or silica absorption cells was used for absorbancy measurements made a t the maximum sensitivity of the instrument with distilled water in the reference cell. Silica cell spacers were used to obtain a 1-mm. optical path when s eci fied. Absorbancy is defined as the negative logarithm o r t h e ratio of the transmittancy of the solution to that of the solvent, A , = --log T m i / T a o l v . A Beckman Model G pH meter was used to check the pH of all buffer solutions. was SSS, Reagent Solution. Eriochrome Black T, C ~ O H ~ ~ O ~ X furnished by the Hach Chemical Co. The dye solution was prepared fresh prior to each determination. For higher concentra- Figure 1. Magnesium Complex with Eriochrome Black T tions of magnesium a 0.5% reagent dye solution in absolute x d.0f2.27 x 10-3 Mdye a d d d to (1 - x)mi. ofequimolar magnesium and diluted to 25 ml. 540 mp, pH 10.1, Lam. cells methanol was used and in the lower concentration range a 0.1%
