obtained. Obviously the sample was a very inhomogeneous one. These data further indicate the desirability of having the instrument perform the integrations by performing slower sweeps of the wave length spectrumsay up to 15 minutes per sweep. Previously the effect of aerosol scattering on the ozone measurement was discussed. It was shown t h a t if Baum's nighttime data was assumed to apply to daytime conditions, errors of 1 to 2 p.p.h.m. in ozone concentrations m r e incurred. Baum's data also suggest t h a t gaseous pollutants which absorb in this region are also included in the error estimate. To strengthen the conclusion in this regard, sulfur dioxide, one pollutant known to be present, was analyzed to determine its effect on these ozone determinations. For sulfur dioxide = 0.0195 km.-' az~o = 0.031 km.-' 0 3 1 3 = 0.007 km.-'
p.p.h.m.-l p.p.h.m.-' p.p.h.m.-l
The pair of a's for ozone and sulfur dioxide give - cY28O)SO~ = -0.11 ( L ~ Z E L - ~yzm)o, = $0.069 (a256
Therefore, 10 p.p.h.m. of sulfur dicxide would give an error of about 2 p.p.h.m in ozone. Thomas ilutometer sulfur dioxide data for Los Angeles indicate sulfur dioxide concentration averages about 10 p.p.h.m. during the middle of high oxidant or ozone days. If the other pair of lines are used, one obtains (a265
(at66
-
-
Ly313)SOp
(Y8lS)Oa
= $0.0126 = +0*122
Thus, 10 p.p.h.m. of sulfur dioxide would be read as 1 p.p.h.m. of ozone. It should be noted that these effects are in opposite directions. Therefore, averages of ozone values determined from both ratios would essentially
eliminate the sulfur dioxide effect a t these wave lengths and a t these low concentrations. The use of this instrument on the smog studies in Pasadena has indicated the desirability of making similar ozone measurements in other parts of the Los Angeles Basin. Toward this end, as well as meeting the objective of making ozone measurements automatically for its large-scale air monitoring program, the Air Pollution Control District has had two additional instruments built and is currently evaluating their performance in the field. ACKNOWLEDGMENT
The author gratefully acknowledges the advice on methodology of W. A. Baum. R. S. Estey, then of Borman Engineering, Inc., designed the apparatus and supervised its construction and operation in the field. E. M. Liston of the Air Pollution Foundation assisted in its operation. Ralph Stair of the Yational Bureau of Standards graciously made available his experience in operating the Army Ordnance equipment and suggested its loan from the Rock Island Arsenal. The Los Angeles County Air Pollution Control District and A. J. Haagen-Smit kindly made their oxidant data available. LITERATURE CITED
W. A., Ph. D. thesis, Cnlifornia Institute of Technology,
(1) Baum,
1950.
Baum, W. A , , Dunkelman, L.. J .
Opt. SOC.Amer. 45, 166 (1955). Bowen, I. G., Regener, V. H., J . Geophys. Research 56, 307 (1951) Bradley, C. E., Haagen-Smit, A. < J , Rubber Chem. and Technol. 24, 750 (1951). Chalonge, D., Vassy, E., J. phvs. radium 5,309 (1934). Dauvillier. 8..Comat. rend. 201. 679 (1935). ' Dauvillier, A., J. phys. radium 5, 455 (1934).
(8) Fahry, C., Buisson, H., Compt. rend. 192,457 (1931). (9) Fabry, C., Buisson, H., J . phys. radium 2 , 197 (1921). (10) Fowler, A , , Strutt, R. J., Proc. Roy. SOC.(London) 93A, 577 (1917). (11) Francis, A. G., Parsons, A4.T., Analyst 50, 262 (1925). (12) Gluckauf, E., Heal, H. G., Martin, G. R., Paneth, F. A., J . Chem. SOC.1944.1. (13)
(14)
(15) (16)
(17) (18) (19) (20) (21) (22) (23) (24)
(25) (26) (27) (28) (29) (30) (31) (32) (33)
RECEIVED for review September 13, 1956. Bccepted January 19, 1957. Sponsoi:ed in part by contract No. 55-2564 with Rock Island Arsenal, Ordnance Corps, Dept. of the Army.
Qualitative Microdetermination of Organic Phosphorus Compounds CLARK M. WELCH and PHILIP W. WEST Coates Chemical laboratories, louisiana State University, Baton Rouge, l a .
Phosphorus-containing organic compounds are of great importance in biological systems, insecticides, and war gases. Methods are proposed for the sampling, degradation, and detection of minute amounts of such materials. A newly discovered phos-
874
ANALYTICAL CHEMISTRY
phorus reagent has been adapted for use in detecting as little as 0.2 y of combined phosphorus. The proposed procedures are applicable to acids, esters, acyl halides, and anhydrides together with their thio analogs.
T
R E WIDE OCCURRENCE of organic phosphorus compounds in biological systems, as well as their frequent use in insecticides and chemical warfare agents, makes their determination a problem of great importance in many fields. The most generally ap-
plicable approach to the microdetection of these compounds is their conversion to inorganic phosphate, for which sensitive tests now exist. Only in rare cases do phosphorus-containing functional groups possess characteristic chemical properties which would permit their direct detection and positive identification. Until recently, the principal methods of detecting inorganic phosphates were subject t o a number of interferences. The discovery by Robinson and West (4) of a more highly selective reagent, o-dianisidine molybdate, has made possible the development of correspondingly selective tests for organic phosphorus compounds. Two new procedures are described here and a direct comparison is made with an adaptation of a previous test. Each of the tests exhibits characteristics Ivhich would be advantageous under a variety of conditions. The application of the most general method to the detection of a phosphorus compound in a mixture of gases has also been demonstrated. EXPERIMENTAL
Sulfuric Acid-Dianisidine Molybdate, Method A. A very general and efficient reagent for degrading organic compounds of phosphorus is refluxing, concentrated sulfuric acid. I n a few cases, it is advantageous to add mercury(I1) sulfate as a catalyst to speed the degradation of volatile substances which would otherwise escape before decomposing. The catalyst also minimizes carbon formation by organic contaminants in the sample. The brief digestion is followed by neutralization, buffering, and addition of o-dianisidine molybdate. The unknown can be detected as the solid or the liquid. It is often more conveniently handled as the carbon tetrachloride solution or as an adsorbate on silica gel. CHEMICALS. The organic phosphorus compounds studied were commercially available materials, except for sarin (isopropyl methylphosphonofluoridate, a nerve gas), and were used without further purification. All Tvere reagent grade with the exception of the phenylphosphonothionic dichloride, which was technical grade, and Malathion, which contained 9570 of the insecticide. Research samples of octylphenyl acid phosphate and trihexyl phosphite were kindly donated by the VirginiaCarolina Chemical Corp., trimethyl phosphite, by the hlonsanto Chemical Co., phenylphosphinic acid, phenylphosphonic acid, and phenylphosphonothionic dichloride. bv the Victor Chemical Works. REAGENTS.Sulfuric acid, 96%. Sodium carbonatesodium formate solution. For samples in carbon tetrachloride solution: 21.0% sodium carf
"
bonate (anhydrous), 4.10% sodium formate; for samples on silica gel: 14.0% sodium carbonate (anhydrous), 2.75y0 sodium formate. The carbonate should not contain more than 0.0003% phosphate as an impurity. The formate should not contain more than 0.001% phosphate. o-Dianisidine molybdate reagent. Dissolve 2.5 grams of sodium molybdate dihydrate in 15 ml. of water and 5 nil. of concentrated hydrochloric acid. Dissolve 0.125 gram of o-dianisidine in 2 ml. of glacial acetic acid and add this with stirring to the molybdate solution. Allow the mixture t o stand overnight and filter. Store the solution in a glass-qtoppered bottle. It is stable for 6 t o 12 months if agitation with air is avoided. The droppers used to deliver the sulfuric acid and sodium carbonatesodium formate solutions are heated in a flame and their tips drawn to 1 mni. or less in outside diameter. They will then deliver roughly 100 drops of sulfuric acid or 45 drops of carbonateformate solution per milliliter. This decreases the dilution factor. I n the bottom of a PyPROCEDURE. rex S o . 7740 test tube, 3 X :/* inches, is placed 1 drop of sulfuric acid. The sample, in 0.01 t o 0.50 nil. of carbon tetrachloride or on approumately 0.02 gram of silica gel, is dropped in. The tube is warmed in a flame along most of its length t o d r k e off the solvent without heating the sulfuric acid a t the bottom (30 to 40 seconds). Only then is the acid heated. It is refluxed not more than one fourth of the way up the tube for at least 30 seconds or until any carbonaceous matter has dissolved. The tube is air cooled by being waved vigorously (10 seconds) , the bottom half is n-ater cooled (10 seconds), and 3 drops of carbonate-formate solution are added. The liquid is rolled up the inner walls to ensure complete mixing and neutralization. Two drops of odinnisidine molybdate reagent are added.
A reddish-brown precipitate indicates the presence of phosphorus compounds. At microgram concentrations, the cloudiness is easily seen against a black background. The test appears within 30 seconds; the procedure requires 2 minutes. If the unknown is relatively volatile or if the sample solution contains much organic matter, a pinch of mercury(I1) sulfate (about the mass of a wheat grain) may be added as an oxidation catalyst prior to the digestion. The tejt should then be carried out in a hood, as the mercury salt tends to sublime. Any red precipitate of mercury oxide initially formed on addition of the e x bonate-formate solution should redissolve to give a colorless solution after mixing is complete. The blanks remained clear and colorless, and proved to be unnecessary. SESSITIVITT. I n Table I are listed the compounds which have been detected in carbon tetrachloride solution
Table tected
I.
Phosphorus Compounds Deby Sulfuric Acid-Dianisidine Molybdate Method
Detection Limit, Compound Tributyl phoPphate O,O,S-triethyl phosphorodithioate Tri-p-told phosphate O,O,O-tri"-rn-toi)-l phosphorothionate Malathion" Tetraethyl pyrophosphate Trimethyl phosphite Trihexyl phosphite Triphenyl phosphite Phenylphosphonic grid
Y
PO4
Equiv., Y
2
07
1 2
0 4 0 5
2 2
0 5 0 6
1 1 1
0; 0.8 0 6 0 3
1
0.6
2
Diethyl 1.7 ethylphosphonate 3* Dibutyl 2 0.8 butylphosphonate Bis-(2-ethylhexy1)P-ethylhexyl2 0 5 phosphonate 0 7 Phenylphosphinicacid 0.5 10 15d Sarinc a 0,O-Dimethyl phosphorodithioate of diethyl mercaptosuccinate. * Mercuric sulfate required; sensitivity, 10 t o 15 y with no catalyst. c Isopropyl methylphosphonofluoridate. d Mercuric sulfate required; sensitivity, 30 t o 60 y with no catalyst.
by this method. Those compounds which required a catalyst are specifically noted. The sensitivity of the o-dianisidine molybdate reagent for phosphate ion is known to be 0.3 t o 0.5 y. It is apparent that the majority of the orgaiiic phosphorus compounds were efficiently converted to phosphate by the above procedure. ?Vith compounds containing phohphorus bound only t o oxygen or sulfur atoms, the volatility of the unknown has little effect on the test sensitivity. Trimethyl phosphite, for example, boils a t 111-12" C., or 230" below the reflux temperature of sulfuric acid, and it might have been expected to escape before it could be degraded to less volatile acids. The phosphites, phosphates, and their thio analogs were easily decomposed. Compounds containing a carbon-tophosphorus bond were much less reactive, however, and their volatility became a factor in determining test sensitivity. Thus, sarin, which boils a t about 150" C., gave tests of rather poor sensitivity, even with mercuric sulfate present. Diethyl ethylphosphonate, boiling point 200" C. (130" less than the reflux temperature of sulfuric acid) , gare sensitive tests, but only with the catalyst present. Dibutyl butylphosphonate and other less \-ohtile phosphonates were efficiently deVOL. 29, NO. 6: JUNE 1957
* 875
composed and detected with or without a catalyst. IXTERFCRENCES. If the sample contains amounts of extraneous organic matter, heating i t with the sulfuric acid will cause excessive carbon formation which obscures the test. Also, the sulfuric acid consumed in oxidizing such excess organic material can be considerable, and this causes a change in the final p H obtained after addition of the carbonate-formate solution. The o-dianisidine molybdate reagent cannot be used a t a p H much above 7 without giying cloudy, green blanks. Of the relatively few interferences which Itrest and Robinson encountered in detecting inorganic phosphates, several of the most important are eliminated by the sulfuric acid digestion employed here. For esample, inorganic and organic sulfides n-ere completely removed. Silicon compounds yielded an inert, dehydrated film of silica n-hich was invisible in the test tube while w t . Inorganic nitrites and nitrates interfered by giving a cloudy red color, but 1% isoamyl nitrite in carbon tetrachloride showed no interference. Organic nitrogen conipounds containing nitro, azo, or amino groups also were without effect. The procedure avoids direct heating of the sulfuric acid while carbon tetrachloride is present, as this generates phosgene and consumes acid. When the test was run on silica gel samples, the moisture contained in the gel caused volatilization of some of the sulfuric acid as the hydrated acid. A less concentrated base-buffer solution was therefore used. Hydrocarbon solvents cannot be used for the sample, as their vapors are charred by hot, concentrated sulfuric acid. A suitable solvent that can be used in place of carbon tetrachloride is 1 , l - dichloro - 2 , 2 - difluoroethane. APPLIC.4TIoX T O A I R AXALYSIS. It mas of interest to demonstrate not only the sensitivity of the test to samples adsorbed on silica gel, but also the efficiency with rrhich silica gel collects vapors of phosphorus compounds from air. Trimethyl phosphite was selected as the substance to be detected because it has a fairly low boiling point (111-12" C.), and also because its vapor pressure is known (3) a t 1%-idelydifferent temperatures. The silica gel tubes used to collect the samples were 2 mm. in inside diameter and contained a n 0.8-em. column of the fine granular gel (60 mesh). The synthetic gas niistures were prepared by bubbling filtered air through carbon tetrachloride solutions of the trimethyl phosphite a t room temperature (30" C.), the saturated vapor then being passed through a silica gel tube. After 3 ml. of the original 7 ml. of solution had been vaporized (30 to 45
876
ANALYTICAL CHEMISTRY
minutes), the silica gel was transferred to a test tube and the above test was run (without catalyst). Positive tests were obtained 1% ith carbon tetrachloride solutions containing as little as 3 y per ml. of trimethyl phosphite in the original solution. Blanks run on the entire procedure were negative. The vapor pressure of the ester was estimated to be 37 mm. a t 30" C., the known data for it being similar to that for toluene. Assuming the solutions to be ideal, the ratio of phosphite to carbon tetrachloride in the vapor was 0.26 of t h a t in the liquid. The procedure detected 3 y of trimethyl phosphite in 4.1 liters of air-carbon tetrachloride mixture (19yo carbon tetrachloride by volume). The fact t h a t such small silica gel tubes vere able to strip microgram quantities of the phosphite from the gas mixture may indicate that most organic phosphorus compounds can be similarly collected. The difference in boiling point between the phosphite and carbon tetrachloride is only 35" C., and it is possible their adsorption affinities for silica gel do not differ by a large factor. It is remarkable that the gaseous carbon tetrachloride did not elute the trimethyl phosphite from the silica gel. The majority of organic phosphorus compounds are much less volatile than the phosphite, and should be adsorbed even more efficiently. It is also evident that the detection method is sensitive to phosphoruscontaining adsorbates on silica gel. Sulfuric Acid-Hydrazine Molybdate, Method B. Although West and Robinson found i t advantageous t o add 85% hydrazine hydrate t o t h e precipitate obtained from o-dianisidine molybdate and inorganic phosphate, the blanks obtained in the present tests were unsatisfactory when tliis was done. However, the reduction of phosphomolybdic acid by hydrazine to give molybdenum blue can be carried out on a separate sample which has been digested with sulfuric acid, and this may s e n e as a useful confirmatory test. The heteropoly blue test is well known ( I ) , but its application in the follon-ing way is novel, and comparison of its characteristics with those of other tests is of interest. REAGENTS. Sulfuric acid, 96%. Sodium carbonate-acetic acid-hydrazine solution: 17.0y0sodium carbonate (anhydrous), 0.85% hydrazine monohydrate, 2.3% acetic acid, freshly made. Sodium molybdate solution: 3.00y0 sodium molybdate dihydrate. The droppers used to deliver all these reagents are prepared as described before. PROCEDURE. I n the bottom of a Pyrex S o . 7740 test tube, 3 X 3/8 inches, is placed 1 drop of sulfuric acid
and 1 to 20 drop3 of the unknoiyii in carbon tetrachloride solution. The sohent evaporation, digestion, and cooling are carried out as before. Three drops of the carbonate-acetate-hydrazirie solution are added, taking the usual care in mixing. Then 1 drop of molybdate solution is added. The solution turns hlue within 1 minute if phosphorus compounds are present. The color is best, seen if the liquid is poured onto a white spot plate. The blank remains practically colorless. SFSSITIVITY. Mercuric sulfate cannot be used as a catalyst in the digestion as it gives a gray precipitate nith the hydrazine and molybdate. The test, therefore, applies to compounds nhich do not require a catalyst. The sensitivity to tributyl phosphate, O,O,Striethyl phosphorodithioate, and phenylphosphonic acid was two to four h i e s that of the method using o-dianisidine molybdate reagent. INTERFERENCES. Excessive amounts of organic matter will interfere as mentioned previously. The heteropoly blue test is considerably less selective than the o-dianisidine molybdate reagent. Arsenic compounds give a positive test when in sufficiently high concentration. As much as 100 y of triphenylarsine can be tolerated, hon-ever. KO interference occurs from silicon compounds, which are decomposed by the digestion process as mentioned previously. Sodium Perborate-Dianisidine Molybdate, Method C. FORACIDS, ACYLHALIDES, AND d X H Y D R l D E S CONTAINIXG PHOSPHORUS. Organic phosphorus coinpounds may, if desired, be divided into subclasses based on their chemical properties. One such subgroup is composed of acids, alkyl or aryl acid esters, salts, and very readily hydrolyzed acyl derivatives. These are converted by alkaline sodium perborate solution into nonvolatile salts which are readily degraded to sodium phosphate by strong heating with excess perborate. The o-dianisidine molybdate reagent can then be added directly without the neutralization and buffering required in the preceding methods.
REAGESTS.Sodium perborate, 1% aqueous, freshly made. o-Dianisidine molybdate reagent, diluted to half the strength used in l\lethod A. Dropper. of ordinary size are satisfactory, a9 the dilution factor is small in this method. PROCEDURK;. I n the bottom of a Pyrex To. 7740 test tube, 3 X inches, is placed 1 drop of perborate solution and 1 to 20 drops of the sample in a volatile solvent such as water, isopropyl alcohol, or carbon tetrachloride. The tube is warmed along its length to drive off the solvents (45 seconds). The small amount of white residue is heated strongly oyer a flanie until it dis-
-
Table 11. Phosphorus Compounds Detected by Sodium PerborateDianisidine Molybdate Method
Detection Limit,
PO, EqUlv.,
Compoiind 1 Sarin 0.5 0 3 Phenylphosphonic acid 1 O B Tetraethyl pyrophos1 phate 0 7 Octylphenyl acid phosphaten 5 1 4 Phenylphosphonot hionic dichloride 1 0 5 4 1 3 Parathionb O,O,S-triethyl -12 0 phosphorodithioate 80 Tributyl phosphate 200 72 0 a Mixture of mono- and diary1 acid phosphates, approximately equimolar. 0,O-Diethyl-0-p-nitrophenyl phosphorothionate. The liquid mixture should be boiled for 45 seconds before solvents ale driven off t o ensure complete hydrolysis.
appears (30 seconds). The tube is aircooled by being waved vigorously (20 seconds), and then the bottom half is water-cooled (10 seconds). Two drops of dianisidine molybdate reagent are added. 4 reddish-brown precipitate indicates the presence of phosphorus compounds. At microgram concentrations it can be viewed as a light cloudiness against a black background. The test appears within 30 seconds. SENSITIVITY.The compounds studied by this method are listed in Table 11. I n the detection of sarin, a nerve gas which is more volatile than most of the conipounds studied, this method was far superior to Methods A and B. With
other members of this subgroup, the sensitivity equaled t h a t of Method A. With difficultly hydrolyzed compounds such as esters, it tvas ineffective. Requiring only two reagents, i t is the most convenient method where applicable. IKTERFERENCES. The method does not permit the presence of a large excess of organic matter n-hich is likely to be carbonized and obscure the test. Most of the interferences observed by West and Robinson in detecting inorganic phosphate are observed here. The test tolerated as much as 230 y of sodium metasilicate; more than this gave a positive reaction. The use of dianisidiiie molybdate reagent a t full strength caused cloudiness in the blanks. Apparently this was due to a reaction with sodium borate. DISCUSSION
The best test for organic phosphorus compounds t h a t has been previously described appears t o be t h a t of Feigl (W), in which the u n k n o m is ignited with calcium oxide a t red heat, and the resulting calcium phosphate is detected by the benzidine molybdate method. The procedure requires five reagents, a considerable amount of time, and is said to apply to nonvolatile compounds only. Where it is applicable, its sensitivity approximately equals t h a t of the tests which utilize o-dianisidine molybdate. Calcium oxide as a degradative reagent is relatively ineffective because it is not an oxidant or even a strong base. The Feigl test relies on conversion of the phosphorus compound to a salt before the unknown escapes through
volatilization. The salt can then be ignited strongly and air-oxidized to calcium phosphate. The types of compounds that will give salts in this way are about the same as those to nhicli Method C is applicable: acids, acyl halides, and anhydrides. It is unlikely t h a t trialkyl phosphates, dialkyl alkylphosphonates, or many of their thio analogs would respond. Method A appears to be the niobt general one now available for organic compounds of phosphorus, and is also the most selective with respect to other hetero-elements (4). Method B is most sensitive, while Method C is the most convenient and selective for acids and easily hydrolyzed acyl derivatives. All three methods are much more nearly independent of the volatility of the unknon-n than previously described procedures. ACKNOWLEDGMENT
This work has been sponsored by t h r United States Army Chemical Corps, whose technical advice and permission for publication are appreciated by the authors. LITERATURE CITED
(1) Boltz, D. F., hIellon, RI. G I . ~ N A L CHEM 19,873 (1947). (2) Feigl, F., “Spot Tests,” 4th ed , 5’01. 2 , p. 77, Elsevier, Sew Tork,
1954.
G. A1 , “Organophosphorus Compounds,” p. 203, Kiley, Yew York, 1950. (4) Robinson, J. IT., West, P. W , in press. (3) Kosolapoff,
RECEIVEDfor review December 7, 1956. Accepted February 18, 1957.
Detection of Nerve Gases by Chemiluminescence JEROME GOLDENSON Chemical Corps Chemical Warfare laboratories, Army Chemical Center,
b Nerve gases can b e detected by the chemiluminescence produced in the presence of a solution containing 5amino 2,3 dihydro 1,4 phthalazinedione (luminol) and sodium perborate; 0.5 y of nerve gas can be readily detected. A plot reasonably close to a straight line was obtained when the amounts of nerve gas were plotted against the maximum luminosity values, indicating that the reaction may also b e used for quantitative purposes. The most promising potential use indicated for the reaction is the applica-
-
-
-
-
Md.
tion to continuous automatic sampling of the atmosphere.
D
have been given of specific colorimetric ( 2 ) and fluorescence (3)reactions suitable for the detection and determination of the nerve gases which are organic pentavalent phosphorus compounds having structures either of the type R(R’O)(PO)F or (R2N)(R’O)(PO)CS (4, 8) with very reactive P-F or P-CN linkages. These reactions are outlined in Table I. -4 paper indicator test described ESCRIPTIONS
in a German report (10) has come to be known as the Schonemann reaction. It was based on the oxidation of otolidine to a colored substance by alkaline peroxide in the presence of the nerve gas. A greatly improved reaction based on the use of o-dianisidine was devrloped by Gehauf and others ( 2 ) . It had the desired specificity and a sensitivity comparable t o the best colorimetric methods, but it was realized t h a t a new order of sensitivity would be needed to meet some of the problems imposed by the high toxicity and rapid VOL. 2 9 , NO. 6, JUNE 1957
877
