ciuded ligands whose donor atoms were oxygen, nitrogen, sulfur, phosphorus, and arsenic. Triphenylphosphine, trip henyiarsine, and tri(pto1yI)thiophosphate were insoluble in water and formed precipitates when their alcoholic solutions were added to the a.queous Hg12/KIsolutions. Determination of the mercury(II1 in the filtrates from the above solutions yielded erratic results. The erratic results were possibly due to failure to remove consistently the finely divided precipitate; however, the low results (Table V) found for triphenylphosphine are probably due to the formation of an insoluble complex with mercury(I1) iodide (7). Ligands containing nitrogen or oxygen donor atoms did not interfere with .the determination of mercury(I1) (Table V) when present at concentations of 2 X 10-4M or less. Thioacetamide, which is a sulfur donor ligand, did not interfere at 1 y IO-'M or less but caused a slight positive interference Increased interference by sulfur donor at 2 X IO-". ligands would be expected since mercury(I1) has a greater tendency to coordinate with sulfur than with nitrogen or oxygen (8). The large errors in the determination of mercury(I1) when N,N-dimethyldithiooxamidewas present were due, in part, to the yellow color of the ligand but could also reflect the greater stability of complexes involving chelate ligands. In summation, spectrophotometric measurement in 1.OM aqueous potassium iodide provides a relatively simple and iapld means of determining mercury(I1) in inorganic compounds. The method can provide analyses with a probable error of 1.3z.The insensitivity of the determination to changes in the pH 3f the solution and to changes in the iodide (7) R. C . Man, H. S . Peiser, and D. Purdie, J. Chem. SOC.,1940, iX)
i 209. F. 4.
Cotton and G. Wilkenson, "Advanced Inorganic Chem-
'stry," 1st Ed., Interscience, New York, 1962, p. 488.
Table V. Determination of Mercury(II) in the Presence of Neutral Donor Ligands (Ligand Concentratration = 2 X lo-* M ) [Hg+7 X 10' Ligand Added Founds Error, 9.60 9.56 -0.4 Urea 9.60 9.56 -0.4 Ethylenediamine 9.60 9.56 -0.4 Triethylenetetraamine 9.60 9.54 -0.4 Acetamide Thioacetamide 9.60 9.89 $3.0 Pyridine-N-oxide 9.60 9.56 -0.4 Ethylenediaminetetraacetic acid 9.60 9.52 -0.8 N,N-dimethyldithiooxamide 9.60 22.3 ... Triphenylphosphine 20.9 1 .o Triphen ylarsine 20.9 23.0 .". 20.9 43.9 ... Tri-ptolylthiophosphate a Each value is the average of two or more samples made from the same mercury(I1) stock solution. .
I
.
ion concentration gieatly simplifiesthe preparation of reagents. This method is suitable for the determination of mercury(I1) in the presence of a variety of extraneous species. However, the method should be most useful for the determination of rnercury(I1) in the presence of halide and pseudohalide (except cyanide) ions which severely interfered with the previously reported methods. ACKNOWLEDGMENT
We are indebted to Marshall Moorman and Douglas Gegen for the preparation of many of the solutions used in this investigation. RECEIVED for review January 1, 1967. Accepted March 13, 1967.
Spectrophotometric Determination of Primary Aromatic Amines with Thiotrithiazyl Chloride Application to Determination of Toluene-2,4-diisocyanate in Air Vaughn Levin, 8 ,W. Niopoldt, and R. E. Rebertus ','miral
Research Laboruiorks, Minnesota Mining and Manujacturing Co., St. Paul, Minn.
Yighiy coiored intermediates form during the reactions thiotrithiazyi chloriae with some primary aromatic amines. Tne molar absorptivities range from about X C O O !iters molt!-1 cm-1 for the red product from m,)henylenediamirie to about 300 liters mole-' cm-' or the green product from aniline. Rapid color d~veiopmenti s xhieved at room temperature either 3 v direct combination of solid thiotrithiazyl chloride with a solution cjf the amine in methanol-chloroform, or by percolating the amine solution over a bed of thiotrithiazyl chloride mixed with dry sand. Although the colorea species generally decompose within a few mindes, iinear calibration curves are readily obtained by antroiling reaction conditions. These observations w v e been applied to the determination of airborne taluene-2,4-diisocyanate d t concentrations as IQW as 9.01 ppm by volume. df
THEREACTIONof undiluted organic amines with thiotrithiazyl chloride (S4N3+CI-)to give highly colored products has been reported by Cohen, Kent, MacDiarrnid, and Marcantonio ( I ) . Although MacDiarmid (2) has qualitatively tested for thiotrithiazyl ion with aniline, there are no reported examples of the determination of amines with thiotrithiazyl chloride. In this paper we describe a new spectrophotometric method for determining small quantities of some primary aromatic amines with thiotrithiazyl chloride. The sens1tiv:ty of the (1) M. E. Cohen,
R. A. Kent, A. G. MacDiarmid, and N. H. ,Marcantonio, U. S. Depf. Comm., Ogfce Tech. Serc. P B Repf., 161,883(1960).
(2) A. G.
MacQiarmid, J . Am. Chem. Soc., 78, 3871 (1956). VQL 39, NO. 6, MAY 1967
581
method applied to certain diamines rivals that of the commonly used diazotization-coupling procedures (3). The simplicity permits specialized applications such as a field test which is also described. for airborne toluene-2,4-diisocyanate,
0.6
EXPERIMENTAL
Apparatus. Spectra and absorbance measurements were made with a Cary Recording Spectrophotometer, Model 11, and a Beckman Grating Spectrophotometer, Model DB-G. Matched cells with a 1-cm optical path were used. A constant flow Uni-Jet Air Sampler was used to collect air samples. Reagents and Chemicals. o-Phenylenediamine, pphenylenediamine, and toluene-2,4-diamine, all practical grade, were obtained from Eastman Kodak Co. Practical grade rnphenylenediamine and 4,4’-niethylenedianiline were obtained from the Matheson Co., and reagent grade aniline was obtained from Merck & Co., Inc. Fresh stock solutions were prepared daily by dissolving weighed amounts of the amines in chloroform. Standard solutions containing from 0.2 to 200 pg of amine per rnl in 10% (v/v) methanokhloroform were prepared from the stock solutions. Similarly, standard solutions containing from 0.1 to 1.0 pg/ml of toluene-2,4diamine in 0.01Nhydrochloric acid were prepared by dilution of more concentrated solutions. Thiotrithiazyl chloride was prepared from tetrasulfur tetranitride (4) and acetyl chloride by the method of MacDiarmid ( 2 ) modified such that the proportion of acetyl chloride was increased tenfold. The product so obtained was a bright yellow powder. Two batches, m.p. 183-6’ and 1856” C, were analyzed by the ultraviolet spectrophotometric and the calmethod of Johnson, Blyholder, and Cordes (3, culated molar absorptivities were in good agreement with their results. The two batches behaved the same in their reactions with the primary aromatic amines. A column packing was prepared by dry mixing 0.2 thiotrithiazyl chloride with washed, ignited sand obtained from G . T. Walker and Co., Inc. Before mixing, however, the sand was sieved to a particle size of 40-100 mesh, washed with benzene, chloroform, methanol, and water, and dried in vacuum at room temperature. Procedure for Determining Primary Aromatic Amines. Two methods of combining the standard amine solutions and the thiotrithiazyl salt were employed, namely, a columnar operation and direct mixing. A 5- X 50-mm column was dry packed with the thiotrithiazyl chloride-sand mixture supported by a small glass wool plug. The column was attached to a 10-ml hypodermic syringe body with a short piece of latex tubing stopped with a pinch clamp. Five milliliters of a standard solution containing 0.2,0.5, 1,2, 5, or 10 pg/ml of toluene-2,4-diamine or rn-phenylenediamine in 10% (v/v) methanol-chloroform was placed in the syringe body. The plunger was inserted, the pinch clamp released, and the solution forced rapidly through the column (about 300 cm min-I). The optical cell was filled after discarding the first two bed volumes of effluent, and the absorbance at 525 mp was recorded as a function of time for about 2 minutes. The value at zero time was determined by linear extrapolation of that portion of the curve having the greatest slope (see Figure 1). Solutions containing from 5 to 200 pg/ml of aniline and 4,4’-methylenedianiline were analyzed similarly, but the flow rate through the bed was reduced to about 15 cm min-1 and the absorbance recorded at 630 mp. The direct mixing method was applied to the determination
2 v)
sf
0.4
c 0
0
0
c
P
e % a
n
0.2
t0
2 Time, minutes
4
Figure 1. Extrapolated absorbance-time curves for various concentrations of toluene3,4-diamine reacted with thiotrithiazyl chloride Reproducibility illustrated by depicting three curves for each concentration
of p- and o-phenylenediamine. Four milligrams of thiotrithiazyl chloride was added to 100 ml of a standard p phenylenediamine solution containing 2, 5 , 10, or 20 pg/ml. After stirring for 2 minutes, the absorbance at 495 mp was measured. Standard solutions containing 10, 20, 50, and 100 pg/ml of o-phenylenediamine were analyzed similarly, but the quantity of thiotrithiazyl chloride was increased to 20 mg and the absorbance measured at 630 mp. Absorbance measurements were corrected for reagent blanks in both the columnar and direct addition procedures. Absorption maxima were determined by rapid scanning techniques. Procedure for Determining Toluene-2,4-diisocyanate in Air. Air containing toluene-2,4-diisocyanate was bubbled through 10 ml of 0.01N hydrochloric acid at a flow rate of 2.83 liters/ min for 10 minutes. The solution was made basic (pH 10-11) with a few drops of 10 sodium carbonate solution and extracted for 2 minutes with 1.0 ml of chloroform. About 0.5 ml of the extract was added to approximately 0.1 mg of solid thiotrithiazyl chloride on a spot plate. Two drops of methanol was added and the mixture was stirred. The red color produced was visually compared with a series of colored paper strips which had been calibrated by comparison with the colors produced from similarly treated standard solutions of toluene-2,4-diamine (dihydrochloride) in 0.01N hydrochloric acid. The concentration of toluene-2,4-diisocyanate in the air sample was calculated from the relation:
CRTV MS
Toluene-2,4-diisocyanate,ppm by volume = -= 0.07C (3) S. Siggia, “Quantitative Organic Analysis,” 3rd ed., Wiley, New York, 1963, p. 511. (4) M. Villena-Blanco, M. S. Thesis, University of California, Berkeley, Calif., 1963. ( 5 ) D. A. Johnson, G. D. Blyholder, and A. W. Cordes, fnorg. Chem., 4,1790(1965).
582
0
ANALYTICAL CHEMISTRY
where concentration of toluene-2,4-diamine in the 0.01N HC1 solution, pg/ml, determined by color comparison R = gas constant, atm liter mole-’ O K-’
C
=
T = temperature of air sample, K M = molecular weight of toluene-2,4-diamine S = sample vol.ume, liter of air V = volume of 0.01NHC1 solution, ml. O
RESULTS AND DISCUSSION Conditions for Color Development. Because thiotrithiazyl chloride undergoes rapid solvolysis in nearly all solvents except some concentrated acids (3, the rate of formation of the colored product must be competitive. Thus, color develops in only a few solvents, particularly the lower alcohols with or without dilution with chloroform. Of the systems tested, 10 (v/v) methanol-chloroform was optimal. Decomposition of the thiotrithiazyl chloride is further minimized by adding it lastly a!; a solid. Color formation then occurs heterogeneously near the solid-liquid interface before solvolysis destroys the rea.gent, which necessitates continuous agitation during this step. The rate of color formation for the primary aromatic amines examined decreases in the order: o-phenylenediamine E p-phenylenediamine > m-phenylenediamine toluene2,4-diamine > 4,4’-methylenedianiline ”= aniline. Thus, a solution containing only a slight molar excess of thiotrithiazyl chloride and eith.er o- or p-phenylenediamine exhibits a maximal absorbance within a few minutes. Furthermore, the maximal absorptivities were achieved under these conditions because the solvolysis products of any additional thiotrithiazyl chloride rapidly destroy the colored species. Color development with m-phenylenediamine and toluene2,4-diamine requires a considerable molar excess of thiotrithiazyl chloride. The reagent is efficiently supplied in a columnar operation whereby a relatively small volume of solution of the amine in the methanol-chloroform solvent is percolated over a bed of solid thiotrithiazyl chloride mixed with dry sand. Loadings of the reagent ranging from 0.04 to 0 . 4 z were tested, and it was found that the 0 . 2 z level is optimal for concentrations of toluene-2,4-diamine ranging from 0.5 to 5.0 pg;/ml. If the sand is activated by ignition prior to mixing, high and erratic blanks result, and decreased absorbances are obtained for the toluene-2,4-diamine samples. Treating the sand with water and drying it at room temperature corrects these difficulties. Although the colored species produced in the columnar operation decompose very rapidly, nearly linear calibration curves and repeatable limiting absorptivities are obtained by extrapolating the color decay curves. Alternatively, the cell solution may be cooled to -50” C, at which temperature the colors are stable for several hours. The columnar operation is also applicable to 4,4 ’methylenedianiline and aniline, but a much slower flow rate must be used. Spectrophotometric Data. The absorption maxima and extrapolated molar absorptivities of the reaction products of the primary aromiitic amines studied are listed in Table I. The molar absorptivities were calculated based upon the assumption that ea’chamine produces an equimolar amount of colored compound. The standard deviations of the molar absorptivities were calculated from data obtained at various amine concentrations within the ranges given. Thus, the precision of the molar absorptivity indicates the degree of linearity of the calibration curve. From a practicai. standpoint, the use of thiotrithiazyl chloride appears to be best suited to the determination of metasubstituted diamines. The highest molar absorptivities are obtained for the products from m-phenylenediamine (e = 21,500) and toluen.e-2,4-diamine (e = 16,000). In addition, calibration curves for these compounds deviate less from
z
Table I. Spectrophotometric Properties of Reaction Products of Some Primary Aromatic Amines with Thiotrithiazyl Chloride Concen€ Approx. tration h (extrapolated), halflife, range, max., liter mole-’ mLc cmmin Amine PEW Aniline 10-200 630 300 =t50 0.7 +Phenylenediamine 10-100 590 300 f 50 ... 4,4 ‘-Methylene&aniline 5-200 630 1,200 f 100 2.0 1-Naphthylamine 2-50 560 3,000 5.0 pphenylenediamine 1-20 495 6,000 f. 1000 10.0 Toluene2,Cdiamine 0.2-5 525 16,000f 350 2.5 rn-Phenylenediamine 0.2-5 525 21,5003~1800 1.5
linearity. Finally, color development is conveniently accomplished within a few seconds by the columnar technique. None of the formulas of the colored species has been established. The complexity of these reactions is illustrated by the fact that o-phenylenediamine yields a green product (as do aniline and 4,4’-methylenedianiline), m-phenylenediamine yields a red product (as does toluene-2,4-diamine), and pphenylenediamine first forms a green product which irnmediately turns red-orange. Examination of a solution of the product from m-phenylenediamine by ESR spectroscopy gave no evidence of the presence of free radicals. The red-orange product from p-phenylenediamine is isolable at room temperature and amenable to further study. Some mixtures of the aromatic diamines cannot be analyzed straightforwardly by this method. For example, equimolar quantities of m- and p-phenylenediamine interact in the presence of oxidizing agents including thiotrithiazyl chloride to form a relatively stable blue product. This species, which results from an overall four-electron oxidation, is probably an indamine-type cationic dye closely related to Toluylene Blue (6). Thus, when thiotrithiazyl chloride is allowed to react with a methanol-chloroform solution of m- and p-phenylenediamine, the blue product forms preferentially to the products from the individual diamines in a quantity limited by the diamine of lower concentration. The excess of the other diamine reacts in the manner predicted from the data given in Table I. Mixtures of toluene-2,4-diamine and p-phenylenediamine behave similarly. Application to Determination of Airborne Toluene-2,4-Diisocyanate. Because thiotrithiazyl chloride shows relatively high sensitivity for toluene-2,4-diamine, it is of interest to apply this reaction to the determination of airborne toluene2,4diisocyanate, which has been assigned a threshold limit value of 0.02 ppm by volume (7). Aqueous solution is required to hydrolyze the diisocyanate to the diamine, but no color development with thiotrithiazyl ion occurs in water. Therefore, the aqueous solution is neutralized and extracted with chloroform. The distribution coefficient of toluene-2,4diamine between aqueous basic solution and chloroform (C~HCIJCH.O,OH-) is about 2.8. Normal color development occurs after the extract is treated with methanol and solid thiotrithiazyl chloride.
H.A. Lubs, “The Chemistry of Synthetic Dyes and Pigments,” Reinhold, New York, 1955, p. 237. (7) “Threshold Limit Values for 1965,” American Conference of Governmental Industrial Hygienists, p. 15, 1965. (6)
VOL 39, NO. 6, MAY 1967
583
Three air samples analyzed spectrophotometrically by the established diazotization-coupling method (8) contained 0.03, 0.01, and less than 0.01 ppm (by volume) toluene diisocyanate. A duplicate set of air samples taken simultaneously was analyzed by the thiotrithiazyl chloride method, and corresponding values of 0.03, 0.02, and less than 0.01 ppm, respectively, were obtained. Although the sensitivities of the two methods are about the same, the procedure employing (8) K. Marc3li, ANAL.CHEM., 29,552 (1957).
thiotrithiazyi chloride is somewhat simpler and is reiatively specific for meta-substituted diamines and diisocyanateo. Thus, an equimolar quantity of aniline does not interfere i * the determination of toluene-2,4-diisocyanatewith thi: trithiazyl chloride, whereas this interference in the diazotization-coupling method leads to a positive error of approximately 5 to 10 %. RECEIVED for review December 23, 1966. Accepted February 20,1967.
Precision and Accuracy in Trace Element Analysis of Geological Materials Using Solid Source Spark Mass Spectrography G . D. Nicholls, A. L. Graham, Elizabeth Williams, and Margaret Wood Department of Geology, University of Manchester, Manchester 13, England Investigations are described which have led to the development of procedures which yield a precision of better than +5% in solid source spark mass spectrographic analysis of geological and similar materials. The accuracy of the results obtained is thought to be within the limits of the precision, and analyses using this technique give results as reliable as other techniques of trace element analysis. The major change from the usually adopted procedures is in the method of electrode preparation, though other minor changes must also be made if maximum precision and accuracy are to be attained. In view of the very wide range of elements that can be determined and the high sensitivity of this technique, adoption of the procedures described makes solid source mass spectrography an extremely important method of trace element analysis.
GEOCHEMISTS have long been aware of the limitations imposed on their studies by the limits of sensitivity of many of those currently available analytical methods which permit a number of elements to be determined in one sample, e.g. optical emission spectrographic techniques, x-ray fluorescence analysis. ‘I’his had led, on the one hand, to the development of prearcing concentration techniques in optical emission spectrography (1,2) and on the other, to the adoption of more sensitive methods for a restricted number of elements, e.g. nuclear activation techniques. More recently, solid source spark mass Spectrography has been investigated as a possible analytical technique in geochemistry (3-5). This technique is highly sensitive and permits the simultaneous determination of a wide range of elements, including many whose geochemical distribution is still imperfectly known. Pioneer appiications of this technique to the analysis of geological materials led to suspicions that it lacked the accuracy and precision necessary for high quality geochemical investiga-
(1) D. M. Hint and G . D. Nicolls, J . Sediment. Petrol., 28, 4% (1 958). (2, R. K. Brooks, L. H. Ahrens, and S. R. Taylor, Geochim Cosmochim. Acta, 18, 162 11960) (3) K. Brown and W. A. Wolstenholrne, Nature (London), 201. 5Y1r (1 964). (4) S R. Taylor, Ibid., ZQ5, 34 (1965). ( 5 ) S. R. Taylor, Geochim. Cosmochim. Acta, 29, 1243 (1965).
584
e
ANALYTICAL CHEMISTRY
tions, and to expression of opinion that the technique is no: suited to such work. Such suspicions are quite unfounded and procedures have been evolved which yield an accu:a:y and precision comparable with, or better than, most of t h ~ other techniques available. These procedures are described in this paper, together with the reasons for adopting them, since if these reasons are fully understood there should be no difficulty in applying this generai technique for the analysis cf geological materials to more specific cases in allied analytical fields, e.g. analysis of semi-conductor materials. EXPERIMENTAL
The instrument used in this work was an Associated Elel.tricai Industries Limited M.S.7. mass spectrograph. General descriptions of this instrument nave been given by severci workers (5-7). Electrodes were prepared by compressip mixtures of the sample under analysis and RingsdorffwerKc RWA grade graphite in an electrode-forming die f8, unde: y. pressure of 7500 psi. Operating pressures in the anaiyzer region of the instrument were in the range to IO-’ torr and in the source region i X to 5 X torr. Fifteer graded exposures of the spectrum from a sample. were recorded polarographically on Ilford 4 2 plates, which were sub. sequendy processed according to the manufacturer instructions. In the approach adopted here to this method o i anaiys:: a basic equation can be written, viz, C E = CS
x
l%PS/hpE
x
IS/IE
>: 1/R
!I
where content of elemen: E in electrode analyzed, (in atomic parts per million) CL3 = content of a second element (9,e.g. an inrerna: standard element, (in atomic parts per millionj CE
=
( 6 ) R. D. Craig, G. A. Erroch, ana j. D. Waldron, Adwn. Musi Spectrometry, 1, 136 (19%; (n R. W. Brown, R. D. Crag, ana R. M. Elliot, Ibid., 2, l i l (1962). (8) R Brown and W. A. Woistenhoime, Roc. Eleventh Con’*
A.S.T.M. Comm. E14 (196%
