in greater accuracy as well as saving time. Howevrr, to prevent tho formation of volatile nitrosyl chloride (9,6 ) the sample should be treatcd with the silver solution before adding the sulfuric acid. Nitrite, when present, can hi effectively removed by adding a small amount of 1% sulfamic acid to the sample a frw minutes before adding the sulfuric acid. The suggested use ( 4 ) of 20% sulfamic acid should be avoided since Cupery (1) claimed that sulfamic acid also reacts with nitric acid giving rise to nitrous oxide. This reaction may occur in strong solutions but has not bcrn noted when dilute solutions are employed. The addition of 1 ml. of 1% sulfamic acid completely removes up to 1 mg. of nitrite nitrogen from the sample without affecting thc recovery of nitrate. Hollrr and Huch (4) noted interference from hydrogen peroxide and recommended preliminaky treatment
with 0.6% potassium perrnniig:innbc solution. Under thew conditions nitrite, if present, is quantitatively oxidized to nitrate 80 large errors can be incurred unless this fact is recognised. Interference from Organic Material. Reduced recoveries of nitrate can occur if any organic compound capable of undergoing nitration is present in the solution to be analymd. I n this case, the nitric acid. liberated will be used t o nitrate, a t least partially, the organic compound concerned, leaving a reduced amount of nitric acid available for the formation of volatile nitroxylenol. Such a case was encountered during trials using toluene to prevent biological formation of nitrate during storage of moist soil. Toluene in solution in the aqurous extract used for nitrate analysis caused extensive reduction in the recovery of nitrate. The nitrotoluene formed is not volatile in steam, so the loss of nitrate is absolute and can be substantial. Thus
if the solution to be analysed for nitrate contains soluble or peptized organic material which can be nitrated, this organic material should be removed before analysis is attempted. Soil organic matter can be removed readily by coprecipitation with aluminum or copper hydroxide as suggested by Harper (9). LITERATURE CITED
(1) Cupery, M. E., Znd. Eng. Ckm. 30,
(2)@%!:$38k
1088 I rkmi:
BuU.
doc.
chim. France 5,
(3) &;per kL J., Ind. By. Chem. 16, 180 (1924) (4) Holler, A. C., Huch, It. V., ANAL. C€IEM. 21, 1386 (1948). (6) Lombard, M.,Lafore, J., Bull. doc. I
dim. France 5, 321 (1909).
D. G . Lmwxe
Department of A ricultural Cbemiatry Waite Agricultura Reaearch f n ~ t i b ~ t o University of Adelaide, 8outh Auotralis
Spectrophotometric Determination of Thallium in Zinc and Cadmium with Rhodamine 6 SIR: Previous work on the drtermination of thallium with rhodanune B has not given an adequate discussion of either the solution conditions or the possible interferences from other ions (2). Woolley ( 4 ) has reported a method of wide applicability which employs a prior extraction of the bromothallate(II1) ion into isopropyl ether. The usefulness of this procedure was limited because neither the permissible ranges of solution conditions (particularly HBr concentration) nor the interferences of specific metallic elementa were given, The present investigation of the application of this method to zinc and cadmium metals shows that, a t lcast for such samples, the HBr concentration should be 1.ON or higher. A mixture of H280, and HBr is more convenient for dissolving zinc and cadmium than the HBr-Brp solvent employed by Woollcy for tin-cadmium alloys. Tho addition of Ce(S04), ensurcs that the thallium is present as TI(II1). Specific interference data arc givcn for the conditions specifird in the prcsrnt proredure.
tional 6 ml. of ,48% HBr and dissolve with gentle heatin to avoid excessive lose of HBr. Add! ml. of ceric sulfate solution (2 mg. of Ce(B01)~.4H@ per ml.) and transfer the mixture quantitatively to 125-ml. separatory funnels. Dilute to approximate1 30 ml., add 15.0 ml. of isopropyl ,tier, and shake for 30 seconds. After the phases have separated complete1 , discard the lower (aqueous) layer, a& 20 ml. of rhodamine B solution (0.01% rhodamine B in 0.5M
HCI), and shake for 30 eeconds. Discard the lower (aqueoua) la er and transfer the organic Is er to &-mi. oentrifuge tubes to e l i d a t e entrained water droplets. Measure the absorbance in l-cm. cells at 660 m r ainst rn isopropyl ether blank. ? % e standard curve is prepared with aynthetifo etandards containing 0- to 5.0-ml. volumas of a B.O-pg.-pr-ml. TI Solutton and enough sinc or cadmium to give approximately the same concentration a8 in the samples. The molar nbRorptiVity
8.6
1 ?
O.'
0.2
Her ColltlwIMTlolltMd~rl
PROCEDURE
Place samples containing up to 25 fig. of T1 into 1 ml. of concentrated H2SOI to which has been added 48% HUr (4 ml. per gram of zinc or 2 ml. per gram of cadmium). Add an addi1128
ANALYTICAL CHEMISTRY
Figure 1 . thallium
Effect of HBr concentration on extraction of
X----- X
1 5 fig. of TI(HI)
0-0
15 pg. of TI(III) and 1 Qrom of
Zn as ZnCln
in samples containing 0.5 gram of Cd was, 114,000 liters mole-’ crn.-’
Possible interferences were deduced from the extraction data for bromides
DISCUSSION
The HBr concentration must be at least 1M for complete extraction of TI(1II) into isopropyl ether in the presence of large amounts of zinc (Figure 1). Above 3M HBr, interference from small amounts of entimony becomes serious (3). Therefore, within the range of 1 to 3114 HBr, extraction of Tl(II1) is complete and free from antimony interference. Concentrations of other reagents, such as the ceric sulfate solution or the rhodamine B-acid solution are not particularly critical (9). Convenient values were selected for the procedure. No oxidizing agent is required to effect solution of zinc and cadmium samples if both sulfuric and h y d r e bromic acids are used. When this is done, thallium remains in the Tl(I) state and R small amount of ceric sulfate must be added to oxidize it to Tl(II1). Contrary to previous reports, a small excess of ceric ion need not be destroyed because it does not appear to cause any difficulty in the rhodamine I3 extraction.
Table 1.
Interference of Diverse Ions
[No interference ia indicated if iom pro. duced a color change e uivdent to lege samples (6% than 1 pg. on 20-pg. relative error)] Effect Ion Cr(VI) Cr(II1)
Amount 10 mg. 10 mg.
As( 111) cu(111 Sn( IV) AI(II1) Ge(IV) Fe(II1) In(1II) Mn(111)
10 pg. 100 mg. 100 mg. 500 pg. 100 Pg. 10 mg. 100 mg. 60
Source
on TI
Detn. LOW
(reduced)
A&O.
MGl
SnCl, Metal Metal
(reduced) Pb(IV) 100mg. Metal l m g . Metal 8b(V) 100 pg. KNO, NO#NO#“0, Large excesa’ Au(II1) 100 pg. Metal HP(IIi 100pg. G d I I ) 100pg. *The sample waa diaeolved acid.
zea
None None None None None None None None None None None None Color fadm High High High in nitria
in ethyl ether and for rhodamine B complexes (1). Table I lists the ions investigated in the interference study. Serious interference occurred with strong oxidizing agents and with Au(III), Hg(II), and Ga(II1). A reasonable separation from these ions was obtained by reducing thallium with hydrazine in acid solution and extracting the Tl(1) with dithizone in CClr (8). The thallium then was determined by the rhodamine B procedure following evaporation of the organic phase and wet oxidation of the remaining organic matter. LITERATURE CITED
H.,Freieer, H., “Solvent Extraction in Analytical Chemiatry,” pp. 131, 164, Wiley, New York,
(1) Morrieon, G.
1957. (2) Sandell, E. B.
“Colorimetrio D: termination of $race8 of Metals 3rd ed., p. 830, Interacience, New York,
1969. (3) Van Amen,
R.E., Hollibsu h, F. D., Kanzelmeyer, J. H., ANAL. &BY. 31,
1783-5 (1969). (4) Woolley, J. F., Analyst 83, 477-9 (1958).
R.E. VANAMAU J. H. KANEIIILIKEE~~~R Zinc Smelting Diviaion St. J m p h Lead CO. Monaca, Pa.
Improved Gas Chromatographic Analysis for Fuel Dilution and Volatile Contaminants SIR: 111 1959 a sensitive, precise, and accurate determination for fuel dilution in lubricating oils wm reported (3). With advances in gas chromatography it is now possible to perform improved and more versatile diluent analyses with greatly simplified e q u i p ment and procedures (4). Diluent concentrations in weight per unit volume are obtained by comparing peak area for diluent with that for internal standard. The standard is blended with the sample in 2% concentration prior to testing. Analyses may be made without internal standard by using the backflush area for oil. Diluent concentrations calculated from calibrated backflush areas are in weight per cent. Fluids with vapor pressures es low BB a few millimeters of Hg at 240’ C., may be treated this way. Heavier oils containing molecular weights >500, which may leave fractions on the column, are better handled by the internal standard method. Sample size depends on the precision desired, with the minimum being less than 10 pl. This compares with 25 to 50 ml. required for leas accurate fuel dilution tests by distillation (1-4). Analyses have been made from 0.01 to 5OoJ, diluent with a maximum
error of h15% of the amount present. Among other advantages, analyses are rapid and give an indication of diluent composition (3, 4). lj-igure 1 shows a typical recorder trace obtained with the improved procedure for fuel dilution analysis. The following conditions are used for dilution tests: The column is 12
feet of i/Cinch 0.d. copper refrigeration tubing. It is packed with 42-60 meahsise Johns-Manville (2-22 insulating brick, which is coated with 28% by weight of esphalt. The asphalt is safaniYa crude, which has been nitrogen blown at 320’ C. for 24 hours. The asphalt is placed on the brick by evaporation of a benzene solution. Other packings will suffice. The detectors
DILMNT
7
25
1 IYI.UIWvRI
Figure 1.
Typical chromatogram for fuel dilution analysis VOL. 33, NO. 8, JULY 1961
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