1022
ANALYTICAL CHEMISTRY
Table V. Comparison of Results on New and Used Oils b>Colorimetric and Gravimetric Procedures
5 .I--Phenyl-1-naphthylamine SRln),le
.iddcd
Found by Nethod C'olorinietric C;ravinietric
\yere obtained with a Beckman DE spectrophotometer using 10-mm. cell?. However, separate calibration curves for both .\~-ph~n~-l-2-iiaphthylamineand S-phenyl-1-naphthylamiiie stnnt1:irtii :ire necessary. INTERFERENCES
S E R - OILS
A B
0 10 10 10 10 10 10
0 0 0 0 0
C
D
E l-
0 10 0 09 0 09
0 0i 0 00 0 10 0 12 0 09
0 OH
0 10 0 0') 0 00
0 09 0 10
L-SED Orre 0 10 0 09' 0 07
1
2
0 Oi 0 13
3
0 0 0 0
4
5
0 0 0 0 0 0
0
13 12
09 09 09 10" 09 OH
10
09 0 09" 0 10 0 11 0 007" 0 07 0 09
11 12
0 04 0 04
7
8 9
a
10
0 07 0 I1 0
o
17 n7
0 010
o
This method is not specific for S-phenyl-1-naphthylamine. The basic react,ion involved in the met>hodis a general one for :ironxitic amines. If any other aromatic amine besides 1l'-phenj.11-naphthylamine i9 present, it ma>-interfere. However, aromatic amines are not likely to be present escept as additives. Therefore. errors due t,o the piesence of other arcmatic amines are not likelx. to occur in knoTi-n oil blends.
in
0 l i 0 03 0 I?
0 08 SI1
0 08 0 01) 0 08 0 03
Results obtained bj- nontechnical man trying method for firit tiiiie.
naphthylamine hut the color foimed is reddish purple instead of bluish purple. With a little experience, i t is easy to distinguish between them. T h e color formed with N-phenyl-2-naphth\ 1amine shows mavimuni absorbance of light around 540 nip instead of 555 mp for .$--phenyl-1-naphthylamine. Of interest too is the fact that 0.1% solutions of both amines have about the mnie absorbance, 0.192 xnd 0.198, respectivelv. The valutb.
SUMMARY
This paper describes a rapid method for determining t>he A*-phenyl-1-naphthylamine content of new and wed industrial oib. A single determination can be run by a nontechnical man i n 18 to 20 minuter. The prerision of the met,hod is about =t10%. which is adequate for blending plant, control n-or1.r and routine analvsis of used oils. The iiiethcd is applicable even n-hen the amine comes from different producers and is purchased a t different times. The method is not specific for X-phenyl-1-naphthylamine. Other aromatic amines, if present, may interfere, b u t are not likely to be present in known oil blends. LITER4TURE CITED
Rurchfield. H. P.. and Judy. J. S . . AI,. CHEM.,19, 786 (1947) (2) Fritz, J. S..Zbid..22, 1028 (1950). (3) Paiit, S. R., IND.ENG.CHEM.,AN.AI..ED., 18, 246 (1916). (4) Petrus. P., private communication. (1)
RECEIVED for review May 2 0 . 1954. .iccepted December 4, 1954. Presented hefore the Anieriran Petroleunr Institute. Houston, Tex., 1954.
Polarographic Determination of lead in Beryllium R.
W. BANE
Chemistry Division, Argonne N a t i o n a l Laboratory, Lemont,
4 rapid polarographic niethod for the determination of small amounts of lead in beryllium metal is described. Yo separations are necessary. A hydrochloric acid solution of beryllium acts as the supporting electrolyte. In the range of 150 to 800 p.p.m. of lead the precision is 10% or better. The simple procedure is readily adaptable for routine use. Evidence for the feasibility of the simultaneous determination of lead, cadmium, and zinc is presented.
I
CONKECTIOS with the analysis of beryllium metal for impurities or alloying constituents it was necessary to investigate methods for the determination of lead in beryllium. The classical colorimetric method using dithizone was deinonstrated to be successful for the determination of microgram quautities of lead in relatively pure beryllium metal. However, when the lead and the impurit.ie.3 were present in the order of several hundred parts per million, t,he colorimetric determination p r o v d t o be tedious and not feasible for routine analysis. Even though the procedure can he simplified by a, sulfate precipitation of the lead using strontium as a carrier prior to the dithizone estrartion (S), i t is still time-consuming and requires considerable manipulation. An electrolytic-polarographic method has been I\;
111. used to determine microgram amounts of lead and other metali in elements, such as barium, beryllium, calcium, magnesium, sodium, and uranium, which are not deposited in the mercury cathode ( 2 , 6 ) . This separation-concentration technique is particularly useful when the element desired is below the polarographic range and solubility limits of the matrix material prohibit adequate concentration. The lead is separated by electrolysis with a mercury cathode and then isolated by volatilizatioii of the mercury, prior to the polarographic determination. The limit of detection has been reported as probably 0.002 mg. of lead (f ). However, t,his electrolytic-distillation separation is not recommended for lead in the milligram range (8). -4lthough this technique has been used successfully in this laboratory for the determination of trace impurities in uranium, it, does not lend itself to rapid or routine analysis since the electrolysis time is 10 hours or longer. Esperiments have now indicated that, lead can be determined directly I-, polarography in the presence of large amounts of beryllium, and a procedure has been developed for the rapid determination of lead in the range of 150 to 800 p.p.m. Advantage is taken of the speed and simplicity of polarographic analysis. S o cheniical or electrochemical separations are required. The procedurr is suitable for routine analysis. Although only the
1023
V O L U M E 27, NO. 6, J U N E 1 9 5 5
c~onrentration is read from the callhi stion curve produced by plotting diffuqion currents or v a v e heights against t h e lead concentration. EXPERIMENTAL RESULTS 4 U D DISCUSSION
AGAR
m L I T R O G E N INLET S A T U R AT E D CALOMEL ELECTRODE
The half-wave potential for beryllium is negative ( - 1.8 volts) following the discharge of hydrogen, and therefore does not interfere with the waves of lead, cadmium, or zinc. A welldefined diffusion current with no maximum is obtained for lead in t,he presence of 2.2.11 beryllium chloride v-ith the half-wave potential occurring about - 0.46 volt L I S . the Eat,urated calomel electrode (Figure 2). T h e lead wave is repressed b y the high concentration of beryllium chloride which acts as t h e supporting electrol?-tt. The ratio of the diffusion current, i d r to the concentration, c, foi lead in 0.1111 pot i>-iuni chloride was found to be 13.0, while in 2.2111 beryllium chloride and i d to c ratio was 9.5. IO0
Figure 1.
3lodified polarographic cell
I
::1t 30p I6o
polarographic determination of lead in beryllium is described in this paper, evidence for t h e feasibility of determining cadnlium and zinc separately or simultaneously with the lead is presented. 4PP41i 4’1-1s
eo
10
1
Tile polurogrsph used \vas the Sargent-Heyrorsk$ 31odcl S I with a 6000-pf. electrolytic condenser connected arross the galvanometer shunts to decrease the galvanometer oscillations. The dropping mercury electrode arrangement of Lingane and Laitinen ( 5 ) was used x i t h a permanent external saturated valomel electrode as the anode. T h e H-cell was modified by sealing a stopcock in t h e bottom of t h e right half of t h e cell to facilit a t e removal of accumulated mercury and sample solution. Sample volumes as small as 5 ml. can be handled. Another stopcock on a side arm near the top of t h e cell permitted the nitrogen to escape during removal of air from the solution. The modified cell is illustrated in Figure 1. The nitrogen is purified by passing over hot copper turnings and then saturated with water vapor by bubbling through a wash bottle. T h e temperature is controlled during analysis b,v immersing the H-cell in a water bath maintained at 25” ==! 0.25’ C. REAGENTS
Beryllium solution, 4.4M,is prepared by dissolving beryllium metal with hydrochloric acid in the ratio of 30 ml. of concentrated acid per 2 grams of beryllium. T h e beryllium metal ( pure) was obtained from t h e Brush Beryllium Co. and contained less t h a n 5 p.p.m. lead b y spectrochemical and colorimetric analysis. For simplicity the solution is referred to as beryllium chloride in the text. Although t h e beryllium metal is completely dissolved the solution is deficient in chloride and conversion to beryllium chloride is not complete. Standard lead solution, 5.00 X 10-4M, is prepared by tiilnting nn electrolytically standardized lead solution. Hydrochloric acid, specific gravity, 1.19, and reagent grade. .ill experimental solutions as well as t h e standard? used, to make the calibration curve were prepared b y adding varying amounts of the standard lead solution to 50 ml. of the beryllium solution and diluting to 100 ml. with distilled water. RECOMMEKDED PROCEDURE
A 2-gram sample of beryllium metal is dissolved by slo\vly adding 30 ml. of concentrated hydrochloric acid. Care must be taken t o prevent excessive frothing, especially if the metal ifinely divided. The solution is diluted t o 100 ml. with distilled water and is introduced into the polarographic cell. Oxygen-free nitrogen is bubbled through the sample solution for 10 to 15 minutes to remove dissolved oxygen. A polarogram is made with the sensitivity set at 5 and a total bridge voltage of 1.5 volts. The height of t h e lead wave is measured on the photographically recorded polarogram b y the intersection point method. The lead
0 , -030
-045
-060 Eda vs
-075
-090
J
S C E , VOLTS
Figure 2,. Polarogram of 6 X 10-6M lead in 2.2.M beqllium chloride
Thus the ii-ave height is decreased by about 27y0 in the more concentrated supporting electrolyte. In order to investigate the sensitivity of the diffusion current to changes in the beryllium or acid concentration, polarograms were made of solutions with increasing amount.5 of beryllium and hydrochloric acid. The wxve height was found to be further decreased by approximately 9% b y either a 20% increase in the ber>-lliuni concentration or the addition of 5 ml. of concentrated hydrochloric arid before diluting t o the final volume of 100 ml. Therefore, if a wave height-concentration plot is to be used to determine the lead concentration, reasonable care should lie taken to maintain the Game beryllium and hydrochloric acid concentrations in the saniples as in the solutions used t o prepare t h e standard curve. The ,Gtandard addition calibration technique, in n-hich polarogranis ure recorded for the unknown before and after t h e addition of a knon-n volunle of a standard lead solution and the lead concentration calculated from the increase in the diftusion current, c:in be used provided the standard lead solution contains the .Game concentration of beryllium chloride as the sample, so t h a t there is no change in the ionic strength when the addition is made. The simplest procedure for an occasional analysis is to divide the sample into two equal portions and make the standard addition t o one of them before diluting to the final volume. Polarograms are then made of the two aliyuots. I n this case the lead standard does not contain beryllium. Although the internal standard method has the distinct advantage of requiring only one standard solution of t h e calibrating or “pilot” ion for the determination of several elements such as lead, cadmium, and zinc, i t is necessary t o determine the relative diffusion rurrent constants of t h e internal standard ion and the ions in question in the same supporting electrolyte. Since the calibration curve is t h e most convenient for routine
1024
ANALYTICAL CHEMISTRY
analysis, and was actually found to yield the most accurate results, it was sekcted as the method of standardization. A curve was constructed by plotting wave heights against the lead concentration A straight line was obtained over the range of 1.5 X lO-51M to 8 X 1 O - W lead corresponding t o a range of about 150 to 800 p.p.m. of lead when the sample of beryllium metal weighs 2 grams and the final dilution is 100 ml. The range can be extended by varying the sensitivity of the polarograph or the concentration of the sample.
-13Oc
-
Table I. Sample No.
Recovery of Lead Added to Beryllium Lead, P.P.M. Added Found 207 195 260 248 260 255 310 310 362
340 300 347
+9 6 -3 2 -4 1
500 518 518 777
504 528 511 770
+o
8 +1.9 -1 3 -0 9
-120
E E -110
Table 11. Comparison of Results on Standard Beryllium Sample
II/
Zn
Laboratory Argonne National Laboratory National Bureau of Standards Battelle Memorial Institute
-50
a
3
-30
0
- 20
a
P
Deviation -5 8 -4.6 -1.9
/
Lead Concn.,
P.P.M. 325 300 360 320 300
Pb
- l0 - 0 3 0 -0.45
Method Polarographic Spectrographic Chemical Spectrographic Spectrographic
-0.75 -090 -105 Ed,e, vs S C E , VOLTS
-060
-120
Figure 3. Simultaneous polarogram of 4 X lO-&Mlead, cadmium, and zinc in 2.2M beryllium chloride
in good agreement with chemical and spectrographic values as indicated by comparison of data on a standard beryllium sample. Evidence is also presented for the feasibility of the simultaneous determination of lead, cadmium, and zinc in beryllium. LITERATURE CITED
( I ) Bricker, C. E., and Furman, N. H., T;. S. Atomic Energy Com-
mission Report, CC-73.
Results obtained with this recommended procedure on synthetic samples prepared from pure beryllium metal with known amounts of added lead are shown in Table I and indicate a precision of 10% or better. A standard deviation of 14 p.p.m. for a single determination was obtained by extracting the square root of the sum of the squares of the deviations divided by one less than the number of determinations. The greatest inaccuracy occurs in the actual physical measurement of the wave height on the photographically recorded polarogram. Table I1 gives results obtained on a standard beryllium sample distributed by the National Bureau of Standards. The polarographic values agree satisfactorily with the values obtained by the chemical colorinetric method and the carefully standardized spertrographic procedures. Experiments with cadmium and zinc indicate that these elements can also be determined polarographically in the presence of beryllium. The half-wave potential for cadmium occurs about -0.67 volt us. the saturated calomel electrode and the half-wave potential for zinc occurs about -1.07 volts os. the saturated calomel electrode (Figure 3). Because the reduction wave for zinc lies very close t o that of hydrogen in highly acid solution, it may be necessary to reduce the acidity by the addition of ammonium hydroxide in order to delay the appearance of the hydrogen wave and to allow the zinc wave to develop fully. CONCLUSION
The basic advantage of the method presented is the simplicity and rapidity with which lead can be determined in the presence of beryllium within the range of 150 to 800 p.p.m. of lead. The determination is made with a minimum of manipulation and requires no time-consuming separations. Data obtained on synthetic samples prepared from pure beryllium metal n-ith known amounts of lead added indicate that the precision is 10% or better. The results obtained by the polarographic method are
(2) Bricker, C. E., Furman, N. H., and McDuffie, B., Ibid., AECD2600, AECD-2601, AECD-2602, and AECD-2603 (1947). (3) Eberle, A. R., and Petretic, G. J., Satl. Bur. Standards Report
NBS, A-2952 (December 1947).
( 4 ) Furman, N. H . , and Bricker, C. E., U.S. Atomic Energy Com-
mission Report, MDDC-691 (1947).
( 5 ) Lingane, J. J., and Laitinen, H. -%., IND.ESG. CHEX, A N ~ LED., . 11, 504 (1939).
RECEIVED for review July 21, 1954. Accepted December 23, 1954.
Determination of Boron in Silicates after Ion Exchange Separation Correction
-
The following corrections should be made in the article on “Determination of Boron in Silicates after Ion Exchange Separation” [ANAL.CHEM.,27, 144 (1955)l. Page 144, the last item a t the bottom of the first column, should read: Sodium hydroxide, standardized 0.05N, prepared from saturated sodium hydroxide solutions and standardized as described in the procedure against weighed amounts of anhydrous boron oxide. Anhydrous boron oxide is prepared by fusion of reagent grade boric acid in a platinum dish. Page 145, second column, the fourth paragraph should read: Hollander and Rieman ( 2 ) report boron oxide values for NBS 92 as 0.65% and for KBS 93 as 12.51% and conclude that their value for S B S 93 is closw to the actual content than the report of the Bureau of Standards. The author is indebted to W. Rieman I11 for pointing out the error in the potentiometric titration of boron as presented-Le., the partial neutralization of the boric acid a t pH 7 and the incomplete neutralization of the mannitoboric acid a t a final end point of 7. Although this error is diminished by the standardization of the sodium hydroxide against boron oxide, it can be eliminated by using a titration correction as described by Hollander and Rieman ( 2 ) . HENRYKRAMER
