V O L U M E 2 3 , NO. 10, O C T O B E R 1 9 5 1 ___
1365 __
than two pears in this laboratory to the determination of the iron cont,ent of crankcase ('lirtnical drainings. The samples anaIron lyzed included crankcase drainl.\v.) iron Diff. deviation iron Diff. deviation iron Diff. de\-iation 0 00230 13 0 0 0025 + a . 0002 0.0026 +o ,0003 8.i 0 0024 +o 0001 4 3 ings from both gasoline and 0.0073 - 0.00018 0 00748 2 4 0 0075 +o 00002 0.3 Diesel engines lubricated with 0.0130 +0.0006 0 0124 4 8 0 0130 f 0 0006 4.8 -0.007 0 055 12 7 0 056 +0 001 0.048 1 8 0 022 -0 003 i i both additive and nonadditivtt -0.002 0 108 2 0 0 126 16.7 0.106 0 Ilb +O 018 +O 008 7 4 . 0 125 +0.002 1 6 0 131 0.127 +O. 006 4.8 1) 129 t o 00-1 3 2 type oils. 0 156 +0.002 1 3 0 159 +o 003 1.9 0 R 0.158 I) 157 + 0 001 0 199 0.000 0 20: 0.199 0 0 +o 006 3.1 0 18'1 - 0 010 i0 While the basic techniyuc of the method could possibl\ -13 be applied to the dettlimination of other elements present in used lubricants, I I O 1wparing and arcing 10 electrodes for each of two samples, iron1 inve-tigation of this sort has been made. (liferent sources, having approsinlately the same iron vontPtit. ACK~OWLEDGNIENT The, results of each spectrogram, together with the deviation The authors uish to express appreciation to T. J. Devlin anti l ' w i i i the mean and from the iron content as determined 1 ) ~ . S D . D'Adarno for their assistance in running samples and fol \ \ e t chemical analysis, are shown in Table 11. t l i ~ i rcontribution to the improvement of the physical techniqucl One of the principal attributes of the method, particular1~-as of the sample preparation. :I pplied to the samples received in this laboratory, is the wide i:irigr of concentrations that can be determined without any LITER4TURE CITED iiiodification or variation of technique. The data shown in l'atile I11 indicate the accuracy a t different levels of concentra(1) Calkins, L. E., and White, h l . lI.,N a t l . Petroleum News,38,S o . t i ~ nits compared to the average of two or more wet chemical 27, 519 (1946). 12) Churchill, J. R., ISD. ENG.'?HEM., - 4 s ~ED., ~ . 16, 653 (1944). :I iialJ.ses. The method described has been successfully applied for niore RECEIVED April 20, 1951. Table 111.
Comparison of Chemical and Spectrochemical Results _ _ Spectrochemical ______~_ Determination 1 -- - - -Determination 2 Determination 3 yo % 7c %70 % ~~
-
~~
~
Spectrographic Analysis of New and Used lubricating Oils C. RI. GARIBRILL, A. G. GASSMANN, AND W. R. O'NEILL Ethyl Corp., Detroit, Mich. The work was begun because rapid, accurate niethods for determining metal content of lubricating oils are needed for controlling the blend of additive oils and for examining used oils to aid engine performance studies. Ordinary methods of chemical analysis are usually too cumbersome and tedious fur this purpose and attempts have been made to utilize the speed of spectrographic methods. A spectrographic method using the porous cup electrode technique is described for the determination of the additives barium, calcium, phosphorus, and zinc in new lubricating oils, and its variables are discussed. An over-
S
I'E.CTROGRAPHIC determination of metals and phouphorus i n lubricating oils presents special problems because of the difficulty of introducing the sample into the excitation discharge ant1 liecause the type of base oil and additive may differ from sample to sample. Three different techniques have been used to introduce the sample into the spark. One technique employing electrodes prepared by quenching hot graphite rods in the oil *ample ( 3 )has limited usefulness (5). A second technique (5, 6) wing porous cup electrodes similar to those described by Feldman (4)has a more general application but is not suitable for anslj zing used oils containing suspended solids. A third technique employing a rotating disb electrode has recently been used for defrrniining phosphorus in unused lubricating oils (1,7 ) . The porous cup technique has been successfully used in these laboratories for routine analysis of new lubricating oils. Its use for determining phosphorus has been described (5, 6). The present paper describes an extension of the method to include the additive metals barium, calcium, and zinc, and discusses further qtudies of some of the variables involved.
all accuracy of 10% is claimed. A second technique uses a rotating disk electrode for the determination of lead, iron, and the additives in used oils. Results for the additives are compared with those obtained using porous cup electrodes. Accuracies of the order of 10% are claimed for the determination of lead and iron and the additives. Film background read adjacent to the element line is used as internal standard in both techniques. The rapid, accurate, and economical spectrographic method described is a specific addition to the literature in that i t applies to the analysis of both new and used lubricating oils.
.4s the porous cup technique cannot be used for determining the total amount of an element in used oils containing suspended solids, a method using the rotating disk electrode technique has been developed for determining lead, iron, and the additives in used oils. EQUIPMENT
The equipment used included a 2-meter grating spectrograph, PIIultisource excitation unit, densitometer, and solution excitat ion attachment manufactured by the Applied Research Lahoratories. POROUS CUP ELECTRODE METHOD
h porous cup electrode is filled with a sample of the unused
lubricating oil to be analyzed. The electrode is made from Sational Carbon Co. special spectroscopic graphite rods 6.35 mm. in diameter. A section of rod is cut to a length of from 22.6 to 22.8 mm. and faced off to an exact length of 22.2 mm. -4. cavity 3.96 mm. in diameter is drilled in the rod, leaving a floor of about 1 mm. The cup is finished by drilling the cavity by hand t o leave a floor thickness of 0.64 f 0.05 mm. using a flatbottomed drill and a stop-collar. The cup is used as the upper electrode; a graphite rod 6.35 mm. in diameter with a 45'
1366
ANALYTICAL CHEMISTRY
Table I.
Oil
Determination of Metals in Oils by Porous Cup Rlethod .4dditivo
Metal
Metal Added
Metal
Keight
5:
Found 0 0 0 0 0
198 136 122 045 049 0 147 0 083
____
__
-
invluded angle cone tip is used as the lower electrode. The spark gap is 3.175 mm. The excitation is a discharge given by setting the 3lultisourc.c. unit at 5-microfarad caDacitance. 25-microhenrv inductance and 0.4-ohm resistance. The charge us? discharge" switch is set at 180". .A 30-second prespark period is followed by a 60-second exposure. The grating aperture is set a t 0.7 of thr maximum A 50-micron slit is used. The spectra are recorded on Spectrum Analysis No. 2 film. These conditions give a film background of approximately 50% transmittance. The film is developed for 3 minutes in D-19 developer a t 20" C . , hardened for 15 seconds in potassium chrome alum hardt,ncr. and fixed for 2 minutes in Kodak rapid liquid fixer. The transmittances of the barium line at 2335.269 A , , the phosphorus line a t 2535.65 A, the zinc line a t 3345.02 A , , the calcium line a t 4302.527 A , , and the film background adjacent to each are measured with the densitometer for concentrations of thew elements from 0.01 to 0.2 weight %. The barium line a t 2347.577 -4.is used for concentrations of this metal between 0.10 and 2.3 weight %. Film background adjacent to the line is used as intrt,nal standard ( 1 ) and the element line is corrected for film 1)arkground. Emulsion calibration is made from iron iipwtra photographed t,hrough a tu.0-step filter.
Table I1 shows the effect of changing esritation. The apparent concentrations given in this table were read from analytical curves used with the excitation previously chosen for phosphorus. N o excitation conditions were observed which appeared to be more favorable than these (Multisource, 5-microfarad capacitance, residual inductance and resistance). Small changes in escitation had little effect on the ticbterrnination of calcium, phosphorus, and zinc; the barium line at 2335 A. was more sensitive to changes. Prespark. l'respark studies showed that line to background intensity ratios obtained for barium and calcium were erratic when prespark pcriods of less than 20 seconds were used with GOsecond exposures. Zinc intensity ratios became constant after a 10-sec.ond prespark, while phosphorus required a 30-second prespark. It, was thus necessary to use a 30-second prespark in order to determine all metals from a single exposure. Electrode Floor Thickness. Previous work in the determination of phosphorus in lubricating oils showed that porous cup olect,rodes having a floor thickness of 1 mm. (0.040 inch) gave erratic results, but that cups having a floor thickness of 0.635 mm. (0.025 inch) were satisfactory. .I further study was made to ertain the optimum floor thickness and the tolerance within which it should be held. Porous cup electrodes having floor thicknesses of 0.38, 0.51, 0.64, 0.76, and 0.89 mm. (0.015, 0.020, 0.025, 0.030, and 0.N5 inch) were cut from r\Tat,ional Carhon Co. special spectroscopic graphit,e rods, the floor thickness being held within 0.05 mm. of the st,ated dimension. Electrodrs were also obtained from United Carbon Co., preformed from the U-2 grade of graphite with floor thicknesses of 0.51,0.64, and 0.76 mm. The electrodes with a floor thickness of 0.61 nim. supplied by United Carbon Co., were drilled with a pointed drill, leaving an electrode floor with a V-ghaped upper surface. All other electrodes were drilled with a flat-end drill. Replicate analyses using electrodes of each floor thickness of cwh brand of graphite ivere made with several series of oil samples containing kno\z.n concentrations of barium, calcium, phosphorus, and zinc. The variation of line to background intensity ratios with electrode floor thickness is illustrated in Figure 1. Intensity ratios became lower as floor thickness inrreased, and were usually different for the two brands of graphite. The electrodes shaped with a pointed drill gave lower intensity tatios than those shaped with a flat drill. Variations of results d t h floor thickness were most pronounced for high metal concentrations, wcre usually greater for barium, calcium, and zinc than for phosphorus, and Yere greater for electrodes made from C'nited Carbon Co. graphite. The spark almost alway punctured cJlectrodeswith 0.38-nini. floors, and occasionally punt*turcxd
1)ISCUSSION OF POROUS CUP ELECTRODE 1IETHOI)
The porous cup technique was adopted by these lnburatutiea for the determination of phosphorus, because it gave results which were not influenced by the nature of the base oil and the additive in the sample. Barium, calcium, and zinc determinations were similarly unaffected by the sample type. Table I shows the results of analyses of a number of samples which included four different base oils and five commercial additives. However, several variables were studied further to evaluate the effects of the excitation used, the lengt'h of prespark period, t h e floor thickness of the porous cup electrode, the use of air and nitrogen streams directed to the analytiral gap, and the viscosity of the oil sample. Excitation. Various discharges given by t hr IIultisource were tried, ranging from sparklike discharges with low amounts of inductance and rrsistance in the discharge circuit to more Table 11. Effects of Excitation Changes arclike discharges given by relatively larger (Porous cup method) amounts of capacitance, inductance, and reApparent Metal Concentration ~ ~ ~ . ~. sistance. In general, with the analysis lines Phosground used, increases in capacitance gave darker Barium Calcium phorus Zinc rranaIkcitation" added added added added niittance, film background, lower intensity ratios of line 0.109% 0.100% %, R 0.150% 0.102% (. I, to background for phosphorus, and somewhat ;! 2-7 .. 0,140 0.098 0.101 0.097 75 0.110 0.100 50 0,103 0 25 .. 0,150 higher line to background intensity ratios for 0,090 6.100 30 .. 0,124 0.112 7 25 calcium without having a marked effect on the 0.097 65 0.101 0.107 1 0.180 3 25 results. Increases in inductance had little effect 0,117 0.112 85 0.11.5 5 0.18,j i 25 0.146 0.112 85 0.157 10 0.180 2J on film background, but tended to give higher r, 50 ., 0,105 0,104 0.109 0.101 45 line to background intensity ratios for all metals. Tr 100 .. 0,120 0,129 0.119 0.111 45 Increases in resistance gave lower film back0.148 0.152 0.150 0.116 85 ,j .50 5 80 0.235 0.153 0.183 5 100 5 0.32 ground and higher line to background intensity 85 0,179 0,173 0.175 0.30 ;.,? 400 100 10 85 ratios. Increasingly arclike conditions produced 100 0,110 b 0,109 0.185 by higher values of capacitance, inductance, 0 , 0 7 0 0 235 0.133 0.156 50 20 150 8 20 40 150 18 0,047 b 0,130 0.200 and resistance gave hotter electrodes, more inXIultisourcr. C , a p a c i t a n c e , microfarads. I,, inductance, microhenrim. R , resisttense lines, and darker film background; line to ance, ohms. b Lines too diuk to niensure. background intensity ratios became higher for calcium, phosphorus, and zinc and lou.er for barium. -. ~
~
~
~~~
~
~
~~
~~
k -
1367
V O L U M E 23, NO. 10, O C T O B E R 1 9 5 1 those with 0.51-nim. floors. Results from punctured electrodes were somewhat erratic, especially for calcium and zinc. A change of 0.13 mm. in electrode floor thickness produced an apparent variation of about 10% of the concentration being determined. However, results were reproducible for a given floor thickness as long as the same grade of graphite was used. If analytical curves were drawn for a particular floor thickness and grade of graphitr, there was little difference in accuracy for different floor thicknesses. The results of a number of analyses, 45 for each floor thickness of both grades of graphite, gave standard deviations of 10 f 2%. These analyses included determinations of barium, calcium, phosphorus, and zinc in concentrations from 0.01 to 0.2Yob.
G
?
U
t z
eI P e 0
0 0 L
m
2 w
spark periods of from 0 to 45 seconds. The samples were analyzed first using the usual excitation conditions, then using first an air stream and next a nitrogen stream of approximately 12 liters per minute directed a t the spark gap through a 3-mm. orifice. Line to background intensity ratios were not reproducible with prespark times under 10 seconds, but became fairly constant after 30-second prespark periods, regardless of whether or not air or nitrogen jets were used. No improvement in results was given by the use of either air or nitrogen. Spectrograms obtained using air and nitrogen had darker film backgrounds. Intensity ratios for calciuni became more nearly constant when neither air nor nitrogen was used; thope for barium became constant least readily when nitrogtin was used, Intensity ratios obtained using nitrogen Ivere least reproducible from film to film. Effect of Viscosity. Previous work in determining phosphorus showed no significant effect due to viscosity within the viscosity range SAE 10 to SAE 40. Pagliassotti and Porsche ( 7 ) , using the rotating disk method, found no viscosity effects within the range SAE 10 to SAE 50. Analyses of oils of SAE 60 viscosity, however, indicated that a viscosity effect did occur, low results being obtained with oils of high viscosity. This effect was most pronounced for high metal concentrations. Table I11 illustrates the tendency toward l n w results as sample v k cosity increased. Each value listed is the average of a t lrast eight determinations. Accuracy of Porous Cup Method. The accuracy of the determination of the additive metals, calculated from thc rcsults of 50 determinations, is given in Table IV. As highest per cent deviations occur a t the lowest concentration level, separate accuracy figures are given for concentrations above the 0.01% level. The average standard deviation from the input for all metals was approximately 10%.
I
PHOGPHORIJS 0.153 '/a P
3
ROTATING DISK METHOD FOR USED OILS
The used oil sample in the original container is heated to 60" C. and agitated until the sample is thoroughly mixed and all solid partirles are suspendrd in the oil. .I, portion of the samplr is
, --,
2
I 0.381
-NATIONAL CARBON GRAPHITE ELECTRODES UNITED CARBON GRAPHITE ELECTRODES ELECTRODE SHAPED WITH POINTED DRILL
I 0,631 0.762 0.889 POROUS CUP ELECTRODE FLOOR THICKNESS. MM.
Table 111.
0308
Figure 1. Effect of Electrode Floor Thickness on Intensity Ratios for Determination of Zinc, Calcium, and Phosphorus
It was concluded that the electrode floor thickness must be greater than 0.51 mni. to avoid puncture by the spark, and must be less than 0.89 mm., because floors thicker than this gave erratic results. Any intermediate value was believed to be satisfactory if held within a 0.05-mm. tolerance. A4cup formed with a flat-end drill was considered preferable to one formed with a pointed drill, as the latter gave lower intensity ratios. Effect of Air and Nitrogen Jets. One of the advantages of the porous cup method was believed to be the fact that the oil sample was introduced into the spark without previous heating, eliminating the possibility of partial decomposition of the sample. Although the excitation chosen did not heat the electrodes appreciably, it was thought that additional cooling of the electrodea by an air stream directed a t the spark gap might be beneficial. Pagliassotti and Porsche ( 7 ) , using rotating disk electrodes, reported a one-third gain in precision through the use of a nitrogen atmosphere a t the spark gap, attributing this effect to the prevention of oxidation The effect of an air and a nitrogen stream a t the spark gap with porous cup electrodes was observed in a series of prespark Rtudies. Two different oil samples were analyzed, using pre-
Effect of Viscosity
1 Porous
cup method) Added
Viscosity S.4E 10
I: I em en t Phosphorus
O A F , 20
Calcium Zinc Phosphorus
SAE 40
l'liosphorus
SAE 60
Phosphorus Calcium Zinc
Table I \ .
Found Weight yo 0.150 0.147 0.050 0.048 0.050 0.046 0,050 0.050 0.101 0.102 0.050 0.050 0,154 0.138 0,054 0.051 0,050 0.041 0,050 0.031 0.050 0.039
Accuracy and Precision of Porous Cup Method Av. % Deviation from
0.01-0.2 2 0 12-2.5
Spiitrographic Mean 6.0 6.1 n .8
0.01-0.2
9.1
Conrentration Range. Element Barium Calcium Phosphorus Zinc
9
o.E&o.
0.05-0.2 0.01-0.2
6.6
0.05-0.2
4.2 7.7 1.2
0.01-0.2 0.054.2
5.4
Deviation from Input, % hverage Standard 5.9 7.8 6.0 7.8 6,O 8.1 8.6 11 7 6.6 8.9 5.6 7.9 4.4 5.9 8.7 12.3 5.5 6.8
ANALYTICAL CHEMISTRY
1368 Table V. Element Lead
Analysis Lines, Rotating Disk Method Concentration Range, Weight
Analysis Line, A .
0.01 -0.1 0 . 1 -2.5 0.001-0.03 0 . 0 1 -0.3 0.01 -0.1 0 . 1 -2.5 0 . 0 1 -0.2 0 . 0 1 -0 2 0.01 -0 2
2833.069 2663.166 2599.396 2625,666 2335.269 2347.577 2535.65 4302,527 3345.02
Iron Barium Phosphorus Calcium Zinc
transferred to a midl porcelain combustion boat (Coors S o . 2), and the boat is inserted in the solution excitation attachment. The solution excitation attachment is mounted inside the arcspark stand on the optical bench of the spectrograph. ,4 platform of nonconducting material supports the boat containing the sample. A graphite disk, 12.7 mm. in diameter and 3.175 mm. thick, used as the lower electrode, is mounted so that it is partly submerged in the oil sample. The disk is supported by a shaft electrically connected t o the lower electrode holder and rotated by a stepped pulley arrangement set to give a speed of rotation of 15 r.p.m. A graphite rod, 6.35 mm. in diameter. pointed to a 45" included angle cone, forms the upper electrode. The spark gap is 3.175 mm. The excitation is a discharge given by setting the Multisource unit a t 4-microfarad capacitance, 100-microhenry inductance, and &ohm resistance. The charge us. discharge switch is set at 180". The grating aperture is set a t the maximum opening. ;i 50-micron slit is used. A 60-second prespark period is follomd by a 90-second exposure. The spectra are recorded on Spectrum Analysis So. 2 film. These conditions give a film background of approximately 50% transmittance. The film is developed for 3 minutes in D-19 developer at 20' c' hardened for 15 seconds in potassium chrome alum hardener, and fixed for 2 minutes in Kodak rapid liquid fixer. The transmittances of the analysis lines and the film background adjacent t o each are measured with the densitometer. The analysis lines are corrected for film background; film background is used as internal standard. The lines used are given in Table V. I
introducing used oil samples into a spark discharge. In this method, the lower electrode is a rotating graphite disk which dips into the sample and continuously carries a portion of the sample into the discharge. This apparatus, called a solution excitation attachment, has been described (1, 7 ) . Excitation. Preliminary experiments with the rotating disk electrode showed that spark evcitation gave satisfactory sensitivity for high lead concentration (1 to 5%) but that it was necessary to select and control excitation conditions to minimize heating of the oil sample. As the temperature of the oil sample increased during the sparking cycle, the intensity of the lead and iron lines increased while that of the film background decreased. Excitation conditions satisfactory for new oils with porous cup electrodes (Multisource, 5-microfarad capacitance, 25-microhenry inductance, 0.4-ohm resistance) heated the oil sample and caused line to background intensity ratios to change rapidly as sparking continued. Evcitation conditions which did not heat the sample more than 10' C. during 2 minutes of sparking (Multisource, 4-microfarad capacitance, 100-microhenry inductance, &Ohm resistance) gave the least change in line to background intensity ratios during continued sparking. Under the same excitation conditions, samples with lorn lead concentrations reached higher temperatures than samples with high lead concentrations. A 60-second prespark period was selected to ensure that all samples reached an equilibrium temperature before the exposure was made. A 90-second exposure Lvith full grating aperture was necessary to give satisfactory line and film background intensities. Disk Speed. Of the speeds at which the disk electrode could be rotated, 2.5, 5, 7.5, and 15 r.p.m., the higher speeds gave the most satisfactory results. Lead and iron line to background intensity
Table TI. Determination of Lead i n Used Oils (Rotating disk electrode method) Lead, T e i g h t % SpectroChemical graphic
.inalysis Line, A . DISCUSSION OF ROTATING DISK ELECTRODE
METHOD
Development of Method. 1-sed oil samples may or may not contain a considerable amount of undissolved material, a fact which makes it difficult to introduce a representative sample directly into the arc or spark. Preliminary ashing or oxidation of the sample is time-consuming and attempts to determine lead and iron by arcing the oil directly, by arcing electrodes saturated with the oil, or by arcing electrodes in which the oil had been ashed all gave unsatisfactory results. More encouraging results were obtained by using electrodes in n-hich the oil had been dried but not ignited. One trial method using bismuth as a spectroscopic buffer with direct current arc excitation gave promising results for lead concentrations belonO.l%, but could not be extended to higher concentrations because of a marked loss of lead line sensitivity with increasing lead concentration. This method also proved to be unsatisfactory for iron. Porous cup electrodes could not be used because of their filtering action, but a rotating electrode technique which was successfully used by Pagliassotti and Porsche ( 7 ) in analyzing new lubricating oils offered a possible means of
Ph 2663
Devia9 tion from Mean
Deviation from Chemical
De&tion from Chemical
1.52 1.01 0.64 0.20 0.113
2.37 1.49 1.03 0.63 0.20 0.114
0.25 0.09 0.076 0.035 0.030 Q.008 0.081
10.6 5.9 7.4 5.5 15.0 7.4 8.6
0.23 0.09 0,073 0,038 0.030 0.008 0.081
10.5 5 9 7.2 5.9 15 0 7 4 8.7 10.5
1 01 0 64 0.20 0.113 0.016 0.032 0.047
1.04 0.64 0.197 0.121 0.016 0.032 0.046
0.066 0.051 0.012 0,011 0.0039 0.0015 0.0056 0.022
6.1 8.0 6.1 9.4 24.2 4.7 12.9 10.1
0.071 0.051 0,013 0,013 0,0039 0.0015 0.0059 0.023
7.1 8 0 6.4 11.2 24.2 4.7 12.5 10.6 15.0
3.40
-1verage Standard deriation Pb 2833
c-
Deviation from Mean
Average standard deriation
Table VII.
Determination of Iron in Used Oils (Rotating disk electrode method)
Iron, ~ Analysia Line, A . Iron 262,5
Average Standard de\.iation Iron 2.399
Average Standard deviation
Chemical 0.28 0.14 0 026 0.01 0.007 0 016
~
e
Di-e:;
g
Spectrographic
from Mean
0.278 0.148 0.025 0.011
0.031 0.009 0.0018 0.0016 0,001 0.002
0,007 0.014
0.008 0 0'26 0.01 0.007 0 006 0.001
0.029 0.010 0,008 0.0039 0,0011
0.0016 0.0006 0.0005 0.0004 0.0003 0.0007
'
%
~Devia-
0-
/'
Mean
Deviation from Chemical
11.1 5.9 6.0 14.8 14.8 13.4 11.0
0.031 0.012 0.002 0.0011 0.001 0,003 0.008
11 1 8.6
5 6
0.0028 0.0006 0.001 0,0004 0.0003 0.0010
10.6 6.4 14.6 6.1 31.3 13.4 19.0
tion
from
6.4 o.,
6.2 28 4
10.5
Deviation fro111 Chemical 7.7 11.3 14.8 18.0 11.9 14.1
V O L U M E 23, NO. 10, O C T O B E R 1 9 5 1
1369
Analysis for Additive Elements. Using the same excitation conditions chosen for the lead and iron determination, the method m-as extended (Rotating disk and porous cup electrode methods) Average % Average % to include the additive elements. Satisfactory Deviation Deviation accuracies were obtained, although phosphorus from Mean from I n p u t Standaid De\ialkio _ _ _ ~ Analysis Rotating Porous Rotating Porous Rotating Porous could not be accurately determined in samples Element Line, A. disk cup disk cup disk cup containing over 0.1% iron because of the inter2335 L O 6.1 Barium 5 6 78 . 8 ference of iron lines with the phosphorus line. Barium 2347 8.1 6.8 8 .. 21 6 .. 00 160.. 33 1 Calcium 4302 8.3 6.6 8.5 6.6 11.3 X !J Comparison of Methods. The results obtained Phosphorus 2532 5.0 4.2 5.0 4.4 6.2 3 !J Zinc 3340 6.5 4.2 6.6 5.5 8.7 ii.8 for additives using rotating disk electrodes were Average 6.6 5.4 6.7 R.7 8.6 7 3 compared with those obtained using porous cup ._ .. . electrodes. A comparison of the accuracies given by each technique, shown in Table VIII, indicated little difference betn een the two, although the porous cup technique appeared to give a slightly higher ratios from i i series of oils containing from 0.015 to 2.5% lead obtained using a disk speed of 7.5 r.p.m. were in fair agreement nccuiacy. The excitation condition used for the rotating disk a i t h intensity ratios obtained with a speed of 15 r.p.m., but those method was selected for the determination of lead and iron. The concentration range covered was from 0 0 2 to 0.20y0 for obtained with the higher speed gave a smoother analytical curve. Use of Air and Nitrogen Jets. The effect of air and nitrogen (*aIcium,phosphorus, and zinc, and from 0.025 to o.3Oy0 for barium. -4 viscosity effect giving low results for oils of S-4E jets directed a t the spark gap was observed in a series of moving film studies on both used and unused oils. With excitation con60 viscosity was found to be present for the rotating disk terhditions which heated the sample and without the use of air or nique as well as the porous cup method. nitiogen jets, line to background intensity ratios increased as When analyzing unused oils, these laboratories find the porous cup technique somewhat simpler and more rapid to use, but lesparking continued without reaching a constant value. The use of air or nitrogen brought the intensity ratios to a constant sults by both techniques appear to br rquallj satisfartory. value after about 30 seconds of sparking. With excitation conditions which did not heat the sample, intensity ratios came to a LITERATURE CITED constant value without the use of nitrogen or air jets, although the time required was somewhat longer. The use of a nitrogen (1) Applied Research Laboratories, Glendale, Calif., “Study of SpectronraDhic Determination of PhosDhorus in Oil.” jet gave increased film background, but the principal effect of (2) Calkins,‘L. E., and White, &I. >I N. h,. Petroleum News, 38, KO. both air and nitrogen jets seemed to be cooling the electrodes and 27, R519-30 (1946). sample. With excitation which did not heat the electrodes, (3) Clark, R. O., and Cooperators, COAR (API) Subcommittee on there appeared to be no particular advantage in the use of air or Emission Spectroscopy, Report on Quenched Electrode Procedure for Analysis of Lubricating Oils, API Meeting, Tulsa, nitrogen jets other than to shorten the prespark period required Okla., 1951. Accuracy of Lead and Iron Determination. Results of spec(4) Feldman, C., ANAL. CHEM.,21, 1041-6 (1949). trographic analyses of chemically analyzed used oil samples arc’ (5) Gassmann, A. G., and O’Keill, W.R., Ibid., 21, 417 (1949). given in Tables VI and \TI. Each spectiographic result is the (6) Gassmann, A. G., and O’Neill, W. R., Proc. Am. Petroleum Inst., 29M,79 (1949). average of a t least eight determinations. As shovm by Table (7) Pagliassotti, J. P., and Porsche, F. IT., ANAL.CHEM.,23, 198VI, the average accuracy of the lead determination was about 202 (1951). +loo/, of the amount present Table VI1 shows the average a w u r J r y of the iron determination to be about =!=l5y0. RECEIVED April 20, 1951.
Table VlII.
~
Comparison of Accuracy and Precision
~
Testing Used lubricating Oils for n-Pentane- and Benzenehsolubles Proposed Semimicro Modijication of ASTM Method J. S. WIBERLEY, R . K. SIEGFRIEDT, AND L. J. DiPAOIA Socony-Vacuum Laboratories, Brooklyn 22, N . Y .
I
Y NORMAL use lubricating oil gradually accumulates small amounts of foreign materials, which are suspended in the oil and may eventually hinder lubrication and promote wear. In internal combustion engines, products of combustion, such : I soot, lead compounds, and partially oxidized pi1 and fuel, nlay find their way into the lubricating oil along with metallic wear particles and dust taken in from the surroundings. In order t o evaluate the condition of the used oil, it is generally desirable t o determine the total quantity of these insolubles. Filtration or centrifugation of oil-solvent mixtures is the conventional procedure for removing the insoluble8 from the oil, but many modifications of techniques and solvents are used by different labora-
tories (7-10). Committee D-2 of the American Society for Testing Materials has published a tentative method for determining n-pentane- and benzene-insolubles in used lubricating oils ( 6 ) . The authors, however, believe that there are a number of important disadvantages to the use of this method. The method is slow. I n the authors’ laboratory one operator can handle only about ten samples per day-Le., ten determinations of the pentane-insolubles and ten determinations of the benzene-insolubles. If the coagulant is added in increments, as directed, the number of samples per day is further reduced. The apparatus is bulky and expensive. Considerable bench space is needed for the 125-ml. centrifuge tubes and the racks to hold them.
