V O L U M E 2 6 , NO. 1 2 , D E C E M B E R 1 9 5 4 Table I. Determination of Palladium in Presence of Foreign Metals with 2-Nitroso-I-naphthol (19.9y of palladium)
a
b
Metal Added, 1 Mg. Platinum ( I V) Iridium(IV1 Rhodium(II1) Rutheniuni(II1) Osmium(1V) Gold(II1) Zirconium( IV) Iron(II1)b Iron(II1) Cobalt(I1) b Cobalt(I1) Copper(I1) Nickel(I1) Chromium(II1) Average of triplicates. 0.5 mg.
Palladium Found, y o
19.9 19.9 20.2
19.9 19.9 19.7 19.7 19.9 19.7 20.0 20.2 19.9 19.8 19.8
tion alkaline. Low results were often obtained on using sodium hydroxide as suggested by Alvarez ( 1 ) . The hydroxides of iron and cobalt were precipitated even in the presence of ethylenediaminetetraacetic acid. Such precipitates might absorb traces of palladium. Satisfactory results were obtained by using ammonium hydroxide instead of sodium hydroxide. Most hydroxides were not precipitated in the presence of ethylenediaminetetraacetic acid and ammonium hydroxide. Interference Studies. Iron, cobalt, copper, nickel, chromium,
1895 and the platinum metals are generally considered as interfering metals in the spectrophotometric determination of palladium ( 4 ) . I n the proposed procedure all above-mentioned metals did not interfere (Table I ) . Cyanide destroyed the palladium complexes of both 2-nitroso-1-naphthol and 1-nitroso-2-naphthol. The procedure is accurate to within 1% palladium. The minimum detectable amount of palladium appears t o be approximately 0.5 p,p.m. LITERATURE CITED
(1) Alvarez, E. R.. Anales direc. gen. ofic. qulm. nacl. (Buenos Aires), 2,88-90 (1949). (2) Ayres, G. H., and Berg, E. W., ANAL.CHEM.,24,465-9 (1952). (3) Ayres, G. H., and Tuffly, B. L., Ibid., 24, 949-52 (1952). (4) Beamish, F. E., and McBryde, W. -4. E., Anal. Chim. Acta, 9, 349 (1953). (5) Fraser, G. J., Beamish, F. E., and NcBryde, W. A. E., ANAL. CHEM.,26, 495-8 (1954). (6) Hillebrand, W. F., and Lundell, G. E. F., “Applied Inorganic -4nalysis,” p. 278, New York, John Wiley & Sons, 1929. (7) Overholser, L. G., and Yoe, J. H., J . Am. Chem. Soc., 63, 3224 (1941). (8) West, P. W., and Amis, E. S., IND.ESG. CEXEM., ANAL.ED., 18, 400 (1946). (9) Yoe, J. H., and Overholser, L. G., J . Am. Chem. Soc., 61, 2058 (1939). RECEIVEDfor review June 4, 1954. Accepted September 14, 1954. Pre. sented before the Division of Analytical Chemistry a t the 126th Meeting of the A M ~ R I C ACHEMICAL N SOCIETY, New York, N. Y.
Determination of Additive Elements in Lubricating Oils by Emission Spectrographic Methods E. L. GUNN Humble O i l and Refining Co., Baytown, Tex.
The widespread use of additive compounds by the petroleum industry in lubricating oil manufacture requires rapid and precise methods of analysis for control purposes i n blending or for performance testing on field samples taken during customer use. Spectrographic methods have proved satisfactory i n routine use for these purposes. Additive barium and calcium in lubricating oils are determined by a carbon matrix method in which a high-voltage spark is used for excitation of these elements in the presence of cohalt, which serves as a n internal standard. The relative accuracy of the method is approximately 5 % for barium and 8% for calcium in synthetic blends, and about 1 hour is required for the analysis. The influence of base stock or viscosity is either minor or negligible on stocks normally tested, and the method is applicable to either new or used oils. Additive phosphorus is determined in the range of 0.01 to 0.05% in new finished oils by means of a porous cup technique. High-voltage spark excitation is employed and a carbon line is measured for internal standard reference. The relative accuracy on synthetic blends is 6% and less than 1 hour is required for the analysis. The influence of viscosity or the presence of other additive elements is negligible.
D
URING recent years the petroleum industry has placed considerable emphasis upon the development of rapid and sensitive physical methods for the determination of additive components in lubricating oils. Although progress has been made in the improvement of chemical procedures for additive
elements, such methods still are time-consuming, tedious, and therefore expensive. Following the lead of Calkins and White (1 ) with their quenched electrode technique, a Subcommittee on Emission Spectroscopy of the American Petroleum Institute (.4PI) undertook an extensive study ( 3 )of the possibilities of using the quenched electrode technique as a means for additive element determination. A number of petroleum laboratories participated in the cooperative project, and it was found that quenched electrode methods were applicable to new oils of known base stock and additive type but not to used oils or to oils of unknown base stock and additive type. A spectrographic procedure for lubricating oil additives involving the use of an absorbent paper mat (9) packed into a carbon electrode crater has been described. This preparation was not considered satisfactory for the types of oils submitted to this laboratory for analysis, one problem being that of matrix homogeneity, especially as employed for the analysis of used oila. A method using the rotating electrode ( 7 ) with manganese added as an internal standard for phosphorus has been extended ( 8 ) by the use of magnesium buffer and nickel internal standard to include barium, calcium, and zinc, giving excellent precision for these elements in the optimum concentration ranges. In this laboratory phosphorus excitation by the rotating electrode has not been found highly reproducible. The authors of the foregoing papers recommended the use of nitrogen gas in the spark stream, however, which this laboratory did not use, nor has a magnesium buffer yet been tried. This consideration of the use of nitrogen gas, plus the added involvement of the rotating electrode mechanism, seemed to require extra manipulations which
ANALYTICAL CHEMISTRY
1896
lessened the instrumental flexibility and the attractiveness of the method for rapid routine use in this laboratory. +4porous cup method ( 5 ) for phosphorus in lubricating oils has been reported which has a precision measured by a standard deviation of 6.8% in concentration- of 0.05 to 0.2%. For concentrations of 0.01 to 0.05% the precision claimed is somewhat less. The background transmittance found was about 50% and the intensity of the background was used for control reference, as had been done by Calkins and White. It was considered possible that the addition of a buffer element might lessen the background by repressing band spectra and thus improve the precision of the method. I n a more recent paper ( 4 ) from the same laboratory, further studies of both the porous cup and the rotating electrode are presented. .4n over-all accuracy of tht, order of 10% is claimed for both methods, with the data slightly favoring the porous cup for new oils. PRIYCIPLE OF TECHNIQUES IYVESTIGATED
This laboratory is interested in the determination of calcium and barium, whether as soluble compounds or as suspended forms in new or used oils, and of phosphorus in an oil-soluble form. S o one spectrographic technique appeared t o be capable of providing the versatility needed or t o be applicable for routine of all lubricating oil samples submitted. Two techniques jvere investigated which have proved satisfactory for the elemental concentration ranges encountered as well as for all the lubricant types of intereat: a carbon matrix technique for calcium and barium and a porous cup technique for phosphorus. For the determination of calcium or barium a small portion of the lubricating oil sample which is to be analyzed is admixed in a known ratio with cobalt oleate, which serves as the internal standard, and spectroscopic graphite powder to form a "pasty mixture" or matrix for analysis. Electrodes loaded iT-ith the matrix mixture are subjected to a high-voltage spark discharge to produce characteristic spectra of elements in the matrix. From t,he measuremenb of selerted spectral lines the concentrations of sought elements in the oil are determined. The carbon powder serves in equalizing the conditions of excitation and in repressing the background, while the cobalt internal st,andard provides spectral lines for intensity reference. Determination of phosphorus in lubricating oils by the porous cup technique involves introducing the oil into the spark zone by seepage through the porous cup>recording the atomic lines of phosphorus and carbon, and measuring the resulting spectrum for intcrpretat,ion of the phosphorus conttarit of the oil. AXALYTICAL PROCEDURE
Barium and Calcium. E Q u i P Y E s T . The excitation bource is the llodel 4 i O O high precision unit supplied by rZpplied Research Laboratories. The spectrograph is an .4RL 1.5-meter instrument with a grating of 24,000 lines per inch and affording a dispersion of about i .4.per nim. Photometry is performed with the :IRL comparator-densitometer C~LIBRLTIOS STASDARDS.Calibration standards are prepared b\- blending an additive concentrate of known composition in vai ying ratios with unblended lubricating oil. The concentrate is carefully analyzed chemically to determine its barium and calcium content, and the concentrations of these elements in the blended lubricant standards are then calculated from the analysis values. For example, in the preparation of 600 grams of a blend the additive is weighed to the nearest milligram and the blend to the nearest gram after admixture. Heating the sample enables thorough mixing to be made. SAMPI,E PREPARATIO\. R) means of an analytical balance 1.000 gram of cobalt oleate standaid ( 2 ) containing l . O O O ~ o cobalt is added to 5.000 grams of the lubricating oil to be analyzed. These two substances are thoroughly admixed in a small weighing bottle. Two or three drops of the mixture are withdrawn and introduced into spectroscopic graphite powder (Sational, Grade SP-2) to prepare a paste matrix. The carbon-oil matrix should be of such consistency that it just fails to flow when the vial containing the matrix is tilted or inverted. Four highpurity '/*-inch electrodes with craters 1/16 inch in diameter and
inch deep are loaded with the matrix by use of a small glass rod plunger. The opposit,e (upper) electrode is a '/*-inch carbon rod with flat. cut ends. If the sample is a used lubricating oil, the oil must be very thoroughly agitated before a portion is withdrawn for the analysis, as it is difficult to \?-ithdrawhomogeneous portions. The high-voltage spark case of the 3i00 SAMPLE EXCIT~TION. Precision ARL source is employed in sample excitation. The primary voltage is set a t 80 volts nnd the total capacitance and inductance provided for this case are retained in the circuit-Le., 0.007 microfarad and 820 microhenries. The sample is presparked for 5 seconds and exposed for 30 ewonds to record the spectrum. A spark gap setting of 2 mm. is made, total light passage is allowed, and the slit Petting is 30 microns. Four spectra are recorded on the sample. Esstrnan SA-1 emulsion PHOTOMETRY AND INTERPRETATIOS. is used for recording the spectra, with development in D-19 dcveloper for 3 minutes a t 68" & 2" F. To determine barium the Ba 3891.8-Co 3894.1 -4. analytical line pair are measured with the photometer, no correct,ion for background being required. The Ca 3179.3-Co 3409.6 A . line pair likewise are measured for the determination of calcium. To convrrt photometrr transmittance values int,o relative intensity units the emulsion response for the two spect'ral regions must, of course, be predetermined. A rotating step sect,or, factor of t x o , with the iron spectrum is used for this purpose. The intensity ratio of each line pair is then used to interpret the results for the respective elements by reference to an :i nalytiral working curve relating intensit,y ratio to concentration, a s shown in either Figure 1 or 2. Phosphortls. CALIBRATWX sT.4SDARDS. .4 lubricating O i l base stock containing no additive is used for preparing calibration blends. Phosphorus is introduced in the form of an additive concentrate, the phosphorus contrnt, of which has been accurately determined. The additive cwic*entrat,eis weighed to the nearest milligram xith an analytical balance. The blend is weighed to the nearest gram in preparation of a 600-gram quantity of the standard and is heated to facilitate thorough mixing. The blends are prepared to cover the concwitration range of interrst in analysis. SAMPLEEXCIT~TIOS. The porous cup is used a s the upper electrode in the emission spectrograph. Porous cup electrodes S. Reed Co., Westof high-purity carbon are supplied by Ha field, N. J., and are fabricated with the following specifications: 0.02 =t0.002 inch flat floor, '/4 inch diameter, 1 inch length, and inch drill hole. The lon.er electrode is a 45' conical tipped '/(-inch carbon rod. An analytical gap of 3 mm. is employed with the optical axis a t the center of the gap. The slit opening is 40 microns and total light passage is allowed. The circuit capacitance and inductance are the same as used for barium and calcium. A prespark period of 20 seconds precedes an espowrp of 180 seconds for recording the spectrum. h-ai,mally. three spectra are recorded per sample. PHOTOMETRY A X D ISTERPRETATION. The P 2535.6 and c 2582.9 A. line pair are nieasurrd and the background density a t a posit,ion of 2 to 4 .4. to the right of each spectral line is also measured, so that the net intensit\. of each line may be used in calculating the intensity ratio. The concentration of phosphorus in 'the sample is found by referring the intensity ratio t o a calihration mrking Curve similar to that shown in Figure 3.
4.0-
3.5 -
1 I I
1
I
I
l
l
1
I
3.0-
i
/
2.OL
J 0.9
0.6
0.5
1
I
0.10
I
0.15
0.20 WEIGHT
Figure 1.
0.30
0.40
0.60
0.80 100
PER CENT BARIUH
Spectrographic Carbon Matrix Calibration for Barium in Lubricating Oil
V O L U M E 2 6 , NO. 12, D E C E M B E R 1 9 5 4
1897
metals where their identity and concentration in the origin:tl additive concentrate is unknown. Furthermore, the sulfated ash test mal- be considerably limited in the analysis of used oily even of known origin, if the test is to provide an indication of the additive elements in the presence of extraneous or w a r contaminants picked up by the oil during me. Since the sulfated ash test is effect,ive for new oils, the results obhined on a series of laboratory-prepared synthetic blends have been compared witli results for barium and calcium by the emission spectrograph on the same blends. Both the additive and base stock compositions must be accurately established to enable comparisons to he mndts as shown in Table I. I n the sulfated ash tabulation the calculated values {yere derived from the known amount of barium and calcium added to each synthetic blend and from the amount of barium and calcium found in each blend by spectrographic analysis. Thew are compared with the experimental sulfated ash test value on each oil. The average deviation of either the ~u1f:~ted ash test or tlir calculated emission spect1,ographicvalues from synthesis is about, 0.03%. This indicates that the emission spectrographic method is comparable in accuracy to the sulfated a311 on t,hese hlenda.
~
I
3 O i - - - T I
_.
15Co 3409 6
9 1009 -
c
08-
075
06-
05-
__
i
I
0.015
002
_
I
I
1
003
004
005
007
L
I 010
W E I G H T PER CENT CALCIUM
Figure 2. Spectrographic Carbon Matrix Calibration for Calcium in Lubricating Oil
Table 11. Emission Spectrographic and Sulfated 4sh Values on Plant Production Lubricating Oils
APPLICATIOSS
Analysis of Synthetic Blends. In Table I the synthesis values for barium and calcium are compared with analysis values by the emission spectrograph. The average deviation from synthesia is 4 , i % for barium and 8.0% for calcium. The determination of the metal additive content of a newly processed lubricating oil by means of a sulfated ash test is among the more precise of the many control tests made in a petroleum r e f i n e r y . Provided the composition of the additive is known and the amount of extraneous trace metals in the base 2 3.0 stock is insignifi$ ,2.0 cant, the sulfated t_ ssh is adequate a8 an index of com1.0position for blendb d d i t i v e Legend: ing control. The 0 P ADDITIVE 0.5 P,Ba,Co AOOITIVE sulfated ash is, of MIXTUREOFABOVE course, i n a d e I I I I I I I I I I I 0.0 I 0.03 0.10 0.20 q u a t e f o r nonWE:OHT PER CENT PHOSPHORUS metal Figure 3. Calibration for SpectroaI&’sis Or for the graphic Porous Cup Determination deterinination of of Phosphorus in Lubricating Oils
Synthetic Blend No. 1 2 3 4 5 6 7 8 9 10 11 12 13
2 3
: ; 8
9 10 11 12 13
Emission Spectrographic Calcd. as 3‘ 3 Ca “c sulf. ash 0.39 0.080 0.072 0.072 0 OW 0.33 0,080 0 . Olili 0.36 0.078 0.074 0.38 0 076 0.071 0.37 OOK4 0.072 0.33 0.078 0 039 0.33 0.066 0,048 0.27 0.080 0,059 0.34 0.30 0.100 0.038 0.54 0.048 1.08 0.35 0.07 0.067 0.115 0.085 0.49
% Ba
Chemical Test, ?4 Sulf. .Ish 0.42 0.43 0.43 0.47 0.42 0.36 0.34 0.32 0.38 0.28 1.12 0.38 0.52
The precision of the porous cup t,echnique as applied in the drtermination of phosphorus in a synthetic blend containing 0,02470 phosphorus was determined by obtaining replicate data. The average of three spectra normally is reported for a phosphorus determination and a t this level a precision measured by a standard deviation of 0.0013% phosphorus (absolute) or 5.5Oj, (relative) on the component was obtained. The wear metals in used oils which this laboratory analyzes constitute 3 small fraction of the additive metals which :we present as inorganic components. The presence of 0.1% zinc added :ts the oleate has no measurable influence on the carhori matrix method. Such possible wear metals cannot be ignoreti, howevei~,and further work will be carried out to estahliah the PO>sihility of their influence upon the messurements . The accuracy of the poroiis cup method may be estimated t)y ohcrvation of the drviations of anAnalysis of Synthetic Blends by Emission Spectrographic alytical values from synthesis values on prepared and Sulfated A s h Methods blends. For esamplc, the average deviation from Synthesis Emiss. Spec. Sulfated Ash, Wt % aynthr.sis on the hlends shown in TableVIII is 6.1yo A n a & s i s Calcd. from Calcd. from E2.A Clienilrnl % Ba % Ca % Ba % Ca synthesis analysis test on the phosphorus component. The accuracy of prrparing the spectrographic calibration blends ob0 , 1 0 0 0.016 0.118 0.015 0.224 0,257 0.22 0.100 0.015 0.221 viously depends upon the accuracy with which the 0.200 0.032 0.194 0 . 0 2 8 0.449 0.425 0.44 0.195 0.032 0.440 0.43 initial chemical determination of phosphorus on 0.295 0.043 0.673 0.647 0.62 0.300 0.048 0.280 0.048 0.639 the additive concentrate is made. 0.150 0.024 0.152 0,024 0.337 0.340 0.35 Analysis of Production Oils. To illustrate appli0.250 0.040 0.240 0.040 0.561 0.544 0.52 0.222 0.023 0.232 0.028 0.455 0.489 0.41 cations of the spectrographic method to the deter0.222 0.023 0,213 0,024 0.465 0.444 0.47 0.111 0.012 0.115 0.014 0.230 0.244 0.21 mination of calcium and barium in new production 0.111 0.012 0.120 0.014 0.230 0.252 0.21 oils submitted to the laboratory for analysis, the 0.333 0.035 0.320 0.037 0.684 0.670 0.60 0.333 0.035 0.340 0.042 0.684 0.721 0.63 data in Table I1 are given. Again the sulfated ash 0.166 0.017 0.155 0.017 0,340 0.322 0.34 0.50 0.278 0.029 0.265 0.031 0,572 0.555 test values are included to provide comparisons with spectrographic resu1t)s. The sulfated ash in every
-
Table I.
Garni~le 1
ANALYTICAL CHEMISTRY
1898 Table 111. Barium and Calcium in Used Lubricating Oils I
Ba, Wt. % Sample Chem." Emiss. spec. 0.066 1 0.054 0.080 2 0.070 0.100 3 0.063 0.540 4 0.520 4 Determined as ignited BaSOr. b Determined as ignited oxalate.
Ca, Wt. % Chem.b Emiss. spec. 0,052 0.048 0.068 0,059 0.059 0.048 0.059 0.048 _______
Table IV. Influence of Barium-Cobalt Line Pair Measured upon Precisionu and Sensitivity to Change in Barium Concentration Ba 2335 3 A Ba 3891 8 A Co 23889 A. Co 3894 1 A 0.11 5 0.60 1 0 . 0 2 7 0 . 8 2 i0.039 6 0.20 0.76i0.031 1.09 f 0 . 0 5 1 5 1.54 1 0.035 0.94 i 0.027 0.31 Precision of intensity ratio measurement is indicated b y i value of standard deviation after ratio.
'70 Ba
No of Spectra
to precision and analytical response to concentration change, synthetic blends were examined with the results shown in Table IF'. Although both pairs appear to have about the same precision in replicate ratio measurements, the Ba 3891.8-Co 3894.1 -4. pair has considerably better response to change in concentration, this pair was chosen for the measurement of barium. For simultaneous measurement of barium and calcium on the same spectrum the Ca 3179.3-co 3409.6 d.line pair was selected Although the spectral remoteness of these lines is nonideal, the unavailability of other more suitable pairs appeared to dictate the choice of the Ca 31i9.3-co 3109.6 A. pair. The use of zinc oleate containing 1% zinc was considered for use as a buffer. I t was added to the oil sample in a 1 to 10 ratio and a portion then was excited as described above. The effect on either the background or the precision of the line measurements was found to be insignificant. The excitation potential of the P(1) 2535.65 .4. line is 7.2 volts, but no reference was available which gave a value for the C(1) 2582.88.4. line. The spectral proximity is favorable and each line has thus far been found free of interference on the oils analyzed. A 3-minute high-voltage spark excitation period with the porous cup was found to be adequate for excitation and detection of phosphorus in the concentration ranges of plant sample interest. To illustrate the character of the spectra obtained with the high-voltage type of spark excitation a t three concentration levels, the photometry measurements are presented in detail in Table V. The background intensity is rather low, the per cent transmittance averaging about 90% a t positions near the analytical lines. A favorable response of intensity ratio with concentration is shown which, of course, is further evinced by the plot of Figure 3. Influence of Carbon-Oil Ratio. Spectroscopic carbon is one of the most commonly used buffer materials in emission spectrographic analysis. As in the present instance the analytical matrix for determining calcium and barium is made up of oil and carbon, the possible influence of their ratio to each other as a critical variable in the method merits consideration. To test the influence of component ratio, two portions of a synthetic sample were prepared: one with the carbon ratio sufficiently great to enable the matrix to take a firm mold; the other sufficiently low in carbon to enable the matrix to flow readily. Each matrix was analyzed, with the results depicted in Table VI. TRo
case except one is higher on these plant samples than the corresponding value calculated from the spectrographic analysis, the average deviation being about 0.05%. -4n explanation which in part accounts for this consistent difference is the occurrence of extraneous trace contaminants in the base stock other than barium and calcium that are recovered in the sulfated ash test. Analysis of Used Lubricating Oils. Although sample homogeneity is exceedingly important in the carbon matrix technique, it is believed that the opportunity of preparing a uniform electrode charge is much better than exists in an electrode impregnation, porous cup, or rotating electrode approach to sampling. Spectrographic results have been compared with those obtained by chemical analysis, as shown in Table 111. These used oils were very sludgy and good repeatability is difficult by any method on such samples. I n consideration of the limitations of the two methods for the concentrations involved as well as the inhomogeneity of the samples, the agreement between the methods may be described as fair. Blending Control. The most significant application of the spectrographic porous cup electrode method for phosphorus is in day-to-day control inspections made on blend stocks from lubricating oil production submitted from a compounding plant. The time required for analyzing a sample and reporting the results to blending personnel is 1 hour or less. This analysis has proved to beamenable to statisTable V. Photometric Measurement of Additive Phosphorus in Synthetic Lubricating tical quality control for in and Oil Blends out of laboratory samples, and C(1) 2582.88 A. P(1) 2535.65 A. regular use of control data is Syn. ~Line Background Line Background Intensity Anal. made. %P % T" I % Ta I NetI NetI I % Ta I NetI Ratio 70 P DISCUSSION
Spectral Line Characteristics. Cobalt has been found useful as an internal standard for the spectrographic measurement of other elements in oils ( d ) , catalysts ( 6 ) , etc. The broad distribution of its spectral lines as well as its absence as a contaminant in the substances analyzed makes it suitable for this purpose. I n the range of concentration of int e r e s t t h e B a 2335.3-co 2388.9 A. and the Ba 3891.8-Co 3894.1 A. line pairs appeared to be the most promising of the lines examined. T o evaluate their relative merits in respect
0.012
54 58 60
9.4 8.8 8.5
89 91 92
4.8 4.5 4.2
4.6 4.3 4.3
38 42 48
12.3 11.4 10.4
86 86 89
5.2 5.2 4.8
7.1 6.2 5.6
0.024
41 55 37
11.6 9.2 12.5
94 94 92
3.9 3.9 4.2
7.7 5.3 8.3
56 60 46
9.1 8.5 10.7
92 93 90
4.3
4.0 4.6
4.9 4.5 6.1
15.5 12.5 13.5
20.5 22.8 22.0
92 89 93
4.2 4.8 4.0
16.3 18.0 18.0
49 40 48
10.2 11.8 10.4
91 87 90
4.5 5.0 4.6
5.7 6.8 5.8
0.65 0.69 0.77
0.011 0.012 0.013 0.012
1.57 1.18 1.36
0.025 0.020 0.022 0,022
AV.
AV. 0,048
2.86 2.64 3.10
Av.
0.044 0,040
0,047 0.044
Per cent transmittance by comparator-densitometer.
Table VI.
Influence of Carbon-Oil Ratio in Matrix upon Excitation Intensity and Intensity Ratio for Analytical Spectral Linesa
Matrix Consistencyb Thick enough to be shaped Thin enough to flow
Ba3891.8 6.5 10.1
Each value average from six spectra. 0.20% Ba, C Equivalent to 0.204% BE. d Equivalent to 0.206% Ba.
a
b Oil synthetic analyzed. C
Co3894.1 6.1 9.4
Ba 3891.8 Co3894.1 1.06O 1.078
Ca3179 5 6 8.8
Co3409.6 6.2 9.6
Ca 3170 Co3409.6 0.91.i 0,94/
V O L U M E 2 6 , NO. 1 2 , D E C E M B E R 1 9 5 4
1899 of the high tension caseof the 4700 Multisource unit would be somewhat difficult to measure, as i t operates from 20 to 35 kv. peak. The nominal primary voltage is low, however (50 to 300 volts), and it can be reasonably well measured to a precision of 2 volts 2238 on the primary voltmeter. To test the influence of Ba Ca s u.w*l v voltage on the measurements of barium and 0.110 0 , 0 1 8 0.196 0.025 the primary i'put was variedand 0 . 2 3 0 0.029 results were obtained for a standard sample, as 0 . 3 7 0 0.049 shown in Table IX. The intensities of the spectral lines increase with voltage, - but the amount of increase for barium and calcium is not DroDortional to that for the cobalt (internal standard). Thus, low results would be obtained a t a voltage lower than the nominal operating level of 80 volts and high results would be obtained above 80. During normal discharge conditions no discernible primary voltage change can be observed, and therefore it is believed that voltage change during excitation, of itself, does not introduce a significant effect upon the final measurements. The influence of voltage change upon porous cup phosphorus excitation was not tested, as it appeared that sufficiently close control of the voltage could be maintained during the sparking period. Elemental Influence. Among the variables considered as possibly contributing to interference in the determination of phosphorus in oils was the presence or absence of other elements, especially additive metals. Interference may be produced by coincidence of spectral lines of two elements a t a given position of measurement or through the suppression or enhancement effect of the influencing element upon either line of the selected analytical line pair. Additive compounds used in present-day lubricating oil production blending differ somewhat in composition in respect to amount of phosphorus as well as in the identity and amount of other component elements present. To test the influence of barium and calcium, three sets of additive synthetic blends were prepared which contained known amounts of phosphorus. One set was prepared with an additive that contained only phosphorus with no metal elements; another set with an additive containing phosphorus, barium, and calcium; the third set contained known amounts of both the foregoing additive types. These standard blends \%-ereanalyzed by the method described above and the results were plotted as intensity ratio against concentration. From the results shown in Figure 3 it was concluded that the presence of barium and calcium in the stocks normally analyzed produced no significant effect upon the determination of phosphorus.
Table VII. Effect of Viscosity of Base Stock upon Amounts of Barium and Calcium Detected at Three Concentration Levels in Synthetic Blends Wt. yo Detected" Synthesis, Yo Ba Ca 0 . 1 1 1 0.012 0.222 0 . 2 3
Viscosity a t 100' F., S.S.U. 333 166 Ba Ca Ba Ca 0 , 1 2 0 0.014 0.115 0,014 0.213 0 . 0 2 4 0.232 0.028
34.8 Ba 0,100 0.204
Ca 0,013 0.026
0.333 0,035 0.286 0 , 0 3 6 a Each value average of 6 spectra.
0.320
0.037
0.340
0.042
-- - ... -
I
I
-
points which these results reveal are that the higher ratio of oil produces greater spectral intensity than the low but the intensity ratio of the two matrices is essentially the same, thus showing no significant effect of oil-carbon proportion on the results. As a matter of uniform practice the matrix for analysis is prepared to be of such consistency that it just fails to flow when the vial containing it is tilted. Effect of Viscosity. To test the effect of viscosity upon spectrographic detection of calcium and barium, blends ranging in viscosity from 34.8 to 2238 S.S.U. a t 100" F. and varying in additive concentration of these elements were analyzed (Table VII). As calibrations had previously been established by the use of standards of 165 and 333 S.S.U.viscosity, the values shown in the table were taken from these calibrations. These results indicate that the barium-cobalt and calciumcobalt intensity ratios tend to increase with the viscosity of the oil-Le., to produce low results for stocks of very low viscosity and high results for stocks of very high viscosity. This laboratory is seldom requested to analyze lubricating oils of the extremes in viscosity shown in Table VII. Corrections for such extremes in viscosity may be made by one of these methods: il standard of similar viscosity may be analyzed concurrently with the unknown to obtain a factor whereby compensation for the viscosity effect may be made, or a curvk may be constructed for a considerable range in viscosity by use of a series of standards of known additive composition and viscosity, so that a predetermined viscosity correction factor is available for the unknown. To test the influence of viscosity in the determination of phosphorus by the porous cup technique, several synthetic blends of diff e r m t viscosities and phosphorus content also were prepared and analyzed by the procedure outlined above (Table VIII). S o significant effect of viscosity as a critical variable in the detcrmination of phosphorus is reflected in these analyses. I t is believed that the range in viscosity shown will cover most lubricating oils normally submitted for analysis. Influence of Excitation Voltage. The gap discharge voltage
ACKNOWLEDG.MENT
The author gratefully acknowledges the experimental sssisb ance of Virginia Harleston and Vincent O'Donnelly and the helpful suggestions of J. T. Horeczy in preparing this paper, and thanks the Humble Oil and Refining Go. for permitting its release.
Table VIII. Influence of Viscosity upon Determination of Phosphorus in Synthetic Blends
LITERATURE CITED
Calkins, L. E., and White, hl. bl., Natl. Petroleum ,Vews. 38, R-519 (1946). - ~Carlson, RI. T., and Gunn, E. L., .&N.~L. CHEM.,22, 118 (1950). G5 2378 Clark, R . O., et al., Ibid., 23, 1348 (1951). Syn. Anal. Syn. Anal. Gambrill, C. R l . , Gassman, A. G., and O'iXeill, W. R., I b i d , 23, 0.012 0.015 0,015 0.012 1365 (1951). 0,024 0.022 0.029 0.029 0.046 0,044 0,040 0,048 (5) Gassman, A. G., and O'Neill, W. R., I b i d . , 21, 417 0.052 0.052 (1949). (6) G u m , E. L., Ibid.. 23, 1354 (1951). Table IX. Influence of Primary Excitation Voltage upon Excitation (7) Pagliassotti, J. p,, and Porsche, F, w., Ibid., 23, Intensity and .4mount of Barium and Calcium Detecteda,* 198 (1951). Primary Ba(1) Co(1) Ba38918 Co(1) c a 3179 (8) Ibid., p. 1820. Voltage 3891.8 3894.1 C o 3 8 9 4 . 1 % Ba $?&) 3409.6 C03409.6 % C a (9) Veldhuis. H. D.. Cohen, S., and Nahstoll, G. A , , 11.9 1.11 0.210 70 13.2 12.7 8.2 0.64 0.024 Petroleum Processing, 7, 1311 (1952). 14.3 1.14 0.220 8.2 80C 16.3 12.7 0.68 0.025 (Weight per cent phosphorus) Viscosity a t 210' F., S.SE. 165 333 Syn. Anal. Syn. Anal. 0.017 0.015 0.016 0.015 0.029 0.031 0.029 0.032 0.050 0.044 0.044 0.042
1.19 18.0 15.2 0.228 14.0 90 17.7 0.80 Each value average of five spectra. Synthetic sample. 0.222% Ba. 0.023% Ca; 333 S.S.U. vis. a t 100' F. C Nominal operating voltage.
a b
_ _ _ _ ~ ~ _ _ _ ~
0.029
RECEIVED for review March 15, 1954. Accepted August 25, 1954. Presented a t the Pittsburgh Conference on Analytical Chemistry and Applied Spectroscopy, Pittsburgh, Pa., March 1954.
