Analysis of Wear Metals and Additive Package

a p p l i c at i o n N o t e
ICP-Optical Emission Spectroscopy
Author
David Hilligoss
PerkinElmer, Inc.
Shelton, CT USA
Analysis of Wear Metals
and Additive Package
Elements in New and
Used Oil Using the
Optima 8300 ICP-OES
with Flat Plate Plasma
Technology
Introduction
The analysis of new and used oil for concentration trends of
wear metals and for formulation or depletion of additive package
metals has been around for over 30 years. Wear metals such
as copper (Cu) and iron (Fe) may indicate wear in an engine
or any oil-wetted compartment. Boron (B), silicon (Si) or sodium
(Na) may indicate contamination from dirt or antifreeze leading
to a failure. Additive elements such as calcium (Ca), phosphorus
(P) and zinc (Zn) are analyzed for depletion which contributes
to wear since these elements contribute to certain key lubrication characteristics. A sound maintenance program, which
routinely measures metals in the lubricating oils, not only
reduces the expense of routinely dismantling the components for visual inspection, but
can indicate unexpected wear before component failure.
Atomic absorption spectrometers (AAS) were first used for these applications in the earlyto-mid 1960s. As the number of elements and samples grew over the years, inductively
coupled plasma-optical emission spectrometers (ICP-OES) were used for oil analysis.
Today, many oil analysis labs will handle between 500 to 2000 samples per day and
analyze from 15 to 24 elements per sample.
Many improvements to ICP technology have taken place over the years with the most
recent being the replacement of the helical load coil used to generate the plasma. The
Optima™ 8x00 ICP-OES series (Figure 1 – Page 2) utilizes the new Flat Plate™ plasma technology
that replaces the traditional helical coil design used since the inception of the inductively
coupled plasma. The Flat Plate plasma technology utilizes two flat induction plates
(Figure 2) to produce a plasma that is compact, dense and
robust. This plasma utilizes about half the argon required
by previous helical coil designs while still delivering exceptional analytical performance. The Flat Plate system produces
a flat-bottom plasma that minimizes the escape of sample
and vapors around the outside of the plasma, making organic
sample analysis easier. Plasma argon flow has been reduced
to 10 L/min versus the typical 15-18 L/min used by helical
systems for this application which helps to reduce the cost
of analysis.
Figure 1. PerkinElmer Optima 8300 ICP-OES spectrometer.
Plasma parameters for the analysis of wear metals and
additive package elements in new and used oil using the
Optima 8300 ICP-OES are listed in Table 1. The analytical
wavelength for the elements analyzed are listed in Table 2.
Several important parameters from the WinLab32™ software’s
oil method conditions are described in Table 3 (Page 3).
Table 1. Plasma parameters for all analytes using the Optima
8300 ICP-OES.
ParameterValue
Source Delay (sec)
15
Plasma Aerosol Type
Wet
Nebulizer Start-up
Instant
Plasma Gas (L/min)
10
Auxillary Gas (L/min)
0.6
Nebulizer Gas (L/min)
0.35
Power (W)
1500
Viewing Distance (mm)
15.0
Viewing Mode
Radial
Table 2. Analytical wavelengths used for detection of wear
metals in oil using ICP-OES.
AnalyteWavelength
Ag
328.066
Al
394.408
B
249.673
Ca
315.890
Co (Int. Std.)
228.613
Cr
205.559
Cu324.757
Figure 2. Torch-box of an Optima 8300 spectrometer showing the revolutionary
Flat Plate plasma technology.
Experimental Conditions
Instrumentation
Data were collected using the PerkinElmer® Optima 8300
ICP-OES with a CETAC® ASX-1400 stirring autosampler
(CETAC Technologies®, Omaha, NE). The standard sample
introduction system is as follows:
• A low-flow GemCone™ nebulizer (Part No. N0770358)
• A 4 mm baffled cyclonic spray chamber (Part No. N0776090)
• A 1.2 mm i.d. quartz injector (Part No. N0781019)
• A screened autosampler probe (Part No. N0771529)
2
Fe
259.940
K
766.494
Mg
279.076
Mn
257.613
Mo
203.843
Na588.995
Ni
231.604
P
214.915
Pb
220.351
Si
288.161
Sn
189.926
Ti
334.943
V
292.397
Zn
213.854
Table 3. WinLab32 for ICP method parameters for the
analysis of wear metals and additive package elements in oil.
ParameterValue
Read Delay Time (sec)
14
Replicates2
Read Time (sec)
Automatic – Min: 0.100, Max: 2.000
Sample Flow Rate (mL/min) 4.00
Sample Flush Time (sec)
5
Sample Flush Rate (mL/min) 6.00
Wash Frequency
Every sample + extra time if limit
exceeded
Wash Rate (mL/min)
5.00
Wash Time (sec)
2
Additional Wash Time (sec) 30
Peak Algorithm Peak area (3-point)
Background Correction
2-point
Internal Standard
Co
Calibration Equation
Linear through zero
Sample Units
ppm
Forty-five sample bottles, or 90 samples poured into small
sample cups for dilution, can be prepared in a batch which
requires approximately 35 seconds preparation time per
sample. All sample information is transferred directly
from the APS-1650 software into the WinLab32 software,
eliminating the need to enter the data twice. Only 5 mL
of diluted solution is required for the analysis. This volume
allows for a sample to be analyzed twice in case of a QC
failure. Cobalt is used during the analysis as an internal
standard to overcome the matrix suppression caused by
different oil viscosities. The cobalt can be added to the
solvent diluent prior to sample dilution, thus eliminating the
need to add the internal standard to each individual sample
or through an online addition tubing. Since the additive
elements are organic-metallic and soluble in the oil, the use
of an internal standard provides a more accurate result. The
wear-metal elements are suspended in the oil matrix and
the results compare favorably to other analysis techniques.
Quality Control Limits (%) ±10
Quality Control Fail Actions Recalibrate, re-analyze check
standard, re-analyze affected
samples.
Reagents
All solutions were prepared with a CETAC® APS-1650
Automated Prep Station. Calibration standards were made
using three V23 (VHG Labs®) blended standards at 500, 100,
and 50 ppm (Part Nos. 500: N0776106; 100: N0776105;
50: N0776104). The V23 standards contain 23 elements (Ag,
Al, B, Ba, Ca, Cd, Cr, Cu, Fe, K, Mg, Mn, Mo, Na, Ni, P, Pb,
Sb, Si, Sn, Ti, V, and Zn) in 75 centistoke (cSt) hydrocarbon oil.
A higher-concentration calibration standard for the additive
elements was prepared using Metals Additives Standard 4
(VHG Labs) which contains Ca at 5000 µg/g plus Mg, P and
Zn at 1600 µg/g (Part No. N9308259). The solvent for all
cases was V-Solv™ (Part No. N9308265). The solvent for all
dilutions was a solution of 2.5 grams of a 6% cobalt standard
(in mineral spirits) (Part No. N0776107) added to one gallon
of V-Solv™.
Sample and Standard Preparation
All samples and standards were diluted 1:10 with V-Solv™
(containing cobalt) on a CETAC® APS-1650 Automated Prep
Station (Figure 3) (Part No. N0777177). The prep station
picks up the oil from standard 2-4 oz bottles or 3 mL sample
cups, dispenses the oil into an autosampler tube, adds solvent
and mixes the sample directly in the autosampler rack. The
sample preparation is done on a volume-to-volume basis.
Figure 3. CETAC® APS-1650 Automated Prep Station for use with an Optima
8300 ICP-OES.
Another sample and standard dilution option would be the
PerkinElmer OilPrep™ 8 Oil Diluter (Figure 4, Page 4)
(Part No. L1610000). To meet the need for increased
throughput in wear-metal analysis programs, the OilPrep 8
Oil Diluter is equipped with ultrasonic liquid-level detection
(patent pending) and an 8-tip Varispan™ pipetting arm option
for rapid “on-the-fly” reformatting and diluting of samples
in various sized vessels. The system utilizes multiple syringes
along with disposable tips to increase sample throughput
while eleminating carryover between samples and solvent
waste (no rinsing is required). The sample preparation
is done on a volume-to-volume basis. Ninety-six sample
bottles, or any larger numbers of smaller sample containers,
can be prepared at a time. Throughput can be as high as
300 samples per hour. All sample information is transferred
directly from WinPREP® software into the WinLab32 software,
eliminating the need to enter the data twice.
3
Results and discussion
Figure 4. PerkinElmer OilPrep 8 Oil Diluter pipettes 8 samples simultaneously.
Increased ICP Sample Throughput
ICP sample analysis time can be greatly reduced by adding
a sampling valve to the ICP such as the CETAC® ASXpress™.
A standard analysis system relies upon a single peristaltic
pump to both deliver samples to the nebulizer and rinse the
sample flow path between sample deliveries. The ASXpress™
system utilizes a high-speed vacuum pump in addition to the
ICP-OES peristaltic pump (Figure 5). The 6-port valve allows
the use of both pumps simultaneously, reducing total sample
analysis time significantly. The use of the valve effectively
divides each analysis into two stages. First, while the valve is
in the load position, the vacuum pump rapidly fills the sample
loop, while the ICP-OES peristaltic pump simultaneously
transports carrier solution, keeping the plasma stable.
In the second position, the loaded sample is pushed into
the nebulizer for analysis via the carrier solution flowing
through the ICP-OES peristaltic pump. At the same time,
the autosampler probe is moved to the rinse station and
the uptake flow path is flushed with rinse solution via the
vacuum pump. Improvements from this approach are:
Table 4. Example of a mean result for the analysis of a used
oil sample using the Optima 8300 ICP-OES (n=2).
Analyte
Conc. (ppm)
Ag
Std. Dev. (ppm)
% RSD
ND ------
Al
6
0.101.6
B
51
0.040.09
Ca
828 101.2
Cr
3
0.031.2
Cu
23
0.291.2
Fe
481 5.11.1
K
6
0.589.6
Mg
18
0.060.3
Mn
12
0.040.31
Mo
3
0.3815
• Less carbon build-up on the torch and/or the injector.
Na
5
0.081.5
• Stability is increased for a longer period of time, requiring
less recalibration and improving QC.
Ni
2
0.2313
P
947
0.130.01
Pb
2
0.2814
Si
24
0.451.9
Sn
1
0.1816
• Analysis time per sample can be as short as 20 seconds
(2 replicates per sample) without any degradation in the
analysis precision or long-term stability.
Figure 5. Schematic of the CETAC® ASXpress™ Rapid Sample Introduction
System.
4
Below are the mean results obtained for the analysis of
a used oil sample utilizing the Optima 8300 without the
ASXpress™ (Table 4). Analysis time per sample was 45 seconds,
which includes washing between samples and two replicate
readings per sample. Two check standards for low (wear
metal – 50 mg/L) (Table 5, Page 5) and high concentrations
(additive elements – 1600 mg/L), were analyzed every 20
to 40 samples with upper and lower limits set at ±10%.
With the stability of the Optima 8300 system, the check
standards rarely failed in an 8-10 hour period. If a check
standard should fail, the action selected in the software is
to recalibrate, rerun the check standard to verify it is within
limits, and then rerun all samples since the last acceptable
check standard. The % RSDs were as expected – low when
analytes were present at typical concentration levels of > 5 ppm
and higher when very little analyte was present. Similar
results would be seen using the ASXpress™ with sample
times of 24 seconds per sample.
Ti
ND ------
V
ND ------
Zn
503 5.51.1
Co (Int. Std.)
92%
0.70
0.76
Conclusion
Table 5. Example of a single 50 ppm QC sample.
Analyte
% Recovery
Std. Dev. (ppm)
% RSD
Ag 100
0.040.09
Al 106
0.591.1
B
99.3
0.050.09
Cr 103
0.290.56
Cu 99.5
0.090.18
Fe 102
0.050.10
K
0.200.39
101
Mn103
1.12.2
Mo 99.2
0.280.56
Na 103
1.02.1
Ni 101
0.611.2
Pb 103
2.03.9
Si 103
1.22.3
Sn 103
0.681.3
Ti 101
1.12.3
V
103
0.040.07
Co (Int. Std.)
100
0.54
The PerkinElmer Optima 8300 ICP-OES handles the diluted
oil matrix very easily and increases sample throughput over
previous Optima models to 45 seconds per sample with little
carryover between samples. The Optima 8300 is the ideal
ICP spectrophotometer for oil laboratories with moderate
workloads. For laboratories with a heavy workload, an
Optima 8300 combined with a CETAC® APS-1650 Automated
Prep Station or a PerkinElmer OilPrep 8 Oil Diluter and
CETAC® ASXpress™ Rapid Sample Introduction System is
suggested.
The Optima 8000 ICP-OES, also equipped with Flat Plate
plasma technology, may also be used for this analysis.
0.54
Ca, Mg, P and Zn were not reported as QC analytes.
PerkinElmer, Inc.
940 Winter Street
Waltham, MA 02451 USA
P: (800) 762-4000 or
(+1) 203-925-4602
www.perkinelmer.com
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