Analytical Instrumentation Table 2. Instrumental Parameters and Conditions
Parameter Nebuliser
Spray Chamber RF Power Torch
Injector
Plasma Gas Flow Aux. Gas Flow
Nebuliser Gas Flow Torch Position Plasma View
Sample Uptake Rate Value
GemCone™ (modified Babbington)
Baffled glass cyclonic 1500 W
3-slot torch for organics 1.2 mm ceramic 10 L/min 0.8 L/min 0.40 L/min -4
Radial
1.60 mL/min (Avio 500) 2.0 mL/min (Avio 200)
Sample Uptake Tubing Black/Black (0.76 mm id), Viton Drain Tubing Read Delay
16 sec (Avio 500) 18 sec (Avio 200)
Replicates
Rinse Time Between Samples
Read Time Range 2
None with ASXpress (Avio 500) 12 sec at 6 mL/min (Avio 200)
0.5-2 sec (Avio 500) 0.2-1 sec (Avio 200)
to minimise sample uptake and washout times. Combining the ASXpress with the simultaneous ICP-OES, sample-to-sample analysis time is 25 seconds – ideal for high throughput labs.
Figure 1 shows the concentrations of seven elements in 10 randomly selected samples (although 23 elements were measured for each sample, only seven elements are shown for clarity). These data clearly show variations between samples, as well as the range of concentrations measured: from 1 ppm to greater than 1000 ppm. While most elements vary greatly between samples, the phosphorus concentration is relatively constant, demonstrating that the methodology is capable of detecting both large and small changes, sample-to-sample.
Table 3. Final QC Check Samples of a 20-Sample Analytical Run with the Avio 200 ICP-OES (hybrid scanning)
Final QC Element Al
Ag B
Ba Ca Cd Cr
Cu Fe K
Mg Mo Mn Na Ni P
Pb Sb Si
Sn Ti V
Zn
Concentration (ppm)
50 48 54 49 45 50 50 50 53 49 46 49 49 49 49 46 50 50 48 49 50 49 47
% Recovery
100 96
108 98 90
100 100 100 106 98 92 98 98 98 98 92
100 100 96 98
100 98 94
Figure 2. QC stability during a 6-hour analytical run of 332 in-service oil samples with the Avio 500 ICP-OES (simultaneous).
Author Contact Details Author: Ken Neubauer, PerkinElmer, Inc. • 710 Bridgeport Ave, Shelton, CT 06484, USA • Tel 001-203-925-4600 • Email:
Kenneth.Neubauer@
perkinelmer.com •
www.perkinelmer.com
To assess the stability of the method, 332 in-service oil samples were analysed, along with QC standards every 11 samples, over 6 hours. The plot in Figure 2 shows the stability for the QC standards, where all elements recovered within 10% of the true value. The results demonstrate the robustness and stability of simultaneous ICP-OES in accordance with ASTM D5185 in a high- throughput environment. An important factor for achieving this stability is the incorporation of a vertical torch which allows non- ionised samples to drain back down the torch rather than pooling in the injector, causing carbon build-up on both the injector and torch.
The stability for the hybrid scanning ICP-OES was determined by measuring the QC samples both at the beginning and end of
a run consisting of 20 in-service oil samples. The results of the last QC sample appear in Table 3 and show that all elements recovered within +/- 10% of true value, meeting the acceptance criteria of typical in-service oil labs. These results demonstrate the stability of the methodology, allowing a low-volume, in-service oil lab to easily perform their daily analyses with a hybrid scanning ICP-OES.
Conclusion
This work has demonstrated the ability of both hybrid scanning and simultaneous ICP-OES instruments to measure in-service oil samples in accordance with ASTM method D5185 in both low and high-throughput environments to meet the specific needs of the lab. Sample throughput is maximized for both instruments by using an enhanced throughput sample introduction system, which eliminates the rinse time between samples. Both accuracy and stability are achieved, showing that ICP-OES is the ideal technique for the analysis of metals in in-service oils.
References
1. ASTM D5185 “Standard Test Method for Multielement Determination of Used and Unused Lubricating Oils and Base Oils by Inductively Coupled Plasma Atomic Emission Spectrometry”, ASTM.
Red/Red (1.14 mm id), SolvaFlex Figure 1. Concentrations of Al, B, Ca, P, Si, and Zn in 10 randomly selected in-service oil samples with the Avio 500 ICP-OES (simultaneous).
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