Dramatic Improvement in Turn Around Times (TAT) using Agilent 7500a ICP-MSby Judy Brown and LinaCel Cadden, Satellite Laboratory Services, LLC. CA, USA
The Company
Satellite Laboratory Services, LLC, is a leading provider of renal laboratory services. An important test conducted by the laboratory is the determination of aluminum and zinc in end-stage renal disease (ESRD) patient plasma samples using ICP-MS.
Instrumentation
Prior to 2003 the laboratory assayed aluminum in plasma using Graphite Furnace Atomic Absorption (GFAA). In response to an increasing number of samples, an ICP-MS was purchased in late 2003. The system underwent validation studies for aluminum (1:20 dilution) and zinc (1:50 dilution) in patient plasma. Trace metal analysis in dialysis water was later added in 2004. Switching the ICP-MS between plasma and water methods proved to be cumbersome and challenging. It required a time-consuming cleaning and maintenance procedure as well as a methanol correction procedure to correct for differences in matrices. By late 2005, the sample load had increased sufficiently to warrant a second ICP-MS dedicated to running plasma samples. An Agilent system was chosen based on its ability to simultaneously assay plasma aluminum and zinc from a single 1:20 dilution in less time than the existing ICP-MS system.
The first Agilent 7500 ICP-MS was installed in the laboratory in late 2005 with a second instrument added in late 2006. Central to the ability of these instruments to handle the laboratory’s ever-increasing sample load are:
Minimal maintenance and start up procedure Stability of calibration curve and consistent internal standard recoveries
Ease of operation
Reduced sample preparation requirements with a single 1:20 dilution
Simultaneous analysis of both aluminum and zinc
Elimination of the methanol correction procedure
Pre-emptive Rinse software function
CETAC ASX-520 autosampler with 270 sample capacity
Procedure
Satellite Laboratory Services provides dialysis units with sample collection tubes that have been lot tested to confirm the absence of aluminum and zinc. Any samples received in tubes other than these are rejected. Samples exhibiting gross hemolysis are also rejected.
High purity reagents are used: Optima Grade of 70% nitric acid and DI and distilled water that meets CAP Type I specifications. Liquid argon is 99.996% pure. Made-to-order reagents include stock solutions for the preparation of aqueous calibrators, three levels of multi-element standards, 10 ppm tuning solution and a multi-level internal standard.
Working Solutions are:
Wash: 0.1% nitric acid
Tuning Solution: 10ppb tuning solution in 1% nitric acid
Sample Diluent: 0.1% nitric acid with 20ppb Yttrium internal standard
Standard 1: 20 ppb each of Al and Zn Calibration Standard
Standard 2: 50 ppb each of Al and Zn Calibration Standard
Standard 3: 100 ppb each of Al and Zn Calibration Standard
Controls: Normal and High Bi-level UTAK Trace Elements Serum Toxicology Controls
50 ppb Check Control (QC Standard 1): Standard 2 above
Standards as well as samples and controls are diluted 1:20 with sample diluent. No further preparation is required.
Analytical Protocol
Diluted calibration standards, controls and samples are loaded into an enclosed CETAC ASX-520 autosampler. To reduce analysis time, the system uses a pre-emptive rinse, and the peri-pump software program is set to increase sample uptake rate during wash cycles. With an autosampler capacity of 270 patient samples and a 2.5min./sample-to-sample analysis time, we are able to load a second set of samples onto each instrument before the end of our normal workday. Since the 7500a continues to run unattended, we program a standby sequence to shut the instrument down when the run is completed.
Results
Acceptance criteria for calibration and controls are:
a. Calibration: r2: > 0.999; BEC: < 0.3 ppb; Internal standard (ISTD) has consistent/stable recovery
b. Controls must be within the established range.
c. Check Controls are run at the beginning of the sample batch, after every 20 samples, and at the end of the batch. If the control is outside the established range, samples in between the last acceptable check control and the out-of-range check control must be repeated.
d. The RSD for the ISTD must be < 10% or the sample must be rerun.
e. The sample’s ISTD measured intensity must be < 25% of the blank’s ISTD measured intensity or the sample must be rerun.
f. The Check Controls’ ISTD must be ≤ 10% of the blank’s ISTD.
The statistics for in-run QC checks (c, d, e, and f above) are included in the report generated by the 7500 ChemStation software and any QC parameter that exceeds the set boundaries is flagged.
Typical calibration curves for Al and Zn are shown in Figures 1 and 2.
Figure 1. Typical calibration curve for aluminum
Figure 2. Typical calibration curve for zinc
The linear ranges were validated as follows:
Aluminum: 0.05 to 300 ug/L (ppb)
Zinc: 0.05 to 300 ug/L (ppb)
Results below the linear range are reported as <1 ug/L. Results with a direct reading >300 ug/L must be further diluted and re-assayed.
Conclusions
Since using the methodology described, turn around times (TAT) have improved dramatically. Historically TAT on GFAA and early-ICP-MS averaged 1 to 2 weeks. They now average 1-3 days. A third Agilent 7500a ICP-MS has been validated for running aluminum and zinc in plasma samples. It is also undergoing validation for dialysis water. Once completed, the bulk of the sample throughput will be handled by Agilent 7500a ICP-MS systems.
More Information
Contact LinaCel Cadden, caddenl@satellitelabs.com or visit the Satellite Laboratory Services web site at: www.satellitelabs.com.