Brooke Katzman (Presenter)
Mayo Clinic
Bio: Brooke Katzman is in her second year of Clinical Chemistry Fellowship at the Mayo Clinic in Rochester, MN. Dr. Katzman earned dual undergraduate degrees in chemistry and biology at Youngstown State University in Youngstown, Ohio. She then received her Ph.D. in chemistry from Emory University in Atlanta, Georgia. Her graduate work focused on the design and synthesis of novel small molecule therapeutics for the treatment of neurological disorders such as Alzheimer’s disease and another project devoted toward the development of pharmaceutical agents that block HIV-1 cellular entry. While in fellowship at Mayo, Brooke has pursued various projects centered on laboratory test utilization, quality assurance, and the development of novel mass spectrometry-based assays. During her final year of fellowship, she serves as the acting director of the Central Clinical Laboratory.
Authorship: Brooke M. Katzman, Waddah Katrangi, Steve Eckdahl, Melissa Maras, David L. Murray, Paul J. Jannetto
Mayo Clinic
| Short Abstract The analysis of trace metals in blood samples by inductively coupled plasma-mass spectrometry (ICP-MS) can be complicated by number of unique challenges—both pre-analytical and analytical in nature. Not only should samples for analysis be collected in metal-free tubes to minimize contamination, but also special precautions must be taken to reduce the effect of polyatomic spectral interferences inherent to ICP-MS. Three approaches are commonly employed to overcome such interferences: 1) selection of isotopes that are free from interference, 2) incorporation of correction equations, and 3) the use of cell technology (i.e. collision cells or dynamic reaction cells). The above approaches were effectively utilized in the development of two robust assays to accurately and precisely quantitate chromium/cobalt and titanium in whole blood samples from patients with metal-on-metal implants. |
Long Abstract
Background
While trace elements account for only 0.012% of the body weight of humans, the ability to monitor their concentrations in various body fluids is important due to the integral roles they play in both normal physiological function and toxicity. Some trace elements are innocuous at typical exposure concentrations; however others can result in severe toxicity even at low concentrations. In patients with metal-on-metal (MoM) implants, elevated concentrations of metals detected in various body fluids can indicate progressive device wear and degradation. The metal debris (ions and particles) that are released into the space surrounding the implant can subsequently enter the bloodstream. As such, failure of some MoM devices can cause bone and/or tissue damage near the implant or joint and can even result in systemic reactions such as neurological changes, impairment of renal function, cardiomyopathy, and other hypersensitivity reactions.
Recently, the Food and Drug Administration (FDA) has recommended that in combination with general clinical evaluations, patients with MoM implants should be followed with serial measurements of metal ion concentrations. Due to the potential for contamination, the FDA has also recommended that testing be performed using EDTA anti-coagulated whole blood samples. However, the determination of metal ion concentrations in these samples by inductively coupled plasma–mass spectrometry (ICP-MS) is plagued with several challenges. Whole blood samples contain large amounts of organic compounds and inorganic salts, which can lead to significant spectroscopic interferences from isobaric overlaps or other nonspectral interferences produced by a combination of solvent and matrix components in the sample. As a result, detection capability by this technique can become severely compromised.
Fortunately, there are several approaches that can be used to overcome such interferences including: 1) selection of isotopes for analysis that are free from interference, 2) incorporation of a correction equation to compensate for the interferences, or 3) the use of collision or reaction modes of analysis. Traditionally, polyatomic interferences can be removed or reduced using a quadrupole-based dynamic reaction cell (DRC). Optimization of the electrical fields within the quadrupole prevents unwanted reactions between the instrument gas and sample matrix/solvent. Additionally, by carefully selecting the optimum carrier gas and gas flows, other reactive gases can be introduced to react with the analyte of interest producing an ion that shifts the analyte mass to a higher mass region, presumably free from the original polyatomic interferences.
Methods
The methods to measure 1) chromium (Cr) and cobalt (Co) and 2) titanium (Ti) were developed on an ICP-MS (Perkin Elmer NexION 350) configured with collision/reaction cell technology. For all methods, calibrating standards, reagent blanks, quality control specimens, and patient samples were diluted with aqueous diluent containing 10mM EDTA and trace NaOH. Calibrating standards for the Cr/Co method were aqueous acidic salt matrix whereas the Ti method utilized a caprine blood matrix. Internal standards were introduced via a t-line and used gallium for the Cr/Co method and a sum of yttrium, scandium, bismuth and lutetium for the Ti method. For both methods, the sample introduction system was an O-ring-free quartz cyclonic spray chamber fitted with a PC3 Peltier chiller (Elemental Scientific) operating at 2 °C and PFA-ST nebulizer (Elemental Scientific). The nebulized solutions suspended in the carrier argon gas stream were directed to and injected into a high temperature (6800 °K) argon gas discharge (plasma). For the measurement of Cr and Ti, each method employed DRC mode whereby ammonia gas is utilized to stimulate chemical reactions within the cell to react away polyatomic interferences. Cobalt ions were separated from interfering substances using the kinetic energy discrimination (KED) mode whereby the non-reactive gas, helium, is introduced into the cell. The gas collides with polyatomic interferences such as calcium oxide (CaO+) and magnesium chloride (MgCl+). The large metal complexes undergo more collisions in the cell. As the complexes lose increasingly more energy, they are excluded from the quadrupole mass filter by the kinetic energy barrier, thereby attenuating the interference.
Results
By controlling and optimizing various instrument parameters, we were able to achieve high analytical sensitivity and specificity in the measurement of Cr/Co and Ti in whole blood specimens from patients with MoM implants. With regard to the method to measure Cr and Co, 40Ar12C+/16O35ClH+ and 43Ca16O+/ 24Mg35Cl+ were the main isobaric interferences with Cr (m/z = 52) and Co (m/z = 59), respectively. These interferences were overcome by varying the flow of the cell gases, ammonia and helium, for Cr and Co, respectively. Potential polyatomic ion interferences for the measurement of Ti included: 97Mo(NH3)2+, 114Cd14NH3+, 48Ca14NH(14NH3)4+, 65Cu14NH(14NH3)3+, and 64Zn14NH2(14NH3)3+. Aqueous solutions with concentrations that targeted normal endogenous concentrations of Ca, Cu, and Zn in human blood were used to determine the effect of the potential polyatomic interferences. Meanwhile, elevated concentrations of Mo and Cd sufficient to identify polyatomic formations, were used to determine a mathematical correction factor. Through documentation of each individual element’s polyatomic presence at m/z = 131, we demonstrated that the above polyatomic ions could be sufficiently attenuated using a mathematical correction for Mo and Cd and a method blank subtraction for Ca, Cu, and Zn.
References & Acknowledgements:
1. Cieslak W, Pap K, Bunch DR, Reineks E, Jackson R, Steinle R, Wang S. Highly sensitive measurement of whole blood chromium by inductively coupled plasma mass spectrometry. Clin Biochem. 2013; 46(3): 266-270.
2. Hsiung C-S, Andrade JD, Costa R, Ash KO. Minimizing interferences in the quantitative multielement analysis of trace elements in biological fluids by inductively coupled plasma mass spectrometry. Clin Chem. 1997; 42(12): 2303-2311.
3. Jacobs JJ, Skipor AK, Patterson LM, Hallab NJ, Paprosky WG, Black J, Galante JO. Metal release in patients who have had a primary total hip arthroplasty. J Bone Joint Surg. 1998; 80(10):1447-1458.
4. Olesik J and Jones DR. Strategies to develop methods using ion-molecule reactions in a quadrupole reaction cell to overcome spectral overlaps in inductively coupled mass spectrometry. J Anal At Spectrom. 2006; 21:141-159.
5. Seiler HG, Sigel A, Sigel H. Chromium and Cobalt. Handbook on Metals in Clinical and Analytical Chemistry 1994; 627-630.
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