Accelerator Mass Spectometry (AMS) is an enabling analytical platform that is unique in four important ways:
These unique analytical characteristics result from the use of the 14C microtracer the tightly controlled four-stage process used by Xceleron. The sensitivity of AMS enables very small samples to be analyzed – a few µL or mg and even down to a few thousand cells.
Client samples can be analyzed as total 14C (all drug-derived material) or fractionated using an appropriate technique (commonly HPLC) in order to measure specific compounds of interest. Qualitative and quantitative methodologies can be designed for every investigation. Overall analytical robustness is conferred by Xceleron’s quality control procedures.
The AMS instrument ionizes the graphitized sample, sequentially selects 12C, 13C and 14C ions and accelerates these to high velocities using a large potential difference (250 kV in the case of Xceleron’s instrument). The abundance of each isotope is then accurately measured using three separate detectors, the most sensitive of which is able to count individual 14C ions. The results are expressed as isotope ratios, which are converted to radioactivity amounts (based on the half-life of 14C) and mass quantities based on the total carbon content of the sample graphitized and the specific radioactivity of the target analyte (ie how much 14C is associated with a given quantity of analyte).
For a more detailed description of how AMS works read the our PDF guide here
All compounds of interest in an AMS investigation are labelled with 14C microtracer. Its use allows us to follow all drug related material containing the 14C label (parent compound and metabolites) after administration of pharmacological- or micro-doses. Typically the 14C microtracer makes up only a few µg of the dose administered. We can also de-convolute drug disposition by following concomitant intravenous microtracer doses on top of an extravascular pharmacological dose. Finally, these properties can be conferred on any target analyte, small molecule or biologic.
Our first task is to collect the fraction from which we wish to analyze the 14C microtracer. This may be as simple as collecting the appropriate matrix (tissue or cell population) and taking that fraction through cleanup for analysis of total 14C (all drug-derived material). It is more likely that appropriate matrices will be subjected to additional chemical extraction and chromatographic separation to collect parent and metabolite compounds of interest.
We isolate the 14C microtracer by combusting the fraction, collecting CO2 and then turning the gas into graphite. This two stage process isolates the 14C target analyte from any potential matrix interferants.
The Xceleron AMS is essentially a carbon atom counter. We are specifically interested in the 12C:14C ratio, using it to quantify the compound of interest (parent or metabolite) containing the 14C microtracer. Therefore, if we are able to attach the microtracer to a compound it does not matter if it is small or large molecular weight or if it is derived by chemical or biological synthesis. We typically operate in the low pg/mL range and can go as low as fg/mL.
The robustness of the entire HPLC + AMS assay must be assessed. Losses or inconsistency may arise during multiple pre-detector processing steps such as extraction, HPLC separation, transfer of HPLC fraction, and graphitization. These must be fully characterized if a quantitative bioanalytical assay is to be considered fit to support clinical development. The transfer of an assay to HPLC+AMS from LC-MS/MS entails significant changes and thus requires care followed by a full validation of the HPLC+AMS assay. Limited aspects of a previously validated LC-MS/MS may be directly transferrable but insufficient testing of an HPLC+AMS method may introduce significant risk to the clinical study objectives and developmental timelines.
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