Bioanalytical assay, sensitivity

Rainville PD, Smith NW, Cowan D, Plumb RS. Comprehensive investigation of the influence of acidic, basic, and organic mobile phase compositions on bioanalytical assay sensitivity in positive ESI mode. J Pharm Biomed Anal 2012 59 138-50. 

Although the lower limit of quantitation is established during assay validation and prior to microdosing, assay sensitivity remains an uncertainty until the actual analysis of the microdose samples as well. There is always the danger that plasma exposures from the microdose are lower than predicted and as a result plasma concentrations from some or all of the time points cannot be detected by the LC-MS/MS method. Reduction of this risk is achieved by collaborative communication between the bioanalytical chemist and the project team. Conservative estimates on bioavailability and clearance can be used to establish the necessary limit of detection needed to determine plasma concentrations for all time points. Updates on the progress of the assay development allow the team to decide if the achievable limit of detection will enable the determination of plasma concentrations from enough time points to make a go-no go decision. Of course, sensitivity is not an issue with AMS, which practically ensures that plasma concentrations will be determined, possibly for several days, enabling the observation of complex PK and clearance from deep compartments. 

For several reasons, most applications of chemo- and biosensors require flow through devices, for example in allowing analysis of samples from multiple sources, removing flow sensitivities, avoiding sterilization and biocompatibility problems, enabling recalibration or performing bioanalytical assays. 

Biomolecule-nanoparticle systems are used extensively in different bioanalytical assays, the major challenge being to improve assay sensitivity by creating a particular amplification path (Willner, 2005 WiUner et al., 2007). In particnlar, metallic or magnetic nanoparticles have been conpled to different biomolecnles, such as DNA or antibodies (Yao et al., 2006 Centi et al., 2007a Chang et al.,... 

Due to its inherent selectivity and sensitivity, Uquid chromatography-tandem mass spectrometry (LC-MS/ MS) has become a tool of choice for quantitative bioanalytical assays that also prove to be fast and accurate [1,2], The first part of this chapter provides the current best industry practice of developing and vahdating an LC-MS/MS method and then applying it for sample... 

Today, electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI) are considered the standard ionization techniques for LC-MS/MS due to their predominant advantages in quantitative analysis of drug molecules in various sample matrices with high sensitivity, selectivity, reliability, robustness, and ease of operation. Other techniques, for example, atmospheric pressure photoionization (APPI), electron capture atmospheric pressure chemical ionization (EC-APCI), and high-field asymmetric waveform ion mobility mass spectrometry (FAIMS) serve as complements to the established ESI and/or APCI technical platforms whenever necessary for an enhanced sensitivity and/or selectivity of a bioanalytical assay [4,5]. 

Close cooperation for a year or more before the first administration to humans is likely to lead to a smooth transfer of the compound and the rapid movement of a compoimd out of preclinical into man. This lead time can be used to devise the ED plan, design the first studies and, when appropriate, to select and develop methodologies that will contribute to the drug s evaluation in man. This may include validation of pharmacod)mamic measures to be used in the clinical pharmacology unit, assessment of various imaging techniques, development of bioanalytical methods. Not infrequently, the assays that were perfectly adequate to support preclinical work are insufficiently sensitive, specific or accurate to quantify the comparatively low concentrations of parent... 

The fundamental parameters for bioanalytical validations include accuracy, precision, selectivity, sensitivity, reproducibility, stability of the drug in the matrix under study storage conditions, range, recovery, and response function (see Section 8.2.1). These parameters are also applicable to microbiological and ligand-binding assays. However, these assays possess some unique characteristics that should be considered during method validation, such as selectivity and quantification issues. 

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