This is particularly applicable for purification development where protein compositions

could differ markedly across a microplate. The contrasting slopes for lysozyme and BSA standard curves when measured in both protein assays in Fig. 7 provide an indication of the noise that could be encountered. For these reasons, the differential method for reducing sugar quantification ZD1839 clinical trial is better suited to samples purified to a greater extent, further downstream in the purification process. Due to its simplicity and ease of automation, particularly when compared to kinetic assays (e.g. kinetic QCL), the PyroGene™ assay was qualified as the principal endotoxin assay [41]. As displayed in Fig. 8, the log–log standard curves were consistent and exhibited good fit with R2 > 0.99 across a range of 0.01–20 endotoxin Screening Library units (EU)/mL. Precision was found to average 7% RSD across the tested range. Several incubation temperatures were evaluated in parallel with the standard incubation temperature of 37 °C ( Fig. 8). Lowering the incubation temperature did not have a deleterious effect on the reproduction of the standard curve. Enabling the incubation period to occur at room temperature is helpful when automating assays with liquid-handling robots situated in room temperature environments. The potential for

various substances to interfere with the PyroGene™ assay was evaluated through positive product control samples (Fig. 9). In these samples, endotoxin was spiked to a final concentration of 1 EU/mL in the presence

of a concentration series of various impurities (i.e. proteins, sugars, and DNA). Chondroitin sulfate, DNA, sodium alginate, ι-carrageenan, and several anionic capsular mafosfamide polysaccharides (data not shown) inhibited the PyroGene™ assay. The severity of the inhibition was high, with dilutions to <1 μg/mL required to abolish the effect. The inhibition was consistent across assays performed on multiple days with freshly made solutions, with multi-day variability of ∼27% (data not shown). Each of the inhibitors was an anionic polysaccharide but other anionic polysaccharides such as HA, gellan gum, and N-acetyl neuraminic acid did not react, nor did the acidic protein, BSA. A common structural feature between the DNA, ι-carrageenan, and chondroitin sulfate is the presence of sulfates. Every species with a sulfate that was tested was found to inhibit the assay, but other anionic groups did not interfere consistently. For example, none of the uronic acid-containing polysaccharides reacted except for sodium alginate (and chondroitin sulfate, which also has sulfate groups). The mechanisms for inhibition are unknown but possibly due to electrostatic interactions with the zwitterionic endotoxin.