Freeze-thaw stability data

The above examples illustrate that it is critical to establish short- and long-term stability, as well as freeze-thaw stability data for any matrix that is being investigated (animal or human plasma, urine, tissue extract, etc.) before any firm conclusions can be drawn from a metabolomics study, especially if the data are to be used for drug development decision-making. 

Figure 4 Comparison of freeze/thaw stability with freeze/dry stability phosphofructo-kinase with additives at 0.5 M. Hatched bar, freeze/thaw solid bar, freeze/dry. (Data from [24].)...

Figure 9 Effects of polyethylene glycols and sucrose on lactate dehydrogenase stability during freeze-thawing. (Data taken from Refs. 59 and 70.)...

Soils stabilized with urea-formaldehyde have strengths comparable to the phenoplasts and like those materials are less sensitive to testing strain rate than other chemical grouts. (For optimum mechanical properties and to keep free formaldehyde levels low, one molecule of urea should be provided with three molecules of formaldehyde.) Little data are available, but it is probable that aminoplasts break down comparatively quickly under cyclic wet iry and freeze thaw conditions. The creep endurance limit is probably a relatively high percentage of the UC. Except as noted above, the resins have good stability and are considered permanent. 

Gika et al. [98,99] investigated short-term sample stability for human urine by LC-MS. Urine samples were collected from normal female and male volunteers into containers containing one protease tablet and frozen at -80°C or -20°C for one month. Upon defrosting, samples were centrifuged at 13,000rpm for lOmin and then diluted 1 4 with 0.1% formic acid for LC-MS analysis. All samples were kept at 4°C in an autosampler. LC-MS analyses showed that there were no differences observed between samples stored at -80°C or -20°C even after 1 month. Therefore, storing urine samples at -20°C for at least one month is acceptable. In addition, based on principal component analysis (PCA) the data obtained from samples that had been subjected from one to nine freeze-thaw cycles showed that overall stability of the samples was also acceptable. 

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