Knowing what quantity of items you have in stock is a basic requirement for anyone involved in inventory management. Knowing that the quality of the items has not deteriorated as a result of storage is also important. This not only ensures that your end customer always receives a quality product, but it also minimizes waste and thus costs.
While this has been well understood in businesses involved in perishable goods warehousing and distribution, it is now increasingly important in sample-management applications within the pharmaceutical and biobanking sectors.
During the last decade, organizations in these sectors have invested heavily in sample-management solutions to deal with ever increasing numbers of samples, whether they be small molecule compounds or biological samples.
This investment often takes the form of automated storage and retrieval systems. Many millions of samples may need to be stored. Automation, and the associated IT and data tracking infrastructure, is the only realistic solution to providing rapid controlled access to individual samples, many of which will be stored at sub-zero temperatures.
In most cases, samples are stored in solubilized form in microtubes. Knowing how much sample is in the microtube and an indication of the quality of that sample is thus key. After all, what could be worse than keeping the sample in storage only to find that when you need to access it, there isn’t the amount that you expected. In the worst-case scenario, it could actually be empty if someone has used it all. Additionally, if the sample has degraded during its time in storage then this will likely impact on any subsequent analytical processes to be performed on that sample.
In the drug discovery process, compound managers typically deliver samples in SBS microplate format to downstream screening groups. They need to have confidence in the quality of their delivered product (i.e., the plate contents). If there are empty wells in the microplate, or perhaps wells with samples at the wrong concentration, this can have a potentially significant effect on the results from the screening process or other downstream analyses being performed. A secondary effect of this is potentially significant levels of waste and cost.
Data gathered by RTS Life Science suggests that in some organizations as many as 5% of plate wells may be erroneously empty and 3–5% of wells may have samples at the wrong concentration. Knowing the volume of sample in the source microtube used to create the plate, and whether there is any precipitate, is key to avoiding screening empty wells or samples at the wrong concentration.
What is required, therefore, is a rapid and accurate method by which liquid samples can be audited so as to determine if there is any sample in the tube, what the volume of sample is in the tube, and if any of the sample has precipitated out of solution.
There are a number of approaches currently used for determining the volume of liquid sample in a tube. These include gravimetric, ultrasonic, and other liquid-level sensing methods (e.g., capacitive probe). However, each of these approaches has certain disadvantages, as summarized in the Table.
Furthermore, these methods cannot determine if any sample has precipitated out of solution. While a manual visual check can help spot precipitates, this is a very onerous task if large numbers of samples need to be audited.