# Concentrate your sample ## Too low bacterial concentration

Samples with low concentration are usually transparent.

Your sample must have [*at least* 30 000 cells/mL](https://help.sbtinstruments.com/encyclopedia/measurements-explained/limits-of-detection) to measure it with BactoBox®. {% hint style="info" %} ## Very low bacterial concentration? BactoBox® is generally not suitable for very low bacterial concentrations. {% endhint %} ### My sample stock contains around 100 000 cells/mL This is just above the lower limit of detection but not by a lot. Theoretically, your sample is good to go since the *cells/mL* concentration is well above the threshold. In practice, however, you must both: * [Hit the right electrical conductivity](https://help.sbtinstruments.com/protocols/prepare-your-sample/hit-the-right-conductivity) * Reach the minimum sample volume of 4 mL Already achieved both? Well, then you're done! Otherwise, this is where it gets a bit tricky. See: {% content-ref url="../hit-the-right-conductivity" %} [hit-the-right-conductivity](https://help.sbtinstruments.com/protocols/prepare-your-sample/hit-the-right-conductivity) {% endcontent-ref %} Specifically the section about [low dilution factors](https://help.sbtinstruments.com/protocols/hit-the-right-conductivity#i-dilute-1-10-or-less). ### My sample stock is below the limit of detection You must concentrate your sample before you measure on it with BactoBox®. We recommend that you use a centrifuge together with membrane filter. We describe this filter-centrifugation approach here: {% content-ref url="concentrate-your-sample/filter-centrifuge-your-sample" %} [filter-centrifuge-your-sample](https://help.sbtinstruments.com/protocols/prepare-your-sample/hit-the-right-concentration/concentrate-your-sample/filter-centrifuge-your-sample) {% endcontent-ref %} ### Motivation BactoBox® counts individual particles. If there are too *few* particles, the concentration estimate is too uncertain. If there are too *many* particles, we can't tell them apart. Therefore, we have limit of detection (LoD). BactoBox® outputs concentrations in these ranges: * 30 000–5 000 000 **cells/mL** (3·10⁴ to 5·10⁵ cells/mL) * 30 000–5 000 000 **total/mL** (3·10⁴ to 5·10⁵ total/mL) See [limits of detection](https://help.sbtinstruments.com/encyclopedia/measurements-explained/limits-of-detection) for more details. BactoBox® uses an electric field to measure individual cells.
Below the LoD (top), next-to-nothing enters the electric field and the cells/mL concentration is uncertain.
Within the LoD (middle), individual cells enter the electric field so we can tell them apart and count them.
Above the LoD (bottom), multiple cells enter the electric field at the same time and we can't tell them apart.

BactoBox® uses an electric field to measure individual cells.
Below the LoD (top), next-to-nothing enters the electric field and the cells/mL concentration is uncertain.
Within the LoD (middle), individual cells enter the electric field so we can tell them apart and count them.
Above the LoD (bottom), multiple cells enter the electric field at the same time and we can't tell them apart.

--- # Agent Instructions: Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter: ``` GET https://help.sbtinstruments.com/protocols/prepare-your-sample/hit-the-right-concentration/concentrate-your-sample.md?ask= ``` The question should be specific, self-contained, and written in natural language. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.