> For the complete documentation index, see [llms.txt](https://help.sbtinstruments.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://help.sbtinstruments.com/advanced/advanced-sample-preparation/hit-the-right-concentration/concentrate-your-sample.md).
# Concentrate your sample
It is generally not recommended to use BactoBox® for measuring samples with very low bacterial concentrations. This page is a collection of tips and tricks for how to do so.
## Too low bacterial concentration
Samples with low concentration are usually transparent.
Your sample must have [*at least* 30 000 cells/mL](/advanced/measurements-explained/limits-of-detection.md) 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](/advanced/advanced-sample-preparation/hit-the-right-conductivity.md)
* 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="/pages/eraTi4yozhJDLsL3jSkq" %}
[Hit the right conductivity](/advanced/advanced-sample-preparation/hit-the-right-conductivity.md)
{% endcontent-ref %}
Specifically the section about [low dilution factors](/advanced/advanced-sample-preparation/hit-the-right-conductivity.md#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="/pages/65zet5lwtpR6jINeCs6A" %}
[Filter-centrifuge your sample](/advanced/advanced-sample-preparation/hit-the-right-concentration/concentrate-your-sample/filter-centrifuge-your-sample.md)
{% 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 5·106 cells/mL)
* 30 000–5 000 000 **total/mL** (3·10⁴ to 5·106 total/mL)
See [limits of detection](/advanced/measurements-explained/limits-of-detection.md) for more details.
---
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