> 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

## Too low bacterial concentration

<figure><img src="/files/SRcjRnjt05nsmBZEny88" alt="" width="375"><figcaption><p>Samples with low concentration are usually transparent.</p></figcaption></figure>

Your sample must have [*at least* 30 000 cells/mL](https://app.gitbook.com/s/CaBGkox4Fd7NCFFCF47X/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](/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 <a href="#motivation" id="motivation"></a>

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://app.gitbook.com/s/CaBGkox4Fd7NCFFCF47X/measurements-explained/limits-of-detection) for more details.

<figure><img src="/files/E3AlxzFo7zHfBRRddUwG" alt=""><figcaption></figcaption></figure>


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