How do I sample from a small package or rigid bottle?


You may wish to measure O2 and / or CO2 without using the pump to draw sample.  For example, measuring the oxygen from a rigid bottle with 50cc (or 50mL) of headspace can create a vacuum condition if you draw 15cc of headspace.   This challenge is easily overcome using a syringe that we can provide.

Sample can be manually injected into our analyzers; activating the pump is not required for analysis. This method can be used with our Model(s) 901, 905, 902D, or 907 analyzers.   In general, 10cc of sample is recommended for best results.

Detailed Background:

An internal diaphragm pump is used in many Quantek analyzers to draw sample from your package or container. The pump draws 5cc/sec and has an adjustable run-time between 2-15 seconds. For the vast majority of applications, this is sufficient.

However, some unique applications have limited headspace or work at partial pressures.  For example, withdrawing 15cc of sample from a rigid bottle containing 100cc of headspace will create a vacuum condition.  We call this “drawing on a vacuum”.

Drawing on a vacuum over thousands of samples can degrade the sensor and/or pump. The analyzer will also display an artificially low reading proportional to the decrease in pressure. Therefore, we recommend pulling sample out with a locking syringe for injection into the analyzer.

The syringe sampling method is recommended when:

1) the sample is either already under partial vacuum,
2) has such a low volume that removing sample would cause a partial vacuum, or
3) where the container is rigid and has very little flexibility (such as a 2L soda bottle filled almost to the top).

The Method:

An airtight syringe with an on/off stopcock is used to draw out the sample. There will be varying resistance to pulling the plunger back. Pull on the plunger and close the stopcock while the needle is still in the package. This picture shows the syringe with the stopcock in the “open” position:

syringe for oxygen analysis

After withdrawing the needle from the container, release the plunger, allowing it to “collapse” to atmospheric pressure. With the end of the syringe connected to the end of the analyzer’s sample probe, slowly inject the sample into the analyzer. This picture shows the syringe with the stopcock in the “locked” position:

syringe for o2 analyzer

Please contact us if you would like to explore the viability of this method with your application. This method has been successfully utilized for oxygen and / or CO2 analysis in applications such as:

  • O2 and CO2 analysis in hummus packages
  • O2 and CO2 analysis in salsa packages
  • O2 analysis in bottles of olive oil
  • O2 analysis in wine bottles with metal caps

For reliable analysis of vials with 0.5 to 5 mL of headspace, you may want to consider our Model 905V, which is engineered specifically for ultra minimum headspace applications.