IODP (International Ocean Discovery Program) at MARUM

An alkaline buffer (NaOH+Na-citrate) converts the ammonium in the IW sample to NH₃ which then diffuses through a gas permeable PTFE membrane in the custom made gas seperating reactor cell. On the other side of the membrane there is an hydrochloric acid solution which then converts the resulting NH₃ back to ammonium. This ammonium then causes a change in conductivity of the HCl solution. This change in conductivity is detected with a flow-through cell connected to a conductivity meter and recorded with a strip chart recorder. Sulfide does not interfere.

• Peristaltic pump (Ismatec IPC)
• Pump tubes white-white or white-black (approx. 1mm / 0.04” ID, tygon3609)
• Injection valve (Rheodyne 7725) with 100 µL loop and injection syringe
• Reactor (custom made)
• PTFE plummer sealing tape
• Conductivity meter with flow-through-cell (Amber science model 1056, cell 529)
• Strip chart recorder

- 0.2M Na-citrate-2hydrate in 10mM NaOH
- 1mM HCl
(Tip: dilute both solutions 1:1 if peaks are too small)

- Ammonium standard (1000 ppm NH₄⁺) as certified reference material

Calibration solutions:

Pre-dilution - prepare a 100 ppm standard (5mL of 1000 ppm standard in 50 mL purified water).
Calibration solutions - to be prepared freshly (stable for 3 days in the fridge) from the 100 ppm work standard
Prepare 0.1 / 0.25 / 0.5 / 1 / 2.5 / 5 / 10 and 20 ppm standards


The following table gives amounts of 100 ppm work standard in 50 mL to obtain calibration standards. For seawater samples dilution solution should be artificial seawater, yet the differences to using puriefied water for dilution are negligible.

Important: Store all standards refrigerated. Warm up to room temperature prior to measurement.
Flush both tube systems with the appropriate solutions (injection side – alkaline, detection side – acidic). Watch the strip chart recorder for straight baseline.
Linear range for this method is 0.25 to 20 ppm. If the sample concentration is higher they have to be diluted.

Release pump tubes after analytical runs and replace them when necessary.
Pressure handles should be on equal settings
To run the pump, turn main switch on, clamp pump tubes and press RUN. Set flow direction. Speed 10.

Connection to conductivity meter: red-red / black-blue
Speed 6 mm min^-1
Switch right below points down
Sensitivity 0.1 Volts

Valve handle set to INJECT: insert the needle of the delivery glass syringe all the way into the valve inlet, in a slow, straight and careful manner.

Turn the valve handle to LOAD (smoothly, not too slow and without moving the syringe needle).

Push the sample with a gentle and constant pressure into the sample loop.

Set the valve handle back to INJECT to start analysis.

Only then remove the syringe needle carefuly from the valve inlet.

(Sample volume per injection: sample loop 100 µL + flushing + dead volume => approx. 300-400 µL is enough)