Timberline Instruments has developed instruments based upon its novel gas diffusion/conductivity method for ammonia analysis.

The TL-2800 ASX analyzer is produced in two versions. One version is the TL2800A ASX. It is a highly sensitive Ammonia Analyzer. The second is the TL2800N ASX. It is a total inorganic nitrogen (TIN) analyzer and provides quantitative data on the total value of ammonia plus nitrate plus nitrite in an aqueous sample. Solutions for TIN are typically produced by pairing the two instruments, TL2800A ASX and the TL2800N ASX. This allows determination of Nitrate/Nitrite by subtraction of the Ammonia component from the TIN.

  • Unique gas diffusion / conductivity principle provides results greatly unaffected by sample turbidity, color, or pH.

  • Commonly used in water, wastewater, and agricultural applications.

  • Optional activated zinc reduction cartridge allows for the user to add the analysis of TIN and nitrate/nitrite in addition to ammonia.

  • TKN and TN can be analyzed directly after digestion without further sample preparation (distillation).

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Ammonia Analysis Methodology

Ammonia analysis is accomplished by the TL2800A ASX. Samples are typically delivered to the instrument via an external autosampler which is controlled by the associated data/control software.

  • A peristaltic pump directs aqueous sample, caustic solution, and a mildly acidic absorbing solution into a tubular diffusion membrane assembly.

  • Within the assembly, sample is mixed with the caustic solution resulting in a mixture with a pH of 11 or higher. At this pH level, virtually all ammonium ions present in the sample are converted to dissolved ammonia gas.

  • As the sample & caustic mixture flows over the tubular membrane, dissolved ammonia gas diffuses through the membrane wall and is absorbed by a buffered solution at pH 6.5 flowing on the inside. At the lower pH, the ammonia gas converts back to the conductive ammonium ion species.

  • The measured change in electrical conductance of the absorbing solution is proportional to the concentration of ammonium ion present in the sample.

The Advantages:

The gas diffusion-conductivity analytical approach provides for a robust and highly sensitive method for determination of ammonia & ammonium content in aqueous samples. This analysis technique has several advantages when compared to alternative approaches including:

  • Low Cost – Low maintenance costs, minimal non-hazardous reagent costs and fast automated operation make the cost of ownership and the cost per sample far lower than other approaches.

  • Wide Dynamic Range – Analysis of samples spanning 4 to 5 orders of magnitude can be accommodated by a single instrument configuration. Standard range instruments are produced covering samples from 50 ppb to 500 ppm while the high sensitivity (low-level) configuration accurately covers analyses from 10 ppb to 10 ppm.

  • Low or no Interference – The method tolerates particulates with minimal or no filtering, is unaffected by turbidity and fully immune to variation in sample color.

  • Fast Analysis – Analysis time is from 1.5 to 2.5 minutes/sample.

  • Simplicity – The low-cost reagents are readily available, easy to make and non-hazardous. You just need deionized water, buffer solution @ 250 ppm and caustic (5% NaOH is typical).

  • Performance – The TL2800 ASX instruments produce excellent accuracy and precision

  • Ease of Use – The intuitive user interface makes operation simple and lends peace of mind in a world where much of what we experience is increasingly complicated. The method is simple, the reagents are simple, the control system is simple, and it runs automatically.

Adding Nitrates & Nitrites

It is possible to convert nitrates and nitrites to ammonium ion by reducing these species.

In the TL2800N ASX instrument, an activated zinc reduction cartridge is placed in the incoming sample stream. The converted nitrates and nitrites add to the existing ammonium ion concentration. All of these ionic species are converted to ammonia gas and measured employing the same analytical method presented above.

Interpretating the Signals

In the chart below, you can see two separate signals plotted versus time. These signals represent the results of the same sample analyzed with and without reduction of nitrate/nitrate species prior to analysis. The green trace is the result from analysis using the TL2800A ASX Ammonia Analyzer and the red trace is the result from analysis using the TL2800N ASX Nitrate Analyzer.

As you can see, the difference of these two signals represents the contribution from the nitrates/nitrites present in the sample.