The AIM600 Programmable Digestion System

The AIM600 Programmable Digestion System performs acid digestion of large numbers of samples under controlled conditions. The digestion block heats samples at a controlled rate in the presence of one or more acids to the required temperature. The AIM600 then holds the samples at that temperature until digestion is complete. Under these conditions, the acid breaks down the samples to release the component elements for subsequent analysis.

Typical applications include:

   TKN and Total Phosphorus Digestion
   Mercury Digestion
   COD digestion
   Metals digestion

The AIM600 is available as a 50 place unit for 75ml or 100ml digestion tubes or a 28 place unit for 250ml digestion tubes. The system comprises the block digester unit, microprocessor controller, tube rack/draftshield, a set of digestion vessels and a cooling stand that supports the tube rack above the block.

The overall unit has been designed for durability and robustness. The block has a stainless steel covering to provide a greater measure of acid resistance. Similarly, the tube rack and cooling stands are also manufactured from the highest quality stainless steel.

If you are looking to automate your digestions, the AIM600 offers enhanced productivity , better quality digestions , and increased safety.

Following are application notes for TKN and Total Phosphorus Digestion of water samples. Similar application notes are available for soil and plant tissue, please inquire.

Application Notes - Total Kjeldahl Nitrogen and Total Phosphorus in Drinking and Ground Water

Introduction:

This method is adapted for use on AIM600 Block Digestion System following US EPA Office of Ground Water and Drinking Water methodology.

Scope & Application:

This is an acid digestion procedure to prepare ground waters, surface waters, drinking waters andindustrial or domestic wastewaters for the subsequent determination of TKN (Total Kjeldahl Nitrogen) and TP (Total Phosphorus) by colorimetric methods. The range for the method is 0.1-20 mg/l as N and P respectively. Samples can be diluted to increase the range.

Note: the digestion procedure may not convert some nitrogen containing compounds sometimes found in industrial waste such amines, nitro compounds, hydrazones, oximes, semicarbazones and some refractory tertiary amines.

Apparatus:

DG-U-A013* AIM600 50 place Block Digestion System. Consists of the DG-U-A002-240V 50 place AIM600 digestion block, DG-U-A003-AIM600 Controller, 8028114 - 50 place tube rack/draftshield, 4003036 - 50 x 100 ml straight tubes, and 5001511 Cooling Stand.

Reagents:

8032173 PTFE boiling chips, 450g

Catalyst Kjeltabs M/1.5 (1.5 g K₂SO₄+ 7.5 mg HgO)
or
Catalyst Kjeltabs Cu/1,5 (1.5 g K₂SO₄+ 0.15 g CuSO₄x 5 H₂0) (alternative catalyst for mercury free digestion solution)

6N Sulphuric Acid - Dilute 167ml of concentrated sulphuric acid to 1 liter with reagent grade water

Reagent Grade Water

Control Program:

STEP to 160 C
HOLD for 60 minutes
RAMP to 380 C at 5 C/min
HOLD for 30 minutes
End

Procedure:

1. Shake sample and transfer 25ml of well mixed sample into a clean dry digestion tube.

2. For mercury catalyst: Carefully add 6ml of 6N sulphuric acid and 1 x Kjeltab MQ and mix
thoroughly. or For copper catalyst: Carefully add 8ml of 6N sulphuric acid and 1 x Kjeltab CQ and mix thoroughly.

3. Add 4 - 8 PTFE boiling chips to each tube.

4. RUN the control program above on the AIM600 Control Module.

5. At the completion of the digestion, raise the digestion tubes in the tube rack to the elevated
position on the cooling stand to facilitate rapid cooling.

6. When cool, dilute to 25ml with reagent grade water.

The sample is now ready for colorimetric FIA analysis of Total Kjeldahl Nitrogen and Total Phosphorus.

Safety Notes:

The AIM600 Digestion Block should be located inside a ventilated acid-resistant fume hood. It is recommended that the AIM600 Program Controller be located outside the fume hood.

Great care should be taken when handling acids. Always add acid to water unless otherwise directed. Protective clothing should be worn including gloves and face mask. If acids are spilled on the skin, immediately wash with copious amounts of water.

Neutralize any acid spills with sodium carbonate (Na₂CO₃) or sodium bicarbonate (NaHCO₃).

Digests must be cool before dilution water is added to avoid a violent reaction during which the acid can shoot out of the flask.

References:

(1) US EPA Method 351.2, "Determination of Total Kjeldahl Nitrogen by Semi-Automated Colorimetry", EPA/600/R-93/100, Methods for the Determination of Inorganic Substances in Environmental Substances, Revision 2, August 1993

(2) US EPA Method 351.4, Potentiometric Ion Selective Electrode Method for determining Total Kjeldahl Nitrogen, EPA/600/4-79/020, Methods for Chemical Analysis of Water and Wastes, March 1983.

(3) US EPA Method 365.4, Colorimetric, Automated, Block Digestor method for determining Total Phosphorus, EPA/600/4-79/020, Methods for Chemical Analysis of Water and Wastes, March 1983.