TDF Analyzer

Refer to the TDF Operator's Manual, sections "IDF/SDF Analysis" and "TDF Analysis."

Refer to the TDF Operator's Manual, sections "IDF/SDF Analysis" and "TDF Analysis."

Follow the steps in this instructional video to perform a pH adjustment: TDF Manually Measuring pH in the IDF Digestion

Note: Measure within the appropriate pH range for your specific testing method.

The MoistureStop Desiccant Pouch is a small, airtight zipper bag, utilized for desiccating all of the Filter Bags that are used with ANKOM instrumentation. A single pouch can hold a full run of F57, F58 or XT4 bags at one time.  When folded, 6 IDF or SDF bags can also be placed into a MoistureStop Desiccant Pouch. Each time a bag has been removed from the desiccant pouch, the air can and should be pushed out. The "zipper" does not have to be used with every bag removal but some action should be taken to keep the air from entering the pouch while the just removed Filter Bag is being weighed. For example, air can be pushed out of the bag by laying it on a firm surface while compressing or flattening the air out of the pouch with your hand.

Many instruments in the marketplace have the capacity to run 6 samples at a time.  After being dried, the beakers, flasks or crucibles are placed into a counter top or cabinet desiccator.  Once cooled, they are then removed one at a time and weighed. Each time the desiccator is opened to remove sample, moist ambient air is introduced inside the desiccator. However, because the lid or door of the desiccator is opened just 6 times, the samples that remain in the desiccator after each item is removed are affected very little by ambient moisture that may be introduced.

However, with Filter Bag Technology, generally larger numbers of Filter Bags are extracted at a time. As with the beakers, flasks and crucibles mentioned above, if the bags are placed in a desiccator after drying, each time the lid or door is opened to remove a bag, moist, ambient air is introduced. Because the desiccator is opened up to 24 times, the moisture can more readily affect the remaining bags. If a collapsible, ANKOM desiccant pouch is utilized, the air can be pushed out of the pouch each time a Filter Bag is removed. This will eliminate a build up of moisture on the remaining Filter Bags and allow for a more accurate and precise result. Every month it is possible to place the small desiccant packets into the oven at 100° - 105°C for a few hours to insure that the desiccant is renewed. In addition, to ensure the integrity of the zip lock bag, regular replacement should be considered.

In order to properly prepare the IDF & SDF bags for Kjeldahl and Ashing procedures, view the documents below or watch the following video: Kjeldahl & Ashing Bag Preparation.

Do NOT run this instrument without an adequate DRY Nitrogen Supply. The instrument is powered by pneumatics that are not compatible with moisture, commonly found in compressed air.  Nitrogen is also recommended as an extra precaution when handling ethanol.  For these reasons Compressed Air is NOT recommended.

Amount of Nitrogen
A typical TDF run requires approx. 1400L (50cu.ft.) nitrogen gas. The nitrogen supply should be 6.9 bar (100 psi). During the run, the nitrogen is used to operate pressure cylinders and also to facilitate bag filtering. During the filtering stage, the nitrogen is regulated to .3 bar (4 psi) and flow rate is approx. 15L/min  (.5cu.ft.).

Nitrogen Purity
A key issue associated with the gas used in the TDF instrument is moisture content. The TDF instrument can suffer damage if moisture is introduced through the gas line. ANKOM recommends the use of nitrogen with a 99.998% purity rating. Theoretically, less pure nitrogen should work if the impurities do NOT include moisture.

We have found that it is best to slowly ramp up the digestion temperatures so that foaming in the digestion tubes is minimized. As a result we would suggest the following times and temperatures: 15 minutes at 150°C followed by 15 minutes at 250°C followed by 15 minutes at 350°C and finally 40 minutes at 420°C.

The TDF instrument requires the following bench space: 132 cm long (52") x 77cm deep (30") x 92 cm high (36"). 
For shipment, some parts are removed and the dimensions are: 107 cm long (42") x 51 cm deep (20") x 76 cm high (30").

The TDF instrument alone weighs about 65 Kgs (142 lbs).  With the controller, attachments, and other spare parts the weight is about 71 kgs (157 lbs). A rinse stand adds 2.75 kgs (6 lbs) to the shipping weight.  The total weight for shipping purposes, when the order includes a rinse stand, is 93.5 kgs (206 lbs).

Some sample types can be difficult to filter, even though the IDF and SDF filter bags have a significantly greater filter surface area than the Gooch crucible. Some samples become gelatinous in an aqueous solution (such as psyllium, chia seeds, or milled beans) and can be difficult to filter.  To accommodate these types of samples, we recommend the following options:

Add filter time before the assay begins
At the beginning of a run a series of user prompts appear on screen, one of which states, “Filter Minutes OK? (for an IDF/SDF run) or “SDF Filter minutes OK?” for a TDF run.  From this screen, you can add filter time if you are working with samples that require more filter time.  Familiarity with a particular sample may dictate 10 minutes of IDF filter time, for example. Be aware that any time changes will be stored to memory and will be there for the next run.  You will, however, be able to change this back to the default or another setting at the beginning of each run.

Add more filter time during the filtering process
During IDF or SDF filtration and during the water or alcohol rinses (when filtering is occurring) one can press the “Filter Time +” button to add one additional minute at a time, up to 50 additional minutes.  The user will need to be present at the time of filtering to take advantage of this option.

Use a smaller sample size
Reduce the sample size to 0.1 g to minimize the filter clogging effect of gelatinous sample types. NOTE: Remember, the TDF values will be greatly influenced by variability in protein and ash values - of a small sample size.

Use Diatomaceous Earth (DE) in the IDF bags 
Use of this technique helps increase filtering capacity. Pre-weigh 0.5-1 g of DE for each IDF bag.  About 2 min before the end of AMG digestion, open Clamp Bar A by pressing "Clamp Bar A", add the DE quantitatively, and then close Clamp Bar A by pressing "Clamp Bar A" again. The DE will be mixed in during the end of the AMG digestion. Adding DE at this point, rather than at the beginning of the run, minimizes the risk of bag wear from abrasive DE in a hot/agitated bag.  Be sure that the DE in the IDF bags is factored into your blank values. We recommend running a blank position when implementing this technique to account for DE loss from the IDF bag, if there are any.

AOAC 991.43 calls for filtration via a fritted crucible of 40-60 microns with diatomaceous earth, or equivalent.  Particle retention per the method is accomplished by the addition of diatomaceous earth contained in a fritted crucible.  The fine filtration and particle retention of the ANKOM SDF bags is also accomplished with diatomaceous earth contained in the filter bag.  The IDF filtration may or may not use the diatomaceous earth but produces the correct particle retention in a water medium.  Therefore, the filtration used in the ANKOM TDF is equivalent to the approved AOAC 991.43 Method.

Utilize a transfer pipette to handle this and follow the procedure below:

1. Weigh the pipette and tare the weight.
2. Fill the pipette with a liquid sample.
3. Place the pipette on the balance and record the weight.
4. Pipette out the liquid into the IDF Bag.
5. Weigh the pipette and subtract that weight from the weight with a sample. This supplies us with the actual sample weight that went into the bag.

Protein determination is performed post the ANKOM TDF Dietary Fiber Analyzer. AOAC methods 991.43, 985.29, and 2001.03 suggest that the Kjeldahl method be used for determining protein content of the residue. 
AOAC methods 2009.01, 2011.25, 2017.16, and 2022.01 describe using either Kjeldahl or combustion methods for determining protein content of the residue. The selection is made by customer preference.
 
To prepare the ANKOM Filter Bags for analysis via Kjeldahl, refer to the TDF Operator’s Manual.
 
To prepare the ANKOM Filter Bags for analysis via combustion methods, cut open the Filter Bag and lightly scrape or brush the particles of sample residue and DE into a small mortar. Grind the mixture with the pestle until homogenous. Take several aliquots of the mixture and run them through your dumas. Use the average protein value of the aliquots for the TDF calculation.
 
Various manufacturer options are available for the nitrogen determination using combustion method. Contact your combustion/dumas manufacturer for further information regarding specific settings and recommendations regarding N2 determinations that involve DE.