How the Elementar Works

The Elementar is a combustion analyzer capable of determining the mass % composition of any compound for the elements C, H, N, and S. Oxygen analysis is also possible, but is seldom available due to the time-consuming modifications required of the instrument.

Samples are combusted at 1150 °C in a flow of helium enriched with oxygen. The elements are converted from your compound to the following gasses: CO₂, H₂O, N₂, NO_x, SO₂, SO₃. These gasses pass through a bed of WO₃ granulate that delivers additional oxygen as a catalyst, prevents the formation of non-volatile sulfates, and binds disturbing alkali and earth alkali elements.

These gasses then enter the reduction column, where NO_x and SO₃ are converted to N₂ and SO₂, respectively, catalyzed by the copper packing in the tube. Any volatile halogen compounds are adsorbed onto the silver wire at the end of the column. After leaving the reduction tube, these gasses enter the adsorption column.

The adsorption column separates the gasses, allowing each gas to be measured by the thermal conductivity detector (TCD) individually. N₂ is not adsorbed on the column and is the first gas measured. The column is then heated stepwise to desorb CO₂, H₂O, and SO₂, in that order. The column is then cooled to prepare for the next sample.

Elementar Run Time

The Elementar is currently being run on Thursday, with results typically available on Friday morning.

Sample Prep and Submission

Samples need to be submitted no later than Thursday at 10 am. They may be left in room 318A either in a box provided by you and left next to the analyzer (to the right of the entrance on the center bench), or in the labeled box near the analyzer. Your samples should be labeled with your name and a sample identifier for you to tell your samples apart. You should be able to pick your samples up by noon on Friday. You must also e-mail the admin and let him know that you are submitting samples, how many, what type, your advisor, and any special information about any of your samples. This also gives the admin a way to return results to you.

You should submit a minimum of 10 mg or dry/solid sample, or 0.25 mL of a liquid sample. This entire amount is not required for one analysis, but makes sample preparation much easier. All solid samples must be a powder or crushed/cut into small pieces. You should take care that large solid samples do not weigh more than 2 mg, and that it is small enough to fit into a space 2mmx4mmx10mm (the size of the sample container). Samples that are too large or otherwise incorrectly prepared will be returned, and can be run once appropriately prepared.

Please be aware that sample preparation is done open to the atmosphere, so sensitive or hygroscopic samples will be difficult to analyze. Also, each analysis requires 15 minutes, so your sample could sit for several hours in queue before it is analyzed. If you do have sensitive or hygroscopic samples you wish to have analyzed, inform the admin of these samples, and arrangements can be made to run these before other less sensitive samples. The sample auto-feeder, which sits on top of the insturment, is warmed from the oven below, and can reach temperatures from 40-50^oC. This may be a problem for volatile liquid samples.

Results

Results will come to you in an excel spreadsheet (example). The first 8 samples are for calibration of the instrument. Generally, the 9th sample is a repeat of a calibration standard, and the results of this sample should closely match the values of samples 5-8.

Your samples will generally be highlighted in a unique color. % Element data is generally found in columns AA - AD, and will be uniquely colored. Included in columns AE-AF are % element comparisons added by the admin using an excel function. You can obtain theoretical values for your compound by drawing your molecule/polymer in ChemDraw.

Questions

If you have questions about the insturment, samples, or your results, please do not hesitate to ask.