Shimadzu TOC-VCHS

The need to measure organic carbon in water, especially environmental samples, requires a Total Organic Carbon (TOC) technique that can deal with large amounts of inorganic carbon that could interfere with the detection process. The Center’s Shimadzu TOC-VCSH is able to do that as well as total nitrogen analysis in a single sample injection.

To understand how this device measures the TOC content of a water sample, one must also understand that this instrument measures the Total Carbon (TC) and Inorganic Carbon (IC) as well as Non-Purgeable Organic Carbon (NPOC). For TOC, the Shimadzu’s 680 C combustion catalytic oxidation method achieves total combustion of samples by heating them to 680 C in an oxygen-rich environment inside the TC combustion tube filled with a platinum catalyst, either a platinum coated ceramic bead or platinum infused quartz wool for high efficiency analysis. This process converts carbon in solution into carbon dioxide and then drives that gas flow to a non-dispersive Infra-Red (NDIR) detector for measurement.

At the same time a similar injection of sample enters a reduction pot filled with phosphoric acid where only the inorganic carbon will be converted to carbon dioxide. This lets the system quickly determine the TOC by performing an internal calculation TOC= TC-IC. This is then reported in the summary report of the analysis.

For environmental samples the inorganic carbon dissolved in solution can often dwarf the organic carbon that researchers are interested in. For that reason the NPOC mode is the primary analysis mode in the Center. Samples are sparged for up to 5 minutes with zerograde (hydrocarbon free) air degassing all inorganic carbon sources. The same flow path as TC is then followed to the NDIR. Range for TC, TOC and NPOC is 5 ppb - 25,000 ppm Carbon.

An add-on Total Nitrogen (TN) module was added to the system to measure total nitrogen dissolved in solution. This works by taking the TC gas from the NDIR detector to an oxidation chamber where nitrogen is converted into Nitrogen dioxide (NO2) and the flow is passed in front of a chemiluminescence detector for quantification. This yields an accurate TN value with no additional chemical waste to clean up with a very wide stanle range, 0-4000 ppm.

The ASI autosampler can hold a variety of sample vials. The Center has three carousels for different sized vials and others are available. Several of these are sample vessels are a proprietary design and must be purchased through Shimadzu.