Analyzing difficult samples with the Total Organic Carbon (TOC) analyzer can cause an extensive amount of wear and tear to the instrument, especially if the user is running samples that exhibit a high salt concentration. The team of researchers at Ol Analytical has evaluated typical problem spots in maintaining a combustion TOC analyzer to develop a series of solutions that can be used to proactively combat these issues to extend the overall life of the instrument, thereby allowing routine maintenance procedures to be rapidly completed.
Preventative Laboratory Techniques
Some additional preventative techniques that can be utilized to improve the life out of the combustion TOC analyzer are listed below:
- Minimize the Total Salt Mass: Prior to running samples, be mindful of what type of sample it is. For example, if the user is aware that the sample contains a more difficult matrix, adjustments to the sample size should be made according to what the TOC analyzer can reasonably manage. In the case of salt samples, it is critical to establish the total salt mass that will be injected into the furnace. The less salt mass that is injected for each sample will result in a greater amount of total samples that will be analyzed before requiring maintenance. The 1080 TOC Analyzer provides an automatic dilution feature for difficult samples.
- Condition the Furnace and Catalyst: When running high-salt samples, it is important to have frequent conditioning of the furnace tube and catalyst to maximize the throughput between maintenance cycles.
In the 1080 TOC Analyzer, a user-selectable furnace conditioning feature called “Acid Conditioning,” injects an acid blank sample after each sample has run. When alkali-organic compounds are analyzed, the non-volatile alkali oxides are left in the combustion tube as deposits that eventually accumulate to readily absorb and desorb carbon dioxide. This accumulation leads to a high background of carbon dioxide present in the gas when it elutes from the reactor as compared to the background of carbon dioxide that is observed when the reactor is in bypass mode. When an acid blank is injected into the system, the alkali oxides react with the acids to form non-volatile salts such as alkali chlorides, which are generated from the alkali oxides by hydrochloric acid blanks, which are commonly alkali sulfates that are generated from the alkali oxides by sulfuric acid blanks. These acid blanks release carbon dioxide from the alkali carbonates present in the reactor. Multiple injections are typically used to fully convert all of the carbonates in these layers of the alkali deposits within the combustion tube without having to remove the tube, physically dissolve the deposits and repack the combustion tube.
- Run Clean Ups: Running a ‘clean up’ sample following the analysis of difficult samples greatly improves the accuracy of each subsequent analysis by reducing any background or carryover that can occur between samples, while also contributing to the overall improved life of the instrument. The Ol Analytical Model 1080 Analyzer is equipped with a clean up sample type that the user can insert anywhere in the sequence without taking up a vial in the auto-sampler tray.
- Maximize the Furnace Tube and Catalyst Lifetime: Due to the total salt mass accumulation in the furnace tube with high-salt samples, a typical Combustion TOC failure mode indicates a clogged or failed furnace tube. The 1080 TOC Analyzer provides an on-screen reading of the backpressure that can increase as the furnace tube begins to clog to allow for the operator to monitor this parameter easily.
The furnace tube itself can also be slowly attacked by the salt samples and eventually lead to premature failure of the instrument. To avoid this issue, the Model 1080 TOC Analyzer is equipped with a large-diameter, thick-walled combustion tube with a high-porosity bottom frit standard with every unit, as well as a layered blend of quartz chips and catalyst to maximize the salt-loading capability of the furnace tube. Additionally, Ol Analytical provides users with an easily replaceable patent-pending “catalyst guard” tube that not only measures the initial thermal stress of the liquid injection, but also provides a surface for the salt to preferentially attack before it is able to reach the furnace tube.
Ultimately, the catalyst and tube will need to be removed and rinsed when there is a significant increase backpressure to ensure a long lifetime of the instrument.
- Clean the Injector Cap and Slider: The injection of high-salt samples into the furnace exhibit a natural tendency to form salt crystals wherever micro droplets of the salt solution comes in contact with a sufficiently hot surface, thereby causing the droplets of a salt solution to lose water. This results in crystals forming on the furnace cap/slider assembly, which can ultimately damage the sealing surfaces and cause leaks. It is therefore important to routinely inspect and clean this cap/slider assembly to maximize the performance of the Model 1080 TOC Analyzer.
- Keep the Scrubber and Dryer Fresh: Running samples that are stabilized with hydrochloric acid, or any samples that contain chloride salts that are stabilized with sulfuric acid can result in hydrochloric vapor to be present within the instrument. Maintaining a fresh and adequate supply of halide scrubber and sample-gas dryer are good preventative measures that can be taken to avoid damage by the production of this vapor. Otherwise an irreversible destruction of the flow path of the NDIR detector is likely to occur.
Aside from these guidelines, the most important method to ensure that the combustion TOC analyzer is protected against potential damage is to be aware of the samples the user is running, as well as the condition of the analyzer’s components following each run. By maintaining a relevant list of the reagent levels, humidifier levels, gas cylinder, halide scrubber and dryer prior to each experiment can assist in this procedure.
The Model1080 Combustion TOC Analyzer was designed with a high visibility for maintenance that is equipped to analyze extremely difficult samples that could potentially harm the instrument.
This information has been sourced, reviewed and adapted from materials provided by OI Analytical.
For more information on this source, please visit OI Analytical.