A typical analysis schedule for the Fusion TOC analyzer starts with a cleaning procedure. The cleaning procedure confirms cleanliness of the system and will ensure low instrument background. Also, tracking cleaning procedure results from day to day will give an indication if any contamination issues may be occurring. It is imperative to have low background and no contamination to achieve superior low-level TOC results.
When running a cleaning procedure, the first replicate is the inorganic carbon (IC) sample pathway cleaning result. The second replicate is the first total carbon (TC) sample pathway cleaning replicate. This replicate is always highest of the TC replicates because the Fusion is performing a repetitive system cleaning procedure. The same water mixture is cycled through the system two more times to obtain the appropriate instrument background. For a clean system the final TC cleaning replicate should be < 3.0 Adjusted ABS. There are four replicates for the cleaning procedure as described below.
- Replicate 1 is for the IC sample pathway Cleaning Procedure
- 10 mL of DI water + 1.0 mL of acid is added to the IC sparger.
- Sparging occurs at 300 mL/min until the pressure reaches 50 psi.
- The resulting ABS is displayed.
- Replicate 2 is for TC sample pathway Cleaning Procedure replicate #1
- 9 mL of the DI water + acid from the IC sparger is transferred to the UV reactor, also 1.0 mL of sodium persulfate reagent is added to the UV reactor.
- Sparging occurs at 300 mL/min until the pressure reaches 50 psi.
- The resulting ABS is displayed.
- Replicate 3 is for TC sample pathway Cleaning Procedure replicate #2
- The water mixture from the UV reactor is transferred back to the IC sparger, to rinse the IC sparger and sample pathway to provide additional cleaning, then back to the UV reactor.
- Sparging occurs at 300 mL/min until the pressure reaches 50 psi.
- The resulting ABS is displayed.
- Replicate 4 is for TC sample pathway Cleaning Procedure replicate #3
(This is an exact repeat of the last replicate)- The water mixture from the UV reactor is transferred back to the IC sparger, to rinse the IC sparger and sample pathway to provide additional cleaning, then back to the UV reactor.
- Sparging occurs at 300 mL/min until the pressure reaches 50 psi.
- The resulting ABS is displayed.
The cleaning procedure cleans all glassware and sample pathway to ensure the lowest possible instrument background. Recycling the same water mixture through the system for the last two replicates indicates the cleanliness achieved and needed to obtain good low level accuracy and precision.
When running a blanking procedure, a cleaning procedure is performed before the acid and reagent values are acquired.
The blanking procedure is equally important. The blank is determined by identifying the separate carbon contributions of the 21% phosphoric acid and the sodium persulfate reagent.
When analyzing TOC or TC samples, the sample requires addition of sodium persulfate reagent to be added to the UV reactor for oxidation of carbon to carbon dioxide for detection by the NDIR detector. The addition of the reagent will also add an amount of carbon that needs to be quantified and subtracted from the result. This is accomplished by analyzing 3.0 mL of reagent in TC mode. The result is divided by three and saved in the instrument blank file. This result is the contribution of carbon of the reagent per milliliter. If the method adds 1.0 mL of reagent, then the full amount is subtracted as the blank value. If the method only adds 0.5 mL of reagent, only half the result is subtracted as the blank value. The Fusion TOC TekLink software automatically performs these calculations and adjustments according to which method is being used.
When analyzing IC samples, the sample requires addition of 21% phosphoric acid to be added to the IC sparger for converting inorganic carbon to carbon dioxide for detection. Similar to the reagent in TOC or TC analysis, the acid adds an amount of carbon that needs to be quantified and subtracted from the result. The IC blank value is derived by analyzing 1.0 mL of 21% phosphoric in IC mode. The result is contribution of carbon of the acid per milliliter. The Fusion TOC Teklink software automatically calculates the IC blank value to subtract from the sample result according to the active method.
It is important to run a Blanking procedure each time fresh sodium persulfate or acid reagent is prepared. Equally important is allowing freshly made sodium persulfate reagent to sit for 24 hours before running the Blanking procedure. This “settling time” allows any impurities in the solid sodium persulfate to interact with the water used in preparing the mixture. The interaction and settling time allow the impurities to be oxidized and gradually effervesce from the mixture. This provides for the lowest and most stable reagent blank value.
Instrument background, acid and reagent blank values are extremely important when determining accurate and precise low-level TOC values. Maintaining low instrument background by running and monitoring Cleaning Procedures along with correctly blanking acid and reagent values will allow the Fusion UV/Persulfate TOC analyzer to provide exceptional results year after year.
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