Application Note•multi N/C® UV HS 사이언스21 입니다.

Application Note•multi N/C® UV HS

TOC Determination in Phosphoric Acid by UV Digestion

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Introduction
Phosphoric acid is used in many industries, for example, in the production of fertilizers and detergents or in food industries as a
preservative in beverages or as an antioxidant in meat products. The monitoring of impurities in phosphoric acid is crucial for these kinds of applications. In addition to other parameters, the TOC is used as a sum parameter in quality control that addresses the whole range of contamination by organic impurities.
There are two very common approaches that can be applied for TOC determination in liquid aqueous matrices: catalytic high uploaderature combustion and wet chemical digestion promoted by UV light and additional chemical oxidants.
Wet chemical UV digestion is the principle of choice for very aggressive matrices, such as concentrated phosphoric acid or other
mineral acids(except hydrochloric acid).
While the phosphoric acid may quickly damage the combustion tube and catalyst in catalytic combustion TOC methods, the big advantage of UV digestion is a minimum of maintenance and wear of he TOC system.

The oxidation power of the multi N/C® UV HS that was used for these measurements is very high due to its high-power, long-life
UV reactor. Hence, a complete oxidation of the organic compounds inside the sample is ensured.

Materials and Methods
: A TOC analyzer multi N/C® UV HS based on the UV/wet chemical digestion principle was used for the measurements of phosphoric acid samples. Sample introduction was done using the automatic sampling system AS vario.

1. Samples and Reagents
- Three different samples of concentrated phosphoric acid were analyzed.
- Phosphoric acid 10%(for optional TIC control measurement)
- Sulfuric acid 2M for automatic acidification in NPOC mode and preparation of oxidation reagent Sodium peroxodisulphate solution 80g/L as oxidation reagent
- Sodium peroxodisulphate solution 80g/L as oxidation reagent

2. Sample Preparation
: All samples were diluted manually before measurement, due to the high viscosity of the original sample. The dilution ratios are
shown in table 2. No further preparation steps were applied. Sample acidification can be omitted for NPOC testing in concentrated acids.

3. Calibration
: Calibration standards of different concentration levels from 0.5- 100 mg/L were prepared from a 1000mg/L TOC stock solution of
potassium hydrogen phthalate in water and acidified with sulfuric acid.
A calibration run was started, and a linear calibration curve was obtained. An example is shown below.

Figure 1: liner regression and method characteristics for TOC calibration Within the method up to 3 calibration ranges can be linked to each parameter in order to cover an over-all working range of up to 3 magnitudes. Detection limits and limits of quantification are depending on the selected working range and can be derived from the method characteristics given above.

4. Instrumentation
: The measurements were performed in the NPOC mode with method settings shown in the table 1.

Table 1

Results and Discussion
: The following table shows the mean values of the NPOC measurements calculated from at least duplicate injections as well as
the relative standard deviation. A typical NPOC measurement curve is shown in the table 2. Results TOC

Table 1

Conclusion
: The results show very good reproducibility. The instrument is very well suited for the determination of TOC in concentrated phosphoric acid and similar samples with aggressive matrices.
By applying the high throughput autosampler AS vario the parallel purge and analyses feature of multi N/C® analyzers assure short sequence runtimes.
A high degree of automation combined with the well-proven Self Check System for trouble free unattended system operation makes TOC analyses by multi N/C® systems the most comfortable parameter in your lab. Headquarters Analytik

Figure 2: example of a measurement signal for sample 2

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Reference(참고문헌): Analytik-jena AG Application Note.
Model Name(모델명): multi N/C® UV HS
The Person in Charge(담당자): Oh Beomjun
Maker(제조사): Analytik-jena
Country of Origin(원산지): Germany
e-mail: saleskorea@analytik-jena.com
Data Services(자료제공): Analytik-Jena Korea

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