Vous avez été redirigé vers la version locale de la page demandée
Faire une demande

Quality control of Ammonium Nitrate

AN-NIR-064

2020-03

fr

Rapid and non-destructive moisture determination

Les produits chimiques spécialisés doivent répondre à de multiples exigences de qualité. L'un de ces paramètres de qualité, que l'on retrouve dans presque tous les certificats d'analyse et spécifications, est la teneur en humidité. La méthode standard pour la détermination de la teneur en humidité est le titrage Karl Fischer. Cette méthode nécessite une préparation reproductible des échantillons, des produits chimiques et l'élimination des déchets. Il est également possible d'utiliser la spectroscopie dans le proche infrarouge (NIR) pour déterminer la teneur en humidité. Avec cette technique, les échantillons peuvent être analysés sans aucune préparation et sans utiliser de produits chimiques.

Specialty chemicals have to fulfill multiple quality requirements. One of these quality parameters, which can be found in almost all certificates of analysis and specifications, is the moisture content. The standard method for the determination of moisture content is Karl Fischer titration.

This method requires reproducible sample preparation, chemicals, and waste disposal. Alternatively, near-infrared spectroscopy (NIR) can be used for the determination of moisture content. With this technique, samples can be analyzed without any preparation and without using any chemicals.

Figure 1. Samples filled in the rotating DS2500 Large Sample Cup.

Ammonium nitrate samples were measured with a DS2500 Solid Analyzer in reflection mode over the full wavelength range (400–2500 nm). To minimize particle size effects, a rotating DS2500 Large Sample Cup was employed. This accessory enables an automated measurement at different sample locations for a reproducible spectrum acquisition. As displayed in Figure 1, samples were measured without any preparation steps. The Metrohm software package Vision Air Complete was used for all data acquisition and prediction model development.

Table 1. Hardware and software equipment overview
Equipment Metrohm number
DS2500 Solid Analyzer 2.922.0010
DS2500 Large Sample Cup 6.7402.050
Vision Air 2.0 Complete 6.6072.208

The obtained Vis-NIR spectra (Figure 2) were used to create a prediction model for the moisture value determination. To verify the quality of the prediction model, correlation diagrams were created, which display the correlation between Vis-NIR prediction and primary method values. The respective figures of merit (FOM) display the expected precision of a prediction during routine analysis.

Figure 2. A selection of ammonium nitrate Vis-NIR spectra obtained using a DS2500 Analyzer and a rotating sample cup. For display reasons a spectra offset was applied.
Figure 3. Correlation diagram for the prediction of moisture content using a DS2500 Analyzer. The reference lab values were evaluated with volumetric Karl Fischer titration.
Table 2. Figures of merit for the prediction of the moisture content using a DS2500 Solid Analyzer.
Figures of merit Value
R2 0.840
Standard error of calibration 0.011 mg/L
Standard error of cross-validation 0.012 mg/L

This application note demonstrates the feasibility of NIR spectroscopy for the analysis of low moisture content in specialty chemicals, specifically ammonium nitrate. In comparison to the standard titration method, the reduction of analysis time and chemicals is a major advantage of NIR spectroscopy.

Table 3. Comparison of running costs for the determination of the moisture content with titration and NIR spectroscopy.
  Lab method NIR method
Number of analyses (per day) 10 10
Cost of operator (per hour) $25 $25
Costs of chemicals for water determination $2 $0
Time spent per analysis 5 min 1 min
Total running costs (per year) $8,288 $938
Figure 4. Comparison of the cumulative costs other three years for the determination of water content with volumetric titration and NIR spectroscopy.
Contact

Metrohm France

13, avenue du Québec - CS 90038
91978 VILLEBON COURTABOEUF CEDEX

Contact