Application Note | TURBIDI.T™
How to measure the concentration of particles in liquid samples using TURBIDI.T™?
by Dimitria Camasão, Assala Larbes and Gloria Pinilla,
Application Scientists, Rheolution Inc.
SUMMARY
- Suspensions are mixtures of solid particles in liquid media and are widely present in various industries. The determination and control of particle concentration is crucial in many applications.
- Turbidimetry is a quick and non-invasive method to measure particle concentration following a simple-to-implement protocol.
- Reference curves of turbidity vs silica particle concentration in distilled water with high precision were established using the TURBIDI.T™ instrument at different wavelengths.
- The reference curve obtained with the most suitable wavelength was used to gain accuracy in the determination of unknown concentrations of silica particles in distilled water.
INTRODUCTION
A suspension is a mixture in which solid particles (organic or inorganic in nature) are dispersed in a liquid medium, but not dissolved. Suspensions are usually opaque or cloudy and can settle over time due to gravity. They have a broad range of applications and are present in various industrial processes, such as chemical, pharmaceutical, food and beverage, and environmental industries. During the production of pharmaceutical formulations for example, professionals may measure particle concentration to assess whether particles have aggregated or formed larger clusters to optimize the process and ensure product quality.
The concentration of particles in a suspension can be measured in different ways, including gravimetric analysis, optical methods, coulter counter, and microscopy analysis. Turbidimetry is one easy and quick option. It gives the turbidity of liquid samples by measuring the amount of light scattered by the particles present in the solution. Because the turbidity of a liquid depends on the amount of particles in suspension, the measurement may be directly correlated to the exact concentration of particles. In addition to its simplicity, this technique is non destructive in the sense that no chemical or physical changes are needed to the sample [1,2].
In order to demonstrate the use of the TURBIDI.T™ for the determination of particle concentration, silica particles in distilled water were tested at various concentrations to build a reference curve. Sample of different concentrations were then prepared and the estimated concentrations obtained from the reference curve were compared with the theoretical values.
MATERIALS AND METHODS
The TURBIDI.T™ (Rheolution Inc., QC, Canada) measures the turbidity of solutions across different ranges. It offers a level of flexibility through several features such as: (1) modifying the optical emitter cartridges to use different wavelengths; (2) selecting sample holders that suit the experimental design; (3) using a wireless tablet to collect, customize, analyze and export data to a dedicated software; and (4) expanding the measurement capacity by pairing multiple instruments to the same tablet.
The TURBIDI.T™ was previously calibrated with formazin standards (FTU). In this study, different reference curves were produced at different wavelengths. The cartridges used for light emission were the Emitt.850, Emitt.635, Emitt.520 and Emitt.405 operating at 850, 635, 520 and 405nm, respectively. The Receiv.ViS optical cartridge was used for reception (wavelength ranged from 400 nm to 1000 nm).
Silica particles, with a size of 1000 nm (Alpha Nanotech Inc., BC, Canada), were diluted in distilled water following 5 concentrations: 150, 200, 300, 400 and 500 mg/L. The solutions were stabilized at 25°C and 3 samples of each concentration were transferred in 10 mL vials for testing (n=3). Each vial was well mixed before introducing into the TURBIDI.T™ for the measurement. Average results are expressed as mean ± standard deviation. Simple linear regression was applied to the data of each wavelength. To validate the accuracy of the particle concentration estimation, mean error (%) was calculated using the following equation:

RESULTS AND DISCUSSION
Figure 1 displays the turbidity (in FTU) of samples containing 5 different concentrations (from 150 to 500 mg/L) of silica particles in distilled water obtained using 4 different wavelengths of light emission. Data points represent the average of triplicates with small error bars featuring the high precision of the measurements. The data at each wavelength was well fitted in a linear regression (R² >0.970). It is possible to observe that the sensitivity of the measurements can be improved by increasing the wavelength (from 405 nm to 850 nm) since the slope of the linear regressions were progressively higher (more signal was detected). These linear regressions constitute reference curves for the estimation of particle concentration from the FTU (turbidity) value of a solution with an unknown concentration of particles.

Figure 1: Turbidity (in FTU) of different concentrations of silica particles in distilled water obtained with the TURBIDI.T™ using different wavelengths.
The equation of the reference curve obtained with the wavelength of 850 is shown in Figure 2. Three new samples with arbitrary (but known) concentrations were then prepared and their concentrations were estimated using this reference curve (Figure 3). Table 1 shows the high level of accuracy of the estimates obtained using the reference curve with errors always lower than 2% when compared with the actual values of concentration.

Figure 2: Reference curve (in FTU) of silica particles in distilled water obtained with the TURBIDI.T™ using the wavelength 850 nm.

Figure 3: Determination of silica particle concentration from the reference curve (blue) of samples with arbitrary concentrations (orange points).
Table 1: Estimation of particle concentration from the reference curve generated by the TURBIDI.T™ using the wavelength of 850 nm.

CONCLUSIONS
The TURBIDI.T™ optical instrument can precisely determine the concentration of suspended particles in a solution using a reference curve obtained with just 5 points. The appropriate wavelength may be selected to obtain the highest levels of sensitivity and accuracy.
PRESPECTIVES
- The concentration of particles in suspension can be measured with high precision and accuracy using the user-friendly TURBIDI.T™ instrument.
- Reference curves and turbidity data can be easily stored in the tablet via the Soft Matter Analytics™ App and exported as needed.
- The different cartridges available allows the user to change the wavelength of light emission and gain accuracy and precision on the measurements of concentration.
- TURBIDI.T™ allows the use of vials with different sizes to perform the measurements that require little volume and avoid sampling manipulation.
- By connecting several TURBIDI.T™ units to a single operating tablet, a flexible testing platform can be built, enabling the assessment of multiple samples simultaneously. This scalability feature accommodates nicely the needs of R&D and QC labs.
REFERENCES
INTRODUCTION
A suspension is a mixture in which solid particles (organic or inorganic in nature) are dispersed in a liquid medium, but not dissolved. Suspensions are usually opaque or cloudy and can settle over time due to gravity. They have a broad range of applications and are present in various industrial processes, such as chemical, pharmaceutical, food and beverage, and environmental industries. During the production of pharmaceutical formulations for example, professionals may measure particle concentration to assess whether particles have aggregated or formed larger clusters to optimize the process and ensure product quality.
The concentration of particles in a suspension can be measured in different ways, including gravimetric analysis, optical methods, coulter counter, and microscopy analysis. Turbidimetry is one easy and quick option. It gives the turbidity of liquid samples by measuring the amount of light scattered by the particles present in the solution. Because the turbidity of a liquid depends on the amount of particles in suspension, the measurement may be directly correlated to the exact concentration of particles. In addition to its simplicity, this technique is non destructive in the sense that no chemical or physical changes are needed to the sample [1,2].
In order to demonstrate the use of the TURBIDI.T™ for the determination of particle concentration, silica particles in distilled water were tested at various concentrations to build a reference curve. Sample of different concentrations were then prepared and the estimated concentrations obtained from the reference curve were compared with the theoretical values.
MATERIALS AND METHODS
The TURBIDI.T™ (Rheolution Inc., QC, Canada) measures the turbidity of solutions across different ranges. It offers a level of flexibility through several features such as: (1) modifying the optical emitter cartridges to use different wavelengths; (2) selecting sample holders that suit the experimental design; (3) using a wireless tablet to collect, customize, analyze and export data to a dedicated software; and (4) expanding the measurement capacity by pairing multiple instruments to the same tablet.
The TURBIDI.T™ was previously calibrated with formazin standards (FTU). In this study, different reference curves were produced at different wavelengths. The cartridges used for light emission were the Emitt.850, Emitt.635, Emitt.520 and Emitt.405 operating at 850, 635, 520 and 405nm, respectively. The Receiv.ViS optical cartridge was used for reception (wavelength ranged from 400 nm to 1000 nm).
Silica particles, with a size of 1000 nm (Alpha Nanotech Inc., BC, Canada), were diluted in distilled water following 5 concentrations: 150, 200, 300, 400 and 500 mg/L. The solutions were stabilized at 25°C and 3 samples of each concentration were transferred in 10 mL vials for testing (n=3). Each vial was well mixed before introducing into the TURBIDI.T™ for the measurement. Average results are expressed as mean ± standard deviation. Simple linear regression was applied to the data of each wavelength. To validate the accuracy of the particle concentration estimation, mean error (%) was calculated using the following equation:

RESULTS AND DISCUSSION
Figure 1 displays the turbidity (in FTU) of samples containing 5 different concentrations (from 150 to 500 mg/L) of silica particles in distilled water obtained using 4 different wavelengths of light emission. Data points represent the average of triplicates with small error bars featuring the high precision of the measurements. The data at each wavelength was well fitted in a linear regression (R² >0.970). It is possible to observe that the sensitivity of the measurements can be improved by increasing the wavelength (from 405 nm to 850 nm) since the slope of the linear regressions were progressively higher (more signal was detected). These linear regressions constitute reference curves for the estimation of particle concentration from the FTU (turbidity) value of a solution with an unknown concentration of particles.

Figure 1: Turbidity (in FTU) of different concentrations of silica particles in distilled water obtained with the TURBIDI.T™ using different wavelengths.
The equation of the reference curve obtained with the wavelength of 850 is shown in Figure 2. Three new samples with arbitrary (but known) concentrations were then prepared and their concentrations were estimated using this reference curve (Figure 3). Table 1 shows the high level of accuracy of the estimates obtained using the reference curve with errors always lower than 2% when compared with the actual values of concentration.

Figure 2: Reference curve (in FTU) of silica particles in distilled water obtained with the TURBIDI.T™ using the wavelength 850 nm.

Figure 3: Determination of silica particle concentration from the reference curve (blue) of samples with arbitrary concentrations (orange points).
Table 1: Estimation of particle concentration from the reference curve generated by the TURBIDI.T™ using the wavelength of 850 nm.

CONCLUSIONS
The TURBIDI.T™ optical instrument can precisely determine the concentration of suspended particles in a solution using a reference curve obtained with just 5 points. The appropriate wavelength may be selected to obtain the highest levels of sensitivity and accuracy.
PRESPECTIVES
- The concentration of particles in suspension can be measured with high precision and accuracy using the user-friendly TURBIDI.T™ instrument.
- Reference curves and turbidity data can be easily stored in the tablet via the Soft Matter Analytics™ App and exported as needed.
- The different cartridges available allows the user to change the wavelength of light emission and gain accuracy and precision on the measurements of concentration.
- TURBIDI.T™ allows the use of vials with different sizes to perform the measurements that require little volume and avoid sampling manipulation.
- By connecting several TURBIDI.T™ units to a single operating tablet, a flexible testing platform can be built, enabling the assessment of multiple samples simultaneously. This scalability feature accommodates nicely the needs of R&D and QC labs.
REFERENCES
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