Concentration measurement in liquids

Concentration measurement explained

In the essential task of concentration measurement in liquids, the industry uses advanced products that guarantee the precision and efficiency of analysis processes. Understanding the exact composition of a solution (whether in pharmaceutical manufacturing, food technology, or chemical processing) is made possible by advanced sensor technology, which, based on refractometric, potentiometric, or spectroscopic principles, enables accurate detection of theconcentration.

These products, equipped with intelligent interfaces for data transmission and analysis, offer the possibility to optimize processes with low maintenance requirements and long service life, thus representing an indispensable resource in quality control and process management.

The ultrasonic measurement process of LiquiSonic

The basis of the measurement process is a time measurement that can be implemented very accurately and with long-term stability. From the speed of sound, the concentration or density of a liquid is calculated. Other parameters can also be determined, such as the Brix content, solid content, dry mass, or suspension density.

Our LiquiSonic^® Concentration and density measuring devices are used in various processes for the analysis of liquids.

In a typical case, a calibration curve is determined from the relationship between the speed of sound and concentration. Based on this, the corresponding concentration is calculated from each measured sound speed value.

Limit value monitoring

Our ultrasonic measuring devices have no mechanical parts that can wear out or age. They offer outstanding advantages over competing measurement methods for determining concentration and density.

High reliability in determining the molar concentration

The measurement process only requires a precise time measurement to determine the molar concentration. The speed of sound is calculated from the sound travel time and the known distance between the transmitter and receiver. The typical sensor design includes transmitter and receiver in a compact housing.

The measurement process is independent of the conductivity, color, and transparency of the liquid due to the sensors and is characterized by high reliability in determining the molar concentration. The measurement accuracy of the devices is between 0.05 m% and 0.1 m%. In addition to sound speed measurement, all LiquiSonic^® Sensors via an integrated measurement of temperature for temperature compensation in the process.

Basics of concentration measurement

The determination of the concentration of different liquids plays a crucial role in numerous procedures of different processes. Here, the ratio of two substances to each other in a mixture or solution is measured and assessed.

A central factor of this concentration measurement is the molar concentration. It is defined as the amount of a substance per unit volume and is of crucial importance, especially in the analysis of solutions. It allows for an accurate assessment of the chemical composition and reactivity, making molar concentration an indispensable tool in many fields.

Furthermore, there are various measurement ranges that allow the molar concentration to be measured in different ways. They significantly expand the possibilities of concentration measurement and increase flexibility regarding the specific requirements of the mixture or solution to be analyzed.

Finally, the amount of liquid to be analyzed plays an important role. It must be sufficient to allow for an accurate measurement, but not so large that it distorts the measurement result or makes the measurement unnecessarily complicated.

A key aspect of concentration measurement is the amount of substance concentration (molarity) in a solution, defined as the amount of a substance per unit volume. This is particularly relevant when analyzing a solution where the amount of substance concentration is crucial for assessing chemical composition, concentrations, and reactivity. Accurate measurement of concentrations of an amount of substance in a solution is essential to control processes, ensure quality, and conduct scientificinvestigations.

Applications of concentration measurements

Concentration measurement is one of the essential methods to analyze the quality and safety-relevant characteristics of products and substances. Therefore, it plays a crucial role in several industries. There are various methods for measuring the concentration of a substance in a solution, depending on the type of substance and the requirements of the application.

A practical example of the application of concentration measurement can be found in the pharmaceutical industry: Here, the precise determination of the concentration of an active ingredient in medicines is essential to ensure their effectiveness and safety. This demonstrates the importance of precise measurement methods for determining the concentration of a substance in quality assurance.

Examples of measuring a substance concentration

Concentration detection is used in the following areas, for example:

• Chemistry/ Chemical production (For monitoring the composition of mixtures)
• Pharmaceutical industry (e.g., for the production of medicines)
• Food production (For controlling the product quality of food)
• Metallurgy (To check the quality of metal ores)
• Environmental analysis (For calculating pollutants in water)

In addition, concentration measurement is also commonly used in other areas, such as industry and science.

Methods for concentration measurement

The precise determination of the substance concentration of substances in liquids is crucial for numerous scientific, industrial, and medical applications. Different methods of concentration measurement are used to quantify the exact content of a substance in a specific volume of liquid.

These methods range from spectrophotometric techniques to chromatographic analyses and electrochemical measurements. The choice of the appropriate method depends on the properties of the substance to be analyzed, the requirements of the specific application, and the available resources. There are various methods for measuring the concentration of solutions. Each of these measurement methods for determining the substance concentration has its own advantages and disadvantages.

Refractometry

The refractometer determines the refractive index of solutions and solid substances to measure concentration. The determination of the refractive index is based on the refraction of light, which is reflected or refracted by a liquid. Depending on the type and concentration of the dissolved substances, the light is refracted differently.

Consequently, the refractive index results from the concentration of the dissolved substances. An optical sensor (window) measures the reflection of a light beam that is reflected by an LED light source after hitting the sample. The process of refractometry is extremely sensitive to influencing factors such as vibrations and requires very extensive and time-consuming calibration as well as regular maintenance.

Radiometry

Radiometry uses radioactive radiation to detect concentrations of a substance. A radioactive preparation sends its radiation through the measuring container, which is received by the detector. A scintillator converts the radioactive radiation into light flashes and evaluates their number. Since the penetration of gamma radiation depends on the substance, the density of the mass is determined from the intensity of the incoming radiation.

Gravimetry

In gravimetry, the measurement of mass concentration is carried out by measuring the mass of a substance before and after a chemical reaction. It is used to determine the concentration of a specific element or compound in a sample. The basic process for determining the molar concentration includes the steps of precipitation, filtration, and weighing. This method is extremely time-consuming and typically requires large samples. Moreover, the measurement principle is very prone to errors as it requires several manual process steps in defining the molar concentration.

Titration

The concentration measurement by titration is carried out by adding a solution with a known concentration value to a solution with an unknown concentration value until a chemical reaction occurs. This method is only suitable for certain solutions and due to manual handling prone to errors in calculating mass concentration.

spectrophotometry for concentration measurement

In spectrophotometry, the volume of the sample plays a crucial role in determining the volume concentration of a substance. Volume concentration is a unit of measurement for the amount of a substance in a mixture relative to the total volume of the mixture. It indicates what portion of the total volume of a mixture consists of a specific substance.

Light absorption, which is a central measurement value in this method, can be significantly influenced by the volume of the sample. Therefore, accurate determination and control of the sample volume are essential for precise measurement results. Spectrophotometry is suitable for a variety of samples, including liquids, gases, and solid materials.

This variant for measuring particle volumes is very susceptible to interference factors, which affect the accuracy of the sample.

Chromatography (such as HPLC, GC)

Chromatography separates components of a mixture based on their interactions with a stationary and a mobile phase.

There are also other measurement methods/procedures that can be used in certain scenarios for concentration measurement. These include:

• Electrochemical methods (such as potentiometry, ion-selective electrodes)
• pH measurement
• NMR spectroscopy
• Mass spectrometry

Selection criteria for concentration measurement methods

The selection of a suitable method for concentration measurement in liquids depends on several factors, including:

• Specificity of the application: The type of substances to be measured and the complexity of the solution.
• Accuracy and sensitivity: Required precision and ability to detect a minimum of concentrations.
• Speed and throughput: Need for quick measurement results and ability to handle large sample volumes.
• Cost efficiency: Acquisition and operating costs of the equipment as well as maintenance requirements.
• User-friendliness: Ease of use and maintenance, especially in environments with little specialized staff.