A photometer is a device used to measure the concentration of substances in a solution. It consists of a light source, a cuvette, a detector, and a display unit. Here you will find a selection of photometers for daily fieldwork. The devices are compact and come from various manufacturers such as Macherey-Nagel, WTW, and Hach.

A photometer for photometric analyses includes a light source, a filter, a sample cuvette, and a detector. Additionally, the device contains diaphragms and mirrors. The light from the source passes through the filter, which determines the wavelength to be measured. The light then travels through the sample solution in the cuvette to the detector. The less light that passes through, the higher the concentration of the sample must be.

The devices vary in design and have different optical components, which influence the measurement quality and the application range.

A photometer can be used for water analysis. The NANOCOLOR photometers from MACHEREY‑NAGEL can be used in various fields. These photometers support a wide range of tests and are utilized for analyzing wastewater, drinking water, process water, surface water, groundwater, and cooling and boiler feed water. They are also used in the food and beverage industry. A single device can perform all these tests. NANOCOLOR photometers can also be used for special applications, such as color measurements.

BOD Measurement

The BOD (Biochemical Oxygen Demand) value indicates how quickly carbon compounds in water are broken down. It is used in water management to assess water quality and the purification performance of wastewater treatment plants.

In the BOD5 measurement, the oxygen content in diluted wastewater is measured before and after incubation. In the BOD self-monitoring measurement using a closed respirometer, the carbon dioxide produced causes a measurable pressure change. The samples must be stored for five days at 20°C. The OxiTop®-IDS systems allow biodegradability tests, such as soil investigations or testing new chemical substances. Modern spectral probes can also determine BOD by using spectral correlation and user calibration based on known BOD laboratory values.

Kjeldahl Method for Nitrogen and Protein Analysis

The Kjeldahl method is an important technique for determining nitrogen and proteins. Developed in 1883 by Johan Kjeldahl, it revolutionized nitrogen analysis. The method is widely used in fields such as food, feed, soil, and water analysis. However, its applications extend beyond these areas to general and pharmaceutical industries—wherever nitrogen content is critical.

The Kjeldahl analysis is highly accurate and straightforward, making it a reference method to this day. It captures all nitrogen components, allowing the determination of specific nitrogen compounds such as ammonium, nitrate, nitrite, and organically bound nitrogen in various samples. The method is particularly useful for analyzing large sample volumes.

The Kjeldahl Analysis Process

Traditionally, Kjeldahl analysis involved manual laboratory heaters and Erlenmeyer flasks. Over time, these have evolved from large cast-iron stands into high-precision devices capable of digestion, distillation, and automatic sample handling.

The Kjeldahl analysis consists of three main steps:

1. Digestion: The samples are broken down using sulfuric acid.
2. Distillation: The resulting solution is distilled.
3. Titration: The distillate is titrated, and the final result is calculated.

While the chemistry behind the method remains largely unchanged, the process is now fully automated and adapted to modern laboratories. Users benefit from enhanced safety, efficiency, and time savings thanks to block digestion systems and steam distillation units with integrated titration.

The advantage of this method is its versatility in analyzing various sample types, including grains, animal feed, dairy products, manure, sewage sludge, compost, soil, aqueous extracts, and wastewater. When dealing with highly heterogeneous samples, Kjeldahl remains the best option.

Extraction Methods

Extraction methods separate soluble components from a solid sample.

• Determining fat content in food
• Identifying contaminants in soil samples
• Analyzing the composition of natural substances

Even brewing coffee is an extraction process. In a laboratory, the goal is to completely extract the desired components under controlled conditions, using minimal dilution. Organic solvents such as hexane or petroleum ether are commonly used for extraction. In all extraction methods, a specified amount of solvent is used to dissolve as much of the target substance as possible. The solvent is repeatedly evaporated and returned to the sample through a reflux condenser—unlike a coffee machine, where the liquid passes through only once. The extracted components accumulate in the distillation flask.

Applications of Extraction Methods:

• Want to analyze fat in food?
  Use hydrolysis followed by Soxhlet extraction, e.g., the Weibull-Stoldt method or AOAC International Hydrolysis Method.

• Want to determine substances in packaging or other objects?
  Use hot extraction to detect plasticizers in packaging, following the Randall method.

• Want to measure fat content in food and animal feed?
  Use hot extraction (Randall method), sometimes preceded by hydrolysis to determine total fat content.

• Want to check for pesticides in food and feed?
  Extract residues and contaminants from food, feed, or other materials without triggering oxidation reactions. Increase detection limits by using larger sample quantities.

Manufacturers

Manufacturers of extraction and analytical instruments include Behr, Gerhardt, A.Krüss, and Büchi.