Quality control of feedstock

Illustration Raw materials

An end product can be only as good as the materials used to make it. Regular and systematic analysis of the incoming starting materials helps to ensure that the end product is not bound to be of poor quality before the production process has even started.

Given the importance of the raw materials' quality, the analyses have to be specific, reliable, and precise – and given the importance of economic aspects such as time to market, the analyses have to be efficient and time-saving.

Metrohm offers a range of systems and products that meet any requirements in raw materials inspection: from easy-to-use out-of-the-box systems to customized setups tailored to your application. In addition, Metrohm gives you access to an extensive pool of industry-specific application know-how free of charge. Learn more about our solutions – applications and instrumentation – on this page:


Regulatory compliance in feedstock analysis


With our instruments, you can perform a wide range of analyses in compliance with international standards (ASTM, ISO, and DIN).

> See how you can comply with international standards using Metrohm instruments


Spectroscopy for raw material testing

Requiring little to no sample preparation, enabling nondestructive measurements, and yielding results almost instantaneously, spectroscopy is one of the foremost analytical techniques for incoming goods inspection.

Watch the video to learn more about the possibilities of spectroscopy in the polymer industry.

> Learn more about the NIRS DS2500 Analyzer

> See what parameters you can analyze with a NIRS DS2500 Analyzer

Hydroxyl end groups in real time

Polyurethane transport foam
In the production of polyurethane, the hydroxyl number of polyols indicates the reactivity with isocyanates. Near-infrared spectroscopy is uniquely suited for analyzing the hydroxyl end groups of polyols. Simultaneously, information regarding the methyl substitution of the polymer backbone is obtained within seconds.


Feedstock identification using Raman spectroscopy

Identification of monomers using Raman spectroscopy

Polymers consist of macromolecules which are made of many identical or similar structural units, the so-called monomers. We have worked out an Application Note that shows how to identify common monomers comfortably and rapidly using the handheld Mira M-1 spectrometer. Monomers such as styrene, various alkyl methacrylates, divinylbenzene, ethylene glycol, phenol, terephthalic acid, and urea can be analyzed within seconds. Moreover, additives or inhibitors such as benzoquinone can be identified quickly and unambiguously.

> Read more about the handheld Mira M-1 analyzer



Metrohm Process Analytics for raw material testing

Process analyzers from Metrohm allow you to monitor parameters in real time, continuously, and fully automatically. They can thus be seamlessly integrated into your production processes. The process analyzers are available for a wide range of parameters and in various configurations – ranging from single-parameter systems to multiparameter analyzers performing titration, voltammetry, photometry as well as direct measurements or measurements with ion-selective electrodes. Besides wet-chemical analyzers, we also offer online NIR spectrometers for the nondestructive analysis of a variety of raw materials.

TBC inhibitor in monomer streams

Online process analyzer for titration, Karl Fischer titration, colorimetry, and more

In the production of styrene, butadiene, and vinylacetate, the stabilizer 4-tert-butylcatechol (TBC) plays a crucial role in preventing premature polymerization during storage and transport.

In order not to compromise the product quality, the TBC concentration in styrene has to be maintained above 10–15 mg/L. TBC requires oxygen to prevent the monomers from polymerizing. To control TBC depletion, close monitoring of the concentration is required.

In the case of liquefied 1,3-butadiene, TBC is added to prevent formation of peroxides and popcorn polymer. For the determination, the sample is bubbled through a solvent which absorbs the TBC while the butadiene evaporates. 

If you need to monitor TBC levels in styrene, butadiene, or vinylacetate, check out the ADI 2045TI Process Analyzer.

> Learn more about the ADI 2045TI Process Analyzer

Caprolactam purity monitoring in accordance with ISO 8660

Structural formula of caprolactam

Caprolactam is a starting material for the production of polyamide 6, a polymer that is widely used in the manufacture of clothing, carpets, and industrial fibers. The quality of caprolactam can be assessed by way of permanganate absorption number (PAN) analysis, as described in ISO 8660. PAN is used as a measure for the purity of the caprolactam, as it expresses the stability of a caprolactam sample in the presence of potassium permanganate.

The ADI 2045TI Process Analyzer from Metrohm Process Analytics meets the requirements for PAN analysis as specified in ISO 8660.

> Learn more about the ADI 2045TI Process Analyzer



Water determination

Water is an important quality parameter both in raw materials and in finished products (read more about water determination in finished products here). Excessive water contents may interfere with the reaction or compromise the properties of the finished product. More importantly, however, the presence of water promotes corrosion of the piping and storage tanks.

You can check the water content in gaseous monomers, liquefied gases, and liquid monomers using Karl Fischer titration:

Water in gaseous monomers

Titration curve for water determination in butadiene

Gaseous monomers and other liquefied gases are used in the production of plastics of all kinds. Aggressive, toxic, and highly volatile as such gases often are, they pose a challenge to the monitoring of critical parameters during the manufacture of downstream products. One of those parameters is the water content.

The 875 KF Gas Analyzer offers you a highly sensitive and safe way of measuring trace levels of water in a variety of gaseous monomers and liquefied gases by coulometric titration.

> Read more about the 875 KF Gas Analyzer


Water in liquid monomers

Titrando titrator system for volumetric water determination

Water determination in weakly basic nitrogen-containing monomers such as melamine and beta-caprolactam is straightforward and takes place via coulometric or volumetric titration. For amines that are prone to side reactions, the Karl Fischer oven method is recommended.

> Learn more about Karl Fischer titration

> Learn more about the oven method for sample preparation



End-group titration

Potentiometric titration is ideally suited for titrating functional groups in monomers, in particular monomeric mono- and polyacids as well as polyols. These titrations are mostly carried out in nonaqueous, nonpolar solutions and are thus accompanied by very little potential change, leading to flat and erratic titration curves. Metrohm has overcome these drawbacks by developing instruments and sensors (e.g., the Solvotrode, see below) that allow endpoints to be determined in these low-conductivity media.

Hundreds of titrations are applied in the polymer industry: from acid, hydroxyl, epoxy, carboxyl, and amine number to the chloride and isocyanate concentration. The most common and readily automated analyses are the hydroxyl and acid number as well as the isocyanate content.

If you are interested in these kinds of analyses, we also recommend watching the C&EN webinar on "Titration Solutions for Difficult Polymer Samples":

> Go to the webinar

Acid number in accordance with ASTM D4662 and ISO 2114

855 Robotic Titrosampler for automated total acid and total base number analysis

The acid number (or acid value, AV) is the most common nonaqueous titration used in raw material inspection. The acid number corresponds to the amount of carboxylic acid functional groups. Potentiometric titration is the ideal method to determine this value in alkyl resins, polyester acrylate resins, or mixtures. It goes without saying that this method can be fully automated.

> Learn more about Metrohm titrators and automation


Hydroxyl number in accordance with ASTM E1899 and EN ISO 4629-2

Lab scene with Titrando potentiometric titrator and ion chromatography system

The hydroxyl number of monomers indicates the degree of esterification. Additionally, in the production of polyurethanes, the hydroxyl number of  polyols is determined to allow an assessment of their relative reactivity with isocyanates.

For the determination of the hydroxyl number, ASTM E1899 and EN ISO 4629-2 recommend potentiometric titration.

Hydroxyl value determination with titration has several benefits:

  • The method is rapid and robust.
  • Sample preparation is straightforward.
  • The determination can be automated.

As a result, you can reduce your interventions to a minimum and save valuable time.

> Learn more about Metrohm titrators and automation 


Isocyanates according to DIN 53185 and DIN EN ISO 14896

Titration curve of isocyanate

The chemical reaction between diisocyanates or polyisocyanates and a diol or polyol leads to the formation of polyurethanes. The isocyanate groups with the cumulated double bond sequence are the essential components in the synthesis. This is where the hydroxyl groups of the polyol attack. The titration of the NCO group is a classical back-titration: The isocyanate is titrated with an excess of dibutylamine, which is back-titrated with a known concentration of chloric acid.

This determination can also be set up to save time and work through the use of a sample changer.

> Learn more about Metrohm titrators and automation


Related products

Sample processor for automated processing of routine samples

814 USB Sample Processor

Robust sample changer for the determination of small and medium-sized sample series.

Learn more …
Electrode for titration in aqueous media with easy-to-clean diaphragm

Solvotrode easyClean

Space-saving electrode for titration in nonaqueous media, with easyClean diaphragm.

Learn more …


Impurity analysis with voltammetry

Voltammetry is a very sensitive technique for the analysis of electrochemically active substances, such as inorganic or organic ions but also neutral organic compounds. This technique combines a wide range of applications, short analysis times, and high precision and sensitivity with comparatively low investment and operation costs.

Given Metrohm’s long-standing experience in this field, we can provide you with instruments, accessories, and know-how for your specific application. Read how you can use voltammetry in the inspection of incoming raw materials in the polymer industry:

Determining 4-carboxybenzaldehyde in terephtalic acid

Voltammetry system with operator

When xylol is used to manufacture terephtalic acid, 4-carboxybenzaldehyde (4-CBA) forms as an impurity. This impurity has to be removed before the terephtalic acid can be further processed, e.g., into polyester fibers or PET bottles.

The residual content of 4-CBA in purified terephthalic acid (PTA) can be easily determined by polarography.

> Learn more about voltammetry


Determining iron in ethylene glycol

Votammogram of iron content in ethylene glycol determined with voltammetry

Voltammetry is ideally suited for the determination of iron in ethylene glycol. In ethylene glycol used as a raw material in PU synthesis, even trace-level iron impurities act as a catalyst and thus have a strong impact on polymerization. As voltammetry does not require sample preparation, the determination is straightforward and sensitive, with detection limits as low as approx. 0.1 µg/L.

> Learn more about voltammetry



Sodium and potassium in polyol with IC

Sodium and potassium determination in polyol sample

The chemical reaction of a di- or polyisocyanate with polyols yields polyurethane foams, resins, and rubbers. Impurities in the raw materials have a great impact on the reaction rates and compromise the quality of the end product. In polyols, alkali metals represent some of the most critical impurities, because they are strong catalysts for linear and branched reactions. Ion chromatography after Inline Matrix elimination is a rapid and precise method for the simultaneous determination of sodium and potassium.

> Learn more about ion chromatography