Applications for Stability Measurement Instruments

The Professional range of Metrohm stability measuring instruments includes the 892 Professional Rancimat, the 895 Professional PVC Thermomat, and the 893 Professional Biodiesel Rancimat. These stability measuring instruments comply with various international standards. This article provides application tips and also offers a choice of standards for the respective sample types.

892 Professional Rancimat

The 892 Professional Rancimat is a contemporary analytical instrument that has been designed to enable easy and consistent measurements of the oxidation stability of cosmetics, fatty foods, fats, and oils using the well proven Rancimat technique (Figure 1).

Figure 1. Principle of the Rancimat method

Oxidation Stability of Vegetable and Animal Oils and Fats

A standard application for the 892 Professional Rancimat is the measurement of the oxidation stability of fats and oils. Oxidation stability refers to the resistance of fats and oils to oxidation. In the Rancimat technique, when the reaction vessel is heated up, and the air is continuously passed via the sample, fatty acid molecules are oxidized rapidly. However, peroxides are initially formed as the main oxidation product, and fatty acids are fully destroyed after some time.

In addition, secondary products of oxidation are also formed, including volatile low-molecular organic acids like formic acid and acetic acid. All of these are transferred to a second vessel through the air stream. This second vessel contains distilled water, whose conductivity is continuously determined. The manifestation of volatile acids is documented in the measuring vessel as an increase in conductivity.

Induction period, induction time, or Oil Stability Index (OSI) is referred to the time that elapses until the appearance of secondary reaction products. This value defines the sample’s resistance to oxidation. If the induction time is longer, the sample would be more stable. Measured by the Rancimat technique, the induction time is a common parameter of quality control in the inspection of incoming goods, production, and additional processing of fats and oils in the food sector. Besides fats and oils from vegetable sources, the 892 Professional Rancimat can also be used to determine the oxidation stability of animal fats like tallow, lard, and fish oil.

Normally, foodstuffs that include antioxidants tend to decelerate the oxidative decomposition of fats and oils. Such antioxidants may be introduced artificially or occur naturally. The 892 Professional Rancimat can even be utilized to control the efficiency of such antioxidants.

Application Literature from Metrohm

  • AB-141 Analysis of edible fats and oils
  • AN-R-001 Oxidation stability of olive oil
  • AB-087 Analysis of dairy products (butter)
  • AB-232 Determination of the antioxidant activity as per the Rancimat technique
  • AB-204 Oxidative stability of oils and fats - Rancimat method
  • AN-R-004 Oxidation stability of corn oil
  • AN-R-003 Oxidation stability of rapeseed oil
  • AN-R-006 Oxidation stability of sunflower oil
  • AN-R-005 Oxidation stability of safflower oil
  • AN-R-014 Oxidation stability of sweet almond oil
  • AN-R-013 Oxidation stability of walnut oil
  • AN-R-007 Oxidation stability of peanut oil

Standards

The Rancimat technique is included in numerous international and national standards, such as:

  • ISO 6886 - Animal and vegetable fats and oils - Determination of oxidative stability (accelerated oxidation test)
  • AOCS Cd 12b-92 (AOCS - American Oil Chemists' Society) Sampling and analysis of commercial fats and oils: Oil Stability Index
  • 2.4.28.2-93 - Fat stability test on autoxidation. CDM, Japan

Oxidation Stability of Foods

There are many foods that include fats and oils, either naturally or as an outcome of production. The fats and oils are also subject to oxidation, similar to the pure substances, and are responsible for their spoilage. The 892 Professional Rancimat can be utilized to measure the oxidation stability of oil- and fat-based foods.

It is possible to directly examine foods with a very high fat content. The only requirement is a reduction in the sample particle size. In foods with a high quantity of proteins or water besides fat, the fat phase has to be initially isolated. This process is carried out through cold extraction with petroleum ether. The 892 Professional Rancimat can then be utilized to measure the separated fat. Following are some examples of applications for direct measurements:

  • Nuts
  • Potato chips
  • Butter cookies
  • Microwave popcorn
  • Instant noodles

Examples of determinations following extraction

  • Chocolate
  • Mayonnaise
  • Waffles
  • Salad dressing
  • Sausage products

Application Literature from Metrohm

  • AN-R-011 Oxidation stability of instant noodles
  • AB-237 Determination of the oxidative stability of biscuits, cookies, and cereals
  • 8.000.6069EN Determination of the oxidation stability of fat-containing solid foodstuffs
  • AN-R-012 Oxidation stability of different solid foodstuffs
  • 8.000.5023EN Food Analysis - Quality control in the food and beverage industry

Oxidation Stability of Cosmetics

There are many natural and other high-quality cosmetic products that include a considerable amount of vegetable fats and oils. Cocoa butter is an ingredient used in many lip and body care products. These cosmetics will spoil over a period of time compared to paraffin-based products, partly due to the intrinsic oxidation of the vegetable fats.

The 892 Professional Rancimat can be used to directly measure the samples based on the amount of fat, or the separated fat can be determined following cold extraction with petroleum ether. Some typical application examples include:

  • Body lotion
  • Lip balm
  • Suntan oil
  • Hand cream

Application Literature from Metrohm

• AN-R-015 Oxidation stability of suntan oil

893 Professional Biodiesel Rancimat

The 893 Professional Biodiesel Rancimat is the latest analytical device designed for easy and consistent measurement of the oxidation stability of biodiesel blends and biodiesel as per the standards EN 15751 and EN 14112.

Oxidation Stability of Biodiesel (Fatty Acid Methyl Esters, FAME) and Biodiesel Blends

Over the past few years alternative fuels harvested from renewable plant sources have become more and more popular, and their use will continue to increase in the coming days. Biodiesel or fatty acid methyl esters (FAME) - also called rapeseed oil methyl esters (RME) - have become another critical source of renewable energy, in addition to other alternative fuels like methanol, ethanol, and biogas.

FAME is often acquired from vegetable oil, but waste products or animal fats from the processing or production of foods can also be employed. Biodiesel is utilized either as a biodiesel blend (combined with standard diesel fuel) or its pure form in the automotive industry. Under a catalyzed process, the vegetable oil used to produce biodiesel is transesterified with methanol, and following this the methyl esters of the fatty acids contained in the oil is produced along with glycerol as a by-product.

Just like all natural fats and oils, FAME is more unstable in storage and is oxidized gradually by atmospheric oxygen. The resulting substances may cause damage to the motor. This is the reason why oxidation stability is a major quality measure for biodiesel and is frequently measured during the production process. The 893 Professional Biodiesel Rancimat is a suitable instrument to measure biodiesel’s oxidation stability in a simple and reliable way.

The measurement principle is that of the Rancimat technique, illustrated above with regard to fats and oils. The sample quality is characterized by determining the induction period or induction time in this manner.

Application Literature from Metrohm

  • AN-R-010 Oxidation stability of biodegradable lubricating oil
  • AN-R-009 Oxidation stability of fatty acid methyl esters (FAME, biodiesel)
  • 8.000.6052EN Quality assurance of biofuels
  • 8.000.6081EN Determination of the oxidative stability of biodiesel (fatty acid methyl esters, FAME)
  • 8.000.5013EN Biofuel analysis - Quality assurance of biofuels

Standards

The FAME’s oxidation stability and their mixtures with diesel fuels are considered to be a critical standard parameter in a set of standards, which define the minimum quality needs of biodiesel sold as heating oil or vehicle fuel.

  • ASTM D 7467 «Standard specification for diesel fuel oil, biodiesel blend (B6 to B20)»
  • ASTM D 6751 (ASTM - American Society for Testing and Materials) «Standard specification for biodiesel fuel blend stock (B100) for middle distillate fuels»
  • EN 14213 «Heating fuels - Fatty acid methyl esters (FAME) - Requirements and test methods»
  • EN 14214 «Automotive fuels - Fatty acid methyl esters (FAME) for diesel engines - Requirements and test methods»
  • EN 14112 «Fat and oil derivatives - Fatty acid methyl esters (FAME) - Determination of oxidation stability (accelerated oxidation test)»
  • EN 590 «Automotive fuels - Diesel - Requirements and test methods»
  • EN 15751 «Automotive fuels - Fatty acid methyl ester (FAME) fuel and blends with diesel fuel - Determination of oxidation stability by accelerated oxidation method»

895 Professional PVC Thermomat

The 895 Professional PVC Thermomat is a contemporary analytical instrument that enables automatic measurement of the thermal stability of chlorine-containing polymers, including polyvinylchloride (PVC), based on the dehydrochlorination technique.

Thermal Stability of Polyvinylchloride and Other Chlorinated Polymers

Polymers based on PVC decompose at higher temperatures, discharging gaseous HCl. Figure 2 shows the principle of the PVC Thermomat technique.

Figure 2. Principle of the PVC thermomat method

During the measurement of PVC’s thermostability according to ISO 182, Part 3 or DIN 53 381, Part 1, a nitrogen stream transfers the discharged HCl inside a measuring cell containing distilled water, where conductivity measurement is used to detect the gas. The stability time is a criterion of the PVC’s thermal stability and is the time that elapses until an adequate amount of HCl is emitted to create a distinct increase in conductivity of 50 pS/cm in the measuring vessel. The technique is utilized for testing PVC in all stages of processing and for assessing the stabilizers.

Application Literature from Metrohm

  • AN-R-016 Thermostability of PVC
  • AB-205 Determination of the thermal stability of PVC and associated copolymers
  • AN-R-008 Thermostability of pure, processed, and blended PVC

Standards

The determination of the thermal stability of PVC is included in various national and international standards, such as:

  • DIN 53 381 Part 1 - Determination of the thermostability of PVC
  • ISO 182 Part 3 - Plastics - Determination of the tendency of products and compounds based on vinyl chloride copolymers and homopolymers to evolve hydrogen chloride and other acidic products at increased temperatures - Part 3: Conductometric method

This information has been sourced, reviewed and adapted from materials provided by Metrohm AG.

For more information on this source, please visit Metrohm AG.

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