Biofuels (001-050)

Convenient ion chromatographic methods for the determination of alkali metals, alkaline earth metals, antioxidants as well as chloride and sulfate in biofuels are described. While the antioxidants are detected by UV/VIS detection, the metal cations and the anions are determined by non-suppressed and suppressed conductivity detection, respectively. The outstanding performance of ion chromatographic determinations, as illustrated by the recent adoption of ASTM D 7319 in ASTM D 4806, underlines the leading
position that IC increasingly assumes in biofuel analysis.

Dissolution of oil in toluene, and titration with standard 0.1 mol/L trifluoromethanesulfonic acid in acetic acid using isobutyl vinyl ether as a thermometric endpoint indicator.

In titration, the titrant reacts with the analyte either exothermically (gives off heat) or endothermically (absorbs heat). The Thermoprobe measures the temperature change during titration. When all of the analyte has reacted with the titrant, the temperature of the solution will change, and the endpoint of the titration is indicated by an inflection in the temperature curve.
Catalytically enhanced titrations using paraformaldehyde as catalyst are based on the endothermic hydrolysis of the paraformaldehyde in the presence of excess hydroxide ions.
Edible oils are dissolved in a mixture of toluene and 2-propanol (1:1) and titrated with standardized TBAH (0.01 mol/L) in 2-propanol to a catalytically enhanced endpoint.

In principle the 774 Oven Sample Processor can be used with all samples that release their water when heat is applied. However, the KF oven method is essential whenever direct volumetric or coulometric Karl Fischer titration is impossible because the sample contains interfering components or, due to its consistency, is difficult to place in the titration vessel.

The combination of the 774 Oven Sample Processor with coulometric Karl Fischer titration (756 or 831 KF Coulometer) is ideal for samples with a low water content. Foodstuffs, pharmaceutical products, plastics or mineral oil products can be analyzed fully automatically and extremely accurately. On the other hand, a volumetric Karl Fischer titration using a KF Titrino is to be preferred for samples with a very high water content (>50%).

In accordance with the gas extraction principle the water is driven out of the heated sample by a stream of dry carrier gas and transferred to the titration vessel, where the water is determined by KF titration.

For temperature-sensitive samples, e.g. foodstuffs, the water can be released gently at lower temperatures by simultaneous extraction with methanol. In this way it is possible to prevent any water being released by decomposition.

This Application Bulletin uses examples from the food, pharmaceutical, plastics and petrochemical industries to describe automatic Karl Fischer water determination using the 774 Oven Sample Processor and a KF Coulometer. Information concerning the combination of the Oven Sample Processor with a volumetric KF titrator is given in brackets.

In the Bulletin the following analytical methods are described and, as far as possible, documented with examples of curves and instrument reports:

• Water content by the Karl Fischer method
• Oxidation stability by the Rancimat method (AOCS Cd 12b-92)
• Iodine number
• Peroxide number
• Saponification number
• Acid number, acid value and free fatty acids (FFA)
• Hydroxyl number
• Nickel traces, polarographic

In these methods particular care has been taken not to use chlorinated solvents.

The determination of the acid or base number plays a significant part in the analysis of petroleum products. This is shown by the numerous standard procedures in use the world over (internal specifications of multinational companies, national and international specifications of ASTM, DIN, IP, ISO, etc.). These procedures differ mainly in the composition of the solvents and titrants used. Fortunately, the days of the work-intensive use of pH meters, glass burets and color indicators seem to be over. Modern titrators are gradually replacing time-consuming manual titrations as well as the calculation of the results.

This Bulletin describes the determination of the acid and base number in petroleum products by means of automatic potentiometric titration.

Modern laboratories involved in routine process and quality control of fats and oils demand high analytical productivity with minimum operator involvement. Automated thermometric titrimetry is well suited to the task. No electrical contact with titrating solutions is required, so samples can be titrated in a totally nonaqueous environment. The endpoint is determined automatically, not prone to operator bias and can be detected in highly colored or turbid solutions, or even in media containing suspended solids. The thermometric sensing probe requires no maintenance, special preparation, regeneration or calibration and can be stored dry between titrations.

Two determinations common in the analysis of fats and oils illustrate the versatility of the technique, namely the free fatty acid (FFA) content and the iodine value (IV). In both analyses, excellent agreement has been demonstrated with results obtained by official methods of analysis. The titrations are very fast, typically less than a minute in duration, and can be conducted using an automatic sample changer.