Automated Analysis of Edible and Marine Oils using MIDI Sherlock

Martin Perkins

31st March 2016

Edible Oil, Fatty Acids, Marine Oil, MIDI, Omega 3, Ray Perkins, Sherlock,

The Field

Edible oils are vegetable-based oils extracted from olives, corn, peanuts and other sources that are used in a variety of food products. Marine oils are extracted from fish and krill that are typically taken as supplements due to the high omega-3 content.

Both edible and marine oils consist principally of fatty acids (typically >90% of their weight). Knowing the specific fatty acids in a product can be used both to determine its authenticity and also its health benefits. Fatty acid analysis of these ingredients is performed by manufacturers, distributors, and commercial customers, to ensure quality and consistency, and to meet labelling requirements.

The Challenge

While extraction of fatty acids from these ingredients is well understood, chemical analysis procedures are not standardized and typically require an expert analytical chemist to spend a significant amount of time manually evaluating each compound in each sample.

Simply determining the compounds in a sample is not typically the end of the sample analysis process. Depending upon the sample, a variety of complex determinations need to be made based on the compounds found: absolute amounts for specific compounds; similarity of the sample to known, high-quality exemplars; calculations – such as computing the iodine value – that give information about the quality and behavior of the sample.

Depending on the situation, an analytical chemist can spend 30-60 minutes analyzing each sample even after it has been prepared and run on a Gas Chromatograph, the standard equipment for these measurements.

This manual approach is time consuming, and it can also be subjective and error-prone. What is needed is an analysis tool that can automate these calculations.

Enter MIDI, Inc.’s Sherlock™ software.

Sherlock can automatically determine the names and amounts of compounds in complex mixtures of edible or marine oils. And Sherlock has a suite of calculation tools to further evaluate samples.

Compound Naming

A fatty acid chromatogram from an edible or marine oil contains a series of peaks, each specific to a particular fatty acid. Each peak elutes at a different retention time and is measured in intensity by the area of the peak. Sherlock uses the retention time information in a unique manner: based on a multiple-compound calibration standard run with each batch of samples, Sherlock determines the Equivalent Carbon Length (ECL) for each peak. For saturated fatty acids ECL is the number of carbons. For instance, palmitic acid, C16 has ECL 16.0000. Compounds that fall in between the saturated fatty acids are given interpolated values. Oleic acid which has eighteen carbons and a double bond in the ninth position, has ECL 18.3628. Because Sherlock uses information from the calibration standard run with each batch, ECL computation is a precise measure for each compound that accommodates instrument variation. In this manner, a broad variety of fatty acids can be automatically identified.

Quantitative Calculations

Having named the fatty acids, the Sherlock system can immediately report the relative percent of each acid based on the relative area response from the GC. If an internal standard is included, Sherlock scales these results to absolute values, in nanograms per gram or per serving as needed.

Sample Identification

Sherlock comes equipped with a library of common oils (olive, corn, peanut, etc.) that can be compared directly to a sample. The result gives a similarity match between 0.000 and 1.000 where greater than 0.500 is considered a definitive match. If a sample is significantly adulterated the match against the library will decrease, indicating the problem.


FAMEs profile of a Fish Oil Supplement, processed by Sherlock Software

Advanced Calculations

Because a sample can have many compounds – a fish oil sample can have more than 50 fatty acids – it is useful to display not just the results for individual compounds but to summarize the results in useful ways. Sherlock can, for example, determine the total amounts of omega-3 and omega-6 fatty acids.  And it can compute ratios, such as saturated to unsaturated fatty acids.

Complex calculations such as iodine value or saponification value can be automated as well. Further, all of these calculations are under user control, selecting exactly which compounds and which computations are needed.


Sherlock automates compound naming for edible and marine oils, saving time, eliminating tedium and reducing errors. Sherlock can calculate absolute amounts of fatty acids, compare the sample to a library of known oils, categorize fatty acids by type, and compute advanced information such as iodine value and saponification value.

Automation using Sherlock assures a complete and objective analysis of edible oils and marine oils.

Anatune will shortly be putting MIDI’s Sherlock™ to work in our applications laboratory. If you want to see it in action, you are welcome to visit us and learn more. Call us on +44 (0)1223 279210 or email: