Writing effective methods for AOCS submission
The Official Methods and Recommended Practices of the AOCS is known throughout the world as the most comprehensive collection of analytical testing methods for fats and oils. The reference contains more than 450 scientific methods that are used to support product quality, industry standards, and fair trade. The process of submitting a method or recommended practice to AOCS is a well-established procedure outlined in detailed, step-by-step instructions. These additional tips from Mark Collison, Editor-in-Chief of AOCS Methods, were excerpted from a presentation he gave at the 2017 AOCS Annual Meeting and Industry Showcases in Orlando, Florida.
Methods are not research papers; they must include an unambiguous set of instructions for achieving the desired analysis, not just guidelines. While additional information supporting the method is welcome, it should not detract from the instructions. Usually, such supporting comments are included as NOTES and are not a part of the method text. Similarly, the essential elements of a method should be included in the method text, not in the NOTES.
Safety statements and recommendations should be clear and articulated in the method before any hazardous chemicals or procedures are referenced. Any limits should be based on reliable sources. For example, The 2016 Guide to Occupational Exposure Values, Compiled by ACGIH® was used to determine current PELs for the 7th Edition of AOCS Methods.
Correct Scientific Terminology
The ACS Style Guide is the master document for scientific usage. The most common mistakes requiring correction involve unit measurements and terms.
- Numbers and unit symbols should have a space between them (e.g., 100 mg, 50 mm, 6 min.) except for percent and degrees-minutes-seconds of arc, which should immediately follow their numbers without a space.
- Abbreviations such as ppm and ppb should be avoided, as they are too easily misinterpreted. The terms ppm and ppb should be replaced by mg/kg and µg/kg.
- The terms % w/w, % v/v are acceptable. % w/v is not. Using % alone, without specifying w/w or v/v is not acceptable.
Cross Referencing Between Methods
Several older methods refer to previously published methods for critical parts of procedures. At the time most of these methods were written, it was assumed that the entire methods book would be present whenever any method was used. The availability of individual methods has made this practice obsolete, and considerable effort has been made to remove cross references. It is fine to state that a procedure is the same as one used in another method, but the entire procedure should be included in the current method.
Title, Definition and Scope
In the case of individual methods, the Title, Definition, and Scope statements are available to customers prior to purchase. Consequently, these statements must provide the specific information customers need to select the correct method before purchasing it. This is not the place to write an abstract of the entire method or to overwhelm customers with too many procedural details.
The method TITLE should be very specific, describing the analysis that is being done and, if applicable, the matrices.
A good recent example is AOCS Official Method Ce 12-16 - Sterols and Stanols in Foods and Dietary Supplements Containing Added Phytosterols.
The original titles of older methods were often imprecise. For example, the 6th Edition included 19 methods for oil in specific matrices, most of them with same title: “Oil.” In the 7th Edition, many titles were revised to communicate more specifically how each method is used. Most of those nonspecific “Oil” titles now read “Oil in Sunflower Seeds,” and so on.
The DEFINITION should describe the analytical technique that is used and the analytes that are determined.
This needs to be a short, concise statement! One or two sentences is all. The DEFINITION should only state what technique is used; it should not explain the theory behind that technique. Include whatever explanations are needed in the METHOD. An example of a bad DEFINITION is AOCS Official Method Cd 11d-96 Mono- and Diglycerides—Determination by HPLC-ELSD, from the 6th Edition.
DEFINITION: “This standard describes a method for the quantitative determination of monoacylglycerides and diacylglycerides. Neutral lipid classes are separated with normal-phase high-performance liquid chromatography (HPLC), and the monoglycerides and diglycerides present are determined with an evaporative light scattering detector (ELSD). Test samples are dissolved in a solvent mixture consisting of n-hexane/2-propanol (90:10, v/v) and analyzed without derivatization. Because the response of the ELSD is not linear, a log(response)/ log(mass) calibration curve must be established for expected analytes based on ELSD response to calibration standards identical to the test sample components. The method quantitation and detection limits (S/N = 2) are approximately 0.25 mg and 0.06 mg, respectively.”
The 7th Edition includes a revised and more appropriate version.
DEFINITION: This standard describes a method for the quantitative determination of monoacylglycerides and diacylglycerides. Neutral lipid classes are separated with normal-phase high-performance liquid chromatography (HPLC), and the monoglycerides and diglycerides present are determined with an evaporative light scattering detector (ELSD).
The SCOPE statement describes the matrices where the method is used and, if applicable, where it cannot be used. This should be a short, concise statement. One or two sentences is usually the appropriate length. This does not necessarily mean the SCOPE will be short, as can be seen in this long but appropriate example:
AOCS Official Method Ch 1-91 Preparation of Methyl Esters of Long-Chain Fatty Acids “SCOPE: The method is applicable to common fats, oils, and fatty acids. Unsaponifiables are not removed but, if present in large amounts, they may interfere with subsequent analyses. The procedure will result in partial or complete destruction of the following groups: epoxy, hydroperoxy, cyclopropenyl, cyclopropyl, conjugated polyunsatured, acetylenic, and possibly hydroxyl, and is not suitable for the preparation of methyl esters of fatty acids containing these groups.
In revising the 7th Edition, significant issues arose with older methods in which the vendors of the analytical equipment described no longer exist. Where possible, the vendors were updated to reflect current sourcing.
As a rule of thumb, methods restricted to specific vendors should be minimized and equipment should be generically described, followed by possible vendor sources only if needed.
Chemicals should also be generically described, followed by possible vendor sources only where needed. Reagent purity / quality expectations should be included in these descriptions.
Solution instructions are also part of Reagents. Explicit instructions for making solutions should be provided.
Analytical procedures should be clear and unambiguous. They should provide a SET OF INSTRUCTIONS on how to perform the method, not a just a description. If additional explanation, beyond the instructions, is useful, that should be added as a NOTE. On the other hand, critical instructions should be included in the PROCEDURES and not relegated to NOTES.
Calculations and Reporting Results
The exact manner in which analyte concentration is to be calculated needs to be specifically and clearly stated in this section. “The software will do the calculations” is an unacceptable statement in most cases. Any instructions for reporting results also need to be clearly stated in this section.
Notes and supporting materials
Authors are free to add any comments they think will be useful in the NOTES, including a lengthy description of theory if that is appropriate. However, all notes should be relevant to the method. This is not a research paper; excessive details will detract from a method, but it is important to add the details that are useful! CHROMATOGRAMS, SPECTRA, DIAGRAMS OF SPECIALIZED EQUIPMENT and other technical illustrations should be included wherever possible.
Any validation data that is included should be in a section at the end of the method. If a collaborative trial has been done, this is the place to include the collaborative data. This validation section should include a complete description of the types of samples analyzed and the results that were achieved.