ISO/TR 5756:2026

ISO/TR 5756:2026 is the first edition of an ISO Technical Report on a volumetric practice for estimating hydrocarbon and ethanol content in fuel ethanol and gasoline blends. It describes a sodium chloride (NaCl) solution phase-separation approach that gives approximate results, mainly for laboratory and gas-station use. The report is informational: it explains how the practice is observed and how the reading is interpreted, rather than setting a formal test method.

What does ISO/TR 5756:2026 specify?

ISO/TR 5756:2026 presents a reported volumetric practice for estimating ethanol and hydrocarbon content in fuel ethanol and gasoline blends. The method relies on phase separation caused by a NaCl solution so the user can observe an upper organic phase and a lower aqueous phase.

ISO/TR 5756:2026 is organized into seven clauses: Scope, Normative references, Terms and definitions, Principle observed in practice, Description of reported practice, Interpretation of results as reported in practice, and Observations and limitations. That structure helps the reader move from the basic idea to the practical steps, then to the way the reading is interpreted and the method's limits.

What are the key requirements of ISO/TR 5756:2026?

ISO/TR 5756:2026 does not set mandatory performance requirements. It describes the practice reported in use and the way results are typically read, so the practical value lies in consistent handling, reading, and interpretation.

Principle observed in practice

Clause 4 explains that a measured amount of blend is mixed with a NaCl solution to create two layers. The aqueous phase contains most of the ethanol, while the organic phase contains the hydrocarbons. In practice, this means the user is looking for a quick separation that gives a rough picture of the fuel composition.

Clause 4 also notes that a NaCl solution of about 100 g/l is commonly used. The report says this solution may be prepared from analytical-grade NaCl and water or obtained as a commercial solution. For the reader, the important point is that the practice depends on a saline solution of known and comparable strength.

Reported procedure

Clause 5 describes a commonly reported sequence for obtaining indicative results. About 50 ml of fuel blend is placed in a clean, dry measuring cylinder, NaCl solution is added to bring the total volume to 100 ml, and the cylinder is stoppered and gently inverted several times.

The report warns against excessive agitation because it can form an emulsion. That matters in practice because poor mixing control can blur the phase boundary and make the reading less clear.

Clause 5 also reports that the cylinder is left on a stable surface until separation appears, typically within a few minutes, and the organic phase is then read visually to the nearest 0.5 ml. This makes the practice fast, but it also means the user must read the meniscus and phase boundary carefully.

Interpreting the reading

Clause 6 links the observed organic-phase volume to an estimated hydrocarbon fraction. The hydrocarbon estimate is then used to infer the ethanol content as the complement to 100%. In practical terms, the user does not measure ethanol directly; the ethanol value is derived from the hydrocarbon estimate.

Clause 6 presents the relation as approximate and indicative only. That means the result is best treated as a screening or comparison value, not as a high-accuracy composition result.

Limits on use

Clause 7 states that the method is simple and rapid, but limited in accuracy. It also notes that other oxygenated components can affect the separation and the reading. For the reader, this means the practice is sensitive to blend composition and should be used with caution when methanol, ethers, or similar compounds may be present.

What terms does ISO/TR 5756:2026 define?

ISO/TR 5756:2026 defines a small set of terms used to describe the phases and fuel type.

• Hydrocarbons - compounds that are the main components of petroleum and natural gas derivatives.
• Fuel ethanol - fuel intended for internal combustion engines, with ethanol as the main component, either anhydrous or hydrated.
• Aqueous phase - the lower phase made up of NaCl solution and water-soluble components of the fuel blend.
• Organic phase - the upper phase made up of the hydrocarbon components of the fuel.

Who uses ISO/TR 5756:2026?

ISO/TR 5756:2026 is used in laboratories and at gas stations where a quick, indicative check of fuel ethanol and gasoline blends is needed. The introduction and Clause 4 place the practice in both laboratory and field assessment contexts.

It is relevant to people who handle fuel blending checks, rapid screening, or simple comparative assessments of blend composition. In practice, that includes analysts and technicians who need a fast visual estimate rather than a full compositional analysis.

What does the ISO/TR 5756:2026 document contain?

ISO/TR 5756:2026 contains two illustrative figures and one comparison table that support the reported practice. Figure 1 shows the measuring cylinder used in the practice, and Figure 2 shows how the aqueous and organic phases are read.

Table 1 gives the approximate relationship between the observed organic-phase volume and the hydrocarbon estimate. The report uses that relationship to explain how users translate a visual reading into an indicative composition estimate.

The document also describes the sample preparation, mixing, settling, reading, and interpretation steps, along with the method's practical limits. That makes it useful as a compact description of how the practice is carried out and where it is most and least reliable.