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Salt Measurement in Food

How to Perform Salt, Sodium, Chloride, and Mineral Content Determinations

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Salt Measurement in Food
Salt Measurement in Food

Used for millennia as a food flavoring and preservative agent, table salt (sodium chloride, NaCl) is widely consumed around the world. While sodium and chloride ions play essential roles in physiological processes, individual sodium intake for both adults and children generally exceeds dietary requirements in most countries.

Elevated dietary sodium has been shown to be a risk factor for high blood pressure. To help reduce the occurrence of cardiovascular disease, the World Health Organization (WHO) has a stated goal of reducing the per capita consumption of table salt by 30% before 2025 with an ultimate aim of limiting sodium intake to no more than 2000 mg per day.

An important aspect of the initiative is the broad implementation of clear and easy-to-interpret nutrition labels on processed foods. To fulfill these labeling requirements, and because of sodium’s multiple sources in baked, processed and prepared foods, choosing an accurate sodium content determination method has become important for food and beverage producers.

    

Salt Determination Guide

The METTLER TOLEDO Guide to Salt Content Determination

Download "An Introduction to Salt Analysis: Techniques for Salt and Ion Determination" for more details about effective techniques for chloride, sodium and salt content determination.

Salt and Its Effect on Taste, Texture and Formulation

Table salt is used to enhance the flavor of foods, adjust its color and texture, and prolong shelf life. Determining the total salt content of a food item also allows processed food manufacturers to monitor these attributes across batches—whether foods are produced in solid, liquid, paste-like, powdered, or other forms.

While salt itself is the greatest contributor to excess sodium intake, sodium is also found in chemical leavening agents such as baking soda (sodium bicarbonate), and in preservatives such as sodium nitrate, sodium nitrite and sodium benzoate. Chloride ion content may likewise be heightened by the addition of potassium chloride (a low-sodium alternative to table salt).

Accurate sodium or salt testing, whether at goods-in, on the line, or during final quality control helps to ensure food processing workflows produce goods that present to consumers with expected characteristics. It can also help to ensure sodium labeling is accurate, which in turn can help consumers make informed choices about the food products they ingest.

Sodium and Salt Measurement Methods

Sodium and Salt Measurement Methods

Various salt testing and sodium determination methods exist. In this application page and the accompanying guide, we look at several different strategies for salt measurement, sodium content determination, chloride determination, and assessment of bulk minerals in food.

Primary emphasis is given to:

  • Argentometric chloride determination
  • Measurement of sodium ion via ion-selective electrodes

The latter can be performed via either the multiple standard addition technique or directly. Cumulatively, methods that perform salt determination by titration or use ion-selective electrodes are simple to execute, reliable and straightforward, and require only standard laboratory equipment.

Several other methods for salt, sodium or mineral determination are also mentioned: thermometric titration, density measurement, ashing and elemental analysis. METTLER TOLEDO instruments that support various salt, chloride and sodium analysis methods are also discussed.
 

Argentometric Titration of Chloride Ion

  • Method: Argentometric Cl- titration
  • Analyte type: Cl- ion
  • Analyte concentration range: ppm to 100%  

The most established titrimetric method to determine salt content is based on chloride measurement. Known as argentometric titration due to the use of silver nitrate (AgNO3) as the titrant, it remains in common use in food laboratories.

Silver ion (Ag+) precipitates from solution upon reaction with Cl- ion, and when all available chloride has been consumed by reaction with Ag+, the electrical potential in the titration vessel rises due to the accumulation of dissolved Ag+ ions in the sample solution. This indicates the endpoint of the titration, permitting calculation of the salt content (based on the assumption that all chloride in the sample was contributed by NaCl).

While chloride determination is rapid and typically does not require specialized equipment, the method will not account for sodium ions contributed by sources other than NaCl, as noted. This means that, while effective in many cases, it may not be suitable for every type of salt analysis.

An example of instrumentation is the METTLER TOLEDO Titrators.

Sodium Content Determination via Multiple Standard Addition (MSA)

  • Method: Sodium analysis in food using multiple standard addition
  • Analyte type: Na+ ion
  • Analyte concentration range: ppm to 100%

Multiple standard addition detects sodium within the sample matrix down to 0.1 mg/L (4.7•10−6 M). A small quantity of a sodium standard solution is dosed into the sample several times in succession, increasing its sodium concentration. The differences in potential resulting from the known volumes of the standard added are used to determine the sample’s intrinsic sodium concentration via an iterative evaluation algorithm based on the Nernst equation.

Importantly, MSA measurements can be performed near the detection limit and temperature effects can be compensated by the instrument for higher accuracy. An approximate sample concentration must be known prior to assay for optimal sample preparation and quantification.

An example of instrumentation is the METTLER TOLEDO Easy Na Sodium Analyzer or Excellence Titrators (including automation).

Thermometric Titration of Sodium Ion

  • Method: Thermometric Na+ titration
  • Analyte type: Na+ ion
  • Analyte concentration range: 100 ppm to 100%

Thermometric titration of sodium ion content is an alternative method to quantitate sodium in food products. Thermometric titration depends on the formation of elpasolite, NaK2AlF6, which is highly exothermic. The heat evolved can be registered by a highly resolved thermoprobe and used to infer the quantity of Na+ ion present in the original sample.

The reaction proceeds in the presence of ammonium fluoride or ammonium hydrogen difluoride (NH4F, NH4HF2), and requires an excess of potassium and aluminum. The toxicity of the former compounds, which are also highly corrosive, mean that appropriate safety precautions should be taken.

Suitable instrumentation for this analysis is the METTLER TOLEDO Excellence Titrators and Thermometric Electrode.

Direct Sodium Measurement

  • Method: Direct Na+ measurement with ISE
  • Analyte type: Na+ ion
  • Analyte concentration range: ppm to 100%

Sodium levels in food, typically in aqueous solution, can be determined directly using an ISE paired with a titrator or ion meter. Accuracy depends on use of a calibration curve to infer sample concentration under the assumption that the electrode’s response is the same for sample and standard solutions. A sodium standard dilution series is used for this purpose.

As with MSA, the detected potential is proportional to the activity of an ion in solution and hence its concentration. Following measurements, the paired instrument can automatically calculate the ion concentration of the sample and display the results.

Suitable instrumentation for this analysis is the METTLER TOLEDO Ion-meters with Ion-selective electrodes.

Other Methods of Salt Content Determination

Salt, sodium, ion and mineral content can also be measured via other techniques with differing levels of specificity. For applications such as the determination of total NaCl or mineral salts, special equipment is not always necessary.  

Additional methods that can be useful for determining chloride, sodium, or mineral content include:

Choosing the Right Salt Content Determination Method for Your Application

As discussed, salt or sodium content determination can be undertaken through both direct and indirect measurement. Which method you choose will depend on both the expected range of the measured ion as well as factors such as accuracy requirements and food composition.

Principle of measurement

LOQ

RSD

Argentometric titration of chloride ion

35 ppm

1%

Multiple Standard Addition (MSA)

< 1 ppm

1%

Thermometric titration of sodium ion

100 ppm

2%

Direct sodium measurement

< 1 ppm

4%

 

Expected Sodium or Chloride Content

In selecting a strategy to measure sodium or salt, it is crucial to ensure that the chosen method will offer reliable measurements in the expected ion concentration range. A discussion and easy-reference charts of these ranges as they relate to the methods discussed here is contained in Appendix 2 of the free Introduction to Salt Analysis Guide.

Other Considerations for Sodium or Salt Determination in Food

Food producers should use the technique that best supports their processes and throughput while enabling compliance with local regulations. From an application standpoint, various aspects that should be considered to help ascertain which method will be ideal for salt or sodium content analysis include:

  • Accuracy: How accurate does the determination need to be?
  • Expected content: What quantity of sodium ion is expected?
  • Specificity: Is the test being performed for salt, sodium, or total mineral content?

A discussion of food characteristics and how these characteristics impact sample preparation (blending, dissolving, homogenization, etc.) can be found in Appendix 2 of the free Introduction to Salt Analysis Guide.
Specific Laboratory Applications in Food Production
Specific Laboratory Applications in Food Production

Specific Applications in Food Production

METTLER TOLEDO offers a variety of application notes that cover various methods for sodium determination in food, assessing chloride content, and more. These include applications for measuring the salt and sodium content of foods such as:

  • Baking powder
  • Bread
  • Cheese
  • Cookies
  • Dressings/sauces
  • Ketchup
  • Liquid seasoning
  • Meat/milk
  • Noodles/pasta
  • Potato chips
  • Ready meals
  • Snacks
  • Yogurt

For a complete listing of application notes that will be helpful to your salt measurement lab and a handy guide for accessing them, please download the free Introduction to Salt Analysis Guide.

Applications

Publications

FAQ

What is the difference between salt content and sodium content?

Table salt, or NaCl, is usually a primary source of sodium in foods; however, sodium (Na+) ions may be contributed by other food ingredients, making the total sodium content higher. Specific salt or sodium analysis techniques may be better suited to particular food types, depending on the sources of sodium and chloride being measured.

How to measure salt content in food?

Sodium measurement in food can be made using ion-selective electrodes, titration, density determination, and more. For details, download the free Introduction to Salt Analysis Guide.

What is the sodium chloride formula?

Sodium chloride, which is commonly known as salt or table salt, is an ionic compound. Its chemical formula is NaCl, which represents a 1:1 ratio of sodium and chloride ions. When accounting for their respective molar masses (22.99 and 35.45 g/mol), a 100 g sample of NaCl contains 39.34 g Na and 60.66 g Cl. Accurate NaCl or salt measurement in food is critical for taste, shelf-life, and health concerns.

How to calculate salt concentration?

The method you will use to calculate salt or sodium content will depend on which determination technique is most applicable for measuring sodium or chloride ion in your salt measurement lab. See “Choosing the Right Salt Content Determination Method for Your Application” above or download the free Introduction to Salt Analysis Guide.

Is gravimetric analysis of a chloride salt as a lab technique viable?

The chloride content of a soluble salt or an aqueous solution can be determined by precipitation of the chloride ion as silver chloride:

AgNO3 + NaCl → NaNO3 + AgCl↓

While a precipitate forms during reaction and can be collected and measured in a previously weighed filtering crucible, an easier, less time-consuming and more accurate result will likely be obtained using argentometric titration.

What is the reaction equation for argentometric titration of chloride content?

Salt determination by titration is still performed in many labs. Argentometric titration relies on silver nitrate (AgNO3) as the titrant and is based on the sparingly soluble nature of silver chloride (AgCl), which precipitates from solution as follows:

AgNO3 + NaCl → NaNO3 + AgCl↓

A silver ring electrode can be used to sense the electrical potential of the silver ions remaining in solution following the reaction. A rise in potential caused by the consumption of all the chloride indicates the endpoint of the titration, permitting calculation of the salt content (based on the assumption that all chloride in the sample was contributed by NaCl).

What is the reaction equation for thermometric titration of sodium ion?

During thermometric titration of sodium ion, elpasolite (NaK2AlF6) is formed in a highly exothermic reaction. Evolved heat can be used to infer the quantity of Na+ ion present in a sample.

Using a titrant composed of aluminum nitrate nonahydrate and potassium nitrate (Al(NO3)3 • 9H2O and KNO3, respectively), the reaction proceeds in the presence of ammonium fluoride or ammonium hydrogen difluoride (NH4F, NH4HF2) as follows:

Na+ + 2K+ + Al3+ + 6F- → NaK2AlF6↓

As elpasolite formation releases energy, the resulting temperature differential can be correlated to the quantity of sodium present in the initial sample using a thermometric sensor.

What is the detection limit for direct measurement of sodium ion?

The detection limit for direct measurement of sodium is 0.1 mg/L (4.7 • 10−6 M) and the limit of quantification is 0.3 mg/L (1.4 • 10−5 M). The linear measurement range of the sodium-sensitive electrode used lies between 0.3 and 70,000 mg/L (1.4 • 10−5 M and 3 M). If the sodium content of a specific sample is higher than this, the sample must be diluted.