What Is Karl Fischer Titration? Measuring Residual Water in Lyophilized Peptides

Published November 2026 · Patriot Labs Research Team · ~18 min read

The short answer

Karl Fischer titration is a chemical method for measuring water. It rests on a reaction in which iodine and sulfur dioxide consume water in a fixed one-to-one ratio of iodine to water, so the amount of iodine used — or the electric charge used to make it — is a direct measure of how much water was in the sample. It is the standard, water-specific way to determine residual moisture in dried pharmaceuticals and research chemicals, including lyophilized peptides.

The method was published by the German chemist Karl Fischer in 1935, and it has endured because it does something no simpler method does cleanly: it reacts with water and almost nothing else.^[1][5] A technique such as drying a sample and weighing it measures the loss of any volatile, not water specifically, and needs a lot of material. The Karl Fischer reaction, by contrast, is selective enough to report water alone and sensitive enough to see it down to a few parts per million, which is exactly what is needed when the quantity in question is the last percent or fraction of a percent of moisture clinging to a freeze-dried solid.

The test comes in two main forms. Volumetric Karl Fischer dispenses an iodine solution of known strength from a burette and reads the water from the volume it takes to consume it; it suits samples with a fair amount of water. Coulometric Karl Fischer generates the iodine electrically inside a sealed cell and reads the water from the charge used, by Faraday's law; it is accurate at very low moisture and is the method usually used for lyophilized products.^[3][5][6] The rest of this guide works through the chemistry behind both, the practical business of measuring a peptide, the standards that define the test, and why the number it produces is one of the quieter but more important lines on a quality report.

What Karl Fischer titration measures

Karl Fischer titration measures water content, expressed as a mass of water or, more usually, as a percentage of the sample's weight. Its defining virtue is specificity: it is a reaction with water, not a general measure of “things that leave when you heat the sample.” That distinction is the whole reason it exists.

Water in a solid sits in several states. Some is free surface moisture, some is adsorbed onto the surface of particles, and some is more tightly held — trapped inside an amorphous matrix or associated with specific sites on a molecule.^[6] A good moisture method has to reach as much of that water as it reasonably can while ignoring everything that is not water. Karl Fischer does this because the water becomes a reactant in a defined chemical reaction rather than simply a mass that disappears. That is also why the technique is described as selective where a gravimetric method is not: a sample can lose residual solvent, a volatile counterion fragment, or decomposition products on heating, and a weight-loss method would count all of it as “moisture,” whereas Karl Fischer titrates only the water.^[6]

For a lyophilized peptide this specificity matters twice over. The powder that comes out of a freeze-dryer is not pure peptide: it carries water, counterions such as trifluoroacetate or acetate, and any excipients used in the formulation, all of which are weighed together with the peptide. Water is one of those non-peptide components, and separating its contribution from the rest is part of knowing what a vial actually contains — a theme developed in What Is Net Peptide Content and TFA vs Acetate in Peptides.

The chemistry of the Karl Fischer reaction

The reaction works because iodine will oxidise sulfur dioxide, but only when water is present to take part — so water is the limiting ingredient that controls how much iodine is consumed. Getting from that idea to an accurate measurement took a refinement of the original chemistry, and the detail is worth seeing because it explains why the reagents are what they are.

The underlying chemistry descends from the Bunsen reaction between iodine, sulfur dioxide and water. In its simplest written form the overall reaction is:

and the key point for measurement is that it consumes exactly one molar equivalent of water for each molar equivalent of iodine — a one-to-one iodine-to-water ratio.^[5] On its own, though, this reaction is neither complete nor stable: the sulfur trioxide and the hydrogen iodide it produces would drive it backwards and stall it. Fischer's insight, and the modifications that followed, was to run it in an alcohol with a base present. The alcohol, usually methanol, and the base combine with the sulfur dioxide and mop up the acid, so the reaction goes to completion and stays there.^[5]

The mechanism that modern practice relies on was established by work including Verhoef and Barendrecht in the 1970s, who studied the reaction and its rate directly.^[2] In this picture the sulfur dioxide first combines with the alcohol and base to form an alkyl sulfite salt; that salt is then oxidised by iodine, in the presence of water, to an alkyl sulfate salt, and it is this oxidation step that consumes the water in the one-to-one ratio. Written with a generic base B and alcohol ROH, the two stages are:

The base therefore has two jobs: it helps form the reactive sulfite ester, and it neutralises the acid so the reaction does not reverse. The original reagents used pyridine for this, which gave the classic Karl Fischer reagent its sharp odour; modern reagents replace pyridine with imidazole or other amines, which buffer the reaction more effectively and are more pleasant to work with.^[3][5] USP notes that water reacts with this sulfur-dioxide-and-iodine system in the presence of a buffer that reacts with hydrogen ions, and that because the stoichiometry in practice is not perfectly exact, the reagent is standardised empirically against a known amount of water rather than assumed from theory.^[3]

That standardisation is done with a primary standard of accurately known water content. A common choice is sodium tartrate dihydrate, whose two waters of crystallisation make up a fixed fraction of its molecular weight — the ratio of twice the mass of water to the compound's molar mass, 36.04 divided by 230.08, or about 15.66 percent by weight — so titrating a weighed amount of it tells the analyst exactly how much water a millilitre of reagent corresponds to.^[3] Pure water itself can also be used as the standard.^[3]

Volumetric and coulometric titration

Karl Fischer titration exists in two forms that share the same chemistry but deliver the iodine in opposite ways, and the choice between them is governed almost entirely by how much water is expected. The more water, the more suited volumetric titration is; the less water, the more coulometric titration earns its place.

In volumetric Karl Fischer titration the iodine is already dissolved in the titrant at a known concentration, and that solution is added from a burette until the water is used up. The volume delivered, multiplied by the reagent's water-equivalence factor, gives the mass of water.^[3][5] Volumetric reagents come as one-component systems, where alcohol, base, sulfur dioxide and iodine are all in a single titrant used with a plain alcohol solvent, or two-component systems, where the solvent carries the sulfur dioxide and base and the titrant carries the iodine. Volumetric titration will measure samples all the way up to pure water, but it becomes impractical at very low moisture because an enormous sample would be needed to consume a measurable volume of titrant — below roughly a twentieth of a percent water it is the wrong tool.^[5] In USP terms the direct form is Method Ia and a back-titration variant, used when water is released only slowly from a sample, is Method Ib.^[3]

In coulometric Karl Fischer titration there is no iodine solution to dispense. The cell contains an iodide-bearing reagent, and iodine is generated in place at an electrode as it is needed, by the anodic oxidation of iodide:

Because generating iodine this way is governed by Faraday's law, the electric charge passed is an absolute measure of the iodine produced, and therefore of the water consumed — so a coulometer needs no titre calibration at all; the charge is measured directly.^[3][5] This makes coulometry exquisitely suited to small amounts of water: its working range runs from a few parts per million up to a few percent.^[5] The generator electrode may sit in a compartment separated from the rest of the cell by a diaphragm, or in a modern diaphragm-free design; diaphragm cells are generally preferred for the very lowest moisture levels.^[3][6] For lyophilized drug products, where the water content is a small percentage or less, coulometric Karl Fischer is the method usually chosen, and it is defined in USP as Method Ic.^[3][6]

How the endpoint is detected

Whichever form is used, the titration needs to know the moment the water runs out, and it finds that moment electrically rather than by eye. The principle is the same one that makes the method so sharp: the reaction holds iodine at essentially zero as long as any water remains, and the first trace of excess iodine signals the end.

The usual indication is bipotentiometric, using a small double-platinum electrode in the solution. A constant current is driven between the two tips, and the voltage needed to sustain it is watched. While water is still present, the solution contains iodide but almost no free iodine, and sustaining the current takes a relatively high voltage; the instant all the water has reacted, a slight excess of iodine appears, the iodide-iodine pair lets current flow easily, and the voltage drops abruptly. That sudden change marks the endpoint.^[5] In the volumetric procedure described by USP, the same idea is run the other way round — a small voltage of about 200 millivolts is applied across platinum electrodes and the endpoint is taken when a slight excess of reagent drives the current up to a defined level and holds it there for a set time.^[3] For the simplest manual work a visual endpoint is possible, where the solution turns from pale yellow to amber as free iodine appears, but the electrometric endpoint is more precise and is what instruments use.^[3] Deeply coloured samples, which defeat a visual endpoint, can be handled with photometric detection instead.^[16]

The oven method for difficult samples

Some samples cannot simply be dropped into the titration cell: they will not dissolve, they react with the reagent, or they would release their water too slowly to give a clean endpoint. For these the water is driven out of the sample first and carried into the cell as vapour, a technique known as the oven or gas-extraction method.

In this arrangement the weighed sample sits in a sealed vial or oven and is heated while a stream of dry inert gas, typically nitrogen, flows over it and carries the released water into a coulometric cell, where it is titrated as usual.^[3][6] Because only the water vapour reaches the reagent, the sample's matrix never touches the iodine, which neatly avoids side reactions with the solid itself. The one firm requirement is that heating must liberate the sample's own water without decomposing the sample into new water — a substance that breaks down on heating to produce water would give a falsely high reading.^[3] The method is valuable for materials that interfere with direct titration; published work on moisture in lyophilized products, for instance, has used oven conditions on the order of 110 °C with a dry-nitrogen flow to extract water cleanly from formulations that were troublesome to titrate directly.^[6]

Why residual moisture matters in a lyophilized peptide

The reason a laboratory goes to the trouble of measuring the last fraction of a percent of water is that, in a freeze-dried solid, water is not inert ballast. It is a chemically and physically active component whose amount helps govern how stable the material is, which is why residual moisture is treated as a critical quality attribute of a lyophilized product.^[6][7]

The central mechanism is plasticisation. A lyophilized cake is largely an amorphous glass, and water dissolved in that glass acts as a plasticiser: it increases molecular mobility and lowers the glass transition temperature, the point at which the brittle glass softens into a more mobile rubbery state.^[6][7] A formulation stored comfortably below its glass transition temperature is kinetically frozen and degrades slowly; let the moisture rise and the glass transition temperature falls toward the storage temperature, mobility increases, and the chemical and physical reactions that spoil a peptide speed up. Those reactions are the familiar ones — aggregation, deamidation and oxidation among them — and higher moisture is broadly associated with poorer stability and shorter shelf life, as well as with physical collapse of the cake in the worst cases.^{[6][7][9][10]} This is the same chemistry of decay described in How Peptides Degrade, seen from the angle of the water that accelerates it.

The relationship is not simply “less water is always better.” A monolayer of water on a protein's surface can be protective, and over-drying some proteins below that point has been reported to promote aggregation or loss of activity, so both extremes can be harmful and each material has its own window.^[7] For lyophilized biological materials the literature commonly cites a residual-moisture region of roughly 0.5 to 3 percent by weight, with many protein products aimed toward the lower part of that band, though the figure that matters is always the specification set for the individual product rather than a universal target.^[7] Because moisture sets the glass transition temperature, it also interacts with how a material must be stored and shipped, the subject of Cold-Chain Peptide Storage.

How a water number is produced for a peptide

Turning a vial of freeze-dried powder into a moisture figure is a careful business, because the quantity being measured is small and the biggest source of error is the water in the room. The whole procedure is organised around keeping atmospheric moisture out of the measurement.

For a lyophilized peptide the usual route is coulometric Karl Fischer titration, following USP Method Ic.^[3][6] A soluble powder can be dissolved in anhydrous methanol and injected into the cell, or extracted with anhydrous methanol so that the water passes into the solvent and the solvent is titrated, with a blank run on the pure solvent and subtracted; difficult formulations may instead go through the oven method described above.^[3][6] Analyses are typically run in duplicate or triplicate, and the sample and vials are handled in a low-humidity glove box, because opening a vial exposes the cake to ambient moisture and a freeze-dried cake is often hygroscopic.^[6] A practical detail is that the vial is often under a partial vacuum, so the vacuum is released with a dry needle before weighing.^[6]

Sample size is its own constraint. Coulometric titration is reliable only when there is enough solid in the cell: work at the National Institute for Biological Standards and Control found the method dependable above roughly 10 milligrams of non-volatile dry weight, with apparent moisture rising spuriously below that, and recommended pooling the contents of several vials into one titration for low-fill products that do not contain enough solid individually.^[7][12] That pooling also helps with a separate reality of freeze-drying: moisture can vary from vial to vial across a batch, so several vials are usually tested and the mean and spread recorded rather than a single result trusted.^[7] The output of all this is a single, unglamorous number — a percentage of water by weight — that stands behind the stability of the material. The drying process that determines it is described in What Is Lyophilization.

The standards: USP <921> and its neighbours

Water determination is a long-standardised measurement, and knowing which document defines what helps when reading a method statement on a report. In the United States the governing text is USP General Chapter <921>, Water Determination, which sets out the recognised approaches and when each applies.^[3]

The chapter's Method I is the Karl Fischer titration itself, divided into the direct volumetric titration (Method Ia), a residual back-titration for samples that give up their water slowly (Method Ib), and the coulometric titration (Method Ic).^[3] Method Ia is the default unless a monograph says otherwise, and the coulometric method is treated as the micro-method for low water levels.^[3] Alongside the Karl Fischer methods, the chapter also defines Method II, an azeotropic distillation that boils the sample with toluene and reads the water that separates in a graduated trap, and Method III, a gravimetric loss-on-heating determination.^[3] These older methods survive for specific sample types but are far less sensitive and far less water-specific than Karl Fischer, which is why Method I dominates for dried pharmaceuticals.

Beyond the compendium, standards bodies publish their own procedures — for example ASTM E203 for volumetric Karl Fischer titration — and other pharmacopoeias describe equivalent Karl Fischer methods, so a specification that cites “Karl Fischer per USP <921>” is naming a defined procedure rather than a general idea of a moisture test.^[3][4] The practical message is the same as for any analytical line on a report: the method and the chapter are part of the result, because a water figure is only interpretable against the technique that produced it.

Alternatives to Karl Fischer

Karl Fischer is the reference, but it is not the only way to look at moisture, and the alternatives are worth knowing because they answer the question differently — some trading specificity for the ability to measure without opening the vial. Each is generally validated by comparison against Karl Fischer rather than the other way round.^[6][7]

Loss on drying is the oldest and simplest approach: weigh the sample, heat it, and weigh it again, taking the lost mass as moisture. It is straightforward and compendial, but it is not specific for water — any volatile counts — and it needs a comparatively large sample and careful, fast handling to avoid picking up atmospheric moisture, which limits its accuracy for low-moisture solids.^[6] Thermogravimetric analysis is a more controlled relative that tracks weight loss against temperature on a small sample, and it can serve as a useful cross-check when a Karl Fischer result is in doubt, though it too measures all volatiles and can over-read if a biological material decomposes on heating.^[6][7]

Two non-destructive options read moisture without breaching the vial. Near-infrared spectroscopy measures water absorption bands through the container and can screen whole batches in seconds, but it is an indirect method: each container format and fill needs its own calibration built against coulometric Karl Fischer, and it depends on an intact cake.^[6][7] Headspace moisture analysis, including laser-based frequency-modulation spectroscopy, measures water vapour in the space above the cake and is attractive for checking moisture across an entire batch non-destructively, though it still needs validating for each formulation.^[6][7] The recurring theme is that these faster or gentler methods are calibrated and judged against Karl Fischer, which remains the definitive chemical measurement of water.

Water content on a certificate of analysis

Where a water figure appears on a certificate of analysis, it sits apart from the purity and identity lines and answers a different question from either of them. Purity by HPLC and identity by mass spectrometry describe the molecule — how much of the material is the target and whether it is the right compound; a water figure describes how much of the weighed powder is simply water.

A water result is typically written as a percentage by weight with the method named, for example “water content by Karl Fischer, USP <921>.” Reading it correctly means remembering what it does and does not cover. It does not speak to chemical purity, to counterion content, or to biological contaminants such as endotoxin, which are the subjects of Understanding Peptide COA Testing and Endotoxin Testing Explained. What it does contribute is a piece of the mass balance: a lyophilized powder's weight is the sum of peptide, water, counterions and any excipients, so a water figure, like a counterion figure, is part of separating the peptide from everything weighed alongside it — the accounting behind What Is Net Peptide Content.

For reference, Patriot Labs is a first-responder-owned, US-based company whose every batch is tested by an independent US laboratory by HPLC and mass spectrometry, with the certificate of analysis published on the product page. Where a residual-water figure is reported, it is a separate measurement from those two, produced by the Karl Fischer methods described here and specific to the lot tested.

What this guide does not establish

This guide is an educational account of an analytical method and why its result matters for a dried solid. A few limits are worth stating plainly.

• It describes a test, not any specific product. Whether a given lot has had its water content measured, and what value it returned, is a property of that lot and its certificate of analysis, not something that can be inferred from a compound's name or from this page.
• The moisture ranges cited are general. The 0.5–3 percent region quoted for lyophilized biological materials is a figure from the literature; the acceptable level for any real material is whatever specification was set for it, and this guide sets none.^[7]
• Nothing here concerns use in a person or animal. Residual moisture is discussed only as it bears on the physical and chemical stability of a research material; it is not a statement about how any product may be used, and this guide does not describe any such use.
• Nothing here describes where any peptide is made. The chemistry of the Karl Fischer reaction and the mechanics of the measurement are general; they are not a claim about the origin, process or moisture status of any specific material.

Frequently asked questions

What is Karl Fischer titration?

Karl Fischer titration is a chemical method for measuring the amount of water in a sample. It is based on a reaction, first described by Karl Fischer in 1935, in which iodine and sulfur dioxide consume water in a defined one-to-one ratio of iodine to water, so the quantity of iodine used, or the electric charge used to generate it, is a direct measure of how much water was present. It is the standard, water-specific technique used to determine residual moisture in dried pharmaceuticals and research chemicals.

How is water content in peptides measured?

The residual water in a lyophilized (freeze-dried) peptide powder is usually measured by coulometric Karl Fischer titration, the technique described in USP General Chapter <921> as Method Ic. A weighed amount of the powder, or an anhydrous-methanol extract of it, is introduced into a sealed titration cell where iodine generated electrochemically reacts with the water; the charge consumed gives the mass of water, which is reported as a percentage by weight. Coulometric Karl Fischer is preferred for freeze-dried material because it is accurate at the low moisture levels these products contain.

What is the difference between volumetric and coulometric Karl Fischer titration?

In volumetric Karl Fischer titration a solution of known iodine concentration is dispensed from a burette until all the water has reacted, and the volume delivered gives the water content; it suits samples with more water, roughly from a tenth of a percent up to pure water. In coulometric Karl Fischer titration the iodine is generated electrochemically inside the cell and the electric charge, through Faraday's law, measures the water directly; it suits very low water contents, from a few parts per million up to a few percent, which is why it is the method of choice for dried pharmaceuticals and lyophilized peptides.

Why does residual moisture matter in lyophilized peptides?

Residual moisture is a critical quality attribute of a freeze-dried solid because water acts as a plasticizer: it increases molecular mobility and lowers the glass transition temperature of the amorphous cake, which can accelerate physical and chemical degradation such as aggregation, deamidation and oxidation. Too much water tends to shorten shelf life and can collapse the cake, while over-drying can also harm some proteins, so a moisture figure is one of the numbers used to judge the stability of a lyophilized material.

How much residual moisture is acceptable in a freeze-dried peptide?

There is no single universal figure; the acceptable level depends on the molecule and the formulation and is set per product. For lyophilized biological materials a residual moisture content in the region of 0.5 to 3 percent by weight is commonly cited in the literature, and many protein products are targeted toward the lower end of that range. The point of measuring it is to show that a given lot falls within whatever specification was established for that material, not to compare it against a fixed number.

Can loss on drying replace Karl Fischer titration?

Not for most low-moisture solids. Loss on drying measures the total weight a sample loses on heating, so it captures any volatile, not water specifically, and it needs a larger sample and careful handling to be reliable. Karl Fischer titration reacts chemically with water alone, so it is specific for water and works on small samples at low moisture levels. Loss on drying remains a recognised compendial method and a useful cross-check, but Karl Fischer is the reference technique for residual moisture in dried pharmaceuticals and research peptides.

Does a Karl Fischer result appear on a peptide certificate of analysis?

It can. Where water content is reported, it is usually given as a percentage by weight with the method named, for example Karl Fischer per USP <921>. It is a separate measurement from HPLC purity and mass-spectrometry identity: purity and identity describe the molecule, while a water figure describes how much of the weighed powder is water rather than peptide. Residual water, like counterions and salts, is part of the mass that is not the target compound, which is why it relates to net peptide content.

References

1. Fischer, K. (1935). Neues Verfahren zur maßanalytischen Bestimmung des Wassergehaltes von Flüssigkeiten und festen Körpern. Angewandte Chemie, 48(26), 394–396. doi:10.1002/ange.19350482605
2. Verhoef, J. C., & Barendrecht, E. (1977). Mechanism and reaction rate of the Karl-Fischer titration reaction. Part II. Rotating ring-disk electrode measurements. Journal of Electroanalytical Chemistry and Interfacial Electrochemistry, 75(2), 705–717. doi:10.1016/S0368-1874(77)80056-7
3. United States Pharmacopeia. General Chapter <921> Water Determination, USP–NF. (Reference text reproduced at drugfuture.com.) https://www.drugfuture.com/Pharmacopoeia/usp38/data/v38332/usp38nf33s2_c921.html
4. ASTM International. ASTM E203-16: Standard Test Method for Water Using Volumetric Karl Fischer Titration.
5. Wikipedia contributors. Karl Fischer titration (reaction, 1:1 iodine-to-water stoichiometry, volumetric and coulometric methods, working ranges, endpoint detection, oven method, interferences). https://en.wikipedia.org/wiki/Karl_Fischer_titration
6. Joseph, E. (2019). Residual Moisture Determination in Lyophilized Drug Products. Pharmaceutical Technology, 43(11), 30–39, 56. https://www.pharmtech.com/view/residual-moisture-determination-lyophilized-drug-products
7. Malik, K., Duru, C., Ahmed, M., & Matejtschuk, P. Analytical Options for the Measurement of Residual Moisture Content in Lyophilized Biological Materials. American Pharmaceutical Review (NIBSC Standardization Science Section). https://www.americanpharmaceuticalreview.com/Featured-Articles/116129-Analytical-Options-for-the-Measurement-of-Residual-Moisture-Content-in-Lyophilized-Biological-Materials/
8. Hubbard, A., Bevan, S., & Matejtschuk, P. (2007). Impact of residual moisture and formulation on Factor VIII and Factor V recovery in lyophilized plasma reference materials. Analytical and Bioanalytical Chemistry, 387(7), 2503–2507.
9. Towns, J. K. (1995). Moisture content in proteins: its effects and measurement. Journal of Chromatography A, 705(1), 115–127.
10. Wang, W. (2000). Lyophilization and development of solid protein pharmaceuticals. International Journal of Pharmaceutics, 203(1–2), 1–60.
11. May, J. C. (2004). Residual moisture measurement in freeze-dried biological products. In L. Rey & J. C. May (eds.), Freeze-Drying/Lyophilization of Pharmaceutical and Biological Products, 2nd ed., Marcel Dekker, pp. 349–384.
12. May, J. C., Grim, E., Wheeler, R. M., & West, J. (1982). Determination of residual moisture in freeze-dried viral vaccines: Karl Fischer, gravimetric and thermogravimetric methodologies. Journal of Biological Standardization, 10(3), 249–259.
13. Wang, D. Q., Hey, J. M., & Nail, S. L. (2004). Effect of collapse on the stability of freeze-dried recombinant factor VIII and alpha-amylase. Journal of Pharmaceutical Sciences, 93(5), 1253–1263.
14. Kamat, M. S., Lodder, R. A., & DeLuca, P. P. (1989). Near-infrared spectroscopic determination of residual moisture in lyophilized sucrose. Pharmaceutical Research, 6(11), 961–965.
15. Lin, T. P., & Hsu, C. C. (2002). Determination of residual moisture in lyophilized protein pharmaceuticals using a rapid and non-invasive method: near infrared spectroscopy. PDA Journal of Pharmaceutical Science and Technology, 56(4), 196–205.
16. Tavčar, E., Turk, E., & Kreft, S. (2012). Simple modification of Karl-Fischer titration method for determination of water content in coloured samples. Journal of Analytical Methods in Chemistry, 2012, 379724. doi:10.1155/2012/379724

For the drying step behind the moisture figure and the report it lands on, see What Is Lyophilization, Understanding Peptide COA Testing and What Is Net Peptide Content; for the chemistry of decay that moisture accelerates and the storage that holds it off, see How Peptides Degrade and Cold-Chain Peptide Storage.

All Patriot Labs products are sold strictly for in-vitro research and laboratory use only. Not for human or veterinary consumption. This guide is educational and describes the chemistry of the Karl Fischer water determination and why residual moisture matters in a dried solid in general terms; it is not medical advice, does not describe how to use any product, and makes no claim about the moisture content, purity or manufacturing location of any specific product.