I'm not expert in this field but I guess that you can add a polar compound in a constant manner. I mean take virgin oil and prepare 30 samples adding 1%, 2%, 3%... 30% of a polar compound that you would like to test in the "real" samples. You can do that with a few compounds and make some calibration curves. I don't know what kind of compounds could you be interested in, but I guess... phenol... glicerol...?

In direct rapid test like yours i think is necessery to make some dilution in solvent,

you can try isopropanol or ethanol for prep this sample, and then make analysis,

it will be depends how sensitive your test is.

Try - 1part of oil and add maximum of polar compounds (0,3 part) and measure how many isopropanol (100 ul by 100 ul) or ethanol you need for dissolv. this will give you tip how many solvent you must use for prep samples with other % polar coumpoundst. then test... The volume of polar compounds with isopropanol shoud be this same on each level.

Lipid or oil (I mean triglyceride) is quite non-polar, but it will tern to be more polar after oxidation which generates many polar compounds (mostly are small fatty acids and free radicals) within such oil. Exposing to oxygen and some catalysts (iron, hydrogen peroxide, oxidase, etc) will accelerate the deteriorate mechanism very very faster. So, you can add small fatty acids (such as propionic acid, butanoic acid, valeric acid or pentanoic acid, hexanoic acid) into your oils to make standard you need. Your comparison should be resulted in equivalent value because the products in real reaction are occurred randomly. ^^...

Normally you would need a matched matrix to prepare a calibration curve. That means, you heat vergin oli to the same extent as you fry samples. In this fried oil which does not contain any samples, you dissolve known amount of polar compounds. Normally, 8 to 10 samples to cover 1 to 30 % (say 1, 2, 5,10, 20, 30,40 and 50% )would define a good calibration curve. With this calibration curve, you can easily calculate amount of polar compounds in the fried oil.

Try with solvet approche....

Prepare 10 vials (from SPME 10 ml) with teflon septa. Measure for each one this same amount (mg), i dont know how big is difference beetwen oils from frites-machines and fresh in density....(?).... that way ml could be not enought... (but you could measure this value)...

Add 100 mg oil to each one (vials). Then prepare solution of Yours polar coumpds (stock - ex. in 100 ul contain 1 mg) of isopropanol - important. Then add adequate amount of standards (polar comps in isopropanol) for recive wanted dilution of samples. And you now how many isopropanol you give and you can accept one POINT of total voulme (1 or 2 ml of total voulme of sample). Then vortex and testing.....

Make some calibration curves and check 0.99 > R2>0,9 - its depends from system type of wich you apply for analysis (Specol UV-VIS) with blank sample (oil with isopropanol only in this same amount of solvent like your POINT of total volume). You recive some pattern and then its easy. you can "check" on some value for recalculate - difference in densities...

Dear Ana,

you have first to study the problem in more detail.

Yes, during frying harmful compounds are generated, polycyclic aromatic hydrocarbons, acryl amide and several others. You will have first to do a literature search an this. However, it is already clear that these compounds are of concern when present in the ppm range. Therefore to study oil with 1 - 30 % of polar compounds sounds ridiculous.

An approach to develop a handy test for users of frying oil might be difficult to achieve. Maybe using fluorescence or a biosensor???

Titus is right. Most of toxic compounds are relatively non-polar and (for aromatic compound) the fluorescence monitoring is a good way.

Dear Ana, there is a nice handeheld testing device on the market (Testo 270 frying oil tester) which you can use to check your oxidised oil, or you check the oils with the reference methods (IUPAC (1987) Standard Method 2.507: Determination of polar compounds in frying fats. In: Standard Methods for the Analysis of Oils, Fats and Derivatives, 7th ed. (ed. International Union of Pure and Applied Chemistry, Blackwell, Oxford).

IUPAC (1992) Standard Method 2.508: Determination of polymerized triglycerides in oils and fats by high performance liquid chromatography. In: Standard Methods for the Analysis of Oils, Fats and Derivatives, 7th ed. (ed. International Union of Pure and Applied Chemistry, Blackwell, Oxford).. Just heat an oil sample for several hours at elevated temperature and take samples over a limited period of time and measure the polar fraction. So you can generate a calibration set.

@Titus the concentration range of 1-30% polar compounds in frying IS NOT ridiculous, it is the real concentration range which can be expected.There is a recommendation that frying oils should not exceed a polar content above 24%!

br Erich

Thank you Erich. I still wonder, whether this level is achieved under practical conditions before other more dangerous (???) compounds reach a level of concern. Or is the polar content only used as an indication that other more dangerous compounds might be present at a level not to be tolerated?

Dear Titus, the formation of the polar fraction happens mainly during high temperature treatment of oils (mainly frying) and this happens under each frying process especially if you do not exchange your frying oil very often and depends on the degree of unsaturation of the oil. Due to the fact that especially refined oils (which are normally used for that purpose) consist of a pure triglyceride fraction this is one of the main reactions which can occur. Beside the formation of the polar fraction a formation of dimer, trimer and even if the process is prolonged polymer triglyceride (a technical process which is used to produce boiled linseed oil as wood preservative) can be formed, this is the main reaction. In addition there might be the possibility of formation of trans fatty acids and of course in much lower concentration all the degradation products of lipid oxidation (mainly aldehyde). These nasty compounds are respondsible for the rancid smell.

Hello! Thank you all for your help.

In response to some coments:

- I have already did research (lots and lots of articles), the problem is that no one as tryed to make standards, they collected lots and lots of samples and work with that. But I want to optimize the study of this rapid test, because of several reasons.

- the legal limits of polar compounds of lots of countries is 24% so the test I'm studying gives results between >5% and

Dear Ana,

if the test is based on the colour change then it might be impossible to use 'standards' you thought of. Do not know exactly but in case of monostearin adding larger amounts likely the colour will fade. This might happen if you add purified compounds mostly. I do not think it is possible to get good correlations.

Would it be possible to determine the correlation between concentration of 'polar compounds' (a group of selected typical compounds) and colour for a range of virgin oils and frying conditions, maybe taking into account the colour value of the starting oil?