Method for hair analysis by polarized light
A method of hair analysis based on microscope pictures of the hair in polarized light includes a hair conditioning phase performed in a container made of polyethylene or a polymer being in a position lower than polyethylene in the triboelectric series; this is followed by a hair testing phase in which polarized light microscope images of the hair, contacted with a turpentine oil, are taken and further processed using unmixing to obtain information on the amount of analytes present in the hair. Advantageously the present method shows high accuracy even in presence of accidental movements applied to the microscope/sample to be analyzed, such as possibly occurring during daily laboratory practice. Also advantageously, the high accuracy is maintained when different operators are involved in the procedure, being thus substantially unaffected by different ways of manipulating/preparing/photographing the hair sample.
1. A method to analyze hair composition, based on processing light patterns obtained from a microscope digital picture in polarized light of a hair sample, wherein the amount of each analyte present in the hair sample is calculated via unmixing, the method comprising
a) a calibration phase, wherein the light patterns of pure analytes are constructed taking one or more microscope digital pictures in polarized light of said pure analytes;
b) a measuring phase, wherein the light pattern of the hair sample is constructed taking one or more microscope digital pictures in polarized light of said hair sample;
each of said light patterns being a construction of a spectral pattern from microscope digital picture, wherein each point (pixel) of the picture is characterized by its wavelength and absorbance;
c) a determination phase, wherein the light patterns of a) and b) are compared and elaborated via software-assisted unmixing, thereby determining the relative contribution of each analyte present in the hair sample, and therefrom its absolute amount or concentration, wherein
prior to said measuring phase b) a conditioning phase is performed, comprising storing the hair sample, during a period of time of at least half a day, in a sealed container made of a polyethylene or a polymer being in a position lower than polyethylene in the triboelectric series; then opening said container, extracting a set of hair and contacting said set of hair with a turpentine oil.
2. The method according to claim 1 , wherein said polymer being in a position lower than polyethylene in the triboelectric series is chosen from the group consisting of: polypropylene, polydiphenyl propane carbonate, polyimide, polyethylene terephthalate, polyvinyl chloride, polytrifluorochloroethylene, and polytetrafluoroethylene.
3. The method according to claim 1 , wherein said turpentine oil is fir turpentine or pinewood turpentine.
4. The method according to claim 1 , wherein said conditioning phase has a duration of from one to five days.
5. Method The method according to claims 1 4 , claim 1 wherein said conditioning phase is performed at a temperature between 15 and 35° C.
6. The method according to claim 1 , wherein said container is a small-volume envelope, bag, tube or box.
7. The method according to claim 1 , wherein set of hair consists of 1 to 20 hairs.
8. The method according to claim 1 , further comprising having an accuracy, expressed as relative standard deviation of at least 6 measures of the same set of hair, ranging from 5 to 20%, preferably from 8 to 18%.
9. The method according to claim 1 , wherein said analytes include metals, amino-acids, drugs, hormones, vitamins, pollutants, poisons.
10. The method according to claim 9 , wherein said metals include alkaline or earth-alkaline metals.