X-ray powder analysis is a method by which the composition of solid samples can be determined and is based on the diffraction of X-rays on crystalline substances. I used this method to identify different compounds or crystalline phases in eleven samples of laundry detergents available in Slovenian stores, as I wanted to know more about the composition of these products, which are used in ordinary household. Additionally, I also wanted to gain more theoretical and practical knowledge about X-ray powder analysis. Qualitative powder analysis based on X-ray powder patterns was performed using the Crystallographica Search-Match (CSM) program and the powder diffraction file PDF-2.
I found that all investigated samples of washing powders contained fairly inexpensive Na2SO4 fillers, and some also NaCl. These two substances were not mentioned in any of the product declarations. All washing powders contained a large amount of Na2CO3 or NaHCO3 being as crystal hydrate or unhydrous as a builder with a washing effect. Those powders used to wash white laundry contained the bleaching agent Na2CO3(H2O2)1.5. When this solid dissolves, hydrogen peroxide is released, which acts as an oxidative bleaching agent. In some powders, I have identified zeolites that are considered as softeners based on cation exchange. In some cases, despite being listed in the product declaration and being crystalline substances, I did not identify them in the samples. This means that they were either not present in the powder or were added only in a very small amount. In individual powders, however, I have also identified different phosphates as builders or softeners. For these, I explained all or most of the diffraction peaks. Nevertheless, certain substances declared on the packaging of products, in particular surfactants, perfumes and enzymes, were not identified in the samples. This is possible either because these were in very low concentrations and consequently below the detection limit or because they are amorphous or not included as standards in the PDF-2 database.