Nonsolvent quantitation of anionic surfactants and other inorganic ingredients in laundry detergent products by X‐ray fluorescence spectrometry

Abstract

This paper reports the development of a method for measuring alkyl-benzene sulfonates, alkyl sulfates, and other inorganic ingredients in laundry detergent products without requiring the use of chlorinated organic solvents such as chloroform. Zeolite is first filtered as a residue on filter paper from an aqueous detergent solution. A calcium solution is then added to the filtrate. Alkyl-benzene sulfonates, alkyl sulfates, and phosphate are precipitated as calcium salts and recovered as residues via filtration. The filters are then subjected to X-ray fluorescence spectrometry (XRF) for measuring the levels of zeolite, phosphate, and total anionic surfactant. The remaining filtrate is also subjected to XRF by using the microdroplet preparation for measuring levels of sulfate and silicate. Separately, the level of alkyl-benzene sulfonates is measured following the same XRF procedure after alkyl sulfates are hydrolyzed using an autoclave. This sample preparation procedure was investigated using XRF and was confirmed to be applicable for simultaneous measurements of alkyl-benzene sulfonates, alkyl sulfates, zeolite, phosphate, silicate, and sulfate without using any organic solvents. In the method described in this paper, interelement effects between anionic surfactants and phosphate are not negligible. Fluorescent X-rays of sulfur or phosphorus are absorbed by calcium complexes of phosphate or anionic surfactants. The slope of calibration curves varies with the levels of coexistent elements; external calibration methods cannot be employed for unknown sample matrices. However, for quality assurance purposes, this method is ideal in terms of turnaround time and laboratory hygiene.Paper no. S1101 in JSD 2, 79-83 (January 1999). KEY WORDS:Alkyl sulfate, alkyl-benzene sulfonate, laundry detergent, phosphate, silicate, sulfate, X-ray fluorescence spectrometry, zeolite.Epton (1,2) developed a two-phase titration for anionic surfactant quantitation that has now become universally accepted methodology for anionic surfactants determination. Chloroform is dictated for two-phase titration in the official methods (3-5), but recently the use of potentially hazardous organic solvents such as chloroform in the working environment is restricted by law (6). Kawauchi (7) developed an inductively coupled plasma atomic emission spectrometry (ICP-AES) method where anionic surfactants and inorganic ingredients in laundry detergent products were determined without using any organic solvents. This ICP-AES method was designed to replace the two-phase titration methodology, providing one potential solution to the issue while also reducing turnaround time without compromising data quality. This time, X-ray fluorescence spectrometry (XRF) was applied for surfactant determination to eliminate the use of organic solvent. The XRF method uses the same sample preparation procedure as the ICP method and has achieved quicker determination for the materials listed above in laundry detergent products. In this paper, the advantages and disadvantages of th...

X-ray fluorescence spectrometry

“…Morel and colleagues 440 evaluated methods for measurement of uranium enrichment by recording emissions from 235 U, 238 U and X-ray ¯uorescence induced within the sample by radiation w100 keV. And ®nally, the role of several techniques, including XRF, in characterizing plutonium for the purposes of international security, stock-pile stewardship and the characterization of mixed oxide fuels were discussed in a conference presentation by Mahan et al 441 XRF has also contributed to an astonishing variety of other industrial applications including: the analysis of drugs; 442 cigarettes widely smoked in Kenya and cigarette ash 443 in which it was reported that signi®cant quantities of As, Ga and Se were ingested during smoking; beauty creams also sold in Kenya, 444 where concern was expressed about the Hg content of some of the samples; anionic surfactants and other inorganic ingredients of laundry detergent products, 445 where the interest lay in determining alkylbenzene sulfonates, alkyl sulfonates, zeolite, phosphate, silicate and sulfate. XRF was also used in the determination of Mn in a dye, FD&C Blue No 1, 446 deposits of aluminium hydroxide and alum±sodium aluminate found in the paper-making process, 447 iodine in iodized salt 448 and wear metals in lubricating oil.…”

Determination of the zeolite and silicate content in detergent products by wavelength‐dispersive x‐ray fluorescence spectrometry

“…or in water (sodium silicates) and measurement of aluminium and silicon in the solution by gravimetry, titration, flame atomic absorption spectrometry (FAAS), inductively coupled plasma atomic emission spectrometry 1 (ICP-AES) or x-ray fluorescence (XRF) spectrometry. 2 The XRF method using the aqueous detergent solution is time consuming. In this method, the zeolite is filtered as a residue on filter-paper on which aluminium is measured and the filtrate is added dropwise on to a microdroplet filterpaper on which silicon is measured.…”