Vol.:(0123456789) 1 3 Journal of the Iranian Chemical Society https://doi.org/10.1007/s13738-020-02029-3 ORIGINAL PAPER A sensitive nanodrop method for the micro‑level determination of cationic surfactant methyltrioctylammonium chloride (MTOAC) in biological fuids and environmental samples Saurabh Kumar Gupta 1  · Kavita Tapadia 1  · Ashima Sharma 1 Received: 15 January 2020 / Accepted: 3 August 2020 © Iranian Chemical Society 2020 Abstract In this study, a rapid, sensitive and novel nanodrop spectrometric approach is used for the trace level determination of cationic surfactant methyltrioctylammonium chloride (MTOAC) based on the reaction of Mo(III)-SCN − complex with MTOAC in acidic condition. The molar absorptivity of red-colored Mo(III)-SCN − complex was enhanced in the presence of MTOAC that is attributed to a hyperchromic shift. The absorptivity value of the complex with respect to MTOAC is 9.8 × 10 4  L mol −1  cm −1 at λ max 415 nm. The quality parameters show the good analytical performance of the proposed method with detection limit (LOD) of 8.3 × 10 −3  mg L −1 and limit of quantitation of 2.7 × 10 −2  mg L −1 . The calibration curve for MTOAC determina- tion obeys Beer’s law with the concentration limit of 0.05–0.40 mg L −1 and determination coefcient (R 2 ) 0.9992 along with slope and intercept 9.5 and 0.002, respectively. The proposed NDS method has been applied successfully in diferent environmental and biological samples for the determination of MTOAC. Keywords Cationic surfactant · Methyltrioctylammonium chloride (MTOAC) · Nanodrop spectrometer (NDS) · Mo(III)- SCN − complex · Biological samples · Environmental samples Introduction Surfactants are also known as a surface active agent and have amphiphilic character. Generally, surfactant consists of hydrophilic and hydrophobic moieties. Hydrophilic group (head) is water-soluble and polar such as phosphate, sulfate, carboxylate or ammonium, whereas hydrophobic group (tail) includes hydrocarbon, fuorocarbon or aromatic ring. Sur- factant has property to decrease the surface tension due to an amphiphilic character. It has an ability to form micelles and bilayer; thus, surfactants are broadly used in various industries like household, cosmetics, drug, pharmaceutics, leather, fber, oil recovery, etc. [1–4]. Surfactants are classifed into four classes based on the presence of hydrophilic groups. If hydrophilic moiety (head) group include carboxylate, phosphate or sulfate, it forms anionic surfactant, positively charged quaternary ammonium salts form cationic surfactants, uncharged hydrophiles form nonionic surfactants (fatty acids), and zwitterionic betaines form amphoteric surfactant. The head or hydrophilic polar part of the surfactant determine its chemical and physical qualities, and the hydrophobic moiety of surfactant also afects nature, i.e., the longer the carbon chain of the tail part, more it will become less water-soluble and nonpolar [5–7]. Cationic surfactants (CSs) are quaternary ammonium compounds (QACs), consisting of positively charged nitro- gen atom with hydrophobic hydrocarbon chain substituent. Other substituents may be methyl or benzyl groups. Because of positive charge, cationic surfactant became able to absorb- able on diferent surfaces. Therefore, it is commonly used to modify the surface properties. Cationic surfactants are most commonly used as softeners in apparel and fabric industry, laundry detergents, as antiseptics, in pigments as disper- sants, in bio-industry as biocides in pharmaceuticals and antistatic agent and as corrosion inhibitors in metal industry [8, 9]. In spite of that, surfactants are widespread in various human activities also [10, 11]. Cationic surfactants (CSs) are widely used in commodity manufacture and in many industrial felds, but they also cause environmental pollution. * Kavita Tapadia ktapadia.chy@nitrr.ac.in 1 Department of Chemistry, National Institute of Technology, Raipur, CG, India