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Water preparation and other industrial processes employ polymer flocculants, derivatives of quaternary ammonium salts, e.g., polydiallyldimethylammonium chloride (PC). The toxicity of PC requires the control of its residual concentration in tap water. As demonstrated in review [1], the problem of the rapid and reliable determination of polymer flocculants in waters is yet to be solved. A spectrophotometric procedure based on the interaction of PC with one of triphenylmethane dyes (TPM), namely, eosine is commonly used for this purpose. Previously the stoichiometry of the interaction of eosine with PC was determined and the conditions of the formation of the colored product (ion pair) were optimized [2,3]. Unfortunately, even under optimum conditions, the sensitivity of the reaction with eosine is insufficient for the determination of PC at a level of the maximum permissible concentration (MPC). Systematic studies of the interaction of other TPM with polymer flocculants could lead to the development of more sensitive procedures for the determination of polymer flocculants, with was the aim of this work.For the study, we selected the following TPM: Pyrocatechol Violet (PCV), Bromophenol Blue (BPB), Bromocresol Green (BCG), Bromothymol Blue (BTB), Phenol Red (PR), Thymol Blue (TB), aluminon (AL), Bromocresol Purple (BCP), Xylenol Orange (XO), fluoresceine (FL), fluorexon (FLX), erythrosine (ER), Bengal Red (BR), and eosine (EO). The reagents were selected for the following reasons: The above reagents are well studied, are used as indicators, and are available in the pure form. Their dissolution in water ( <10 − 3 M) yields true solutions stable on storage and intensely absorbing in the visible spectral region (log ε = 3.5-5.0). All of the reagents have functional groups of the donor character and are potential ligands. Anionic forms of TPM interact with cationic forms of monomeric quaternary ammonium salts yielding ion pairs [4]; hence, changes in absorption spectra are observed. It is expected that TPM will analogously react with polymer quaternary ammonium salts, e.g., with PC. However, the formation of ion pairs of polymer flocculants with dyes must have its specific features, which should be taken into account in the course of analysis. EXPERIMENTALStock 1 × 10 -3 M solutions of dyes were prepared by dissolving weighed portions of chemically pure reagents. Stock solutions of PC (25 mg/L) were prepared in the day of use from a weighed portion of the VPK-402 flocculant (TU 6-05-2009-86; AO Kaustik, Sterlitamak, Russia) containing 39.66% PC and inert impurities. Conventional buffer solutions were used to adjust pH 4-10, and 2 M HCl was added to adjust pH < 4. The absorption spectra of mixtures of TPM and PC were recorded in the range 380-650 nm with a step of 10 nm on SF-26 and KFK-3 spectrophotometers in glass cells (3.0 cm) with reference to a blank solution with the same concentration of TPM and the same pH. PC alone does not absorb in the visible spectral region. All experiments were performed at 20-22°ë withou...

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In the analysis of natural waters, petroleum prod ucts, and other samples of the complex composition, the total concentration of similar compounds (с Σ ) is often estimated from integral indices [1,2]. Such indi ces are often determined by spectrophotometry, mea suring А Σ , the absorbance of a sample solution at a constant wavelength and calculating the integral index с* from a calibration graph built using solutions of a certain reference substance X st . The sensitivity coefficients (K i ) for similar analytes are sufficiently close to each other but not equal, and some or all K i differ from the coefficient K st characterizing the refer ence substance with certainty. Therefore, any integral index presents an approximate and subjective (depending on the choice of X st ) estimate of с Σ and the difference Δс = (с* -с Σ ) gives the systematic error of this estimate. Unfortunately, the metrological aspects of the application of integral indices have not been elaborated. According to Valcarcel, this is the black hole of chemical metrology [2].Researchers have multiply discussed what X st should be better used to determine one or another integral index, for example, to estimate the total con centration of petroleum products in sewage waters [3]. However, the problem has not been considered in gen eral. The algorithm of predicting errors due to the choice of X st was developed only for a special case, when X st is one of the sample components [4]. In this case, the higher the fraction of the internal standard X st in the mixture, the lower the estimation error. This agrees with the analytical practice. For example, in estimating the total concentration of volatile phenols in sewage waters [5], the result (phenol index) is expressed in terms of the simplest phenol С 6 H 5 OH, because it is one of the main components of industrial phenol mixtures.Compounds that surely do not present in the sam ples are also used as reference substances. Thus, many authors expressed the total concentration of antioxi dants (AOs) in foodstuffs or blood plasma in terms of trolox, synthetic analog of a natural AO (vitamin E) [6]. Other authors use ascorbic acid or quercetin as X st , no matter whether these compounds are present in the samples [7]. The integral antioxidant capacity (IAC) expressed in moles X st found from a calibration graph or using the standard addition method differs from the total concentration of antioxidants (с ΣАО ) and can be used only to compare similar samples analyzed by the same procedure using the same X st . Of forthcoming attraction would be to change from the determination of IAC to the objective estimate с ΣАО independent of the choice of X st . This problem is also highly important for other integral indices [2]. To solve it, one can first calculate the systematic error due to the use of a par ticular X st and then introduce an appropriate correc tion.The aim of this work was to develop a generalized algorithm for predicting the above error. The proposed algorithm was tested on model antioxidant mixtures...