Influence of tetraalkylammonium halides on analytical properties of universal acid-base indicator paper

Properties of three types of universal acid-base indicator paper (IP) obtained by means of noncovalent immobilization of five indicators (methyl yellow, methyl red, phenolphthalein, thymol blue, bromothymol blue) in the presence of tetraethylammonium chloride (TEAC) or tetrabutylammonium bromide (TBAB) and in the absence of salts were compared. It was proved that IP-TBAB has advantages in time stability of paper color, reliability of indicators retention in sorbent phase, and accuracy of visual determination of pH values using color scale. Values of acidity constants of indicators were determined by spectrophotometric method in water-ethanol solutions (mass fraction of ethanol is 50%) in the presence and absence of TBAB salt. It was found that modifying action of TBAB on properties of indicators in water-ethanol solutions and on paper is similar to influence of cationic surfactants. Examples of application of the indicator paper are given.