Determination of Potassium, Magnesium and Calcium Ions in Lettuce by Ion Chromatography

Using the same sample solution as the one adopted in the quantitative analysis of nitrate ion in lettuce, which we conducted by way of a prior verification of the analytical method stated herein, simultaneous determinations of potassium ion (K+), magnesium ion (Mg2+) and calcium ion (Ca2+) in lettuce were performed. The concentration of each of the said cations in the sample solution extracted from both leaf lettuce and head lettuce was determined by means of ion chromatography. As a result, the relative standard deviations of the quantitative values were all within five % for both leaf lettuce and head lettuce. Also, our adequacy evaluation of this analytical method (conducted in accordance with the "Guideline for the Adequacy Evaluation of Methods for Testing Metal Contents in Food" prescribed by the Ministry of Health, Labour and Welfare) found the trueness, repeatability and precision within the laboratory for each of the said cations to be: 108.6 %, 1.3 % and 12.6 % for K+; 96.2 %, 1.8 % and 8.5 % for Mg2+; and 104.0 %, 1.8 % and 5.7 % for Ca2+ respectively, attaining the pertinent target values indicated in the said guideline. Based on the above, we deem this analytical method to be effective for determining the concentrations of K+, Mg2+ and Ca2+ in lettuce.