<PAGE>
                                                                   EXHIBIT 31(a)

        CERTIFICATION PURSUANT TO RULE 13A-14 OR 15D-14 OF THE SECURITIES
         EXCHANGE ACT OF 1934, AS ADOPTED PURSUANT TO SECTION 302 OF THE
                           SARBANES-OXLEY ACT OF 2002

I, Thomas E. Mark, certify that:

1.       I have reviewed this quarterly report on Form 10-Q of Detrex
         Corporation;

2.       Based on my knowledge, this quarterly report does not contain any
         untrue statement of a material fact or omit to state a material fact
         necessary to make the statements made, in light of the circumstances
         under which such statements were made, not misleading with respect to
         the period covered by this quarterly report;

3.       Based on my knowledge, the financial statements, and other financial
         information included in this quarterly report, fairly present in all
         material respects the financial condition, results of operations and
         cash flows of the registrant as of, and for, the periods presented in
         this quarterly report;

4.       The registrant's other certifying officer and I are responsible for
         establishing and maintaining disclosure controls and procedures (as
         defined in Exchange Act Rules 13a-15(e) and 15d-15(e) for the
         registrant and have:

         a.       designed such disclosure controls and procedures, or caused
                  such disclosure controls and procedures to be designed under
                  our supervision, to ensure that material information relating
                  to the registrant, including its consolidated subsidiaries, is
                  made known to us by others within those entities, particularly
                  during the period in which this quarterly report is being
                  prepared;

         b.       evaluated the effectiveness of the registrant's disclosure
                  controls and procedures and presented in this report our
                  conclusions about the effectiveness of the disclosure controls
                  and procedures, as of the end of the period covered by this
                  report based on such evaluation; and

         c.       disclosed in this report any change in the registrant's
                  internal control over financial reporting that occurred during
                  the registrant's most recent fiscal quarter that has
                  materially affected, or is reasonably likely to materially
                  affect, the registrant's internal control over financial
                  reporting; and

5.       The registrant's other certifying officer and I have disclosed, based
         on our most recent evaluation of internal controls over financial
         reporting, to the registrant's auditors and the audit committee of the
         registrant's board of directors (or persons performing the equivalent
         function):

         a.       all significant deficiencies and material weaknesses in the
                  design or operation of internal control over financial
                  reporting which are reasonably likely to adversely affect the
                  registrant's ability to record, process, summarize and report
                  financial information; and

         b.       any fraud, whether or not material, that involves management
                  or other employees who have a significant role in the
                  registrant's internal control over financial reporting.

Dated:  August 14, 2003

By:   /s/  Thomas E. Mark
      ----------------------------------------
        Thomas E. Mark
        President and Chief Executive Officer