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                                                                   EXHIBIT 99(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-14 and 15d-14) for the registrant and
         we have:

         a.   designed such disclosure controls and procedures 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 as of a date within 90 days prior to the
              filing date of this quarterly report (the "Evaluation Date"); and

         c.   presented in this quarterly report our conclusions about the
              effectiveness of the disclosure controls and procedures based on
              our evaluation as of the Evaluation Date;

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

         a.   all significant deficiencies in the design or operation of
              internal controls which could adversely affect the registrant's
              ability to record, process, summarize and report financial data
              and have identified for the registrant's auditors any material
              weaknesses in internal controls; and

         b.   any fraud, whether or not material, that involves management or
              other employees who have a significant role in the registrant's
              internal controls; and

6.       The registrant's other certifying officer and I have indicated in this
         quarterly report whether or not there were significant changes in
         internal controls or in other factors that could significantly affect
         internal controls subsequent to the date of our most recent evaluation,
         including any corrective actions with regard to significant
         deficiencies and material weaknesses.

Dated: May 15, 2003

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