<PAGE>   1
                                                                   EXHIBIT 10.41
[COMERICA LOGO]


                              MASTER REVOLVING NOTE
                 VARIABLE RATE-MATURITY DATE-OBLIGATORY ADVANCES
                      (BUSINESS AND COMMERCIAL LOANS ONLY)

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<CAPTION>
AMOUNT                            NOTE DATE                      MATURITY DATE                  TAX IDENTIFICATION #
<S>                               <C>                            <C>                            <C>
         $600,000                 April 17, 2001                 October 31, 2001               77-0187280
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On the Maturity Date, as stated above, for value received, the undersigned
promise(s) to pay to the order of Comerica Bank-California ("Bank"), at any
office of the Bank in the State of California, Six Hundred Thousand and no/100
Dollars (U.S.) (or that portion of it advanced by the Bank and not repaid as
later provided) with Interest until maturity, whether by acceleration or
otherwise, or an Event of Default, as later defined, at a per annum rate equal
to the Bank's base rate from time to time in effect plus 0% per annum and after
that at a rate equal to the rate of Interest otherwise prevailing under this
Note plus 3% per annum (but in no event in excess of the maximum rate permitted
by law). Interest rate changes will be effective for Interest computation
purposes as and when the Bank's base rate changes. Interest shall be calculated
on the basis of a 360-day year for the actual number of days the principal is
outstanding. Accrued Interest on this Note shall be payable on the 30th day of
each Month commencing May 30, 2001 , until the Maturity Date when all amounts
outstanding under this Note shall be due and payable in full. If the frequency
of interest payments is not otherwise specified, accrued interest on this Note
shall be payable monthly on the first day of each month. If any payment of
principal or interest under this Note shall be payable on a day other than a day
on which the Bank is open for business, this payment shall be extended to the
next succeeding business day and interest shall be payable at the rate specified
in this Note during this extension. A late payment charge equal to 5% of each
late payment may be charged on any payment not received by the Bank within 10
calendar days after the payment due date, but acceptance of payment of this
charge shall not waive any Default under this Note.

The principal amount payable under this Note shall be the sum of all advances
made by the Bank to or at the request of the undersigned, less principal
payments actually received in cash by the Bank. The books and records of the
Bank shall be the best evidence of the principal amount and the unpaid Interest
amount owing at any time under this Note and shall be conclusive absent manifest
error. No interest shall accrue under this Note until the date of the first
advance made by the Bank; after that Interest on all advances shall accrue and
be computed on the principal balance outstanding from time to time under this
Note until the same is paid in full.

This Note and any other Indebtedness and liabilities of any kind of the
undersigned (or any of them) to the Bank, and any and all modifications,
renewals or extensions of it, whether joint or several, contingent or absolute,
now existing or later arising, and however evidenced (collectively
"Indebtedness") are secured by and the Bank is granted a security Interest in
all items deposited in any account of any of the undersigned with the Bank and
by all proceeds of these items (cash or otherwise), all account balances of any
of the undersigned from time to time with the Bank, by all property of any of
the undersigned from time to time in the possession of the Bank and by any other
collateral, rights and properties described in each and every deed of trust,
mortgage, security agreement, pledge, assignment and other security or
collateral agreement which has been, or will at any time(s) later be, executed
by any (or all) of the undersigned to or for the benefit of the Bank
(collectively "Collateral"). Notwithstanding the above, (I) to the extent that
any portion of the Indebtedness is a consumer loan, that portion shall not be
secured by any deed of trust or mortgage on or other security interest in any of
the undersigned's principal dwelling or any of the undersigned's real property
which is not a purchase money security interest as to that portion, unless
expressly provided to the contrary in another place, or (II) if the undersigned
(or any of them) has (have) given or give(s) Bank a deed of trust or mortgage
covering real property, that deed of trust or mortgage shall not secure this
Note or any other Indebtedness of the undersigned (or any of them), unless
expressly provided to the contrary in another place.

If the undersigned (or any of them) or any guarantor under a guaranty of all or
part of the Indebtedness ("guarantor") (I) fail(s) to pay any of the
Indebtedness when due, by maturity, acceleration or otherwise, or fail(s) to pay
any Indebtedness owing on a demand basis upon demand; or (II) fail(s) to comply
with any of the terms or provisions of any agreement between the undersigned (or
any of them) or any such guarantor and the Bank; or (III) become(s) insolvent or
the subject of a voluntary or involuntary proceeding in bankruptcy, or a
reorganization, arrangement or creditor composition proceeding, (if a business
entity) ceases(s) doing business as a going concern, (if a natural person)
die(s) or become(s) incompetent, (if a partnership) dissolve(s) or any general
partner of it dies, becomes incompetent or becomes the subject of a bankruptcy
proceeding or (if a corporation of a limited liability company) is the subject
of a dissolution, merger or consolidation; or (a) if any warranty or
representation made by any of the undersigned or any guarantor in connection
with this Note or any of the Indebtedness shall be discovered to be untrue or
incomplete; or (b) if there is any termination, notice of termination, or breach
of any guaranty, pledge, collateral assignment or subordination agreement
relating to all or any part of the Indebtedness; or (c) if there is any failure
by any of the undersigned or any guarantor to pay when due any of its
Indebtedness (other than to the Bank) or in the observance or performance of any
term, covenant or condition in any document evidencing, securing or relating to
such Indebtedness; or (d) if the Bank deems itself insecure believing that the
prospect of payment of this Note or any of the Indebtedness is impaired or shall
fear deterioration, removal or waste of any of the Collateral; or (e) if there
is filed or issued a levy or writ of attachment or garnishment or other like
judicial process upon the undersigned (or any of them) or any guarantor or any
of the Collateral, including without limit, any accounts of the undersigned (or
any of them) or any guarantor with the Bank, then the Bank, upon the occurrence
of any of these events (each a "Default"), may at its option and without prior
notice to the undersigned (or any of them), declare any or all of the
Indebtedness to be immediately due and payable (notwithstanding any provisions
contained in the evidence of it to the contrary), cease advancing money or
extending credit to or for the benefit of the undersigned under this Note or any
other agreement between the undersigned and Bank, terminate this Note as to any
future liability or obligation of Bank, but without affecting Bank's rights and
security interests in any Indebtedness any amounts owing by the Bank to the
undersigned (or any of them), charge Interest at the default rate provided in
the document evidencing the relevant Indebtedness and exercise any one or more
of the rights and remedies granted to the Bank by an agreement with the
undersigned (or any of them) or given to it under applicable law. In addition,
if this Note is secured by a deed of trust or mortgage covering real property,
then the trustor or mortgagor shall not mortgage or pledge the mortgaged
premises as a security for any other Indebtedness or obligations. This Note,
together with all other Indebtedness secured by said deed of trust or mortgage,
shall become due and payable immediately, without notice, at the option of the
Bank, (a) if said trustor or mortgagor shall mortgage or pledge the mortgaged
premises for any other Indebtedness or obligations or shall convey, assign or
transfer the mortgaged premises by deed, installment sale contract instrument,
or (Borrower if the title to the mortgaged premises shall become vested in any
other person or party in any manner whatsoever, or (c) if there is any
disposition (through one or more transactions) if legal or beneficial title to a
controlling interest of said trustor or mortgagor. All payments under this Note
shall be in immediately available United States funds, without setoff or
counterclaim.

If this Note is signed by two or more parties (whether by all as makers or by
one or more as an accommodation party or otherwise), the obligations and
undertakings under this Note shall be that of all and any two or more jointly
and also of each severally. This Note shall bind the undersigned, and the
undersigned's respective heirs, personal representatives, successors and
assigns.

The undersigned waive(s) presentment, demand, protest, notice of dishonor,
notice of demand or intent to demand, notice of acceleration or intent to
accelerate, and all other notices and agree(s) that no extension or indulgence
to the undersigned (or any of
<PAGE>   2
them) or release, substitution or nonenforcement of any security, or release or
substitution of any of the undersigned, any guarantor or any other party,
whether with our without notice, shall affect the obligations of any of the
undersigned. The undersigned waive(s) all defenses or right to discharge
available under Section 3-605 of the California Uniform Commercial Code and
waive(s) all other suretyship defenses or right to discharge. The undersigned
agree(s) that the Bank has the right to sell, assign, or grant participations,
or any interest, in any or all of the Indebtedness, and that, in connection with
this right, but without limiting its ability to make other disclosures to the
full extent allowable, the Bank may disclose all documents and information which
the Bank now or later has relating to the undersigned or the Indebtedness. The
undersigned agree(s) that the Bank may provide information relating to the Note
or to the undersigned to the Bank's parent, affiliates, subsidiaries and service
providers.

The undersigned agree(s) to reimburse the holder or owner of this Note for any
and all costs and expenses (including without limit, court costs, legal expenses
and reasonable attorney fees, whether inside or outside counsel is used, whether
or not suit is instituted and, if suit is instituted, whether at the trial court
level, appellate level, in a bankruptcy, probate, or administrative proceeding
or otherwise) incurred in collecting or attempting to collect this Note or
incurred in any other matter or proceeding relating to this Note.


The undersigned acknowledge(s) and agree(s) that there are no contrary
agreements, oral or written, establishing a term of this Note and agree(s) that
the terms and conditions of this Note may not be amended, waived or modified
except in a writing signed by an officer of the Bank expressly stating that the
writing constitutes an amendment, waiver or modification of the terms of this
Note. As used in this Note, the word "undersigned" means, individually and
collectively, each maker, accommodation party, Indorser and other party signing
this Note in a similar capacity. If any provision of this Note is unenforceable
in whole or part for any reason, the remaining provisions shall continue to be
effective. THIS NOTE IS MADE IN THE STATE OF CALIFORNIA AND SHALL BE GOVERNED BY
AND CONSTRUED IN ACCORDANCE WITH THE INTERNAL LAWS OF THE STATE OF CALIFORNIA,
WITHOUT REGARD TO CONFLICT OF LAWS PRINCIPLES.

The maximum interest rate shall not exceed the highest applicable usury ceiling.

THE UNDERSIGNED AND THE BANK ACKNOWLEDGE THAT THE RIGHT TO TRIAL BY JURY IS A
CONSTITUTIONAL ONE, BUT THAT IT MAY BE WAIVED. EACH PARTY, AFTER CONSULTING (OR
HAVING HAD THE OPPORTUNITY TO CONSULT) WITH COUNSEL OF THEIR CHOICE, KNOWINGLY
AND VOLUNTARILY, AND FOR THEIR MUTUAL BENEFIT, WAIVES ANY RIGHT TO TRIAL BY JURY
IN THE EVENT OF LITIGATION REGARDING THE PERFORMANCE OR ENFORCEMENT OF, OR IN
ANY WAY RELATED TO, THIS NOTE OR THE INDEBTEDNESS.

This Note is subject to the terms of Amended and Restated Loan and Security
Agreement dated May 15, 2000.

   INITIAL HERE:
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PharmChem, Inc.



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<S>                                                                     <C>
By:      /S/ DAVID A. LATTANZIO                                         Its:    Vice President - Finance
    ----------------------------------------------------------               ----------------------------------------------
      Signature of
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