Document:

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                                                                   Exhibit 10.32

                              MKS INSTRUMENTS, INC.

                                 FIRST AMENDMENT

                  TO FIRST AMENDED AND RESTATED LOAN AGREEMENT

     This First Amendment (the "Amendment") dated as of September 1, 2000
concerns the First Amended and Restated Loan Agreement dated as of January 1,
2000 (the "Loan Agreement"), among MKS Instruments, Inc. (the "Borrower") and
Fleet National Bank (f/k/a BankBoston, N.A., "Fleet"), The Chase Manhattan Bank
("Chase"; hereinafter Fleet and Chase may be referred to individually as a
"Lender" or collectively as the "Lenders"), and Fleet in its capacity as agent
for the Lenders (in such capacity, together with any successor agent, the
"Agent"). Capitalized terms used herein but not otherwise defined shall have the
meanings assigned to them in the Loan Agreement.

     WHEREAS, the Borrower has requested that the Lenders agree to change
certain provisions of the Loan Agreement; and

     WHEREAS, the Lenders are willing, on the terms, subject to the conditions
and to the extent set forth below, to amend the Loan Agreement to effect such
changes;

     NOW, THEREFORE, the Lenders and the Borrower agree as follows:

     Section 1. AMENDMENT OF THE LOAN AGREEMENT. Section 7.1(b) of the Loan
Agreement is hereby amended and restated as follows:

          (b) Mergers, Etc. Neither the Borrower nor any Subsidiary will
     consolidate with or merge into any other Person or permit any other Person
     to consolidate with or merge into it, or acquire all or substantially all
     of the capital stock or assets of any Person, or sell, assign, lease or
     otherwise dispose of (whether in one transaction or in a series of
     transactions) all or substantially all of its assets to any Person, except
     that

               (1) a Subsidiary may consolidate with or merge into the Borrower
          or another Subsidiary; and

               (2) the Borrower or any of its Subsidiaries may acquire all or
          substantially all of the capital stock or assets of any Person or
          consolidate or merge with any Person provided (i) such Person is
          engaged in a line of business substantially similar to one or more of
          Borrower's existing lines of business, (ii) the aggregate purchase
          price liability incurred in calendar year 2000, including all
          contingent liabilities, when aggregated with all such acquisitions and
          any Investments permitted under Section 7.4(3) in such calendar year
          shall not exceed $80,000,000 and (iii) based on a pro forma
          calculation of the ratios set forth in Section 7.7 as of the date such
          acquisition is closed, assuming consolidation of the acquired business

<PAGE>   2

          with the Borrower for the four full fiscal quarters ended immediately
          preceding such closing and pro forma debt and debt service payments
          based on scheduled principal payments, including acquisition
          borrowings, if any, and pro forma interest on total debt at then
          prevailing borrowing rates, Borrower is in compliance with the
          financial covenants set forth in Section 7.7.

     Section 2. REPRESENTATIONS AND WARRANTIES. The Borrower hereby represents
and warrants as follows:

          (a) The execution and delivery of this Amendment and the performance
of this Amendment, the Loan Agreement as amended hereby and each of the other
Loan Documents, and the transactions contemplated hereby and thereby, have been
authorized by all necessary corporate actions of the Borrower. This Amendment,
the Loan Agreement as amended hereby and each of the other Loan Documents
constitute the legal, valid and binding obligations of the Borrower, enforceable
against the Borrower in accordance with their respective terms.

          (b) The Borrower has all requisite corporate power and authority to
execute, deliver and perform its obligations under this Amendment, the Loan
Agreement as amended hereby and each of the other Loan Documents. Neither the
authorization, execution, delivery or performance by the Borrower of this
Amendment nor the performance of the Loan Agreement as amended hereby or any
other Loan Document nor the performance of the transactions contemplated hereby
or thereby violates or will violate any provision of the corporate charter or
by-laws of the Borrower, or does or will, with the passage of time or the giving
of notice or both, result in a breach of or a default under, or require any
consent under or result in the creation of any lien, charge or encumbrance upon
any property or assets of the Borrower pursuant to, any material instrument,
agreement or other document to which the Borrower is a party or by which the
Borrower or any of its properties may be bound or affected.

          (c) The execution and delivery by the Borrower of this Amendment and
the performance by the Borrower of the Loan Agreement as amended hereby and the
Loan Documents do not and will not violate any provision of law or regulation
applicable to the Borrower, or any writ, order or decree of any court or
governmental or regulatory authority or agency applicable to the Borrower.

     Section 3. LOAN DOCUMENTS. This Amendment shall be a Loan Document for all
purposes.

     Section 4. CONDITIONS TO EFFECTIVENESS. The effectiveness of this Amendment
is conditioned on the following:

          (a) The Borrower and the Lenders shall each have executed and
delivered a counterpart of this Amendment;

                                      -2-

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          (b) The representations and warranties contained in Article IV of the
Loan Agreement shall be true and correct in all material respects as of the date
hereof as though made on and as of the date hereof;

          (c) No Default or Event of Default under the Loan Agreement shall have
occurred and be continuing;

          (d) The conditions set forth in Section 5.1(b) - (e) of the Loan
Agreement shall have been met as of the date hereof, provided that for purposes
thereof and Section 4.5 of the Loan Agreement, the "Balance Sheet Date" shall
mean June 30, 2000 and the financial statements referred to therein shall mean
the unaudited statements for the period ended June 30, 2000, that have been
furnished to the Lender.

     Section 5. MISCELLANEOUS.

          (a) On and after the date hereof, each reference in the Loan Agreement
to "this Agreement" or words of like import shall mean and be deemed to be a
reference to the Loan Agreement as amended hereby.

          (b) Except as amended and modified hereby, the Loan Agreement is in
all respects ratified and confirmed as of the date hereof, and the terms,
covenants and agreements therein shall remain in full force and effect.

          (c) This Amendment and the modifications to the Loan Agreement set
forth herein shall be deemed to be a document executed under seal and shall be
governed by and construed in accordance with the laws of The Commonwealth of
Massachusetts.

          (d) This Amendment may be executed in counterparts, each of which
shall be deemed an original, but all of which together shall constitute one and
the same document.

     IN WITNESS WHEREOF, the parties have caused this Amendment to be duly
executed as of the date and the year first above written.

                                 MKS INSTRUMENTS, INC.

                                 By:    /s/ William P. Donlan
                                    ---------------------------------------
                                 Title: Treasurer
                                       ------------------------------------

                                 FLEET NATIONAL BANK

                                 By:    /s/ Sharon A. Stone
                                    ---------------------------------------
                                 Title: Director
                                       ------------------------------------

                                 THE CHASE MANHATTAN BANK

                                 By:    /s/ A. Neil Sweeny
                                    ---------------------------------------
                                 Title: Vice President
                                       ------------------------------------

                                      -3-<PAGE>   1
                                                                   Exhibit 10.35

                              MKS INSTRUMENTS, INC.

                                 SIXTH AMENDMENT

                                TO LOAN AGREEMENT

     This Sixth Amendment (the "Amendment") dated as of September 1, 2000
concerns the Loan Agreement dated as of October 31, 1995 (the "Loan Agreement"),
between MKS Instruments, Inc. (the "Borrower") and Fleet National Bank (f/k/a
BankBoston, N.A. and The First National Bank of Boston, the "Lender"), as
amended on February 23, 1996, February 4, 1997, February 3, 1998, January 28,
1999 and January 1, 2000. Capitalized terms used herein but not otherwise
defined shall have the meanings assigned to them in the Loan Agreement.

     WHEREAS, the Borrower has requested that the Lender agree to change certain
provisions of the Loan Agreement; and

     WHEREAS, the Lender is willing, on the terms, subject to the conditions and
to the extent set forth below, to amend the Loan Agreement to effect such
changes;

     NOW, THEREFORE, the Lender and the Borrower agree as follows:

     Section 1. AMENDMENT OF THE LOAN AGREEMENT. Section 7.1(b) of the Loan
Agreement is hereby amended and restated as follows:

          (b) Mergers, Etc. Neither the Borrower nor any Subsidiary will
     consolidate with or merge into any other Person or permit any other Person
     to consolidate with or merge into it, or acquire all or substantially all
     of the capital stock or assets of any Person, or sell, assign, lease or
     otherwise dispose of (whether in one transaction or in a series of
     transactions) all or substantially all of its assets to any Person, except
     that

               (1) a Subsidiary may consolidate with or merge into the Borrower
          or another Subsidiary; and

               (2) the Borrower or any of its Subsidiaries may acquire all or
          substantially all of the capital stock or assets of any Person or
          consolidate or merge with any Person provided (i) such Person is
          engaged in a line of business substantially similar to one or more of
          Borrower's existing lines of business, (ii) the aggregate purchase
          price liability incurred, including all contingent liabilities, when
          aggregated with all such acquisitions and any Investments permitted
          under Section 7.4(3), in calendar year 2000 shall not exceed
          $80,000,000 and in any other calendar year shall not exceed 25% of
          Consolidated Tangible Net Worth as of the end of the most recent
          fiscal quarter or, if 80% or more of the purchase price is paid in
          capital stock of the Borrower, 50% of Consolidated Tangible Net Worth
          as of the end of the most recent fiscal quarter and (iii) based on a

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          pro forma calculation of the ratios set forth in Section 7.7 as of the
          date such acquisition is closed, assuming consolidation of the
          acquired business with the Borrower for the four full fiscal quarters
          ended immediately preceding such closing and pro forma debt and debt
          service payments based on scheduled principal payments, including
          acquisition borrowings, if any, and pro forma interest on total debt
          at then prevailing borrowing rates, Borrower is in compliance with the
          financial covenants set forth in Section 7.7.

     Section 2. REPRESENTATIONS AND WARRANTIES. The Borrower hereby represents
and warrants as follows:

          (a) The execution and delivery of this Amendment and the performance
of this Amendment, the Loan Agreement as amended hereby and each of the other
Loan Documents, and the transactions contemplated hereby and thereby, have been
authorized by all necessary corporate actions of the Borrower. This Amendment,
the Loan Agreement as amended hereby and each of the other Loan Documents
constitute the legal, valid and binding obligations of the Borrower, enforceable
against the Borrower in accordance with their respective terms.

          (b) The Borrower has all requisite corporate power and authority to
execute, deliver and perform its obligations under this Amendment, the Loan
Agreement as amended hereby and each of the other Loan Documents. Neither the
authorization, execution, delivery or performance by the Borrower of this
Amendment nor the performance of the Loan Agreement as amended hereby or any
other Loan Document nor the performance of the transactions contemplated hereby
or thereby violates or will violate any provision of the corporate charter or
by-laws of the Borrower, or does or will, with the passage of time or the giving
of notice or both, result in a breach of or a default under, or require any
consent under or result in the creation of any lien, charge or encumbrance upon
any property or assets of the Borrower pursuant to, any material instrument,
agreement or other document to which the Borrower is a party or by which the
Borrower or any of its properties may be bound or affected.

          (c) The execution and delivery by the Borrower of this Amendment and
the performance by the Borrower of the Loan Agreement as amended hereby and the
Loan Documents do not and will not violate any provision of law or regulation
applicable to the Borrower, or any writ, order or decree of any court or
governmental or regulatory authority or agency applicable to the Borrower.

     Section 3. LOAN DOCUMENTS. This Amendment shall be a Loan Document for all
purposes.

     Section 4. CONDITIONS TO EFFECTIVENESS. The effectiveness of this Amendment
is conditioned on the following:

          (a) The Borrower and the Lender shall each have executed and delivered
a counterpart of this Amendment;

                                      -2-

<PAGE>   3

          (b) The representations and warranties contained in Article IV of the
Loan Agreement shall be true and correct in all material respects as of the date
hereof as though made on and as of the date hereof;

          (c) No Default or Event of Default under the Loan Agreement shall have
occurred and be continuing;

          (d) The conditions set forth in Sections 5.2-5.5 of the Loan Agreement
shall have been met as of the date hereof, provided that for purposes thereof
and Section 4.5 of the Loan Agreement, the "Balance Sheet Date" shall mean June
30, 2000 and the financial statements referred to therein shall mean the
unaudited statements for the period ended June 30, 2000, that have been
furnished to the Lender.

     Section 5. MISCELLANEOUS.

          (a) On and after the date hereof, each reference in the Loan Agreement
to "this Agreement" or words of like import shall mean and be deemed to be a
reference to the Loan Agreement as amended hereby.

          (b) Except as amended and modified hereby, the Loan Agreement is in
all respects ratified and confirmed as of the date hereof, and the terms,
covenants and agreements therein shall remain in full force and effect.

          (c) This Amendment and the modifications to the Loan Agreement set
forth herein shall be deemed to be a document executed under seal and shall be
governed by and construed in accordance with the laws of The Commonwealth of
Massachusetts.

          (d) This Amendment may be executed in counterparts, each of which
shall be deemed an original, but all of which together shall constitute one and
the same document.

     IN WITNESS WHEREOF, the parties have caused this Amendment to be duly
executed as of the date and the year first above written.

                                   MKS INSTRUMENTS, INC.

                                   By:    /s/ William P. Donlan
                                      ---------------------------------------
                                   Title: Treasurer
                                         ------------------------------------

                                   FLEET NATIONAL BANK

                                   By:    /s/ Sharon A. Stone
                                      ---------------------------------------
                                   Title: Director
                                         ------------------------------------

                                      -3-

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