<PAGE>

                                                                  EXHIBIT 4.2(b)

                  SECOND AMENDMENT TO NOTE PURCHASE AGREEMENT

     This SECOND AMENDMENT TO NOTE PURCHASE AGREEMENT (this "Second Amendment")
is dated as of September 30, 2001, and entered into by and between iGate Capital
Corporation, formerly known as Mastech Corporation, a Pennsylvania corporation
(the "Company"), and GE Capital Equity Investments, Inc., a Delaware corporation
("GE Capital").

                                   WITNESSETH

     WHEREAS, the Company and GE Capital are party to a Note Purchase Agreement,
dated as of July 22, 1999, by and between the Company and GE Capital, as amended
by the First Amendment to Note Purchase Agreement dated as of August 1, 2000 and
the letter agreement dated November 21, 2000 (the "Note Purchase Agreement");

     WHEREAS, the Company has requested certain amendments to the terms of the
Note Purchase Agreement;

     WHEREAS, GE Capital has agreed to make such amendments upon the terms and
conditions set forth herein; and

     WHEREAS, concurrently with the execution of this Second Amendment, the
Company is entering into a Second Amendment to the Credit Agreement dated as of
August 1, 2000 with certain financial institutions party thereto, as lenders,
and PNC Bank, National Association, as Agent and as Swing Loan Lender and
Issuing Bank;

     NOW, THEREFORE, in consideration of the foregoing premises, the mutual
covenants and agreements contained herein and other good and valuable
consideration, the receipt and sufficiency of which are hereby acknowledged, and
with the intent to be legally bound hereby, the parties hereto agree as follows:


                                   ARTICLE I
                     AMENDMENTS TO NOTE PURCHASE AGREEMENT

     Section 1.1  Amendments to Section 1 of the Note Purchase Agreement.
                  ------------------------------------------------------
     (a) The following defined terms and the definitions therefor amend and
restate the following terms defined in Section 1 of the Note Purchase Agreement:

                    "Credit Agreement" shall mean the Credit Agreement dated as
          of August 1, 2000, among the Company, as borrower, the financial
          institutions party thereto as lenders, and PNC Bank, National
          Association, as Agent and as Swing Loan Lender and Issuing Bank, as
          the same may be amended from time to time, and the related
<PAGE>

          ancillary documents thereto, including without limitation, the
          security agreements, the patent, trademark and copyright security
          agreements, the subsidiary guaranty agreements and the pledge
          agreements entered into in connection therewith.

                    "Note" shall mean the Second Amended and Restated
          Convertible Promissory Note of Company in the principal amount of
          $10,000,000 to be issued to Purchaser by Company in connection with
          the Second Amendment to Note Purchase Agreement dated as of September
          30, 2001 amending and restating the convertible promissory note dated
          July 22, 1999 issued to Purchaser by Company in connection with the
          Note Purchase Agreement.

                    "Permitted Liens" shall mean the following:   (i) Liens for
          taxes or assessments or other governmental charges or levies, either
          not yet due and payable or to the extent that nonpayment thereof is
          permitted by the terms of this Agreement; (ii) pledges or deposits
          securing obligations under workmen's compensation, unemployment
          insurance, social security or public liability laws or similar
          legislation; (iii) pledges or deposits securing bids, tenders,
          contracts (other than contracts for the payment of money) or leases to
          which Company or any of its Subsidiaries is a party as lessee made in
          the ordinary course of business; (iv) Liens arising solely by virtue
          of any statutory or common law provision relating to bankers' liens,
          rights of set-off or similar rights and remedies as to deposit
          accounts or other funds maintained with a creditor depository
          institution; (v) workers, mechanics, suppliers, carriers,
          warehousemen's or other similar liens arising in the ordinary course
          of business and securing indebtedness, not yet due and payable; (vi)
          deposits securing or in lieu of surety, appeal or customs bonds in
          proceedings to which Company or any of its Subsidiaries is a party;
          (vii) Liens arising in the ordinary course of business in connection
          with obligations that are not overdue or which are being contested in
          good faith and by appropriate proceedings, including, but not limited
          to, Liens under bid, performance and other surety bonds, supersedeas
          and appeal bonds, landlord Liens arising under leases of real
          property, Liens on advance or progress payments received from
          customers under contracts for the sale, lease or license of goods,
          software or services and upon the products being sold or licensed, in
          each case securing performance of the

                                       2
<PAGE>

          underlying contract or the repayment of such advances in the event
          final acceptance of performance under such contracts does not occur,
          and Liens upon funds collected temporarily from others pending payment
          or remittance on their behalf; (viii) zoning restrictions, easements,
          licenses, or other restrictions on the use of real property or other
          minor irregularities in title (including leasehold title) thereto, so
          long as the same do not materially impair the use, value, or
          marketability of such real property, leases or leasehold estates; (ix)
          Liens permitted pursuant to the last sentence of Section 7.02 of the
          Credit Agreement as in effect on September 30, 2001; and (x) Liens or
          pledges arising from or created pursuant to the Credit Agreement.

     (b) The following new defined term and the definition therefor shall be
added to Section 1 of the Note Purchase Agreement in its appropriate
alphabetical order:

               "Consolidated Income from Operations" shall mean the income or
         loss from operations, before (i) depreciation, amortization and one-
         time items related to impairment of goodwill in accordance with SFAS
         No. 121 "Accounting for the Impairment of Long-Lived Assets to Be
         Disposed Of", effective for Company through December 31, 2001, or if
         subsequent to December 31, 2001, SFAS No. 142 "Goodwill and Other
         Intangible Assets", effective for Company through January 1, 2002, (ii)
         other one-time gains and losses not related to operations and (iii)
         taxes, of Company and its consolidated Subsidiaries, with the exception
         of Mascot Systems Private Limited, determined on a consolidated basis
         in accordance with GAAP.

     Section 1.2 Amendment to Section 5.1(b) of the Note Purchase Agreement.
                 -----------------------------------------------------------
Section 5.1(b) of the Note Purchase Agreement shall be amended by deleting the
word "and" at the end of clause (vi) thereof, by deleting the punctuation "." at
the end of clause (vii) and inserting the punctuation and word "; and" in its
place and inserting at the end thereof a new clause (viii) as follows:

          (viii)  10 Business Days' prior written notice of any amendment to the
          Credit Agreement, describing in reasonable detail the proposed terms
          of any amendment, and, promptly upon the execution of any amendment to
          the Credit Agreement, a copy of such executed amendment.

     Section 1.3  Amendment to Section 5.2(h) of the Note Purchase Agreement.
                  ----------------------------------------------------------
Section 5.2(h) of the Note Purchase Agreement shall be amended to add at the end
thereof the following sentence:

                                       3
<PAGE>

          Notwithstanding the foregoing, advance notice of any amendment of the
          certificate or articles of incorporation of a Subsidiary, the sole
          purpose of which is to change the corporate name of such Subsidiary,
          shall not be required; provided that Company shall provide notice to
          Purchaser of any such name change within ten (10) days of the
          effective date thereof.

     Section 1.4  Amendment to Section 5.2(i) of the Note Purchase Agreement. A
                  -----------------------------------------------------------
new paragraph (d) shall be inserted at the end of Section 5.2(i) of the Note
Purchase Agreement, which shall read in its entirety as follows:


          (d) Minimum Consolidated Income from Operations.  The Company shall
              -------------------------------------------
          not permit Consolidated Income from Operations for any fiscal quarter,
          as determined at the end of such quarter, to be less than the
          applicable amount designated below:


<TABLE>
<CAPTION>
                                                             Minimum Consolidated
                      Quarter Ended                        Income from Operations
          -----------------------------------------------------------------------
          <S>                                              <C>
          September 30, 2001                                            ($500,000)
          -----------------------------------------------------------------------
          December 31, 2001                                             ($100,000)
          -----------------------------------------------------------------------
          March 31, 2002                                               $        0
          -----------------------------------------------------------------------
          June 30, 2002                                                $  500,000
          -----------------------------------------------------------------------
          September 30, 2002                                           $1,000,000
          -----------------------------------------------------------------------
          December 31, 2002 and thereafter                             $1,500,000
          -----------------------------------------------------------------------
</TABLE>

     Section 1.5 Amendment to Section 8.1 of the Note Purchase Agreement. A new
                 --------------------------------------------------------
paragraph (m) shall be added to Section 8.1 of the Note Purchase Agreement which
shall read as follows:

                    (m) Without the prior written consent of Purchaser, the
          Credit Agreement shall be amended, modified or supplemented, or any
          provision thereof waived, in any manner which has or would reasonably
          be expected to have a material adverse effect on the repayment of the
          Note or on the rights of Purchaser under the Loan Documents, including
          without limitation, (i) any increase in the "Revolving Credit
          Commitments" (as defined in the Credit Agreement), (ii) any increase
          in (or any change which has the substantive effect of increasing) the
          "Advance Rate" (as defined in the Credit Agreement) and

                                       4
<PAGE>

          (iii) the making of (or any change which has the substantive effect of
          the making of) any overadvance in excess of the Borrowing Base (as
          defined in the Credit Agreement).

                                  ARTICLE II
                              CONDITIONS PRECEDENT

     The amendments to the Note Purchase Agreement set forth in Article I
hereof shall become effective on the date that each of the following conditions
precedent are satisfied (such date, the "Amendment Effective Date"):

     Section 2.1  GE Capital shall have received counterparts of this Second
Amendment duly executed by Company.

     Section 2.2 GE Capital shall have received the principal prepayment
required pursuant to Article IV hereof.

     Section 2.3 GE Capital shall have received payment of $161,000,
representing payment of accrued interest through the date hereof on the
outstanding principal prepaid pursuant to Article IV hereof.

     Section 2.4 GE Capital shall have received such other documents from
Company as GE Capital shall request in writing.

                                  ARTICLE III
                                 ACKNOWLEDGMENT

     Section 3.1 The amendments set forth in Article I hereof do not alter,
waive or amend, except as expressly provided in this Second Amendment, the
provisions of the Note Purchase Agreement, as previously amended. Nothing in
this Second Amendment shall be deemed or construed as a waiver or release of, or
a limitation upon, the exercise by GE Capital of any rights and remedies under
the Note Purchase Agreement, whether arising as a consequence of any Events of
Default which may have previously existed or now exist or otherwise, and any and
all such rights and remedies are hereby expressly reserved.


                                       5
<PAGE>

                                  ARTICLE IV
                              PREPAYMENT OF NOTE

     Notwithstanding anything in the Note Purchase Agreement to the contrary,
the Company and GE Capital agree that, concurrently with execution and delivery
of this Second Amendment, the Company will pay to GE Capital, by wire transfer
of immediately available funds, the sum of TEN MILLION DOLLARS ($10,000,000)
(such sum, the "Principal Prepayment").  GE Capital shall have no obligation to
readvance the Principal Prepayment.  Such Principal Prepayment shall reduce the
principal amount outstanding or the Note dated July 22, 1999 to the amount of
TEN MILLION DOLLARS ($10,000,000).  To evidence the reduction of the outstanding
principal amount, the Company shall deliver to General Electric Capital
Corporation, 120 Long Ridge Road, Stamford, Connecticut 06927 Attn:  GE Equity
Group - Technology and Communications Group, an amended and restated note in the
form attached as Annex A (the "Second Amended and Restated Note").  Upon receipt
of the Second Amended and Restated Note, GE Capital will send the note that is
amended and restated by the Second Amended and Restated Note, marked
"$10,000,000 Paid" and signed by an authorized officer of GE Capital, by Federal
Express Overnight Delivery, to the attention of Michael Zugay, Chief Financial
Officer, iGate Capital Corporation, Foster Plaza 10, 680 Andersen Drive,
Pittsburgh, Pennsylvania 15220.  Following the wire transfer by the Company of
the Principal Prepayment, together with the accrued interest specified in
Article II hereof, any and all references in the Note Purchase Agreement, as
amended hereby, to the Note shall be deemed to be a reference to the Second
Amended and Restated Note.

                                   ARTICLE V
            REPRESENTATIONS, WARRANTIES AND COVENANTS OF THE COMPANY

     Section 5.1  Representations and Warranties of the Company.  The Company
                  ---------------------------------------------
represents and warrants that:

     (a) the execution, delivery and performance by Company of this Second
Amendment has been duly authorized by all necessary or proper corporate action
and the Second Amendment is a legal, valid and binding obligation of Company,
enforceable against it in accordance with its terms, subject to applicable
bankruptcy, insolvency, fraudulent conveyance, reorganization, moratorium and
similar laws affecting creditors' rights and remedies generally, and subject, as
to enforceability, to general principles of equity, including principles of
commercial reasonableness, good faith and fair dealing (regardless of whether
enforcement is sought in a proceeding at law or in equity).


     (b) the execution, delivery and performance by Company of this Second
Amendment shall not contravene, result in a breach of, or violate, any provision
of Company's articles of incorporation or by-laws; any law or regulation, or any
order or decree of any court or governmental instrumentality, or any indenture,
mortgage, deed of trust, lease, agreement or other instrument to which Company
or any of its Subsidiaries is a party or by which Company, any of it
Subsidiaries or any of their property is bound.

     (c) there are no Defaults or Events of Default which have occurred under
the Note Purchase Agreement, as previously amended and after giving effect to
this Second Amendment.

                                       6
<PAGE>

     (d) subject to the Supplement to Disclosure Schedule attached hereto, the
representations and warranties of the Company contained in the Note Purchase
Agreement are true and correct as of the date hereof (except such
representations and warranties that refer to an earlier date which are true and
correct as of such earlier date).

     (e) the registration statement on Form S-3 with respect to the shares
issuable upon conversion of the Second Amended and Restated Note was declared,
and continues to be, effective, and the terms and provisions of the Registration
Rights Agreement have been fully complied with by Company and remain in full
force and effect, without amendment or modification.

                                  ARTICLE VI
                              GENERAL PROVISIONS

     Section 6.1  References.  All notices, communications, agreements,
                  ----------
certificates, documents or other instruments executed and delivered after the
execution and delivery of this Second Amendment in connection with the Note
Purchase Agreement or the transactions contemplated thereby may refer to the
Note Purchase Agreement without making any specific reference to this Second
Amendment or the First Amendment thereto, but nevertheless all such references
shall include this Second Amendment unless the context otherwise requires. From
and after the Amendment Effective Date, all references in the Note Purchase
Agreement and the Note to the "Agreement" shall be deemed to be references to
the Note Purchase Agreement as previously amended and as amended hereby.

     Section 6.2  Incorporation into Note Purchase Agreement.  This Second
                  ------------------------------------------
Amendment is deemed incorporated into the Note Purchase Agreement as previously
amended. To the extent that any term or provision of this Second Amendment is or
may be deemed expressly inconsistent with any term or provision of the Note
Purchase Agreement as previously amended, the terms and provisions hereof shall
control.

     Section 6.3  Capitalized Terms.  Except as otherwise defined herein,
                  -----------------
capitalized terms used but not defined herein shall have the same meanings
herein as are ascribed to them in the Note Purchase Agreement.

     Section 6.4  Section and Other Headings.  The section and other headings
                  --------------------------
contained in this Second Amendment are for reference purposes only and shall not
affect the meaning or interpretation of this Second Amendment.

     Section 6.5  Counterparts.  This Second Amendment may be executed in any
                  ------------
number of counterparts, each of which shall be deemed to be an original and all
of which together shall be deemed to be one and the same instrument.

     Section 6.6  Publicity.  Neither the Company nor GE Capital shall issue
                  ---------
any press release or make any public disclosure regarding the transactions
contemplated hereby unless such press release or public disclosure is approved
by the other party in advance. Notwithstanding the foregoing, each of the
parties hereto may, in documents required to be filed by it with the SEC or
other regulatory bodies, make such statements

                                       7
<PAGE>

with respect to the transactions contemplated hereby as each may be advised by
counsel is legally necessary or advisable, and may make such disclosure as it is
advised by its counsel is required by law.

    Section 6.7  Governing Law; Waiver of Jury Trial.  This Second Amendment
                 -----------------------------------
shall be governed by, and construed and enforced in accordance with, the laws of
the State of New York applicable to contracts made and performed in such state,
without regard to the principles thereof regarding conflict of laws, and any
applicable laws of the United States of America. The parties hereto waive all
right to trial by jury in any action or proceeding to enforce or defend rights
hereunder.

     Section 6.8  Ratification of Terms.  Except as expressly amended by this
                  ---------------------
Second Amendment, subject to the Supplement to Disclosure Schedule attached
hereto, the Note Purchase Agreement as previously amended and each and every
representation, warranty, covenant, term and condition contained therein shall
remain in full force and effect and is specifically ratified and confirmed. This
Second Amendment, the Note Purchase Agreement and the other Loan Documents may
be amended, modified, supplemented or waived only in a writing executed by the
parties thereto.

                  [REMAINDER OF PAGE INTENTIONALLY LEFT BLANK]

                                       8
<PAGE>

          IN WITNESS WHEREOF, the Company and GE Capital have executed this
Second Amendment as of the day and year first above written.

                              iGATE CAPITAL CORPORATION


                              By:  ____________________________

                              Name:

                              Title:


                              GE CAPITAL EQUITY INVESTMENTS, INC.


                              By:  ____________________________

                              Name:

                              Title:

                                       9
<PAGE>

                       SUPPLEMENT TO DISCLOSURE SCHEDULE
                  SECOND AMENDMENT TO NOTE PURCHASE AGREEMENT

     This Supplement to Disclosure Schedule supplements, as of September 30,
2001, the schedules attached to the Note Purchase Agreement dated as of July 22,
1999 by and between iGate Capital Corporation (f/k/a Mastech Corporation) and GE
Capital Equity Investments, Inc., as amended by the First Amendment to Note
Purchase Agreement and Waiver dated as of August 1, 2000 and the letter
agreement dated as of November 27, 2000  ("Note Purchase Agreement").
Capitalized terms used but not defined herein have the meanings given to them in
the Note Purchase Agreement as amended by the Second Amendment to Note Purchase
Agreement dated as of September 30, 2001.
<PAGE>

                                  SCHEDULE 4.1


Options:

Borrower has granted stock options in its Common Stock.  The stock options
outstanding as of September 30, 2001 were:

     Number of shares subject to outstanding options:             3,341,367
     Number of shares reserved for options available for grant:   5,212,626

Conversion Rights:

          872,143 exchangeable non-voting shares of Quantum Information
Resources Ltd. are currently outstanding, which shares may be converted into
shares of Common Stock of the Borrower at any time prior to June 1, 2002.*

    *In connection with Borrower's purchase of Quantum Information Resources
     Limited, a Canadian corporation ("Quantum"), the selling shareholders
     received exchangeable non-voting shares of Quantum which convert into the
     Common Stock of  Borrower.  This was done in order to allow the selling
     shareholders to receive tax-free treatment for the transaction under
     Canadian tax laws.  In order to comply with the requirements for pooling of
     interest accounting, Borrower created a new class of preferred stock
     (Series A Preferred Stock) whose sole right is to permit the trustee to
     vote that number of shares of Common Stock equal to the number of non-
     voting shares held by the selling shareholders.
<PAGE>

                                  SCHEDULE 4.5
                                  SUBSIDIARIES

     A schedule of Subsidiaries is attached.

     The following Subsidiaries have adopted stock option plans pursuant to
which eligible participants may purchase shares of such subsidiaries' capital
stock:

          Innovative Resource Group, Inc.
          itiliti, Inc. (f/k/a Ex-tra-Net Applications, Inc.)
          eJiva, Inc.
          Mascot Systems Ltd.
          MobileHelix, Inc.
          Red Brigade Holdings Ltd.
          Symphoni Interactive, LLC
<PAGE>

                                SCHEDULE 4.7(c)
                             FINANCIAL STATEMENTS

     (a) Material obligations reflected in the unaudited consolidated balance
sheet of Company as at June 30, 2001 as filed with the SEC on August 14, 2001.

     (b) As of September 30, 2001 Borrower has repurchased 813,500 shares
of Common Stock pursuant to Borrower's Share Repurchase Program adopted
September 13, 1999.
<PAGE>

                                 SCHEDULE 4.12
                                OTHER VENTURES



1.  Limited Partnership Agreement of Highgate Venture Partners I, L.P. dated
    February 23, 2000, by and among Highgate Venture Management, LLC, as general
    partner, and David Whitmore, Ajmal Noorani and iGate Ventures, Inc., as
    limited partners.

2.  Limited Partnership Agreement of Highgate Ventures I, L.P. dated February
    24, 2000, by and among Highgate Venture Partners I, L.P., as general
    partner, and iGate Ventures, Inc., as limited partner.

3.  Limited Liability Company Agreement of Highgate Venture Management, LLC, by
    and among iGate Ventures, Inc., as the initial member, and David Whitmore
    and Ajmal Noorani, as the initial managers.

4.  Amended and Restated Limited Liability Agreement of Symphoni Interactive,
    LLC, by and between Symphoni Holdings, Inc. and Wolf Group (USA), Inc.

5.  Borrower has purchased stock in Air2Web, Inc. (23%) through iGate Holding
    Corporation.

6.  Borrower has purchased stock in the following entities through Highgate
    Ventures I, L.P.:

                    Bluewater Information Convergence, Inc.  (9%)

                    Brainbench, Inc.  (8%)

                    eNDP  (8%)

                    Escend Technologies, Inc.  (12%)

                    SpeechWorks International, Inc.  (less than 1%)

                    vCampus Corporation  (14.4%)

                    Versata, Inc.  (0.1%)

                    Xpede, Inc.  (3.8%)
<PAGE>

                                 SCHEDULE 4.13
                                     TAXES


          iGate Capital Corporation has signed a statute extension agreement for
the 1997 and 1998 payroll tax year.  This agreement extends the statute until
December 31, 2003.