713 South Pear Orchard Road, Suite 102 Ridgeland, MS 39157

Exhibit 10.25

September 19, 2006

VIA E-MAIL

Mr. Darrell Dubroc, CEO

Vanguard Synfuels, LLC

P.O. Box 399

Pollock, LA 71467

Gentlemen:

First South Farm Credit, ACA (“First South”) has considered the request to release the existing six individual guarantors (the “Guarantor”) for Vanguards loans, and accept a guarantee of Diametrics Medical, Inc. (“DMED”). This is to advise that First South agrees to release the (six individual) Guarantors provided all of the following conditions are met, satisfied, and delivered to First South, on or before 4:00 p.m. CDT, Friday, September 29, 2006.

(1) DMED acquires 100% of the membership/ownership interest in Vanguard Synfuels, LLC, and satisfactory evidence thereof is furnished to First South;

(2) First South is furnished with a copy of the Articles and By-Laws of DMED, as amended, to date, along with a certificate of good standing from the State of its incorporation;

(3) Furnish evidence satisfactory to First South, in its sole discretion, of the cash investment of $7,000,000.00 in equity in DMED;

(4) Furnish a certified resolution of the board of directors of DMED acknowledging that Vanguard is a 100% owned subsidiary of DMED and that it serves a legitimate business purpose for DMED to unconditionally and in solido (jointly and severally) with Vanguard, guarantee the timely payment and performance of all indebtedness and obligations of Vanguard to First South, which resolution would also authorize a duly designated (named) officer to execute the continuing guaranty agreement in the form of Exhibit “A” hereto (the “Guaranty”) for any and all of the present and/or future indebtedness and obligations of Vanguard to First South. First South would also need to be furnished with Vanguard’s Board of Managers/Directors consent resolution authorizing a named official to enter into the amendment to the loan agreement, under such terms and conditions as said official deems appropriate.

(5) DMED would execute and deliver the Guaranty to First South.

(6) Vanguard and First South would execute and deliver a First Amendment to Loan Agreement in the form of Exhibit ‘B’ attached hereto.

(7) Upon timely satisfaction of the above conditions, First South will promptly (within 2 business days) deliver to an agent for Vanguard, DMED and each of the Guarantors (“Agent”), as set forth in the First Amendment to Loan Agreement, the original of each of the existing Guarantors guaranty agreements, each marked “Cancelled and Released.” The delivery of the original guaranty agreements will be made by sending each of the six original guaranty agreements by U.S Certified Mail addressed to Agent as set forth in the First Amendment to Loan Agreement.

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First South’s agreement to release the existing Guarantors is further conditioned upon all of the documents, documentation and supporting evidence required above to be satisfactory in form and substance to First South, in its sole discretion, and Vanguard shall promptly (on or before September 29, 2006) pay all costs and expenses related to the negotiation of this agreement and finalizing the proposed transaction, including paying First South’s attorney fees of $3,000.00. Failure to timely pay said sums shall be an Event of Default under the Loan Agreement. Finally, this proposal will expire and terminate unless Vanguard and DMED both accept this proposal in writing and return their signed acceptance to First South or on before 4:00 p.m. CDT Wednesday, September 20, 2006. Fax or electronic signatures will be deemed acceptable as originals, and the acceptance may be executed in multiple counterparts.

EXHIBIT “A”

CONTINUING GUARANTY

In consideration of FIRST SOUTH FARM CREDIT, ACA (“Creditor”) making loans or advances or otherwise giving credit to the above named debtor (“Debtor”), as Creditor and Debtor may from time to time agree upon, the undersigned guarantor (“Guarantor”), does hereby unconditionally and in solido with Debtor, guarantee to Creditor, its successors and assigns, and all future holder or holders of this Continuing Guaranty, which is hereby declared to be transferable, the prompt payment of all debts, obligations, and liabilities, whether direct, indirect, absolute, contingent, secured, or unsecured, (hereinafter collectively referred to some times as “Obligations”) which Debtor may now or at any time, or times, hereafter owe, or be liable to pay to Creditor, and Guarantor agrees to pay the same promptly when due and at all times thereafter, without notice or demand. Should Debtor be or become insolvent, then Guarantor agrees to pay all Obligations forthwith whether then due or not due.

Creditor may sell, pledge, assign, discount, rediscount, surrender, compound, release, renew, extend, forebear, alter, exchange, or otherwise deal with and/or dispose of any and all property, securities, collateral, endorsements and guaranties now or hereafter held by said Creditor as security, indemnity, or otherwise, upon such terms and conditions as Creditor in its sole discretion may deem advisable, and Creditor may, from time to time, make such changes in, renewals and extensions of time, mode and terms of payment of said Obligations of Debtor, and of the time, mode and terms of payment of all or any endorsements and guaranties of said Obligations made by others, as Creditor in its sole discretion may deem advisable; all without in any way affecting, limiting, or prejudicing the Creditor’s rights or the Guarantor’s liability under this Continuing Guaranty. Creditor is hereby irrevocably authorized and empowered at any and all times to impute or apply, as it may see fit, any payment or payments which may be made by Debtor or by others on Debtor’s Obligations.

This guaranty shall be a continuing guaranty, and shall remain in full force and effect until terminated by the Creditor’s receipt of 30 days prior written notice of its termination; but such termination shall not affect or impair said Guarantor’s liability hereunder as to any Obligations of the Debtor existing on the effective date of such termination, or as to any subsequent modifications, renewals, extensions or changes in the form or evidence of said existing Obligations, whether such Obligations are matured or not upon the effective date of termination. Such termination shall not affect Creditor’s right to release, modify or otherwise change the security or collateral Creditor may hold, or to release or modify the liability of any of the undersigned signor(s) or of any other surety or guarantor of Debtor’s Obligations it being agreed that Creditor may take such action in regard to such security or collateral or sureties or guarantors as Creditor in its sole discretion may deem advisable. It is further agreed that upon receipt of notice of termination, Creditor is under no obligation to take any steps to enforce or collect Debtor’s Obligations and Creditor’s failure to take any steps to enforce or collect Debtor’s Obligations shall not affect Guarantor’s liability herein for all Obligations of Debtor to Creditor as of the effective date of the termination or as to any renewals, extensions or modifications or changes in the form of evidence of those Obligations.

It is further agreed that the Guarantor’s liability under this Continuing Guaranty shall not be affected or impaired by any failure of Creditor to realize for any reason, upon any property, securities, collateral, endorsements or guaranties, nor by any alteration of any contract express or implied, nor by any change in Debtor, by death, dissolution, withdrawal, or otherwise, but Guarantor agrees to pay in any event the entire ultimate balance of Debtor’s Obligations (including principal, interest, attorney fees and costs of collection), now or hereafter due or owing by Debtor to Creditor. Creditor shall, at no time, and under no circumstances, be bound to resort to any collateral, securities, endorsements or guaranties now

or hereafter held by Creditor as security, indemnity, or otherwise, the undersigned Guarantor being bound to pay by this continuing Guaranty to the same extent as and in solido with Debtor, and said Guarantor specifically waives the right and the benefits of demanding division and discussion.

Guarantor hereby waives any formal acceptance and waives notice of the acceptance of this Continuing Guaranty by Creditor, and Guarantor also waives notice of any loans, advances, discounts, or credits that may be made to Debtor, it being the intention of Guarantor that Creditor shall have the right to make loans, advances, and discounts, and to give credit to the Debtor on the faith hereof without notice to Guarantor.

Guarantor hereby also waives notice of all defaults by said Debtor or others, and of all things now existing, or hereafter occurring in any dealings between or among Creditor, Debtor and others.

The liability of Guarantor for payment shall be in solido with Debtor, and as to each undersigned Guarantor, if there be more than one, each shall be and shall, remain obligated to Creditor in the full amount set forth herein. Creditor may obtain other guarantees for Debtor in whole or in part, and may release the guarantors or any of them in whole or in part without affecting the liability of any Guarantor under this Continuing Guaranty. Each of the undersigned signers waives and renounces as to each other and any other guarantors and/or sureties of Debtor’s Obligations, the right of demanding, and the benefits of, division and discussion.

This agreement, regardless where actually signed, shall be construed under and governed by the laws of the State of Louisiana and Guarantor consents to the personal jurisdiction of any federal or state court in Louisiana, if suit is filed to enforce this guaranty agreement.

In the event this Continuing Guaranty is referred to an attorney at law for collection by suit, or otherwise, Guarantor will also owe and pay reasonable attorney fees relating to such collection efforts.

THUS DONE, READ AND SIGNED in Los Angeles, California, on the 20^th day of September, 2006.

EXHIBIT “B”

FIRST AMENDMENT TO LOAN AGREEMENT

WHEREAS, Vanguard Synfuels, LLC (“Vanguard”) entered into a Loan Agreement with First South Farm Credit, ACA (“First South”) dated January 12, 2006, (the “Original Agreement”) and in which the six individual existing guarantors of the liabilities and obligations of Vanguard to First South intervened;

WHEREAS, as part of the sale of 100% membership interest in Vanguard to Diametrics Medical, Inc. (“DMED”), Vanguard has requested that First South release the original guarantors and accept DMED as a successor guarantor;

WHEREAS, First South has agreed to that release conditioned upon certain terms and conditions, including the execution of this First Amendment to Loan Agreement (the “Amended Agreement”);

NOW, THEREFORE, IT IS HEREBY AGREED as follows:

In the event of any conflict between the terms of this Loan Agreement and any of the other Loan Documents, the terms of such other Loan Documents shall control. Borrower and Lender agree that this Loan Agreement shall be governed by the laws of the jurisdiction listed in the address of Lender as shown on the first page of this Loan Agreement. The Loan is further subject to the following terms, covenants and special conditions.

Conditions Precedent: The following shall be conditions precedent to any obligation of Lender to make the Loan to Borrower:

Additional Covenants

Financial Covenants: The Borrower warrants and covenants to the following:

New Covenants

VI. No Novation. It is expressly agreed that this First Amendment does not constitute a novation of Vanguard’s existing obligations and/or any collateral and security for those obligations, except for the release of the original individual guarantors. Except as expressly and specifically modified herein, all of the terms and provisions of the Original Agreement remain in full force and effect.

VII. This agreement may be executed in multiple originals and fax and/or electronic signatures shall be deemed effective as originals.