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Chemistry (including Biochemistry)/Biochemistry Buffer Solution Help


Hi there! I have to prepare a solution for a biochemistry lab, and I'm not sure how to go about it. The instructions call for one Liter of  0.1 M Benzylamine in 16 mM Potassium Phosphate, pH 7.8. I'm guessing that I start by making two separate 16 mM solutions, one of Potassium Phosphate monobasic, the other dibasic, and add the monobasic to the dibasic until the pH meter reads 7.8? Then the benzylamine part...

So the MW of benzylamine is 107.15, so 0.1 M would be 10.71. Do I just treat the phosphate solution like water and add 10.71 g of benzylamine to a volumetric flask and fill the rest of the way to 1 L? If so, I'm not really sure how to measure a liquid in grams. Do I use the density of benzylamine (0.981 g/mL) to come up with the volume in mL (10.92 mL) and add 10.92 mL of benzylamine to the flask, then fill to 1 L, or do I tare the flask on the scale, then add 10.71 grams of benzylamine to the flask, then fill to 1 L?

Thanks for any help you can provide. I think I blew a circuit. I remember learning this stuff, but that was a decade ago and I'm verrry rusty!

Hi there Hannah. I've recently started teaching, and as such time just seems to vanish.

For buffers, there are two strategies that you can use.

One is to pick the buffer salt that has a pKA closest to your desired pH. Monobasic has a pKa of 6.8-7.2, so we'd start with that. Put enough salt in 90% of the eventual solution volume. Then weigh out benzylamine and add that to the solution. Stir up to dissolve, and then use the pH meter and NaOH or H3PO4 to adjust pH to final. Then add enough water to make up the final solution volume. (1L)

Two, take a gander at the Henderson-Hasselbalch equation.  Benzylamine has a pKa of 9.35 and would be the major species at 0.1M concentration.

pH = pKa + log {[base]/[acid])

pH = 9.35 + log {[.016/[0.1 M]}

pH = 9.35 + 0.795

pH = 10.14 as mixed

Then you could further use the HH eqn to calculate the approximate NaOH to add to get the pH you wanted. Since CO2 tends to dissolve in water, though, it's always a good idea to make up a solution in 90% volume and check and adjust the pH with your pH meter.  :)

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Trista Robichaud, PhD


No homework questions, especially ones copied and pasted from textbooks. I will answer questions about principles or give hints, but I do not do other's homework. I'm comfortable answering basic biochemistry, chemistry, and biology questions up to and including an undergraduate level of understanding. This includes molecular biology, protein purification, and genetics. My training/inclination is primarily in structural biology, or how the shapes of things affect their function. Other interests include protein design, protein engineering, enzyme kinetics, and metabolic diseases such as cancer, atherosclerosis, and diabetes. My chemistry weaknesses are that I do not know organic or inorganic synthesis well, nor am I familiar with advanced inorganic reactions. I will attempt quantum mechanics and thermodynamics questions, but primarily as they relate to biological systems. Furthermore, I cannot tell you if a skin photograph is cancerous, or otherwise diagnose any disease. I can tell you how we currently understand the basic science behind a disease state, but I cannot recommend treatment in any way. Please direct such questions to your medical professional.


I hold a PhD in Biomedical Science from the University of Massachusetts Medical School in Worcester. I specialize in Biochemistry, with a focus on protein chemistry. My thesis work involved the structure and functions of the human glucose transporter 1. (hGLUT1) Currently I am a postdoc working in peptide (mini-protein) design and enzymology at the University of Texas Health Science Center in San Antonio, Texas. I am in Bjorn Steffensen's lab (PhD, DDS), studying gelatinase A and oral carcinoma.

2001 American Association for the Advancement of Science
2007 American Chemical Society
2007 Protein Society
2011 UTHSCSA Women’s Faculty Association

Levine KB, Robichaud TK, Hamill S, Sultzman LA, Carruthers A. Properties of the human erythrocyte glucose transport protein are determined by cellular context. Biochemistry 44(15):5606-16, 2005. (PMID 15823019)
Robichaud TK, Appleyard AN, Herbert RB, Henderson PJ, Carruthers A “Determinants of ligand binding affinity and cooperativity at the GLUT1 endofacial site” Biochemistry 50(15):3137-48, 2011. (PMID 21384913)
Xu X, Mikhailova M, Chen Z, Pal S, Robichaud TK, Lafer EM, Baber S, Steffensen B. “Peptide from the C-terminal domain of tissue inhibitor of matrix metalloproteinases-2 (TIMP-2) inhibits membrane activation of matrix metalloproteinase-2 (MMP-2)” Matrix Biol. 2011 Sep;30(7-8):404-12. (PMID: 21839835)
Robichaud TK, Steffensen B, Fields GB. Exosite interactions impact matrix metalloproteinase collagen specificities. J Biol Chem. 2011 Oct 28;286(43):37535-42 (PMID: 21896477)

Poster Abstracts:
Robichaud TK, Carruthers. A "Mutagenesis of the Human type 1 glucose transporter exit site: A functional study." ACS 234th Meeting, Boston MA. Division of Biological Chemistry, 2007
Robichaud TK, Bhowmick M, Tokmina-Roszyk D, Fields GB “Synthesis and Analysis of MT1-MMP Peptide Inhibitors” Biological Chemistry Division of the Protein Society Meeting, San Diego CA 2010
Robichaud TK; Tokmina-Roszyk D; Steffensen B and Fields GB “Catalytic Domain Exosites Contribute to Determining Matrix Metalloproteinase Triple Helical Collagen Specificities” Dental Science Symposium. UTHSCSA 2011
Robichaud TK; Tokmina-Roszyk D; Steffensen B and Fields GB “Exosite Interactions Determine Matrix Metalloproteinase Specificities” Gordon Research Conference on Matrix Metalloproteinase Biology, Bristol RI 2011

Oakland University, Auburn Hills MI BS, Biochemistry 1998
University of Massachusetts Medical School, Worcester MA PhD, Biochemistry & Molecular Pharmacology 2001-2008
University of Texas Health Science Center, San Antonio TX Postdoc, Biochemistry 2009-Present

Awards and Honors
1998 Honors College Graduate, Oakland University
2009 Institutional National Research Service Award, Pathobiology of Occlusive Vascular Disease T32 HL07446
2011 1st Place, Best Postdoctoral Poster, Dental Science Symposium, UTHSCSA, April 2011

Past/Present Clients
Invited Seminars:
Robichaud TK, Fields GB. “Synthesis and Analysis of MTI-MMP Triple Helical Peptide Inhibitors” Pathology Research Conference, University of Texas Health Science Center San Antonio Pathology Department (June 18th, 2010)
Robichaud TK & Hill, B “How To Give A Great Scientific Talk” Invited Lecture, Pathobiology of Occlusive Vascular Disease Seminars, UTHSCSA (Nov 11th 2010), Cardiology Seminar Series, Texas Research Park (Feb 21st, 2011)
Robichaud TK; Tokmina-Roszyk D; Steffensen B and Fields GB “Exosite Interactions Determine Matrix Metalloproteinase Specificities” Gordon-Keenan Research Seminar “Everything You Wanted to Know About Matrix Metalloproteinases But Were Afraid to Ask” Bristol, RI (Aug 6th, 2011)

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