Precipitating Sodium Chloride from its Solution. Description: When concentrated HCl is added to a saturated solution of sodium chloride, a white precipitate forms. When water is added to this mixture, the precipitate redissolves.

A precipitation reaction can occur when two solutions containing different salts are mixed, and a cation/anion pair in the resulting combined solution forms an insoluble salt; this salt then precipitates out of solution.

We used NaCl to make the saline solutions. Six drying experiments were performed with different concentrations of NaCl including 1, 2, 3, 4, 5, and 6 M (mole of NaCl/kg of water). At 30°C, the solubility limit of NaCl in water is 6.14 M.

Where more rain or snow falls over the ocean, it dilutes the salts in the seawater there. As a result, the water becomes fresher with time. If seawater becomes saltier, it may mean that rates of evaporation have increased or that precipitation has decreased over time.

If an insoluble salt forms by the reaction of soluble substances in water and falls out of solution, we call it a precipitate (see image). When a salt such as sodium chloride (table salt) dissolves in water, its ionic lattice is pulled apart so that the individual sodium and chloride ions go into solution.

At a very high ionic strength, protein solubility decreases as ionic strength increases in the process known as ‘salting-out’. Thus, salting out can be used to separate proteins based on their solubility in the presence of a high concentration of salt.

Salting out is typically used to precipitate large biomolecules, such as proteins or DNA. Because the salt concentration needed for a given protein to precipitate out of the solution differs from protein to protein, a specific salt concentration can be used to precipitate a target protein.

Desalting is used to remove salts from protein solutions, phenol or unincorporated nucleotides from nucleic acids or excess crosslinking or labeling reagents from conjugated proteins.

For 2D it is small dilution. You can also desalt your sample by ultrafiltration to 1 tenth of previous volume, that dillute again and repeat UF step. The best method for desalting is desalting by gel filtration against 50 mM buffer, than ultrafiltration (classical, not centrifugal).

The procedure I have used is to add 1/10 volume of 72% (w/v) TCA and 1/10 volume of 0.15% (w/v) sodium deoxycholate. Store the samples on ice for at least 10 minutes, then spin at 16,000 x g for 10 minutes. Remove the supernatant thoroughy, being very careful to avoid removing the pellet.

Leucine and lysine will be positively charged and will stick to the column. To elute leucine, raise the pH to around 6. To elute lysine, raise the pH to around 11. Gel-filtration chromatography is a useful method for removing salts, such as ammonium sulfate, from protein solutions.

Glutamic acid will be eluted first because the column pH is close to its pI. Leucine and lysine will be positively charged and will stick to the column. To elute leucine, raise the pH to around 6.

High temperature weakens the inherent bonds in protein. However, at very high salt concentration, the increased surface tension of water generates a competition between protein and salt ions for hydration. Salts strip off the essential layer of water molecules from the protein surface eventually denaturing the protein.

What technique is used to differentiate among several different amino acids? Serum protein electrophoresis is routinely performed on the serum obtained from a clotted blood specimen.

The Kjeldahl method was developed in 1883 by a brewer called Johann Kjeldahl. A food is digested with a strong acid so that it releases nitrogen which can be determined by a suitable titration technique. The amount of protein present is then calculated from the nitrogen concentration of the food.

The Kjeldahl technique is based on the quantification of the nitrogen content of protein. It is estimated that the average nitrogen content of protein is 16% of the total weight.

Terms in this set (49) The biuret method is the most commonly used method in the clinical laboratory to measure total serum protein. The peptide bonds of proteins react with biuret reagent containing Cu 2+ ions in an alkaline solution to form a blue-violet color.

The biuret method is based on the fact that proteins (and, as a rule, all substances containing two or more peptidic bonds) react with copper to form a colored complex whose absorption (λmax= 454 nm), in the presence of excess copper, is proportional to the amount of protein present.

Immunoglobulin G (IgG), the most abundant type of antibody, is found in all body fluids and protects against bacterial and viral infections. Immunoglobulin M (IgM), which is found mainly in the blood and lymph fluid, is the first antibody to be made by the body to fight a new infection.

69 Cards in this Set

Kjeldahl’s procedure for total protein is based upon the premise that	the nitrogen content of proteins is constant
which statement about the biuret reaction for total protein is true	polypetides & compounds w/ repeating imine groups react

Normal Results The normal range is 6.0 to 8.3 grams per deciliter (g/dL) or 60 to 83 g/L. Normal value ranges may vary slightly among different laboratories. Talk to your provider about the meaning of your specific test results.

Result: Biuret test positive: color changes to purple. all peptides and protein give the test positive.

Biuret Reagent The reagent turns violet in the presence of peptide bonds — the chemical bonds that hold amino acids together. The reagent’s copper ions, with a charge of +2, are reduced to a charge of +1 in the presence of peptide bonds, causing the color change.

purple

A negative result (lack of violet colour formation) may mean lack of protein, or the presence of free amino acids (without peptide bonds).

The biuret (IPA: /ˌbaɪjəˈrɛt/, /ˈbaɪjəˌrɛt/) test, also known as Piotrowski’s test, is a chemical test used for detecting the presence of peptide bonds. In the presence of peptides, a copper(II) ion forms mauve-colored coordination complexes in an alkaline solution.