Determination of free amine

The same authors described a method [19, 21] for measuring the free 

Weigh a lOg sample in a 250 ml beaker. Dissolve in 150 ml 50% aqueous propan-2-ol. Purge with a stream of nitrogen for 5 min and maintain purging during the titration. 

Neutralise to thymol blue with 0.1 M sodium hydroxide and add 1 ml excess. 

Insert pH electrodes and titrate with 0.1 M hydrochloric acid through two points of inflection. 

Carry out a blank experiment in exactly the same way, but omitting the sample. 

---

Akzo Chemie Method VE/2.010 Alkyldimethylbetaines Determination of free amine. 

Comite Europeen des Agents de Surface et leurs Inteimddiaires Organiques, Determination of free amine in amine oxides by TLC, CESIO/AIS Analytical Method 7-91, available from European Chemical Industry Council, Brussels. 

Arens, M., H. P. Wingen, Alkyldimethylbetaines—Determination of free amine—collaboration of the DGF. Communication 149 German standard methods for study of fats, fatty products, surfactants and related materials. Communication 115 Analysis of surface active materials XXIV (in German), Fett Wiss. TechnoL, 1995, 97,430-431. 

In a subsequent paper on the use of the Stille reaction to form biaryls,58 the reaction was carried out under ambient conditions to allow robotic automation of the process. Attachment of the tin species to resin was very straightforward, in that 4-tri-n-butylstannylphenyl acetic acid was linked to Rink amide resin simply using a DIC coupling. Loading of this species was determined by tin elemental analysis and correlated with a quantitative ninhydrin test of free amines remaining on the support (Scheme 24). 

While the determination of total lysine is rather straightforward, the determination of free or available lysine is more problematic. In this situation, the term free is meant to imply that the e-amine of the lysine side chain has not reacted with various components of the sample matrix (most commonly carbohydrates via Maillard browning). This is important because reaction of the e-amine can render lysine nutritionally unavailable and the nutritive value for that protein is then diminished if lysine is the limiting amino acid (which is often the situation with soy proteins). While enzymatic digestion in the human gut may not release the modified lysine in a nutritionally available state, often these lysine adducts are labile to the standard acid hydrolysis in 6N HC1 at 110°C. This results in total lysine values that overestimate the amount of nutritionally available lysine. 

Tartrazine was separated by ion-pair HPLC from its subsidiary dye 3-carboxy-5-hydroxy-1 -p-sulfopheny-4-phenylazo-pyrazole disodium salt (195) and from its intermediates sulfanilic acid and l-(4-sulfophenyl)-3-carboxy-5-hydroxypyrazolone (pyrazolone-T) by means of TBA hydroxide (194,212). Ion-pair chromatography was also used for the determination of free and bound nonsulfonated aromatic amines in tartrazine after reduction with dithionite, diazotization with sodium nitrite, and coupling with R-salt (202). 

The hydrolysis reaction is carried out in a sealed test-tube in 1 N hydrochloric acid at 150 °C for 8-16 h. The resulting solution is made basic and the mixture is then dansylated [156]. Triazines such as atrazine, simazine and propazine yield different combinations of free amines on hydrolysis, thus enabling their characterization using the fluorogenic labeling technique. The limits of detection range from 5 to 10 ng per spot. Concentrations of 0.05 ppm in food crops may be determined. 

We conclude this section with a discussion of inversion of amines of the type NR.jR.2R375>76). In general this process is too rapid to be studied except in special circumstances 100). Nevertheless, Saunders and Yamada 101 were able to determine the very high rate of inversion of dibenzylmethylamine (Fig. 50) (k = 2x 10s sec-1 at 25 °C) by the elegant trick of partially neutralizing the amine with hydrochloric acid. Since the hydrochloride cannot invert, the benzylic protons in it are diastereotopic and hence anisochronous. Only the small amount of free amine in equilibrium with the salt at a given pH (the measurements were carried out on the acid side) inverts at the rate indicated and it can be easily shown i01) that kobs. = k [amine]/[salt + amine] where kobs. is the observed rate of site exchange of the diastereotopic protons at... 

Figure 9 The effect of mild acid hydrolysis on N-NMR of HMW DOM. Nitrogen in HMW DOM is primarily amide (180 ppm), with smaller amounts of free amine (90 ppm). Treatment of HMW DOM with dilute hydrochloric acid increases the amount of amine and decreases the amount of amide. The decrease in amide equals the amount of acetic acid and amino acids released by hydrolysis of poly-N acetyl amino sugars and proteins. The relative amount of protein and amino sugar can be determined by the ratio of acetic acid to amino acids in the hydrolysis product.

Contrast agents in plasma may also be determined by spectrophotometric procedures (440,443) or by radiotracer techniques using or I-labeled materials (442-446). Felder et al. (447)measured the concentration of water-soluble radiopaques by colorimetric determination of free aromatic amine function using the Bratten-Marshall reaction. Hart-... 

Abalos, M., Bayona, J. M., and Ventura, F., Development of a SPE GC-NPD. Procedure for the determination of free volative amines in wastewater and sewage-polluted water. Anal Chem., 71, 3531-3537, 1999. 

Determination of free ethanolamine y ester amine and free fatty acid or glycerol... 

Free amine and amino acid. An aliquot of the original sample is titrated with perchloric acid in acetic acid solvent, with addition of mercuric acetate. This titration determines the sum of free amine, free amino acid, and chloride concentrations (140). Chloride is easily determined separately by ion chromatography or by silver nitrate titration. 

Secondary amines give only a monosubstituted product. Both of these reactions are thermally reversible. The product with ammonia (3,3, 3 -nitrilottispropionamide [2664-61-1C H gN O ) (5) is frequently found in crystalline acrylamide as a minor impurity and affects the free-radical polymerisation. An extensive study (8) has determined the stmctural requirements of the amines to form thermally reversible products. Unsymmetrical dialkyl hydrasines add through the unsubstituted nitrogen in basic medium and through the substituted nitrogen in acidic medium (9)). 

---