Matrix acidified

As with urine, saliva (spumm) is easy to collect. The levels of protein and lipids in saliva or spumm are low (compared to blood samples). These matrices are viscous, which is why extraction efficiency of xenobioties amoimts to only 5 to 9%. By acidifying the samples, extraction efficiencies are improved as the samples are clarified, and proteinaceous material and cellular debris are precipitated and removed. Some xenobioties and their metabohtes are expressed in hair. Hair is an ideal matrix for extraction of analytes to nonpolar phases, especially when the parent xenobioties are extensively metabolized and often nondetectable in other tissues (parent molecules of xenobioties are usually less polar than metabolites). Hair is a popular target for forensic purposes and to monitor drug compliance and abuse. Human milk may be an indicator of exposure of a newborn to compounds to which the mother has been previously exposed. The main components of human milk are water (88%), proteins (3%), lipids (3%), and carbohydrates in the form of lactose (6%). At present, increasing attention is devoted to the determination of xenobioties in breath. This matrix, however, contains only volatile substances, whose analysis is not related to PLC applications. 

What is the reason for the overwhelming acceptance of stationary phases based on high-purity silicas in the pharmaceutical industry The answer is simple superior peak shapes for analytes with basic functional groups, which has been a problem with older phases. The older, low-purity silicas contain metal ions buried in the matrix of the silica. These contaminants acidify the surface silanols, and the consequence is a strong and non-uniform interaction with basic analytes. This in turn results in tailing peaks, which is an impediment for accurate peak integration and peak resolution. Of course, adding appropriate additives, such as amine modifiers, to the mobile phase can solve these difficulties. But this is an unnecessary and undesired complication in methods development. Therefore, silicas that are free from this complication are much preferred. 

Not surprisingly, the use of acidified water increased the level of fluoride release from the glass, and this effectively models what happens in a setting cement. The acid-base reaction between the glass and the water-soluble polymeric acid liberates fluoride from the glass, causing it to move to the matrix, from where it is gradually leached as the cement releases fluoride [227,228]. 

Liquid-liquid partitioning cleanup on a hydrophilic matrix can also be employed for purification of the primary sample extract. This procedure was only applied in the determination of zearalenone and its metabolites in milk using a Chem Elut disposable column to partition an acidified aqueous milk extract into dichloromethane (430). 

Catalytic reforming Pt, Pi-Re or Pt-Sn on acidified A1203 or on zeolite in matrix (adiabatic, fixed beds, or moving bed, with interstage heating)... 

Tecator [3] has described a flow injection method for the determination of 0.5 -100 mg/1 aluminium in 0.1M potassium chloride extracts of soils in which the acidified soil extract is injected into a carrier stream which has the same composition as the sample matrix, (i.e., 0.1 M KC1) and merged with a masking... 

Aqueous samples are extracted with diethyl ether while soils, sediment, and solid wastes are extracted with acetone and diethyl ether. Prior to extraction, the sample is acidified with HC1 to a pH below 2. Such acidification is necessary due to the fact that in nature or in the environmental matrix, herbicides may occur as acids, salts, or esters. Acidification converts all these forms into chlorophenoxy acids. 

Immediately add a droplet of 0.2 piL of a saturated solution of matrix 4HCCA in 50% acetonitrile in acidified water. 

Analytical methods used for determining DNOC in environmental samples are given in Table 6-2. Most of the methods for products, waters, soils, and sludges rely on extraction of DNOC from an acidified matrix acidification minimizes dissociation of the phenolic hydrogen and thus facilitates extraction into an organic solvent or adsorption onto a solid phase extraction medium. The influence of pH on the adsorption of DNOC to humic materials in coal waste waters has been studied (Porschmann and Stottmeister 1993) and significant adsorption was found to occur at pH 7 but not... 

The electronic absorption spectrum of the cation-radical of thiophene itself has been observed following low-temperature y-radiolysis of the heterocycle in a Freon matrix.The radical has also been implicated in the oxidation of thiophene by dibenzoyl peroxide it is believed to be formed at the contact of certain transition metal layer-silicates with thiophene.The anodic oxidation of 2,5-dimethylthiophene has been studied by Japanese workers who found strong evidence for the formation of the cation-radical as the primary oxidation product.In the presence of strong nucleophiles such as cyanide ion, the cation-radical undergoes nucleophilic attack before further oxidation. In the presence of more basic species such as acetate ion, the cation-radical is deprotonated to give a thienylmethyl radical which undergoes further reaction. The results were compared with similar observations for the oxidation of 2,5-dimethylfuran. Czech workers have also studied the anodic oxidation of substituted thiophenes. This work has focused on the preparative value of anodic oxidations in acidified methanol. Cation-radical formation is implied for the primary step, but the value of the method lies in the fact that sulfur is ultimately eliminated from the substrate and functionalized y-dicarbonyl compounds result. 

M Corp. developed the Empore Strontium Rad Disks allowing the fixing of strontium by simple filtration of the water sample. No preconcentration step is required. Samples are acidified in 2-4 M nitric acid. Recoveries greater than 85 % have been observed for filtered volumes up to 3 These disks contain a strontium-selective crown ether extractant bonded to a solid silica support inserted in an inert PTFE matrix. ... 

---