Aqueous extract analysis

The analysis of clinical samples is often complicated by the complexity of the sample matrix, which may contribute a significant background absorption at the desired wavelength. The determination of serum barbiturates provides one example of how this problem is overcome. The barbiturates are extracted from a sample of serum with CHCI3, and extracted from the CHCI3 into 0.45 M NaOH (pH 13). The absorbance of the aqueous extract is measured at 260 nm and includes contributions from the barbiturates as well as other components extracted from the serum sample. The pH of the sample is then lowered to approximately 10 by adding NH4CI, and the absorbance remeasured. Since the barbiturates do not absorb at this pH, the absorbance at pH 10 is used to correct the absorbance at pH 13 thus... 

Analysis of soils and sediments is typically performed with aqueous extraction followed by headspace analysis or the purge-and-trap methods described above. Comparison of these two methods has found them equally suited for on-site analysis of soils (Hewitt et al. 1992). The major limitation of headspace analysis has been incomplete desorption of trichloroethylene from the soil matrix, although this was shown to be alleviated by methanol extraction (Pavlostathis and Mathavan 1992). 

The floss silk from Chorisia speciosa furnished a polysaccharide with a main chain of (1 -> 4) linked P-Xylp substituted at 0-2 by 5 % of uronic acid. The xylan structure also was interposed with a-Rhap units in small amounts. The defatted seeds furnished on aqueous extraction a major fraction, ((9-acetyl, 10 % and protein, 45 %) wich was hydrolysed and analysed by p.c. and GLC, showing Rha (20 %), Ara (16 %), Gal (64 %) and also uronic acids (45 %). Partial hydrolysis gave rise to a polysaccharide free of arabinose, with 46 % of uronic acids. Methylation analysis (GLC -MS) indicated a chain of (1 4) - linked Gal/ (42 % of 2,3,6-Me3-Gal). 

Drugs have been purified by SPE in the analysis of amphetamine (AM) by Kaleta et al. [98], by various consecutive washing steps with hexane in the analysis of methamphetamine (MA) by Jones-Lepp and Stevens [99], and by simple centrifugation after addition of water, to separate the aqueous extract from a bottom sediment layer and a top fat layer, in the analysis of AM, MA, cocaine (CO), and benzoylecgonine (BE) by Langford et al. [100], who found little improvement in reducing matrix effects when applying SPE cleanup. 

Raggi et al. [21] described a spectrophotometric analysis method with ammonium tetrachloropalladate for penicillamine in pharmaceutical formulations. An aqueous solution of penicillamine (298 pg/mL) was treated with 1.5 mL of 20 mM (NH4)2PdCl4 in 1 M HC1. The mixture was diluted to 10 mL, and the absorbance measured at 403 nm after 20 min. The method has a recovery of 98.8%, and was used to determine penicillamine in aqueous extracts of capsules. 

Two ml of aqueous extract followed and the eluent discarded. Two additional ml of the plant extract were then passed through the Sep-Pak and retained for HPLC analysis. Histamine is not retained on the packing and will always remain in the liquid fraction. 

Among the numerous applications of SPE are separations of phenolic acids and flavonoids from wines and fruit juices. Sep-Pak Cig cartridges have been used for the fractionation of flavonol glycosides and phenolic compounds from cranberry juice into neutral and acidic parts before HPLC analysis. Antimutagenic flavonoids were identified in aqueous extracts of dry spinach after removal of lipophilic compounds by SPE. ... 

Electrical/Electronic Grade Epoxy. TGA and DSC analyses revealed no difference in thermal degradation below 200°C due to the presence of FR. DSC and EGA measurements showed that the FR breaks down above 350°C, in the range where it can perform its designated function. However, the EGA analysis did detect a small quantity of bromine-containing fractions below 200°C, and aqueous extraction revealed a fairly high Br concentration of 160 ppm. 

It has been recently reported (109) that use of both Penase and lactamase II hydrolysis and screening assays prior to chromatographic analysis can tentatively classify -lactams into three subgroups the first group includes a ceftiofur metabolite represented by desfuroyl-ceftiofur-cysteine the second, cephapirin and the third, penicillin G, ampicillin, amoxicillin, and cloxacillin. In this approach, portions of aqueous extracts of tissues are treated separately with Penase and lactamase II, and results are compared with those of untreated samples and positive controls. Bioactive ceftiofur metabolites are present, provided that the extracts retain inhibitory activity after Penase treatment but lose activity after lactamase II treatment and are positive in response to the immunochemical Lac-Tek-Cef test but negative to the Lac-Tek-Bl test (113). This approach can eliminate a large number of negative samples and, therefore, increases the efficiency of the assay. 

Flavan-3-ols are key precursors of the quality-determining black tea pigments known as theaflavins, theafulvins, and thearubigins (139). The stability of major theaflavins (theaflavin, theaflavin-3-gallate, theaflavin-3 -gallate, theaflavin-3, 3 -digallate) during automated HPLC analysis was also evaluated due to the concern about the instability of aqueous extract of black... 

Figure 2. The change in HAPS (as N Is), aluminium, and calcium concentrations after aqueous extraction. The analysis angle was 15°. U = uncoated surface C = coated surface W= the silanized surface after extraction with warm water at 50°C H = the silanized surface after extraction with hot water at IGO°C.

Osborne [3] has described a method for the determination of bromate in flour using aqueous extraction and photometric flow injection analysis. 

Titration is one of the most commonly employed techniques in wet analysis. Many routine analysis of wastewaters, potable waters, and aqueous extracts of sludges and soils can be effectively performed using various titrimetric techniques. 

Aqueous samples or aqueous extracts of nonaqueous samples directly injected onto a C-18 reverse phase column for HPLC analysis with UV detection at 195 nm (U.S. EPA Method 8316, 1992) mobile phase, water flow rate 2 mL/min pressure 38 atm. 

Solid samples extracted with water aqueous extract analyzed by HPLC-UV at 225 nm (see under Air Analysis below). 

---