Longer Digestion Times Research Articles

Rapid determination of chemical oxygen demand (COD) using focused microwave digestion followed by a titrimetric method.

water-pollution control analysis. It is closely related to the organic contamination level of a water or wastewater sample. The Cr-COD method is used as the standard in USA and Taiwan. Compared to Japanese Mn-COD method, it has a higher detection limit and severe chloride ion interference because of the stronger oxidant and the longer digestion time. In order to reduce the chloride-ion interference, the mercury salt (e.g. HgSO4) is usually added to mask the chloride ion. On the other hand, the closed reflux-titrimetric method is recommended by the Standard Method to reduce the large amount of hazardous waste.1 However, it still requires a long time (2 h) for the digestion step to be completed in this COD analysis, and the tolerance of the chloride ion interference is only up to 2000 mg Cl–/L. The objective of this research was to investigate the availability of a rapid procedure to determine the COD in water and wastewater by digesting samples in open vessels located in a focused microwave system followed by ferrous ammonium sulfate titration. The results obtained using this microwave system were also compared with those obtained by a closed reflux method described in the Standard Method.

Anatomy and physiology of the gastrointestinal tract of the Julia Creek dunnart, Sminthopsis douglasi (Marsupialia : Dasyuridae)

The gastrointestinal tract of the endangered Julia Creek dunnart (Sminthopsis douglasi), the largest member of the genus Sminthopsis, consists of a simple, unilocular stomach and an intestine of relatively uniform calibre throughout. There is no hindgut caecum, in common with other Australian carnivorous marsupials. Brunner’s glands form a collar at the proximal end of the duodenum; they consist of simple uncoiled tubes at Day 45 of pouch life but are well differentiated at Day 60, before the young take their first solid food at Day 65–70. Rate of passage of digesta was measured in nine adult Julia Creek dunnarts on diets of minced meat with either mealworm larvae or adult crickets added, using pulse doses of the solute marker Co–EDTA and large (0.5–1.0 mm) particles of plant cell walls mordanted with Cr. Transit time (time of first appearance in the faeces) of both markers (P < 0.001) and mean retention time (the average time markers are retained in the tract) of the solute marker (P < 0.05) were shorter on the diet containing mealworms than the cricket diet. These results suggest that emptying of the stomach (the main site of digesta retention in carnivores) was delayed on the cricket diet, possibly because of longer digestion times as a result of a tougher exoskeleton. Comparison with other data suggests that total tract passage times increase among dasyurids as body size increases.

Peptide map procedure using immobilized protease cartridges in tandem for disulfide linkage identification of neu differentiation factor epidermal growth factor domain

Immobilized proteolytic enzyme cartridges were used to rapidly digest neu differentiation factor EGF domain in order to obtain improved peptide maps useful for assignment of disulfide linkages. The procedure described here involves an on-line digestion of proteins using immobilized trypsin and endoproteinase Glu-C cartridges connected in series, followed by on-line RP-HPLC separation of the peptides. The entire process can be automated using a commercially available workstation; and the total time required for both proteolytic digestion and the HPLC separation can be shortened to within 1 h. Using these immobilized columns, we demonstrated that disulfide structure assignment of the EGF domains of recombinant human neu differentiation factor can be performed by isolation of individual disulfide-containing peptides followed by assignment of disulfide linkages with prompt fragmentation of peptides using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. The use of immobilized protease cartridges in tandem eliminates undesirable digestion artifacts associated with longer digestion time and higher protease-to-substrate ratio and results in the development of a reproducible and high quality peptide map.

Location of the Quinine-Dependent Epitope on Platelet Glycoprotein IlIa

Quinine-dependent (Q) IgG antibodies (Q.Ab) in drug-induced immune thrombocytopenia are heterogeneous and bind to different platelet surface glycoproteins (GP), namely GPIb, IX, IIb, IIIa and an unidentified 57-kDa membrane proteins. Although both the Q-dependent epitope on GPIIIa and the P1A1 antigen require intact disulphide bonds for their expression, they are distinct because Q.Ab bind to GPIIIa lacking P1A1. Epitopes for both antigens were examined on Western blots of either intact washed human platelets or purified GPIIIa. When intact platelets were digested with trypsin and washed and solubilised prior to electrophoresis, membrane-associated fragments of GPIIIa of 78 kDa were found to be reactive with both antibodies. In addition, 60- and 68-kDa fragments bound anti-P1A1 but not Q.Ab. Similar digestion with chymotrypsin produced only 60-kDa fragments containing both epitopes. Digestion of purified GPIIIa with chymotrypsin produced 60-kDa peptides reactive with Q.Ab and anti-P1A1 in immunoblotting studies. Similar digestion with elastase produced 58-kDa fragments also containing the epitopes for both antibodies. Longer digestion times or sequential digestion with different enzymes did not reveal extra fragments. However, immunoprecipitation of trypsin-digested 125I-labelled GPIIIa with affinity-purified Q.Ab produced a 17-kDa fragment containing the Q-dependent epitope.

An endodeoxyribonuclease of human KB cells. Purification and properties of the enzyme.

An endodeoxyribonuclease has been purified 750-fold from human KB cells. The purified endonuclease requires Mg2+ for maximum activity: Mn2+ was less than half as active and Ca2+ inhibited the reaction. The optimum pH is 8.8 in Tris-HCl and the optimum buffer concentration is 10 mM. KCl (and NaCl), --SH-reacting reagents, and tRNA strongly inhibit the reaction. An apparent molecular weight of 54,000 was determined by sedimentation in a glycerol gradient. The purified endonuclease cleaved native, double-stranded adenovirus 2 DNA, and the reaction proceeded stepwise during the initial stage of degradation by cleavage of the DNA substrate in half, then in half again, etc. At longer digestion times, single strand scissions were detected. RNA was not a substrate for the enzyme. Poly(dG) . poly(dC) was susceptible but poly(dA) . poly(dT) was resistant to degradation. Hydrolysis of adenovirus 2 DNA yielded double-stranded polynucleotides containing 5'-phosphoryl and 3'-hydroxyl termini with short, single-stranded regions presumably at the ends. More than 50% of the product of a limit digest had a chain length greater than 35 to 40 nucleotides. Analysis of the 5' and 3' end groups of the digestion products indicated a preference for the site of the enzymatic cleavage; thymidylic acid residues were present at the 5' end and deoxyguanosine residues at the 3' end, each with a frequency of 40 to 50%.

Determination of Phosphorus in Coal and Coke (I)

In this paper we describe an experimental studies on the direct determination of phosphorus in coal and coke by the wet oxidation technique, shown in ISO/TC 27-493 E. Informations obtained from our experiments are as follows:1) A significant correlation was observed between the times required for sample digestion and the ranks of coalification of samples. It means that higher rank coals need longer digestion times.2) The precision and accuracy of the wet oxidation method bear comparison with that of indirect methods.3) The required time for wet oxidation method is 1 to 4 hours and is more rapid than that of the indirect methods.4) The conditions for development of colour shown in ISO/TC 27-493 E should be improved as follows:Conditions for colour development ISO/TC 27-493 E Improved conditionQuantity of 5 N sodium hydroxide 7. 5ml 10mlQuantity of 5 N sulphuric acid: 8. 5ml 10mlQuantity of 1 % ammonium molibdate: 5ml 8mlQuantity 0.3 % hydrazine sulphate: 5ml 5mlStanding time in boiling water: 12min. 18mlThese improvements are effective to broaden the stable range of the colour developed.