Trace analysis of phosphates in small aqueous volumes

The indirect determination of trace amounts of phosphate through estimation of the molybdenum in the phosphomolybdic acid complex has been improved. The lower limit of spectrophotometric determination is about 0.10 μg

Application of ion-selective electrodes for the microdetermination of chlorine and bromine in volatile organic compounds

A method is described for the determination of chlorine and bromine in mg samples of highly halogenated volatile organic compounds. The samples are introduced into the combustion system by injection and burnt in a stream of oxygen at 1000° over platinum and quartz. The combustion gases are absorbed in a solution of 80% acetic acid containing some hydrogen peroxide, nitric acid and mercuric chloride or bromide. The halide is then titrated with mercury. The end-point is determined by an ion-specific electrode. One determination takes approximately 15 minutes. The relative standard deviation of the determination is about 1%. The reversibility and durability of the silver sulphide electrode are unaffected as long as the mercury ion concentration is less than 10−3M

Adjacent Channel Interference in UMTS Networks

One of the purposes of receive filtering in a Universal Mobile Telecommunication System (UMTS) handset receiver is to attenuate out-of-channel interference to provide channel selectivity. A UMTS handset receiver using a receive filter adaptive on out-of-channel interference level can be more computationally efficient than a handset with a fixed receive filter provided that the hand-set operates in low out-of-channel interference conditions often enough. The UMTS Adjacent Channel Selectivity (ACS) test case requires the adaptive receive filter to provide a worst case ACS of 33 dB. An adaptive receive filter is more computationally efficient than a fixed receive filter when the required ACS is less than 23 dB, because the added complexity of measuring the out-of-channel interference is compensated for by the reduction in the required number of filter taps to achieve the ACS. Measurements of the out-of-channel interference show that currently the interference levels for which the maximum ACS of 33 dB is required are hardly ever reached in practice. For the currently measured interference levels an adaptive receive filter will be computationally more efficient than a fixed\ud receive filter 97% of the time. However, the current out-of-channel interference measurements might be on the optimistic side, because the loads of the UMTS networks are low. When these loads increase in the future, the out-of-channel interference levels may increase and the advantage in computational efficiency of the adaptive receive filter will be reduced

The synthesis and characterization of polypeptide-adriamycin conjugates and its complexes with adriamycin. Part I

Poly(α-l-glutamic acid) (PGA) was grafted with amino acid and oligopeptide spacers up to 5 amino acids with the use of N,N'-carbonyldiimidazole and 2,3-dihydro-1,2-benz-isothiazole-3-on-1, 1-dioxide (saccharin) as an additive, and these polypeptides were characterized. The antitumor antibiotic adriamycin was covalently coupled via an amide bond onto PGA and onto the grafted polymers with the use of N-ethoxycarbonyl-2-ethoxy-1, 2-dihydroquinoline (EEDQ); these conjugates were characterized. The conjugates containing Gly—Gly—l-Leu spacer arms did yield free adriamycin upon digestion with papain. Adriamycin gave fairly stable complexes with PGA—adriamycin and branched poly peptide—adriamycin conjugates; these complexes were characterized

Characterization of new membrane materials by means of fouling experiments Adsorption of bsa on polyetherimide-polyvinylpyrrolidone membranes

The hydrophilicity of polyetherimide-polyvinylpyrrolidone (PEI-PVP) microfiltration membranes can be adjusted by means of a suitable post-treatment. The influence of the nature of the membrane surface on fouling properties was studied using permeation experiments before and after exposure to a protein (BSA) solution and adsorption experiments with 14C labelled BSA. A correlation between the permeation experiments and the radiolabelled BSA adsorption experiments was found. The PVP in the membrane matrix prevents BSA adsorption taking place to a large extent and it appeared that heat-treated PEI-PVP membranes showed the same nonfouling behaviour as, for example, cellulose acetate membranes

Optimization of macromolecular prodrugs of the antitumor antibiotic adriamycin

In our earlier work [10] on aminoribosyl-bound prodrugs of adriamycin (ADR) using poly(α-l-glutamic acid) (PGA) grafted in high yield (90–100 mol.%) with various peptide spacers as a plasma-soluble macromolecular carrier we observed rather low cytotoxic activities in L1210 leukemia and B16 melanoma in vitro assays. These results may be tentatively explained by a decreased susceptibility of the spacer-bound adriamycin moiety to hydrolysis by lysosomal enzymes due to the high spacer load. This hypothesis was tested by the study of two conjugates prepared by a different route. Peptide conjugates of adriamycin (Gly-Gly-Leu—ADR and Gly-Gly-Gly-Leu—ADR) were synthesized using the trityl N-protecting group and were coupled to PGA in 4.5 mol.% load according to the method described earlier [11]. However, these conjugates were almost totally devoid of cell growth-inhibiting activity in L1210 and B16 in vitro tests. The data suggest that either the uptake of the polymeric prodrugs into the cell by pinocytosis is highly dependent on spacer load or molecular weight, or that lysosomal digestion is too slow for efficient release of ADR. Possibly, enzymatic degradation of PGA which is known to occur only between pH 4 and 6 is rate-limiting for release of the drug. Current studies include the enzymatic degradation of PGA—peptide spacer—drug systems using p-nitroaniline as a model drug and papain as the enzyme. By variation of the length and load of spacer it can be estimated under which conditions the release of drug (using UV spectrometry) is faster than degradation of the polymer (as determined by viscometry). In addition, the uptake of PGA and derivatives with a fluorescent label into tumor cells is studied using laser flow cytometry and laser microscopy

Biodegradable hollow fibres for the controlled release of drugs

Biodegradable hollow fibres of poly-l-lactic acid (PLLA) filled with a suspension of the contraceptive hormone levonorgestrel in castor oil were implanted subcutaneously in rats to study the rate of drug release, rate of biodegradation and tissue reaction caused by the implant. The in vivo drug release was compared with the release in vitro using different release media. Fibres, disinfected with alcohol showed a zero-order release, both in vitro and in vivo, for over 6 months. Fibres, either γ-sterilized or disinfected with alcohol were harvested at time intervals ranging from 1 d to 6 months after implantation. Molecular weights of PLLA, tensile strengths, and remaining amounts of drug were determined as a function of time.\ud \ud The tissue reaction can be described as a very moderate foreign body reaction with the initial presence of macrophages, which are gradually replaced by fibroblasts which form a collagen capsule. Molecular weight determinations of PLLA showed a decrease from an initial Mw of 1.59x10 5 to 5.5 × 10 4 in 4 months (after alcohol sterilization). A gradual decrease in fibre strength with time was observed which did not significantly impair the release rate of levonorgestrel