Biomedical subjects

G Seeber

Publications and source records attributed to G Seeber.

7 recordsLinked to original sources

PubMed2000

Quantification of lanthanides in rocks using succinic acid-derivatized sorbents for on-line SPE-RP-ion-pair HPLC

The use of new poly(norbornene-block-7-oxanorborn-2ene-5,6-dicarboxylic acid)-coated silica-based sorbents as well as of beaded polymers based on poly(norborn-2-ene-5,6-dicarboxylic acid-co-1,4,4a,5,8,8a-hexahydro-1,4,5,8-exo-endo-dimethanonaphthalene) for the on-line preconcentration of lanthanides from rock digests and their subsequent RP-ion-pair HPLC separation is described. Block co-polymers of norborn-2-ene and 7-oxanorborn-2-ene-5,6-dicarboxylate used for coating were prepared by ring-opening metathesis polymerization (ROMP) and poly(norborn-2-ene-5,6-dicarboxylic acid-co-1,4,4a,5,8,-8a-hexahydro-1,4,5,8-exo-endo-dimethanonaphthalene)-based polymer beads were prepared by ring-opening metathesis precipitation polymerization. Both types of sorbents exhibit an extraordinarily good pH stability, are hydrophilic and therefore easily wetable by water alone, and show high extraction efficiencies for lanthanides within a pH of 3.5-5.5. The rare earth element (REE) content in the investigated rocks varied over 3 orders of magnitude (0.19-108 microg/g). REE concentrations prior to enrichment were typically in the range of 1-25 ng/mL; the total amount of each REE sorbed onto the precolumn was in the range of 8-270 ng. Extraction selectivities of the sorbent may be enhanced by adding 5-sulfosalicylic acid as a masking agent for iron and aluminum as well as methanol as an inhibitor for the precipitation of o-silicic acid. Gradient elution of the lanthanides from the precolumn and their subsequent separation on a RP-C18 column was achieved using hydroxyisobutyric acid (HIBA) and sodium octanesulfonate. Depending on the actual concentration of the lanthanides in the digests and in order to suppress interfering cations, UV detection was carried out with two different postderivatization reagents, 4-(2-pyridylazo)resorcinol (PAR) and arsenazo III. The high selectivity in enrichment as well as the complementary use of post-derivatization reagents allows the fast, quantitative, and highly reproducible quantification of REEs present in rocks by complete removal or suppression of all other interfering components. Thus, recoveries were found to be within a range of 97-103% for most REEs with relative standard deviations of 2-5%.

Journal Article↗

PubMed1998

Determination of airborne, volatile amines from polyurethane foams by sorption onto a high-capacity cation-exchange resin based on poly(succinic acid).

A high-capacity carboxylic acid-functionalized resin prepared by ring-opening metathesis polymerization based on cross-linked endo,endo-poly(norborn-2-ene-5,6-dicarboxylic acid) was used for the sampling of volatile, airborne amines from polyurethane (PU) foams. Six tertiary amines which represent commonly used promotors for the formation of PUs from diisocyanates and polyols, namely pentamethyldiethylenetriamine, diazabicyclooctane, N-methylmorpholine, N-ethylmorphine, 1,4-dimethylpiperazine and N,N-dimethylethanolamine, were sorbed onto the new resin. The sorption behavior of the new material was investigated in terms of loading capacities, the influence of concentration, flow-rate as well as of the amount of resin. Breakthrough curves were recorded from each single component as well as of mixtures thereof. Finally, the resin was used for the sampling of amines evaporating from PU foams applied in buildings. Further information about time dependent concentration profiles were obtained using a combination of GC-MS and Fourier transform IR spectroscopy.

Adsorption↗

PubMed1991

[Tumor recurrence at the neck in papillary thyroid gland cancer. A statistical analysis of the recurrence probability after radical surgery].

308 cases of papillary thyroid carcinoma (82.6% of our patients operated on between 1952 and 1987) who had undergone potentially curative surgery were analysed postoperatively. The follow-up ranges from 1 month to 29.4 years (median 4.58 years). In 32 cases (10.4%) a cervical tumour recurrence (local recurrence and/or cervical lymph nodes) was found. 8 of these are not free of tumour at the end of the follow-up, 6 had died of thyroid carcinoma (case fatality rate 18.8%, mortality rate 66.7%, in the entire material 2.9% and 29.0% respectively). The cumulative recurrence rate is 9.98% after 5 years and 16.98% after 10 years. A statistical analysis of the probability of recurrence was carried out only for patients who could be followed at least 5 years or those who died within 5 years. Age, sex, stage of tumour and histological criteria were taken into account as statistical variables. The state of cervical lymph nodes, the differentiation of the tumour and the patients' sex turned out to be determining factors for tumour recurrence after 5 years. In order to improve the recurrence rate a differentiated surgical radicality, depending on the above mentioned variables, is recommended.

Adolescent↗

PubMed1987

Stage T1, grade 3 transitional cell carcinoma of the bladder: an unfavorable tumor?

Transurethral resection only was performed in 172 patients with initial stage Ta, T1 transitional cell carcinoma of the bladder. Additional treatment during the course of disease was given to 9 patients with carcinoma in situ and to 8 patients with tumor progression. The mean followup was 106 months. The 10-year survival rates were 95 per cent for patients with stage Ta, grade 1 disease, 89 per cent for stage Ta, grade 2, 84 per cent for stage Ta, grade 3, 78 per cent for stage T1, grade 2 and 50 per cent for stage T1, grade 3. The percentage of first tumor recurrence at the same site increased with tumor grade (stage T1, grade 3 was 74 per cent). The recurrence rate in stage T1, grade 3 tumors (4.08) differed significantly from the other groups of superficial tumors. The tumor progression rate for stage T1, grade 3 tumors (32.5 per cent) was significantly higher as well. The characteristics of stage T1, grade 3 tumors with and without progression were different in regard to multiplicity, recurrence rate, mean interval to recurrence and type of tumor invasion. Of the 13 patients who died of progressive neoplastic disease 11 presented initially with stage T1, grade 3 tumors. When these results are considered it is obvious that a patient with a stage T1, grade 3 tumor deserves additional therapy, such as chemotherapy, immunotherapy or phototherapy.

Aged↗

PubMed1985

[Differentiated thyroid carcinoma in an endemic area. Clinical aspects, prognosis, therapeutic considerations].

A retrospective analysis was undertaken of 179 cases of differentiated thyroid carcinoma (89 follicular and 90 papillary; first operations 1952-1977). At the time of the diagnosis there was no significant difference between the two types of malignancy as to age, sex, stage of tumour and degree of local radical operation. Nor was there any difference as to clinical course, but for papillary carcinoma the recurrence rate was higher and the survival time significantly shorter. Simple histological classification as to type did not help in prognosis. Compared with published reports, the unfavourable course of papillary carcinoma can be explained by the high proportion of haematogenous metastasizing tumours and the great prognostic significance of distant metastases, especially with papillary carcinoma. The differences in prognosis of other clinical examinations is ascribed to the broad spectrum of tumour-biological aggressivity which hides under the expression "differentiated carcinoma". Our results underline the need to take into account different clinical and histopathological influences which differ for each tumour type.

Carcinoma↗

PubMed1984

[Follicular thyroid cancer. A multivariate analysis].

The prognosis of malignant tumors is determined by a number of factors and their interaction. These factors may be assessed statistically by means of regression models for the hazard rates, which are assumed to be proportional. 89 follicular thyroid cancers from 1952 to 1975 were analysed according to clinical, macropathological and special histological criteria. Those variables which significantly influence the survival function were defined precisely and quantified by multivariate analysis. The age of the patients at the time of diagnosis (primary operation), sex, and local tumor extent (and therefore radical surgery) proved to be prognostically significant. Thus, the TNM system alone is sufficient neither for individual prognostic pronouncements nor for forming risk groups.

Adenocarcinoma↗

PubMed1984

[Papillary thyroid cancer--prognosis and prognostic factors].

90 papillary thyroid carcinomas (operated on between 1952 and 1977) were retrospectively analysed. The median follow-up is 5.29 years (range 0.08-29.42 years). After the primary operation only 68.9% of all patients may be classified as "tumor free". The lethality rate from thyroid cancer is 28.9%, the cumulative survival rates at 10 and 20 years are 50.92% and 32.06%, respectively. Thus survival is not significantly different from the one of our follicular carcinomas. The whole material was characterized thoroughly by clinical and morphological parameters. The simultaneous examination of the variables as to their prognostic relevance was performed by means of a log-logistic regression model for survival data. Age, extension of primary tumor, vascular invasion and presence of colloid determined prognosis. For the histopathological practice a differentiation between vascular and lymphatic invasion is demanded.

Adolescent↗