Biomedical subjects

C Schneider

Publications and source records attributed to C Schneider.

At least 73 records · Page 4Linked to original sources

PubMed2001

Caspase-2-induced apoptosis is dependent on caspase-9, but its processing during UV- or tumor necrosis factor-dependent cell death requires caspase-3.

Mammalian caspases are a family of cysteine proteases that plays a critical role in apoptosis. We have analyzed caspase-2 processing in human cell lines containing defined mutations in caspase-3 and caspase-9. Here we demonstrate that caspase-2 processing, during cell death induced by UV irradiation, depends both on caspase-9 and caspase-3 activity, while, during TNF-alpha-dependent apoptosis, capase-2 processing is independent of caspase-9 but still requires caspase-3. In vitro procaspase-2 is the preferred caspase cleaved by caspase-3, while caspase-7 cleaves procaspase-2 with reduced efficiency. We have also demonstrated that caspase-2-mediated apoptosis requires caspase-9 and that cells co-expressing caspase-2 and a dominant negative form of caspase-9 are impaired in activating a normal apoptotic response and release cytochrome c into the cytoplasm. Our findings suggest a role played by caspase-2 as a regulator of the mitochondrial integrity and open questions on the mechanisms responsible for its activation during cell death.

Amino Acid Substitution↗

PubMed2001

T-cell activation by recombinant receptors: CD28 costimulation is required for interleukin 2 secretion and receptor-mediated T-cell proliferation but does not affect receptor-mediated target cell lysis.

Recombinant T-cell receptors with antibody-like specificity are successfully used to direct CTLs toward a MHC-independent immune response against target cells. Here we monitored the specific activation of receptor grafted CTLs in the context of CD28 costimulation. Peripheral blood T cells were retrovirally engrafted with recombinant anti-CD30 and anti-carcinoembryonic antigen receptors, respectively, that harbor either the Fc epsilonRI-gamma or the CD3-zeta intracellular signaling domain. Cross-linking of recombinant receptors by solid-phase bound ligand, i.e., CD30 and a carcinoembryonic antigen receptor-specific anti-idiotypic antibody, respectively, induces IFN-gamma secretion that is further enhanced by CD28 costimulation of grafted T cells. Induction of interleukin (IL)-2 secretion, in contrast, requires CD28 costimulation in addition to receptor cross-linking, irrespective of T-cell preactivation by anti-CD3 monoclonal antibody plus IL-2 or by anti-CD3 monoclonal antibody plus anti-CD28 monoclonal antibody. Accordingly, induction of IL-2 secretion upon receptor cross-linking by membrane-bound antigen requires CD28/B7 costimulation whereas IFN-gamma secretion and cell proliferation does not. The efficiency of cytolysis by receptor-grafted CTLs does not depend on and is not affected by CD28 costimulation. The data demonstrate that CTL proliferation, cytokine secretion, and cytolysis upon receptor cross-linking are differentially modulated by CD28 costimulation and that cytolysis does not require B7 expression on target cells.

Animals↗

PubMed2001

Structure of a Bag/Hsc70 complex: convergent functional evolution of Hsp70 nucleotide exchange factors.

Bag (Bcl2-associated athanogene) domains occur in a class of cofactors of the eukaryotic chaperone 70-kilodalton heat shock protein (Hsp70) family. Binding of the Bag domain to the Hsp70 adenosine triphosphatase (ATPase) domain promotes adenosine 5'-triphosphate-dependent release of substrate from Hsp70 in vitro. In a 1.9 angstrom crystal structure of a complex with the ATPase of the 70-kilodalton heat shock cognate protein (Hsc70), the Bag domain forms a three-helix bundle, inducing a conformational switch in the ATPase that is incompatible with nucleotide binding. The same switch is observed in the bacterial Hsp70 homolog DnaK upon binding of the structurally unrelated nucleotide exchange factor GrpE. Thus, functional convergence has allowed proteins with different architectures to trigger a conserved conformational shift in Hsp70 that leads to nucleotide exchange.

Adenosine Diphosphate↗

PubMed2001

Detection and cellular localization of 12R-lipoxygenase in human tonsils.

Formation of the 12R-lipoxygenase product, 12R-hydroperoxyeicosatetraenoic acid (12R-HPETE), has been detected previously only in human skin (Boeglin et al. (1998) Proc. Natl. Acad. Sci. USA 95, 6744). The unexpected appearance of an EST sequence (AA649213) for human 12R-lipoxygenase from germinal center B lymphocytes purified from human tonsils prompted our search for the existence of the enzyme in this novel source. Incubation of [1-14C]arachidonic acid with homogenates of human tonsillar tissue yielded mixtures of radiolabeled 12-HETE and 15-HETE. Stereochemical analysis showed varying ratios of 12S- and 12R-HETE, while 15-HETE was exclusively of the S-configuration. Using stereospecifically labeled [10S-3H]- and [10R-3H]arachidonic acid substrates we detected pro-R hydrogen abstraction at carbon 10 associated with formation of 12R-HETE. This mechanistic evidence implicates a 12R-lipoxygenase in the biosynthesis of 12R-HETE. The mRNA for the enzyme was identified in tonsils by RT-PCR and Northern analysis. The cellular distribution was established by in situ hybridization. Unexpectedly, hybridization was not observed in the lymphocytes of the germinal centers. Specific reaction was restricted to squamous epithelial cells, including the epithelium lining the tonsillar crypts. In this location the 12R-lipoxygenase might help regulate differentiation of the epithelium or participate in lymphocyte- epithelial cell interactions.

12-Hydroxy-5,8,10,14-eicosatetraenoic Acid↗

PubMed2001

Biogenesis of volatile aldehydes from fatty acid hydroperoxides: molecular cloning of a hydroperoxide lyase (CYP74C) with specificity for both the 9- and 13-hydroperoxides of linoleic and linolenic acids.

A novel member of the plant cytochrome P450 CYP74 family of fatty acid hydroperoxide metabolizing enzymes has been cloned from melon fruit (Cucumis melo). The cDNA is comprised of 1,446 nucleotides encoding a protein of 481 amino acids. The homology at the amino acid level to other members of the CYP74 family is 35-50%, the closest relatives being allene oxide synthases. The cDNA was expressed in Escherichia coli, and the corresponding protein was purified by affinity column chromatography. The native enzyme showed a main Soret band at 418 nm, indicative of a low spin ferric cytochrome P450, and a 447-nm peak appeared in the CO-difference spectrum. Using [U-14C]radiolabeled substrate, HPLC, UV, and GC-MS, the products of conversion of 9S-hydroperoxy-linoleic acid were identified as 9-oxo-nonanic acid and 3Z-nonenal. Kinetic analysis of this hydroperoxide lyase showed the highest rate of reaction with 9-hydroperoxy-linolenic acid followed by 9-hydroperoxy-linoleic acid and then the corresponding 13-hydroperoxides. Overall, the newly characterized cytochrome P450 enzyme is a fatty acid hydroperoxide lyase with a preference, but not absolute specificity for the 9-positional hydroperoxides of linoleic and linolenic acids.

Aldehyde-Lyases↗

PubMed2001

Interleukin 1 beta (IL-1 beta) action in porcine thyroid cells involves the ceramide signalling pathway.

Interleukin 1 beta (IL-1beta) is often associated with thyroidal autoimmune diseases. This cytokine has been largely described to trigger an important biological signalling pathway: the sphingomyelin/ceramide pathway. In this report we show that IL-1beta induces ceramide formation and sphingomyelin degradation in porcine thyroid cells via the activation of a neutral sphingomyelinase. Among the potential targets of IL-1beta and ceramides action, we have investigated the role of an atypical protein kinase C (PKC), the PKC zeta. We show that both IL-1beta and ceramides lead to an increase of PKCzeta activity. All these results suggest an important role for ceramides and IL-1beta in regulation of thyroid function, leading to cell survival or to apoptosis.

Animals↗

PubMed2001

CD30-mediated cell cycle arrest associated with induced expression of p21(CIP1/WAF1) in the anaplastic large cell lymphoma cell line Karpas 299.

One of the major characteristics of anaplastic large cell lymphomas (ALCL) is the expression of the Ki-1/CD30 antigen. While the receptor mediates NF-kappaB-activation in Hodgkin's lymphomas, some data suggest the CD30-mediated apoptosis of other CD30-expressing cells. We were able to demonstrate that activation of CD30 leads to different effects regarding cell proliferation of the ALCL-derived cell lines Karpas 299 and JB6. Western and Northern blotting analysis revealed that CD30-induced growth inhibition of Karpas 299 cells correlated with a strong upregulation of the cell cycle inhibitor p21(CIP1/WAF1). We found a non activating point mutation at codon 273 in exon 8 of the p53 gene in Karpas 299 cells which indicates an p53-independent mechanism for induced p21 expression. Abundant p21 protein expression resulted in hypophosphorylation of the retinoblastoma protein (Rb) and inhibition of the proliferating cell nuclear antigen (PCNA). CD30-stimulated cells showed no indications of apoptotic cell death, like genomic DNA fragmentation or cleavage of the caspase-3 target protein poly (ADP-ribose) polymerase (PARP). Our results indicate that CD30 is able to mediate an p21-associated cell cycle arrest in ALCL with possible implications for prognosis and clinical treatment.

Antibodies↗

PubMed2001

Molecular dynamics simulation reveals conformational switching of water-mediated uracil-cytosine base-pairs in an RNA duplex.

A 4 ns molecular dynamics simulation of an RNA duplex (r-GGACUUCGGUCC)(2 )in solution with Na+ and Cl- as counterions was performed. The X-ray structure of this duplex includes two water-mediated uracil-cytosine pairs. In contrast to the other base-pairs in the duplex the water-mediated pairs switch between different conformations. One conformation corresponds to the geometry of the water-mediated UC pairs in the duplex X-ray structure with water acting both as hydrogen-bond donor and acceptor. Another conformation is close to that of a water-mediated UC base-pair found in the X-ray structure of the 23 S rRNA sarcin/ricin domain. In this case the oxygen of the water molecule is linked to two-base donor sites. For a very short time also a direct UC base-pair and a further conformation that is similar to the one found in the RNA duplex structure but exhibits an increased H3(U)...N3(C) distance is observed. Water molecules with unusually long residence times are involved in the water-mediated conformations. These results indicate that the dynamic behaviour of the water-mediated UC base-pairs differs from that of the duplex Watson-Crick and non-canonical guanine-uracil pairs with two or three direct hydrogen bonds. The conformational variability and increased flexibility has to be taken into account when considering these base-pairs as RNA building blocks and as recognition motifs.

Base Pairing↗

PubMed2001

15S-Hydroxyeicosatetraenoic acid activates peroxisome proliferator-activated receptor gamma and inhibits proliferation in PC3 prostate carcinoma cells.

15-Lipoxygenase (15-LOX)-2 is expressed in benign prostate secretory cells and benign prostate produces 15S-hydroxyeicosatetraenoic acid (15S-HETE) from exogenous arachidonic acid (AA). In contrast, 15S-LOX-2 and 15S-HETE formation are reduced in prostate carcinoma (Pca). The mechanisms whereby reduced 15-LOX-2 may contribute to Pca development or progression are not known. We investigated the expression of peroxisome proliferator-activated receptor (PPAR) gamma in benign and malignant prostate tissues and the ability of 15S-HETE to activate PPARgamma-dependent transcription and modulate proliferation of the Pca cell line PC3. In contrast to benign prostate and similar to most Pca tissues, 15-LOX-2 mRNA was not detected in PC3 cells, and they did not produce detectable 15-HETE from [14C]AA. By reverse transcription-PCR, PPARgamma mRNA was present in 18 of 18 benign and 9 of 9 tumor specimens. The PPARgamma ligand BRL 49653 and 15S-HETE caused a dose-dependent inhibition of PC3 proliferation in a 14-day soft agar colony-forming assay (IC50 of 3 and 30 microM, respectively). 15S-HETE (10 microM) caused greater inhibition than 10 microM 15R-HETE. At 3 days, BRL 49653 and 15S-HETE caused a slight increase in cells in G0-G1 and a corresponding decrease in cells in S phase. In PC3 cells transiently transfected with a luciferase reporter linked to a PPAR response element, 1 microM BRL 49653 and 10 microM 15S-HETE caused approximately threefold and greater than twofold induction of PPAR-dependent transcription, respectively. By quantitative real-time reverse transcription-PCR and Northern analysis, 3-day treatment with BRL 49653 and 15S-HETE caused a reduction of PPARgamma expression but a marked up-regulation of the PPAR response element containing adipocyte type fatty acid binding protein. These results support the hypothesis that 15-LOX-2-derived 15S-HETE may constitute an endogenous ligand for PPARgamma in the prostate and that loss of this pathway by reduced expression of 15-LOX-2 may contribute to increased proliferation and reduced differentiation in prostate carcinoma.

Agar↗

PubMed2001

Cartilage-specific autoimmunity in rheumatoid arthritis: characterization of a triple helical B cell epitope in the integrin-binding-domain of collagen type II.

Cartilage-specific proteins are considered potential autoantigens that could continuously fuel autoimmune responses directed to the joints in rheumatoid arthritis (RA). Using recombinant chimeric collagen type II we have identified one major type II collagen (CII) epitope (denoted U1) recognized by RA sera. The U1 epitope is a triple helical structure formed by 11 amino acids (triple helical position 494-504) and colocalizes with the recently described alpha1beta1/alpha2beta1 integrin binding site. It is a major epitope, found in 14/22 RA sera positive for antibodies to CII. One individual could be followed for a long time and the results showed that IgG antibodies specific for the U1 epitope were maintained along the chronic disease course but suppressed during periods of cyclosporin A and anti-CD4 treatment. We also found that the U1 epitope was recognized in rats susceptible to collagen-induced arthritis. A monoclonal autoantibody (mAb 126.30) was raised from DA rats, which bound the same epitope. The antibodies bound the cartilage in vivo showing that the epitope is exposed to the immune system for immune complex formation in the intact joint.

Animals↗

PubMed2001

Mode of bleaching phytotoxicity of herbicidal diphenylpyrrolidinones.

A mode of action study of herbicidal diphenylpyrrolidinones was carried out through carotenoid analyses in intact Scenedesmus cells and by a cell-free plant-type phytoene desaturase assay using Escherichia coli transformants. A series of forty-eight diphenylpyrrolidinones decreased the carotenoid content of Scenedesmus cells in the light and inhibited phytoene desaturase. The relationship between substituents at various positions and inhibition of phytoene desaturase is discussed. Using very active bleaching diphenylpyrrolidinones, a 10(-5) M concentration affected neither the zeta-carotene desaturase nor the protoporphyrinogen-IX oxidase. Although some differences in their inhibitory activity were found between the in vivo and cell-free assays, it is concluded that the compounds are essentially bleachers affecting carotenoid biosynthesis in plants. Enzyme kinetics studies with recombinant phytoene desaturase revealed a non-competitive inhibition with respect to the substrate phytoene. A competition against the inhibitor was shown by the cofactor NADP+, suggesting an interaction of pyrrolidinones at the cofactor-binding site of phytoene desaturase.

Biological Assay↗

PubMed2001

Importance of conversion for results obtained with laparoscopic colorectal surgery.

PURPOSE: The need for a conversion is a problem inherent in laparoscopic surgery. The present study points up the significance of conversion for the results obtained with laparoscopic colorectal surgery and identifies the risk factors that establish the need for conversion. METHOD: The study took the form of a multicentric, prospective, observational study within the Laparoscopic Colorectal Surgery Study Group. A total of 33 institutions in Germany, Austria, and Switzerland participated. The study period was 3.5 years. Cases were documented with the aid of a standardized questionnaire. RESULTS: Within the framework of the Laparoscopic Colorectal Surgery Study Group, a total of 1,658 patients were recruited to a multicenter study over a period of three and one-half years (from August 1, 1995 to February 1, 1999). The observed conversion rate was 5.2 percent (n = 86). The patients requiring a conversion were significantly heavier (body mass index, 26.5 vs. 24.9) than those undergoing pure laparoscopy. Resections of the rectum were associated with a higher risk for conversion (20.9 vs. 13 percent). Intraoperative complications occurred significantly more frequently in the conversion group (27.9 vs. 3.8 percent). The duration of the operation was significantly increased after conversion in a considerable proportion of the procedures performed. Postoperative morbidity (47.7 vs. 26.1 percent), mortality (3.5 vs. 1.5 percent), recovery time, and postoperative hospital stay were all negatively influenced by conversion, in part significantly. Institutions with experience of more than 100 laparoscopic colorectal procedures proved to have a significantly lower conversion rate than those with experience of fewer than 100 such interventions (4.3 vs. 6.9 percent). CONCLUSION: Although, of itself, conversion is not considered to be a complication of laparoscopic surgery, it is true that the postoperative course after conversion is associated with appreciably poorer results in terms of morbidity, mortality, convalescence, blood transfusion requirement, and postoperative hospital stay. The importance of experience in laparoscopic surgery can be demonstrated on the basis of the conversion rates. Careful patient selection oriented to the experience of the surgeon is required if we are to keep the conversion, morbidity, and mortality rates of laparoscopic colorectal procedures as low as possible.

Age Distribution↗

PubMed2001

[Incompatibility of olanzapine and amisulpride in multisystemic myotonic myopathy].

There is evidence for the occurrence of psychopathological symptoms in the adult form of myotonic dystrophy such as disturbance of concentration and memory, chronic depression, disturbed social behaviour, mental retardation, and hypersomnia. In this report we present a patient suffering from multisystemic myotonic myopathy without a cytosine-thymine-guanine [corrected] repeat expansion on chromosome 19q13.3 and schizophrenia. In this patient, a severe increase of creatine kinase (CK) occurred during treatment with olanzapine and amisulpride. The following risperidone medication was well tolerated without side effects. Susceptibility for malignant hyperthermia was detected by a positive in vitro contracture test. The occurrence of elevated muscle enzymes during treatment with atypical neuroleptics is suspicious as a possible side effect of neuroleptic medication and muscle disease.

Adult↗

PubMed2001

[Myotonic dystrophy (DM/Curschmann-Steinert disease) and proximal myotonic myopathy (PROMM/Ricker syndrome). Myotonic muscle diseases with multisystemic manifestations].

Myotonic disorders are characterised by slowed muscle relaxation and myotonic discharges in the electromyogram. "Pure" myotonic disorders affect only muscle and can be separated into ion channel disorders affecting either the chloride channel (myotonia congenita Thomsen or myotonia congenita Becker) or those affecting the sodium channel (paramyotonia, hyperkalemic periodic paralysis, and myotonia fluctuans). The genetic defects in these disorders are point mutations or deletions within the respective channel genes. A second group of myotonias consists of multisystem disorders with muscle weakness and atrophy plus extramuscular symptoms and signs including cardiac arrhythmias, cataracts, hypogonadism, and pain. Classic myotonic dystrophy (Steinert's disease or DM 1), and proximal myotonic myopathy (PROMM or Ricker's syndrome) are the major syndromes. PROMM is characterised by predominantly proximal muscle weakness and myalgias. Similarly to DM 1, anticipation also occurs in PROMM, but the disease course is usually milder. Steinert's disease belongs to the group of trinucleotide repeat-associated disorders. The DM 1 mutation is an unstable CTG trinucleotide repeat expansion on chromosome 19q13.3 which is diagnostic for the disease. A number of families with PROMM have been linked to a gene locus on chromosome 3q, but the mutation is still unknown. Therefore, direct molecular genetic testing for PROMM is not yet possible.

Biopsy↗

PubMed2001

The growth arrest specific gene (gas6) protein is expressed in abnormal embryos sired by male golden hamsters with accessory sex glands removed.

Expression of growth arrest specific gene (gas6) and its receptors in embryonic and uterine tissues in normal pregnancy and pregnancy that produces abnormal embryos sired by hamsters with partial or total deletion of male accessory sex glands was studied by in situ hybridization, immunohistochemistry, reverse-transcription polymerization reaction and enzyme-linked immunoabsorbant assay. At oestrus, very strong gas6 mRNA and Gas6 expression were seen only in the uterine epithelium and endometrial glands. Upon implantation, both of them could be demonstrated in the decidualizing stroma. From day 4 to day 7 p.c, gas6 mRNA was present in the embryo, but Gas6 immunoreactivity was only found in those showing features of degeneration. The gas6:beta-actin mRNA ratio was low in oestrus and at day 4 of pregnancy but rose as the embryo grew. As for the receptors, Rse was detected in embryonic cells during days 5-7 p.c., and decidual cell from days 4 to 7 p.c., but Mer could be found in decidual cells and trophoblasts. It was concluded that gas6 had a role in endometrial transformation during decidualization and trophoblastic invasion. In the embryo, gas6 was transcribed, but the protein was only produced in response to need, such as when normal progression of development was threatened.

Actins↗

PubMed2001

Experience as a factor influencing the indications for laparoscopic colorectal surgery and the results.

BACKGROUND: The influence of experience on the results of treatment with laparoscopic surgery is indisputable. The establishment of indications and contraindications is relative, and varies depending on the experience of the surgeon. Learning curves have been described for a number of laparoscopic interventions, in particular laparoscopic cholecystectomy. The current prospective multicenter study investigates, among other things, the interrelation between experience and the results of treatment using laparoscopic colorectal surgery. The study makes no pronouncements on the long-term results achieved in patients with colorectal carcinoma who underwent an operation with curative intent, although relevant data were indeed collected. RESULTS: Between August 1, 1995 and February 1, 1999, a total of 1,658 patients were recruited to the prospective multicenter study initiated by the Laparoscopic Colorectal Surgery Study Group. To investigate the influence of surgical experience, two groups were formed. Group A comprised all the institutions and surgeons with experience of more than 100 laparoscopic colorectal operations. Group B contained institutions and surgeons with experience of fewer than 100 such interventions. The results of this study clearly show that in Group A, significantly more procedures involving the rectum were performed (26.7% vs 9.5%), and significantly more carcinomas were surgically managed (37.3% vs 17.3%). Despite this significantly higher level of technically difficult procedures in the patient population of group A, which was comparable in terms of age, gender, height, and weight with the patient in group B, the postoperative mortality and morbidity was, with the exception of urinary tract infections, identical between the two groups. Conversion to open surgery was significantly less frequent in group A (4.3% vs 6.9%), and, finally, the duration of the procedures performed by the more experienced surgeons of group A was appreciably shorter than in institutions with a smaller frequency of such operations. CONCLUSIONS: Laparoscopic colorectal surgery is very demanding, and can be performed with low morbidity and mortality rates only by a surgeon with above-average experience with this type of surgery and a large caseload of laparoscopic colorectal procedures. The learning curve for such procedures is appreciably longer than for other laparoscopic operations. With increasing experience, technically more demanding operations, including radical oncologic rectal laparoscopic procedures, can be performed with appreciably reduced operating times and conversion rates, but with no increase in morbidity or mortality.

Adult↗

PubMed2001

Efficacy of surgical measures in preventing port-site recurrences in a porcine model.

BACKGROUND: Port-site recurrences are serious complications of laparoscopy performed for cancer. Incidences reported in the literature vary between 0% and 21%, suggesting an influence of the surgeon. METHODS: The aim of this experimental, prospective, randomized, single-blind study was to investigate the influence that the quality surgery has on the incidence of port-site recurrences. After a 12-mmHg carbon dioxide (CO2) pneumoperitoneum was created, 10(7) human HeLa cell were injected into the peritoneal cavity of 18 pigs, creating a xenogeneic tumor. Laparoscopic sigmoid resections then were performed using four trocars and a transanal double-stapling technique. The following protective measures were applied in nine animals: trocar fixation, prevention of gas leaks, rinsing of instruments with povidone-iodine, minilaparotomy protection, rinsing of trocars before removal, peritoneal closure, and rinsing of all wounds with povidoneiodine. Surgeons and type of procedures were randomized. After 4 weeks, the animals were killed and all portsites excised. Blinded immunohistologic analysis with antihuman pancytokeratin antibody was performed. RESULTS: Tumor recurrence was present in 23 of 36 port sites (63.8%) in the control group, but only in 5 of 36 port sites (13.8%) in the group that received protective measures (p = 0.002; Fisher's exact test). No peritoneal carcinosis nor anastomotic recurrences were observed. CONCLUSION: These results strongly suggest that the quality of surgical technique has an influence on the incidence of port-site recurrences. From now on, we propose to use these protective measures routinely in cancer laparoscopy.

Animals↗

PubMed2001

Silicic acid (Si(OH)(4)) is a significant influence upon the atomic absorption signal of aluminium measured by graphite furnace atomic absorption spectrometry (GFAAS).

We have identified silicic acid (Si(OH)(4)) as an important modifier of the absorbance signal of aluminium measured by graphite furnace atomic absorption spectrometry (GFAAS). The presence of Si(OH)(4) enhanced the signal by as much as 50%. The extent of the enhancement was dependent upon both [Al] and [Si(OH)(4)] and was maximal when [Al]< or =4.44 micromol dm(-3) and [Si(OH)(4)]> or =0.50 mmol dm(-3). The enhancement of the Al absorbance signal was not linearly related to [Si(OH)(4)] and the effect was, generally, saturated, for all [Al] tested, at [Si(OH)(4)]> or =0.50 mmol dm(-3). Si(OH)(4) was significantly more effective in enhancing the Al absorbance signal than Mg(NO(3))(2). However, the co-occurrence of 10 mmol dm(-3) Mg(NO(3))(2) and 2 mmol dm(-3) Si(OH)(4) in samples abolished the enhancement due to Si(OH)(4). The presence of Si(OH)(4) in samples could result in an overestimation of the Al content of those samples by as much as 50%. Errors in the measurement of Al in samples containing Si(OH)(4) could be prevented using matrix-matched calibration standards. Our observation could have serious implications for the determination of Al in aqueous samples of both geochemical and biological interest. It may also point towards the application of Si(OH)(4) as a novel and effective matrix modifier in the determination of Al by GFAAS since the inclusion of Si(OH)(4) in standards and samples improved the limit of detection of Al from ca 8 nmol dm(-3) to 3 nmol dm(-3).

Absorption↗