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PubMed2004

A systematic review of the influence of different titanium surfaces on proliferation, differentiation and protein synthesis of osteoblast-like MG63 cells.

OBJECTIVES: Titanium is the standard material for dental and orthopaedical implants. The good biocompatibility has been proven in many experimental and clinical investigations. Different titanium topographies were tested in vitro using different cell culture models. The aim of this systematic review was to evaluate and summarize the medical/dental literature to assess on which kind of titanium surface structure the osteoblast-like osteosarcoma cells MG63 show the best proliferation and differentiation rate, and the best protein synthesis. METHODS: A systematic search was carried out using different on-line databases (PubMed, Web of Science, Cochrane Library, International Poster Journal), supplemented by handsearch in selected journals and by examination of the bibliographies of the identified articles. Inclusion and exclusion criterias were applied when considering relevant articles. Studies which met the inclusion criteria were included and data extraction was undertaken by one reviewer. RESULTS: The search yielded 348 references. Nine articles referring to nine different studies were relevant to our question. Additionally 8 less relevant articles were identified. It was found that regularly textured surfaces of pure titanium with R(a) values (average roughness) of around 4 mum are well-accepted by MG63 cells. CONCLUSIONS: The surfaces and culture conditions vary widely. Therefore it is still difficult to recommend one particular surface. It seems that there are no differences in cell proliferation and differentiation on surfaces treated by blasting and etching. Standardization in fabrication and size of the different test surfaces as well as homogeneity in culture times and plating densities should be aspects for future research.

Algorithms↗
PubMed1996

Identification of complex chromosome rearrangements in the gibbon by fluorescent in situ hybridization (FISH) of a human chromosome 2q specific microlibrary, yeast artificial chromosomes, and reciprocal chromosome painting.

Chromosome painting has revealed that the human chromosome homologs in lesser apes are often fragmented and translocated to a number of different hylobatid chromosomes. We investigated the fragmented human chromosome 2 homologs in gibbons to illustrate a new strategy in mapping regional and band-specific chromosomal homologies between species. Previous research showed that the DNA library specific to human chromosome 2 paints parts of four gibbon (lar species group) chromosomes (viz., 1, 10, 12, and 16) and yields five distinct hybridization signals (including two on gibbon chromosome 16). However, the exact segments of human chromosome 2 that were translocated to the various gibbon chromosomes could not be distinguished. To determine the origin of the human chromosome 2 signals, we hybridized a microlibrary for the long arm of human chromosome 2, as well as YACs specific for most of the major bands on this chromosome, to metaphases of the gibbon. For reciprocal chromosome painting, we hybridized flow-sorted gibbon chromosome probes to human chromosome 2. Each method added additional insights that helped clarify the shuffling of human chromosome 2 material in the highly reorganized gibbon genome. There was an excellent correspondence between these complementary techniques. YAC 958d2 identified the breakpoint between human chromosome 2 material present on gibbon chromosomes 10 and 16. The reciprocal chromosome painting permitted a more complete and regional assignment of homology between segments on various gibbon chromosomes to human chromosome 2. The results show that a combination of reciprocal chromosome painting, subregional microlibraries, and band-specific probes (such as YACs) can be used to identify homologies between species and to rapidly construct detailed comparative chromosome maps, especially when the karyotypes are highly rearranged.

Animals↗
PubMed1998

Two-dimensional parallel array technology as a new approach to automated combinatorial solid-phase organic synthesis

An automated, 96-well parallel array synthesizer for solid-phase organic synthesis has been designed and constructed. The instrument employs a unique reagent array delivery format, in which each reagent utilized has a dedicated plumbing system. An inert atmosphere is maintained during all phases of a synthesis, and temperature can be controlled via a thermal transfer plate which holds the injection molded reaction block. The reaction plate assembly slides in the X-axis direction, while eight nozzle blocks holding the reagent lines slide in the Y-axis direction, allowing for the extremely rapid delivery of any of 64 reagents to 96 wells. In addition, there are six banks of fixed nozzle blocks, which deliver the same reagent or solvent to eight wells at once, for a total of 72 possible reagents. The instrument is controlled by software which allows the straightforward programming of the synthesis of a larger number of compounds. This is accomplished by supplying a general synthetic procedure in the form of a command file, which calls upon certain reagents to be added to specific wells via lookup in a sequence file. The bottle position, flow rate, and concentration of each reagent is stored in a separate reagent table file. To demonstrate the utility of the parallel array synthesizer, a small combinatorial library of hydroxamic acids was prepared in high throughput mode for biological screening. Approximately 1300 compounds were prepared on a 10 μmole scale (3-5 mg) in a few weeks. The resulting crude compounds were generally >80% pure, and were utilized directly for high throughput screening in antibacterial assays. Several active wells were found, and the activity was verified by solution-phase synthesis of analytically pure material, indicating that the system described herein is an efficient means for the parallel synthesis of compounds for lead discovery. Copyright 1998 John Wiley & Sons, Inc.

Journal Article↗
PubMed1994

Identification of the U-937 membrane-associated proteinase interacting with the V3 loop of HIV-1 gp120 as cathepsin G.

We have purified a serine proteinase from the membrane of U-937 cells that was inhibited in a tight-binding manner by recombinant gp120 and by peptides mimicking the V3 loop of gp120 [(1993) FEBS Lett. 317, 167-172]. This proteinase has now been characterized, both structurally and functionally. It has a dual trypsin- and chymotrypsin-like specificity, and N-terminal sequence analysis of the first 32 residues indicates complete identity with leukocyte cathepsin G. Cathepsin G-like material was located at the surface of U-937 cells using a monoclonal antibody directed against leukocyte cathepsin G, and polyclonal anti-cathepsin G antibodies precipitated the purified proteinase. However, the U-937 enzyme differs slightly from commercial leukocyte cathepsin G in its apparent M(r) because of different glycosylation. No other protein structurally related to cathepsin G was found upon screening a U-937 cDNA library using several oligonucleotide probes constructed from the membrane proteinase N-terminal amino acid sequence. The possible interaction of a cathepsin G-like proteinase at the surface of U-937 cells with the V3 loop of HIV-1 gp120 is discussed.

Amino Acid Sequence↗
PubMed1988

A new cloning system for Bacillus subtilis comprising elements of phage, plasmid and transposon vectors.

A new cloning system for Bacillus subtilis was devised which makes use of a combination of Tn917-containing phage SP beta derivatives and Tn917-containing Escherichia coli-B. subtilis shuttle plasmids. This system allows the initial cloning of genes in single copy, via 'prophage transformation', with a selection for complementation of mutational defects in B. subtilis hosts and permits subsequent transfer of the cloned material by homologous recombination to low-copy and high-copy vectors that replicate in both B. subtilis and E. coli. Because cloned sequences are adjacent to pB322-derived DNA in the recombinant phages, inserts can also be 'rescued' directly from the phage DNA after digestion with appropriate restriction enzymes, circularization of the fragments by ligation and transformation of an E. coli recipient. Two genomic libraries of B. subtilis chromosomal Sau3A-generated partial-digest fragments in the size ranges of 5-8 kb and 8-10 kb were constructed and screened for the complementation of mutations aroI906, cysA14, dal-1, glyB133, metC3, purA16, purB33, thrA5, trpC2 and recE4. In all cases, specialized transducing phages carrying inserts that complemented the selected markers were recovered. Inserts complementing the dal-1 and trpC2 mutations could be transferred from recombinant phages to Tn917-containing plasmids by homologous recombination without in vitro subcloning. Another insert complementing the purB33 mutation was rescued directly into E. coli from a recombinant phage DNA.

Bacillus subtilis↗
PubMed2003

Highly sensitive in vitro selections for DNA-linked synthetic small molecules with protein binding affinity and specificity.

We have developed in vitro selections for DNA-linked synthetic small molecules with protein binding affinity and specificity. These selections require only generally accessible equipment, offer high degrees of enrichment of active molecules from mixtures of predominantly inactive species, can be applied to a variety of unrelated proteins, and require approximately 108-fold less material than existing synthetic molecule screening methods. Iterating these selections multiplies the net enrichment of active molecules, enabling enormous overall enrichment factors exceeding 106 to be achieved. Further, the selections can be adapted to select for binding specificity in addition to binding affinity. The application of methods described in this work may play a key role in the discovery of desired molecules from DNA-templated synthetic libraries.

Combinatorial Chemistry Techniques↗
PubMed1991

Recombinant Escherichia coli clones expressing Chlamydia trachomatis gene products attach to human endometrial epithelial cells.

To identify Chlamydia trachomatis genes involved in attachment to host cells, a chlamydial genomic library was screened on the basis of binding characteristics by two methods. In the whole-cell screen, individual recombinant Escherichia coli clones were assayed for adherence to eukaryotic cells. In the membrane-binding screen, each recombinant colony of E. coli was treated with CHCl3 and assayed for binding to purified, 3-[(3-cholamidopropyl)-dimethyl-ammonio]-1-propanesulfonate (CHAPS)-solubilized, 35S-labeled eukaryotic membrane material. Initial screening with McCoy cells was refined by using HEC-1B cells, a human endometrial epithelial cell line, which discriminate among recombinants adhering to McCoy cells. Some recombinants demonstrate significantly greater adherence to HEC-1B cells than to McCoy cells and appear, by transmission electron microscopy, to associate with electron-dense areas of the epithelial cell plasma membrane, resembling coated pits. Recombinants positive by one or both screening methods were examined by Southern and Western (immunoblot) analyses, which revealed the presence of chlamydial sequences inserted in the plasmids and the expression of novel 18-, 28-, and approximately 82 kDa, and perhaps of 18 Maxicell analysis of selected recombinants confirmed that the proteins of 28 and approximately 82 kDa, and perhaps of 18 kDa, are plasmid encoded. Antiserum generated against the recombinant approximately 82-kDa protein reacted in Western analysis with a similar-sized protein from C. trachomatis serovar E elementary bodies (EB) and reticulate bodies, serovar L2 EB, and C. psittaci EB. E. coli JM109(pPBW58) contains a 6.7-kb plasmid insert which encodes proteins of all three sizes. Under a number of different conditions in the whole-cell attachment assay--i.e., at 4 degrees C, in Ca(2+)- and Mg(2+)-free medium, in the presence of trypsin or dextran sulfate, and with rabbit aortic endothelial cells--the binding specificity of JM109(pPBW58) parallels that of C. trachomatis EB. Finally, the adherence phenotype of E. coli JM109(pPBW58) correlates directly with the presence of the recombinant plasmid; the phenotype is lost concurrently with loss of the recombinant plasmid, and the into E. coli JM109. The role of the 18-, 28-, and approximately 82-kDa proteins in mediating attachment, whether they act in concert as a complex or individually, has yet to be determined.

Antigens, Bacterial↗
PubMedDate not supplied

[Expectations of continuing medical education at first level of attention in Chiapas].

OBJECTIVE: To analyze the expectations of first level of attention physicians (FLAP) about continuing medical education. MATERIAL AND METHODS: An exploratory qualitative study was made from the cognitive view of motivation, in order to know the expectations of the FP at the Mexican Institute of Social Security (IMSS) in Chiapas. RESULTS: The FLAP show little interest in continuing medical education staff, because they find traditional professors and training courses off their work schedule, becoming difficult for them to attend. However, FLAP consider the library facilities and research activities as strategies to keep themselves updated, but they lack the required time to do so. CONCLUSIONS: The FLAP have low expectations caused by direct and indirect negative experiences at the work place as a result of ineffective communication among them and with the respective authorities of each unit. The FLAP show personal characteristics which limit their participation in the programs made by the continuing medical education staff, as well as their professional development.

Adult↗
PubMed1996

Amplification of genes, single transcripts and cDNA libraries from one cell and direct sequence analysis of amplified products derived from one molecule.

We report a procedure to generate and amplify cDNA libraries and to amplify and sequence genes and single RNA transcript molecules from the same cell without cloning. An absence of cloning steps minimizes potential sources of contamination, which can be especially problematic when working at the single cell level. Potential contamination is further reduced by an absence of any purification step prior to PCR amplification. Amplifications are designed to minimize the production of aberrant molecules in favor of full-length products, which is especially advantageous when generating cDNA libraries. Genes are amplified from isolated single nuclei, which are segregated from cytoplasmic lysates by microcentrifugation. Specific cDNA, total cDNA or both are synthesized from aliquots of the cytoplasmic lysate, and single cDNA molecules are isolated from others of the same species by limiting dilution prior to PCR amplification. In this way, the frequency of amplified products provides for a direct calculation of cDNA copy number by a Poisson analysis. Incorporation errors by Taq DNA polymerase occur at a low frequency and can be eliminated by sequencing independently amplified cDNA molecules from the same cell. Single molecule amplifications provide sufficient material for numerous (approximately 150) direct DNA sequencing reactions. The limiting dilution approach also permits sequence information to be obtained from a single cDNA, when highly related transcripts derived from distinct genes are present in the same cell and simultaneously amplified with the same primers. In sum, this method provides for a maximum amount of nucleic acid information to be extracted from one cell. It has a wide range of applications to studies of the immune system where, to a first approximation, each lymphocyte has a unique receptor identity, where specific states of differentiation may be difficult to assess in a mixed cell population, and where cell immortalization procedures are not always possible nor practical.

Animals↗
PubMed2004

Recent advances in peptide-based microarray technologies.

Peptide array is a rapidly growing tool that provides both large-scale and high-throughput capabilities for protein detection and activity studies. Materials presented in this review will examine the recent advances in the field of peptide microarray with special emphasis on the generation and applications of high-density arrays of peptides on glass slides.

Enzymes↗
PubMed2004

Information-seeking behavior changes in community-based teaching practices.

A National Library of Medicine information access grant allowed for a collaborative project to provide computer resources in fourteen clinical practice sites that enabled health care professionals to access medical information via PubMed and the Internet. Health care professionals were taught how to access quality, cost-effective information that was user friendly and would result in improved patient care. Selected sites were located in medically underserved areas and received a computer, a printer, and, during year one, a fax machine. Participants were provided dial-up Internet service or were connected to the affiliated hospital's network. Clinicians were trained in how to search PubMed as a tool for practicing evidence-based medicine and to support clinical decision making. Health care providers were also taught how to find patient-education materials and continuing education programs and how to network with other professionals. Prior to the training, participants completed a questionnaire to assess their computer skills and familiarity with searching the Internet, MEDLINE, and other health-related databases. Responses indicated favorable changes in information-seeking behavior, including an increased frequency in conducting MEDLINE searches and Internet searches for work-related information.

Adult↗
PubMed2006

Echinacea for preventing and treating the common cold.

BACKGROUND: Preparations of the plant Echinacea (family Compositae) are widely used in some European countries and in North America for common colds. Most consumers and physicians are not aware that products available under the term Echinacea differ appreciably in their composition, mainly due to the use of variable plant material, extraction methods and addition of other components. OBJECTIVES: The objective of this review was to assess whether there is evidence that Echinacea preparations are 1) more effective than no treatment; 2) more effective than placebo; 3) similarly effective to other treatments in A) the prevention and B) the treatment of the common cold. SEARCH STRATEGY: We searched the Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library Issue 3, 2005); PubMed (1997 to April 2005), EMBASE (1998 to June 2005), AMED (to August 2005), Centre for Complementary Medicine Research (in Munich) (1988 to May 2005), contacted experts, and screened references of reviews. SELECTION CRITERIA: We included randomized controlled trials that compared mono-preparations of Echinacea with a placebo, no treatment, or another treatment for the prevention or treatment of common colds. Trials on combinations of Echinacea and other herbs were excluded. DATA COLLECTION AND ANALYSIS: For all studies, at least two authors independently assessed eligibility and trial quality, and extracted data. Outcomes of interest in prevention trials were: numbers of individuals with one or more colds, and severity and duration of colds; and in treatment trials: total symptom scores, nasal symptoms, and duration of colds. MAIN RESULTS: Sixteen trials including a total of 22 comparisons of an Echinacea preparation and a control group (19 with placebo, 2 with no treatment, 1 with another herbal preparation) met the inclusion criteria. All trials except one were described as double-blind. The majority had reasonable to good methodological quality. Three comparisons investigated prevention of colds and 19 comparisons tested treatment of colds. A variety of different Echinacea preparations were used. None of the three comparisons in the prevention trials showed an effect over placebo. Comparing an Echinacea preparation with placebo as treatment, a significant effect was reported in nine comparisons, a trend in one, and no difference in six. More than one trial was available only for preparations based on the aerial parts from Echinacea purpurea (E. purpurea). AUTHORS' CONCLUSIONS: Echinacea preparations tested in clinical trials differ greatly. There is some evidence that preparations based on the aerial parts of Echinacea purpurea might be effective for the early treatment of colds in adults but results are not fully consistent. Beneficial effects of other Echinacea preparations, and for preventative purposes might exist but have not been shown in independently replicated, rigorous randomized trials.

Common Cold↗
PubMed1970

Computer simulation of the non-steady-state radioactive labelling of a system of metabolite pools with constant rates of influx and efflux.

The derivation is given of the general case of a differential equation describing the labelling of a single metabolite pool that is subjected to constant rates of influx of radioactive material when the pool size is itself changing at constant rate. A programme, written in ALGOL, is briefly described that solves a set of these differential equations, and that can be used to simulate the radioactive labelling of a system of metabolite pools. A copy of the programme, together with examples of input and output, has been deposited as Supplementary Publication no. SUP 50001 at the National Lending Library for Science and Technology, Boston Spa, Yorks. LS23 7BQ, U.K., from whom copies can be obtained on the terms indicated in Biochem. J. (1970), 116, 7.

Computers↗
PubMed2001

Anisotropy functions for low energy interstitial brachytherapy sources: an EGS4 Monte Carlo study.

Anisotropy functions for low energy interstitial brachytherapy sources are examined. Absolute dose rates around 103Pd seed model 200 and 125I seed models 6702 and 6711 have been estimated by means of the EGS4 Monte Carlo simulation system. The DLC-136/PHOTX cross section library, water molecular form factors, bound Compton scattering and Doppler broadening of the Compton-scattered photon energy were considered in the calculations. Following the formalism developed by the Interstitial Brachytherapy Collaborative Working Group, anisotropy functions, F(r, theta), have been calculated. Our Monte Carlo results were compared against a limited set of measured data selected from the literature and other Monte Carlo results. Binding corrections and phantom material selection have been found to have no influence on the anisotropy function. The accuracy of the geometrical source models used for the Monte Carlo calculations was validated against experimental measurements of in-air relative fluence at 100 cm from the source. More detailed knowledge about the geometrical design of 103Pd seed model 200 is needed in order to improve the agreement with experimentally measured in-air fluence. Values for in-air fluence of 125I model 6702 are sensitive to source position within the inner seed cylinder. Excellent agreement between calculated and measured in-air fluence is found for 125I model 6711. It was observed that using in-air relative fluence at 100 cm from the source to calculate the anisotropy function yields a less anisotropic dose distribution at distances close to the source than full Monte Carlo simulation, in contradiction with experimental data. Our results have estimated statistical uncertainties of 1%-3% at the 1sigma level within clinically relevant regions, but contain systematic uncertainties related to the assumed geometrical details.

Algorithms↗
PubMed1993

Detection of complete and partial chromosome gains and losses by comparative genomic in situ hybridization.

Comparative genomic in situ hybridization (CGH) provides a new possibility for searching genomes for imbalanced genetic material. Labeled genomic test DNA, prepared from clinical or tumor specimens, is mixed with differently labeled control DNA prepared from cells with normal chromosome complements. The mixed probe is used for chromosomal in situ suppression (CISS) hybridization to normal metaphase spreads (CGH-metaphase spreads). Hybridized test and control DNA sequences are detected via different fluorochromes, e.g., fluorescein isothiocyanate (FITC) and tetraethylrhodamine isothiocyanate (TRITC). The ratios of FITC/TRITC fluorescence intensities for each chromosome or chromosome segment should then reflect its relative copy number in the test genome compared with the control genome, e.g., 0.5 for monosomies, 1 for disomies, 1.5 for trisomies, etc. Initially, model experiments were designed to test the accuracy of fluorescence ratio measurements on single chromosomes. DNAs from up to five human chromosome-specific plasmid libraries were labeled with biotin and digoxigenin in different hapten proportions. Probe mixtures were used for CISS hybridization to normal human metaphase spreads and detected with FITC and TRITC. An epifluorescence microscope equipped with a cooled charge coupled device (CCD) camera was used for image acquisition. Procedures for fluorescence ratio measurements were developed on the basis of commercial image analysis software. For hapten ratios 4/1, 1/1 and 1/4, fluorescence ratio values measured for individual chromosomes could be used as a single reliable parameter for chromosome identification. Our findings indicate (1) a tight correlation of fluorescence ratio values with hapten ratios, and (2) the potential of fluorescence ratio measurements for multiple color chromosome painting. Subsequently, genomic test DNAs, prepared from a patient with Down syndrome, from blood of a patient with T-cell prolymphocytic leukemia, and from cultured cells of a renal papillary carcinoma cell line, were applied in CGH experiments. As expected, significant differences in the fluorescence ratios could be measured for chromosome types present in different copy numbers in these test genomes, including a trisomy of chromosome 21, the smallest autosome of the human complement. In addition, chromosome material involved in partial gains and losses of the different tumors could be mapped to their normal chromosome counterparts in CGH-metaphase spreads. An alternative and simpler evaluation procedure based on visual inspection of CCD images of CGH-metaphase spreads also yielded consistent results from several independent observers. Pitfalls, methodological improvements, and potential applications of CGH analyses are discussed.

Aneuploidy↗
PubMed2003

Eosinophil chemotactic factor-L (ECF-L): a novel osteoclast stimulating factor.

UNLABELLED: Screening a cDNA library enriched for genes expressed in OCLs identified ECF-L. ECF-L enhanced OCL formation without increasing RANKL levels. Anti-ECF-L inhibited RANKL-induced OCL formation. These results support a potent role of ECF-L in osteoclastogenesis. INTRODUCTION: To investigate the molecular mechanisms that control osteoclastogenesis, we developed an immortalized osteoclast (OCL) precursor cell line that forms mature OCLs in the absence of stromal cells and used it to form pure populations of OCLs. MATERIALS AND METHODS: Polymerase chain reaction (PCR) selective cDNA subtraction was used to identify genes that are highly expressed in mature OCLs compared with OCL precursors employing OCL and OCL precursors derived from this cell line. RESULTS: Eosinophil chemotactic factor-L (ECF-L), a previously described chemotactic factor for eosinophils, was one of the genes identified. Conditioned media from 293 cells transfected with mECF-L cDNA, or purified ECF-L Fc protein, increased OCL formation in a dose-dependent manner in mouse bone marrow cultures treated with 10(-10) M 1,25(OH)2D3. OCLs derived from marrow cultures treated with ECF-L conditioned media formed increased pit numbers and resorption area per dentin slice compared with OCLs induced by 1,25(OH)2D3 (p < 0.01). Addition of an antisense S-oligonucleotide to mECF-L inhibited OCL formation in murine bone marrow cultures treated only with 10(-9) M 1,25(OH)2D3 compared with the sense S-oligonucleotide control. Time course studies demonstrated that ECF-L acted at the later stages of OCL formation, and chemotactic assays showed that mECF-L increased migration of OCL precursors. mECF-L mRNA was detectable in mononuclear and multinucleated cells by in situ hybridization. Interestingly, a neutralizing antibody to ECF-L blocked RANKL or 10(-9) M 1,25(OH)2D3-induced OCL formation in mouse bone marrow cultures, although ECF-L did not induce RANKL expression. CONCLUSIONS: These data show ECF-L is a previously unknown factor that is a potent mediator of OCL formation, which acts at the later stages of OCL formation and enhances the effects of RANKL.

Animals↗
PubMedDate not supplied

Combinatorial materials research applied to the development of new surface coatings I: a multiwell plate screening method for the high-throughput assessment of bacterial biofilm retention on surfaces.

Combinatorial, high-throughput capabilities have been established to aid in the rapid development of new and effective antifouling marine coatings for naval applications. A biological screening process involving marine bacteria was developed that allows for rapid and effective quantification of bacterial biofilm growth and retention on large numbers of coating surfaces in parallel. The screening process involves (1) multiwell plate modifications for coating deposition, (2) deposition of combinatorial coating libraries via an automated liquid dispensing robot, (3) coating thickness measurements of cured coatings, (4) preconditioning of coatings via immersion in deionized water, (5) bacterial incubation, (6) plate processing, and (7) data analysis for identification of promising candidates. The details of the method developed are described in this document.

Automation↗
PubMed2005

A combination atmospheric pressure LC/MS:GC/MS ion source: advantages of dual AP-LC/MS:GC/MS instrumentation.

Modification of commercial LC/MS instrumentation to allow both atmospheric pressure (AP) LC/MS and GC/MS is described. Advantages of this additional capability versus LC/MS alone include higher chromatographic resolution in the GC versus LC mode, greater peak capacity for complex mixture analysis, higher sensitivity for a variety of volatile compounds, and the ability to observe compounds of low polarity that are not readily observed in LC/MS. Advantages over conventional GC/MS include the ability to use higher carrier gas flow and shorter columns for passing less volatile materials through the gas chromatograph, selective ionization, and rapid switching between positive and negative ion modes. Other advantages include application of the enhanced capabilities of LC/MS instrumentation to GC/MS analyses such as cone voltage fragmentation, MS(n), high mass resolution, and accurate mass measurement. Limitations of APGC/MS include the inability to observe saturated hydrocarbon and certain other highly nonpolar compounds and less odd-electron fragmentation for computer aided library searching. For some analyses, the limitation related to ionization of highly nonpolar compounds is advantageous, as is the simplified mass spectrum and easy molecular weight identification that results from less fragmentation observed in the AP ionization mode.

Chromatography, High Pressure Liquid↗