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PubMed1993

[Determination of phenobarbital by polarized fluoroimmunoanalysis. The effect of immunogen structure and tracer on specificity and detection limit].

The influence of the immunogen's tracer's structure on properties of antibodies to phenobarbital was studied by the polarisation fluoroimmunoassay method. It was shown that in homogeneous method of polarisation fluoroimmunoassay the titer of antibodies to phenobarbital (1/1000-1/10,000) is affected by the position of linker binding the antigen with carrier-protein and by the structure of the linker. The affinity constant ((1-4) x 10(9) M-1), cross-reactivity, limit of the detection (0.6-2.6 micrograms/ml) phenobarbital with different combinations of antibodies and tracers were calculated. The antisera grew the more heterogeneous in affinity and specificity, the longer became the linker. The more heterogeneous antibodies are preferable in the class specific assay of barbiturates.

Animals↗
PubMed1993

Limiting detection of an amplification signal for HLA-D region and VNTR genes by 32P-PCR.

The limiting detection signal for identification of human genetic markers, such as HLA-D and VNTR genes, was determined using DNA isolated from a series of decreasing numbers of lymphocytes carrying the target marker in the polymerase chain reaction (PCR). The PCR procedure was assembled by incorporating 32P-labeled dCTP in the reaction mixture. Primers specific for detection of MHC Class II genes such as HLA-DR1, -DR2, -DRw52 and -DRw53 were utilized when cells were mismatched by one DR type, and primers for the identification of the region of variable number of tandem repeats (VNTRs) were utilized where cells had the same DR types. The 32P-incorporated amplified DNA was analyzed by polyacrylamide gel electrophoresis followed by exposure to x-ray film. The sensitivity of the test varied for different allelic markers as evaluated by amplification of DNA from each set of a mixture of lymphocytes. The target HLA-DR markers were detectable in a cell ratio of as high as 1:100,000, whereas the VNTR markers were detectable at a 1:1000 cell ratio. The approach described here offers certain advantages: 1) increased sensitivity, 2) quantitative power, 3) reduced assay time, 4) simplified procedure and 5) less expense. This method provides valuable information for studies involving forensic specimens and marrow engraftment after allogenic bone marrow transplantation (BMT) that require discrete representation of one allele relative to another in a heterozygous sample where limited quantities of target DNA are available.

Base Sequence↗
PubMed2005

Iron pentacarbonyl detection limits in the cigarette smoke matrix using FT-IR spectroscopy.

Endogenous metals present in tobacco from agricultural practices have been purported to generate metal carbonyls in cigarette smoke. Transition metal catalysts, such as iron oxide, have been investigated for the reduction of carbon monoxide (CO) in cigarette smoke. These studies motivated the development of an analytical method to determine if iron pentacarbonyl [Fe(CO)(5)] is present in mainstream smoke from cigarette models having cigarette paper made with iron oxide. An FT-IR puff-by-puff method was developed and the detection limit was determined using two primary reference spectra from different sources to estimate the amount of Fe(CO)(5) present in a high-pressure steel cylinder of CO. We do not detect Fe(CO)(5) in a single 35 mL puff from reference cigarettes or from those cigarette models having cigarette paper made with iron oxide, with a 30-ppbV limit of detection (LOD). Also, it was shown that a filter containing activated carbon would remove Fe(CO)(5).

Air Pollutants↗
PubMedDate not supplied

Detection limits of different approaches in behavioral teratology, and correlation of effects with neurochemical parameters.

Five laboratories collaborated in the evaluation of detection limits of different testing concepts in behavioral teratology. In one laboratory, rat dams were treated by gavage with five doses of methylmercury (0.0, 0.25, 0.05, 0.5, and 5.0 mg/kg/day). The treatment period was restricted to days 6 to 9 of gestation. The usual reproduction parameters were assessed in the dams. The offspring (88-99 per group) were subjected to a routine developmental and behavioral testing battery. After completion of these tests, random samples of the animals were further investigated in four other laboratories using the following techniques: auditory startle habituation, visual discrimination and figure-8 activity monitor; wheel-shaped activity monitor and spatial alternation operant conditioning; two-compartment locomotor activity, passive avoidance and male ultrasonic vocalization during sexual behavior; assays of the weight of different brain areas, their glial fibrillary acidic (GFA) protein and S-100 protein concentration. The following dose-dependent effects were noted in ascending dose sensitivity order: delayed vaginal opening; increased and more variable passiveness in spatial alternation; impaired swimming behavior, increased GFA protein concentration in the cerebellar vermis; increased auditory startle amplitude, decreased intertrial interval pokes in the visual discrimination test, increased percentage of visits in passive area of figure-8 activity monitor, increased path iteration frequencies and decreased local activity in the wheel-shaped activity monitor, decreased locomotor activity in the two-compartment monitor, increased cerebellar vermis weight, and decreased S-100 protein in the hippocampus. Therefore, this study showed comparable sensitivities for the behavioral testing battery, for some automated multiparametric test systems and for the neurochemical assays.

Animals↗
PubMed2005

Linearity and detection limit in the measurement of serum M-protein with the capillary zone electrophoresis system Capillarys.

We studied the linearity and detection limits of the capillary zone electrophoresis system Capillarys in the measurement of serum monoclonal protein. Three monoclonal proteins with different isotypes and electrophoretic migrations were diluted with a hypo-gamma-globulinemic polyclonal serum pool. Mathematical linearity was observed for all monoclonal protein isotypes in the ranges studied without removing the polyclonal gamma-globulin background. Theoretical concentrations of 0.43, 0.89 and 0.33 g/L for monoclonal proteins immunoglobulin (Ig)G, IgA and IgM, respectively, gave a discernible spike by Capillarys, although they were measured as 0.76, 1.09 and 0.76g/L, respectively. We observed overestimation of monoclonal protein inversely correlated to concentrations below 15 g/L. All these limitations have to be taken into account when monitoring monoclonal proteins, because the loss of linearity and the protein background may hide an increase in concentration at low levels.

Blood Protein Electrophoresis↗
PubMed2005

Detection limits of matrix-assisted laser desorption/ionisation mass spectrometry coupled to chromatography--a new application of solvent-free sample preparation.

The detection limits of matrix-assisted laser desorption/ionisation mass spectrometry (MALDI-MS) by semi-online coupling with chromatography were investigated using various mixtures of polyethylene oxides (PEOs) with different end groups. In contrast to the common 'dried-droplet' sample preparation technique, which results in an inhomogeneous sample-to-matrix ratio within the MALDI spot, the used coupling technique offers a very high reproducibility combined with surpassing sensitivity of a few femtograms over a broad range of sample-to-matrix ratios. These results are in correlation with the results of the recently established solvent-free MALDI-TOFMS method utilising the grinding approach and are also of assistance towards the more theoretical aspect of MALDI that suggests that there is no necessity for an analyte incorporation into a matrix crystal for excellent matrix-assistance.

Journal Article↗
PubMed2001

Measurement of near zero concentration: recording and reporting results that fall close to or below the detection limit.

Issues relating to the recording and reporting of analytical data obtained where the concentration of analyte is around or below the detection limit are discussed. The following recommendations are proposed. Analytical results should be recorded by the analyst exactly as they occur, including any negative results, and such records retained for an appropriate length of time. For the purposes of quality assurance in the laboratory (including method validation, internal quality control, and proficiency testing), negative results should be used as they stand. Analytical results reported to a customer should be accompanied by a statement of uncertainty including, in the present context, uncertainty at low concentrations of analyte. The method of editing of reported results must be a contractual matter between the analyst and the customer, but a statement of the procedure used should accompany the results and should be explicit. Normally such editing should be restricted to setting negative results to zero. The customer should be encouraged to pass on the statement to all end users. Data intended for the public domain should be accompanied by a statement detailing the uncertainty, the method of editing, and the location of the unedited data. Most types of statistical processing of datasets containing low concentrations of analyte should be undertaken on the unedited data.

Journal Article↗
PubMed1989

Postoperative pentagastrin-stimulated serum calcitonin concentrations in patients with medullary thyroid carcinoma: reoperations in patients with concentrations bordering the detection limit.

The case reports on two patients with medullary thyroid carcinoma show that even postoperatively stimulated serum calcitonin (CT) concentrations near the detection limit (using a polyclonal antibody against synthetic CT) can demonstrate persistent disease. Stimulated CT concentrations can be lowered to nondetectable levels by a second and third operation if a meticulous technique is used for dissection of the lymph compartments. The patient can then be assumed to be cured. Diagnostic accuracy at very low CT concentrations can be improved by selective venous catheterization with blood sampling for CT after stimulation.

Adult↗
PubMed1999

Silicon-29 nuclear magnetic resonance spectroscopy detection limits.

We show that an unmodified, commercially available high-field (17.61T) NMR spectrometer using the DEPT pulse sequence is capable of detecting silicon-containing species down to concentrations of 150 ng/mL (150 ppb) per spin site. This is in the range given for the concentration of silicon in the blood of silicone breast implant recipients, as determined by ICP analysis, and demonstrates that, contrary to the view expressed in the literature, in theory 29Si NMR may be sufficiently sensitive to be of use in determining the nature of the silicon-containing species present. A summary of the factors affecting the detection limits in NMR spectroscopy is given.

Breast Implants↗
PubMed2001

Detection limits of beta-lactam antibiotics in ewe milk by penzym enzymatic test.

The Penzym is an enzymatic test widely used for the detection of beta-lactam antibiotic residuals in milk. It is a specific method with good sensitivity to this group of antibiotics and enables results to be obtained within a short time. In the present work, the detection limits of 10 beta-lactam antibiotics were determined in ewe milk, given the lack of previous studies of the Penzym test in ovine milk. For each antibiotic, eight concentrations were tested on 20 ewe milk samples proceeding from individual ewes (160 analyses per drug). The limits of the Penzym test were determined by means of logistic regression models, as follows: 5 microg/kg amoxicillin, 4 microg/kg ampicillin, 33 microg/kg cloxacillin, 3 microg/kg penicillin "G," 43 microg/kg cephadroxil. 10 microg/kg cephalosporin "C," 16 microg/kg cephalexin, 900 microg/kg cephoperazone, 120 microg/kg Ceftiofur, and 77 microg/kg cephuroxime. The percentages of positive results for those antibiotics at the maximum residue limit (MRL) concentration established by the European Union (EU) were: 100% (penicillin "G"), 93.3% (ampicillin), 93.3% (cloxacillin), 56.7% (Ceftiofur), and 56.7% (amoxicillin).

Animals↗
PubMed2003

Practical considerations in the gas chromatography/combustion/isotope ratio monitoring mass spectrometry of 13C-enriched compounds: detection limits and carryover effects.

This paper describes a methodological investigation of the use of gas chromatography/combustion/isotope ratio monitoring mass spectrometry (GC/C/IRMS) for the compound-specific stable isotope analysis of 13C-enriched compounds. Analysis of two 13C-enriched fatty acid methyl esters, possessing delta13C values of approximately 500 per thousand, at a range of concentrations, demonstrated that detectable responses, i.e. chromatographic peaks, could be observed in the 45/44 output even when the compound was present in such low abundance that no peak was observed in the m/z 44 ion chromatogram. A limit of detection, defined as the point at which the signal-to-background ratio was equal to 3, was calculated for two compounds and for both ion chromatograms. The limit of detection in the 45/44 chromatogram was found to be ca. 30 pg injected for methyl 13C-hexadecanoate and ca. 20 pg injected for methyl 13C-octadecanoate, whilst, in the m/z 44 ion chromatogram, detection limits were approximately 180 and approximately 200 pg, respectively. The delta13C value recorded for the analytes was found to be both inaccurate and imprecise below 5 ng of each component injected, although this would not represent a significant drawback in qualitative tracer-type experiments. In a further study of co-injected mixtures of labelled (approximately 500 per thousand) and unlabelled (natural abundance, -20 to -30 per thousand ) fatty acid methyl esters a significant within-run carryover effect was observed, where the isotope values recorded for compounds eluting immediately after enriched components were significantly affected. Whilst this would not affect qualitative results, quantitative data for mixtures containing enriched compounds should be considered with caution. The standards employed in this investigation were enriched to approximately 500 per thousand in 13C; however, these effects would probably be accentuated at higher levels of labelling and with other elements. The limit of detection work demonstrated the potential of GC/C/IRMS as a highly sensitive and selective detector with many possible applications.

Journal Article↗
PubMed2005

Determination of biochemical relapse after radical prostatectomy by biological detection limit (BDL) after cystoprostatectomy using two PSA assays.

The monitoring of PSA values following prostatectomy demands for the use of highly sensitive tests with low detection level. The possibilities to use the EIA Dialab test to monitor the PSA values after radical prostatectomy for early detection of persistent diseases were investigated by determining the biological detection limit (BDL) in serum of patients who unrewent cystoprostatectomy. The obtained values were compared with Abbott Imx test for PSA determination. A good correlation between the two studied methods was establisahed, r = 0.9827 with the regression curve Yx = 0.20463 + 0.96277. Test indicated that there was no significant difference (p < 0.001) between the investigated methods.

Cystectomy↗
PubMed2004

A universal nucleic acid sequence biosensor with nanomolar detection limits.

A quantitative universal biosensor was developed on the basis of olignucleotide sandwich hybridization for the rapid (30 min total assay time) and highly sensitive (1 nM) detection of specific nucleic acid sequences. The biosensor consists of a universal membrane and a universal dye-entrapping liposomal nanovesicle. Two oligonucleotides, a reporter and a capture probe that can hybridize specifically with the target nucleic acid sequence, can be coupled to the universal biosensor components within a 10-min incubation period, thus converting it into a specific assay. The liposomal nanovesicles bear a generic oligonucleotide sequence on their outer surface. The reporter probes consist of two parts: the 3' end is complementary to the generic liposomal oligonucleotide, and the 5' end is complementary to the target sequence. Streptavidin is immobilized in the detection zone of the universal membranes. The capture probes are biotinylated at the 5' end and are complementary to another segment in the target sequence. Thus, by incubating the liposomal nanovesicles with the reporter probes, the target sequence, and the capture probes in a hybridization buffer for 20 min, a sandwich complex is formed. The mixture is applied to the membrane, migrates along the strip, and is captured in the detection zone via streptavidin-biotin binding. The biosensor assay was optimized with respect to hybridization conditions, concentrations of all components, and length of the generic probe. It was tested using synthetic DNA sequences and authentic RNA sequences isolated and amplified using nucleic acid sequence-based amplification (NASBA) from Escherichia coli, Bacillus anthracis, and Cryptosporidium parvum. Dose-response curves were carried out using a portable reflectometer for the instantaneous quantification of liposomal nanovesicles in the detection zone. Limits of detection of 1 fmol per assay (1 nM) and dynamic ranges between 1 fmol and at least 750 fmol (1-750 nM) were obtained. The universal biosensors were compared to specific RNA biosensors developed earlier and were found to match or exceed their performance characteristics. In addition, no changes to hybridization conditions were required when switching to the detection of a new target sequence or when using actual nucleic acid sequence-based amplified RNA sequences. Therefore, the universal biosensor described is an excellent tool for use in laboratories or at test sites for rapidly investigating and quantifying any nucleic acid sequence of interest.

Animals↗
PubMed2005

A novel approach for the determination of detection limits for metal analysis of environmental water samples.

Despite the widespread use of the USEPA method (U.S. Environmental Protection Agency, 40 CFR 136 Appendix B) for the determination of method detection limit (MDL), criticisms have been raised that the method does not account for measurement bias and outliers that subsequently lead to a common misunderstanding of the requirement for the determination of MDL. This paper demonstrates that it is difficult to follow the USEPA method for verifying the MDL for analysis involving multiple metals and proposes a precision and bias criterion for determining the MDL. A multiple-point fitted profile, based on the correlation between relative standard deviation (RSD) and concentration, is used to derive a robust MDL value. Representative examples of As, Ca, Cr, and Cu are used to illustrate this procedure. A procedure for identifying outliers is also discussed.

Arsenic↗
PubMed2004

Wall-less sample preparation of microm-sized sample spots for femtomole detection limits of proteins from liquid based UV-MALDI matrices.

Previously, we introduced wall-less sample preparation (WaSP), technology that involves the use of an electrodynamic balance (EDB) to prepare microm-sized sample spots for analysis by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS). In that work we demonstrated the detection of femtomole quantities of a low molecular weight peptide and a hydrophobic ester (both <600 Da). Here we use WaSP to test the hypothesis that the use of small sample spot sizes and an instrument equipped with delayed extraction would increase the analytical utility of liquid sample spots for peptide and protein (>2500 Da) analysis by UV-MALDI-TOF-MS (Sze et al.; J. Am. Soc. Mass Spectrom. 1998, 9, 166-174). To aid the optimization of preparing microm-sized sample spots by WaSP, optical microscopy and mass spectrometry were used to investigate nonvolatile solute concentration effects on droplet fission and sample spot size, modifications of the EDB electric field to control droplet ejection, and the use of multiple droplet deposition to increase sample loading. Also described is a rapid deposition mode of operation for WaSP that allows single droplets generated at 1 Hz to be levitated briefly ( approximately 500 ms) before being ejected autonomously and deposited as a concentrated sample spot with a spatial accuracy of +/-5 microm. To test the sensitivity of the method, one hundred glycerol droplets (270 pL each, 27 nL total) each containing 32 amol lysozyme were deposited on top of each other one-at-a-time to create a single sample spot. Using a mass spectrometer equipped with delayed extraction to analyze this sample spot, we verified the hypothesis of Sze et al. by achieving detection limits three orders of magnitude below that previously observed for the detection of a protein by UV-MALDI-TOF-MS with a chemical-doped liquid matrix sample preparation.

Adrenocorticotropic Hormone↗
PubMed1993

Modified assay of prostate-specific antigen with a detection limit < 0.01 microgram/L.

We modified the Hybritech Tandem-E prostate-specific antigen (PSA) assay by increasing the sample volume, increasing enzyme-substrate incubation time, and using diethanolamine buffer. Our modified method has a detection limit of 0.009 microgram/L (P < 0.01). The assay curve is linear from 0.01 to 1.0 micrograms/L and has an overall assay time of about 4 h. Linear plots are obtained when the 1.0 micrograms/L standard is diluted with either matrix buffer or serum from men containing PSA < 0.01 microgram/L. Recovery of PSA (0.10 microgram/L) added to serum from men averaged 94%. Interassay CVs were 13%, 7%, and 4% at PSA concentrations of 0.04, 0.07, and 0.30 micrograms/L, respectively (n = 33). This assay should be useful in the detection of early recurrence of prostate cancer after radical prostatectomy.

Autoanalysis↗
PubMed1989

Radioimmunoassay detection limits for 19-OH F1 alpha/F2 alpha prostaglandin in normal, infertile and vasectomized semen stains. Analysis of saliva, sweat and urine for possible non-specific or matrix effects.

The sensitivity of a simple radioimmunoassay (RIA) for the detection of 19-OH prostaglandin F1 alpha/F2 alpha (PG F) has been evaluated on a number of semen samples from vasectomized, infertile and fertile donors. The specificity of the test has been examined by testing saliva, sweat and urine from a number of male and female donors. The assay technique could readily detect the PG in semen stains prepared from 0.2 microliter of semen from normal, infertile and vasectomized donors. The detection limit of the assay system, based on the observed displacement, was calculated to be approximately 0.05 microliter semen. The assay could be conducted over a pH range of 7.5-10.5 even after the PG has been heated to 100 degrees C. The 19-OH series of PG were absent from sweat, saliva and female urine using the normal assay protocol; volumes in excess of 100 microliters of some urines particularly from women in labour and those with acute urinary tract infection showed some displacement. Low levels of PG were detected in 50% of the male urine analysed. However, urine samples from men who had engaged in recent sexual activity contained relatively high concentrations of PG which could be readily detected in 10 microliters of urine. These results emphasise the potential of these compounds as specific and sensitive markers for the presence of human semen.

Dinoprost↗