SEARCH · PubMed Health

Results for “Limit of Detection”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 37 records · Page 2Linked to original sources

PubMed2002

An HPLC method for the measurement of 5-fluorouracil in human plasma with a low detection limit and a high extraction yield.

High performance liquid chromatographic (HPLC) techniques for the quantification of 5-fluorouracil (5-FU) in human plasma have been reported in the literature, however, a low limit of detection was generally found to result in a comparatively low extraction yield. We have developed a simple, rapid and sensitive HPLC method for the measurement of 5-FU in plasma which provides both a low limit of quantification and a high extraction yield. This method involves the solid phase extraction of 5-FU from a 500 microl plasma sample. The extract is then injected into an HPLC system equipped with a C18 (mu)Bondapak column, and a UV detector set at 260 nm. Ethyl acetate and potassium dihydrogen phosphate are used for the solid phase extraction and the HPLC mobile phase, respectively. This method provides in a good baseline, a sharp and symmetrical peak for 5-FU, and a high resolution between 5-FU and the internal standard. The retention time of 5-FU using this method is 4.7 min with a limit of detection of 5 ng/ml, and an extraction yield of 96.2+/-0.5% (SE). The next injection is possible in 11 min, and the coefficients of variation are 4.2-8.9% for interday precision, and 5.2-10.6% for day-to-day reproducibility. An HPLC method has been developed that has a low limit of detection and a high extraction yield. This technique was successfully applied in a clinical pharmacokinetic study of 5-FU.

Chromatography, High Pressure Liquid↗

PubMed2001

Detection limits for GC/MS analysis of organic explosives.

Method detection limits are determined and compared for analysis of liquid injections of organic explosives and related compounds by gas chromatography-mass spectroscopy utilizing electron impact (EI), negative ion chemical ionization (NICI), and positive ion chemical ionization (PICI) detection methods. Detection limits were rigorously determined for a series of dinitrotoluenes, trinitrotoluene, two nitroester explosives, and one nitramine explosive. The detection limits are lower by NICI than by EI or PICI for all explosives examined, with the exception of RDX. The lowest detection limit for RDX was achieved in the PICI ionization mode. Judicious choice of the appropriate ionization mode can enhance selectivity and significantly lower detection limits. Major ions are reported for each analyte in EI, PICI, and NICI detection modes.

Journal Article↗

PubMed1993

Application of systematic error bounds to detection limits for practical counting.

Overly optimistic estimates of detection limits can result in the use of unrealistic conservatism for decisions about the presence of activity. In some practical counting situations, overly conservative detection limits can result in economically impractical actions. To help preclude such actions, systematic error bounds, uncertainties, and confidence levels can be used when determining critical levels (Lc), detection limits (Ld), and minimum detectable concentrations. This note discusses the selection of such error bounds and the development of detection limit parameters for practical applications. These parameters are shown to be successfully employed in sample activity and measurement process capability decisions for typical counting instruments.

Radiometry↗

PubMed1992

Detection limit concepts: foundations, myths, and utilization.

Detection limit parameters such as the minimum detectable concentration have been widely discussed in the literature for more than 30 y. Misunderstanding and misapplication of these parameters continue to be widespread and, indeed, even encoded into computer programs, especially those developed in recent years for use with PC-based analyzer boards. This brief review of the principal concepts related to the most common types of detection limits provides guidance for correctly using these parameters. In particular, several myths concerning issues such as the "sample-specific minimum detectable concentration" and the "unreliability" of measurements made below this concentration are discussed.

Radiometry↗

PubMed2002

Evaluation of the separate equilibrium processes that dictate the upper detection limit of neutral ionophore-based potentiometric sensors.

The upper detection limit of polar ionophore-based ion-selective electrode membranes is predicted by utilizing the coextraction constant of dissociated electrolyte, the stability constant of the ionophore, and the membrane composition. The coextraction constant of dissociated electrolytes into the polar poly(vinyl chloride) membrane plasticized with o-nitrophenyl octyl ether (PVC-NPOE) is here measured by a novel approach. The sandwich membrane technique is utilized, with one membrane segment containing a lipophilic cation exchanger and the other containing an anion exchanger. This yields information about the coextraction constant and the free ion concentrations of the electrolyte in the two segments. Predictions correlate quantitatively with the upper detection limit observed for ion-selective electrodes based on the ionophores valinomycin, tert-butylcalix[4]arene tetraethyl ester, and calcimycin. The difficulties of the prediction of the upper detection limit for nonpolar poly(vinyl chloride) membranes plasticized with bis(2-ethylhexyl sebacate) (PVC-DOS) due to ion association are discussed in detail. A thermodynamic cycle experiment with a series of sandwich membranes shows that the principal processes governing the upper detection limit of PVC-DOS membranes are identical to those for the PVC-NPOE membranes. However, the stability of the ion pairs between the ionophore-metal ion complexes and the extracted anion are different from that of ion pairs formed between the same anion and the lipophilic anion exchanger. This makes it difficult to quantitatively predict the upper detection limit on the basis of simple apparent coextraction and complexation data alone. The approach reported herein is useful not only for mechanistic purposes but also to shed light onto the many cases where coextraction effects need to be understood but are not directly experimentally accessible.

Algorithms↗

PubMed1993

Specificity and detection limit of ten pregnancy tests.

Pregnancy tests have sufficiently low detection limits (25-200 IU/L of human chorionic gonadotropin, hCG) and good specificity as judged by lack of cross-reaction with lutropin (LH) and follitropin (FSH). However, little information is available on the specificity of the tests for subunits and fragments of hCG. The dominating form of hCG immunoreactivity in pregnancy urine is actually a 10 kD fragment of the beta chain of hCG called the core fragment. We have evaluated ten commonly used pregnancy test with respect to specificity for various forms of hCG and detection limit. Our results show that the detection limits of the tests are close to that claimed by the manufacturers and that the main form of hCG immunoreactivity detected is intact hCG. Four of the tests also measure the free beta subunit of hCG and one method also the hCG beta core fragment, but the detection limits were 7-70 fold those for hCG.

Chorionic Gonadotropin↗

PubMed1998

Statistical procedures for estimating the detection limit and determination limit of the Ames Salmonella mutagenicity assay.

Novel and flexible procedures for estimating the detection limit as well as the determination limit of the Ames mutagenicity assay were proposed to evaluate the genetoxicity of a water sample. The accumulated data under the test conditions of TA 100-S9 by our group were taken as examples and analyzed to estimate the detection limit and the determination limit. The detection limit was estimated at 1.7 as the MR value when duplicate plates were used in the negative control test. However, it decreased to 1.4 as the MR level when quadruple plates were used in the negative control test. Therefore it was found that the sensitivity of the Ames mutagenicity assay was improved very easily by increasing the number of plates for the negative control test from two to four. The application of the conventional twofold rule to the data obtained with the strain TA100 was considered too conservative. The determination limit was regarded at 2.2 as the MR value under the following conditions: (a) quadruple plates were used in the negative control test; (b) three dose-steps including negative control step were designed at regular intervals; and (c) duplicate plates were used for each dose-step. It was proved by comparing data of two students that the detection limit and the determination limit estimated in this study were considered acceptable to any well trained students.

Biometry↗

PubMed2003

An unusual systematic behaviour of detection limits for elements from 55Cs to 73Ta.

A representative database for detection limits for all elements from (55)Cs to (73)Ta reveals that these limits are governed by a systematic zigzag pattern, according to which the odd atomic number elements have systematically lower detection limits than the even atomic number neighbour elements. This is true even when the actual detection limits vary by several orders of magnitude. We propose that such a systematic pattern be used as a requisite analytical criterion to evaluate the detection limit data, and any departure from this pattern be looked on with caution to check the analytical technique for any interference or matrix effect problems.

Journal Article↗

PubMed1988

The determination of detection limits for insulin antibody assays.

In order to define the detection limit of a radioimmunoassay for insulin-antibody a correction was made for binding in the presence of an excess of unlabelled insulin and assay precision was calculated. One hundred forty control sera were assessed; all were islet cell antibody negative. For each sample, binding of 125-I human insulin was determined both with and without excess unlabelled insulin, subtraction of the latter acting as a correction. The distribution of uncorrected binding was skewed while corrected binding was normally distributed, (mean (SD) = 0.149 (0.298%)) Precision, defined as the mean of the standard deviations of replicates, was 0.263%. Detection limits calculated from the estimate of precision (0.263%) or from the standard deviation of the corrected binding (0.298%) were similar. Two hundred thirty sera from insulin-treated patients were studied. Precision was plotted as a 'precision profile' and the detection limit calculated from the precision for binding of less than 1% [0.261%]; 88% of the sera were positive [cut-off 1.3%, p less than 0.01]. We conclude that corrected binding is normally distributed in antibody-negative sera and that an estimate of assay precision can be used to define the detection limit of the assay.

Antigen-Antibody Complex↗

PubMed2005

Sample preparation for evaluation of detection limits in X-ray fluorescence spectrometry.

The influence of analyte mass concentration on determination of detection limits in X-ray fluorescence spectrometry has been investigated experimentally. Both the total reflection X-ray fluorescence (TXRF) and the conventional energy-dispersive X-ray fluorescence techniques have been used to derive the dependence of analyte mass concentration on the values of detection limits. Results obtained indicate that values of detection limits are optimum, or in other words, they are closer to the true detection limit of the technique, when analyte concentrations are in the range of 10 times of the detection limit.

Journal Article↗

PubMed2005

Estimation of a method detection limit for an in vivo XRF arsenic detection system.

An x-ray fluorescence measurement system has been developed with an 125I source to detect arsenic in superficial layers of phantoms and tissue. Based on in vivo measurements, in conjunction with Monte Carlo simulations, the detection limit for arsenic in skin ranges between 2.6+/-0.5 and 5.7+/-1.1 microg g(-1), depending on skin thickness and assuming that arsenic is uniformly distributed in the skin. The effect of skin arsenic distribution was also examined.

Arsenic↗

PubMed2001

Effect of lipophilic ion-exchanger leaching on the detection limit of carrier-based ion-selective electrodes.

The equilibrium partitioning of lipophilic ion-exchanger salts from ion-selective polymeric membrane electrodes (ISEs) and its possible effect on the lower detection limit of these sensors is described. Predictions are made on the basis of various parameters, including the knowledge of tetraphenylborate potassium salt partitioning constants, the selectivity of ionophore-free ion-exchanger membranes, and ionophore stability constants in the membrane. Ion-exchanger lipophilicities are significantly increased if the membrane contains an ionophore that strongly binds the primary ion. Predicted detection limits are on the order of 10(-5)-10(-8) M for ionophore-free membranes, and may reach levels as low as 10(-18) M with adequate ionophores in the membrane. Experiments are performed for well-described lead-selective membranes containing different tetraphenylborate derivatives, and detection limits appear to be independent of the ion-exchanger used. However, they are much higher if a more hydrophilic carborane cation-exchanger is incorporated in the membrane. The first finding confirms recent theory, which states that transmembrane ion fluxes, given by a small level of ion-exchange at the sample side by interfering ions, normally dictate the detection limit of these sensing systems. Predicted detection limits on the basis of ion-exchanger leaching alone are here listed for a number of analytically relevant cases. For potassium-selective electrodes containing BME-44 and tetraphenylborate as ion-exchanger, the experimental detection limits are in agreement with predicted values. These results suggest that the detection limit of many current ISEs for ultratrace level analysis are, in optimal cases, dictated by transmembrane ion fluxes; however, because improved chemical solutions are being developed to reduce such effects, simple ion-exchanger partitioning may indeed become an important mechanism that can give higher detection limits than practically desired, and should not be ruled out.

Biosensing Techniques↗

PubMedDate not supplied

The biologic lower detection limit of six ultrasensitive PSA assays.

BACKGROUND: The benefit of monitoring patients with prostate cancer (PCA) by ultrasensitive measurement of prostate specific antigen (PSA) is frequently discussed. Usually, the analytic lower detection limit of an ultrasensitive assay is determined by the manufacturer. As the analytic lower detection limit does not take into account interfering factors of human serum, the biologic lower detection limit, which is defined as PSA concentration detected in PSA-free human serum, plus 3 standard deviations, is of greater interest. MATERIALS AND METHODS: We investigated the biologic lower detection limit of six ultrasensitive PSA assays. Sera from 15 men with bladder cancer after radical cystoprostatectomy and from 30 healthy women were applied. Hence, we expected no PSA of prostatic origin. RESULTS: The biologic lower detection limit obtained using these sera was up to 30 fold higher (men, 0.29-0.63 ng/ml; women, 0.03-0.69 ng/ml) than the analytic lower detection limit (0.01-0.09 ng/ml). CONCLUSIONS: PSA measurement in sera obtained from men without prostate and women results in PSA values above the ultrasensitive range. Therefore, advantages provided by ultrasensitive PSA measurement in monitoring PCA patients after radical prostatectomy are limited.

Environmental Monitoring↗

PubMed1984

[A radioimmunoassay for the determination of human myoglobin: lower detection limit, precision and use in control of myoglobinuric kidney failure].

The lower detection limit of a radioimmunoassay for human myoglobin was determined by two "precision from day to day" methods (90% and 3 s methods), and by two "precision in series" methods (95% confidence range and the method of Markowetz & Munz). According to Markowetz & Munz, the lower detection limit (as a measure of sensitivity) is the lowest myoglobin concentration which, in 15-fold assays, shows no binding value in common with that of the next highest concentration, and no activity value in common with that of the reference binding value. On theoretical grounds (precision in series) and from a practical standpoint (determination of the lower detection limit using one sample assay), this method is the most suitable for the determination of the lower detection limit as a measure of sensitivity. It remains to be seen whether this is a valid generalization for other methods.

Creatinine↗

PubMed1997

Detection limits for samples that give rise to counting data with extra-Poisson variance.

Detection limits are presented for duplicate background samples that produced counting data with extra-Poisson variance that was attributed to a nonuniform activity distribution in the background sample medium. The presence of extra-Poisson variance was detected using the chi-squared test, where the presumed change in baseline activity from sample to sample was interpreted as an increase in experimental population variance. The runs test and Wilk-Shapiro test verified, respectively, the acceptable randomness of the data and the hypothesis that the data are normally distributed. Confidence intervals for detection limits therefore were based on the normal and t-distributions. The reduced chi-squared statistic was incorporated into the equations for the critical level and lower limit of detection to account for experimental variance beyond the expected Poisson value. The incorporation of extra-Poisson variance increased these detection limits for a well-defined background by a factor of 2.3 compared to the expected values for the paired-sample method which were derived under the assumption of Poisson variance, where the 30 background measurements have a reduced chi-squared statistic of 9.44.

Air Pollutants, Radioactive↗

PubMed2004

Epidemiologic evaluation of measurement data in the presence of detection limits.

Quantitative measurements of environmental factors greatly improve the quality of epidemiologic studies but can pose challenges because of the presence of upper or lower detection limits or interfering compounds, which do not allow for precise measured values. We consider the regression of an environmental measurement (dependent variable) on several covariates (independent variables). Various strategies are commonly employed to impute values for interval-measured data, including assignment of one-half the detection limit to nondetected values or of "fill-in" values randomly selected from an appropriate distribution. On the basis of a limited simulation study, we found that the former approach can be biased unless the percentage of measurements below detection limits is small (5-10%). The fill-in approach generally produces unbiased parameter estimates but may produce biased variance estimates and thereby distort inference when 30% or more of the data are below detection limits. Truncated data methods (e.g., Tobit regression) and multiple imputation offer two unbiased approaches for analyzing measurement data with detection limits. If interest resides solely on regression parameters, then Tobit regression can be used. If individualized values for measurements below detection limits are needed for additional analysis, such as relative risk regression or graphical display, then multiple imputation produces unbiased estimates and nominal confidence intervals unless the proportion of missing data is extreme. We illustrate various approaches using measurements of pesticide residues in carpet dust in control subjects from a case-control study of non-Hodgkin lymphoma.

Bias↗

PubMed1990

Estimation of analytical values from sub-detection limit measurements for water quality parameters.

A method is described for estimating analytical values for water quality parameters from sub-detection limit measurements. The method, which is referred to as the error approximation (EA) procedure, relies on quality control analytical procedures and on the assumption that the bulk of the analytical error associated with measurements at or near the detection limit exists within k = -3 to +3 standard deviations for normally (or approximately normally) distributed errors. The EA procedure also assumes that the analytical errors are equally distributed on each side of half the detection limit and that the sub-detection limit value lies between zero and the detection limit.

Indicators and Reagents↗

PubMed2000

Effect of incident angle of light on sensitivity and detection limit for layers of antibody with surface plasmon resonance spectroscopy.

The effect of the incident angle of light on sensitivity and the detection limit for surface-plasmon resonance spectroscopy were examined. The sensitivities and the detection limit were experimentally measured using an antibody as a modeled analyte in the incident angles of a light region of 66-76 degrees. The results showed that the sensitivity of a smaller incident angle was higher than that of a larger one. For instance, the sensitivity of a 66 degree incident angle was three times higher than that of a 76 degree incident angle. The detection limit with a 66 degree incident angle was one-tenth of that with a 76 degree incident angle. These sensitivities and detection limits were compared with those of a commercially produced surface-plasmon resonance instrument. This comparison demonstrated that a wavelength resolution of the order of less than 10(-2) nm was necessary to obtain satisfactory sensitivities and detection limits. In addition, the refractive index and thickness of the antibody layer formed on a sensor surface was proposed by experimental results and theoretical calculation.

Adsorption↗