Quantitative Detection Limit Research Articles

Quantitative bioassays for determining residues and availability to plants of sulphonylurea herbicides

SummaryA bioassay procedure for quantitative determination of sulphonylurea herbicides is described. Turnips (Brassica rapa) were found very suitable as test plants and gave results within 10 days. Six sulphonylurea compounds were investigated for their activity in three widely differing soils. The potential availability to plants was calculated from the dose‐response curves of vermiculite (non‐sorptive substrate) and the corresponding ED50‐values of the soils. The dose‐response relationship (logistic curve) was described by a computer model by a position parameter, the slope of the curve and the minimum and maximum fresh weights of plants. The limit of quantitative detection in the range of ED30 in vermiculite was 0·06 μg 1−1 for sulfometuron and 1·03 μg 1−1 for DPX‐L5300, methy12‐([4‐methoxy‐6‐methyl‐1,3,5‐triazin‐2‐yl (methyl)carbamoyl]‐sulphamoyl) benzoate. Results with turnips showed that sulfometuron was the most active compound in all substrates (ED50 in vermiculite 0·12 μg 1−1) followed by chlorsulfuron, metsulfuron‐methyl, triasulfuron, DPX‐M6316, methyl 3‐([(4‐methoxy‐6‐methyl‐1,3,5‐triazin‐2‐yl)aminocarbamoyl]‐aminosulphaphamoyl)‐2‐thiophenecarboxylate, and DPX‐L5300 which had ED50 or 1·98 μg 1−1, The Horotiu sandy loam soil showed the highest ED50‐values and the lowest plant availability for all compounds compared to the other soils. Probit and logistic evaluation methods for deriving dose‐response relationships are compared and their applicability is discussed.

INSTRUMENTAL DETERMINATION OF INDIUM IN GEOCHEMICAL REFERENCE SAMPLES BY EPICADMIUM NEUTRON ACTIVATION ANALYSIS AND KO ‐STANDARDIZATION

The determination of indium in geological materials is difficult by usual analytical techniques because of their lack of sensitivity. Neutron activation analysis with special irradiation and counting conditions allows to determine indium ultra‐traces with a quantitative detection limit about a few parts per billion. The method developed is fast and very sensitive and has been tested successfully for several American and French geochemical standards.

Determination of physostigmine in plasma by high-performance liquid chromatography and fluorescence detection

Physostigmine (PHY) is an anticholinergic drug used in the treatment of neuromuscular disorders and organophosphate poisoning. We described a sensitive, accurate, and reproducible method for PHY determination in biological materials. The method utilized a liquid/liquid, ion pair extraction, normal phase HPLC separation, and fluorometric quantitation at 240 nm excitation and 360 nm emission wavelength. We used neostigmine as a stabilizing agent to protect PHY from degradation and dimethylphysostigmine as an internal standard. The peak-height ratio vs concentration was linear over a working range from 0.50 to 25.0 ng/ml of PHY in plasma. Sensitivity of the method was 100 pg/ml of plasma which was the limit of quantitative detection under the experimental conditions used. Precision of the method was evaluated using plasma spiked with two concentrations of PHY: 1.0 and 10.0 ng/ml. Intraday coefficient of variation (CV) ranged from 3.8 to 5.3%, and inter-day CV ranged from 1.8 to 3.6% for the two levels. The average recovery was 92%. We applied the method to examine the stability of PHY in plasma stored at −15 and −80°C. The data indicated that PHY can be stored at either temperature for 9 weeks without undergoing significant alterations.

The simultaneous determination of diacetoxyscirpenol and T-2 toxin in fungal cultures and grain samples by capillary gas chromatography.

A method for the quantitative determination of the toxic fungal products diacetoxyscirpenol and T-2 toxin is described. Initially intended for the screening of fungal cultures grown on maize, it has subsequently been used successfully for the analysis of maize and oat grain samples. The method involves extraction with aqueous methanol followed by a two-stage clean-up procedure utilizing a commercial kieselguhr column and a silica gel cartridge. The heptafluorobutyryl derivatives of the trichothecenes, including neosolaniol monoacetate used as an internal standard, are separated on a 25 m X 0.32 mm SE-30 fused silica capillary column and measured with a 63Ni electron capture detector. The quantitative detection limit was found to be of the order of 200 ng/g (ppb) with an average recovery from maize of 88% for both toxins. The method was found to be rapid and practical with the advantage that the kieselguhr packing material could be easily regenerated and re-used. The method was compared with those reported in the literature which are currently in use.

Rapid determination of p-hydroxylated methamphetamine metabolites by column liquid chromatography—electrochemistry

A method for electrochemical determination of p-hydroxymethamphetamine and p-hydroxyamphetamine in human urine was investigated by column liquid chromatography. A rapid and simple extraction of these substances from urine was performed using a solid-phase extraction column. The detection limit for quantitation was approximately 50 pg for the metabolites. The simplicity and sensitivity of this method allows for analysis of these metabolites in the fields of toxicology and forensic medicine.

The medical and scientific evidence in alleged tubocurarine poisonings. A review of the so-called Dr. X case

The problem of proving the presence or absence of a poison in a buried cadaver is the central theme of this presentation. Certain general questions are posed which may serve to guide those seeking to determine the cause of death in buried cadavers and allegedly due to a poison. Medicolegal and scientific evidence is presented from the court records of five deaths which were alleged homicides due to intravenous tubocurarine. As to the medical evidence: The prosecution claimed absence of adequate medical causes but full congruence with intravenous tubocurarine as the cause of death. The defense claimed and presented its evidence, including history, clinical picture, gross and microscopic pathological findings — for the deaths having occurred from competent natural causes in all but one case. In that one case the cause was undetermined. In two of the four cases evidence was presented for the mechanism of death and why they died at the time that they did. As to the forensic toxicological evidence: The prosecution claimed qualitative identification but with no particular quantitative detection or identification limits of tubocurarine in the remains based on results of combinations of HPLC followed by RIA and of some selected ion direct inlet mass spectrometry. The defense corroborated — along with a quantitative estimate — the presence of a substantial concentration of tubocurarine in the liver specimen of one case. However the chain of custody of this particular specimen was compromised for a period of several days between post-exhumation autopsy and submission to the prosecution toxicologists. With respect to all the other specimens examined by the defense, direct inlet mass spectrometry failed to show ions which are critical for establishing the identity of tubocurarine. The defense also presented results of experiments which showed that the tissues of the cases in question destroyed tubocurarine at such a rate that no reasonably conceivable administered amount could have survived the 10 years of burial of these cases. In each of the five cases exhumation and re-autopsy would have been found to be neither justified nor even indicated had an objective examination of the available record been made and supplemented by a similarly objective review of the literature and the simple stability experiments used by the defense. After an 8-month trial, the jury brought in a not guilty verdict on all counts after less than 2 h of deliberations.

Metal Oxide Solubility in Eutectic Li/K Carbonate Melts

The equilibrium solubility of NiO, CuO, ZnO, LiFeO/sub 2/, and LaNiO/sub 3/ in binary Li/K carbonate was quantitatively measured between 823 and 1223 K under a simulated molten carbonate fuel cell cathode environment. The solubility of all materials, except LaNiO/sub 3/, was found to increase with increasing temperature. Equilibrium solubilities at 923 K, the operating temperature of a molten carbonate fuel cell, were determined to be 13 X 10/sup -6/, 32 X 10/sup -6/, 63 X 10/sup -6/, and 16 X 10/sup -6/ mole fraction for NiO, CuO, ZnO, and LiFeO/sub 2/, respectively. The LaNiO/sub 3/ solubility remained below the quantitative detection limit until the melt's temperature exceeded 1123 K, at which time material decomposition was detected.

The decomposition of benzodiazepines during analysis by capillary gas chromatography/mass spectrometry.

A capillary gas chromatography column directly interfaced to a mass spectrometer was used for the analysis of sixteen benzodiazepines. The thermal stability of the drugs was found to be related to their chemical structure. Nine of the benzodiazepines were thermally unstable indicating that care should be taken in the interpretation of gas chromatographic data from this class of drugs. The unstable benzodiazepines were: ketazolam which decomposes to diazepam; N-4 oxides (chlordiazepoxide and demoxepam) which lose an oxygen radical; aromatic 7-nitro compounds (nitrazepam and clonazepam) which are partially reduced to the corresponding amine; alpha-hydroxy ketones (lorazepam and oxazepam) which decompose with the loss of water and N-methyl-alpha-hydroxy ketones (lormetazepam and temazepam) which partially decompose with the loss of a hydrogen molecule to produce the corresponding alpha, beta-diketones. Few problems were encountered in distinguishing the drugs by their mass spectra, the exceptions being ketazolam which decomposes to diazepam and demoxepam which decomposes to desmethyldiazepam. In general, good spectra were obtained from 20-50 ng of drug injected. However, for those compounds where the decompositions were not quantitative (nitrazepam, clonazepam, lormetazepam, temazepam) detection limits were poor.

Simplified determination of serotonin in plasma by liquid chromatography with electrochemical detection.

This simplified determination of serotonin in human plasma involves "high-performance" liquid chromatography with electrochemical detection. Deproteinated samples of platelet-poor plasma are injected directly into the chromatograph without preliminary chromatographic purification. The limit of quantitative detection of serotonin in plasma is 5 nmol/L (equivalent to 250 fmol injected). Intra- and inter-assay CVs ranged from 5.6% to 7.7% and 3.5% to 14.9%, respectively, for concentrations of serotonin from 0.02 to 10.0 mumol/L. Results agreed well with those by spectrofluorometry, both for plasma standards (r = 0.985, range 100 nmol/L to 100 mumol/L) and for pathological samples obtained from four carcinoid syndrome patients (r = 0.964). The method is also applicable to the concurrent measurement of 5-hydroxytryptophan and 5-hydroxyindoleacetic acid.

A comparison of secondary ion mass spectrometry and auger electron spectroscopy as surface analytical techniques

This review presents a comparison on the use of SIMS and AES for surface analysis. Topics covered include instrumentation and analytical procedures, sample destruction and charging effects, information depth and depth profiling, qualitative and quantitative analyses, lateral resolution and detection limits. From this discussion, guidelines for the selection of the most appropriate technique should become apparent.

Routine determination of plasma catecholamines using reversed-phase, ion-pair high-performance liquid chromatography with electrochemical detection

A procedure is described for the determination of plasma catecholamines using reversed-phase, ion-pair high-performance liquid chromatography coupled with electrochemical detection. Optimisation of chromatographic conditions with respect to detector performance and adherence to procedures and precautions described, render the method applicable to both neurochemical research and routine clinical analysis. The limit of quantitative detection of the method was found to be approximately 30 pg per injection for individual catecholamines. A single chromatographic run, providing adequate resolution of each component, could be completed in approximately 12 min.

Development of a method for the analysis of T-2 toxin in maize by gas chromatography-mass spectrometry

A ground sample is homogenised with ethyl acetate, the mixture filtered, and the extract recovered by evaporation of the solvent. The residue is defatted by partition between aqueous methanol and hexane. The aqueous phase is evaporated to dryness and the residue dissolved in dichloromethane and passed through a cartridge of silica. T-2 toxin is eluted with methanol-dichloromethane, the solvents removed and risidue silylated. O-Trimethylsilyl T-2 toxin is detected by gas chromatography-mass spectrometry with monitoring of the ions at m/ z 350 and m/ z 436. The quantitative detection limit is 5 ppb (μ/kg) with an average recovery of 80%.

High-Pressure Liquid Chromatographic Analysis of Indocyanine Green

The development of a specific high-pressure liquid chromatographic (HPLC) assay, having a quantitative detection limit of 0.4 μg/ml, is described for plasma indocyanine green. In a preliminary study, the HPLC method demonstrated that the traditional spectrophotometric procedure inaccurately quantitates the dye's degradation in aqueous medium since degradation products that absorb light at 770 nm are formed. In a further study, the spectrophotometric method yielded an erroneously low clearance of indocyanine green in the rabbit. In addition, the HPLC assay points to the possibility of metabolite formation of the dye in vivo.

Quantitative determination of ochratoxin A in vegetable foods

A simple method for the quantitative determination of ochratoxin A (OA) in rice and other vegetable foods (oatmeal, coconut flakes and peas) is described. This procedure implies an acetonitrile-4% KCl -6N HCl (88+10+2) extraction of the acidic OA, subsequent twodimensional thin-layer chromatography (TLC) and detection by fluorescence after exposure to ammonia fumes (excitation at 340 nm; emission at 475 nm). The quantitative detection limit for OA in rice or coconut flakes is 2.4–4 μg/kg and the recovery is 96%. For oatmeal and peas the detection limit is only 20 μg/kg because of the interference by other metabolites.

Quantitative gas chromatographic determination of low-molecular-weight straight-chain carboxylic acids as their p-bromophenacyl esters after extractive alkylation in acidic medium

The measurement of acetate by gas chromatography at low concentrations in biological fluids is a difficult task. A significant improvement can be brought about by derivatization of acids as p-bromophenacyl esters. By such a procedure, the determination of low-molecular-weight straight-chain carboxylic acids (acetic, propionic and butyric acids) was enhanced with respect to sensitivity and specificity. The volatile fatty acids were esterified by means of an extractive alkylation mechanism in acidic conditions from ageous solutions. Tetrahexylammonium was used as counter-ion and and the alkylating agent was a, p-dibromoacetophenone. The phenacylation reaction was studied with respect to pH, concentration of counter-ion and kinetics. The yield of derivatization was ca. 70% after 2 h at 42°C. A mass spectrometry study was performed in order to ascertain the structure of derivatives using electron impact and chemical ionization. The gas-liquid chromatrographic behaviour of the p-bromephenacyl esters of acetic, propionic and butyric acids was studied on an OV-225 packed column and an OV-1 capillary column. Flame ionization detection was shown to be linear between 0.2 and 4 nmol injected, with a quantitative limit of detection of 31 pmol ( i.e. 1.8 ng of acetic acid).

Modern Methods for Solid Surface and Thin Film Analysis

Several of the more popular analytical methods suitable for solid surfaces and thin films are described, viz, Auger electron spectroscopy, X-ray photoelectron spectroscopy, secondary ion mass spectrometry, and low and high energy ion scattering. The principle underlying each method is explained, and their main features are discussed with respect to qualitative and quantitative analyses, detection limits, lateral and depth resolution, chemical and structural information, insulator specimens, and sample alteration and destruction.

Derivatization procedure for the determination of chloroacetyl chloride in air by electron capture gas chromatography

A gas chromatographic method is described for the determination of chloroacetyl chloride (CAC) in air in the presence of monochloroacetic acid (MCA). Air containing CAC was bubbled through a reactant solution of 2,4,6-trichlorophenol (TCP) and pyridine in toluene to produce the derivative 2,4,6-trichlorophenyl chloroacetate (TCPC). Excess TCP was removed by extractions with 1 N sodium hydroxide, and TCPC was determined via electron capture gas chromatography. An average recovery of 76 ± 4% (mean ±S.D.) was obtained when CAC was added directly to the reactant solution. When air samples containing CAC were scrubbed and analyzed, recoveries averaged 70 ± 5% (mean ±S.D.). The quantitative detection limit (2.5 × noise) was 1 ng CAC/ml in the extracted organic layer [1 ppb 1 1 Throughout this article the American billion (10 9) meant. in air for a 5-1 sample]. The general applicability of this method for volatile acid halides was also explored.

A Direct Determination of Tertiary Amyl Alcohol in Plasma

A method is described for the determination of tertiary amyl alcohol in plasma. The procedure employs direct Injection of heparinized plasma, separation by gas-liquid-solid chromatography, and subsequent quantification via selective ion monitoring mass spectrometry. Tertiary amyl alcohol is determined by monitoring fragment ions at m/e 59 and m/e 73. Recoveries averaged 99% _+ 9% (-+S.D.) with a quantitative detection limit (2.5 x noise) of 0.1 /Jg/ml. The coefficient of variation for five replicate determinations at various plasma concentrations of tertiary amyl alcohol varied from 3.8% at 160/~g/ml to 8.5% at 0.16/Jg/ml. Analyses can be accomplished with as little as 50 ~1 of blood In approximately 15 minutes.

Some considerations on quantitative methodology and detection limits in organic mass spectrometry.

Mass spectrometric sensitivity data for the compounds cholesterol, cholestane, DDT, decafluorotriphenylphosphine, morphine, LSD and methyl stearate have been developed over a period of time and under a variety of conditions. This information is presented on both a relative and an absolute basis. With the exception of morphine, relative sensitivies were reproducible to within a factor of three over a six month period. This reproducibility facilitates quantitation and a single standard can be used for calibration of organic compounds from various classes. Detection limits of 50 femtograms for LSD are realized for samples introduced via the direct inlet probe.

Evaluation of low-temperature electron paramagnetic resonance in analytical chemistry

An evaluation of low-temperature electron paramagnetic resonance has been completed and the possibility of enhanced quantitative lower limits of detection is discussed. By lowering the temperature of the cavity, the Q-factor is considerably increased producing a more efficient system. Also, the relaxation time is optimized by decreasing the temperature of the sample. Different temperatures for each system produced a maximum signal owing to a combination of these two factors. Thus, in order to improve the lower limits of detection for these metal ions, the analytical curves were run at the optimum temperature for each system. These data are compared to the data obtained at room temperature. Also, the instrumental parameter effects have been evaluated. The metal ions investigated are copper(II), manganese (II), titanium(III), vanadium(IV), chromium (III), gadolinium(III), and iron(III).