Showing papers on "Detection limit published in 1972"

The determination of acrylamide in water by using electron-capture gas chromatography

Abstract: A method is described for the determination of residual acrylamide in water at levels likely to arise from the use of acrylamide polymers and copolymers in water treatment. After bromination of the sample, the α,β-dibromopropionamide obtained is extracted with diethyl ether and the extract analysed by electron-capture gas chromatography. Replicate samples of acrylamide added to River Thames water at concentrations of 500, 50, 5 and 0·25 µg 1–1 were analysed with relative standard deviations of ±5, ±5, ±9 and ±10 per cent., respectively.A detection limit of 0·1 µg 1–1 of acrylamide was achieved with River Thames water and 0·25 µg 1–1 was determined with a relative standard deviation of ±10 per cent. Yields of α, β-dibromopropionamide vary with water quality, ultraviolet light intensity and other reaction conditions. To overcome effects caused by these variables, when present, an internal standardisation procedure is used. The detection limit in River Thames water remained at 0·1 µg 1–1 but with this procedure 0·25 µg 1–1 was determined with a relative standard deviation of ±20 per cent.

X-Ray Fluorescence Determination of Chlorine in Standard Silicate Rocks

Abstract: Chlorine has been determined in seventeen international silicate rock standards by x-ray fluorescence analysis, yielding values which compare well with published values. The detection limit for the method is about 10 ppm. Sources of chlorine contamination are considered.

Radiometric determination of trace amounts of anionic surfactants in ground water and potable water

Abstract: The water sample is treated with an excess of ferroin solution labelled with iron-59. The solution is extracted with chloroform and the activity of a portion of the extract is measured. The anionic surfactant content of the sample is determined by the standard addition of sodium lauryl sulphate.The application of the method to river-water and tap-water samples gives results that agree with those obtained by using Abbott's methylene blue method. The present method requires 30 minutes for each reading, i.e., blank, sample or sample plus standard.The over-all standard deviation for river-water samples has been calculated to be ±4·3 per cent. at the level of 0·1 p.p.m. of sodium lauryl sulphate.The limit of detection is 0·1 µg of sodium lauryl sulphate (0·005 p.p.m. in a 20-ml sample). This limit is the equivalent of the average blank. Blanks are minimised by extracting at pH 4 with chloroform equilibrated with water, by performing only one extraction, by centrifuging for a fixed period and by removing the extract for counting with a capillary device.No species have been found to interfere when present at the levels that are normally encountered in river waters. Potential interferences by fluoride or iron are compensated for by the internal standard.

pH-sensitive fluorogenic spray reagents. II. Quantitative studies with pesticides

Abstract: A new spray using DDQ (1,2-dichloro-4,5-dicyanobenzoquinone) for thein situ fluorometric detection of sulfurcontaining pesticides on thin-layer chromatograms was studied in order to evaluate the quantitative potential of the method. The effects of pH, various adsorbents, spray solvents and concentrations, U.V. irradiation and time on the fluorescent intensity of the spots were investigated and the optimum conditions were established. An average reproducibility of 5.0% rel. standard deviation and an average detection limit of 0.05 μg per spot were obtained. Linear calibration curves up to 5.0 μg per spot and extending through the point of origin were observed. This method was used successfully to analyze a natural water sample containing 2 ppb of malathion.

Confidence Limits for Measurement of Fiber Diameter Using the Mikronmeter

Abstract: using the clamping and combing method. The problem in actual use of such an instrument would, therefore, be that of estimating the slippage zone, in order to correct the small bias in the projected mean length. As pointed out by Tallant and Pittman, one way of limiting the bias would be to use clamps of as large a width as practical. With reference to Figure 1 ~6~, we did not test the intercept for non-zero value. Tallant and Pittman have correctly pointed out this shortcoming. The confidence interval for the intercept is, on calculation, ±0.9432. This means that the intercept of 0.4396 is not significantly different from zero. We, therefore, recalculated the slope, as suggested by Tallant and Pittman, and have found that the slope is not significantly different from 1.0. There is, therefore, no significant difference between the 60 mm and 2 in

Detection limits for radioisotopic counting techniques

Abstract: The method of defining detection limits which has been adopted by the 222-S Analytical Laboratory counting room is described. The system for reporting limits defines two levels of detection limits: the critical level (L/sub c/) which must be exceeded before a sample can be said to contain any material above the background level and a detection limit (L/sub D/) at which we can be 95% sure that we will detect material. The common method of using twice the standard deviation of the background as a lower detection limit was found to lead to erroneous results. Equations relating L/sub c/ and L/sub D/ to the magnitude and standard deviation of the background were derived. Two examples illustrate the use of these levels. (auth)

Stability-Indicating High Performance liquid Chromatographic Determination of Diltiazem Hydrochloride

Abstract: A rapid, selective and accurate high-performance liquid chromatography method (HPLC) for the determination of diltiazem hydrochloride using clonazepam as internal standard is developed. The investigated compounds were eluted from 5 u Micropak MCH-5 reversed phase column at ambient temperature with a mobile phase comprising of acetonitrile-water (48:52%) at pH 3.3 and containing 0. 01M sodium-n-octane sulfonate as an ion pairing substance. The mobile phase was pumped at a flow rate of 1 ml min−1 and the effluent was monitored at 239 nm. The retention times of the internal standard and diltiazem were at 3 min and 9 min, respectively. A linear relationship was derived between the peak height ratio (diltiazem/clonazepam) and diltiazem concentration over the range 1–10 μg ml−1. Detection limit for the drug is 0.2 μg ml−1 at 0.01 aufs. The developed procedure was applied to study the stability of diltiazem in the presence of its degradation products as well as in the presence of formulation excipients.