Showing papers on "Detection limit published in 1983"

Spectrophotometric determination of phosphate in river waters with molybdate and malachite green

Abstract: On the basis of the coloration formed with molybdate and malachite green in aqueous solution, trace amounts of phosphate were determined. The molar absorptivity was 7.8 × 104 l mol–1 cm–1 at 650 nm. The absorbance of the reagent blank was about 0.02, and its relative standard deviation was less than 10%. The recommended concentration range of phosphorus was 0.1–5 µg and the limit of detection was 0.01 µg of phosphorus. The sample solution was acidified with sulphuric acid and heated in a water-bath above 90 °C for 40 min, and subsequently it was coloured with molybdate and malachite green. The colour was stabilised by adding poly(vinyl alcohol). The method was applied to the determination of parts per billion (109) amounts of phosphorus in river and tap waters; the relative standard deviation was less than 4% and the recovery was 95–101%.

Peroxyoxalate chemiluminescence detection of polycyclic aromatic hydrocarbons in liquid chromatography

Abstract: Peroxyoxalate chemiluminescence is applied to the high-performance liquid chromatographic detection of polycyclic aromatic hydrocarbons (PAH). PAH are excited by energy transfer from the decomposition products of the reaction between hydrogen peroxide and bis(2,4,6-trichlorophenyl) oxalate. These reagents are introduced by postcolumn mixing, and the emission is observed by using a conventional fluorescence detector with its source turned off. The method yields linear responses to PAH over 3 orders of magnitude, and in some cases detection limits are better than those determined by fluorescence using the same fluorometer. Chemiluminescence detection is compared to ultraviolet absorbance and fluorescence detection of PAH in terms of sensitivity and selectivity.

Attogram detection limit for aqueous dye samples by laser-induced fluorescence

Abstract: A modified flow cytometer has been used to detect attogram quantities of aqueous rhodamine 6G by laser-induced fluorescence analysis. A detection limit of 28 attograms (35,000 molecules) was obtained, nearly two orders of magnitude better than earlier measurements. The detection limit in concentration units was 1.4 x 10(-13) mole per liter. During the 1-second measurement period, the total volume sampled was 0.42 microliter. On average, only half a rhodamine 6G molecule was present in the 6-picoliter probed volume.

Determination of selenium in biological materials with platform furnace atomic-absorption spectroscopy and Zeeman background correction

Abstract: The presence of phosphate and iron provides a spectral interference for the determination of selenium at its primary resonance line at 196.0 nm that is avoided by using Zeeman background correction. Good quality pyrolytic graphite tubes, platform atomisation and integrated absorbance readings provide an acceptable quantitative environment for selenium and permit most analyses to be performed against a simple calibration graph using selenium in a nickel matrix modifier. Remaining problems appear to relate to loss of selenium prior to atomisation in the presence of certain matrices, notably the combination of sodium and sulphate. Charring in the presence of oxygen did not improve the analytical situation, nor did the use of silver, molybdenum or copper as a matrix modifier. We found a 2σ detection limit of 28 pg and a sensitivity of about 25 pg per 0.0044 As (A = absorbance units), expressed as characteristic amount. A preliminary direct method is presented for selenium in urine, with nickel, nitric acid and magnesium nitrate present, with a detection limit in urine of about 10 µg 1–1.

Direct determination of cadmium in urine with use of a stabilized temperature platform furnace and Zeeman background correction.

Abstract: In this determination of Cd in urine, simple aqueous standards were used to which NaCl and the matrix modifier were added. The urine was diluted fivefold with water. The mean analytical recovery of added Cd for urine samples was 101%, with individual variations of less than 4%. We used the stabilized temperature platform furnace, Zeeman background correction, pyrolytically coated graphite tubes, and (NH4)2HPO4 plus HNO3 as a matrix modifier. The sensitivity of the method provided a characteristic amount of 0.35 pg of Cd per 0.0044 A X s, obtained with integrated absorbance readings. The absolute Cd detection limit in urine was 0.15 pg, corresponding to 0.04 microgram/L of urine. Lower relative detection limits for Cd in urine can be attained if the analytical situation demands it.

The Determination of the Chemical Species of Some of the “Hydride Elements” (Arsenic, Antimony, Tin and Germanium) in Seawater: Methodology and Results

Abstract: A number of elements in the fourth, fifth and sixth group of the periodic system form hydrides upon reduction with sodium borohydride, which are stable enough to be of use for chemical analysis (Ge, Sn, Pb, As, Sb, Se, Te). Of these elements, we have investigated in detail arsenic, antimony, germanium and tin. The inorganic and organometallic hydrides are separated by a type of temperature-programmed gas-chromatography. In most cases it is optimal to combine the functions of the cold trap and the chromatographic column in one device. The hydrides are quantified by a variety of detection systems, which take into account the specific analytical chemical properties of the elements under investigation. For arsenic, excellent detection limits (≅40 pg) can be obtained with a quartz tube cuvette burner which is positioned in the beam of an atomic absorption spectrophotometer. For some of the methylarsines, similar sensitivity is available by an electron capture detector. The quartz-burner/AAS system has a detection limit of 90 pg for tin; for this element much lower limits (≅10 pg) are possible with a flame photometric detection system, which uses the extremely intense emission of the SnH molecule at 609.5 nm. The formation of GeO at the temperatures of the quartz tube furnace makes this device quite insensitive for the determination of germanium. Excellent detection limits (≅140 pg) can be reached for this element by the combination of the hydride generation system with a modified graphite furnace/AAS.

Increase in the sensitivity of the fluorescent reaction of the complexing of aluminium with morin using surfactant agents

Abstract: The effects of surfactants on fluorescence analysis were studied. The addition of non-ionic surfactants (ethylene oxide - propylene oxide condensates) to a metal complex solution causes a remarkable enhancement of fluorescence, by which means the sensitivity of the fluorimetric determination of aluminium is increased ten-fold over conventional methods.The optimum conditions in which the increase in fluorescence intensity is produced were studied and are as follows: 3% surfactant, pH 3.8 in acetic acid - acetate buffer at 25 °C; and the intensity of fluorescence is measured at 495 nm and excited at 430 nm. Using a morin concentration of 0.005% in the solution under analysis, the calibration graph is linear up to 35 p.p.b. (35 parts in 109) of aluminium. The relative standard deviation for the analysis of ten replicates of a solution containing 2 p.p.b. of aluminium is 3%; when it contains 10 p.p.b. the relative standard deviation is 2%.The detection limit of the method is 0.2 p.p.b., using an excitation slit of 10 nm and an emission slit of 5 nm.From the study of interfering ions it was deduced that the presence of surfactants gives a higher selectivity than a conventional method.

High Resolution Gas Chromatographic Analysis of Nonpolar Chlorinated Hydrocarbons in Human Milk

Abstract: A gas chromatographic method is described for the analysis of human milk to determine polychlorinated biphenyls (PCBs) as 72 congeners plus p,p'-DDE, mirex, hexachlorobenzene, and octachlorostyrene. The detection limit for individual compounds is about 0.05 ng/g when 30 g milk is analyzed. Total PCBs can be estimated with a detection limit of 1-5 ng/mL milk. Analytical precision is better than +/- 10% for all compounds at 20-50 ng/mL whole milk.

Cold Vapor Atomic Absorption determination of mercury by Flow Injection Analysis using a Teflon membrane phase separator coupled to the absorption cell

Abstract: A Flow Injection Analysis (FIA) procedure for the determination of trace amounts of mercury by the Cold Vapor Atomic Absorption (CVAA) method is presented. In order to make efficient use of the FIA technique, a new flow cell was developed to permit a rapid separation of elemental mercury from the carrier solution. The design of this device is based on the permeability of Hg 0 in commercially available Teflon (PTFE) tape, which acts as a membrane phase separator. The calibration curve is linear up to 70 ng.ml −1 ( A = 0.005 + 0.008 Hg(ng.ml −1 ); r = 0.9996) using a 15-cm open cell approach, with a detection limit of 1.4 ng. ml −1 (0.66 ng of mercury), considering a signal to noise ratio of three. The standard deviation is s = ±0.004 absorbance units, calculated at a level of 50 ng.ml −1 of Hg 2+ . The sampling rate was 110 samples per h.