Standard Deviation Of Blank Values Research Articles

Ultra-trace determination of mercury by platinum-coated tungsten coil trapping cold vapour atomic absorption spectrometry

ABSTRACT Within the scope of this study, a simple, highly sensitive and rapid trapping method for the determination of mercury (Hg) was developed. In this method, the surface of the tungsten coil (W-coil) was coated with platinum using the electrolytic deposition technique. Scanning electron microscopy–energy-dispersive X-ray analyses were performed to examine the surface morphology of Pt-coated W-coil. During the experiment, firstly, Hg vapour generated by tetrahydroborate, used as a reducing agent, was efficiently trapped on the Pt-coated W-coil at collection temperature in hydrochloric acid medium. Subsequently, Hg trapped on the surface of the Pt-coated W-coil was revolatilised by the effect of releasing-stage gases at the optimised releasing temperatures and transported to quartz T-tube atomiser. The experimental conditions have been optimised. Under the optimised conditions, a limit of detection (LOD) of 8.8 ng L−1 was obtained using three times the standard deviation of blank values using Pt-coated W-coil trap cold vapour atomic absorption spectrometry (CVAAS) system. The precision of the measurements was evaluated by relative standard deviation of 4.4%, which is obtained by 11 consecutive measurements of reagent blanks for a collection volume of 6.83 mL corresponding to 90 s collection. The enhancement factors for both LOD (3 s) and characteristic concentration (Co) were found to be 5.09 and 5.02 when compared with the regular CVAAS system without trap. The accuracy of the proposed method was evaluated by analysing BCR 146 R (Sewage sludge), RTC (Sandy Loam 7), ERM-BD151 (skimmed milk powder) and NIST 1641e (mercury in water) certified reference materials (CRMs). There was a good agreement between certified and found values for all CRMs. The results of the application of the developed method in seawater showed the spike recovery ranges from 94.2% to 102.4%.

Determination of Trace Element Quantities in Ultra High-Purity Iron by Spectrochemical Analysis after Chemical Separation

When trace elements in an ultra high-purity iron were determined, an analytical blank on a chemical analysis interfered with the determination of them. Similarly, the existence of major component in a sample interfered with the determination of trace elements. Therefore, in order to determine trace elements, it was examined that how to remove or decrease an analytical blank and how to separate trace elements from major component of a sample. For example, when C and S in an ultra high-purity iron were determined by combustion/infrared absorption method, an accelerator for combustion of an analytical sample contained C and S as blank. The accelerator consisted of a mixture of tungsten and tin. By heating it in ambient atmosphere, carbon blank was removed to be zero and sulfur blank was decreased to lower level. Consequently, when detection limit was defined as a value corresponding to 3 times of the standard deviation of blank value, it of carbon was infinitesimal and it of sulfur was 0.2 μg g -1 Infinitesimal detection limit of carbon resulted from zero of the blank value of carbon. For that reason, detection limit of carbon was read as 0.01 μg g -1 of carbon that was minimum scale for carbon on the analytical instrument, because the standard deviation of the blank value could not to be calculated. Independently, in order to determine trace Sn, Ag and Au in a high-purity iron, these elements were separated from major component (iron) by co-precipitation. Metallic Pd was used as co-precipitant. Metallic Pd had been rarely used as co-precipitant. The elements were determined by electrothermal atomic absorption spectrometry (ET-AAS). When these elements were detected by ET-AAS, the Pd was available as chemical modifier. By the separation, content 0.002-0.02 μg g -1 of the elements was determined.

On-line bidirectional electrostacking of chromium(III) and chromium(VI) for flame atomic absorption spectrometry determination

An on-line bidirectional electrostacking-flow injection-flame atomic absorption spectrometry method has been developed for the simultaneous separation, pre-concentration and determination of Cr(III) and Cr(VI). The electrostacking-flow injection unit was established, the pH and components of the support buffer and sample medium were investigated. Results indicated that the ionic mobility, electric field strength and sample area cross-section are the main influence factors on the electrostacking. The calibration range for both, Cr(III) and Cr(VI), was from 20 to 400 μg l −1. The limit of detection was 7 μg l −1 for three-times the standard deviation of blank values using a electrostacking time of 350 s. The recovery percentages of 100 μg l −1 Cr(III) and 25 μg l −1 Cr(VI) added to samples were 100 and 94% with variation coefficients of 7 and 10%, respectively.

Determination of Cadmium and Lead in Tap Water by Graphite-Furnace Atomic Absorption Spectrometry after Preconcentration on a Finely Divided Ion-Exchange Resin as the Pyrrolidinedithiocarbamate Complexes

A rapid and simple preconcentration method based on the combined use of ammonium pyrrolidinedithiocarbamate (APDC) and a finely divided anion-exchange resin has been described for the determination of trace amounts of cadmium and lead by graphite-furnace atomic absorption spectrometry (GFAAS). Cadmium- and lead-APDC complexes were extracted simultaneously on the resin at pH 6. The resin particles holding the cadmium- and lead-APDC complexes were separated by filtration and dispersed in 1.0 ml of 0.1 mol 1 -1 hydrochloric acid containing 100 μg of palladium(II). The resulting suspension was introduced directly into the graphite furnace by an automatic sampler. The detection limits of cadmium and lead in a 150-ml sample aliquot were 0.17 and 5.7 ng 1 -1 , respectively, based on three-times the standard deviation of blank values. The proposed method was applied to the determination of nanograms per liter levels of cadmium and lead in tap water.