Detection limit mercury fluorescence

As atomic fluorescence spectrometer a mercury analyzer Mercur , (Analytik-Jena, Germany) was used. In the amalgamation mode an increase of sensitivity by a factor of approximately 7-8 is obtained compared with direct introduction, resulting in a detection limit of 0,09 ng/1. This detection limit has been improved further by pre-concentration of larger volumes of samples and optimization of instrumental parameters. Detection limit 0,02 ng/1 was achieved, RSD = 1-6 %. 

Funk et al. have used a low-pressure mercury lamp without filter to liberate inorganic tin ions from thin-layer chromatographically separated organotin compounds these were then reacted with 3-hydroxyflavone to yield blue fluorescent chromatogram zones on a yellow fluorescent background [22]. Quantitative analysis was also possible here (XoK = 405 nm, Xji = 436 nm, monochromatic filter). After treatment of the chromatogram with Triton X-100 (fluorescence amplification by a factor of 5) the detection limits for various organotin compoimds were between 200 and 500 pg (calculated as tin). 

Haapakka and Kankare have studied this phenomenon and used it to determine various analytes that are active at the electrode surface [44-46], Some metal ions have been shown to catalyze ECL at oxide-covered aluminum electrodes during the reduction of hydrogen peroxide in particular. These include mercu-ry(I), mercury(II), copper(II), silver , and thallium , the latter determined to a detection limit of <10 10 M. The emission is enhanced by organic compounds that are themselves fluorescent or that form fluorescent chelates with the aluminum ion. Both salicylic acid and micelle solubilized polyaromatic hydrocarbons have been determined in this way to a limit of detection in the order of 10 8M. 

Godden and Stockwell [11] have described a specific fluorescence detection system to provide fully supported analytical systems for routine analysis of mercury at low levels. The fluorescence approach provides a wide linear dynamic range and extremely low detection limits. P.S. Analytical s Merlin Plus System provides a fuUy automated system which will produce results at a rate of around 40 per hour. This is due to the optimization of the optical design of the detector, coupled to the inherent features of the fluorescence technique. 

Elements such as As, Se and Te can be determined by AFS with hydride sample introduction into a flame or heated cell followed by atomization of the hydride. Mercury has been determined by cold-vapour AFS. A non-dispersive system for the determination of Hg in liquid and gas samples using AFS has been developed commercially (Fig. 6.4). Mercury ions in an aqueous solution are reduced to mercury using tin(II) chloride solution. The mercury vapour is continuously swept out of the solution by a carrier gas and fed to the fluorescence detector, where the fluorescence radiation is measured at 253.7 nm after excitation of the mercury vapour with a high-intensity mercury lamp (detection limit 0.9 ng I l). Gaseous mercury in gas samples (e.g. air) can be measured directly or after preconcentration on an absorber consisting of, for example, gold-coated sand. By heating the absorber, mercury is desorbed and transferred to the fluorescence detector. 

A number of analytical methods were developed for determination of elemental mercury. The methods are reviewed in Refs. [1-4]. They include traditional analytical techniques, such as atomic adsorption spectroscopy (AAS), atomic fluorescence spectroscopy (AFS), and atomic emission spectroscopy (AES). The AAS is based on measurements of optical adsorption at 253.7 or 184.9 nm. Typical value of the detection limit without pre-concentration step is over 1 pg/l. The AEF is much more sensitive and allows one to detect less than 0.1ng/l of mercury... 

In EMEP, ICP-MS is dehned as the reference technique. The exception is mercury, where cold vapor atomic fluorescence spectroscopy (CV-AFS) is chosen. Other techniques may be used, if they are shown to yield results of a quality equivalent to that obtainable with the recommended method. These other methods include graphite furnace atomic absorption spectroscopy (GF-AAS), flame-atomic absorption spectroscopy (F-AAS), and CV-AFS. The choice of technique depends on the detection limits desired. ICP-MS has the lowest detection limit for most elements and is therefore suitable for remote areas. The techniques described in this manual are presented with minimum detection limits. Table 17.2 lists the detection limits for the different methods. 

The separation of organomercury was conducted by using a SB-methyl-100 capillary column and pure CO2 as the mobile phase. FID and atomic fluorescence were used for detection. The same column was also used for separation of mercury, arsenic, and antimony species using carbon dioxide as the mobile phase. A chelating reagent, bis(trifluoroethyl)dithiocarbamate, was used in this case to convert the metal ions to organometallic compounds before the separation. The detection limit of FID was 7 and 11 pg for arsenic and antimony, respectively. 

A mong the preferred analytical methods for determining mercury con-centrations in natural samples save been closed system reduction-aeration procedures using mercury detection by gas phase atomic absorption or atomic fluorescence spectrophotometry (I-I5). In studies in the oceanic regime, where the amount of mercury in a liter sample of open-ocean seawater can be as small as 10 ng (11,15,16,17), a. pre-concentration stage may be required. The lowered detection limits which accompany a preliminary concentration step are most desirable when the sample materials are rare or in limited quantities such as carefully collected open-ocean biota, open-ocean rain water, and deep-ocean seawater. 

An X-ray fluorescence (XRF) technique has been used to measure mercury in the wrist and temporal areas of dentists exposed to various heavy metals in the work place (Bloch and Shapiro 1986). This technique allows simultaneous evaluation of the tissue burden of a number of different metals. Bone levels may be more closely related to long-term exposure than levels in blood, urine, and hair. The detection limit for XRF is in the low ppm. 

If the components to be detected fluoresce, a fluorescence detector can be employed. A mercury or xenon lamp with a monochromator is used as the source for the exitation wavelength. Modern systems use lasers as light source, but such systems are mainly used in trace analysis and not in preparative systems. The main advantage of fluorescent detectors is their high sensitivity. Their reduced robustness and limitation to fluorescent compounds makes them not widely used in preparative chromatography. 

Various measurement techniques have been used after matrix destruction. Small amounts of mercury are generally determined by conversion from an ionic species in aqueous solution to the elemental vapor, which is measured spectroscopically by atomic fluorescence, ultraviolet, or atomic absorption techniques (1,5, 6,9,10,11,12,13,14,15,16). Review articles covering the determination of small amounts of mercury in organic and inorganic samples (17) and the determination of mercury by nonflame atomic absorption and fluorescence spectroscopy (18) have recently appeared. In certain instances detection limits of 1 ng/g have been possible. 

Photo-acoustic spectroscopy has been used for ultratrace levels of Hg in air and snow (de Mora etal. 1993). X-ray fluorescence is nondestructive, rapid, requires minimal sample preparation, and was, for example, used successfully to determine the maximal level of mercury in maternal hair to assess fetal exposure (Toribora et al. 1982). However, the procedure is less sensitive compared to AAS and INAA if no pre-concentration is used. Electrochemical methods have been replaced as detectors in chromatography by other instrumental techniques because of poorer detection limits. High-performance liquid chromatography (HPLC) with reductive amperometric electrochemical reduction, however, was shown to be capable of speciating Hg(II), methyl- ethyl- and phenylmercury, with detection limits <2pgL (Evans and McKee 1987). 

The use of atomic fluorescence for the determination of mercury was first reported by Thomson and Reynolds in 1971 [2]. Since then, several authors [3-6] have described enhancements to the technique that have reduced formal instrument detection limits (IDL) for the fluorescence technique to the 1-10 ng/1 range. Knox et al. [7] report on the use of atomic fluorescence detection limit for mercury to less than 1 ng/1. A European standard EN 13506 was published in 2001. This uses vapor generation coupled to direct atomic fluorescence measurement. The most recent version of the US EPA standard 1631 utilizes an additional gold amalgamation step. The amalgamation provides the potential for an additional order of sensitivity but also requires considerable attention to detail and cleanliness to avoid contamination. 

A mercury metal vapor lamp emits a very intense line spectrum. It is possible to use the line spectrum of mercury to excite the fluorescence spectra of elements other than mercury if line overlap exists. Omenetto and Rossi have been able, by this technique, to produce fluorescence spectra of iron, manganese, nickel, chromium, thallium, copper, and magnesium. Table 11-1 illustrates some of these results and also gives detection limits obtained by this method. 

Hydride generation techniques are superior to direct solution analysis in several ways. However, the attraction offered by enhanced detection limits is offset by the relatively few elements to which the technique can be applied, potential interferences, as well as limitations imposed on the sample preparation procedures in that strict adherence to valence states and chemical form must be maintained. Cold-vapor generation of mercury currently provides the most desirable means of quantitation of this element, although detection limits lower than AAS can be achieved when it is coupled to other means of detection (e.g., nondispersive atomic fluorescence or micro-wave induced plasma atomic emission spectrometry). 

For trace analysis, the main ceramic elements of interest are Zn, Pb, Cu, Bi, Sb, Sn, Ag, As, Mn, Cr, Se, and Hg. Many of these are environmentally important. In certain cases the detection limits of flame AAS are inadequate, so that hydride generation for antimony, selenium, arsenic and bismuth, cold vapor for mercury, and graphite furnace AAS for lead and cadmium are required. A variation of AAS is atomic fluorescence, and this is used to achieve the detection limits needed for Hg and Se in environmental samples. Microwave digestion techniques for sample preparation are becoming more common, where, unlike fusion, there is no risk of loss of volatile elements from unfired samples and fewer reagents are... 

FIA analyzers or FIA components. One company produces a series of instruments that are flow injection systems with atomic absorption spectrometric detection dedicated to determination of mercury. Some companies produce flow injection analyzers for a large number of ions. One supplier has an analyzer that comprises three separate units a basic analytical module, an automatic sample module, and a data capture module, all these units being completely automated. The instrument is capable of analyzing nutrients, ions, and metals. It offers a wide analytical choice using ion-selective electrodes (ISEs), chemiluminescence, or fluorescence. With analysis speeds up to 120 samples per hour and detection limits down to parts per billion levels, this flow injection analyzer performs determinations well compared with other techniques. 

Hg from melted ice was measured by reduction to Hg(0), which was purged from solution by bubbling Ar gas. Hg(g) was trapped by metallic Au coated on sand. (Mercury is soluble in gold.) For analysis, the trap was heated to liberate Hg, which passed into a cuvet. The cuvet was irradiated with a mercury lamp, and fluorescence from Hg vapor was observed. The detection limit was 0.04 ng. Blanks prepared by performing all steps with pure water in place of melted glacier had 0.66 0.25 ng Hg/L, which was subtracted from glacier readings. All steps in trace analysis are carried out in a scrupulously clean environment. 

In the past, mercury (Hgx) in seawater was mainly determined by cold-vapour atomic absorption spectrometry (CVAAS) following oxidative pretreatment of the samples, reduction of the mercury ions, purging and collection of the Hg on a trap, revaporisation and detection. During the last decade, the detection limit of the method has been lowered by a factor of > 10, mainly due to further reduction of the blank values. In addition, replacing the AAS detection at 253.7 run by more powerful fluorescence detectors allows detailed and reUable studies on different mercmy species in relatively small sample volumes and even automation at ultratrace levels. 

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