Author John Entwisle LGC Queens Roa

Author John Entwisle LGC Queens Road Teddington Middlesex TW11 0LY, UK
Abstract
The quantitative determination of mercury in foodstuffs is presented using a 7500i ICP-MS. Microwave digests were prepared and then analyzed by ICP-MS. To avoid memory effects often experienced with mercury, gold was added offline to all standards/samples and wash solutions to act as a cleansing agent. The instrumental setup used a second vacuum pump, the integrated sample introduction system in the high sample throughput mode, and a micro- flow concentric nebulizer. This allowed the robust and rapid determination of mercury in the digests at the ppt range. Excellent agreement with the certified value was obtained for two certified reference materials and stabil- ity of the system was demonstrated over a 36-hour analytical run.
Introduction
The determination of sub-ppb concentrations of mercury has always been of special importance in the field of trace metal analysis. Even at trace levels, mercury is toxic and causes neurological damage, particularly in fetuses and young children. Anthropogenic sources of mercury in the environ-
Determination of Mercury in Microwave Digests of Foodstuffs by ICP-MS Application
ment include coal-fired power stations and chlor-alkali works. In the aquatic environment, bacteria convert elemental mercury Hg(0) to methylmercury which is accumulated and passed up the food chain. It has been reported that some whale meat contains 5000 times the Japanese legal limit of 0.4 µg/g. In addition, fish and shellfish are significant contributors to the human diet. Today mercury pollution is a global problem and exten- sive monitoring of foodstuffs is required. Therefore fast efficient and robust methods are needed. Mer- cury however is recognized as a problem element. It is known to adsorb onto the walls of storage con- tainers and volatilize as mercury vapor. Addition- ally, its high first ionization potential and numerous isotopes have limited its sensitivity in ICP-MS analysis. ICP-MS allows the rapid determi- nation of ultratrace levels of metals in food digests, however, extensive washout times have been required to reduce carryover for mercury analysis. Other workers have tried the addition of a number of chemical agents in the past. One of the most effective washout agents is gold chloride. To avoid memory effects and ensure stability, gold chloride (at the 5-ppm level) was added offline to all samples/standards and wash solutions. Extensive washout times were reduced by using by the inte- grated sample introduction system (ISIS). With the use of the high throughput pump, a large flush volume can be pumped through in a much shorter time. By summing the responses for multiple iso- topes (199, 200, 201, and 202) and with the help of a second interface vacuum pump and a micro-flow concentric nebulizer, detection levels of between 10 and 30 ppt were routinely achieved for the digests.
Food Safety
2
Procedure
Microwave Digestion
Varying aliquots of each sample (generally between 0.2 and 0.6 g, depending on the moisture content of the sample) were weighed to the nearest 0.01 g into the digestion vessels. Wet oxidation was induced using concentrated, ultra-high purity nitric acid (10 mL, from Romil LTD, Cambridge, UK) with the addition of a 0.2 mL of concentrated hydrochloric acid (Romil LTD, Cambridge, UK). Oxidation was carried out in heavy-duty vessels (HDV) using a high-pressure microwave digestion oven (Mars 5 from CEM). Temperature control was used as opposed to pressure control. Samples were ramped to 180 °C over 20 minutes and held at 180 °C for 10 minutes before cooling to below 50 °C before venting the vessel. Both pressure and temperature were monitored by direct measurement throughout the digestion to ensure that samples attained the critical temperature of 180 °C, at which food com- ponents, such as fat, are digested. The sample digests were then made up to 100 g using ultra- high purity water (18 mega ohms, from Elga Maxima). The resultant solution was used for determination.
Operating and Acquisition Parameters
Ten milliliter portions of the sample digests were accurately pipetted into sample tubes, and using a micropipette, 20 µL of a 1000-ppm gold chloride solution (Romil LTD, Cambridge, UK) was added. This gives a final gold concentration of 5 ppm in solution. Fifty milliliters each, of blank and four standard solutions covering the range, were pre- pared from a 100 µg/g stock mercury solution (from SPEX CertiPrep Assurance, Metuchen, New Jersey, USA). Ten percent wt/wt nitric acid con- taining 5 ppm of gold was used as the wash solu- tion for the autosampler and nebulizer. Gold is thought to have its effect by acting as an oxidizing agent ensuring that mercury stays in an ionized form in solution. Gold was added at elevated levels to ensure that any residual amounts of organic compounds in the digests would not reduce Au(III) to elemental gold and render it ineffective. A 250-ppb Thalium

ผลลัพธ์ (อังกฤษ) 2:

Author LGC Queens Road Teddington Middlesex TW11 John Entwisle 0LY, UK
Abstract
The quantitative determination of Mercury in foodstuffs is Presented using ICP-MS a 7500i. Microwave digests were prepared and then analyzed by ICP-MS. To avoid memory effects often experienced with mercury, gold was added offline to all standards / samples and wash solutions to act as a cleansing agent. The instrumental setup used a second vacuum pump, the integrated sample introduction system in the high sample throughput mode, and a micro- flow concentric nebulizer. This allowed the robust and rapid determination of mercury in the digests at the ppt range. Excellent Agreement with the Certified Value was obtained for Two Certified reference Materials and Stabil- ity of the System was demonstrated over a 36-hour analytical Run.
Introduction
The determination of Sub-ppb concentrations of Mercury has always been of special importance in the field of. trace metal analysis. Even at trace levels, mercury is toxic and causes neurological damage, particularly in fetuses and young children. Anthropogenic sources of Mercury in the Environ-
Determination of Mercury in Foodstuffs by ICP-MS Microwave Digests Application of
Coal-fired Power ment include Chlor-Alkali Works and stations. In the aquatic environment, bacteria convert elemental mercury Hg (0) to methylmercury which is accumulated and passed up the food chain. It has been reported that some whale meat contains 5000 times the Japanese legal limit of 0.4 μg / g. In addition, fish and shellfish are significant contributors to the human diet. Today mercury pollution is a global problem and exten- sive monitoring of foodstuffs is required. Therefore fast efficient and robust methods are needed. Mer- cury however is recognized as a problem element. It is known to adsorb onto the walls of storage con- tainers and volatilize as mercury vapor. Addition- ally, its high first ionization potential and numerous isotopes have limited its sensitivity in ICP-MS analysis. ICP-MS allows the rapid determi- nation of ultratrace levels of metals in food digests, however, extensive washout times have been required to reduce carryover for mercury analysis. Other workers have tried the addition of a number of chemical agents in the past. One of the most effective washout agents is gold chloride. To avoid memory effects and ensure stability, gold chloride (at the 5-ppm level) was added offline to all samples / standards and wash solutions. Extensive washout times were reduced by using by the inte- grated sample introduction system (ISIS). With the use of the high throughput pump, a large flush volume can be pumped through in a much shorter time. By summing the responses for multiple iso- topes (199, 200, 201, and 202) and with the help of a second interface vacuum pump and a micro-flow concentric nebulizer, detection levels of between 10 and 30 ppt were routinely achieved for the. digests.
Food Safety
2
Procedure
Microwave Digestion
Varying aliquots of each sample (generally between 0.2 and 0.6 G, depending on the Moisture content of the sample) were weighed to the nearest 12:01 a.m. G Into the Digestion vessels. Wet oxidation was induced using concentrated, ultra-high purity nitric acid (10 mL, from Romil LTD, Cambridge, UK) with the addition of a 0.2 mL of concentrated hydrochloric acid (Romil LTD, Cambridge, UK). Oxidation was carried out in heavy-duty vessels (HDV) using a high-pressure microwave digestion oven (Mars 5 from CEM). Temperature control was used as opposed to pressure control. Samples were ramped to 180 ° C over 20 minutes and held at 180 ° C for 10 minutes before cooling to below 50 ° C before venting the vessel. Both pressure and temperature were monitored by direct measurement throughout the digestion to ensure that samples attained the critical temperature of 180 ° C, at which food com- ponents, such as fat, are digested. The sample digests were then made ​​up to 100 g using ultra- high purity water (18 mega ohms, from Elga Maxima). The resultant Solution was used for determination.
Operating and Acquisition Parameters
Ten Milliliter Portions of the sample digests were accurately Pipetted Into sample Tubes, and using a micropipette, 20 ΜL of a in 1000-PPM Gold chloride Solution (Romil LTD, Cambridge, UK) was. added. This gives a final gold concentration of 5 ppm in solution. Fifty milliliters each, of blank and four standard solutions covering the range, were pre- pared from a 100 μg / g stock mercury solution (from SPEX CertiPrep Assurance, Metuchen, New Jersey, USA). Ten percent wt / wt nitric acid con- taining 5 ppm of gold was used as the wash solu- tion for the autosampler and nebulizer. Gold is thought to have its effect by acting as an oxidizing agent ensuring that mercury stays in an ionized form in solution. Gold was added at elevated levels to ensure that any residual amounts of organic compounds in the digests would not reduce Au (III) to elemental gold and render it ineffective. A 250-ppb Thalium