Icp-ms İle Demir Analizlerindeki Girişim Etkilerinin Gıda, Cam Ve Su Örneklerinde İncelenmesi

Abstract

ICP-MS günümüzde eser element analizlerinde oldukça yaygın bir teknik olup, gıda, çevre, klinik, maden ve endüstriyel alanlarda kullanılmaktadır. Diğer eser element analiz yöntemlerine göre daha hızlı olması, daha düşük konsantrasyon limitlerinde çalışılmasına imkan sağlaması ve izotop analizlerine imkan vermesi bakımından bir çok avantaja sahiptir. ICP-MS tekniği sunduğu birçok avantajın yanısıra, analiz esnasında bir takım dezavantajlara sahiptir. Bu dejavantajlardan en önemlisi ICP-MS analizlerinde karşılaşılan girişim etkileridir. Birçok element ve bu elementlere ait farklı izotoplar için girişimler oluşabilir.Bu girişimler poliatomik veya tek bir izotopun neden olduğu izobarik girişimler olabilir. Teknolojinin her geçen gün ilerlemesi ile birlikte uygulanan yeni tekniklerle bu girişimlerin etkisinin azaltılmasına çalışılmaktadır. ICP-MS tekniğinde demir analizlerinde karşılaşılan poliatomik girişimleri ortadan kaldırabilmek amacıyla, bu çalışmada Evrensel Hücre Teknolojisi kullanılmıştır. Kullanılan hücre içerisinde üç farklı modda analizler yapılmış ve sonuçlar karşılaştırılmıştır. Aynı zamanda izobarik girişimlerin ortadan kaldırılması için matematiksel eşitliklerin ne şekilde yazılacağı da belirtilmiş ve incelenmiştir. Girişimlerin incelenmesi sırasında demir elementinin dört farklı izotopu ile çalışılmıştır. Dört demir izotopu için de girişim etkileri oldukça belirgindir. Analiz sonuçlarını kıyaslamak, girişim etkilerinin nasıl yanlış sonuçlar verdiğini incelemek için tüm analizler farklı çalışma modlarında tekrarlanmıştır. Standart mod kullanılarak girişimlerin varlığı gösterilmiş, reaksiyon ve çarpışma modları kullanılarak girişimlerin ne ölçüde engellenildiği araştırılmıştır. Ayrıca farklı izotoplar kullanılarak hangi demir izotopunun doğruluğunun ve tekrarlanabilirliğinin daha iyi olduğu belirlenmiştir. Yapılan tüm çalışmaları desteklemek amacıyla sertifikalı referans malzemeler kullanılmıştır. Ayrıca su örnekleri için demir girişim etkisinin olmadığı ICP-OES tekniği ile sonuçlar karşılaştırılmıştır. Gıda, cam ve su örnekleri bu çalışmada farklı matriksler olarak seçilmiştir. Bunun en önemli nedeni bu örneklerin farklı ve yüksek konsantrasyonlarda kalsiyum içermeleridir. Kalsiyum, demir için en önemli girişimleri yaratan bir element olup moleküler girişimlere sebep olmaktadır. Girişim etkilerini daha detaylı inceleyebilmek ve izotop davranışlarını izlemek için değişen konsantrasyonlarda kalsiyum matriksleri hazırlanmış ve bu matriksler içerisine düşük konsantrasyon aralıklarında demir ilavesi yapılmıştır. Standart mod kullanılarak yapılan okumalarda girişim etkileri gösterilmiş ve bu girişimlerin nasıl giderilceği üzerine farklı modlar için aletsel parametreler belirlenmiştir. Farklı modlar kullanılarak yapılan çalışmalardan elde edilen sonuçlar üzerinde yorumlar yapılmıştır.

For nearly 30 years, inductively coupled plasma–mass spectrometry (ICP-MS) has been gaining favor with laboratories around the world as the instrument of choice for performing trace metal analysis. While atomic absorption (AA) and inductively coupled plasma-optical emission (ICP-OES) systems dominate the inorganic analysis landscape, ICP-MS continues to make in roads into laboratories that are requiring the lowest detection limits and the greatest level of productivity. According to recent data provided by the Joint ALSSA-JAIMA-Eurom II Global Laboratory Analytical Instruments Booking Report, over 15% of all new instruments purchased for trace metal analysis are ICP-MS instruments. The primary reasons for the growing popularity of ICP-MS can be summarized in a few points: • Instrument detection limits are at or below the single part per trillion (ppt) level for much of the periodic table • Analytical working range is nine orders of magnitude • Productivity is unsurpassed by any other technique • Isotopic analysis can be achieved readily A number of different ICP-MS designs are commercially available today, each with its own strengths and limitations. They all share similar components such as the nebulizer, spray chamber, plasma torch, interface, and detector, but can differ significantly in the design of the mass spectrometer and in particular the mass separation device. The sample, which must be in a liquid form, is pumped at 1 mL/min (usually with a peristaltic pump) into a nebulizer, where it is converted into a fine aerosol with argon gas at about 1 L/min. The fine droplets of the aerosol, which represent only 1 - 2% of the sample, are separated from larger droplets using a spray chamber. The fine aerosol then emerges from the exit tube of the spray chamber and is transported into the plasma torch via a sample injector. Despite these advantages, ICP-MS has some disadvantages during the analysis. One of the most important disadvantage of ICP-MS is interferences effects on analysis. There are lots of interferences for most elements and isotopes of these elements. These interferences can be polyatomic or isobaric. Polyatomic interferences means that interference occurs with combining two atoms that maintained in plasma. These polyatomic interferences can be caused from plasma species or matrix atoms. Isobaric interference means that interference occurs one isotope of interest element overlap the same mass of other isotope of element. There can be given some examples to polyatomic and isobaric interferences. For polyatomic interferences there are two possibility that make the interference. Matrix and plasma species. In this study Fe isotopes and interferences on these isotopes are investigated. For 56Fe, CaO polyatomic interferance can be occured because of matrix. If the matrix contains Ca in high concentrations, in mass 56 concentration of 56Fe is more than real value. Also there is an another interferences on mass 56 that causes of plasma species. ArO can be given as an example to this. For isobaric interferences 58Fe isotope can be given. If the samples contain Ni, the 58Ni isotope occurs in the same mass anc causes of wrong concentration results for iron. For these kinds of interferences mathematical equations can be written to make correction on results. But if the sample does not contain nickel and equation uses for correction, sometimes there will be wrong results on concentrations. New technologies has been developed to avoid these kind of interferences. In this study to investigate interferences and their effects there working mode were used. Standart, Dynamic Reaction Cell and Kinetic Energy Discrimination. For better understandaing four isotopes of iron were studied by using different working modes. Calcium matrix is choosen for demonstrate the interference effect on iron. Because Ca is one of the major comonents that easiliy combine with oxygene and form CaO which causes an important interference. Also some certificated referance materials were used to verify this study. In standart mode no extra gas is used. Only pure argon is used to obtain plasma and nebulazition. Standart mode results are showed that how wrong results can be obtaion for iron in calcium matrices. In this study the instrument that used for obtaining these results has an universal cell technology. The universal cell, containing the capability of operating in both collision cell and reactioncell modes, is placed between the ion optic(s) and the analyzer quadrupole. When operating in the collision cell mode, the universal cell works on the straight-forward principal that the interfering ion ArO+ in this case is physically larger than the analyte ion Fe+. If both ions are allowed to pass through a cloud of inert gas molecules, the interferent ion will collide more frequently with the inert gas atoms than will the analyte ion, due to its larger size. Each of these collisions removes a certain amount of the kinetic energy possessed by the ion. It follows then, that at the end of the ion‟s journey through this cloud of inert gas molecules, the analyte ion will retain more of its energy when compared to the interferent ion. An energy barrier is placed at the exit of the cell, can be adjusted so that the higher-energy analyte ions are allowed to pass through it, while the lower-energy interferences are not. This process is commonly referred to as Kinetic Energy Discrimination or KED. The collision cell will often reduce the background, but the analyte signal will also be reduced with this technique. The strength of the collision cell is the ease of method development. For samples which have great variation, such as environmental samples, one gas and one set of cell parameters will often provide an acceptablereduction in interferences. When the universal cell is operating in the reaction cell mode,a different principal is used. Reaction cells use chemistry and take advantage of exothermic (fast) and endothermic (slow) reactions. Interferent ions tend to react with an active gas, (like ammonia), exothermally, while analyte ions react endothermally. If we pass interferent ions and analyte ions through a cloud of a reactive gas, we will find that the interferent ions will be chemically converted to anew species. In our example where ArO+ is our interferent, the interferent ion is converted to a neutral atom. Since the neutral atom no longer carries a charge, it is not stable in the reaction cell quadrupole, and it is rapidly ejected from the cell. The analyte ion is unaffected and passes through the reaction cell and into the filtering quadrupole. The strength of the reaction cell is that it most effectively removes interferences,while almost fully preserving the analyte ions. For Dynamic Reaction Mode methane was used as a reaction gas. For the optimization of methane gas flow 20 ppm calcium matrix was used as a matrix and 10 ppb iron is spiked into that matrix to create spiked matrix samples. To verify methane gas flow, optimization is repeated for different concentraion of calcium matrices. And the gas flows for different matrices are nearly same. For Kinetic Energy Discrimination Mode, helium was used as a collision gas. For optimizing He gas flow, the instrument producer istructions were followed. ClO and Co were used for optimization of helium gas flow. Where the ratio of ClO/Co is 0,005 is choosen. All reading are replicated for different modes of reading and results are compared. While standart mode gives mostly wrong results for most of iron isotopes, DRC and KED modes gave acceptable results commonly for 54Fe and56Fe isotopes. Also how the calcium concentration effect the results are also investigated.