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Introduction

Title of the article:

Ionic liquids improved reversed-phase HPLC on-line that are coupled with ICP_MS for selenium specifications.

Beibei Chen, Man He, Xiangju Mao Ran Cui, Daiwen Pang and Bin Hu.

Science Direct Journal Talanta 2011, 83

The RTILs which implies the Room- temperature ionic liquids that, is improved reversed phase for the high performance of the liquid chromatography (RP-HPLC) that is on line combined with the inductively plasma which is coupled with mass spectroscopy, is a study that focuses on the development of selenium speciation. This study focuses on the new approach of selenium speciation development, in which it would also be possible to ascertain the concentration, quickness, low injection volume and the simplicity in which it gives a broader perspective in the elemental speciation as it is expected in the realm of biology. For instance, in a Se- enriched yeast; it was evident that the SeCys2 which were spiked were able to be transformed to SeMet. This is a result of the snailase that is obtained during the extraction of the enzymatic action. Snailase is unable to dissolve the cell wall of the yeast. This means that the proteins which are in the yeast would remain active during the enzymatic action. This study has incorporated the data and theory to actuate the functionality of this new proposed approach. Indeed, the author elucidates the factual evidence with examples that makes the whole concept to be thoroughly understood. The author uses quantitative research that elaborates further the occurrence of the experiment.

Aim of the study:

In this article, authors have studied development of room-temperature ionic liquids, the improved reversed-phase high performance liquid chromatography, and on-line combined with inductively coupled plasma mass spectrometry for selenium speciation. This brings the interest of developing a new technique of the RTILs that has an improved version of RP-HPLC-ICP-MS that finds the application in the speciation of the organic and inorganic selenium in the biological samples. They have also studied different parameters that upset the retention behaviors of six target selenium species and mostly the result of RTILs as mobile phase additive. As well known trace mineral selenium is an important nutrient of primary significance to an organism while it has a very narrow range of concentration between selenium deficiency and its toxicity. The biological effects, of toxicity and different bioavailability of selenium are mostly dependent on chemical forms it posses. Selenium is primarily found as organoselenium compounds in living organism. Many selenium nutritional supplements are used for human beings for example yeast, clover and medicinal plant. Different speciation of selenium is of much importance and significance than its total concentration determination.

Elemental analysis is generally achieved by hyphenation methods where, a high efficient separation technique is engaged to detach different species of interested element. Sensitive recognition technique is used to determine the target elementary species in very low level. Plasma mass spectrometry widely used in the elemental-specific detection technique because, it offers high sensitivity and good methodology when reference compounds are present, and comparatively easy of interfacing with normally used division techniques. HPLC is the largest part widely used technique for selenium speciation because it is easily interfaced to ICP-MS through different conventional nebulizers. It has different separation modes, does not need any derivatization to create volatile compounds which are mostly needed in gas chromatography (GC) analysis, and often display good reproducibility of which electrophoresis (CE) analysis is often lacking.

This study also focuses of the effect of the RTILs in a given form of mobile phase additives as the selenoamino acids and the inorganic selenium possess their retention behaviours. It is noted that, the addition of 0.1% (v/v)[BMIM]BF4 resulted to a decrease in the retention time (tr) and, its factor k for the given selenium Se(IV) and Se(VI). The study also focuses on the retention behavior as a result of the mobile phase ph for the given selenium species. This was done on the pH ranging from 3-8. The study also aimed at focusing the effect of the methanol concentration on a given mobile phase on the various retention selenium species.

The study also analyses the column temperature and the flow rate effects on the retention characteristics of the selenium species. This castigates the mobile flow rate which occurs in a range of 0.5-1.1mL /min. The column variance in the temperature was investigated at a temperature ranging 15-50oC. This condition tries to ascertain if the temperature have any effect on the retention of the selenium species. In addition, this study aimed to focus on the relationship of RTILs with the normally used ion pair reagents. This took the advantage of perflourocarboxylic acid that acted as the mobile phase additives in the HPLC separation of the selenium species. This is due to the fact that some inorganic compounds may not be easily separated. At times the separation times may be extended or be faced with long chromatography peaks.

Reasons for choosing this article:

The relevance of this study puts across a keen interest in the choice of this article. These include: Firstly, mineral selenium is widely used as a nutrient of great importance to organism. The influence of RTILs as mobile phase additives on the retention behaviors of inorganic selenium and seleno-amino acid species and, different concentrations of RTILs had been investigated in this article. Their results have also been shown and it was worth learning. Secondly, Room-temperature ionic liquids (RTILs) have been investigated following their unique properties of slight vapor pressure, good thermal strength and solubility for inorganic and organic compounds. Also, the possibility of designing them to give a range of distinguished properties simply by synthesis. Thirdly, Due to the much attention RTILs are receiving as environmentally benign solvents in heterogeneous catalysis, synthesis, electrochemistry, sensors, battery applications, clover and medicinal plant.

ICP-MS Instrumentation:

The analysis was validated by the speciation of selenium in a certified reference material of SELM-1 yeast which, was bought from NRCC (Ottawa, Canada). Novel approach was developed using RTILs as mobile phase additives in RP-HPLC–ICP-MS. Extraction procedure was based on the method recommended by McSheehy. Analytical outcome was 3323± 39µg SeMet g−1 for SeMet was in good concurrence with the certified value of 3389±173µg SeMet g−1. This study uses the yeast cell and the ionized water to perform its function which provides more accurate results. Previously, this technique was achieved through barbington, and USN samples that brought about insensitivity issues.

Results:

From the primary results, it is indicated that the addition of 0.1% (v/v) [BMIM]BF4 had no significant effect on the retention behaviors of four seleno-amino acids species, but led to a decline in retention time (tR) and retention factor (k) for Se(IV) and Se(VI). Increase of [BMIM]BF4 concentration from 0.1% to 0.5% (v/v), the k and tR for MeSeCys, SeMet, SeEt, Se(IV)and Se(VI) were reduced and mostly for two inorganic selenium. RTILs also showed a similar concentration effect on tR or k for the target selenium species. There was no baseline separation of six target selenium species that was obtained except [BMIM]Cl. Using 0.4% (v/v) [BMIM]sCl as mobile phase additive was important in providing a baseline separation of six target selenium species. The withholding time for Se(VI) was longer than twenty minutes. Different RTILs had an effect on the tR and k of two inorganic selenium species, which was highly dependent on the anionic part of RTILs. Retention behaviors were to a certain extent different for Se(IV) and Se(VI) when the anionic parts of the RTILs were BF4 and Cl, respectively. When compared to Cl, more amount of chaotropic anion BF4 was adsorbed on the stationary phase.

In addition Se(IV) and SeMet were separated, all the rest of the selenium type were separated using baseline with the total division time that was less than eight minutes. In the yeast cells matrix, although the retention time of Se(VI) was reduced from 5.12 to 4.92min the analytical performance of this method was evaluated. There is also incomplete extraction which takes place, due to the addition of the additives emanating from the supplements.

Plasma mass spectrometry widely used in the elemental-specific detection technique because, it offers high sensitivity and good methodology when reference compounds are present, and comparatively easy of interfacing with normally used division techniques. HPLC is the largest part widely used technique for selenium speciation because it is easily interfaced to ICP-MS through different conventional nebulizers. It has different separation modes, does not need any derivation to create volatile compounds which are mostly needed in gas chromatography (GC) analysis, and often display good reproducibility of which electrophoresis (CE) analysis is often lacking.

The limits of detection (LODs, 3α) for six selenium species were between 0.27–5.37 ngmL−1. Relative standard deviations (RSDs) was between 0.8–4.6% (cSe(IV) = 100 ng mL−1, cSe(VI), SeCys2, SeMet, MeSeCys, SeEt =50ngmL−1, n = 7). The linear range for Se(IV) and Se(VI) was taken to be between 20–50,000 ngmL−1 (r2 = 0.99697) and 10–10,000 ngmL−1 (r2 = 0.99969), respectively. The linear range for other four selenoamino acids species were between 5–10,000 ngmL−1 (r2 > 0.999). The LODs for the selenium species gotten by this method are comparable with the LODs reported values in the literature. This study also uses the alternative tetra-alklammonium hydroxide and the chromatographic selenium species to overcome the effect of deterioration that might be brought about by low pH values of perfluorocarboxylic acids.

Different speciation of selenium is of much importance than its total concentration determination. Elemental analysis is generally achieved by hyphenation methods where, a high efficient separation technique is engaged to detach different species of interested element. Sensitive recognition technique is used to determine the target elementary species in very low level.

The critical evaluation of this article:

The article elucidates a fascinating data in relation to Ionic liquids improved reversed-phase HPLC on-line that are coupled with ICP_MS for selenium speciation which is widely adopted by different analytical labs. It is evident that this study was aiming at the development of room-temperature ionic liquids, improved reversed-phase high performance liquid chromatography, and on-line combined with inductively coupled plasma mass spectrometry for selenium speciation and, the analysis was validated by the speciation of selenium in a certified reference material of SELM-1 yeast which was bought from NRCC (Ottawa, Canada)[1].

This new study has an advantage as; the sensitivity of the experiment is enhanced due to use of perflourocarboxylic acid as ion pair reagent. The older techniques proof to have difficulty in the sensitivity of the results. This is brought about due to the clogging of the ICP sample at the interface during the analysis process. In older technique, the decrease in sensitivity is exhibited after an hour’s time. Different parameters affecting the retention behaviors of six target selenium species especially the effect of RTILs as mobile phase additives was targeted in this study and the aim was to develop a new method of RTILs enhanced RP-HPLC–ICP-MS for the speciation of inorganic and organic selenium in biological samples [1]. In general words, the study was well designed and was supported by the results and clear explanations and justification of the procedures that have been done.

The study takes into account all of the parameters that might interfere with the validity of the results. To achieve this, the optimum conditions were considerably put to practice. This would provide the effect of counteracting the behavior that might be experienced from the changing results exhibited (Zheng, et al ., 2000). The study illustrates clearly the instruments that are used during the experiment. In addition, the sources where the reagents may be obtained have also been stipulated. The techniques and criterion that are used to perform the experiment has been elaborated and, tabulated to give a clearer view and background analysis.

The article plays a vital role in the future study of analytic chemistry and, may be approached at different perspectives to deal with different parameters that upset the retention behaviors of selenium species and mostly the result of RTILs as mobile phase additive. Indeed, the article suffices well in other related studies that deals with the importance and may find evidence of biological effects, of toxity and different bioavailability of selenium and they may modify some of parameters or aspects that can be applied with other elements. From the results, it is evident that the use of single RTIL as mobile phase additive could not meet the constraint of baseline separation of six target selenium species in a rather short time. To make sure that full use of these characteristics of RTILs, a mixture of [BMIM] Cl and [BMMIM] BF4 were investigated to achieve a baseline separation of all target selenium species in a short time. This is usually carried out so as to overcome the effect the peaks overlapping exhibited in the selenomino acids and the inorganic selenium to attain the required ion strength and the required ratio. The effect of the ratio of [BMMIM] BF4 to [BMIM] Cl on the retention characteristics of six target selenium species which had RTILs concentration at 1.0% (v/v). As could be seen, the ratio of [BMMIM]BF4 to [BMIM]Cl had no realizable effect on the selenoamino acids[1]. some limitation associated with the subsequent ICP-MS detection include; use of 0.4%(v/v) [BMIM]Cl and 0.4% (v/v) [BMMIM]BF4 as mobile phase additives and an isocratic elution ,no ICP-MS sensitivity shift was found in this work. RTILs have no effect on the mobile phase pH unlike acids and amines. However, the challenge that possess to this technique is that, the use of organic additives would affect carbon deposition on the surface of sampling cone and thus worsen the detection limits of ICP-MS. Secondly, adoption of gradient elution effect induction of severe matrix variation which leads to sensitivity drift in ICP-MS.

In conclusion, the article presumes the novel approach in which it elucidate the RTILS as a mobile phase obtained in the additive of the RP-HPLC-ICP-MS in a more functional speciation. This has seen the merit achieved in the ability to select the required RTILs given the low injection volume and its rapidness. This gives a retention time in the selenium species target.

References

[1] Chen, B., He, M., Mao, X., Cui, R., Pang, D., and Hu, B., 2011. Review of article: Ionic liquids improved reversed phase HPLC online coupled with ICP-MS for selenium speciation, Talanta [e-journal] 83, Available through: Elsevier science database [Accessed 15 may 2011], pp724-731.

[2]Zheng, J., Ohata, M., Furuta, N., and Kosmus, W., 2000. Speciation of selenium compounds with ion- pair reversed phase liquid chromatography using inductively coupled plasma mass spectrometry as element- specific detection.[ e-Journal of chromatography] 874, Available through: Elsevier science database[Accessed 16 may 2011], pp55-64.