Looking to maximize your chromatography and mass spectrometry systems, to ensure quality ultra-trace analysis? In this webinar, Dr. Detlev Lennartz from Thermo Fisher Scientific explains how the addition of inert-glass autosampler vials can optimize chromatography and mass spec systems. Dr. Lennartz also offers top tips on who can benefit the most from using inert-glass vials, and how using inert-glass vials may solve many common instrument issues.
Read the highlights from the Q&A session below and watch the webinar in full on demand.
Q: Are you able to define more compounds, aside from doxepin, which can take benefit from using the Chromacol GOLD-Grade Vials, or maybe product molecule classes or business segments?
DL: Yes, we have chosen doxepin because it was the first real lab problem which led to a modification of the SOP and the lab had to stop their routine analysis. So it solved a real problem, not a standard sample in water in high quantities, but patient samples in matrix, human serum, plasma, urine, and blood. I had tertiary amines on one slide which can be found to adsorb significantly on glass walls, but it's not only in the medical region where we find these kinds of polar compounds. We have these compounds in pest control systems, such as pesticides and herbicides. Sometimes we have to go down to nano, femtogram, and even lower measurements, because we have to extract something out of plant materials or out of soil.
Additionally, when we are looking for very low quantities in drinking water from plastic bottles, I increase the list to a lot of compounds. The major thing you have to look for is a molecule which is very polar, with multiple carboxylic acids functions or amino acid functions, or has two or three substituents on the nitrogen. If you think the molecule could adsorb or interact with an SiOH surface, you should try to use a Chromacol GOLD Vial in order to have a direct comparison to your standard vial to see if recovery and reproducibility could be improved. In the situation of the case study, it was an improvement of 80% recovery, not only for a few minutes or hours, but for days. And so, the complete process could run without any issue overnight, which was not possible before.
Q: Which septa is most suitable for HPLC vials?
DL: The septa quality has two aspects. One is penetration, so the septum needs to be compatible with the needle you use, and needle form. Another aspect to consider is hardness: some people prefer very soft septa because it won’t damage very thin, tiny needles. Other people prefer a harder septum because of the re-sealability.
In GC, you definitely need to have the best of the best, because of the nonpolar solvents: chloroform methylene, chloride, or hexane cyclohexane, which would extract everything out of a natural rubber septum, for instance. So, here, my recommendation is clearly a silicone septum PTFE covered.
In HPLC, you have more choices because you work with water. I would say first consider your needle and then I’d say a good silicone PTFE septum should be OK, as it is not too thick. And if you have blunt needles or want to inject higher quantities, take a pre-slit septum in order to avoid a vacuum in the vial.
Q: How do we know which glass grade we should use for autosampler vials?
DL: There is no rule, but today it's common to use first hydrolytic class glass, of which there are three types: 33-type, 51-type, and 70-type. All three quality steps are still first hydrolytic class glass, but the results show, that not every vial from each of these three steps can be used for highly reproducible results, or for low quantities and glass wall adsorbing compounds.
If you want a good result and high reproducibility, you need to have a good vial. If you want the best of the best, you have to pay for it and you have to look for it.
Q: Are there any vials you'd recommend which are both reproducible and also have the lowest absorbency on the vial surface?
DL: Yes, we recommend the Thermo Scientific Chromacol Gold-Grade Vial because this vial has the lowest adsorption tendency with the lowest pH shift. If you put water in of pH 7, the maximum difference you get is maybe 6.7 or 7.3. If you use different vials, it may hit you with an unexpected high pH shift.
Q: With regards to the percentage relative standard deviation (RSD) of a standard solution using the same vial, is that beneficial or should we keep an individual vial for each individual injection into the HPLC?
DL: In an ideal world, the RSD should be perfect when you use two different vials for two different injections. As we are not living in an ideal world and glass is differing, I would say that RSD depends on the method. Let's say you are a medical lab and a pharmaceutical lab in a ring contest. You are told the variance should be maximum 50%. The worst case would be that you have five vials, so you split your sample into five pieces and you get five totally different results. In order to avoid that, you should always be aware, whatever the RSD is, you want the one value which is the right one and you want to be as close as possible. If one of the major targets in your lab is to have the lowest RSD values possible, take a vial where you minimize the risk that the glass surface influences your reproducibility from vial to vial.
Q: Can I work without a buffer because of the low pH shift of a GOLD grade vial?
DL: I would say normally no, as this low pH shift is just one piece of the puzzle. Because you put your sample into the vial, and normally your sample in HPLC isn’t neutral, it has a functional group which may influence the pH. As the molecule you analyze modifies the pH — and in order to have the right pKa value and be in a comfortable position that all your molecules are protonized or neutral, so you have a good and reproducible reversed-phase HPLC — you should use a buffer. However, if you have very low concentrations of analytes, you can use very low concentrations of buffers and this directly improves your detectability in traces.
Q: Does this new vial replace silanized vials completely?
DL: No – you still have the requirement and necessity to use silanized vials. In some cases, you still need a totally covered surface because a standard glass vial surface is a polar surface. If you silanize it, it is an etherification, which means you replace the OH or the proton of the OH group by a nonpolar organic or silicium organic group, so you make a nonpolar surface out of a polar surface. After silanization, the glass vial itself becomes a nonpolar sample container.
Think of a glass vial as a polar container, a plastic vial as a nonpolar sample container, and the silanized vial as a little bit in between. The surface is nonpolar, but you have the stability of glass. So, you can use a silanized vial with solvents or molecules that you would never put into a plastic vial. And if you put them in a non-silanized glass vial, you may have very non-countable interactions and side effects, so still the answer is no. This inert vial will not replace silanized vials.
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