Advantages of AQ™ Brand NDX™-Depth Filters

Some analysts may think that selection of a syringe filter for their sample preparation step is of trivial importance. However, there is more to the syringe filter than just membrane material (e.g. nylon vs. PTFE). For instance, lower quality syringe filters may have extractable compounds that can end up in your filtrate. These extractables then show up as unknown peaks in your chromatograms, potentially interfering with peaks of interest. In a study comparing AQ™ Brand NDX filters to those of market leaders, the AQ™ Brand was shown to produce a lower peak area of the extractable and even more so after an initial wash step.

                Another aspect to consider is the hold-up volume. Suppose you have a sample that is available in limited supply. It could be expensive or simply rare. In this case, you don’t want to waste any of the sample and that is exactly what happens in a low quality filter. After the filtration, the amount of liquid remaining in the filter membrane is called the hold-up volume. It is best to minimize this volume and the MicroSolv AQ™ Brand NDX™ Depth Filters outperform competitive filters in this respect.

                If you have to filter a large amount of liquid with a single syringe filter, then lifetime becomes significant. The AQ™ Brand was shown to have a comparable lifetime to competitive filters. These three aspects of the syringe filter should not be overlooked as they can all cause unnecessary problems for the analyst.

                Click the link for more info:

http://mtc-usa.host4kb.com/article/AA-02363 

Method Transfer from 4um to 2.o™ HPLC column

Methods developed on the 4um Cogent™ line of HPLC column products can be readily adapted with near-UHPLC Cogent 2.o™ phases. In this blog, we have a method for forced degradation of atorvastatin (Lipitor®). The gradient separates the main API (atorvastatin) from its more hydrophobic lactone degradant.  The retention is comparable between the 2.2um column (Figure A) and 4um column (Figure B). However, efficiency is higher on the 2.2um phase which is a significant advantage for the user. With higher efficiency, you can obtain better resolution from closely eluting peaks. Also, you will get higher sensitivity due to the increased peak height. The efficiencies for the API were 88,420 plates/meter for the 4um column but 134,800 plates/meter for the 2.o™ phase.

                In this application, a standard HPLC (Agilent HP 1100) was used in both cases. With near-UHPLC columns, you don’t need a full UHPLC system to obtain the benefits of efficiency, resolution, and sensitivity. This is an important aspect since many QC laboratories don’t use UHPLC instrumentation in their routine assays. The only thing to keep in mind is that your column pressure will be higher and you should not exceed 120 bar on a regular HPLC system.

1 - Atorvastatin

2 - Atorvastatin Lactone

Limonin Content in Citrus Juices

We used the Bidentate C18 2.o™ column to separate limonin from matrix components in citrus juice extracts. The column produces high-efficiency, sharp peaks which is important in order to obtain good limits of quantitation. The quantitaitve studies first used limonin standard solutions covering a range of 2.0–200ppm in order to establish a calibration curve. The detector response was shown to be linear in this range. Next, a non-citrus juice was chosen to serve as a matrix blank (apple juice). This juice extract had no peaks in the region where limonin elutes and therefore would be a good candidate for percent recovery studies. The extract was spiked at both 5 and 10ppm levels. Recovery was observed to be within 97.8–100.2% at these levels. Finally, two orange juice samples were analyzed and the limonin peak was correlated with the calibration cruve. The amounts of limonin were found to be 1.20 and 3.70ppm in two different juices. The approach can be used towards development of a fully validated method for limonin quantitation.

 

New Retention Possibilities for Polar Compounds using Cogent Diol Column

TYPE-C Silica™ columns can be used for separation of a variety of polar compounds.  The new Cogent Diol™ column makes an excellent addition to these stationary phases. Consisting of a short alkyl chain with vicinal alcohol groups, this material has additional separation capabilities compared to other phases. Since it is on a TYPE-C Silica™ surface, the bonding is very strong and durable. The diol group can interact with analytes via hydrogen-bonding interactions, resulting in new selectivity. 

In the following example, we demonstrate the capabilities of this intriguing material. The test solutes chosen for the separation were seven common hydrophilic vitamins. The results show that baseline separation could be obtained for all seven analytes. The retention range is adequate as well, with no analytes eluting at the solvent front or sticking to the column. Peak shapes were sharp and symmetrical, and no tailing was observed. 

This column makes a wonderful addition to the TYPE-C Silica™ line of HPLC columns and should be a great benefit to every chromatographer’s toolbox. 

1. Ascorbic acid
2. Niacin
3. Riboflavin
4. Folic acid
5. Pyridoxine
6. Metformin
7. Thiamine

See the following link for full details:

http://kb.mtc-usa.com/article/AA-02102/0/ 

Simple Strategies for Improving Analyte Recovery

Suppose you’re doing an HPLC assay of a basic pharmaceutical and find a 66% recovery for the API. What happened? Did the drug not extract completely? Did degradation occur? These types of scenarios take up valuable laboratory time and resources with investigations, troubleshooting, and re-run analyses. In this case, it may be simply due to the autosampler glass. Regular glass has silanols on the surface that can bind with basic analytes and therefore lead to lower recovery. However, this problem can be prevented with some simple considerations.

In this example using a basic test analyte (cetylpyiridinium chloride), we can see how use of either an ammonium acetate buffer (red trace) or a formic acid additive (blue trace) can reduce the effect of analyte loss compared to DI water alone (green trace).  Using 0.1% formic acid, the silanols become protonated and neutral, which prevents ionic interactions with the analyte from occurring. This is the more effective of the two additives. Ammonium acetate helps the problem by a different approach. The ammonium ion competes with the analyte for the silanols groups, and so fewer sites are available for analyte loss to occur.

Here we use a different strategy for reducing the analyte loss. Reduced Surface Activity (RSA™) glass is made with almost no surface silanols and we can see a major improvement for analyte recovery compared to regular glass. For best results, you can use a combination of RSA glass vials and a formic acid diluent. For solubility reasons though, sometimes you might have to use an ammonium acetate diluent. In that case, RSA glass shows significantly better recovery than regular glass.

                When analysts plan a sample preparation procedure, they may put much thought into the extraction method, dilution procedures, and so on. However, the role of the vial is often overlooked.  Vials are inexpensive and disposable, so they can be seen as relatively unimportant in the analysis process. This data shows how they are not inert and can significantly skew your analytical results. A careful selection of vial and diluent is all it takes to prevent your laboratory from experiencing these kinds of problems.