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Some notes about Fats and Oils in Food and about FAME and FAMEWAX

In Europe, the last transition periods named in REGULATION (EU) No 1169/2011 on the provision of food information to consumers are running out on Dec. 13th, 2016. Since then, a nutrition declaration is mandatory for nearly all packed food in Europe, wherein the amounts of fat, saturates, carbohydrate, sugars, protein and salt have to be included. The content of the mandatory nutrition declaration may be supplemented with an indi­cation of the amounts of one or more of the following:
(a) mono-unsaturates;
(b) polyunsaturates; …

This was my starting point to investigate some of the Restek solutions in measuring Fat content in Food. The nutrient fat is one of the main energy providers from Food. Fortunately the civilized world is not suffering from a lack of nutrient energy, but from the opposite, which, unluckily, leads to some of the so called lifestyle diseases. This underlines the importance of such nutrition declarations, but also the importance of scientific investigations about different fat classes.

Different fats are all built in the same simple way. The trivalent alcohol Glycerine is esterified by fatty acids. Though simple in its basic structure, fats are varying by hundreds of different fatty acid combinations, some of them identified as healthy, others as unhealthy. For example, mono- and polyunsaturated fatty acids (MUFA and PUFA) are known as more healthy than saturated fatty acids (SFA). Unfortunately we also have to divide between cis- and trans-unsaturated fatty acids, whereas cis-fatty acids are recognized as more healthy than trans-fatty acids. A special role is given to  polyunsaturated fatty acids (PUFAs) depending upon the position of the double bond closest to the ester group: n-3 (also notated as ω -3) systems and n-6 (ω -6) systems, wherein the ω -3 systems seem to have a special healthy role in human metabolism.

Sounds confusing? It is, especially for the analyst, who is asked to classify fats in food and other matrices. The huge amount of different, structurally nearly identical compounds, which cannot be easily resolved in an MS, makes it impossible to use an LC approach for this task. Fats itself cannot be transferred into the gas phase to use an easy GC approach. So a lot of techniques are standardized from organizations like AOAS, ISO or DGF to cut the fats into glycerine and its fatty acids, followed by derivatization of the fatty acids into their Fatty Acid Methyl Esters (FAME) for further GC measurement.

The next question is, which GC column would be best to analyze the remaining complex mixture of Fatty Acid Methyl Esters? Restek has developed a wax column, specially designed for such a challenging approach, the FAMEWAX column. So what, if I would recommend this column? I am sure that you are sure that I believe in the quality of Restek products. I am a Restek employee and in the end you would have to trust in my or Restek’s reliability. Or you have to check different columns by your own.

But what, if others would have done this before? Think about the most demanding ones? Instrument suppliers. If they have to proof their complex systems in front of a customer, they do well to know everything about the performance of a strategic compound like a GC column. And so they do. I recently found an application note from Shimadzu Europe, comparing different types of GC columns for this approach, including Restek’s FAMEWAX column, which I mentioned before.

The finding of the Shimadzu scientists was that under six different types of columns the FAMEWAX column with a 30m length performed as good or better as five others with 60 m length. The complete application note can be found here:

analysis-of-37-fames-using-6-types-of-capillary-columns_eg252

Another interesting publication using our FAMEWAX column was published by young scientist Annika Ostermann from the research group of PD Dr. Schebb at the University of Veterinary Medicine in Hannover, Germany.

This research group investigates the role of ω -3 fatty acids in human and veterinary metabolisms. For this work, Annika Ostermann compared different derivatization and extraction procedures suitable for the determination of the fatty acid composition in plasma and tissues as fatty acid methyl esters using gas chromatography. Sample preparation and derivatization methods for the analysis of small amounts of tissue and low plasma volumes is more challenging than determining FAME in food, where sample amounts may not play such a big role.

Annika Ostermann provided the following chromatogram, showing this nice separation for the interesting compounds in her work. The complete work was published in PLEFA (Prostaglandins, Leukotrienes and Essential Fatty Acids) and can be found here.

fame-chromatogramm

 

 

Why Biphenyl is a very interesting primary choice as stationary phase in LC..

2011-jaapBeing a GC chemist for almost 38 years I always wondered why most LC separations are performed on a C18. A C18 is an extremely good non-polar stationary phase and is the foundation of reversed-phase chromatography, where polar mobiles phases are used with non-polar stationary phases. But there are so many C18 phases, how do you choose the correct one? There are also a lot of separations where analytes are polar, one of the big advantages of LC is that you can analyze much more polar analytes than GC without derivatization. For these types of analytes why do you choose a C18 at all?

A basic rule in chromatography is that you choose a stationary phase that shows interaction with your analytes. In a GC hydrocarbon separation, for example, a polydimethyl siloxane like Rtx-1 is used. For alcohols and glycols, a polyethylene glycol like Rtx-Wax is used, or for optical isomers a chiral stationary phase is used that shows specific affinity to one type of isomer.

In LC, multi-ringed structures, substituted ring structures, and small polar analytes are frequently analyzed. These analytes will interact with C18 through dispersive forces, but they may also interact with the silica substrate through hydrogen bonding or cation-exchange. These interactions are often referred to as “silanol” interactions and they are often thought of as undesirable. In fact, with many separations these silanol interactions contribute significantly to the retention of the analytes. This means silanols can be both beneficial, by creating retention; and detrimental, if they are not controlled or if the silica surface is not consistent. Differing silica substrates is one of the main reasons all C18’s are not the same.

Fig,1 Surface of C18 silica.

Fig,1 Surface of C18 silica.

So the question that came to my mind is how do you take advantage of additional retention mechanisms for polar analytes in reversed-phase? One way is with the Biphenyl stationary phase which was originally developed at Restek.

 

The Biphenyl stationary phase retains compounds through the same dispersive forces as a C18 but it also allows for more polarizable substances to be retained. Basically, the pi electrons available on the Biphenyl phase create retention with analytes which are electron deficient. Because there are so many pi electrons in conjugation you get much better retention for small and polar analytes than on a phenyl-hexyl or diphenyl type phase.

biphenyl-jpg

Fig. 2 Biphenyl

I would argue this actually make the Biphenyl an even BETTER choice than a C18 when starting your method development. An example I saw at a recent food meeting showed >600 pesticides in one run using LC/MS/MS on Restek’s Raptor Biphenyl phase.

As with any phase chemistry there is always some type of downfall and in the case of the Biphenyl it is UV bleed. A dirty little industry secret is that ALL phases bleed whether you know it or not, it just so happens that with C18 you don’t see the bleed with UV or MS detectors. In the case of the Biphenyl you can see phase bleed in certain instances by UV. If this is the case contact Restek Technical Support and they can coach you through how to minimize or eliminate it.

So where did the Biphenyl phase come from? A number of really intelligent people were involved in making it happen at Restek and it included GC polymer chemists, LC R&D chemists, and Applications personnel. It’s a great story about experimentation, fundamental chemistry, and teamwork making a really great and unique product. If you want to learn more about the biphenyl story go to www.restek.com/biphenyl.

Special thanks to Ty Kahler and Paul Connolly for their input in this blog

Two Detector Solution to Analyzing Sulfur

Dan Li, Katarina Oden, Chris English, and Jason Herrington

Sulfur compounds are reactive, corrosive to pipes, and destructive to catalysts in petroleum refineries. Sulfur emission are strictly regulated globally. When released into the atmosphere sulfur dioxide converts to sulfuric acid resulting in adverse effects on human health and the environment. Sulfur detection is found useful in many other industries; therefore, detection of sulfur compounds in matrices serves a vital role in many application areas.

Sulfur analysis is typically done by gas chromatography (GC). The frequently used sulfur detectors are sulfur chemiluminescence detector (SCD), flame photometric detector (FPD), and mass spectrometry detector (MSD). As sulfur selective detectors, SCD and PFPD have the advantages of measuring components of interest and providing an equimolar response for sulfurs. Compared to SCD, FPD is more robust, less expensive and less complicated for maintenance. One challenge of FPD or PFPD is the hydrocarbon interference, especially those from the chromatographic coelutions, which can cause quenching or signal suppression. In order to minimize the quenching effect, one can either use high split ratio to reduce the amount of hydrocarbon injected or resolve the sulfur species from the hydrocarbons chromatographically. In most cases, small injection volumes or high split ratios are unsuitable for trace-level detection. If cryogenic cooling cannot be used, it is difficult to avoid coelutions using a single detector.

Mass spectrometry is a universal detector widely used in many applications. It provides structural information of the analytes in full scan mode and enhanced selectivity / sensitivity in selected ion mode (SIM). For some volatile sulfur compounds, unique qualifier ions are not available in the presence of impurities; however, selected ion monitoring can reduce the coelution problems in many applications.

Using the MS in tandem with the FPD mitigates the disadvantages of both detectors. FPD provides accurate sulfur amount due to the equimolarity characteristics while MS gives a total profile to include matrix not seen by the FPD. This paper describes the design of a parallel GC FPD-MS and demonstrates its applications.

Analysis of sulfur samples was performed on a Shimadzu GC-MS QP 2010 Plus system equipped with an FPD. Sample introduction was done by manual injection through a split/splitless injector at 200 °C. The injection volume was 1 mL. The GC analytical column was a 15 m × 0.25 mm × 0.25 µm Rtx-1 (Cat # 10120). A three-port SilFlow device (SGC Analytical Science) was employed to split the flow at the end of analytical column to both MS and FPD. Two deactivated, uncoated fused-silica transfer lines (restrictors) were employed to couple the splitter device with MS and FPD, one with a dimension of 84 cm × 100 µm I.D (connected to MS) and the other 75 cm × 250 µm I.D (connected to FPD). Figure 1 shows a schematic drawing of the GC with parallel FPD and MS. Details of instrumentation are listed in Table 1. Both FPD and MS chromatograms for the gas samples were acquired simultaneously.

setup

Figure 1. A schematic diagram of GC-MS-FPD setup.

 

Table 1. Instrument Conditions

table-1

Sulfur standards were purchased from DCG Partnership 1, LTD. (Pearland, TX). They were prepared in two blends due to the stability issue. The components and concentrations are listed in Table 2.

Table 2. Sulfur Standards

table-2

Peak shapes are greatly impacted by the inertness of the column. Rtx-1 column offers great inertness as well as sufficient resolution for heavy matrix sulfur analysis, as seen in Figures 2-4.

By using the dual detectors system, a sulfur chromatogram and a simultaneous hydrocarbon chromatogram can be generated from a single injection. For the following examples, the top chromatogram displays the FPD signals and the bottom window displays the corresponding MS profiles. The retention time from both chromatograms matched well. This hardware configuration can be applied to other sulfur application areas.

Figure 2 shows a set of FPD and MS Total Ion Chromatograms (TIC) of sulfurs and hydrocarbons. In this case, a series of hydrocarbons coeluted with sulfur components. Recognizing specific sulfur compounds using FPD makes it possible to accurately pinpoint the retention time in complex TIC. Quenching, which is caused by the coelution of hydrocarbons, is illustrated in Figure 2. Sulfur signals can be significantly suppressed by the matrices, leading to inaccurate quantification. With the assistance of cryogenic devices or longer columns, sulfurs with limited number of hydrocarbons may be resolved. It is impossible to avoid quenching or signal suppression in gasoline samples containing hundreds of different hydrocarbon compounds with a wide range of concentrations. The use of the MSD in SIM mode can reduce this problem in many cases, while operating in scan mode assists in initial method development, unknown matrices identification, and finding the retention time of interferences.

figure-2

Figure 2. GC-FPD-MS (full scan mode) detection of sulfur standards (Blend 1) in hydrocarbon matrices.

 

Figure 3 is a display of sulfur analysis with FPD and MS under SIM conditions. The SIM ions are listed below the chromatograms. The ions are carefully chosen to avoid interferences from hydrocarbons; however, the confirmation of peaks 1, 3, and 4 may be questionable because the qualifier ions were also shared by matrice ions. When a unique ion is not available, different chromatographic column / conditions should be tried to resolve the analytes. Fortunately, we have the ability to use Restek’s free ProEZGC library tool which will allow us to model the elution times of both sulfurs and hydrocarbon interferences under a specific set of conditions, in this case, using the Rtx-1. Conditions can be optimized for specific conditions and allow the use of SIM and the specific retention time as a reliable means of compound identification.

figure-3

Figure 3. GC-FPD-MS (SIM) detection of sulfur components (Blend 1) in hydrocarbon matrices.

 

In Figure 4, both FPD and extracted ion chromatograms were collected for all 20 sulfur compounds (Blends 1 and 2). The SIM ions used for each sulfur compound are listed. The relative abundances are different in FPD and SIM responses, which results from the different detection mechanisms. The SIM chromatogram showed improved resolution on hydrogen sulfide and carbonyl sulfide.

figure-4

Figure 4. GC-FPD-MS (SIM) detection of sulfur components (Blends 1 and 2).

 

The GC-FPD-MS coupling allows positive identification of sulfurs in complex matrixes and eliminates the need for multiple injections using different columns and detectors.

Dimethyl polysiloxane stationary phases (Rtx-1) provide good retention and resolution for sulfurs. Historically, thick film columns are used since they provide excellent inertness and peak shapes since analytes spend less time in contact with the deactivated fused silica surface. Columns with thinner films demand excellent surface inertness, for example, a thin-film short column (15 m × 0.25 mm ×1µm) was employed, resulting in a 10-minute analysis time. Conditions were optimized using ProEZGC resolving 16 out of 20 compounds (Figure 4) to include low-molecular-weight volatile sulfurs.

The FPD-MS combination is a powerful tool for unknown compounds, especially in the presence of complex matrices. Using tandem FPD/MS detectors provides an additional measure of confirmation not available from using either detector alone.

This paper demonstrates the capabilities of this hardware configuration for sulfur analysis. Further optimizations can be done on different column dimensions, oven temperatures, flow rates, and other parameters by using EZGC programs.

Acknowledgements

The authors would like to thank Shimadzu Corporation for their consultation with the operation of the QP2010 Plus GC-MS instrument and the FPD. http://www.ssi.shimadzu.com/

Which guard cartridges and holders go with which LC analytical columns?

As our family of LC products has grown, so have our choices for columns and accompanying guard cartridges. Here is a handy chart to show which guard holder and guard cartridges were intended for use with each type of analytical column. Please feel free to click the links to access each group of products on our website.

 

Analytical Column Guard Holder Guard Cartridges
Raptor EXP Direct Holder, catalog #25808 Raptor EXP Cartridges
Force (3um & 5um) EXP Direct Holder, catalog #25808 Force EXP Cartridges
Force (1.8 um)* Use UltraShield  or UltraLine filters
Roc Roc LC Guard Holder, catalog #25812 ROC Cartridges
Ultra Trident LC Holders Ultra Cartridges
Viva Trident LC Holders Viva Cartridges
Allure Trident LC Holders Allure Cartridges
Pinnacle DB (3um & 5 um) Trident LC Holders Pinnacle DB Cartridges
Pinnacle DB  (1.9 um)* Use UltraShield  or UltraLine filters

 

*Guard cartridges not available for this column. Options for column pre-filters are listed.

Please note that the Trident LC Holders shown above are also available for use with filters only, as catalog numbers 27470/27471. However, this is less common, as most analyses benefit from including the guard cartridge for full column protection.

You may also find these blog posts useful:

Choosing a guard cartridge holder for LC

Choosing a guard cartridge for LC

 

Thank you reading and for using our LC products.

Leak Detector Lithium Ion Battery

Lithium ion batteries have been in the news quite a lot recently, and not all of it has been positive.  22655There have been numerous incidents of different products from airplanes to hoverboards to mobile phones catching fire during charging or operation.  These problems occur when there has been damage to the cells’ structure or to the protective circuit.  The protective circuit helps to avoid over-voltage and under-voltage (over-discharge).

Over-Voltage

If the charging voltage is increased beyond the recommended upper cell voltage, typically 4.2 Volts (Restek Leak Detector 4.275 V), excessive current flows giving rise to two problems.

  • Lithium Plating
    With excessive currents the Lithium ions can not be accommodated quickly enough between the intercalation layers of the anode and Lithium ions accumulate on the surface of the anode where they are deposited as metallic Lithium. This is known as Lithium plating. The consequence is a reduction in the free Lithium ions and hence an irreversible capacity loss and since the plating is not necessarily homogeneous, but dendritic in form, it can ultimately result in a short circuit between the electrodes. Lithium plating can also be caused by low temperature operation.
  • Excessive current also causes increased Joule heating of the cell, accompanied by an increase in temperature and thus overheating22653_ph_so_gca

Under-voltage / Over-discharge

Rechargeable Lithium cells suffer from under-voltage as well as over-voltage. Allowing the cell voltage to fall below about 2 Volts (Restek Leak Decector 2.3 V) by over-discharging or storage for extended periods results in progressive breakdown of the electrode materials.

  • Anodes – First the anode copper current collector is dissolved into the electrolyte. This increases the self discharge rate of the cell however, as the voltage is increased again above 2 volts, the copper ions which are dispersed throughout the electrolyte are precipitated as metallic copper wherever they happen to be, not necessarily back on the current collector foil. This is a dangerous situation which can ultimately cause a short circuit between the electrodes.
  • Cathodes – Keeping the cells for prolonged periods at voltages below 2 Volts results in the gradual breakdown of the cathode over many cycles with the release of Oxygen by the Lithium Cobalt Oxide and Lithium Manganese Oxide cathodes and a consequent permanent capacity loss. With Lithium Iron Phosphate cells this can happen over a few cycles.

All of these scenarios can be bad for the lifetime of a leak detector battery, and the safety of the end user and their facilities, that is why we too have the protective circuit in our Li ion batteries.

“But what does this mean to me as an owner of a leak detector?” you may ask.  Well first it means you cannot over-charge and overheat the unit, but it does mean that you could discharge the battery below the 2.3 volt limit, and thus not be able to recharge it because the protective circuit will not allow it to accept current.

“So what should I do to avoid this?” I hear you ask.  Leak detectors are not to be used occasionally, they should be used every day to check critical seals and the gas delivery system in GCs, and labs.

Where to check on a daily basis:

Septum and septum nut

Weldment

Gas lines connections to inlet

Reducing nut

Column nut

Filter connections

Gas supply lines

Regulator

Making this part of your daily preventative maintenance routine will ensure that leaks are caught very early, potentially saving columns from being ruined, and also wasting valuable gases.  Using the leak detector regularly also means that you will have to charge the leak detector regularly.  At a minimum the leak detectors should be charged every 3-4 months, but in reality they should be charged more frequently, or when not in use be left on charge – remember they can’t be over-charged because of the protective circuit.

Product information on the Restek Leak Detector (22655) – http://www.restek.com/catalog/view/8175/22655

References

http://www.mpoweruk.com/lithium_failures.htm

Material Composition of Resprep® Manifold Replacement Parts

A customer asked me yesterday what material certain items for our SPE manifolds were made from.  The answers are below.

 

spe-parts

 

Catalog # 26083 is Nylon

Catalog #’s 26130 & 26131 are Polypropylene

Catalog # 26084 is PTFE

 

For those of you who need to avoid sample contact with PTFE, we also sell Stainless Steel Sample Guide Needles as a custom item (#563878); call or email customer service or your sales rep/distributor for pricing and availability.  Thank you.

 

“Absolute” Pressure (psia) vs “Gauge” Pressure (psig)

Here is the scenario:

  1. You have just received your brand new Ashcroft Test Gauge.
  2. Why??? Because you know that the gauge on your canister is not accurate enough for making reliable quantitative dilutions.
  3. You notice that your brand-spanking-new Ashcroft Test Gauge is not reading zero, like so:
  4. customer-gaugeNow you are starting to FREEAAK OUT!!! Because let’s face it… these gauges are not cheap.
  5. But before jumping off a cliff and/or throwing your gauge off one… let us review the following:

Like the gauge on your canister, the Ashcroft Test Gauge will read pressure/vacuum in what is called “gauge” pressure. This is not to be confused with “absolute” pressure, which is related. What am I talking about here?

Absolute pressure is zeroed against a perfect vacuum. Gauge pressure is zeroed against the local atmospheric pressure. This means when you are standing at sea level your body is experiencing ~14.7 (14.696) pounds/square inch of pressure, due to the atmosphere above you. We call this atmospheric pressure [i.e., 1 atmosphere (atm) of pressure]. You have no clue you are experiencing this every day, because you are used to it. However, you do realize things are different when you dive into a pool and experience an increase in the pressure or fly in a plane and experience a decrease in pressure. I know you know what I am talking about. In any event, this atmospheric pressure may be measured as 14.7 psia (“a” for absolute), at sea level.

However, your fancy new Ashcroft Test Gauge has been zeroed against this local atmospheric pressure. So when you are standing on the beach with your gauge it would read 0 psig. To further elaborate, when you are at sea level and you pressurize your canister to 30 psig (“g” for gauge), you have actually put 44.7 psia in the canister.

So when you see that your zero is off on the gauge, this is probably due to the fact that it was zeroed at a different elevation. This does not mean it is un-calibrated. In fact, we ship all of these calibrated, but you do have to adjust your zero. In the case of the customer example above, it just so happens they work at a higher elevation, which had a lower atmospheric pressure (e.g., 14 psia) than the elevation the gauge was originally zeroed at. This lower atmospheric pressure expresses itself as a lower gauge pressure, which looks like the zero is off.

 

Quick recap:

Gauge pressure = absolute pressure – atmospheric pressure

Using the pressurization examples above:

30 psig = 44.7 psia – 14.7 psi (atmospheric pressure at sea level)

0 psig = 14.7 psia – 14.7 psi (again, at sea level)

 

Now how about re-zeroing that test gauge? It as simple as the following: The smaller outer screw at six o’clock (red arrow) is a set screw. Loosen the set screw and then adjust the zero with the larger, inner screw (green arrow). Then re-tighten the set screw.

gauge-re-zero

Mixing up gauge pressure and absolute pressure seems to be a fairly common mistake. So always be sure to double check what exactly are you dealing with.

What can I use to filter my mobile phase?

If you are using mobile phase that contains salts or, generally, any components that are weighed out for its preparation, you will need to filter the solution before using with HPLC or UHPLC.

The most common type of filtration is membrane microfiltration. microfiltration

We sell an extensive group of products for this and they are discussed very well in a blog post written by one of my colleagues:

“Simplifying your Membrane Microfiltration Glassware purchase”

We sell membrane filters in polypropylene and nylon to go with the above glassware, although it is possible to use membranes made of other materials that you might find in 47 mm diameter size from other vendors.  Nylon is often preferred for aqueous solutions that are fairly neutral or slightly basic. Polypropylene is preferred over nylon if your solution is acidic or when using less polar organic solvents.

 

The other type of filtration you might consider is our Hub-Cap Filter Kit.

26395-kit

The Hub-Cap Filter Kit can be used with 4 Liter solvent bottles, or with any media bottle that has the same type of threads (which are 38-429).  An example of such a media bottle is the one shown here from Wheaton, the container in the middle:

http://wheaton.com/media/catalogs/Containers%20Guide/files/assets/basic-html/page5.html

The 4-Liter solvent bottles are the ones that normally come with solvents when they are purchased for your lab from a supplier. These are usually amber and look like this:

bottle-cropped

 

Hub-Cap Filter Kit, catalog 26395, comes with the following:

hubcap-filter-labelled-final

 

  1. ¼” OD x 1/8” ID FEP lined Tygon® tubing
  2. Tube compression fitting (HDPE)
  3. Hub-Cap bottle adaptor nut (HDPE), which is the external ring included in the Hub-Cap adaptor bottle top, catalog #26541
  4. Filter inlet cap (HDPE)
  5. 47 mm polypropylene filter membranes (one of each included): 0.22 µm polypropylene filter membrane, catalog #26399 and 0.45 µm polypropylene filter membrane, catalog #26398.  Please see * for other options.
  6. 47 mm grid (FEP)
  7. Grid support (PTFE)
  8. Bottle adaptor (PTFE)
  9. Vacuum hose barb (HDPE). Fits tubing ID between 5/16” to 3/8”, can be purchased separately as catalog #25925.

*Also available are 47 mm Nylon filter membranes, which are not included in kit, but available for purchase separately:  0.22 µm Nylon filter membrane, catalog #26397 and 0.45 µm Nylon filter membrane, catalog #26396

To use the hub cap filter kit, you would attach a vacuum pump to the barb on the side of the cap and then draw in the unfiltered solution through the tubing on top. The membrane would be replaced after each usage.

Although this kit is designed for use with 4-liter solvent bottles, you can purchase the Opti-cap adapter, catalog #27197, to use this kit with a GL-45 bottle.

I hope you find this post helpful.

Thank you for reading.

 


				

A brief introduction to DiatoSorb-W

diatosorb

.

DiatoSorb-W is a diatomaceous earth material that Restek will sell in packed columns and as a coated packing material (% loading with a liquid phase of your choice), which will replace Chromosorb-W products/packings. For those of you who may not know, the “W” stands for “white”, and is simply the color of the untreated, uncoated material.

If your method references USP S1A, or Chromosorb-W/AW (acid-washed), you will request/receive DiatoSorb-W/AW unless the material is designated as DMDCS (or DMCS) treated/deactivated, in which case you will receive DiatoSorb-W/HP.

If your method references USP S1NS, or Chromosorb-W/NAW (non-acid washed), you will receive/request DiatoSorb-W/NAW.

 

In summary:

.

USP S1A

DiatoSorb-W/AW = Chromosorb-W/AW

DiatoSorb-W/HP = Chromosorb-W/AW-DMDCS

 

USP S1NS

DiatoSorb-W/NAW = Chromosorb-W/NAW

 

Acronyms:

W = white

AW = acid washed

NAW = non-acid washed

HP = high performance

DMDCS = dimethyldichlorosilane (this is a deactivation treatment reagent). It may also be referred to as DMCS (dimethylchlorosilane).

 

For packed columns containing Silcoport-W, the name will remain the same but the starting material will now be DiatoSorb-W instead of Chromosorb-W.  The proprietary deactivation used for past and present Silcoport-W packings will remain the same.  Silcoport-W carries the USP designation of S1A.

For packed columns containing Chromosorb-W/HP, you will request/receive DiatoSorb-W/HP.  Note, Chromosorb-W/HP is known as both USP S1A and USP S1AB.

 

To receive a quote for a packed column or packing, please complete this form and a customer service representative will respond within one business day (Monday-Friday).

If you have any technical questions, email support@restek.com

 

Please note: DiatoSorb-W diatomaceous earth materials are not to be confused with other packings, such as Chromosorb P* (Pink crushed firebrick) or Chromosorb porous polymers**.

*Chromosorb P, P/AW, P/NAW, P/AW-DMDCS

**Chromosorb 101, 102, 103, 105, 106, 107, 108, N, P, Q, R, S, T

.

Concentration Units for Air Folks

A couple of customers have recently asked about standard concentrations and converting from ppmto mg/m³. Honestly, I have no clue how I have never blogged about this subject, especially considering how fundamental and critical this topic is. So here we go:

Air concentrations at ppm are parts per million by volume and should therefore be expressed as ppmv. Although sometimes people forget the “v” at the end, it is implied. Unless of course they meant parts per million by mole, which is sometimes used for air as well; and just so happens to be conveniently identical for an ideal gas and practically identical for most compounds in air at standard temperature and pressure (STP).

But for the most part it should go as follows:

equation-1

Which you may then conceptualize as:

equation-2

Now… I have encountered some confusion as to the fact that ppmv may be directly interpreted as mg/m3. Please do not make this mistake! The water and soil folks have the luxury of jumping from ppm to mg/L. But that is because they are not dealing with the density of gases, which are temperature and pressure dependent.

So how do we go from ppmv to mg/m3 (this is exactly the same for ppbv to µg/m³)… here is how:

equation-3

Where T = temperature in K = 273.15 + °C and 0.08205 is the Universal gas constant in L atm K-1 mol-1, which you may find on the good ole interweb.

Or you could stick to the short version of the aforementioned, which only requires you to remember an ideal gas will occupy 24.45 L/mol at 1 atm and 25 °C. Yes, not the 22.4 L/mol you see littered all over the internet. Unless of course your STP includes 0 °C. Therefore, the above equation simply reduces to the following:

equation-4

Remember, use the exact same equation for ppbv to µg/m³.