Why should you change your filters and valves?

Exhaust filters and valves are permanently exposed to vapours, dust particles and pollutants.

By exchanging these filters and valves regularly you can:

- Maintain your workspace safety

- Keep your solvent reservoirs clean from vapours, dust particles and pollutants

Lab Unlimited have a variety of exhaust filters and mobile phase valve replacements available on our online store – http://www.labunlimited.com/Online-Shop/Chromatography/LC-Supplies/.

We stock products from Vici International, S.C.A.T. Europe and the Duran Group.

If you need any further information give us a call on 01-4523432 or you can email us at chromatography@labunlimited.com.

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The final Labortops promotion of 2011 is now available to all our customers.

 With promotions including:

This promotion is valid until the 15th of January 2012.

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The NEW Lab Unlimited 2012 Catalogue is now available to all our customers.

To Request your NEW Lab Unlimited 2012 Catalogue please click here.

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Food and beverage manufacturers run viscosity tests on all kinds of products ranging from relatively thin water-like juices and soft drinks to sauces with variable flow behaviour, thick creams and pasty icings.  Measurement of viscosity is necessary for QC purposes. This is certainly true for the final product before shipment to the customer but also at other times during the process to make sure that the evolution of the mixture is progressing correctly.

The popular workhorse in most QC labs is the rotational viscometer (see Figure 1). This instrument can measure a broad viscosity range depending on choice of spindle and rotational speed. Manufacturers with an array of products find this flexibility helpful because they can use the same instrument for more than one item. Diligent use of the viscometer ensures that customer acceptance specs will always be satisfied, at least for anticipated flow behaviour.

When the viscosity data from a QC test is out of spec, the first thought is that something may be wrong with the viscometer. Blaming the instrument is the easy way out. If the food or beverage item is not in spec, production may have to stop while the process is investigated to determine where the problem is originating. This level of hassle is the driving reason why operators want to pin the difficulty on the instrument. The instrument problem is easier to fix, at least in the short term.

Laboratories which have carefully developed policies know that the use of viscosity standard fluids is the right way to quickly resolve this type of potential problem (see Figure 2). The viscosity standard has a known value established by the manufacturer of the liquid and the instrument should measure that same value when testing the fluid.

Viscosity standards come in a number of stock values which range from 5 centipoise to 100,000 centipoise. (Values outside this range are also available but this is the range most often considered by industrial QC labs that work with viscosity standards.) The customer will often at times select a standard with centipoise value that closely matches the actual viscosity of the product that they are making.

There are times when a stock value for available viscosity standards does not come close enough for the customer’s purpose so they will request a special blend, for example 2000 centipoise. The stock values that come close to this are 1000 and 5000 centipoise.

This new product is made by experimentally blending the two stock values in appropriate portions until the desired value of 2000 centipoise is achieved. While the cost may be slightly higher for the special blend, the need for precision in the QC lab becomes the higher objective and is ideally satisfied by using the correct viscosity standard.

The manufacturer produces each viscosity standard with a label on the fluid and a separate certificate which clearly identifies the viscosity value and the temperature at which it was calibrated, in most cases this is 25°C. The customer may also request additional calibration temperature(s) when needed. This document should be kept on file for reference and in case of audit. The regular use of viscosity standards to check your viscometer is an important practice to avoid the types of problems described above.

View our full Brookfield Viscosity range.

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Lab Unlimited strive to supply HPLC columns that provide the chromatographer with the longest possible column lifetime. However, columns do inevitable fail at some point. There are many causes for the failure of HPLC columns. It’s the goal of this series to look at the possible causes of column failures and to offer solutions.

Mobile Phase

The mobile phases used for HPLC analysis may lead to column failures through a number of ways.

1. Generally, HPLC grade solvents are filtered through 0.2um porosity filters by solvent suppliers. This level of filtration is more than adequate to protect the HPLC column from plugging or clogging. In addition most HPLC water purification systems used in laboratories contain 0.2 um filter as a final polishing step. However, many solvents (including minor modifiers additives) are non‐HPLC grade and these chemical must be filter thru 0.2um filters. Solid chemicals including buffer salts may be chemically pure and even HPLC grade, but unfortunately these chemicals may contain physical contaminants. These contaminants may come from various sources and can clog or plug a HPLC column after a period of use. In these cases it is very useful to filter prepared mobile phases, especially when they contain buffer salts or ion pairing reagents.
2. A major cause of column failure is related to buffer solubility in various mobile solvents such as acetonitrile. Phosphate buffers are particularly problematic when used with acetonitrile. When acetonitrile/water composition is about 50/50 v/v and the phosphate buffer is 50 mM. At this composition a precipitate will form, may be not immediately but slowly as a recrystallization process. These crystals will coat the pumping system and clog the column. Recrystallization of buffer salts can occur with pre‐mixed mobile phases as well as gradient mixtures. In the case of pre‐mix mobile phases the concentration of buffer salts can be critical and if there is a possibility of recrystallization then the solvent should be prepared a day in advance to observe the formation of any crystals. The chromatographer should be careful with the concentration of buffer used for gradient mixing. If there is a question of precipitation or recrystallization occurring with gradient mixing, then a pre‐mix mobile phase mixture should be tested using the highest level of organic solvent used in the gradient profile to check for crystal formation. In addition, care must be exercised when cooling columns below sub‐ambient because crystals may form at these reduced temperatures. Also when salt buffers are used it is critical that the salt buffer solvent be removed from column before storage. If a column is stored containing salt buffers there is a very high probability that the column will clog.

Sample

The injected sample may lead to column failures through several ways.

1. Particulate matter from injected samples may lead to column clogging. To prevent sample particulate clogging samples should be pre‐filtered. However, for small volume samples the hold‐up of the filter maybe too great. In these cases centrifugation of the sample can be used.
2. Unfortunately, many samples can’t be filtered. For these samples guard columns are most useful. A guard column is basically a small HPLC column packed with a material similar to the analytical column.

We provide guard columns that are easy to change and protect the analytical column. For more information, contact chromatography@labunlimited.com.

Next month: Extending column life part II

This information was kindly provided by ES Industries, one of the marker leaders in the manufacture of high Quality HPLC columns.

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Eli Mulvey joins us as the latest addition to the Lab Unlimited team. Eli is an experienced Technical Sales Specialist who has come to us from a leading laboritory water purification equipment company.  Eli’s mainly areas of responsibility are Chromatography consumables as well as General Laboratory instrumentation and consumables.

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Carl Stuart Quality has had a busy week with both the ISO 9001:2008 and ISO 17025:2005 surveillance audits taking place.
The INAB (17025) audit was our first since attaining the accreditation in September. We are happy to report that this and our ISO 9001 audit went without a hitch, with no major issues raised.

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