Hints and tips

HPLC connections (TN #539)

This technical note shows possible types of connection between column and LC system. Bad connection may influence peak separation and should be avoided. The right connection is presented below.

Allowable Adjustments to HPLC Methods

Chromservis HPLC columns corresponding to USP and Eur. Pharmacopoeia methods and the extent to which the various parameters of a chromatographic test may be adjusted without fundamentally modifying the pharmacopoeial analytical procedures are listed in this technical note. Changes other than those indicated require revalidation of the procedure.

HOW TO CORRECTLY CRIMP VIALS

Crimp vials are excellent sample containers for automatic dispensers of gas and liquid chromatographs and for storing samples or calibration solutions. The technique of closing them is very important for proper tightness. Due to leakage caused by improper sealing, solvent evaporation or loss of analytes may occur.
A correctly closed vial can be recognized by the fact that its cap rotates with difficulty after closing and the septum is straight.
A vial that is closed with too much force can be recognized by the fact that its cap cannot usually be turned at all and, in addition, it has a bent septum (inwards). If the septum is punctured by the needle of the microsyringe, the septum will be heavily stressed and thus the vial's tightness will be compromised.
A vial that does not have a properly closed cap due to the low power of the crimping pliers is manifested by easy rotation of the cap and, in some cases, unfastened aluminum material around the lower edge of the vial neck.
You can set the correct force of the closing pliers.
In older types of pliers, the force is adjusted by turning the Allen key inside the jaws. Pliers also have a stop screw, which is used to set the safety distance, in order not to use too much force and thus to avoid leakage or even mechanical damage to the vial.

Troubleshooting

Many GC and LC problems can be avoided with routine preventive maintenance. If you are seeking the cause of the chromatography problem, go step by step. Never make more changes in your instrument at the same time, otherwise you will never find, what caused the problem.

Select your category of chromatography to read more about the troubleshooting:

GC troubleshooting

LC troubleshooting

Signal to noise ration improvment in GC

Today's laboratory needs are:

• Lower detection and quantitation limits (LOD, LQD)
• Stability improvment in GC and GC/MS systems
• More inert and stable GC parts (columns, septa, vials, liners, ...)

Lower detection and quantitation limits can be achieved by:

• Reducing the Noise
• Increasing the signal

GC septa selection

Agilent GCs

DANI GCs

Perkin-Elmer GCs

Shimadzu GCs

Varian GCs

Thermo Scientific GCs

Syringes

Syringe Cleaning and Maintenance

Chromatography syringes are the finest quality precision fluid measuring devices available. With proper care and handling, syringes will provide unsurpassed performance in precision fluid measuring year after year. The life of your syringe is directly related to its cleanliness!

Some solvents, such as halogenated hydrocarbons, may attack and deteriorate the highly resistive adhesives (cements) used to affix needles and other terminations to Hamilton syringes, which may result in frozen plungers and plugged needles.

Cleaning Syringe Barrels

To clean Hamilton syringes, it is best to use solvents known to be effective in solvating the sample and preferably are non-alkaline, non-phosphate and non-detergent based. A biodegradable, non-phosphate, organic Cleaning Concentrate is available from Hamilton (ordering number 18311).

Rinse the syringe thoroughly after use with deionized water, acetone, or another solvent compatible with the sample. Allow the syringe to air dry. Avoid prolonged immersion of the syringe while cleaning.

MICROLITER™ Syringes (Series 600, 700, 800 and 900)

• Rinse the syringe thoroughly with a solvent known to be effective in solvating the sample. Residual dissolved solids may result in frozen plungers and plugged needles.
• To clean the plunger, remove it from the syringe barrel and gently wipe with a lint-free tissue. Reinsert the plunger into the barrel and pump deionized water, acetone or another solvent compatible with the sample through the needle and syringe. Allow syringe to air dry. When working with dissolved solids, storing the plunger outside of the syringe will reduce the possibility of frozen plunger.

GASTIGHT® Syringes (Series 1000, 1700 and 1800)

• Rinse the syringe thoroughly with a solvent known to be effective in solvating the sample. Residual dissolve d solids may result in frozen plungers and plugged needles.
• To clean the plunger, remove it from the syringe barrel and gently wipe with a lint-free tissue. Insert the plunger into the barrel and pump deionized water, acetone or another solvent compatible with the sample through the needle and syringe. Allow syringe to air dry. When working with dissolved solids, storing the plunger outside of the syringe will reduce the possibility of frozen plunger.

Syringe Storage

We recommend to store syringes in the original packaging. This with help to protect the syringe, and allows for easy identification. Remove product description label from the end of the box, and placing it to the outside packaging. This will make re-ordering the same syringe quick and easy.

Thermal desorption

In this section you will finde informations important in the area of thermal desorption. It is quite difficult analytical technique and these informations can help you with your work with it. If you do not find required information, do not hesitate to contact our specialists.

Sorbent parameters

Material emission monitoring

Storage and transportation of sorbent tubes

ChromShell columns and solvents

There are several critical characteristics that must be taken into consideration when selecting the appropriate organic solvent to use in the mobile phase with ChromShell^® columns. Viscosity is one of the most important as high viscosity solvents may produce backpressures that are too high for the HPLC system used. Other important solvent characteristics include UV cutoff, cost and polarity index; where a solvent with a high UV cutoff will result in poor sensitivity with UV/Vis detection and use of high cost solvents will result in a poor laboratory that can't afford to buy new columns. Solvents with low polarity indices generally result in faster elution of organic compounds and are commonly used for column cleaning.

Acetonitrile

is arguably the best organic solvent as it results in the lowest system backpressure in water mixtures and also has a very low UV cutoff for better UV/Vis detection sensitivity. Although acetonitrile production is starting to increase with the turnaround of the economy, thus dropping cost, this still remains a major drawback of acetonitrile usage.

Methanol

is another popular organic solvent as it is comparable in elution strength to acetonitrile, has a relatively low UV absorbance, and is significantly less expensive than acetonitrile. The major drawback of methanol, especially when used with small particle size HPLC columns, is that its use can result in backpressures that exceed many HPLC system limits.

Acetone

is less commonly used as it has high UV absorbance, but can be used successfully if analytes absorb at higher UV wavelengths or if other detector types such as MS are used as it has similar elution properties to acetonitrile but is significantly less expensive.

Ethanol

is generally not recommended as it results in very high backpressures in water mixtures.

Iso-, n-propanol

have relatively strong elution strength and are most commonly used in column cleaning at low flow rates as they also results in high backpressures.

Tetrahydrofuran

has similar elution strength to n-propanol but is less commonly used as it is much more expensive.

Glassware deactivation

Glassware deactivation with DMDCS

Dimethyldichlorsilane (DMDCS) reacts with active hydroxyl groups present on glass surface producing a deactivated layer. This ensures inert glassware used for sensitive compounds.

Procedure

During the deactivation process, the reaction releases hydrogen chloride (HCl). So we strongly recommend to do this procedure in a fume hood.

• Use 5% DMDCS solution in toluene. You can prepare this solution by diluting 20 ml of DMDCS with 400 ml toluene. Store the solution in an amber glass at room temperature.
• Soak glassware in 5% DMDCS solution for 15 to 30 minutes.
• Rinse glassware twice with toluene.
• Soak glassware in methanol for 15 minutes.
• Rinse glassware with methanol.
• Dry glassware with high purity nitrogen (moisture and hydrocarbon free).