Selection and Cleaning of the HPLC /GC autosampler Vials

Selection of Autosampler Vials

Most analysts are more interested in the chemistry of their compounds or their reactions, but it is important not to overlook the chemistry of your sample handling supplies. The chemical composition, as well as other related factors, can have a dramatic effect on the quality of your separations. It also affects the reproducibility of your analysis, efficiency of your automated process, and overall vial performance.

 

An experiment is a multifactorial process, and assigning the effects of errors or failures from each small element can be a challenge. When a chromatography system is underperforming from a physical issue with a sample vial, cap, or septum, autosampler misalignments, crashes or hangs that cause sequence problems can result. These problems can result in unnecessary downtime, expensive repairs, and even the loss of your precious samples.

 

The effects of inconsistent or suboptimal chemical composition of these components are less easy to see, but are potentially damaging to your workflow or results.

The ideal chemical composition of a glass vial

Perhaps the key metric in determining the suitability and analytical performance of a vial is the linear COE (coefficient of expansion). COE is a standardized measure of the fractional change in size per degree change in temperature at a constant pressure.

 

COE is a result of the concentration of Boric Acid in the borosilicate glass used to manufacture a vial, and the chemical resistance properties of the glass. Clear borosilicate glass with a COE of 33 or 51, and amber borosilicate glass with a COE of 51 are known as Type 1. They deliver the best overall vial performance, with:

 

• Lower pH shifts
• Increased stability above 100 °C
• Greater chemical resistance

 

It is important to note that the elemental composition of borosilicate glass includes a wide range of metal oxides in addition to Boron. Aluminum, Magnesium, Sodium, Potassium, Iron, Barium, and Titanium can all be incorporated into the recipe in varying amounts. The higher the metal content, the higher the COE. Some manufacturers offer budget vials with a COE in the range 70–71. This is because higher metal concentrations mean that significantly lower amounts of heat are required in the annealing process. It can reduce the cost of manufacturing by up to 75% but will affect vial performance.

 

It is well proven that 70–71 COE vials are significantly more fragile and less chemically inert. With this type of glass, metals can migrate to the surface of the vial during the annealing process, forming active sites that ‘react’ with your sample. More information about this effect and the full chemical composition of the borosilicate glass.

 

The Agilent specification

• The COE of Agilent vials is 32–33±1.5 for clear glass, and 48–56±1.5 for amber glass
• All vials meet ASTM E438 ‘laboratory class glass’ standards
• All vials use Type 1 borosilicate glass.

 

Choosing the right septa for your work

In the same way that chemical composition underpins the choice of a vial, chemistry is an important factor in choosing the right septa for your work. The best analytical performance will be achieved with a septum in the cap of your vial that protects your sample and is as chemically inert as possible. It should resist leaching or bleeding of materials from the septum into the sample matrix.

 

Material combinations often used for septa include: PTFE, silicone, red rubber, fluoroelastomers and butyl, for example, with PTFE having by far the widest chemical compatibility. The materials are layered in one of three ways to form a finished septum:

• Single layer – PTFE or red rubber, for single use only
• Bilayer – one layer forms the barrier, the other allows the septa to reseal after injection, usually PTFE and silicone, for repeat injections and sample storage
• Tri-layer – PTFE surrounded on both faces by silicone, improved chemical compatibility, for repeat injections and sample storage.

 

To limit the impact of siloxane bleed, a phenomenon that can compromise analytical sensitivity and reduce lab productivity, Agilent has developed an industry-leading conditioning process. Siloxane leeches from the silicone layer of the septum and, in untreated septa, levels increase due to multiple injections, elevated temperatures or solvent interaction. Agilent certified septa offer significantly improved vial performance in all areas.

 

Cleaning Procedure 

Due to the large number of samples, a large number of HPLC vials need to be cleaned during the test, which not only wastes time and reduces the working efficiency, but also sometimes results in deviation of the test results due to the failure of the cleanliness of the sample bottles after cleaning.

The chromatographic sampling bottle is made of glass, rarely plastic. Disposable sampling bottles are costly, wasteful and seriously polluted to the environment. 

Most laboratories reuse the bottles after cleaning. At present, the methods commonly used in the laboratory to clean the sample bottles are mainly to add washing powder, detergent, organic solvent and acid and alkali lotion, and then to brush with a small test tube. 

The conventional cleaning method has many disadvantages, such as large amount of detergent and water, long washing time, easy to leave a dead Angle. If it is plastic into the sample bottle, it is easy to leave a brush mark on the inner bottle wall, which takes up a lot of human resources. For glassware seriously polluted by lipid and protein residues, xie zhenhua et al. [1] used alkaline cracking solution for cleaning, and achieved good results.

When LC/MS/MS analysis samples, the cleaning of the sample bottle is very important. According to the washing method of glass apparatus, the cleaning method is selected according to the degree of pollution. There is no fixed mode.

There are a lot of methods of cleaning the vials and closures, and here are five of them.

Method 1

1. Rinse the vial with tap water many times

2. Ultrasound for 15 minutes in a beaker with clear water.

3. After changing the water, ultrasound for 15 minutes.

4. Immerse it in water-ethanol in a beaker.

5. Lastly, let the natural air dry the vial.

Method 2

1. Rinse with water before soaking in sulfate potassium chromite lotion.

2. Infiltrate the vial for more than 4 hours with medical alcohol.

3. Ultrasound for half an hour.

4. Pour out medical alcohol.

5. Use water ultrasound for half an hour.

6. Rinse with water after drying it.

Method 3

1. Soak in methanol (pure color spectrum) for 20 minutes. Then do the ultrasonic cleaning, then the methanol dry.

2. Fill the chromatographic sample vial halfway with water. Then do the ultrasonic cleaning for 20 minutes and drain the water.

3. Following the drying of the chromatographic sample bottle.

Method 4

1. First, soak for 24 hours in a strong oxidation cleaning solvent (heavy potassium chromate).

2. Then clean three times with deionized water in ultrasonic conditions,

3. Lastly, clean once with methanol. Dry it afterward.

4. You must replace the bottle pad with a new one, especially when assessing pesticide residues. Otherwise, you will indeed affect the quantitative findings.

Method 5

1. Reverse-drying chromatographic sample in-bottle test solution.

2. Soak it in 95% alcohol, wash it twice with ultrasonic, and dry it. You must dry it since alcohol quickly gets into a 1.5mL container and dissolves most organic solvents.

3. Fill with clean water and use ultrasound twice.

4. Pour the lotion into the drying container and bake for 1-2 hours at 110 degrees Celsius. Make sure you’re not baking at a high temperature.

5. Refrigeration and preservation.

It is advisable to get sample vials of clear and amber colors at once when purchasing. For example, your laboratory must complete two projects. The projects are A and B. The A project uses a clear sample vial the first time, whereas the B project uses an amber sample vial. After the test, you clean the vial according to the above method.

In the second experiment, use the amber color for the A project and the clear color for the B project. You can differentiate specific colors corresponding to different items. Also, it can avoid the trouble caused by pollution to your work.