Labeling of tubes and vials in the laboratory – from pen labeling to fully automatic labeling.

This was the subject of a technical article by Dirk Peters in Labo 3/2023, which we would like to briefly reproduce here.

It is obvious that machine marking or labeling of laboratory tubes is state of the art today and offers numerous advantages for users. Especially in areas that are subject to the regulations of a GLP-compliant mode of operation or in the research area to the “Guidelines for Safeguarding Good Scientific Practice”, clear labeling is essential.
In general, there are options for direct labeling of the laboratory tubes, e.g., using an ink-jet printing process, or for labeling using a laser marker, in which part of a previously applied layer is burned away. However, by far the most common, because the simplest process is the so-called thermal transfer printing. This means printing a label and then applying it to the tube. In this process, a black dye, which is located on an ink ribbon, is usually applied to a white label by a print head with targeted heat pulses. Alternatively, there are also transparent and other colored labels and ribbons.

Label materials and differences

Users and operators have a wide choice of different materials (see table). PE film labels are most commonly used due to their very good resistance to typical chemicals, very good manageability and for cost reasons. Polypropylene (PP) labels tend not to be considered for labeling tubes due to their high rigidity, as the label – depending on the diameter – will peel off by itself.
The ribbon used must match the label material and application. The label manufacturers usually also offer the matching ink ribbons. Resin ribbons are suitable for the above PE film labels.
Self-laminating labels are also available as a special solution. In addition to the actual labeling area, these also have a transparent area which is sufficient to wrap around the tube. The marking is particularly well protected, as the transparent film prevents the actual marking from coming into direct contact with the solvent.

Manual to integrated labeling – differences and solution concepts

Once the decision to use labels and codes has been made, the question of implementation arises, which can be answered differently depending on the number of tubes and the requirement. In general, two basic questions arise: Where does the label come from? And how does it get on the tube?
If you only need to clearly identify the tubes used, e.g. with a barcode, pre-labeled tubes from the manufacturer can be a simple solution to implement. Many manufacturers offer this service for at least some of the tubes. Here, however, one usually has little influence on the content of the labeling and the code used.

Manual pressure

But if you want more and more specific information on the label, you can easily make your own labels. Commercially available label sheets are labeled using a standard laser printer. In this case, however, the labels must then be applied manually to the tube.
Having labels custom-made in advance at an appropriate label printing company also makes deployment quick and easy.

On-demand printing

If you need on-demand data, such as the date, batch numbers or special sample data on the label, you can’t avoid a dedicated label printer. At the same time, however, this increases the possibilities for layout, for further information on the label and, above all, for integration into the laboratory workflow. Often the labels can be generated directly from the LIMS.

Label information and LIMS connection

Depending on the code used, limited information can be accommodated in a machine-readable manner, and with “talking” codes one quickly reaches the limits here.
Talking codes are solutions in which the actual information, such as manufacturer, filling date, or processor, solvent, etc., is already encoded directly in the barcode or 2D code. The advantage is that there does not have to be a common database. Anyone who knows the specification can generate the code and also read it.
Alternatively, the code is used exclusively to transmit a one-to-one identification number. The actual information about the sample or tube is then available in a database. The key for the data set is the identification number. This procedure is typically used in conjunction with laboratory information and management systems (LIMS).
In addition to barcodes and 2D codes, a lot of other information can be applied to the label, such as plain text for the codes or pictograms, logos and other information.

Manual application/application

The simplest variant is the manual application of the label to the tube. In this process, the label is detached from the liner and then glued to the tube by hand. Especially when many tubes have to be labeled, this is not done with consistent quality. Labels may be applied crooked and/or often have a height offset or are applied with a crease. In the worst case, the label protrudes above the bottom and causes the tube to wobble or the barcode cannot be read by the machine. The manual work is also very monotonous.

Semiautomatic application/application

A remedy for this is provided by label printers with an attached applicator, which are offered by various companies. In this process, the label is printed on demand, automatically detached from the liner and rolled onto the tube. The tube is prepared and removed by hand.

Automatic application/application

Manufacturers of corresponding compact devices go one step further. Here, the tubes are either pre-sorted in racks or provided individually via so-called “tube feeders” from bulk or bulk material. The device removes the laboratory tubes and feeds them fully automatically to the labeler and back again after labeling. It can label a certain stock of tubes independently or compile a predefined set of tubes with the same label. This procedure is used, for example, in the preanalytics of a clinic when different blood tubes are assembled for a patient.

Integrated labeling

In integrated labeling, the label is applied to the laboratory tube during a process chain. The labeling system can be supplemented by a filling module, for example, so that the tubes can be labeled and filled directly. In this way, the labeling, filling and screwing operations can be carried out in a single draw frame. This process is used, for example, when filling substances for the production of analysis kits. The empty tube is removed from the template, filled with the substance, closed with a provided lid and then labeled. It is not only possible to write a pre-entered batch ID on the tube, but also the exact filling time or the consecutive number in the batch if desired.

Machine readability – barcode and 2D code briefly explained

A major advantage of machine marking is the application of machine-readable codes for fast and reliable data acquisition with a hand-held scanner or within the processing and analysis equipment. A distinction is made between a bar code and a 2D code.
The barcode is only suitable for relatively short content. A distinction is made between codes that can only represent numbers (e.g. Interleaved 2/5) and those that can also include letters and special characters (e.g. Code 128). The bar code has the advantage that it is easily readable with all common scanners and, if the code has been applied along the rotation axis of the tube, it also does not show any distortions. The disadvantage is the information density of the code. Usually only up to 10 or 12 digits or letters can be put on the label for a tube.
2D codes do not have this disadvantage. The information density is much higher. Thus, the data matrix code can be used to encode up to 3116 digits or 2335 characters in a very small space (ASCII 1-255), with a different symbol size depending on the amount of data. And precisely this is also a disadvantage when marking round or curved surfaces. There is always a distortion of the two-dimensional code. This limits the information content or the size of the code that can be used. In addition, suitable 2D barcode scanners are required to read 2D codes (e.g. Datamatrix, QR code).

Conclusion

The labeling of sample material or test substances in laboratory tubes by means of labeling can already be done with simple tools. Printing and applying the label to the tube can be done separately. Special laboratory equipment is available for labeling a large number of laboratory tubes, on-demand labeling or complete processing of the laboratory tube including labeling. Process data can also be noted on the label. The selection of the concept, the label material, the layout of the label including the 1D and 2D codes and the integration into the laboratory workflow must be coordinated and determine a successful solution for sample identification.