Questions & Answers

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Use and operation

For which laboratories is the Serial Diluter intended?

The Serial Diluter is designed for users performing dilutions for the plate count method in microbiological testing. The instrument supports the lab staff by providing them perfectly diluted and mixed samples in bags for accurate and precise testing results in a very convenient way, absolutely reliable and with nearly no prior work preparation. The instrument has the footprint of a vortex mixer and a test tube rack and can be placed on the lab bench where sample dilutions and plating are carried out.

For what sample throughput is the Serial Diluter wort using?

Testing labs having an average daily throughput of 30 samples for serial dilutions, the Serial Diluter will be normally amortized in about one year depending on the costs for the preparation of test tubes or the costs for prefilled ready-to-use dilution tubes or cups.

How does the Serial Diluter work?

The Serial Diluter works similar to a pipeting aid. Vacuum aspirates the desired amount of liquid and an excess pressure dispenses the liquid into the Serial Dilution Bag with the sample. The aspirated volume is determined by an optical sensor placed on the side of a 10 ml pipette. Thus, the optical sensor simply replaces the human eye in the determination of the volume making the use of the Serial Diluter even simpler as of a pipeting aid.

How is a homogeneous mixing in the Serial Dilution Bags ensured?

The Serial Dilution Bags have been developed together with the Serial Diluter TA for homogeneous dilutions and are characterised as follows:
1. the bags are divided in the Serial Diluter into an addition and removal zone in order to exclude carry-over with higher concentrated sample material
2. 45° bevels on the bottom ensure a targeted deflection of the incoming liquid jet, creating a perfect counter-clockwise vortex.
3. the liquid jet is accelerated by an additionally generated pressure surge to quickly form an intensive vortex.
4. the rising air at the end of the liquid delivery causes an abrupt reversal of the vortex’s direction of rotation.

The Serial Diluter UA has an integrated mixer which ensures homogeneous mixing of sample and diluent in the Serial Dilutioni Bags by simply moving the handle from one position to the next.

What materials does the diluting solution in the Serial Diluter come into contact with?

The diluting solution comes into contact with silicone, stainless steel, glass or polystyrene (depending on the 10 ml pipette used), polyethylene and polypropylene.

Which directives and ISO standards were taken into account in the development?

Serial dilution with the Serial Diluter complies with the standard method according to ISO 6887-1:2017 and the associated normative reference ISO 7218:2007.
The product is subject to the technical directives: 2006/42/EC, 2004/ 108/EEC. Normen: EN 61010-1:2001, EN 61010-2-081:2002 + A1:2003, EN 61326-1:2006.

How was compliance with the standards verified?

The serial dilution with the Serial Diluter was verified against the standard technique with dilution tubes according to ISO 6887-1 by the Zurich University of Applied Sciences (ZHAW Wädenswil). In addition, the Serial Diluter was tested by ISO 17025 accredited users of the Serial Diluter on the basis of direct comparisons with the test tube technique using various food samples (see test results Campden BRI). These accredited laboratories regularly take part in proficiency tests, which confirm the consistently high accuracy and reliability of the Serial Diluter (see Labo 11/2017).

Is there a quality certificate for the Serial Diluter?

The CE-certificate for the Serial Diluter is in the manual.

What material are the bags made of?

The bags are made of high purity virgin polyethylene (PE) under clean room conditions. The bags comply with the regulations EU No. 10/ 2011 of 14.1.2011, 1935/ 2004 of 27.10.2004 and 2013/ 2006 of 22.12. 2006 and U.S. FDA 21, CFF 04, Title 21 (plastic materials and articles in contact with food).

How is the sterility of the Serial Dilution Bags ensured?

The Serial Dilution Bags are manufactured under cleanest conditions according to DIN EN ISO 13485 for medical device manufacturers. An independent test laboratory has proven through dosimetric and microbiological validation that no microbial growth can be detected and that the Serial Dilution Bags are sterile. The sterility of the produced Serial Dilution Bags is continuously checked.

How is the sterility of the system ensured?

All parts in contact with the liquid are autoclavable (see operating instructions). During operation, the system is ventilated via sterile filters to secure sterility. Since the Serial Diluter only dispenses sterile liquid and never aspirates liquid through the dispensing nozzle, the system sterility is efficiently ensured.

Are the sterile filters hydrophobic or hydrophilic and are they autoclavable?

The PTFE (Teflon) filters used are hydrophobic and autoclavable.
Attention: Do not use hydrophilic filters, especially not to ventilate bottles with diluent, which are no longer permeable to air when wet as the pores are closed.


What kind of process improvements can be achieved?

With the Serial Diluter, the accuracy of the testing results is ensured regardless of sample throughput, time pressure, unplanned work peaks, employee experience, etc. This is achieved by the user-friendly standardisation of the dilution, which eliminates the person-dependent differences at work and minimises the risk of errors. The high-purity bags are free of inhibitory residues and guarantee highest sensitivity in the cell count determination of sensitive organisms.

Which steps are simplified with the Serial Diluter?

The Serial Diluter automates dilution and mixing with easy integration into existing workflows. No specially trained staff is required and the workflow continues as before. In addition, the cost of purchasing and maintaining the Serial Diluter is low.

How fast can I work with the Serial Diluter?

A serial sample dilution over three steps with the inoculation of two Petri dishes per dilution step (total 6 Petri dishes) takes about one minute. A diltution is made in approx. 3 seconds.

What do I save in costs and time?

Cost and time savings are realized by eliminating the preparation of test tubes or the expensive pre-filled dilution tubes, by faster carrying out the dilutions as no manual vortexing and no handling of tubes and caps has to be performed, by reduced costs for transport, storage and disposal of the consumables.

What can be omitted if preparing decimal dilutions for plate counts?

Beside no handling of test tubes and cups as well as no manual vortex mixing for 5 s to 10 s, no test tubes have to be cleaned, dried, filled, sterilized and stored. Accordingly, time savings and savings of water, electricity and cleaning agents if Serial Dilution Bags are used. Also the need for storage space and cooling space is reduced by a factor of 20 to 30. Investment and maintenance in autoclaves, washing dishes and dispensers are lower because less operating cycles, wear, smaller equipment, etc.

What maintenance and service is required?

There is no need for regular maintenance and service. The instrument itself detects e.g. clogged filters, leaks, etc. and reports these to the user. Maintenance is limited to changing the easily accessible filters and adhesion grippers (see operation manual).

How is the service of the products ensured?

Inlabtec products are sold through authorised distributors, who can perform all service work. The Serial Diluter is based on very solid, proven technology, which keeps service work to an absolute minimum.

What is the energy consumption for the production of Serial Dilution Bags?

The energy required to manufacture 1’000 Serial Dilution Bags is approximately 20 MJ. Of this, 8 MJ (40%) is recovered in waste incineration. The net energy requirement is therefore around 12 MJ for 1’000 Serial Dilution Bags if the Serial Dilution Bags used are not recycled. For comparison: a washing cycle for 1’000 test tubes with a dishwasher consumes about 4 – 6 MJ of energy and sterilization in a steam autoclave about 8 – 10 MJ. The cleaning and sterilization of the test tubes consumes more energy than the use of the disposable Serial Dilution Bags, without taking into account the water consumption for cleaning and sterilization, without energy consumption for the rinsing and disinfection agents, etc.

Is it ecologically sensible to use Serial Dilution Bags?

In our view, it is very useful to use Serial Dilution bags instead of glass tubes.
– The waste weight and volume produced by the use of the bags is minimal. For comparison: a shopping bag of medium size made of plastic corresponds to about 150 – 200 Serial Dilution Bags 
– The energy consumption for the cleaning and sterilization of test tubes is higher than the energy demand for the production, use and disposal of Serial Dilution Bags (see: Is it ecologically sensible to use Serial Dilution Bags?)
– Polyethylene is a valuable energy storage free of pollutants, which is used in its combustion for energy production or which can be recycled
– The bags are stored at room temperature, therefore no space is needed in the refrigerator/ cold room
– The weight for transportation is about 16 x lower than for standards test tubes

Is the supply secured with bags? How long are the delivery times?

We always have sufficient quantities in stock and the target delivery date is within five working days of receipt of order. Due to the small storage volume and low costs, it is recommended to keep a stock of at least four weeks. In this way possible delays in transport, customs, etc. can be prevented.

How much space do I save?

A box with 1’000 Serial Dilution Bags requires a storage volume of approx. 2.5 l, for 1’000 tubes approx. 74 l are needed.

How long is the warranty period?

The warranty period for all device components is two years. Details can be found in our AGB (General Terms and Conditions)


Can I use the Serial Diluter without any training?

Yes, the Serial Diluter is very easy to install and use. The operating instructions are also illustrated in detail and various training videos are available in the InfoCenter. You can also request support from Inlabtec or your distribution partner at any time.

How precisely can be dispensed?

The volume is determined by the position of the optical IR sensor on the pipette scale. A set volume of 9 ml is dispensed with an imprecision of max. ± 0.6 %.

What is the difference between accuracy and precision?

Accuracy indicates how close the average actual value, i.e. the mean value, is to the target value. The deviation is also called systematic error. The precision indicates how close the individual measured values are to each other. The statistical measure of precision is the standard deviation, often called random error.

Under which conditions should the dispensed volume be checked and calibrated?

The accuracy of the pipettes used should be checked before using a new pipette type/pipette manufacturer or a new lot (batch number) of the pipettes used to ensure that the specified accuracy of the dispensed volume is maintained. The systematic error of the pipettes can be determined by calibration (check) and compensated for by the corresponding sensor position ( see InfoCenter Operating Manual chapter 9).

How reliable is the opening of the bags? Is there wear and tear?

A microstructured silicone is used to open the bags, which develops an enormous adhesive force on smooth surfaces. This adhesive force is wear-free. If the adhesive force would decrease due to dirt, the adhesion gripper can be cleaned with water, 70 % ethanol, etc. and is then functional again. If not, the gripper can be removed and a new, self-adhesive adhesion gripper can be attached (see operating instructions).

How can I be sure that the set volume was actually dispensed?

The volume can be checked visually before dispensing by reading the meniscus in the pipette. The sensor monitoring of the aspirated liquid ensures that dispensing of the liquid is only released when the correct volume is available in the pipette. Deviations caused by air bubbles, an empty bottle, etc. are detected immediately and reported to the user via the display. The internal pressure sensor also monitors the dispensing and ensures complete delivery of the dilution solution.

Which serological pipettes and graduated pipettes can be used?

All 10 ml serological pipettes and graduated pipettes in the standard version can be used. Other pipette sizes are possible as long as the outer diameter of the pipette is between 8 – 15 mm and the length between 150 – 350 mm.

What solvents is the system resistant to?

The solvents used must be compatible with the silicone tubes and the material of the pipette used (glass, polystyrene). Aqueous solutions are usually compatible.

How do I make sure that the diluter is working properly and that the dilution was done correctly?

Simply briefly check the position of the meniscus before you start the dilution by pressing a button and pay attention to the air bubbles after dispensing the liquid. If the position of the meniscus is correct and air is released at the end of the dispensing, the sample is correctly diluted.

What influence do the serological pipettes used have on the accuracy of the Serial Diluter?

The volume determining element in the Serial Diluter is a pipette in combination with an optical sensor. Since the Serial Diluter dispenses exactly the volume that is aspirated into the pipette and indicated by the meniscus position of the liquid column, the accuracy of the dispensed volume depends on the accuracy of the scale / graduation of the pipette used. The inaccuracy of the volume indication of serological pipettes made of plastic is approximately ± 2 %, for graduated pipettes made of glass ± 0.5 % for class AS and ± 1 % for class B.

How do I check the volume dispensed by the Serial Diluter?

Volume testing of the dispensed liquid is most easily done with a measuring cylinder or with a balance, as is often done in the laboratory to check volume measuring devices. Dispensed liquid = weight of filled bag – weight of empty bag. The Serial Diluter manual contains detailed instructions for checking and the corresponding Excel template can be downloaded from

How can I test whether the components used were sterile and the results obtained are correct?

A sterility check can be carried out before the actual start of work and at the end of the work. For this purpose, the first and last 9 ml dispensing is carried out without sample and one sample each is used for sterility control.

What do I do if the system is not sterile?

If the system is not sterile, it can be assumed that the bottle with the diluting solution or the tubing set with the dosing tip has not been completely autoclaved. When autoclaving, use an autoclave tape as a control, which indicates that steam sterilization has been completed. For reliable sterilization of the tubing set and dosing tips in autoclaves, sterilization bags with a paper layer should be used to ensure the penetration of steam.

Can I leave the Serial Diluter operational overnight and continue working the next day?

The Serial Diluter can be left operational until the connected diluent is used up. Since the dosing tip is always flushed with sterile diluent in one direction only and never comes into contact with the sample, contamination risk of the dosing tip and diluent is very low. The dosing tip is also protected against external contamination by the attached pipette tip and, when the dosing arm is in the parked position, is shielded from the outside by the integrated protective sleeve. As an additional precautionary measure, the dosing tip can be parked in 70 % ethanol when not in use for a longer period of time, e.g. over the weekend. For details please refer to the operating instructions.

What maintenance and service is required?

There is no need for regular maintenance and service. The instrument itself detects e.g. clogged filters, leaks, etc. and reports these to the user. Maintenance is limited to changing the easily accessible filters (see next question)

Are there components that need to be replaced regularly?

According to the filter manufacturer, the sterile filters of the bottles containing the diluting solution should be replaced after eight autoclaving cycles. The sterile filter on the unit should be changed every 6 – 9 months.

How is the service of the products ensured?

Inlabtec products are sold through authorised distributors, who can perform all service work. The Serial Diluter is based on very solid, proven technology, which keeps service work to an absolute minimum.

How do I clean the diluter?

The liquid-bearing parts can be removed from the Serial Diluter after use, cleaned and autoclaved. The device surfaces can be cleaned with a commercial cleaner/soap water and disinfected with 70% ethanol.

Which system components can be autoclaved?

All parts in contact with the liquid can be steam sterilised: tubing set, dosing tip, connection cap GL 45 kpl, as well as the sterile filters.

Can the system be operated in the sterile bench and UV-sterilized overnight?

The compact Serial Diluter can be easily operated in a sterial bench, laminar flow, etc. and the device is UV-resistant for regular surface sterilisation.

Can the system also be used in a cold store?

The Serial Diluter can be used at an ambient temperature of 4°C to 40°C.

Can I store the filled bags?

The used Serial Dilution Bags intended for disposal or storage can be stored in the Bagshell. A Bagshell is included in the scope of delivery.

What is the evaporation rate with filled bags compared to classical dilution tubes?

The evaporation rate for filled bags and dilution tubes in the refrigerator is identical with approx. 5 – 10 mg (µl) per 24 hours per bag or capped test tube with 9 ml of diluent.

How long is the durability of the bags?

The durability and sterility at room temperature of the bags is guaranteed for five years after production, provided the box is shrink-wrapped in the protective film.

How long can an opened box of bags be used?

After removing the protective film from the packaging it is recommended to use the bags within 3 months

What are the optimal storage conditions for the bags?

Store protected from direct solar light at 10 – 30 °C. Maximum rel. air humidity: 50 – 60 %.

Do the bags contain any substances that could inhibit bacterial growth?

As the bags are made of high-purity virgin polyethylene, there are no substances that could inhibit the growth of micro-organisms.

Which pipette tips can be used with the Serial Diluter TA?

Practically all known 1 ml pipette tips can be used, as the Serial Diluter can be adjusted accordingly. However, due to the speed and reliability of the process we recommend the use of our universal LO pipette tips with a nozzle diameter of 1.9 mm (standard tips: 0.7 – 0.8 mm).