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Gas burner

A Bunsen burner or a Teclu burner is used for annealing and flaming. If no gas connection is available, a cartridge burner can be used, which is placed on a propane or butane gas cylinder (Fig. 1).

Fig. 1: Valve cartridge burner

Burners with toggle levers that can be operated with the heel of the hand are ideal for conveniently switching between flame and pilot flame (Fig. 2).

Fig. 2: Bunsen burner with toggle lever

From the perspective of improved occupational safety, electric burners that do not require a pilot flame or that do not emit gas when flameless, even when the gas tap is open, also work well (Fig. 3).

Fig. 3: Electrical safety Bunsen burner

Water bath

Water baths can be used in microbiology labs for various purposes, such as dissolving and liquefying agar culture media, tempering agar culture media, tempering or cooling cultures, etc.

Water baths that have an agitator or pump to constantly circulate the water, offer high temperature accuracy and consistency. Water baths can help to reach the desired temperatures more quickly than an incubator. The bath can usually be set to temperatures of 5-100 °C.

Useful features include a temperature selector limiter, a level controller to compensate for evaporation loss and tap water cooling, as well as a sloping or domed lid that minimises heat and evaporation loss and drains condensation water so that it does not drip onto the culture vessels.

Water baths may only be filled with distilled and demineralised water to prevent calcification. A non-liquid preservative can be added to the water to prevent bacterial growth in the bath.

Balances

Balances are mainly used in microbiological laboratories for weighing culture medium components. In most cases, balances with a readability of 0.01 g should be sufficient. In isolated cases, certain substances (e.g. minerals, antibiotics) may need to be added in even smaller quantities, which may require precision scales with a readability of 0.001 g.

pH meter

Checking the pH value of culture media plays an important role in microbiology, as the growth behaviour of microorganisms is decisively influenced by the pH value. It should be noted that the pH value must be measured before and after autoclaving, as this can change the pH value.

In addition to the standard pH electrodes for measuring in liquids, puncture electrodes may also be recommended for determining the pH value of solid culture media.

Due to physico-chemical properties of these substances, a number of effective enrichment processes are available for analysis using gas chromatography and can be summarized as follows:

• pentane extraction

• adsorption onto solid materials using thermal desorption (purge and trap)

• headspace techniques

Pentane extraction
The sample is cooled with ice and extracted using chilled pentane. Subsequently, the pentane phase is separated with a micro separator.

Purge and Trap
The purge gas, as a rule, the carrier gas of the gas chromatograph, passes through the exhaust vessel filled with the water sample. Through stripping, the volatile substances are driven out and then accumulate on the sorbent, e.g., Tenax. After the stripping process is complete, the substances are thermally desorbed by rapidly heating the adsorber column. They are then conveyed to the gas chromatograph through a heated transfer tube.

Headspace techniques
The static headspace method is an ideal technique for the analysis of the volatile substances found in water, due to the simple sample preparation and the substantial sensitivity of the analysis. A further advantage of this procedure is that particulate matter as well as other substances present in the sample with a low volatility and high molecular weight do not interfere with the analysis, since they are not carried by the steam into the headspace and are therefore do not reach the separation system. Moreover, the high degree of automation combined with the aforementioned short time required for sample preparation allows for a rapid, precise and user-friendly analysis for water samples.

Gas chromatography
For the gas chromatographic analysis, an electron capture detector (ECD) is employed due to its high selectivity and high sensitivity. If the ECD is combined with a flame ionization detector (FID), methylene chloride, benzene and its homologues can also be analyzed. With the aid of cryo-focusing, this method can be adapted to detect more volatile substances, such as vinyl chloride or chlorofluorocarbons.

Contaminants are transferred from carbon dioxide or other gases to water and are detected through a sensory test.

By law, compressed gases are considered food additives [1]. Therefore, the gas bottle should be checked for the following:

manufacturer name with address

lot/batch number

expiration date/best before date 

The method facilitates the determination of trace amounts of acrylamide monomers in aqueous matrices and is based upon the bromination of the acrylamide double bond. The reaction product (2,3-dibromopropionamide) is extracted from the mixture with ethyl acetate after precipitation with sodium sulfate. The extract is purified in a Florisil column and analyzed using gas chromatography (GC/ECD). The detection limit in aqueous matrices is approx. 0.032 µg/l.

The unfiltered water sample is extracted using a non-polar solvent (e.g., pentane), and the extract is measured using gas chromatography with a flame ionization detector.