WO2021054926A1

WO2021054926A1 - Hydrogen-assisted, t-shaped slotted quartz tube atom trap system for trace element analyses in flame atomic absorption spectrophotometer device

Info

Publication number: WO2021054926A1
Application number: PCT/TR2020/050867
Authority: WO
Inventors: Sezgin BAKIRDERE; Cagdas BÜYÜKPINAR
Original assignee: Yildiz Teknik Üniversitesi
Priority date: 2019-09-19
Filing date: 2020-09-18
Publication date: 2021-03-25
Also published as: TR201914275A1

Abstract

The present invention relates to a holder (20) arranged for being attached to an FAAS device; and to a T-shaped slotted tube (30) having secondary flame exit openings (34), said tube is for being aligned onto the flame head of the FAAS device by means of said holder. The present invention further proposes an FAAS apparatus (10) provided with such holder(20) and tube (30).

Description

HYDROGEN-ASSISTED, T-SHAPED SLOTTED QUARTZ TUBE ATOM TRAP SYSTEM FOR TRACE ELEMENT ANALYSES IN FLAME ATOMIC ABSORPTION SPECTROPHOTOMETER DEVICE Technical Field of the Invention

The present invention relates to an atom trapping system for use in atomic absorption spectrophotometry. The present invention further relates to a holder for enabling the adjustment and stabilization of the position of such atom trapping system with regard to the flame, in atomic absorption spectrophotometers. Background of the Invention

Flame atomic absorption spectrophotometry (FAAS) is a widely used method due to that it is useful in analysis of wide variety of elements such as heavy metals, short durations in analyses, and low operational costs. Despite these advantages, its low precision causes that it finds a rather limited range of fields of application. Representation of a typical FAAS device is shown in Fig.l.

The main reason of low precision in FAAS device is low nebulization efficiency in nebulizators employed as sampler. Prior to being fed into atomizer, sample solution is brought into aerosol form by being sprayed as fine droplets by means of air. Liquid droplets in the aerosol are categorized in accordance with their sizes, and only the smallest thereof are allowed to be drifted towards the flame. During this operation, larger droplets which constitute about 95% of the total volume of the sample solution, are purged out of the system without being analyzed. The matrix containing the analyte is another factor which causes low precision. The liquid solution reaching to the flame evaporates and forms a gas cloud which also contains the analyte atoms. Carbon-containing combustion products which can absorp the cathode rays or cause scattering depending on the matrix content, can form radicals which potentially interact with analyte atoms. This phenomenon results in noise in the system, and lowers the signal/noise ratio.

Because of the low precision, the FAAS method is not widely used particularly in trace analyte analyses. Therefore, in trace analyte analyses, inductively coupled plasma mass spectrophotometer (ICP-MS) devices which have high investment and operational costs, are used for trace analyses of elements.

In cases where FAAS method is insufficient, trace element analyses in biological and environmental samples can only be performed using inductively coupled plasma optical emmision spectrophotometer (ICP-OES) and inductively coupled plasma mass spectrophotometer (ICP-MS) devices, which have have high investment and operational costs and which require qualified personnel as operator. As of 2019, the median investment cost for a FAAS system is 30.000$, whereas said cost reaches up to about 350.000$ for an ICP-MS system. Median annual operational cost varies around 3.000-5.000 TRY for an FAAS device, 30.000-40.000 TRY for an ICP-OES device, and 50.000-75.000 TRY for an ICP-MS device. Said high costs of ICP-OES and ICP-MS systems delimit the availability of such high-technology systems. Therefore the literature gets more and more focussed on studies for increasing the precision of AAAS systems. To this end, various pre-concentrating methods are employed. Main purpose of these methods are minimization of the noise by separating the analytes from the matrix prior to the atomization, and/or maximization of the absorbance by increasing the atom content on the light path which extends from the hollow cathode lamp. Mostly used means for this purpose include graphite furnace (GF), hydrides formation (HF) and slotted quartz tube (SQT). Although the graphite furnace technique has a high precision, introduction of the respective system to an MS device highly increases the investment and operational costs (of about 2-3 folds). HF technique is only useful in a limited variety of elements which can form hydrides, and mandates the employment of highly toxic and costly chemicals such as sodium boron hydride. Slotted quartz tube is a simple and low-cost add-on, yet it can increase the precision of MS devices only up to 2-5 folds.

SQT add-on which is used in increasing the precision of FMS systems, can also be used in atom trapping operations. Atom trapping is based on instantaneous release of analytes present in concentrations below analytical lower limits of systems at mg/L-pg/L levels -therefore being untraceable- depending from analyte to analyte, after trapping the same on the inner surface of SQT for a certain time period. Analyte-containing sample/standard is directed into the SQT for a certain time period by being sprayed by means of nebulizer, at a flow rate which usually has an optimum value within the range between 4.0-8.0 mL/min; and thus the analytes are partially trapped on the inner surface of the SQT. After completion of the analyte trapping period, the respective medium is provided with an organic solvent such as methyl isobutyl ketone or methyl ethyl ketone to enrich the flame in combustibles, thereby the reductivity and temperature of the medium are increased. By shifting/changing of flame characteristics and increment in temperature, analyte atoms summoned on said surface get released en masse, and form a high density analyte cloud on the path of the rays passing through a center of the quartz tube. The high extent of interaction between atoms and rays which takes place in a short period of time of about a few milliseconds, boosts the precision at up to several hundred folds. US 4,913,648 A discloses an example to such structures. In such types of atom trapping systems, methyl isobutyl ketone is used as fuel to release the trapped analytes. Yet, this substance is notorious of being highly toxic. As explained in the 2018 paper of Uslu et al. (Microchemical Journal 137 (2018) 155-159), use of hydrogen assisted T-shaped slotted quartz tube in flame atomic absorption spectrometry is known. Fig.5 shows a representative drawing of the SQT as employed in such system. Flames formed when the SQT is in use, horizontally exit from distal flame exit openings (32) of the SQT, and proceed in a direction opposite to that of the gravity. Said horizontal exit not only decreases labor safety, but also cause that the high-temperature flames approach towards the sensors of the spectrometer, thereby creating a potential of negatively affecting the service life of the respective equipment. To prevent that, the paper suggests formation of air curtain between the sensors and each of the openings (32) by means of air knives. Air provided by an air compressor forms a thin curtain, thereby stopping and curtaining the flame. The requirement to use air knives brings extra costs to the system, and furthermore, the air knives horizontally occupy extra space/footprint in the equipment. Flence, it is necessary to develop a low-cost, high precision means for use in trace element analyses, which at the same time complies with labor safety requirements.

Objects of the Invention

Primary object of the present invention is provision of a solution to the shortcomings mentioned in the Background section. Another object of the present invention is provision of a low-cost system with high precision in trace element analyses, and with improved labor safety.

Summary of the Invention

The present invention relates to a development for use in atomic absorption spectrophotometry, which enables analysis/detection of elements at decreased extents of limits. The present invention further relates to a holder for enabling the adjustment and stabilization of the position of such atom trapping system with regard to the flame, in atomic absorption spectrophotometers. The above- mentioned objectives are achieved by means of the developments described in the present application.

Brief Description of the Drawings

The figures brief explanation of which is herewith provided are solely intended for providing a better understanding of the present invention and are as such not intended to define the scope of protection or the context in which said scope is to be interpreted in the absence of the description.

Fig.l shows a schematical perspective view of a prior art FAAS apparatus without any atom trap.

Fig.2 shows a schematical perspective view of a FAAS apparatus according to the present invention, suitable for use with a T-shaped slotted quartz tube (SQT). Fig.3 shows a schematical perspective view of an exemplary holder embodiment for use in FAAS apparatuses according to the present invention, in positional adjusting and stabilization of the position of the T-shaped SQT.

Fig.4 shows a schematical perspective view of another exemplary holder embodiment for use in FAAS apparatuses according to the present invention, in positional adjusting and stabilization of the position of the T-shaped SQT.

Fig.5 shows a schematical perspective view of a prior art SQT. Fig.6 shows a schematical perspective view of an exemplary SQT embodiment for use in FAAS apparatuses according to the present invention.

Fig.7 shows a schematical perspective view of another exemplary SQT embodiment for use in FAAS apparatuses according to the present invention. Fig.8 shows a schematical perspective view of a further exemplary SQT embodiment for use in FAAS apparatuses according to the present invention.

Fig.9 shows a schematical perspective view of an even further exemplary SQT embodiment for use in FAAS apparatuses according to the present invention.

Fig.10 shows a schematical perspective view of an even further exemplary SQT embodiment for use in FAAS apparatuses according to the present invention.

Fig.11 shows a schematical perspective view of an even further exemplary SQT embodiment for use in FAAS apparatuses according to the present invention.

Detailed Description of the Invention

Referring to the drawings, brief description of which being provided above, the present invention is described in detail as follows. FAAS is a system widely used in analysing trace elements. In said system, analytes in a liquid sample are atomized and then subjected to light at respective specific wavelengths, to measure the amount of light they absorb. The FAAS device is provided with a tube (30) (T-SQT, SQT) for being integrated onto the flame head. When the tube (30) is positioned onto the light path such that the flame observation axis (A) and the light path overlap; the tube (30) traps the analyte atoms formed in the flame, and with the assist of hydrogen gas, the trapped analyte atoms are released after a certain period of time. The number of analyte atoms interacted with light in unit volume increases, significantly increasing the signal/noise ratio which is considered as a measure of system precision. Considering that these operations take place at elevated temperatures and rely on atom-light interactions, the T-SQTs can be manufactured of a material which do not absorb light from hollow cathode lamp and which have high thermal resistance, such as quartz as a preferred material. The holder (20) described in the present specification is used for positioning of the tube (30) onto the flame head, along the light path to allow the light to horizontally pass through the tube (30), and for stabilizing said positioning.

Designed for being annexed ot the FAAS device, and being subjected to elevated temperatures when in use, the holder (20) can be formed from a material with high thermal resistance, preferably from a metallic material. Hydrogen gas can be used in provision of the reductiveness to the flame for, upon expiry of the trapping period, enabling en masse release of the atoms trapped on the inner surface of the tube (30) positioned onto the flame head of the FAAS system. For releasing the trapped analyte atoms upon expiry of the trapping period, an adjustable gas valve (not shown) can be used in directing hydrogen gas into the T-SQT at a predetermined flow rate.

Horn-like shaped flames appear at one or more main flame exit openings (32) at one or more ends of a tube (300) which is to be substantially horizontally positioned onto the flame head (11) in a FAAS system, and in particular upon the direction of hydrogen gas to the system, said flames reach to elements (e.g. to quartz lenses) of the AAAS system, thereby harming the same. To prevent this phenomenon, the prior art systems include air knives which stop the extension of the flame by shaping a patelliform air curtain. The air knives are formed from a material which endures elevated temperatures, such as a metallic material.

The present invention relates to improvements in use of T-shaped slotted quartz tube (30) in flame atomic absorption spectrophotometers (FAAS). An aspect of the present invention relates to a holder (20) for holding such tube (30) and for reversibly fixing the position of the same. The holder (20) according to the present invention comprises a fixing means (201) for being fixed onto an FAAS device, and adjusting means (210, 220, 230) for adjusting and fixing the positioning with respect to a plurality of axes. Thus the a precise positioning of the tube (30) is enabled, such that the analysis performance is guaranteed. Fig.2 shows a schematical perspective view of an FAAS apparatus (10) suitable for use along with the tube (30) according to the present invention.

Fig.3 and Fig.4 show schematic perspective views of two different holders (20) for use in alignment of the SQT (10) and reversibly fixing the position of the same in FAAS apparatuses according to the present invention. The holder (20) can comprise respective adjusting means suitable for adjusting and fixing in a plurality of axes, preferably in a first horizontal axis (x), in a second horizontal axis (y) and in a vertical axis (z) orthogonal to both of the first and second axes (a first horizontal adjusting means (210), a second horizontal adjusting means (220) and a vertical adjusting means (230), respectively).

In an exemplary embodiment, the holder (20) comprises a fixing means (201) for reversible or irreversible fixing of an aligning arm (a first horizontal aligning arm (21), a second horizontal aligning arm (22) or a vertical aligning arm (23)) to an FAAS device. In the exemplary embodiment according to the present invention schematically depicted in Fig.3, the fixing means (201) is shown as positioned on the first horizontal aligning arm (21). Each one of the first horizontal aligning arm (21), second horizontal aligning arm (22) and vertical aligning arm (23) can be, mechanically or electromechanically, slidably connected to another of the alignment arms (21, 22, 23). The first horizontal aligning arm (21), second horizontal aligning arm (22) and vertical aligning arm (23) are arranged suitable to enable the sliding of an arm selected from the aligning arms (21, 22, 23) relative to another one of the aligning arms connected thereto, along a first horizontal axis (x) (i.e. in an +x / -x orientation) or as an alternative thereto, along a second horizontal axis (y) (i.e. in a +y / -y orientation) or as an alternative thereto, , along a vertical axis (z) (i.e. in a +z / -z orientation), respectively. This arrangement can be designed to include e.g. a mechanical sliding means such as a threaded or geared one, and to further include a fixing means for maintaining an alignment upon obtention thereof; such designing can be performed by a person skilled in the art of mechanics upon reading the information on the holder (20) provided in the present description, by various ways within his common professional knowledge. As exemplified in Fig.3, with respect to the first horizontal aligning arm (21), a bearer arm (203) comprising one or more bearers (202) for contacting the

SQT is positioned on the most indirectly connected one amongst the second horizontal aligning arm (22) and the horizontal aligning arm (23) in terms of mechanical connection to the fixing means (201); preferably connected thereto in a slidable and fixable fashion. These technical features of the holder (20) enable a user to arrange and fix the position of the SQT in any FAAS device relative to the flame.

The adjusting means (210, 220, 230) can be designated as a first horizontal adjusting means (210), a second adjusting means (220) and a vertical adjusting means (230) suitable for position adjustment and fixing on a first horizontal axis (x), a second horizontal axis (y) orthogonal to the first horizontal axis (x), and a vertical axis (z) orthogonal to both of the first horizontal axis (x) and second horizontal axis (y), respectively.

An embodiment according to the present invention can comprise a first horizontal aligning arm (21), a second horizontal aligning arm (22) and a vertical aligning arm (23) which are respectively positioned on a first horizontal axis (x), on a second horizontal axis (y) and orthogonal to the first horizontal axis (x), and on a vertical axis (z) orthogonal to both of the first horizontal axis (x) and second horizontal axis (y), respectively. In such embodiment, each of said aligning arms can respectively include a first horizontal adjusting means (210), a second horizontal adjusting means (220) and a vertical adjusting means (230) suitable for being mechanically or electromechanically slidable and reversibly fixable to at least another one of said aligning arms. Thus, the present invention also relates to a holder (20) according to at one least of the descriptions above, coupled/matched with a T-shaped slotted quartz tube for use in an FAAS apparatus (10). The present invention further proposes an improvement for a tube (30) (T-SQT, SQT) to be employed in an FAAS apparatus along with a holder (20) according to at least one of the descriptions above, for constituting an FAAS apparatus (10) according to the present invention. Said tube (30) comprises one or more slots (33) for introduction of flame into an inner cavity thereof through a side surface (35); the tube (30) further comprises one or more flame exit openings (32) on its one or more ends, said flame exit openings being encircled by said side surface (35) and being arranged to be positioned on a flame observation axis (A); and the tube (30) further comprises a connection arm (31) for allowing introduction of a gas into said inner cavity through a side surface; and can be made of quartz. Thus the tube (30) bears the qualification of being a T- shaped slotted quartz tube. The tube (30) according to the present invention comprises one or more secondary flame exit openings (34) on the side surface (35) thereof. Said one or more secondary flame exit openings (34) decreases the horizontal extension of a flame which tends to blow towards the main flame exit opening(s) (32) at high linear velocities based on volumetric expansion due to combustion heat, by partly releasing said flame at an early stage (i.e. before reaching to the ends where the main flame exit openings (32) are located). Thus an effective use of the horizontal distance (e.g. along +x/-x orientation on the x axis) is enabled in FAAS apparatuses (10) in which the tube (30) according to the present invention is to be employed. Furthermore, with the present improvement, the employment of air knives in FAAS apparatuses which include a T-SQT, is rendered optional instead of being mandatory. Representational perspective views of exemplary tube (30) embodiments for use in AMS apparatuses according to the present invention are presented in Fig.6 to Fig.11.

T quartz connection arm (31) has a diameter lower than that of a main body (e.g. having a cylindrical geometry) which comprises side surfaces (35) of the tube (30) and slot (33) provided thereon, one or more main flame exit openings (32) and second flame exit openings (34), to direct the hydrogen gas towards the flame; and preferably extends along a direction substantially perpendicular to a flame observation axis (A) on which the main body extends. It is preferably made of quatrz material due to its non-absorbing character against the light from hollow cathode lamp and due to its resistance against high temperatures.

The slot (33) can have an elongate shape extending parallel to the flame observation axis (A). In such embodiment, when the tube (30) is in use, flame introduction is provided in a radial direction onto the flame observation axis (A).

In the tube (30) according to the present invention as described in any of the statements above, said one or more secondary flame exit openings (34) can be arranged to radially oppose the flame entrance with regard to the flame observation axis (A). Fig.10 and Fig.11 show exemplary representative drawings directed to such embodiment. With such embodiment, a part of the flame can be released/discharged even before commencing to proceed horizontally, thus a range of horizontal extension of the flame can be further shortened.

In the tube (30) described in any of the statements above, said one or more secondary flame exit opening (34) can be embodied such that an orthogonal projection of the same on the flame observation axis (A) is disposed between an orthogonal projection of the slot (33) on the flame observation axis (A) and the main flame exit opening (32). Representational examples to secondary flame exit openings (34) in such embodiment as described in the present paragraph, are depicted in Fig.6 to Fig.9. One or more secondary flame exit openings (34) as described here, allow the flame inside the tube (30) along the flame observation axis (A) to an extent (thereby allowing an enhanced detection precision with the FAAS); and on the other hand, they simultaneously enable a timely/early release/discharge of a part of the flame from the tube (30).

In an exemplary embodiment of the tube, the secondary flame exit openings (34) can be present in a multiplicity. A set comprising a plurality of tubes (30) can be constituted, which show a variety in shape, distribution, number and opening sizes of secondary flame exit openings (34). Accordingly, a set of tubes (30) is hereby proposed, which allows a tube (30) to be selected based on momentary requirements.

One or more secondary flame exit openings (34) in the tube (30) described in any of the statements above, can be positioned such that the orthogonal projections of said one or more secondary flame exit openings (34) on the flame observation axis (A) constitute/have a symmetry relative to the T quartz connection arm.

Considering that the secondary flame exit openings (34) can be formed by substraction from quartz material, a symmetric and easy to use tube is thus provided in terms of weight balance, which has an improved stability at positioning and aligning by means of the holder (20). The improvement proposed within the present inventive context enables and improves the introduction of environmentally friendly and non-toxic hydrogen instead of high cost and toxic substances into the trapping system.

The release of the trapped analyte atoms can be achieved based on creation of a reductive medium instead of sudden temperature rise. Upon completion of the trapping period, a low-term hydrogen gas flow towards the flame can be applied

(e.g. for short durations of about 1 second, preferably at a flow rate within the range between 800-2500 mL/min), thereby shifting the flame characteristics to enable the release of atoms from the surface. The only side product appearing at this process is the combustion product of hydrogen. By means of a simple annex to the accessible and low-cost FAAS system, a precise, environmentally friendly and low-cost analysis/detection of trace elements is thus enabled. As of 2019, the tubes (30) according to the present invention can be obtained at only 4.0-6.0 TRY, and a single tube (30) can be used for about 200 times in analyses; and the system precision can be increased 100 to 1000 folds depending on the analyte type. The tube (30) and holder (20) according to the present invention are easily applicable to present AAS systems used for trace element analyses in industry. The tube (30), in particular when used along with the holder according to the present invention, can be positioned and aligned to the flame head of any present FAAS apparatus without necessitating any further apparatus/system. With the FAAS system (10) constituted as mentioned above, high precison heavy metal analysis/detection can be performed on various food, environmental and biological samples. Steps of such analysis are exemplified below:

- A sample containing one or more analytes is sent to a combustion zone at which the tube (30) is positioned, via a nebulizer unit (not shown) in an FAAS (10) system. At this operation, it is required to form a flame with a low acetylene/air ratio.

- During conduction of sample, the analyte atoms present in the sample is trapped by being adsorbed onto the inner surface of the tube (30). Thus the analyte concentrations below the detection limits of the apparatus is increased by pre-concentrating inside the tube (30).

- Upon completion of the trapping period (e.g. an optimum trapping period), gas (e.g. hydrogen gas or a mixture containing the same) is sent into the tube (30) at a suitable flow rate (e.g. at an optimum flow rate) e.g. set by means of an adjustable/regulated gas valve (not shown). The gas renders the flame a reductive medium when brought into contact with the flame.

- Analyte atoms inside the reductive flame medium get instantly released back from the inner surface of the tube (30). Due to the presence of analyte atoms at momentarily high concentration in a unit volume on the light/rays path passing through the tube (30) (and preferably, at least partly overlapping with the flame observation axis (A) thanks to the position of the tube (30) arranged by means of the holder (20)), a high extent of atom-light interaction takes place, thereby an intense analyte absorbance is achieved.

The use of FAAS (10) apparatus constituted in accordance with the present invention can include the following steps:

- Positioning the tube (30) to the holder (30), onto a flame head (10), such that light-atom interaction is not affected;

- Adjusting the distance of the tube (30) along the vertical axis (z), to the flame head (10) by means of the holder (20), to obtain a high (e.g. maximized) extent of light-atom interaction;

- Adjusting sample transmitting flow rate to the nebulizer (not shown), to obtain a high (e.g. maximized) nebulizing efficiency;

- Arrangement of an acetylene/air mixing ratio, to obtain a suitable (e.g. optimized) flame medium for increasing atom trapping efficiency on the inner surface of the tube (30);

- Specifying a high (e.g. maximum) trapping capacity of the inner surface of the tube (30), based on a suitable (e.g. optimal) trapping period;

- Arrangement of a reductive flame medium for enabling instant and complete release of atoms trapped on the inner surface of the tube (30), by means of arranging (e.g. optimizing) of a suitable (e.g. optimal) hydrogen flow rate. Reference signs:

10 FAAS apparatus according to the present invention

11 flame head

100 prior art FAAS apparatus 20 holder

21 first horizontal aligning arm

22 second horizontal aligning arm

23 vertical aligning arm 201 fixing means 202 bearer

203 bearer arm

210 first horizontal adjusting means 220 second horizontal adjusting means 230 vertical adjusting means 30 tube (SQT according to the present invention, or T-SQT according to the present invention)

31 connection arm

32 main flame exit opening

33 slot 34 secondary flame exit opening 35 side surface of the tube 300 prior art tube A flame observation axis x first horizontal axis y second horizontal axis z vertical axis

Claims

1. A holder (20) for holding a T-shaped slotted quartz tube and for reversibly fixing the position of said quartz tube in flame atomic absorption spectrophotometers (FAAS), said holder (20) comprising the following: - a fixing means (201) for being fixed onto an FAAS device,

- adjusting means (210, 220, 230) for adjusting and fixing the positioning with respect to a plurality of axes.

2. Holder according to the claim 1, wherein said adjusting means include a first horizontal adjusting means (210), a second adjusting means (220) and a vertical adjusting means (230) suitable for position adjustment and fixing on a first horizontal axis (x), a second horizontal axis (y) orthogonal to the first horizontal axis (x), and a vertical axis (z) orthogonal to both of the first horizontal axis (x) and second horizontal axis (y), respectively.

3. Holder according to any of the claims 1 or 2, comprising a first horizontal aligning arm (21), a second horizontal aligning arm (22) and a vertical aligning arm (23) which are respectively positioned on a first horizontal axis (x), on a second horizontal axis (y) and orthogonal to the first horizontal axis (x), and on a vertical axis (z) orthogonal to both of the first horizontal axis (x) and second horizontal axis (y), respectively; said aligning arms including a first horizontal adjusting means (210), a second horizontal adjusting means (220) and a vertical adjusting means (230) suitable for being mechanically or electromechanically slidable and reversibly fixable to at least another one of said aligning arms.

4. Holder (20) according to any of the claims 1 to 3, coupled with a T-shaped slotted quartz tube for use in an FAAS apparatus (10).

5. A quartz tube (30) for being employed in an FAAS device along with a holder according to any of the claims 1 to 3; the tube comprising

- a slot (33) for for introduction of flame into an inner cavity of the tube through a side surface (35) thereof, - one or more main flame exit openings (32) on one or more ends of said tube (30), said flame exit openings being encircled by said side surface, arranged to be positioned on a flame observation axis (A);

- a connection arm (31) for allowing introduction of a gas into said inner cavity through a side surface (35); wherein the tube further comprises one or more secondary flame exit openings (34) on the side surface (35).

6. Tube (30) according to the claim 5, wherein the slot (33) having an elongate shape extending parallel to the flame observation axis (A).

7. Tube (30) according to any of the claims 5 or 6, wherein an orthogonal projection of the the one or more secondary flame exit openings (34) on the flame observation axis (A) is disposed between an orthogonal projection of the slot (33) on the flame observation axis (A) and the main flame exit opening (32).

8. Tube (30) according to any of the claims 5 or 6, wherein an orthogonal projection of the the one or more secondary flame exit openings (34) on the flame observation axis (A) is disposed between an orthogonal projection of the slot (33) on the flame observation axis (A) and the main flame exit opening (32).

9. Tube (30) according to any of the claims 5 to 8, comprising a plurality of the secondary flame exit openings (34).

10. Tube (30) according to any of the claims 5 to 9, wherein the one or more secondary flame exit openings (34) are positioned such that the orthogonal projections of said one or more secondary flame exit openings (34) on the flame observation axis (A) are symmetric relative to the T quartz connection arm (31).