The Flame Photometer

The flame photometer consists essentially of an atomizer, a burner, some means of isolating the desired part of the spectrum, a photosensitive detector, sometimes an amplifier and, finally, a method of presenting the desired emission, whether by galvanometer, null meter, or chart recorder. 

Two main types are in common use (a) an atomizer which produces an aerosol which passes through a spray chamber before reaching the flame (Fig. 1) (b) an atomizer which sprays directly into the flame. This type is sometimes an integral part of the burner, as with the Beckman or Zeiss atomizer-burner (Fig. 2). Atomizers of type (a) are usually 

In the author s opinion the integral type is much superior for most purposes. Unlike the spray chamber atomizer, the integral type reaches equilibrium almost instantly when solutions are sprayed and, if correctly designed, is extremely robust in use. A further important distinction is 

As will have been gathered from the preceding description, two main types of burners are employed. The Meker type burner is most often used for cooler flames. In this type the flame gases are mixed inside the burner tube and are prevented from striking back by a grid at the mouth of the tube. Different grids are employed for different gas mixtures, but 

Three types are used. (I) Barrier-layer cells. These are satisfactory only for simple filter instruments. (2) Vacuum phototubes. These tubes require an external power supply, unlike barrier-layer cells, and their output is usually amplified before measurement. (3) Photomultiplier tubes are easily the most satisfactory detectors for use in flame photometry. The photocurrent is amplified inside the tube in such a way that much lower light levels can be detected and measured accurately than is possible with vacuum phototubes with amplifiers. A stable source of high voltage up to perhaps 2000 volts is required to operate the photomultiplier tubes, but these tubes are almost universally used in high-performance instruments and are essential if the advantages of using narrow band width are to be obtained. 

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Potassium in potassium sulphate. Weigh out accurately about 0.20 g potassium sulphate and dissolve it in 1 L de-ionised water. Dilute 10.0 mL of this solution to 100 mL, and determine the potassium with the flame photometer using the potassium filter. 

At present, calcium and magnesium are estimated almost exclusively by atomic absorption (36). Present instrumentation permits the dilution of the specimen to approximately 1 - 100 for calcium and even higher for magnesium. For many instruments, the two elements are not read out simultaneously such as is practicable for sodium and potassium with the flame photometer. The lower limit of serum volime at present, for the practical assay for calciim and magnesiim in the laboratory of Neonatology, is approximately 10 ul The instruments are very readily automated, and it is not uncommon for results to be available at the rate of 240 per hour in the routine laboratory, where a typical atomic absorption instrument such as a Perkin-Elmer has been attached to an automatic feed system. 

It has been long believed that a lithium ion-selective electrode would render obsolete the flame photometer in the clinical laboratory. Lithium is administered to manic depressive psychiatric patients. Since the therapeutic range (0.5-1.5 mM) is quite close to the toxic range (>2 mM), it must be closely monitored. Most of the iono-phores propo d to date have not met the Li" /Na selectivity required for an interference-free assay. However, it has been reported that calibration in the presence of 140 mMNa permitted the analysis of Li in serum The errors observed are due to fluctuations in the Na concentrations in the sample. More selective ionophores would certainly improve the accuracy of this method. 

Procedure. Switch on and set up the flame photometer according to the manufacturer s instructions. The standards (including a 50% sulphuric acid blank) and sample solutions in 50% sulphuric acid obtained from the Kjeidahi digest... 

Its rapidity and detection limits, which are in the order of a few ppt (10-12) for many elements, make atomic emission one of the best techniques currently available for elemental analysis. These sophisticated instruments, however, are not intended to replace the flame photometers that are still used for many simple measurements. 

Atomic spectroscopy is a quantitative technique used for the determination of metals in samples. Atomic spectroscopy is characterized by two main techniques atomic absorption spectroscopy and atomic emission spectroscopy. Atomic absorption spectroscopy (AAS) is normally carried out with a flame (FAAS), although other devices can be used. Atomic emission spectroscopy (AES) is typified by the use of a flame photometer (p. 168) or an inductively coupled plasma. The flame photometer is normally used for elements in groups I and II of the Periodic Table only, i.e. alkali and alkali earth metals. 

With the use of fuels that produced hotter flames, earlier flame photometers became useful for analyzing elements beyond the alkali and alkaline earth metals. The development of atomic absorption spectrophotometers in the late 1960s provided the analytical chemist with a better tool for many of these applications. Later developments in high-temperature flame photometry narrowed the analytical applications of low-temperature flame photometry even further. The utility of the flame photometer to the clinical chemist, however, was not diminished until the development... 

Pass 0.6 N HCI at a rate of 1 B /10 minutes through the resin and collect the eluate in 1 B fractions,. nal se the fractions for cations. Typical results show that sodium starts eluting after 2 B have been collected and ceases after 7 BV Potassium elution starts at 8 BV and finishes after 14 BV have been collected. I o speed up the elution of magnesium, the molarity of the hydrochloric acid is raised to I Sodium and potassium may be conveniently estimated using the flame photometer, and magnesium by KD IW (ethylenediaminetetraacctic acid). 

Presentation of the diluted sample to the flame photometer can make use of an automatic device (details available from Evans Electro-Selenium Ltd.), but a preferable alternative is to attach a polyethylene capillary tube (30 cm long) to the atomizer intake this tube may then be inserted into the diluted samples or into the standard without removing the individual containers from the sample rack. Carry-over from one specimen to the next is negligible. 

To measure the volume of the Sephadex at equilibrium the equilibrated samples were contained in a calibrated tube (0.1 mL/division). An apparent volume was obtained from visual observation of the boundary defined by the layer to obtain the true volume an aliquot of the equilibrated solution phase was analysed for sodium by flame photometry. Most of the supernatant solution was then removed until 2.0 zt 0.025 mL of solution remained above the gel-defined boundary. Exactly 1.00 mL of water was added and the mixture was stirred sufficiently to assure a homogeneous aqueous phase. The solution phase was sampled immediately for sodium analysis with the flame photometer. From the observed dilution of the aqueous phase the true volume of the Sephadex gel at equilibrium was obtained. A correction for the matrix volume was based on the monomeric molecular weight of the Sephadex ( 220 25 capacity of 4.5 0.5 meq/dry g). In our samples, which contained about 88% water or 0.12 g acid/g sample, a volume of about 0.13/g is estimated for the matrix by assuming a density of approximately 0.9 for the dehydrated Sephadex. 

The flame photometer must be carefully maintained. It is the authors experience that an integral burner atomizer should be thoroughly and carefully cleaned every day. In addition, one or two spare burners should be available. These should be ordered when the flame photometer is being purchased. 

The sodium in a series of cement samples was determined by flame emission spectroscopy. The flame photometer was calibrated with a series of NaCl standards that contained sodium equivalent to 0,20.0,40,0,60.0, and 80.0 pg Na20 per ml,. The instrument readings R for these solutions were 3.1.2I 5.40,9. 57.1. and 77..3. 

Warm up the flame photometer or flame atomic absorption spectrometer in emission mode, following manufacturer s directions. Using an air-acetylene burner, set the flow rates of air acetylene to (a) oxidizing flame, (b) stoichiometric flame, and (c) reducing flame, following manufacturer s directions. 

A hydrogen/air premixed flame has a burning velocity of the order of 0 5 m s which the linear gas flow must exceed. A typical value would be 1-0 m s . Such a flame would show a slight contraction if burned isothermically. However the burnt gases are actually at a temperature of the order of 2000 K, so there is a sevenfold expansion. Some part of this is taken up by a transverse expansion, but a significant portion produces an acceleration of the burnt gas, with a resultant back pressure across the flame front. The burnt gases pass up the flame with a velocity of the order of 2-0 m s 1 cm height corresponds to 500 fis. Several techniques are available to study flames which have a spatial resolution of 100 fis. The flame photometer in particular can resolve measurements at intervals of 10 /is. 

On the matter of correlations between electrode and spectroscopic data, there can be some bias but while electrode potassium values are very slightly higher in one study [145], it is the flame photometer potassium data that are higher in another [148]. The bias in the second example [148] was attributed to faulty electrode calibration. 

The desirable features of the flame photometer are sensitivity, stability, and relatively large linear dynamic range. FPDs also require very little maintenance, and are ready to use in a very short time. An FPD s response to phosphorous is a first-order relationship, while its response to sulfiir components is second order because sulfur is detected as Sj. Analysis by an FPD without a GC column is considered real-time detection. Unfortunately, without GC involvement, the detector cannot provide possible compound identification due to its generic nature. The addition of GC capability permits identification of sample components that contain targeted elements, and reduces the false alarm rate. 

As some test methods use flammable gases such as propane in the flame photometers and ethylene, die safe handling of these gases is viul. 

Set the flame photometer wavelength to 670.9 nm and adjust the slit, zero and gain controls of the flame photometer until 0% and 100% scale readings are obtained for 1 N nitric acid solution and the 1 or 10 ppm Li standard solution. Obtain the scale readings for each standard solution in turn, followed by the sample at 670.9, 685.9 and 655.9 nm. 

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