w16891.pdf

13 / 44

* Visit for additional information from this link
t "EKVTUBCMF $SPTT 'MPX
t )JHI 1SFTTVSF 'JYFE $SPTT 'MPX .",
t #BCJOHUPO 7 (SPPWF IJHI TPMJET
t (., #BCJOHUPO IJHI TPMJET
t )JMEFCSBOE EVBM HSJE IJHI TPMJET
t &CEPO TMVSSZ IJHI TPMJET
t $POF 4QSBZ IJHI TPMJET
The concentric and fixed cross-flow are still the most common designs. The construction of both types is described in the following
article by ICP expert Robert Thomas (see Figures 4 & 5): A Beginner's Guide to ICP-MS Part II: The Sample-Introduction System*
ICP manufacturers will give you an option as to the type of nebulizer to use depending upon your analytical requirements and
the instrumental design.
Ultrasonic Nebulizer with Axial ICP-OES*
Sound can be used instead of a gas as the energy source for converting a liquid to a mist. These nebulizers use an ultrasonic
generator at a frequency of between 200 kHz and 10 MHz to drive a piezoelectric crystal. A pressure is produced that breaks
the surface of the liquid - air interface. Ultrasonic nebulizers are more expensive and difficult to use but they will improve
(lower) detection limits by about a factor of 10.
Spray Chambers
The basic designs that have remained over the years are the Scott
double-pass and the Cyclonic. To review the designs of these two
components, see Figures 8 & 9 in Robert Thomas' article: A Be-
ginner's Guide to ICP-MS Part II: The Sample-Introduction System*
The Cyclonic design is relatively new but is very popular. The
purpose of the spray chamber is to remove droplets produced by
the nebulizer that are > 8μm in diameter. Considerations include
the wash-in-time, washout time, stability, and sensitivity. The
drainage characteristics are important in part due to pressure
changes that may occur during drainage. It is important that
the drainage process be smooth and continuous. The analyst
may observe faster washout times with the Cyclonic design. The
chamber material of construction as well as the sample matrix
and the chemistry of the element will influence the washout time.
In addition, the analyst may observe faster washout times with glass construction than with polymers. This is due in part to
better wet ability of the glass (lack of beading). Both designs are excellent and the analysts may wish to experiment with each
to determine which yields the best performance for their specific analyses.
Torches
The two basic torch designs are the Greenfield and Fassel torches. The Greenfield torch requires higher gas flows and RF
powers. The Greenfield torch is more rugged (less likely to extinguish due to misalignment and introduction of air) whereas
the Fassel torch requires less Ar and power. Both designs produce similar detection limits.
Some nebulizer designs work better with one torch design over another. Before experimenting with torches, it is best to
contact your instrument manufacturer to determine the torch design recommended for your instrument as well as any design
specifications, operating conditions, and dimensions that must be observed.
Considerations
The following are some questions you may want to consider, whether you are looking to purchase a new ICP or already have
one or more existing units:
t 8IBU UPSDI EFTJHO JT VTFE BOE XIBU BSF UIF QPXFS BOE "S HBT ĘPX SFRVJSFNFOUT *U NBZ CF IFMQGVM UP DBMDVMBUF EFUFSNJOF
your annual Ar expense).
t 8IBU OFCVMJ[FS BOE TQSBZ DIBNCFS EFTJHOT BSF BWBJMBCMF BOE DBO UIFZ CF PCUBJOFE GSPN BMUFSOBUF TVQQMJFST
t "SF UIFSF TQFDJĕD OFCVMJ[FS EFTJHOT UIBU DBOOPU CF VTFE XJUI UIF SFDPNNFOEFE UPSDI TQSBZ DIBNCFS
t 8IBU BSF UIF DPTUT PG UIF JOEJWJEVBM JOUSPEVDUJPO TZTUFN DPNQPOFOUT BOE XIBU BSF UIF VQLFFQ DPTUT PWFS B ZFBS PG PQFSBUJPO
t 8IBU JT UIF MJGFUJNF PG UIF UPSDI BOE XIBU JT UIF NPTU DPNNPO SFBTPO GPS GBJMVSF
t )PX UPMFSBOU JT UIF TZTUFN UP TMJHIU DIBOHFT JO UPSDI BMJHONFOU
Assorted spray chambers
For more information on ultrasonic nebulizers, visity the following
link: CETAC U-5000+