Here are a couple of pictures that appeared in science magazines and companies' newsletters:
Analytical inorganic chemist Dr. Gouda analyzing a sample.
Chemist, Paul Gouda at our geochemical laboratory inspecting the effect of TISAP ion release methodolgy when utilizing fluoride electrode.
PAUL GOUDA GRADUATES
Congratulations to Paul Gouda (Analytical Lab) for graduating this summer and
receiving his M.A. Degree. Paul is presently working towards his Ph.D. Engelhard
employees (back row) celebrating the event with Paul in Toronto are (l to r) Roman Mucha, Eddy Wong, Isak Estulin, Alex Chan, Joseph Ching and Henk Pris. Also shown in front row (l to r) are Janet Ching, Afrah Gouda, Wendy Wong, Elizabeth
In particular, two of my papers achieved wide circulation and global recognition:
* Hydrargyrum, a paper on mercury analysis procedures.
The paper presents comparative methodology involving gravimetric, titimetric and instrumental approaches.
The paper in particularly elucidates the intricacies of the cold vapour technique by Atomic Absorption.
The cold vapour principal:
Mercury ions in acidic solution are reduced by reaction with stannous chlorid to ground state atoms. The solution is vigorously stirred until mercury vapour over solution reaches equilibrium with the mercury left in the solution. The total mercury atoms (atomic mercury vapour) is driven by use of purge gas; nitrogen or argon, into quartz cell located in the optical path of AAS. Hg, being in a ground state is amenable to atomic absorption of radiation and Hg atoms are monitored at 253.7 nm wavelength.
* Hydride generation technique by atomic absorption for the analysis of soil and water samples for
three parameters: Arsenic, Selenium and Antimony.
The principal of the paper is based on presenting metalloid elements "As, Se, Sb" in acidic medium to convert them to arsenate, selenate and antimonate and introduce them to sodium borohydride to reduce them to arsine, hydrogen selenide and stibine. The volatile hydrides are carried by argon into a cell heated by air/acetylene flame and is situated in the optical path of AAS where gaseous hydrides are reduced to atomic species and are then determined by atomic absorption.
The paper can be summerized in these notes:
H2SO4 + HCL + FeSO4 = H2SeO3 + FeCL3 + Fe2(SO4)3 + H2O [Ferrous sulfate accelerates the reaction. The oxidation of selenides and its conversion to selenites is as follows]:
Selenium forms halides with flurine and chlorine and to lesser degree with terhalogen compounds and bromine. It decomposes hydrogen iodie to liberate iodine. Selenium dissolves in alkali-metal sulfites forming selenosulfates, M2SSeO3
Selenium is oxidized by solutions of alkali-metal dichromates, permanganates, chlorates and calcium hypochlorite. It forms serlenocynates, MSeCN with many inorganic and organic derivateves of HSeCN.
The role of KI is evident in the thiosulfate titration as follows:
Arsenic diiodide causes a disproportionation with the formation of arsenic and arsenic trioxide as follows: 3 As2I4 = 4 AsI3 + 2 As
Organoaersenic compounds are derived from arsenic by replacing one, twoor three hydrogens by an alkyl, cycloalkyl, aryl or even heterrocyclic group b. Examples are tetrachlorophenylarsrane C6H5AsH2 and trifluoromethylarsine CF3AsH2.
Alkali metal borohydrides are used to reduce antimony III in acidic aqueous solution to stibine. Several metallic antimonides, antimony trioxides, tetraoxides, pentoxides, trifluorides, trichlorides, tribromides, triiodides, trisulfides, pentafluorides, pentachlorides, pentabromides, pentaiodides, pentasulfides play important role in the process of Sb determination by hydrides generation technique.
Both phenylstibine and dipheystibine are easily oxidized. Diphenylstibine is a strong reducing agent reacting with acides (in this case HCL) and liberates hydrogen:
(C6H5)2SbH + HCL = (C6H5)2SbCL3 + H2
A few dialkylstibinic acids exist in soil samples as a result of hydrolysis of the corresponding dialkyltrichloroantimony compounds as follows:
(CH3)2SbCL3 = (CH3)2SbO(OH)
Other chemistry papers by the Paul Gouda:
- Comparative background interference using ICP, AAS, DCP for trace analysis of environmental and
industrial water, soil and food samples.
- Comparative study on analytical methods employed to environmental & industrial samples; e.g. hydride generation VS graphite furnace (atomic absorption) and Hg cold vapour AAS.
- Inorganic contaminants in fish and food products.
- Manipulation of neurochemical compounds for medical research purpose.
- Pharmaceutical development of several products.
Stibonic acids can be produced during sample digestion as follows:
ArSbCL4 + H2O = ArSbO(OH)2 + HCL
ArN2CL + SbCL3 = ArSbL4 + N2
When a diazoniom salt is present in the sample and is then allowed to react with antimony pentachloride or with an aryltertrachloroantimony compound, the onium salts [ArN2][SbCL6] or [ArN2][ArSbCL2] are formed. They decompose in organic solvents with formation of diaylantimony trichloride as follows:
