title: Determination of phosphate concentration and pH in artificial tear drops.
abstract: OBJECTIVE
  To determine phosphate concentration and pH in artificial tear eye drops commercially available in Spain.
  
  
  METHODS
  A total of 71 examples of artificial tear preparations were identified in a search of Vademecum 2014 and the Spanish Medicines Agency website. In the 24 artificial tear products containing phosphates, quantification of these was performed by ultraviolet molecular absorption spectrophotometry, and the determination of pH was performed using scan image analysis algorithms of pH strips.
  
  
  RESULTS
  Of the 71 artificial tears tested, 24 contained phosphate among their excipients in the data sheet, three of which had a concentration level below detection limit (<0.1mM). The mean phosphate concentration was 17.91±23.87mM. The artificial tear sample containing a higher concentration was Colircusi Humectante (87.1mM). Lubricants based on hypromellose showed the highest phosphate concentration (41.59±32.1mM), showing statistically significant differences compared to povidone (P=.0196) and hyaluronate (P=.0067). Statistically significant differences were found between products containing preservatives (32.39±20.91mM), and preservative free ones (8.49±11.98mM) (P=.0498). However, no difference was found between multidose (20.21±26.91mM) and unidose (9.31±14.39mM) samples, or between brand name (15.44±23.3mM) and generic eye drops (20.81mM). The mean pH was 6.93±0.26 (6.2-7.22). No statistical correlation was detected between phosphate concentration and pH (Spearman's Rho -0.1089 and P=.6125).
  
  
  CONCLUSIONS
  A total of 24 (33.8%) of the 71 artificial tears contained phosphate. We believe identifying the phosphate concentration of artificial tears is useful information in order to avoid complications in high-risk patients.
authors.affiliation: Servicio de Oftalmología, Hospital Universitario Donostia, San Sebastián, Guipúzcoa, España. Electronic address: mdefrutoslezaun@gmail.com.
authors.forename: M
authors.initials: M
authors.lastname: de Frutos-Lezaun
authors.affiliation: Servicio de Oftalmología, Hospital Universitario Donostia, San Sebastián, Guipúzcoa, España.
authors.forename: I
authors.initials: I
authors.lastname: Martínez-Soroa
authors.affiliation: Departamento de Química Analítica, Facultad de Químicas, Universidad del País Vasco, San Sebastián, Guipúzcoa, España.
authors.forename: M
authors.initials: M
authors.lastname: Ostra Beldarrain
authors.affiliation: Departamento de Química Analítica, Facultad de Químicas, Universidad del País Vasco, San Sebastián, Guipúzcoa, España.
authors.forename: A
authors.initials: A
authors.lastname: Egia Zurutuza
authors.affiliation: Servicio de Farmacia, Hospital Universitario Donostia, San Sebastián, Guipúzcoa, España.
authors.forename: M B
authors.initials: MB
authors.lastname: Irastorza Larburu
authors.affiliation: Departamento de Química Analítica, Facultad de Químicas, Universidad del País Vasco, San Sebastián, Guipúzcoa, España.
authors.forename: A
authors.initials: A
authors.lastname: Fernandez Iriarte
authors.affiliation: Servicio de Farmacia, Hospital Universitario Donostia, San Sebastián, Guipúzcoa, España.
authors.forename: M P
authors.initials: MP
authors.lastname: Bachiller Cacho
mesh_terms: D002021:Buffers; D016568:Drugs, Generic / Q000737:chemistry; D006801:Humans; D006820:Hyaluronic Acid / Q000032:analysis; D006863:Hydrogen-Ion Concentration; D065347:Hypromellose Derivatives / Q000032:analysis; D065346:Lubricant Eye Drops / Q000737:chemistry*; D010710:Phosphates / Q000032:analysis*; D011205:Povidone / Q000032:analysis; D011310:Preservatives, Pharmaceutical / Q000032:analysis; D013030:Spain; D013056:Spectrophotometry, Ultraviolet
chemical_list: D002021:Buffers; D016568:Drugs, Generic; D065346:Lubricant Eye Drops; D010710:Phosphates; D011310:Preservatives, Pharmaceutical; D065347:Hypromellose Derivatives; D006820:Hyaluronic Acid; D011205:Povidone
keywords: Artificial tear; Calcificación corneal; Corneal calcification; Excipient; Excipientes; Fosfatos; Lágrima artificial; Phosphate; pH